Using arterial measurement waves to non-invasively determine cardiac output in an external wearable medical device

Abstract

A non-invasive cardiac monitoring system configured to determine a cardiac output of an ambulatory patient includes a non-invasive wearable monitoring device including a monitoring unit configured to be disposed on the patient's body. The monitoring unit includes at least one arterial measurement transmitter configured to transmit arterial measurement waves towards one or more arteries, at least one arterial measurement receiver configured to receive reflected / transmitted arterial measurement waves from the one or more arteries, and arterial measurement circuitry configured to generate arterial measurement signals corresponding to the one or more arteries. The monitoring system also includes cardiac output processing circuitry configured to identify an arterial pulse waveform from the arterial measurement signals, analyze the arterial pulse waveform to identify arterial pulse landmark(s), determine an area under the arterial pulse waveform using the arterial pulse landmark(s), and calculate a cardiac output for the patient using the area under the arterial pulse waveform.

Description

USING ARTERIAL MEASUREMENT WAVES TO NON-INVASIVELY DETERMINE CARDIAC OUTPUT IN AN EXTERNAL WEARABLE MEDICAL DEVICECROSS-REFERENCE TO RELATED APPLICATION

[0001] This nonprovisional application claims priority to U.S. Provisional Patent Application Serial No. 63 / 777,269, filed on March 25, 2025, titled “USING ARTERIAL MEASUREMENT WAVES TO NON-INVASIVELY DETERMINE CARDIAC OUTPUT IN AN EXTERNAL WEARABLE MEDICAL DEVICE,” the entirety of which is hereby incorporated by reference.BACKGROUND

[0002] The present disclosure relates to using various electromagnetic and other types of waves generated by an external wearable medical device to non-invasively determine, measure, and / or monitor the cardiac output for a patient.

[0003] A caregiver monitoring a patient’s cardiovascular health may want to take cardiovascular measurements for a patient. Taking cardiovascular measurements often requires a caregiver to manually take a patient’s cardiovascular measurements using equipment in a caregiver’s office. Sometimes these cardiovascular measurements may require the caregiver to perform invasive procedures on the patient. Otherwise, a patient may be required to purchase equipment and take their own cardiovascular measurements.

[0004] However, because cardiovascular measurements are manually taken, either by a caregiver or the patient, this limits the number of cardiovascular measurements that may be taken from the patient. In turn, the limited number of cardiovascular measurements may provide a caregiver with an incomplete view of the patient’s cardiovascular health. This incomplete view may be compounded by the fact that conditions in the caregiver’s office, or at the patient’s home, when cardiovascular measurements are being taken may not be representative of the patient’s day-to-day conditions that affect cardiovascular readings. Additionally, some of these cardiovascular measurements may be taken through invasive procedures that carry increased risks to the health of the patient compared to non-invasive procedures.SUMMARY

[0005] In one or more examples, a non-invasive cardiac monitoring system configured to determine a cardiac output of an ambulatory patient is provided. The cardiac monitoring systemincludes a non-invasive wearable monitoring device configured to be worn on a body of an ambulatory patient. The non-invasive wearable monitoring device includes a monitoring unit configured to be disposed on the patient’s body. The monitoring unit includes at least one arterial measurement transmitter configured to transmit arterial measurement waves towards one or more arteries of the patient, at least one arterial measurement receiver configured to receive at least one of reflected or transmitted arterial measurement waves from the one or more arteries of the patient, and arterial measurement circuitry configured to generate arterial measurement signals corresponding to the one or more arteries of the patient using the received at least one of reflected or transmitted arterial measurement waves. The non-invasive cardiac monitoring system also includes a cardiac output processing circuitry in electronic communication with the arterial measurement circuitry. The processing circuitry is configured to identify an arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals, analyze the arterial pulse waveform to identify one or more arterial pulse landmarks of the arterial pulse waveform, determine an area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculate a cardiac output for the patient using the determined area under the arterial pulse waveform.

[0006] Implementations of the non-invasive cardiac monitoring system can include one or more of the following features. The non-invasive wearable monitoring device further includes an adhesive patch configured to be removably attached to the patient’s torso. The monitoring unit is configured to be disposed on the adhesive patch. The non-invasive wearable monitoring device further includes a garment configured to be removably worn around the patient’s torso. The monitoring unit is configured to be disposed on the garment.

[0007] The monitoring unit includes the cardiac output circuitry. The non-invasive cardiac monitoring system further includes a gateway configured to communicate with the monitoring unit and with a remote server. The gateway includes the cardiac output processing circuitry. The monitoring unit includes a network interface configured to communicate with the gateway and transmit at least the arterial measurement signals to the gateway. The non-invasive cardiac monitoring system further includes a remote server in electronic communication with the monitoring unit. The remote server includes the cardiac output processing circuitry. The monitoring unit includes a network interface configured to communicate with the remote server and transmit at least the arterial measurement signals to the remote server. The non-invasivecardiac monitoring system further includes a gateway configured to communicate with the monitoring unit and with the remote server. The network interface of the monitoring unit is configured to communicate with the remote server via the gateway.

[0008] The monitoring unit is configured to be removably attached to the patient’s torso. The monitoring unit is configured to be removably attached to an extremity of the patient. The monitoring unit is configured to be removably attached to an arm of the patient.

[0009] The arterial measurement signals include radiofrequency (RF) signals. The at least one arterial measurement transmitter and the at least one arterial measurement receiver include at least one RF antenna configured to transmit RF waves towards the one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient. The arterial measurement circuitry includes RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

[0010] The cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further based on a heart rate of the patient. The non-invasive wearable monitoring device includes one or more electrocardiogram (ECG) electrodes configured to sense cardiac electrical activity of the patient and ECG circuitry configured to generate ECG signals using the sensed cardiac electrical activity of the patient. The cardiac output processing circuitry is configured to determine the heart rate of the patient using the ECG signals. The cardiac output processing circuitry is configured to determine the heart rate of the patient using the arterial measurement signals.

[0011] The wearable monitoring device is configured to be worn on the patient’s skin in an area around a major artery of the patient. The major artery includes a radial artery of the patient. The major artery includes a brachial artery of the patient. The major artery includes a subclavian artery of the patient. The major artery includes the patient’s aorta.

[0012] The one or more arterial pulse landmarks include a beginning and an end of a systolic portion of the arterial pulse waveform. The one or more arterial pulse landmarks includes a systolic peak and a dicrotic peak of the arterial pulse waveform. The cardiac output processing circuitry is configured to analyze the arterial pulse waveform to identify the one or more arterial pulse landmarks using local minima and maxima analysis. The cardiac output processing circuitry is configured to identify the beginning and the end of the systolic portion of the arterial pulse waveform using the systolic peak and the dicrotic peak of the arterial pulse waveform. The areaunder the arterial pulse waveform includes an area of the systolic portion of the arterial pulse waveform.

[0013] The arterial pulse waveform includes a representative arterial pulse waveform. The cardiac output processing circuitry is further configured to identify a plurality of segmented arterial pulse waveforms for the one or more arteries of the patient from one or more segments of the arterial measurement signals and generate the representative arterial pulse waveform from the plurality of segmented arterial pulse waveforms. The cardiac output processing circuitry is configured to generate the representative arterial pulse waveform by averaging the plurality of segmented arterial pulse waveforms. The cardiac output processing circuitry is further configured to repeat identifying the arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals to identify a plurality of arterial pulse waveforms. The cardiac output processing circuitry is further configured to repeat, for each of the plurality of arterial pulse waveforms, analyzing the arterial pulse waveform to identify the one or more arterial pulse landmarks of the arterial pulse waveform, determining the area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of arterial pulse waveforms. The cardiac output processing circuitry is further configured to calculate a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of arterial pulse waveforms. The representative cardiac output for the patient includes an average of the plurality of cardiac outputs for the plurality of arterial pulse waveforms. The representative cardiac output for the patient includes a median of the plurality of cardiac outputs for the plurality of arterial pulse waveforms. The cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further using one or more of heart rate, arterial compliance, or slope of the arterial pulse waveform.

[0014] The cardiac output processing circuitry is further configured to calibrate the cardiac output relative to a baseline of the patient. The cardiac output processing circuitry is configured to calibrate the cardiac output relative to the baseline of the patient by determining a calibration factor for the patient. The cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further using the calibration factor for the patient. The cardiac output includes an absolute cardiac output. Thebaseline of the patient includes one or more absolute calibration values for the patient. The cardiac output processing circuitry is further configured to receive the one or more absolute calibration values for the patient. Determining the calibration factor includes determining the calibration factor using the one or more absolute calibration values. The processing circuitry is further configured to periodically receive updated one or more absolute calibration values for the patient. Determining the calibration factor includes determining the calibration factor using the updated one or more absolute calibration values for the patient The one or more absolute calibration values for the patient include one or more absolute cardiac output values for the patient. The one or more absolute cardiac output values for the patient are measured using echocardiography. The one or more absolute cardiac output values for the patient are measured using thermodilution. The one or more absolute calibration values for the patient include one or more blood pressure values for the patient. The one or more blood pressure values for the patient are measured using a sphygmomanometer. The one or more blood pressure values for the patient are measured using a plurality of patch-based monitoring devices worn along a plurality of locations on an artery.

[0015] Determining the calibration factor includes determining a baseline cardiac output for the patient. The cardiac output processing circuitry is further configured to calibrate the cardiac output relative to the baseline of the patient by normalizing the cardiac output for the patient using the baseline cardiac output for the patient. The normalized cardiac output for the patient includes a relative cardiac output for the patient. Determining the baseline cardiac output for the patient includes identifying a calibration arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals, analyzing the calibration arterial pulse waveform to identify one or more calibration arterial pulse landmarks of the calibration arterial pulse waveform, determining an area under the calibration arterial pulse waveform using the one or more calibration arterial pulse landmarks, and calculating a calibration cardiac output for the patient using the determined area under the calibration arterial pulse waveform, wherein the baseline cardiac output is based on the calibration cardiac output. The baseline of the patient includes the calibration cardiac output. The cardiac output processing circuitry is further configured to repeat identifying the calibration arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals to identify a plurality of calibration arterial pulse waveforms. The cardiac output processing circuitry is further configured to repeat, for each of the plurality of calibration arterial pulse waveforms, analyzing the calibration arterial pulse waveform to identify the one ormore calibration arterial pulse landmarks of the calibration arterial pulse waveform, determining the area under the calibration arterial pulse waveform using the one or more calibration arterial pulse landmarks, and calculating the calibration cardiac output for the patient using the determined area under the calibration arterial pulse waveform to produce a plurality of calibration cardiac outputs for the plurality of calibration arterial pulse waveforms. The baseline of the patient includes a statistical output of the plurality of calibration arterial pulse waveforms. The statistical output of the plurality of calibration arterial pulse waveforms includes an average of the calibration arterial pulse waveforms. The statistical output of the plurality of calibration arterial pulse waveforms includes a median of the calibration arterial pulse waveforms.

[0016] The cardiac output processing circuitry is further configured to generate a baseline arterial pulse waveform for the patient. The cardiac output processing circuitry is configured to generate the baseline arterial pulse waveform for the patient by identifying a plurality of segmented baseline arterial pulse waveforms for the one or more arteries of the patient from one or more baseline segments of the arterial measurement signals and generating the baseline arterial pulse waveform for the patient from the plurality of segmented baseline arterial pulse waveforms. Generating the baseline arterial pulse waveform includes averaging the plurality of segmented baseline arterial pulse waveforms. The cardiac output processing circuitry is further configured to calculate the baseline cardiac output using the baseline arterial pulse waveform. The cardiac monitoring system of claim 97, wherein the cardiac output processing circuitry is configured to calculate the baseline cardiac output by analyzing the baseline arterial pulse waveform to identify one or more baseline arterial pulse landmarks of the baseline arterial pulse waveform, determining an area under the baseline arterial pulse waveform using the one or more baseline arterial pulse landmarks, and calculating the baseline cardiac output for the patient using the determined area under the baseline arterial pulse waveform.

[0017] The cardiac output circuitry is further configured to determine a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient. The cardiac output circuitry is further configured to present the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver. The cardiac output circuitry is further configured to alert a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

[0018] In one or more examples, a method for determining a cardiac output of an ambulatory patient using a non-invasive cardiac monitoring system can be executed. The method includes identifying an arterial pulse waveform for one or more arteries of an ambulatory patient from arterial measurement signals corresponding to the one or more arteries of the patient generated by a non-invasive wearable monitoring device, configured to be worn on a body of the ambulatory patient and further configured to transmit arterial measurement waves towards the one or more arteries of the patient, using at least one of reflected or transmitted arterial measurement waves received by the non-invasive wearable monitoring device. The method also includes analyzing the arterial pulse waveform to identify one or more arterial pulse landmarks of the arterial pulse waveform, determining an area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculating a cardiac output for the patient using the determined area under the arterial pulse waveform.

[0019] Implementations of the method for determining a cardiac output of an ambulatory patient using a non-invasive cardiac monitoring system can include one or more of the following features. The non-invasive wearable monitoring device includes a monitoring unit. The monitoring unit includes at least one arterial measurement transmitter configured to transmit the arterial measurement waves towards the one or more arteries of the patient, at least one arterial measurement receiver configured to receive the at least one of reflected or transmitted arterial measurement waves from the one or more arteries of the patient, and arterial measurement circuitry configured to generate the arterial measurement signals corresponding to the one or more arteries of the patient using the received at least one of reflected or transmitted arterial measurement waves. The non-invasive wearable monitoring device further includes an adhesive patch configured to be removably attached to the patient’ s torso. The monitoring unit is configured to be disposed on the adhesive patch. The non-invasive wearable monitoring device further includes a garment configured to be removably worn around the patient’s torso. The monitoring unit is configured to be disposed on the garment.

[0020] The method further includes receiving at least the arterial measurement signals from the non-invasive wearable monitoring device. The arterial measurement signals include radiofrequency (RF) signals.

[0021] Calculating the cardiac output for the patient includes calculating the cardiac output for the patient using the determined area under the arterial pulse waveform and further based on a heartrate of the patient. The method further includes determining the heart rate of the patient. Determining the heart rate of the patient includes determining the heart rate of the patient using ECG signals generated from sensed cardiac electrical activity for the patient. Determining the heart rate of the patient includes determining the heart rate of the patient using the arterial measurement signals.

[0022] The one or more arteries of the patient include a radial artery of the patient. The one or more arteries of the patient include a brachial artery of the patient. The one or more arteries of the patient include a subclavian artery of the patient. The one or more arteries of the patient include the patient’s aorta.

[0023] The one or more arterial pulse landmarks include a beginning and an end of a systolic portion of the arterial pulse waveform. The one or more arterial pulse landmarks includes a systolic peak and a dicrotic peak of the arterial pulse waveform. The area under the arterial pulse waveform includes an area of the systolic portion of the arterial pulse waveform.

[0024] The arterial pulse waveform includes a representative arterial pulse waveform. Repeating identifying the arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals to identify a plurality of arterial pulse waveforms. The method further includes repeating, for each of the plurality of arterial pulse waveforms, analyzing the arterial pulse waveform to identify the one or more arterial pulse landmarks of the arterial pulse waveform, determining the area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of arterial pulse waveforms. The method further includes calculating a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of arterial pulse waveforms.

[0025] The method further includes calibrating the cardiac output relative to a baseline of the patient. Calibrating the cardiac output relative to the baseline of the patient includes determining a calibration factor for the patient. Calculating the cardiac output for the patient includes calculating the cardiac output for the patient using the determined area under the arterial pulse waveform and further using the calibration factor for the patient. The cardiac output includes an absolute cardiac output. The baseline of the patient includes one or more absolute calibration values for the patient. The method further includes receiving the one or more absolute calibration values for the patient. Determining the calibration factor includes determining the calibrationfactor using the one or more absolute calibration values. The one or more absolute calibration values for the patient include one or more absolute cardiac output values for the patient. The one or more absolute calibration values for the patient include one or more blood pressure values for the patient. The method further includes periodically receiving updated one or more absolute calibration values for the patient, wherein determining the calibration factor includes determining the calibration factor using the updated one or more absolute calibration values for the patient.

[0026] Determining the calibration factor includes determining a baseline cardiac output for the patient. Calibrating the cardiac output relative to the baseline of the patient further includes normalizing the cardiac output for the patient using the baseline cardiac output for the patient. The normalized cardiac output for the patient includes a relative cardiac output for the patient.

[0027] The method further includes determining a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient. The method further includes presenting the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver. The method further includes alerting a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

[0028] In one or more examples, a non-transitory computer-readable medium storing instructions is provided. The instructions are configured to, when executed by one or more processors, cause the one or more processors to identify an arterial pulse waveform for one or more arteries of an ambulatory patient from arterial measurement signals corresponding to the one or more arteries of the patient generated by a non-invasive wearable monitoring device, configured to be worn on a body of the ambulatory patient and further configured to transmit arterial measurement waves towards the one or more arteries of the patient, using at least one of reflected or transmitted arterial measurement waves received by the non-invasive wearable monitoring device. The instructions are also configured to analyze the arterial pulse waveform to identify one or more arterial pulse landmarks of the arterial pulse waveform, determine an area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculate a cardiac output for the patient using the determined area under the arterial pulse waveform.

[0029] The non-invasive wearable monitoring device includes a monitoring unit. The monitoring unit includes at least one arterial measurement transmitter configured to transmit the arterial measurement waves towards the one or more arteries of the patient, at least one arterial measurement receiver configured to receive the at least one of reflected or transmitted arterialmeasurement waves from the one or more arteries of the patient, and arterial measurement circuitry configured to generate the arterial measurement signals corresponding to the one or more arteries of the patient using the received at least one of reflected or transmitted arterial measurement waves. The non-invasive wearable monitoring device further includes an adhesive patch configured to be removably attached to the patient’ s torso. The monitoring unit is configured to be disposed on the adhesive patch. The non-invasive wearable monitoring device further includes a garment configured to be removably worn around the patient’s torso. The monitoring unit is configured to be disposed on the garment.

[0030] The instructions are further configured to cause the one or more processors to receive at least the arterial measurement signals from the non-invasive wearable monitoring device. The arterial measurement signals include radiofrequency (RF) signals.

[0031] The instructions are configured to cause the one or more processors to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further based on a heart rate of the patient. The instructions are further configured to cause the one or more processors to determine the heart rate of the patient. The instructions are configured to cause the one or more processors to determine the heart rate of the patient by determining the heart rate of the patient using ECG signals generated from sensed cardiac electrical activity for the patient. The instructions are configured to cause the one or more processors to determine the heart rate of the patient using the arterial measurement signals.

[0032] The one or more arteries of the patient include a radial artery of the patient. The one or more arteries of the patient include a brachial artery of the patient. The one or more arteries of the patient include a subclavian artery of the patient. The one or more arteries of the patient include the patient’s aorta.

[0033] The one or more arterial pulse landmarks include a beginning and an end of a systolic portion of the arterial pulse waveform. The one or more arterial pulse landmarks includes a systolic peak and a dicrotic peak of the arterial pulse waveform. The area under the arterial pulse waveform includes an area of the systolic portion of the arterial pulse waveform.

[0034] The arterial pulse waveform includes a representative arterial pulse waveform. The instructions are further configured to cause the one or more processors to repeat identifying the arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals to identify a plurality of arterial pulse waveforms. The instructions are further configuredto cause the one or more processors to repeat, for each of the plurality of arterial pulse waveforms, analyzing the arterial pulse waveform to identify the one or more arterial pulse landmarks of the arterial pulse waveform, determining the area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of arterial pulse waveforms. The instructions are further configured to cause the one or more processors to calculate a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of arterial pulse waveforms.

[0035] The instructions are further configured to cause the one or more processors to calibrate the cardiac output relative to a baseline of the patient. The instructions are configured to cause the one or more processors to calibrate the cardiac output relative to the baseline of the patient by determining a calibration factor for the patient. The instructions are configured to cause the one or more processors to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further using the calibration factor for the patient. The cardiac output includes an absolute cardiac output. The baseline of the patient includes one or more absolute calibration values for the patient. The instructions are further configured to cause the one or more processors to receive the one or more absolute calibration values for the patient. The instructions are further configured to cause the one or more processors to determine the calibration factor using the one or more absolute calibration values. The one or more absolute calibration values for the patient include one or more absolute cardiac output values for the patient. The one or more absolute calibration values for the patient include one or more blood pressure values for the patient. The instructions are further configured to cause the one or more processors to periodically receive updated one or more absolute calibration values for the patient. Determining the calibration factor includes determining the calibration factor using the updated one or more absolute calibration values for the patient.

[0036] Determining the calibration factor includes determining a baseline cardiac output for the patient. The instructions are configured to cause the one or more processors to calibrate the cardiac output relative to the baseline of the patient further by normalizing the cardiac output for the patient using the baseline cardiac output for the patient. The normalized cardiac output for the patient includes a relative cardiac output for the patient.

[0037] The instructions are further configured to cause the one or more processors to determine a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient. The instructions are further configured to cause the one or more processors to present the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver. The instructions are further configured to cause the one or more processors to alert a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

[0038] In one or more examples, a non-invasive cardiac monitoring system configured to determine a cardiac output of an ambulatory patient. The non-invasive cardiac monitoring system includes a non-invasive patch-based monitoring device configured to be worn on a body of an ambulatory patient. The non-invasive patch-based monitoring device includes an adhesive patch configured to be removably attached to the patient’s body and a monitoring unit configured to be disposed on the adhesive patch. The monitoring unit includes at least one radiofrequency (RF) antenna configured to transmit RF waves towards one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient and RF circuitry configured to generate RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves. The non-invasive cardiac monitoring system also includes cardiac output processing circuitry in electronic communication with the RF circuitry. The processing circuitry is configured to identify an RF arterial pulse waveform for the one or more arteries of the patient from the RF signals, analyze the RF arterial pulse waveform to identify one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determine an area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculate a cardiac output for the patient using the determined area under the RF arterial pulse waveform.

[0039] Implementations of the non-invasive cardiac monitoring system can include one or more of the following features. The monitoring unit includes the cardiac output processing circuitry. The non-invasive cardiac monitoring system further includes a gateway configured to communicate with the monitoring unit and with a remote server. The gateway includes the cardiac output processing circuitry. The monitoring unit includes a network interface configured to communicate with the gateway and transmit at least the RF signals to the gateway. The non-invasive cardiac monitoring system includes a remote server in electronic communication with the monitoring unit. The remote server includes the cardiac output processing circuitry. The monitoring unit includesa network interface configured to communicate with the remote server and transmit at least the RF signals to the remote server. The non-invasive cardiac monitoring system further includes a gateway configured to communicate with the monitoring unit and with the remote server, wherein the network interface of the monitoring unit is configured to communicate with the remote server via the gateway.

[0040] The adhesive patch is configured to be removably attached to the patient’s torso. The adhesive patch is configured to be removably attached to an extremity of the patient. The adhesive patch is configured to be removably attached to an arm of the patient.

[0041] The cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further based on a heart rate of the patient. The patch-based monitoring device includes one or more electrocardiogram (ECG) electrodes configured to sense cardiac electrical activity of the patient and ECG circuitry configured to generate ECG signals using the sensed cardiac electrical activity of the patient. The adhesive patch includes the one or more ECG electrodes. The cardiac output processing circuitry is configured to determine the heart rate of the patient using the ECG signals. The cardiac output processing circuitry is configured to determine the heart rate of the patient using the RF signals.

[0042] The at least one RF antenna is sized for the one or more arteries of the patient to which the at least one RF antenna is configured to transmit the RF waves. The one or more arteries of the patient include a radial artery of the patient. The at least one RF antenna includes a surface area no greater than approximately 1.5 x 2.5 cm. The surface area of the at least one RF antenna is no greater than approximately 1.0 x 2.0 cm.

[0043] The patch-based monitoring device is configured to be placed on the patient’s skin in an area around a major artery of the patient. The major artery includes a radial artery of the patient. The major artery includes a brachial artery of the patient. The major artery includes a subclavian artery of the patient. The major artery includes the patient’s aorta.

[0044] The one or more RF arterial pulse landmarks include a beginning and an end of a systolic portion of the RF arterial pulse waveform. The one or more RF arterial pulse landmarks include a systolic peak and a dicrotic peak of the RF arterial pulse waveform. The cardiac output processing circuitry is configured to analyze the RF arterial pulse waveform to identify the one or more RF arterial pulse landmarks using local minima and maxima analysis. The cardiac output processingcircuitry is configured to identify the beginning and the end of the systolic portion of the RF arterial pulse waveform using the systolic peak and the dicrotic peak of the RF arterial pulse waveform. The area under the RF arterial pulse waveform includes an area of the systolic portion of the RF arterial pulse waveform.

[0045] The RF arterial pulse waveform includes a representative RF arterial pulse waveform. The cardiac output processing circuitry is further configured to identify a plurality of segmented RF arterial pulse waveforms for the one or more arteries of the patient from one or more segments of the RF signals and generate the representative RF arterial pulse waveform from the plurality of segmented RF arterial pulse waveforms. The cardiac output processing circuitry is configured to generate the representative RF arterial pulse waveform by averaging the plurality of segmented RF arterial pulse waveforms. The cardiac output processing circuitry is further configured to repeat identifying the RF arterial pulse waveform for the one or more arteries of the patient from the RF signals to identify a plurality of RF arterial pulse waveforms. The cardiac output processing circuitry is further configured to repeat, for each of the plurality of RF arterial pulse waveforms, analyzing the RF arterial pulse waveform to identify the one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determining the area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of RF arterial pulse waveforms. The cardiac output processing circuitry is further configured to calculate a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms. The representative cardiac output for the patient includes an average of the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms. The representative cardiac output for the patient includes a median of the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms. The cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further using one or more of heart rate, arterial compliance, or slope of the RF arterial pulse waveform.

[0046] The cardiac output processing circuitry is further configured to calibrate the cardiac output relative to a baseline of the patient. The cardiac output processing circuitry is configured to calibrate the cardiac output relative to the baseline of the patient by determining a calibration factor for the patient. The cardiac output processing circuitry is configured to calculate the cardiac outputfor the patient using the determined area under the RF arterial pulse waveform and further using the calibration factor for the patient. The cardiac output includes an absolute cardiac output. The baseline of the patient includes one or more absolute calibration values for the patient. The cardiac output processing circuitry is further configured to receive the one or more absolute calibration values for the patient. Determining the calibration factor includes determining the calibration factor using the one or more absolute calibration values. The cardiac output processing circuitry is further configured to periodically receive updated one or more absolute calibration values for the patient. Determining the calibration factor includes determining the calibration factor using the updated one or more absolute calibration values for the patient. The one or more absolute calibration values for the patient include one or more absolute cardiac output values for the patient. The one or more absolute cardiac output values for the patient are measured using echocardiography. The one or more absolute cardiac output values for the patient are measured using thermodilution. The one or more absolute calibration values for the patient include one or more blood pressure values for the patient. The one or more blood pressure values for the patient are measured using a sphygmomanometer. The one or more blood pressure values for the patient are measured using a plurality of patch-based monitoring devices worn along a plurality of locations on an artery.

[0047] Determining the calibration factor includes determining a baseline cardiac output for the patient. The cardiac output processing circuitry is further configured to normalize the cardiac output for the patient using the baseline cardiac output for the patient. The normalized cardiac output for the patient includes a relative cardiac output for the patient. The determining the baseline cardiac output for the patient includes identifying a calibration RF arterial pulse waveform for the one or more arteries of the patient from the RF signals, analyzing the calibration RF arterial pulse waveform to identify one or more calibration RF arterial pulse landmarks of the calibration RF arterial pulse waveform, determining an area under the calibration RF arterial pulse waveform using the one or more calibration RF arterial pulse landmarks, and calculating a calibration cardiac output for the patient using the determined area under the calibration RF arterial pulse waveform, wherein the baseline cardiac output is based on the calibration cardiac output. The baseline of the patient includes the calibration cardiac output. The cardiac output processing circuitry is further configured to repeat identifying the calibration RF arterial pulse waveform for the one or more arteries of the patient from the RF signals to identify a plurality of calibration RF arterial pulsewaveforms. The cardiac output processing circuitry is further configured to repeat, for each of the plurality of calibration RF arterial pulse waveforms, analyzing the calibration RF arterial pulse waveform to identify the one or more calibration RF arterial pulse landmarks of the calibration RF arterial pulse waveform, determining the area under the calibration RF arterial pulse waveform using the one or more calibration RF arterial pulse landmarks, and calculating the calibration cardiac output for the patient using the determined area under the calibration RF arterial pulse waveform to produce a plurality of calibration cardiac outputs for the plurality of calibration RF arterial pulse waveforms. The baseline cardiac output includes a statistical output of the plurality of calibration RF arterial pulse waveforms. The statistical output of the plurality of calibration RF arterial pulse waveforms includes an average of the calibration RF arterial pulse waveforms. The statistical output of the plurality of calibration RF arterial pulse waveforms includes a median of the calibration RF arterial pulse waveforms.

[0048] The cardiac output processing circuitry is further configured to generate a baseline RF arterial pulse waveform for the patient. The cardiac output processing circuitry is configured to generate the baseline RF arterial pulse waveform for the patient by identifying a plurality of segmented baseline RF arterial pulse waveforms for the one or more arteries of the patient from one or more baseline segments of the RF signals and generating the segmented baseline RF arterial pulse waveform for the patient from the plurality of baseline segment RF arterial pulse waveforms. Generating the baseline RF arterial pulse waveform includes averaging the plurality of segmented baseline RF arterial pulse waveforms. The cardiac output processing circuitry is further configured to calculate the baseline cardiac output using the baseline RF arterial pulse waveform. The cardiac output processing circuitry is configured to calculate the baseline cardiac output by analyzing the baseline RF arterial pulse waveform to identify one or more baseline RF arterial pulse landmarks of the baseline RF arterial pulse waveform, determining an area under the baseline RF arterial pulse waveform using the one or more baseline RF arterial pulse landmarks, and calculating the baseline cardiac output for the patient using the determined area under the baseline RF arterial pulse waveform.

[0049] The cardiac output circuitry is further configured to determine a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient. The cardiac output circuitry is further configured to present the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver. The cardiac output circuitry is further configuredto alert a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

[0050] In one or more examples, a method for determining a cardiac output of an ambulatory patient using a non-invasive cardiac monitoring system is executed. The method includes identifying a radiofrequency (RF) arterial pulse waveform for one or more arteries of an ambulatory patient from RF signals corresponding to the one or more arteries of the patient generated by a non-invasive patch-based monitoring device, configured to be worn on a body of the ambulatory patient and further configured to transmit RF waves towards the one or more arteries of the patient, using reflected arterial measurement waves received by the non-invasive patch-based monitoring device. The method also includes analyzing the RF arterial pulse waveform to identify one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determining an area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculating a cardiac output for the patient using the determined area under the RF arterial pulse waveform.

[0051] The non-invasive patch-based monitoring device includes a monitoring unit. The monitoring unit includes at least one RF antenna configured to transmit the RF waves towards the one or more arteries of the patient and receive the reflected RF waves from the one or more arteries of the patient and RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves. The non-invasive wearable monitoring device further includes an adhesive patch configured to be removably attached to the patient’s torso. The monitoring unit is configured to be disposed on the adhesive patch. The non-invasive wearable monitoring device further includes a garment configured to be removably worn around the patient’s torso. The monitoring unit is configured to be disposed on the garment.

[0052] The at least one RF antenna is sized for the one or more arteries of the patient to which the at least one RF antenna is configured to transmit the RF waves. The one or more arteries of the patient include a radial artery of the patient. The at least one RF antenna includes a surface area no greater than approximately 1.5 x 2.5 cm. The at least one RF antenna is no greater than approximately 1.0 x 2.0 cm.

[0053] The method further includes receiving at least the RF signals from the non-invasive patchbased monitoring device. Calculating the cardiac output for the patient includes calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform andfurther based on a heart rate of the patient. The method further includes determining the heart rate of the patient. Determining the heart rate of the patient includes determining the heart rate of the patient using ECG signals generated from sensed cardiac electrical activity for the patient. Determining the heart rate of the patient includes determining the heart rate of the patient using the RF signals.

[0054] The one or more arteries of the patient include a radial artery of the patient. The one or more arteries of the patient include a brachial artery of the patient. The one or more arteries of the patient include a subclavian artery of the patient. The one or more arteries of the patient include the patient’s aorta.

[0055] The one or more RF arterial pulse landmarks include a beginning and an end of a systolic portion of the RF arterial pulse waveform. The one or more RF arterial pulse landmarks includes a systolic peak and a dicrotic peak of the RF arterial pulse waveform. The area under the RF arterial pulse waveform includes an area of the systolic portion of the RF arterial pulse waveform. The RF arterial pulse waveform includes a representative RF arterial pulse waveform. The method further includes repeating identifying the RF arterial pulse waveform for the one or more arteries of the patient from the RF signals to identify a plurality of RF arterial pulse waveforms. The method further includes repeating, for each of the plurality of RF arterial pulse waveforms, analyzing the RF arterial pulse waveform to identify the one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determining the area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of RF arterial pulse waveforms. The method further includes calculating a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

[0056] The method further includes calibrating the cardiac output relative to a baseline of the patient. Calibrating the cardiac output relative to the baseline of the patient includes determining a calibration factor for the patient. Calculating the cardiac output for the patient includes calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further using the calibration factor for the patient. The cardiac output includes an absolute cardiac output. The baseline of the patient includes one or more absolute calibration values for the patient. The method further includes receiving the one or more absolute calibrationvalues for the patient. Determining the calibration factor includes determining the calibration factor using the one or more absolute calibration values. The method further includes periodically receiving updated one or more absolute calibration values for the patient. Determining the calibration factor includes determining the calibration factor using the updated one or more absolute calibration values for the patient. The one or more absolute calibration values for the patient include one or more absolute cardiac output values for the patient. The one or more absolute calibration values for the patient include one or more blood pressure values for the patient.

[0057] Determining the calibration factor includes determining a baseline cardiac output for the patient. Calibrating the cardiac output relative to the baseline of the patient further includes normalizing the cardiac output for the patient using the baseline cardiac output for the patient. The normalized cardiac output for the patient includes a relative cardiac output for the patient.

[0058] The method further includes determining a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient. The method further includes presenting the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver. The method further includes alerting a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

[0059] In one or more examples, a non-transitory computer-readable medium storing instructions is provided. The instructions are configured to, when executed by one or more processors, cause the one or more processors to identify a radiofrequency (RF) arterial pulse waveform for one or more arteries of an ambulatory patient from RF signals corresponding to the one or more arteries of the patient generated by a non-invasive patch-based monitoring device, configured to be worn on a body of the ambulatory patient and further configured to transmit RF waves towards the one or more arteries of the patient, using reflected RF waves received by the non-invasive patch-based monitoring device. The instructions are also configured to cause the one or more processors to analyze the RF arterial pulse waveform to identify one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determine an area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculate a cardiac output for the patient using the determined area under the RF arterial pulse waveform.

[0060] Implementations of the non-invasive computer-readable medium can include one or more of the following features. The non-invasive patch-based monitoring device includes a monitoring unit. The monitoring unit includes at least one RF antenna configured to transmit the RF wavestowards the one or more arteries of the patient and receive the reflected RF waves from the one or more arteries of the patient and RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves. The non-invasive patch-based monitoring device further includes an adhesive patch configured to be removably attached to the patient’s torso. The monitoring unit is configured to be disposed on the adhesive patch. The non-invasive patch-based monitoring device further includes a garment configured to be removably worn around the patient’s torso. The monitoring unit is configured to be disposed on the garment.

[0061] The at least one RF antenna is sized for the one or more arteries of the patient to which the at least one RF antenna is configured to transmit the RF waves. The one or more arteries of the patient include a radial artery of the patient. The at least one RF antenna includes a surface area no greater than approximately 1.5 x 2.5 cm. The surface area of the at least one RF antenna is no greater than approximately 1.0 x 2.0 cm. The instructions are further configured to cause the one or more processors to receive at least the RF signals from the non-invasive patch-based monitoring device.

[0062] The instructions are configured to cause the one or more processors to calculate the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further based on a heart rate of the patient. The instructions are further configured to cause the one or more processors to determine the heart rate of the patient. The instructions are configured to cause the one or more processors to determine the heart rate of the patient by determining the heart rate of the patient using ECG signals generated from sensed cardiac electrical activity for the patient. The instructions are configured to cause the one or more processors to determine the heart rate of the patient using the RF signals.

[0063] The one or more arteries of the patient include a radial artery of the patient. The one or more arteries of the patient include a brachial artery of the patient. The one or more arteries of the patient include a subclavian artery of the patient. The one or more arteries of the patient include the patient’s aorta.

[0064] The one or more RF arterial pulse landmarks include a beginning and an end of a systolic portion of the RF arterial pulse waveform. The one or more RF arterial pulse landmarks includes a systolic peak and a dicrotic peak of the RF arterial pulse waveform. The area under the RF arterial pulse waveform includes an area of the systolic portion of the RF arterial pulse waveform.

[0065] The RF arterial pulse waveform includes a representative RF arterial pulse waveform. The instructions are further configured to cause the one or more processors to repeat identifying the RF arterial pulse waveform for the one or more arteries of the patient from the RF signals to identify a plurality of RF arterial pulse waveforms. The instructions are further configured to cause the one or more processors to repeat, for each of the plurality of RF arterial pulse waveforms, analyzing the RF arterial pulse waveform to identify the one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determining the area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of RF arterial pulse waveforms. The instructions are further configured to cause the one or more processors to calculate a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

[0066] The instructions are further configured to cause the one or more processors to calibrate the cardiac output relative to a baseline of the patient. The instructions are configured to cause the one or more processors to calibrate the cardiac output relative to the baseline of the patient by determining a calibration factor for the patient. The instructions are configured to cause the one or more processors to calculate the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further using the calibration factor for the patient. The cardiac output includes an absolute cardiac output. The baseline of the patient includes one or more absolute calibration values for the patient. The instructions are further configured to cause the one or more processors to receive the one or more absolute calibration values for the patient. The instructions are further configured to cause the one or more processors to determine the calibration factor using the one or more absolute calibration values. The instructions are further configured to cause the one or more processors to periodically receive updated one or more absolute calibration values for the patient. Determining the calibration factor includes determining the calibration factor using the updated one or more absolute calibration values for the patient. The one or more absolute calibration values for the patient include one or more absolute cardiac output values for the patient. The one or more absolute calibration values for the patient include one or more blood pressure values for the patient.

[0067] Determining the calibration factor includes determining a baseline cardiac output for the patient. The instructions are configured to cause the one or more processors to calibrate the cardiacoutput relative to the baseline of the patient further by normalizing the cardiac output for the patient using the baseline cardiac output for the patient. The normalized cardiac output for the patient includes a relative cardiac output for the patient.

[0068] The instructions are further configured to cause the one or more processors to determine a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient. The instructions are further configured to cause the one or more processors to present the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver. The instructions are further configured to cause the one or more processors to alert a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Various aspects of at least one example are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide an illustration and a further understanding of the various aspects and examples, and are incorporated in and constitute a part of this specification, but are not intended to limit the scope of the disclosure. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and examples. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure.

[0070] FIG. 1 depicts an example system including a non-invasive wearable monitoring device.

[0071] FIG. 2 depicts an example adhesive patch.

[0072] FIG. 3 depicts an example monitoring unit.

[0073] FIG. 4 depicts an example of a monitoring unit being attached to an adhesive patch.

[0074] FIG. 5 depicts another example monitoring unit.

[0075] FIG. 6 depicts an example exploded view of a monitoring unit.

[0076] FIG. 7 depicts an example electronic architecture for a monitoring unit.

[0077] FIG. 8 depicts an example electronic architecture for RF functionality of a monitoring unit.

[0078] FIG. 9A depicts an example of a non-invasive wearable monitoring device being worn by a patient.

[0079] FIG. 9B depicts another example of a non-invasive wearable monitoring device being worn by a patient.1

[0080] FIG. 10 depicts an example of a non-invasive wearable monitoring device being used by a patient.

[0081] FIG. 11 depicts an example of an aortic region.

[0082] FIG. 12 depicts another example of a non-invasive wearable monitoring device being worn by a patient.

[0083] FIG. 13 depicts an example process flow for taking arterial measurements from a patient.

[0084] FIG. 14 depicts an example process flow for a measurement relating to an output of the patient’s heart

[0085] FIG. 15 A depicts an example of an ECG waveform and an RF -based arterial pulse waveform over time.

[0086] FIG. 15B depicts example graphs of arterial pulse waveforms derived from RF signals and arterial pulse waveforms derived from pressure signals.

[0087] FIG. 15C depicts additional example graphs as a continuation of FIG. 15B.

[0088] FIG. 15D depicts an example of an arterial pulse waveform over time.

[0089] FIG. 16 depicts another example of an arterial pulse waveform over time.DETAILED DESCRIPTION

[0090] In a cardiology practice, a caregiver may want to determine, measure, and / or monitor the condition of a patient’s circulatory system. As such, a caregiver may take measurements relating to the patient’s arterial characteristics that represent the status of the patient’s circulatory system. In various cases, the caregiver may take various measurements relating to the output of the patient’s heart. Examples of such measurements may include stroke volume, cardiac output, ejection fraction, and / or the like. As an illustration, stroke volume may measure the amount of blood ejected from the patient’s heart, such as at the left ventricle, during systolic cardiac contractions. As another illustration, cardiac output may measure the amount of blood that the heart pumps in one minute (e.g., measured in L / min). As another illustration, ejection fraction may measure the proportion of total blood in the patient’s left ventricle that the left ventricle pushes out with each heartbeat (e.g., measured as a percentage).

[0091] However, measuring the output of the patient’s heart may require that the caregiver take the measurements in a healthcare office setting. For example, many healthcare providers may measure cardiac output through intermittent pulmonary thermodilution, where a predetermined amount of cold fluid is injected into the patient’s blood near the right atrium and a catheter isinserted into the patient’s pulmonary artery to measure the temperature before and after injection of the cold fluid. A curve of the temperature in the pulmonary artery over time can be constructed and the area under the curve used to determine the patient’s cardiac output. Because this method of determining cardiac output is invasive, a caregiver may need to perform it in a healthcare office or other clinical setting. Other invasive methods of determining cardiac output may include, for instance, transesophageal echocardiography, where an ultrasound probe is inserted into the patient’s esophagus (e.g., near the descending aorta) to create images of the patient’s heart. Stroke volume is calculated by measuring the left ventricular outflow tract (LVOT) diameter and the velocity-time integral (VTI) of blood flow through the LV OT.

[0092] Caregivers may alternatively use less invasive methods of determining cardiac output, but these less invasive methods may still employ equipment that requires a clinical setting. To illustrate, examples of non-invasive methods of determining cardiac output may include non-invasive echocardiography, transthoracic Doppler, electrical bioimpedance, electrical bioreactance, magnetic resonance imaging (MRI), and computed tomography (CT). Non-invasive echocardiography may function similarly to transesophageal echocardiography, except that the ultrasound probe is placed in a less invasive location such as on the patient’s chest. Transthoracic Doppler functions similarly to transesophageal cardiography, with an ultrasound probe being place, for instance, in the patient’s jugular notch to image the left ventricle. The transthoracic Doppler system measures blood flow velocity and can estimate stroke volume based on the flow profile. Electrical bioimpedance and electrical bioreactance measure changes in electrical resistance (bioimpedance) or phase shifts in electrical signals (bioreactance) as blood flows through the thorax. These changes are used to calculate stroke volume. Cardiac MRIs can measure stroke volume with high accuracy by imaging the heart chambers and calculating the difference in volume between end-diastole and end-systole. Similarly, cardiac CT scans can be used to measure stroke volume by calculating the volumes of the heart chambers at different phases of the cardiac cycle. Still, some of these methods for measuring cardiac output may be impossible to implement outside of a clinical setting, such as cardiac MRIs and cardiac CT scans, which require MRI and CT scanners, respectively. Other of these methods may use equipment that is not calibrated to be used by an ambulatory patient. For instance, echocardiography may use bulky equipment that requires the patient to be in a still position during use.

[0093] Another method of measuring cardiac output may be implemented by performing a pulse contour analysis. Existing systems that use pulse contour analysis require inserting an arterial catheter into a patient. The arterial catheter may be fed into the aorta or, more commonly, into a peripheral artery such as a radial artery or femoral artery. A blood flow sensor or a pressure sensor is attached to the catheter, and using the data from the sensor, the system can construct a pressure waveform for the artery. The cardiac output can then be calculated based on the volume under the pressure waveform. However, these pulse contour analysis methods are invasive. Moreover, these methods are performed in a clinical setting due to the presence of the arterial catheter and cannot provide continuous readings for an ambulatory patient.

[0094] This disclosure relates to a non-invasive cardiac monitoring system configured to determine the cardiac output and / or other measures relating to the output of a patient’s heart. The non-invasive cardiac monitoring system includes a non-invasive monitoring device configured to be worn on a torso of an ambulatory patient and processing circuitry. The non-invasive wearable monitoring device includes a monitoring unit configured to be disposed on the patient’s torso. For example, the non-invasive wearable monitoring device may be a patch-based device that includes an adhesive patch configured to be removably attached to the patient’s torso and a monitoring unit configured to be disposed on the adhesive patch.

[0095] The monitoring unit includes at least one arterial measurement transmitter configured to transmit arterial measurement waves towards one or more arteries of the patient, at least one arterial measurement receiver configured to receive at least one of reflected or transmitted arterial measurement waves from the one or more arteries of the patient, and arterial measurement circuitry. The arterial measurement circuitry is configured to generate arterial measurement signals corresponding to the one or more arteries of the patient using the received at least one of reflected or transmitted arterial measurement waves. In implementations, for example, the at least one arterial measurement transmitter and the at least one arterial measurement receive may include at least one radiofrequency (RF) antenna configured to transmit arterial measurement waves in the form of RF waves towards the one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient. The arterial measurement circuitry may similarly be configured as RF circuitry configured to generate RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

[0096] The processing circuitry is in electronic communication with the arterial measurement circuitry. Using the arterial measurement signals, the processing circuitry is configured to identify an arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals. For example, the arterial pulse waveform may be an RF arterial pulse waveform generated from the RF signals, where the RF arterial pulse waveform may be representative of the patient’s arterial pressure over time. The processing circuitry then analyzes the arterial pulse waveform to identify one or more arterial pulse landmarks of the arterial pulse waveform and determine an area under the arterial pulse waveform using the one or more arterial pulse landmarks. In implementations, the arterial pulse landmarks may include the beginning of the systolic portion of the arterial pulse waveform and the dicrotic notch, representing the end of the systolic portion and the beginning of the diastolic portion. The processing circuitry may then determine the area under the arterial pulse waveform between the beginning and end of the systolic portion of the arterial pulse waveform.

[0097] Finally, the processing circuitry is configured to calculate a cardiac output (and / or other measure relating to the output of the patient’s heart) using the determined area under the arterial pulse waveform. In implementations, the processing circuitry may determine the patient’s heart rate. As an example, the processing circuitry may use the arterial measurement signals to identify the number of arterial pulse waveforms within a predetermined period of time and thereby calculate the patient’s heart rate. As another example, the non-invasive wearable monitoring device may include one or more electrocardiogram (ECG) electrodes configured to sense cardiac electrical activity of the patient and ECG circuitry configured to generate ECG signals using the sensed cardiac electrical activity. To illustrate, the ECG electrodes may be incorporated as part of an adhesive patch that can be removably attached to the patient. The processing circuitry may thus count the number of R waves in the ECG signals within a predetermined amount of time, using the count to determine the patient’s heart rate. Using the patient’s heart rate and the determined area under the arterial pulse waveform, the processing circuitry can calculate the patient’s cardiac output. In implementations, the patient’s cardiac output may be an uncalibrated measure. For instance, the processing circuitry may present the patient’s cardiac output as relative trends, showing increase, decrease, or steadiness in cardiac output over time. In implementations, the patient’s cardiac output may be a calibrated measure. As an example, the processing circuitry may further include a calibration factor in the calculation of cardiac output, where the calibration factoris configured to adjust the cardiac output calculated from the patient’s heart rate and determined area under the arterial pulse waveform to be an absolute measure of cardiac output. The calibration factor may be determined, for instance, based on blood pressure measurements for the patient, based on calibrating cardiac output measurements taken for the patient (e.g., using echocardiography, pulmonary thermodilution, and / or the like), and / or the like.

[0098] In one example use case, a caregiver may prescribe that a patient with cardiovascular issues wear a non-invasive, patch-based monitoring device for a certain amount of time (e.g., 15 days, 30 days, 60 days, 90 days, and / or the like). The wearable monitoring device is configured as an adhesive patch that can be removably adhered to the patient and a monitoring unit configured to be attached to the adhesive patch. For instance, the wearable monitoring device may be attached to the patient’s thorax, such as over an area around the patient’s aorta. The monitoring device is configured to generate RF signals based on RF waves that are transmitted into the patient, such as in an aortic region, and reflected back to the monitoring device. The RF measurements may be gated based on, for example, the patient’s activity level. As an illustration, the monitoring unit may wait until the patient is sedentary, until a certain time of day (e.g., at night when the patient is more likely to be sleeping) to take the RF measurements, and / or the like. The monitoring unit may generate RF signals using the received reflected RF waves and transmit the RF signals to a remote server. For example, the monitoring unit may transmit the RF signals via a gateway device configured to establish a wireless connection between the monitoring unit and the remote server.

[0099] The remote server analyzes the RF signals to identify an RF arterial pulse waveform and identify RF pulse landmarks that correspond to the start and end of the systolic portion of the RF arterial pulse waveform. The remote server then determines an area under the RF arterial pulse waveform using the RF pulse landmarks and uses determined area under the RF arterial pulse waveform to calculate a cardiac output for the patient. The remote server repeats calculating the cardiac output for the patient over time, such as once a day, once every two days, once every three days, once every five days, once a week, and / or the like. Using the cardiac outputs over time, the remote server prepares and provides to a caregiver for the patient a trend of the patient’s cardiac outputs. For instance, the remote server may update an online portal that shows different metrics for the patient including cardiac output. In examples, the remote server may additionally or alternatively alert the patient’s caregiver in response the cardiac output trend. As an illustration, the remote server may alert the patient’s caregiver (e.g., by sending the caregiver an email) if thecardiac output trend from week-to-week or over a certain number of weeks reaches a certain slope. Examples may include the cardiac output trend becoming negative or reaching or exceeding a predetermined slope value, such as -0.25, -0.50, -0.75, and / or the like.

[0100] In another example use case, a caregiver may prescribe that a patient with cardiovascular issues wear a non-invasive wearable monitoring device for a certain amount of time (e.g., 15 days, 30 days, 60 days, 90 days, and / or the like). The wearable monitoring device may include a monitoring unit that is configured to be worn by the patient around their wrist. For example, the monitoring unit may include or be mountable to a wrist strap, where the wrist strap is elastic or can be buckled onto the patient’s wrist. As another example, the monitoring unit may be attachable to a removable adhesive patch configured to be placed around the patient’ s wrist. The wearable monitoring device is configured to transmit RF waves into the arteries around the patient’s wrist and receive reflected RF waves back from the wrist arteries. Based on the received reflected RF waves, the monitoring device is configured to generate RF signals.

[0101] The monitoring device may transmit the RF signals to a remote server for analysis by processing circuitry of the remote server and / or the monitoring device may include processing circuitry configured to analyze the RF signals. In implementations, the processing circuitry is configured to identify an RF arterial pulse waveform, identify the systolic portion of the RF arterial pulse waveform, determine an area under the RF arterial pulse waveform corresponding to the systolic portion, and calculate a cardiac output for the patient using the determined area under the RF arterial pulse waveform, similar to the example use case above. Additionally, in implementations, the processing circuitry may be configured to calibrate the cardiac output according to the patient to produce an absolute cardiac output. For instance, the processing circuitry may receive one or more absolute calibration values for the patient, which in examples may be cardiac output measurements for the patient determined using cardiography, blood pressure, and / or the like. The processing circuitry may then adjust the cardiac output calibration according to the absolute calibration value(s), as discussed in further detail below. The processing circuitry may then output the absolute cardiac output for the patient and / or the patient’s caregiver to review. As an example, the processing circuitry may update an online portal that the patient’s caregiver can log into to review the patient’s cardiac output, along with other cardiac information for the patient. As another example, the processing circuitry may show the patient the cardiacoutput on a display associated with the processing circuitry, such as via an app that the patient can download to a personal electronic device from an app store.

[0102] The cardiac monitoring system described herein provides several advantages over prior art systems. As discussed above, many prior art systems for determining cardiac output and other arterial health measurements are invasive, requiring arterial catheters or at least the insertion of a probe into the patient’s esophagus. For example, existing commercial systems that use pulse contour analysis to determine cardiac output all require the use of an arterial catheter. By contrast, the present cardiac monitoring system is non-invasive. To illustrate, the cardiac monitoring system may include an external monitoring unit that the patient can wear, such as on an adhesive patch, an elastic band, a buckled band, and / or the like. As such, the cardiac monitoring system may provide a less risky way for a caregiver to monitor the patient’s cardiac health, as well as provide the patient with a more positive experience. For example, the cardiac monitoring system may require less time to take measurements compared to invasive systems, as well as provide the patient with minimal discomfort and no recovery time.

[0103] Additionally, while many prior art systems require use in a clinical setting, either due to their invasiveness or the nature of the equipment used in taking cardiac output and other arterial health measurements, the present cardiac monitoring system is configured to be wearable and used by an ambulatory patient. As such, the present cardiac monitoring system can provide caregivers with more real-time, continuous monitoring of the patient’s arterial health. This can allow the cardiac monitoring system to provide caregivers with more up-to-date information on the patient, as well as better track and visualize trends for the patient, which can be an indicator of improving or worsening cardiac health.

[0104] In implementations, the cardiac monitoring system described herein measures the pressure wave at or around the patient’s aorta to determine cardiac output. Taking measurements from the aorta may have advantages over taking measurements from other arteries. For example, the pulse waveform at the aorta is less influenced by arterial compliance compared to peripheral arteries. As another example, the pulse waveform at the aorta may be less affected by pressure changes due to the patient’s temperature. Accordingly, implementations of the present cardiac monitoring system may produce a more precise and / or accurate measure of cardiac output compared to systems or methods that use the peripheral arteries to determine cardiac output.

[0105] Alternatively or additionally, in implementations, the cardiac monitoring system described herein measures the pressure wave at or around arteries of the patient’s extremities. For example, the patient may wear a non-invasive monitoring device on a wrist, around an upper arm, on an ankle, and / or the like. In such implementations, the cardiac monitoring system may receive stronger RF reflections from arteries in the patient’s extremities because the size of the arteries allow for tuning the dimensions of the one or more RF antenna of the cardiac monitoring system to that arterial size. In turn, the RF signals produced from the received RF reflections may include more granular RF information compared to RF signals produced from other arteries.

[0106] FIG. 1 shows a non-invasive cardiac monitoring system configured to be used by an ambulatory patient, where the cardiac monitoring system includes a non-invasive wearable monitoring device 100 configured to be worn on the patient’s body. In implementations, the monitoring device 100 is in communication with a remote server 102, as shown in FIG. 1, and is configured to provide arterial measurement signals to the remote server 102. For example, the arterial measurement signals may be RF signals that the monitoring device 100 generates by transmitting RF waves towards one or more arteries of the patient and receiving reflected RF waves back from the one or more arteries. In embodiments, the monitoring device 100 includes a monitoring unit 104 configured to be disposed on the patient’s body. As an illustration, and as shown in FIG. 1, the monitoring device 100 may further include an adhesive patch 106 configured to be removably attached to the patient’s body, where the monitoring unit is configured to be disposed on the adhesive patch 106. In examples, the adhesive patch 106 may be configured to be disposed on the patient’s thorax, on an extremity of the patient such as an arm or a leg, and / or the like. In other illustrations, the monitoring unit 104 may be disposed on the patient’s body through another mechanism. For instance, the monitoring unit 104 may include a garment such as an elastic band, a band closable with hook and loop fabric, or a buckled band configured to be worn around the patient’s body (e.g., around the patient’s thorax, around an extremity such as the patient’s wrist or ankle, and / or the like). In implementations, the non-invasive monitoring device 100 is configured to be placed on the patient’s skin around a major artery of the patient. Examples of major arteries include the aorta and other arteries in the cardiac region, the radial artery, the brachial artery, the subclavian artery, and / or the like. Additionally, as further shown in FIG. 1 , the cardiac monitoring system may include other components in various implementations, such as a portable gateway 108 and a charger 110.

[0107] The monitoring unit 104 is configured to transmit arterial measurement waves towards one or more arteries of the patient and receive reflected and / or transmitted arterial measurement waves back from the patient. Using the received reflected and / or transmitted arterial measurement waves, the monitoring unit 104 is configured to generate arterial measurement signals corresponding to the one or more arteries. Examples of arteries may include the aorta and other arteries in the cardiac region, the brachial artery, the subclavian artery, the radial artery, the femoral artery, the tibial artery, and / or the like. As such, the monitoring unit 104 includes at least one arterial measurement transmitted configured to transmit the arterial measurement waves, at least one arterial measurement receiver configured to receive the reflected and / or transmitted arterial measurement waves, and arterial measurement circuitry configured to generate the arterial measurement signals. In implementations, the arterial measurement waves may be RF waves, and the monitoring unit 104 may generate RF signals using received reflected RF waves from the one or more arteries of the patient. Accordingly, the monitoring unit 104 may include at least one RF antenna configured to transmit the RF waves and receive the reflected RF waves from the patient, as well as RF circuitry configured to generate the RF signals.

[0108] The adhesive patch 106 is configured to be adhesively coupled to the skin of a patient, where the monitoring unit 104 is configured to be removably attached to the adhesive patch 106. For example, the adhesive patch may include a frame 112 in the same general shape of the monitoring unit 104, and the monitoring unit 104 is configured to removably couple, connect, or snap into the frame 112. In implementations, the adhesive patch 106 is configured to be adhered to the patient’s body on the patient’s thorax, on an extremity of the patient such as around the patient’s wrist or on the patient’s leg, and / or the like. Alternatively, as noted above, in implementations the monitoring device 100 may not include an adhesive patch 106. Instead, the monitoring unit 104 may be configured to be attached to the patient using a garment such as an elastic band, a band with hook and loop fabric, a buckled band, and / or the like.

[0109] In embodiments, the monitoring unit 104 and / or the adhesive patch 106 may include one or more additional sensors configured to sense other signals of the patient. For instance, one or more ECG electrodes 114 may be embedded into the adhesive patch 106, where the one or more ECG electrodes 114 are configured to sense cardiac electrical activity of the patient. As such, the monitoring unit 104 may receive signals from the ECG electrodes 114 indicative of the ECG of the patient. To this end, the monitoring unit 104 may further include ECG circuitry configured togenerate ECG signals using the sensed cardiac electrical activity of the patient. As another illustration, the monitoring unit 104 may include a motion sensor configured to generate motion signals associated with the patient. Examples of this motion sensor may include a 1 -axis channel accelerometer, 2-axis channel accelerometer, 3-axis channel accelerometer, multi-axis channel accelerometer, gyroscope, magnetometer, ballistocardiograph, and the like. In some embodiments, the portable gateway 108 may include one or more additional sensors configured to sense other biometric signals of the patient. For example, the portable gateway 108 may include a 3D accelerometer configured to generate motion signals associated with the patient.

[0110] The monitoring unit 104 and adhesive patch 106 are configured for long-term and / or extended use or wear by, or attachment or connection to, a patient. For example, devices as described herein may be capable of being continuously used or continuously worn by, or attached to connected to, a patient without substantial interruption (e.g., 24 hours, 2 days, 5 days, 7 days, 2 weeks, 1 month, or beyond, such as multiple months, or even years). In some implementations, such devices may be removed for a period of time before use, wear, attachment, or connection to the patient is resumed. As an illustration, devices may be removed to change batteries, change adhesive patches 106, carry out technical service, update the device software or firmware, and / or take a shower or engage in other activities, without departing from the scope of the examples described herein. Such substantially or nearly continuous use, monitoring, or wear as described herein may nonetheless be considered continuous use, monitoring, or wear.

[0111] In embodiments, the monitoring unit 104 is configured to monitor, record, and transmit signals (e.g., RF sensor signals) to the portable gateway 108 continuously. The monitoring unit 104 monitoring and / or recording additional data may not interrupt transmitting already acquired data to the portable gateway 108. As such, in embodiments, both the monitoring / recording and the transmission processes may occur at the same time or nearly the same time. In embodiments, if the monitoring unit 104 does suspend the monitoring and / or recording of additional data while it is transmitting already acquired data to the portable gateway 108, the monitoring unit 104 may then resume monitoring and / or recording additional data prior to all of the already acquired data being transmitted to the portable gateway 108. To illustrate, the interruption period for monitoring and / or recording may be less in comparison to the time it takes the monitoring unit 104 to transmit the already acquired data (e.g., between about 0% to about 80%, about 0% to about 60%, about 0% to about 40%, about 0% to about 20%, about 0% to about 10%, about 0% to about 5%,including values and subranges therebetween). This moderate interruption period may facilitate the near-continuous monitoring and / or recording of additional data during transmission of already acquired physiological data. For example, in one scenario, when a measurement time is around two minutes, any period of suspension or interruption in the monitoring and / or recording of subsequent measurement data may range from a few milliseconds to about a minute. Illustrative reasons for such suspension or interruption of data may include allowing for the completion of certain data integrity and / or other online test of previously acquired data. If the previous data has problems, the monitoring unit 104 may notify the patient and / or a remote technician of the problems so that appropriate adjustments can be made.

[0112] In embodiments, the monitoring unit 104 may be configured to monitor, record, and transmit some data in a continuous or near-continuous manner as discussed above, while monitoring, recording, and transmitting some other data in a non-continuous manner (e.g., periodically, non-periodically, etc.). For example, the monitoring unit 104 may be configured to record and transmit ECG data from the ECG electrodes 114 continuously or nearly continuously while RF signals are transmitted periodically (e.g., because RF measurements may be taken only when the patient is in a good position for recording RF data, such as when the patient is not moving). As an illustration, ECG data may be transmitted to the portable gateway 108 (and, via the portable gateway 108, to the remote server 102) continuously or near-continuously as additional ECG data is being recorded, while RF signals may be transmitted once the RF measuring process is completed. In embodiments, monitoring and / or recording of signals by the monitoring unit 104 may be periodic and may be accomplished as scheduled (e.g., periodically) without delay or latency during the transmission of already acquired data to the portable gateway 108. For example, the monitoring unit 104 may sense signals or acquire signals from the patient in a periodic manner and transmit the data to the portable gateway 108 in a continuous manner as described above.

[0113] As discussed above, in various embodiments, the non-invasive monitoring device 100 may include the portable gateway 108. The patient may carry the portable gateway 108 throughout their daily activities, for example, as shown in FIG. 12. In implementations, the portable gateway 108 may communicate with the patient. As an example, the portable gateway 108 may provide the patient with screens indicating that the monitoring unit 104 needs to be charged. As another example, the portable gateway 108 may allow the patient to input a patient event, such as aninstance of elevated heartrate, difficulty breathing, sudden tiredness, and / or the like. As another example, the portable gateway 108 may provide patient reports to the patient, as described in further detail below. In implementations, the portable gateway 108 is a patient device that has been configured to communicate with the monitoring unit 104. For instance, the patient device may execute a patient monitoring application that configures the patient device to communicate with the monitoring unit 104 and with the remote server 102, as discussed in further detail below. In implementations, the portable gateway 108 is a separate, dedicated device configured to communicate with the monitoring unit 104.

[0114] The portable gateway 108 is configured to receive the signals provided by the monitoring unit 104 (e.g., RF sensor signals and light sensor signals) and transmit the signals to the remote server 102. In this way, the portable gateway 108 may be configured to communicate with both the monitoring unit 104 and the remote server 102, where a network interface of the monitoring unit 104 is configured to communicate with the remote server 102 via the portable gateway 108. Accordingly, the portable gateway 108 may be in wired and / or wireless communication with the monitoring unit 104 and the remote server 102. As an illustration, the portable gateway 108 may communicate with the monitoring unit 104 via Ethernet, via Wi-Fi, via RF, via Bluetooth®, via near-field communication (NFC), and the like. The portable gateway 108 may further communicate with the remote server 102 via cellular networks, via Bluetooth®-to-TCP / IP access point communication, via Ethernet, via Wi-Fi, and the like. As such, the portable gateway 108 may include communications circuitry configured to implement broadband cellular technology (e.g., 2.5G, 2.75G, 3G, 4G, 5G cellular standards) and / or Long-Term Evolution (LTE) technology or GSM / EDGE and UMTS / HSPA technologies for high-speed wireless communication. In implementations, the communications circuitry in the monitoring unit 104 and / or the portable gateway 108 may communicate with the remote server 102 over a Wi-Fi communications link based on the IEEE 802.11 standard. In implementations, the monitoring unit 104 and / or portable gateway 108 may be part of an Internet of Things (loT) and communicate with each other and / or the remote server 102 via loT protocols (e.g., Constrained Application Protocol (CoAP), Message Queuing Telemetry Transport (MQTT), Wi-Fi, Zigbee, Bluetooth®, Extensible Messaging and Presence Protocol (XMPP), Data-Distribution Service (DDS), Advanced Messaging Queuing Protocol (AMQP), and / or Lightweight M2M (LwM2M)).

[0115] In embodiments, the portable gateway 108 may continuously transmit the signals provided by the monitoring unit 104 to the remote server 102. Thus, for example, the portable gateway 108 may transmit the signals from the monitoring unit 104 to the remote server 102 with little or no delay or latency. To this end, in the context of data transmission with the non-invasive monitoring device 100, continuously includes continuous (e.g., without interruption) or near continuous (e.g., within one minute after completion of a measurement and / or an occurrence of an event on the monitoring unit 104). Continuity may also be achieved by repetitive successive bursts of transmission (e.g., high-speed transmission). Similarly, immediate includes occurring or done immediately or nearly immediately (e.g., within one minute after the completion of a measurement and / or an occurrence of an event on the monitoring unit 104).

[0116] Further, in the context of signal acquisition and transmission by the non-invasive monitoring device 100, continuously also includes uninterrupted collection of data sensed by the monitoring device 100, such as RF sensor signals, with clinical continuity. In this case, short interruptions in data acquisition of up to one second several times an hour, or longer interruptions of a few minutes several times a day may be tolerated, and still seen as continuous. As to latency as a result of such a continuous scheme as described herein, the overall amount of response time (e.g., time from when an event onset is detected to when a notification regarding the event is issued) can amount, for example, from about five to fifteen minutes. As such, transmission / acquisition latency may therefore be in the order of minutes.

[0117] In embodiments, the bandwidth of the link between the monitoring unit 104 and the portable gateway 108 may be larger, and in some instances, significantly larger than the bandwidth of the acquired data to be transmitted via the link (e.g., burst transmissions). Such embodiments may ameliorate issues that may arise during link interruptions, periods of reduced / absent reception, etc. In embodiments, when transmission is resumed after the interruption, the resumption may be in the form of last-in-first-out (LIFO). Additionally, in embodiments, the portable gateway 108 may be configured to operate in a store and forward mode where the data received from the monitoring unit 104 is first stored in an onboard memory of the portable gateway 108 and then forwarded to the remote server 102. In some embodiments, the portable gateway 108 may function as a pipeline and pass through data from the monitoring unit 104 immediately to the remote server 102. Further, in embodiments, the data from the monitoring unit 104 may be compressed usingdata compression techniques to reduce memory requirements as well as transmission times and power consumption.

[0118] Alternatively, in embodiments, the monitoring unit 104 may be configured to transmit the sensed or acquired signals directly to the remote server 102 instead of, or in addition to, transmitting the signals to the portable gateway 108. Accordingly, the monitoring unit 104 may be in wired or wireless communication with the remote server 102. As an illustration, the monitoring unit 104 may communicate with the remote server 102 via cellular networks, via Ethernet, via Wi-Fi channels, and the like. Further, in embodiments, the non-invasive monitoring device 100 may not include the portable gateway 108. In such embodiments, the monitoring unit 104 may perform the functions of the portable gateway 108 described above. Additionally, in such embodiments, the monitoring unit 104 may include communications circuitry configured to implement broadband cellular technology (e.g., 2.5G, 2.75G, 3G, 4G, 5G cellular standards) and / or Fong-Term Evolution (LTE) technology or GSM / EDGE and UMTS / HSPA technologies for highspeed wireless communication. In implementations, the monitoring unit 104 may be configured to communicate with the remote server 102 using any of the communications protocols discussed above with reference to the portable gateway 108.

[0119] The charger 110 includes charging cradles configured to hold and recharge the monitoring unit 104 and the portable gateway 108. Alternatively, in embodiments, the non-invasive monitoring device 100 may not include the portable gateway 108, and accordingly, the charger 110 may be configured to hold the monitoring unit 104 alone.

[0120] The remote server 102 is configured to receive and process signals transmitted by the non-invasive monitoring device 100. Accordingly, the remote server 102 may include a computing device, or a network of computing devices, including at least one database (e.g., implemented in non-transitory media or memory) and at least one processor configured to execute instructions (e.g., stored in the database, with the at least one processor being in communication with the database) to receive and process the signals transmitted by the monitoring device 100. In various embodiments, the remote server 102 may determine the patient’s cardiac output and / or other measurements indicative of the patient’s cardiac health, as described in further detail below. Alternatively, or additionally, the monitoring unit 104 and / or the portable gateway 108 may determine the patient’s cardiac output and / or other measurements indicative of the patient’s cardiac health, and further transmit this determined information to the remote server 102.

[0121] As shown in FIG. 1, in embodiments, the cardiac monitoring system further includes one or more user interfaces, such as technician interfaces 116 and caregiver interfaces 118. The technician interfaces 116 and caregiver interfaces 118 are in electronic communication with the remote server 102 through a wired or wireless connection. For instance, the technician interfaces 116 and caregiver interfaces 118 may communicate with the remote server 102 via Wi-Fi, via Ethernet, via cellular networks, and the like. Additionally, as shown, at least some of the technician interfaces 116 may also be in electronic communication with at least some of the caregiver interfaces 118 through a wired or wireless connection, such as via Wi-Fi, via Ethernet, via cellular networks, and the like. The technician interfaces 116 and the caregiver interfaces 118 may include, for example, desktop computers, laptop computers, and / or portable personal digital assistants (e.g., smartphones, tablet computers, etc.).

[0122] In embodiments, the technician interfaces 116 are configured to electronically communicate with the remote server 102 for the purpose of viewing and analyzing information gathered from one or more monitoring units 104. For example, such information may include cardiac outputs and / or other measurements indicative of patients’ cardiac health. For example, a technician interface 116 may provide one or more instructions to the remote server 102 to prepare a summary report of the cardiovascular measurements for the patient for a certain time period. Accordingly, a technician interface 116 may include a computing device having a processor communicably connected to a memory and a visual display. The technician interface 116 may display to a user of the technician interface 116 (e.g., a technician) information gathered from the one or more monitoring units 104. The user of the technician interface 116 may then provide one or more inputs to the remote server 102 to guide the remote server 102 in preparing a report on the patient. As an example, a user may select a time period to use for a report, and the remote server 102 may prepare a report corresponding to the selected time period. As another example, a user may view a report prepared by the remote server 102 and draft a summary of the report that is included in a summary section of the report. As another example, a user may view waveforms provided by a monitoring unit 104 and select landmarks on those waveforms. The remote server 102 may then use the landmarks input by the user to determine one or more cardiovascular measurements for the patient. Alternatively, in some embodiments, the remote server 102 may analyze and / or summarize the information gathered from one or more monitoring units 104 with minimal or no input or interaction with a technician interface 116. In this way, the remote server31102 may analyze and / or summarize the information gathered from the one or more monitoring unit 104 through a completely or mostly automated process.

[0123] The caregiver interfaces 118 are configured to electronically communicate with the remote server 102 for the purpose of viewing information on patients using monitoring units 104. As such, a caregiver interface 118 may include a computing device having a processor communicably connected to a memory and a visual display. The caregiver interface 118 may display to a user of the caregiver interface 118 (e.g., a physician, a nurse, or other caregiver) arterial measurement waveforms, landmarks on the arterial measurement waveforms, cardiovascular measurements, reports summarizing cardiovascular measurements, and / or the like for a patient. In implementations, the user of the caregiver interface 118 may be able to interact with the displayed information for a patient using a monitoring unit 104. For example, the user of the caregiver interface 118 may be able to select a portion of a patient report and, in response, be able to view additional information relating to the selected portion of the report, such as the arterial measurement waveforms used to generate the data included in the report. In implementations, the user of the caregiver interface 118 may instead view a patient report without being able to interact with the patient report.

[0124] In implementations, a technician interface 116 and / or a caregiver interface 118 may be a specialized user interface configured to communicate with the remote server 102. As an example, the technician interface 116 may be a specialized user interface configured to receive preliminary patient reports from the remote server 102, receive inputs from a user to adjust the preliminary report, and transmit the input to a remote server 102. The remote server 102 then uses the input from the technician interface 116 to prepare a finalized patient report, which the remote server 102 also transmits to the technician interface 116.

[0125] In implementations, a technician interface 116 and / or a caregiver interface 118 may be a generalized user interface that has been adapted to communicate with the remote server 102. To illustrate, the technician interface 116 may be a user interface executing a technician application configured to communicate with the remote server 102. For example, the technician application may be downloaded from an application store or otherwise installed on the user interface. Accordingly, when the user interface executes the technician application, the user interface is configured to communicate with the remote server 102 to receive and transmit information on patients using monitoring units 104. Similarly, the caregiver interface 118 may be a user interfaceexecuting a caregiver application that configures the user interface to communicate with the remote server 102. The caregiver application may be similarly downloaded from an application store or otherwise installed on the user interface and, when executed, may configure the user interface to communicate with the remote server 102 to receive and display information on patients using monitoring units 104. The application store is typically included within an operating system of the device implementing the user interface.

[0126] In various cases, the technician application and the caregiver application may be the same application, and the application may provide different functionalities to the device executing the application based on, for example, credentials provided by the user. For instance, the application may provide technician functionalities to a first user interface in response to authenticating technician credentials entered on the first user interface, and may provide caregiver functionalities to a second user interface in response to authenticating caregiver credentials entered on the second user interface. In other cases, the technician application and the caregiver application may be separate applications, each providing separate functionalities to a user device executing them.

[0127] In implementations, the system shown in FIG. 1 may include other types of interfaces. To illustrate, in examples, the system may include patient interfaces. Thus, the remote server 102 and / or a technician interface 116 may provide a report on a patient using a monitoring unit 104 to the patient via a patient interface. This patient report may be the same as a report provided to a caregiver via a caregiver interface 118, or this patient report may be different from the report provided to a caregiver via a caregiver interface 118. For instance, the report provided to a patient may be an abridged version of the patient report prepared for the caregiver. In various implementations, the patient interface may be configured similarly to and function similarly to the caregiver interface 118 discussed above (e.g., with some additional restrictions on what is included in a report and / or functionalities the patient can access). As an example, a patient interface may be configured as a personal electronic device that is possessed by the patient and is operating an application configured to communicate with the remote server 102 and / or with the monitoring unit 104. As another example, the portable gateway 108 may also be configured as a patient interface and display screens configured to convey information, such as patient reports, to the patient.

[0128] Returning to the non-invasive monitoring device 100, FIGS. 2-4 show the monitoring unit 104 and the adhesive patch 106 according to various implementations. The adhesive patch 106 may be disposable (e.g., single- or few-use patches) and may be made of a biocompatible, non-woven material. Additionally, as shown in FIG. 2, and as noted above, the adhesive patch 106 may include a patch frame 112 delineating the boundary of the region of the adhesive patch 106 that is configured to house the monitoring unit 104. In some embodiments, the monitoring unit 104 may be designed for long-term usage. In such embodiments, the connection between the adhesive patch 106 and the monitoring unit 104 may be configured to be reversible such that the monitoring unit 104 may be configured to be removably attached to the adhesive patch 106. For example, as shown in FIG. 3, the monitoring unit 104 may include components such as snap-in clips 300 that are configured to secure the monitoring unit 104 to the adhesive patch 106 upon attachment to the patch frame 112. After the monitoring unit 104 is attached to the patch frame 112, a user may press the snap-in clip 300 to subsequently release the release the monitoring unit 104 from the patch frame 112. The monitoring unit 104 may also include positioning tabs 302 that facilitate the attachment process between the monitoring unit 104 and the adhesive patch 106. For example, the positioning tabs 302 may guide a user to insert the monitoring unit 104 onto the correct portion of the patch frame 112 such that the monitoring unit 104 can then be coupled, connected, or snapped into the patch frame 112 using the snap-in clip 300, as shown in FIG. 4. In embodiments, the adhesive patch 106 may be designed to maintain attachment to skin of a patient for several days (e.g., in a range from about 4 days to about 10 days, from about 3 days to about 5 days, from about 5 days to about 7 days, from about 7 days to about 10 days, from about 10 days to about 14 days, from about 14 days to about 30 days, etc.). After the period of use, the adhesive patch 106 may be removed from the patient’s skin and the monitoring unit 104 can be removed from the patch 106. The monitoring unit 104 can be removably coupled, connected, or snapped onto a new adhesive patch 106 that is reapplied to the patient’s skin.

[0129] Additionally, in embodiments, the adhesive patch 106 may include additional components that facilitate or aid with the monitoring and / or recording or acquiring of physiological data by the monitoring unit 104. For instance, as discussed above, the adhesive patch 106 may include conductive elements such as one or more ECG electrodes 114 (e.g., a single lead, two leads, etc.) configured to sense the patient’s cardiac electrical activity. The one or more ECG electrodes 114 can be used when recording ECG signals from the surface (e.g., skin contacted directly or through a covering) of a patient’s body. The one or more ECG electrodes 114 may be coupled to the monitoring unit 104 by dedicated wiring within the patch. In embodiments, the one or more ECG electrodes 114 may have a sampling rate in the range from about 250 Hz to about 500 Hz, fromabout 300 Hz to about 450 Hz, from about 350 Hz to about 400 Hz, including values and subranges therebetween. In embodiments, the sensed cardiac electrical activity may be sampled after bandpass filtering by a 12-bit analog-to-digital converter (“ADC”). During normal operation, data may be transferred to the server “as-is” and can then be used by the remote server 102 for analysis. In embodiments, an internal process allows for real-time evaluation of the ECG signal quality upon each attachment of the device to the patient.

[0130] In embodiments, the remote server 102, the monitoring unit 104, and / or the portable gateway 108 may process the ECG signals to detect an arrhythmia of the patient. Types of arrhythmias detected by the remote server 102, the monitoring unit 104, and / or the portable gateway 108 may include ventricular ectopic beats (VEB), ventricular runs / ventricular tachycardia, bigeminy, supraventricular ectopic beats (SVEB), supraventricular tachycardia, atrial fibrillation, ventricular fibrillation, pauses, 2nd AV blocks, 3rd AV blocks, bradycardia, and / or other types of tachycardia. Additionally, the remote server 102, the monitoring unit 104, and / or the portable gateway 108 may perform other processing or analyses of the ECG signals, such as band pass filtering, detecting R-R intervals, detecting QRS intervals, and / or heart rate estimation.

[0131] As described, the monitoring device 100 may include the monitoring unit 104 configured to be attached to an adhesive patch 106, which in turn is configured to be removably mounted onto the patient’s skin. However, in embodiments, the non-invasive monitoring device 100 may be implemented differently. To illustrate, the non-invasive monitoring device 100 may not include the adhesive patch 106 and may be attached to the patient’s skin through another mechanism. As an example, the monitoring device 100 may instead include garment such as a band configured to be worn by the patient, where the monitoring unit 104 is permanently attached or integrated into the band or is removably attached to the band. The band may, for instance, include a frame similar to frame 112 that the monitoring unit 104 can snap into. The band may be worn across the patient’s torso, around a leg, around an arm, and / or the like. In embodiments, the monitoring device 100 may include bands of different lengths and / or widths to which the monitoring unit 104 can be interchangeably attached. The different sizes of bands may be configured such that the monitoring device 100 can be worn around various parts of the patient’s anatomy, such as a longer band configured to be worn around the patient’s torso and a shorter band configured to be worn around the patient’s wrist. In implementations, the band may include the functionality of the adhesivepatch 106 discussed above. For instance, the band may include embedded ECG electrodes similar to electrodes 114. An example of the monitoring device 100 including a band is shown in FIG. 12.

[0132] As another illustration, the monitoring device 100 may be implemented such that the monitoring unit 104 is not directly attached to the patient’s skin using, for instance, an adhesive patch or a band. Instead, the components used to take certain measurements from the patient, such as RF measurements as explained in further detail below, may be attached to the patient’s skin, with the monitoring unit 104 worn elsewhere. For example, FIG. 5 illustrates the monitoring unit 104 being worn on a belt of the patient. As an illustration, the monitoring unit 104 may include a belt clip configured to clip to the patient’s clothing. In the example of FIG. 5, the monitoring device 100 includes sensor patches in wired communication with the monitoring unit 104, such as a first sensor patch 400 and a second sensor patch 402. As shown, the first sensor patch 400 and the second sensor patch 402 are connected to the monitoring unit 104 via cables 1704. In implementations, the first sensor patch 400 and the second sensor patch 402 may be changed periodically, with replacements including additional sensor patches that can be attached to the cables 1704 or additional sensor patch / cable units that can be reconnected to the monitoring unit 104.

[0133] In implementations, the sensor patches 400 and 402 may include at least some of the sensor components used to take measurements from the patient (e.g., sensor components shown and described with reference to FIGS. 1, 5, and 6). Examples include one or more RF antennae and / or ECG electrodes. As an illustration, the first sensor patch 400 may include a transmitting RF antenna configured to transmit RF waves into the patient, as described in further detail below, and the second sensor patch 402 may include a receiving RF antenna configured to receive reflected and / or scattered RF waves from the patient. Each of the first sensor patch 400 and the second sensor patch 402 may also include an ECG electrode. As another illustration, one or more RF antennae may be included in the first sensor patch 400, as well as an ECG electrode, and the second sensor patch 402 may include only an ECG electrode. Additionally, embodiments of the monitoring device 100 that are not attached to the patient’s skin may include additional sensor patches and / or the sensor patches may be adhered to different parts of the patient’s torso. For instance, a monitoring device 100 may include three sensor patches, where each sensor patch has an ECG electrode and the sensor patches are configured to be positioned on the patient in a standard three-ECG lead configuration.

[0134] FIG. 6 provides an exploded view of the monitoring unit 104, according to various embodiments. The exploded view of FIG. 6 illustrates components of the monitoring unit 104. For example, the monitoring unit 104 may include a power source, such as a battery 500. In examples, the battery 500 may be a rechargeable lithium-ion battery configured to supply power for at least one month of continuous or near-continuous measurements. The monitoring unit 104 may also include network interface, such as a wireless communications circuit 502. The wireless communications circuit 502 may be a Bluetooth® unit, in various embodiments, although in addition to or alternatively to the Bluetooth® unit, other modules facilitating other types of communications (e.g., Wi-Fi, cellular, etc.) may be included in the monitoring unit 104. As shown in FIG. 6, the monitoring unit 104 may include other components such as a radio frequency shield 504 (e.g., a metallic cover, for instance, to prevent interferences with arterial measurement circuitry), a digital circuit board 506, and / or the like.

[0135] These components may be provided between a front cover 508 forming an upper surface of the monitoring unit 104 and a back cover 510 forming a bottom surface of the monitoring unit 104. For example, the back cover 510 may be configured to contact the adhesive patch 106, and the front cover 508 may be configured to face away from the patient such that the front cover is accessible when the monitoring unit 104 is attached to the adhesive patch 106. In embodiments, a light indicator 512 and / or a button 514 may be embedded into the front cover 508 visible through the upper surface. The light indicator 512 may provide feedback on the status of the monitoring unit 104 and its components, such as the charging and / or power level of the power source of the monitoring unit 104 (e.g., the battery 500), the attachment level of the monitoring unit 104 to the adhesive patch 106, the attachment level of the adhesive patch 106 to the surface of the patient’s body, etc. The button 514 may be configured for the patient and / or a caregiver to provide feedback to the monitoring unit 104 and / or the remote server 102. For instance, the button 514 may allow the patient and / or a caregiver to activate or deactivate the monitoring unit 104. As another illustration, the button 514 may be used to reset the monitoring unit 104, as well as pair the monitoring unit 104 to the portable gateway 108 and initiate communication with the portable gateway 108. As another illustration, the button 514 may allow a user to set the monitoring unit 104 in an “airplane mode,” for example, by deactivating any wireless communication (e.g., Wi-Fi, Bluetooth®, etc.) with external devices and / or servers, such as the portable gateway 108 and / or the remote server 102.

[0136] FIG. 7 illustrates an example electronic architecture for the monitoring unit 104. In embodiments, as shown in FIG. 7, the monitoring unit 104 includes one or more external interfaces, either connected to or embedded in the monitoring unit 104. For example, the monitoring unit 104 may include the button or switch 514 for activating the monitoring unit 104, deactivating the monitoring unit 104, pairing the monitoring unit 104 with the portable gateway 108, receiving a patient input, and / or the like. In embodiments, the monitoring unit 104 may also include the light indicator 512, as described above, and / or a buzzer 600 for providing haptic and / or audio feedback to a user of the monitoring unit 104. For example, the buzzer 600 may activate in response to the patient activating the button 514 or tapping the monitoring unit 104 to record that the patient is experiencing symptoms suspected to be related to an arrhythmia.

[0137] Further, in embodiments, the monitoring unit 104 may be connectable to the ECG pads or electrodes 114 coupled to the patient. For example, the monitoring unit 104 may be connectable to the ECG pads 114 embedded in the adhesive patch 106 when the monitoring unit 104 is attached to the adhesive patch 106 as shown in FIG. 4. In embodiments, the monitoring unit 104 may also be connectable to a charger, such as the charger 110, via a charging link 602. As an illustration, the back cover 510 of the monitoring unit 104 may include metal contacts configured to connect to the ECG pads 114 when the monitoring unit 104 is attached to the adhesive patch 106 and to a charging power source when the monitoring unit 104 is attached to the charger 110. Alternatively, or additionally, in embodiments, the monitoring unit 104 may include an inductive circuit configured to charge the monitoring unit 104 via a wireless inductive charging link 602. The ECG circuits 624 may receive data from the ECG pads 114 when the monitoring unit 104 is attached to the adhesive patch 106, where the data received from the ECG pads 114 include cardiac electrical activity of the patient. The ECG circuits 624 may then generate ECG signals using the sensed cardiac electrical activity of the patient. As shown in FIG. 7, the charging link 602 may be coupled to a power management circuit 604 (e.g., when the monitoring unit 104 is attached to the charger 110, when the monitoring unit 104 is placed in proximity to an inductive charging pad, and / or the like), where the power management circuit 604 is configured to charge an onboard power source, such as the battery 500.

[0138] Internally, in embodiments, the monitoring unit 104 may include a microprocessor (e.g., being connected to a separate non-volatile memory, such as memory 608) or a microcontroller 606. The microcontroller 606 stores instructions specifying how measurements (e.g., RFmeasurements, ECG measurements, and / or the like) are taken, how obtained data are transmitted, how to relay a status of the monitoring unit 104, how / when the monitoring unit 104 can enter a sleep level, and / or the like. In embodiments, the instructions may also specify the conditions for performing certain types of measurements. For example, the instructions may specify that, based on the signals from an accelerometer (e.g., accelerometer 622) of the monitoring unit 104, the monitoring unit 104 may not commence measurements unless the patient using the monitoring unit 104 is at rest or maintaining a certain posture. As another example, the instructions may identify the conditions that may have to be fulfilled before measurements can commence, such as a sufficient attachment level between the monitoring unit 104 and the adhesive patch 106 and / or a sufficient attachment level between the adhesive patch 106 and the surface of the patient’s body. In embodiments, the microcontroller 606 may have internal and / or external non-volatile memory banks (e.g., memory 608) that can be used for keeping measurement directories and data, scheduler information, and / or a log of actions and errors. This non-volatile memory allows saving power via a total power down while retaining data and status information.

[0139] As discussed above, in various embodiments, the monitoring unit 104 includes at least one RF antenna for directing electromagnetic RF waves into a body of a patient and receiving waves that are scattered and / or reflected from internal tissues. The at least one RF antenna may be flat, printed, set flush against the skin, with or without an interface material, and / or the like. The at least one RF antenna may be in a bow-tie, spiral, monostatic, bistatic, and / or like configurations. Further, the monitoring unit 104 includes RF circuitry configured to process the received waves so as to determine properties of the tissues that are on the path of the scattered / reflected waves. For example, the at least one RF antenna may direct RF waves towards one or more arteries in an aortic region of a patient. The RF circuitry may receive scattered / reflected waves from the aortic region and generate RF signals that include information about an arterial pulse waveform of the patient, as described in further detail below with respect to FIGS. 13 and 14.

[0140] As such, FIG. 7 shows an example embodiment of the monitoring unit 104 including two RF antennae 610a and 610b, in this instance, as well as an RF circuit 612, and other circuits for controlling the RF circuit (e.g., field-programmable gate array (FPGA) circuits 614). In various embodiments, the RF antennae 610a, 610b are configured to transmit RF waves to the body of a patient to which the monitoring unit 104 is attached and receive scattered / reflected RF waves from the body of the patient. FIG. 8 includes block diagrams that illustrate examples of RF sensorfunctionality implemented within the RF circuit 612. Such functionality may be used to monitor the volume of the patient’s arteries over time in accordance with the techniques described herein. As shown in FIG. 8, initially, one or more RF wave signals (e.g., a single local oscillator (LO) signal, or different “LOi” and “LO2” signals, collectively “LO signals”) can be generated by a broadband synthesizer 700. For example, the broadband synthesizer 700 may be a pulse generator and synthesizer, or local oscillator. Such a synthesizer 700 may include moderate phase noise performance and / or fast settling time capabilities. The RF circuit 612 also includes a transmitter portion 702, coupled to a transmitter RF antenna 610a (e.g., Tx) and associated circuitry for transmitting RF waves directed, for example, towards one or more arteries of the patient. The RF circuit 612 further includes a receiver portion 704 coupled to a receiver RF antenna 612b (e.g., Rx) and associated circuitry 482 for receiving reflected or scattered RF waves.

[0141] In embodiments, the LO signal of the transmitter portion 702 is multiplied with an external sine wave at a low frequency intermediate frequency (IF) signal, generated by an IF source 706, and directed to the output of the transmitter portion 702. As noted above, the LO signal at the transmitter portion 702 and the receiver portion 704 can be generated by one or more LO signal sources (e.g., synthesizer(s) 700). Output power may be controlled via a digitally controlled attenuator (DCA) on the LO signal transmitter path. An external, reflected RF wave returning to the receiver RF antenna 610b may be directed to the receiver portion 704 and down -converted to an IF frequency by a down conversion mixer. The reflection characteristics (e.g., phase and amplitude) can be transformed to a new IF carrier (e.g., on the order of 250 kHz), filtered, and amplified, before being forwarded to an analog-to-digital converter (ADC) 708. In embodiments, digital control for the functionality described with respect to FIG. 8 may be achieved directly by a processor and / or digital logic (e.g., an FPGA 614), which may be configured to control the transmitter and receiver configuration processes, IF signal adjustments, and associated switching. As shown in FIG. 8, the output of the RF circuit 612 may be in the form of serial peripheral interface (SPI).

[0142] In implementations, the at least one RF antenna (e.g., the transmitter RF antenna 610a and the receiver RF antenna 610b) is sized for one or more arteries to which the at least one RF antenna is configured to transmit the RF waves. For example, as described in further detail below with respect to FIG. 12, the at least one RF antenna may transmit RF waves to the patient’s radial artery. As such, the at least one RF antenna may be configured to be small and sized to the radial arteryto allow the at least one RF antenna to better receive reflected / scatted RF waves from the patient’s radial artery. As another example, as described in further detail below with respect to FIGS. 9 A and 9B, the at least one RF antenna may transmit RF waves to the patient’s aorta and aortic region and may be sized accordingly. In examples, the at least one RF antenna may have a surface area no greater than approximately 1.5 x 2.5 cm. To illustrate, each of the transmitter RF antenna 610a and the receiver RF antenna 610b may have a surface area no greater than approximately 1.5 x 2.5 cm. In examples, the at least one RF antenna may have a surface area no greater than approximately 1.0 x 2.0 cm. Having the at least one RF antenna sized for the one or more arteries may help with, for example, reducing noise and improving the signal quality by improving the interface with the patient’s skin.

[0143] In implementations, the monitoring unit 104 may also carry out depth tuning to generate a better quality RF signal. For example, the RF circuit 612 may generate RF waves configured for a number of different depths depending on the one or more arteries the RF waves are being directed towards. The RF circuit 612 may generate the RF waves for different depths, for instance, by varying the frequency and / or amplitude of the RF waves. To illustrate, the RF waves may be generated for depths of 2 to 4 cm with a range of 0.2 to 0.5 cm if the one or more arteries include the radial artery. As another illustration, the RF waves may be generated for depths of 3 to 10 cm with a range of 0.5 to 1.5 cm if the one or more arteries include the radial artery. The monitoring unit 104 may then determine which resulting reflected / scattered RF waves received back from the one or more arteries are the most periodic and differentiated. The monitoring unit 104 may then set characters of the RF waves to be transmitted into the patient based on which depth configuration produced the best reflected / scatted RF waves. Performing this process of depth tuning may therefore improve the signal quality of the RF signals.

[0144] In embodiments, the monitoring unit 104 may also include or be connected to one or more additional sensors. For example, as shown in FIG. 7, the monitoring unit 104 may include a motion sensor such as a 3D accelerometer 622. Using the 3D accelerometer 622, the monitoring unit 104 may acquire data on patient movements, patient orientation, patient respiration, and / or the like. The monitoring unit 104, the portable gateway 108, and / or the remote server 102 may use the acquired accelerometer data to determine physiological information for the patient, such as the patient’s posture or orientation, activity rate, respiration rate, and / or the like. In implementations, the monitoring unit 104 may use the physiological information, for example, to determine whento take RF measurements from the patient. As an illustration, to reduce artifacts and other bad readings, the monitoring unit 104 may only or primarily take RF measurements from the patient when the monitoring unit 104 determines from the accelerometer data that the patient is substantially stationary or otherwise inactive. For example, the monitoring unit 104 can determine from the accelerometer data (e.g., accelerometer counts) that the patient motion is below a preset threshold to determine that the patient is substantially stationary or otherwise inactive.

[0145] As discussed above, the non-invasive monitoring device 100 is configured to be worn on the patient’s skin in an area around a major artery of the patient. In implementations, the non-invasive monitoring device 100 is configured to be worn on a patient’s torso. As shown in FIG.9A, in implementations, the patient may apply the non-invasive monitoring device 100 to a location on their chest on the left side of the patient’s sternum 800. For example, the location may be a costoclavicular region on the patient. Alternatively, the patient may place the non-invasive monitoring device 100 over their sternum 800, as shown in FIG. 9B. In the examples shown in FIGS. 9A and 9B, the monitoring device 100 may be used to take measurements from the patient’s aorta and other arteries in the aortic region.

[0146] As an illustration, referring to FIG. 10, an embodiment of a non-invasive monitoring device 100 being used on a patient is shown. For example, an adhesive patch 106 has been applied to a thorax 1000 of the patient above the patient’s sternum 800. A monitoring unit 104 has been attached to the adhesive patch 106. The monitoring unit 104 includes an RF transmitter 1002 and an RF receiver 1004. The RF transmitter 1002 and the RF receiver 1004 are shown as larger components in FIG. 10 for purposes of illustration but may, in implementations, be flat components printed as part of a printed circuit board. For example, the RF transmitter 1002 and the RF receiver 1004 may be configured similarly to the RF transmitting and receiving components discussed above with reference to FIGS. 6 and 7, above. As illustrated in FIG. 10, the RF transmitter 1002 is configured to transmit RF waves 1006 through the patient’s thorax 1000 in the general direction of the patient’s heart 1008. In particular, the RF transmitter 1002 may transmit RF waves 1006 to an aortic region 1009 around the patient’s aorta 1010, as shown in FIG. 10. At least some of the transmitted RF waves 1006 may be scattered or reflected by the arteries in patient’s aortic region 1009, and reflected RF waves 1012 may be received at the RF receiver 1004.

[0147] In embodiments, the aortic region 1009 may include the patient’s aorta 1010 and / or one or more arteries that branch off of the aorta 1010 and are proximate to the aorta 1010. To illustrate, FIG. 11 shows an example of the aortic region 1009. As shown in FIG. 11, the aortic region 1009 may include the patient’s ascending aorta 1018, aortic arch 1020, and / or descending aorta 1022. Alternatively, or additionally, the aortic region 1009 may include one or more of the arteries branching off of the ascending aorta 1018, aortic arch 1020, and descending aorta 1022, such as the patient’s right coronary artery 1024, left coronary artery 1026, brachiocephalic artery 1028, right subclavian artery 1030, right common carotid artery 1032, left common carotid artery 1034, and / or left subclavian artery 1036.

[0148] Referring back to FIGS. 9A and 9B, in examples, the location of the monitoring device 100 may be adjusted to allow the monitoring device 100 to take measurements from another part of the patient’s thorax. For instance, the monitoring device 100 may take measurements from a subclavian artery of the patient. To illustrate, the monitoring device 100 may be positioned upwards on the patient’s torso to be close to or over the patient’s clavicle 802.

[0149] In implementations, the non-invasive monitoring device 100 may, additionally or alternatively, be configured to be worn on or otherwise removably attached to an extremity of the patient. For example, FIG. 12 illustrates another embodiment of the monitoring device 100. Whereas the monitoring device 100 shown in FIGS. 9 A and 9B includes an adhesive patch 106 configured to be adhesively attached to the patient, the embodiment illustrated in FIG. 12 includes a garment configured as a band 900 configured to be worn around the patient’s extremity. The monitoring unit 104 is mounted onto the band 900. In examples, the monitoring unit 104 may be permanently attached to the band, while in other examples, the monitoring unit 104 may be removably attached to the band. For instance, the band 900 may include a frame similar to frame 112 that the monitoring unit 104 can snap into (e.g., as shown in the process illustrated in FIG. 4). As another example, the monitoring unit 104 may include hook or loop fabric configured to attach to mating hook or loop fabric on the band 900. The band may be attached to the patient through elastic, a buckle, a hook-and-loop fabric closure, and / or the like. In the example of FIG. 12, the band 900 is worn on the patient’s arm over the patient’s wrist. For example, the band 900 may be positioned such that the monitoring device 100 may take measurements from the patient’s radial artery.

[0150] In examples, the band 900 may be configured to be positioned over a different part of an extremity. As an illustration, the band 900 may be configured to be worn on the patient’s upper arm. In such instances, the monitoring device 100 may be configured to take measurements from the patient’s brachial artery. As another illustration, the band 900 may be configured to be worn on a different part of the patient’s lower arm, such as partway between the patient’s elbow and their wrist. The monitoring device 100 may be configured to take measurements from a different part of the patient’s radial artery, in such instances. As another illustration, the band 900 may be configured to be worn on the patient’s leg. In this instance, the monitoring device 100 may be configured to take measurements from the patient’s femoral artery. Alternatively, the monitoring device 100 may include an adhesive patch (e.g., adhesive patch 106) instead of the band 900 and be configured to be worn on any of these locations using the adhesive patch. Additionally, the monitoring device 100 may be configured to be attached to other locations near major arteries of the patient.

[0151] FIG. 13 illustrates a sample process flow for taking arterial measurements from a patient. For example, the sample process 1100 as shown in FIG. 13 can be implemented by the monitoring unit 104 shown and described above. As an illustration, one or more processors of the monitoring unit 104 (e.g., the microcontroller 606 shown in FIG. 7) may execute instructions configured to cause components of the monitoring unit 104 to perform the sample process 1100. The monitoring unit 104 may store the instructions in non-transitory computer-readable memory (e.g., stored at the microcontroller 606 and / or at separate memory 608, as shown in FIG. 7).

[0152] As shown in FIG. 13, the monitoring unit 104 transmits arterial measurement waves towards one or more arteries at step 1102. The one or more arteries may include a major artery of the patient, as described above. For example, the one or more arteries may include the aorta, arteries in an aortic region, a subclavian artery, a brachial artery, a radial artery, a femoral artery, and / or the like. In implementations, the monitoring unit 104 may include at least one arterial measurement transmitter configured to transmit arterial measurement waves towards the one or more arteries of the patient. As an illustration, the at least one arterial measurement transmitter may be or include at least one RF antenna configured to transmit RF waves towards the one or more arteries. For instance, in embodiments, the at least one arterial measurement transmitter may include the transmitter RF antenna 610a shown in FIGS. 7-8. Accordingly, the transmitter RFantenna 610a may transmit RF waves towards one or more arteries of the patient as described above with reference to FIGS. 7-8.

[0153] The monitoring unit 104 receives reflected and / or transmitted arterial measurement ways from the one or more arteries at step 1104. In implementations, the monitoring unit 104 may include at least one arterial measurement receiver configured to receive the reflected and / or transmitted arterial measurement waves from the one or more arteries. To illustrate, the at least one arterial measurement receiver may be or include at least one RF antenna configured to receive reflected / scattered waves from the one or more arteries. In embodiments, the at least one arterial measurement receiver may include the receiver RF antenna 610b shown in FIGS. 7-8, and the receiver RF antenna 610b may receive the reflected / scattered RF waves as described above with reference to FIGS. 7-8. In embodiments, the at least one arterial measurement transmitter and at least one arterial measurement receiver may be implemented in the same component. For example, the monitoring unit 104 may include a transceiver, such as an RF transceiver, configured to both transmit and receive arterial measurement waves.

[0154] In embodiments, the non-invasive monitoring device 100 may instead be configured to receive transmitted arterial measurement waves, instead of or in addition to reflected / scattered arterial measurement waves. For instance, the non-invasive monitoring device 100 implemented as a monitoring unit 104 mounted on a band 900, as shown in FIG. 12, may include an arterial measurement transmitter in the monitoring unit 104 and an arterial measurement receiver embedded or otherwise incorporated into the band 900 such that the arterial measurement receiver sits on the other side of the patient’s wrist from the arterial measurement transmitter when worn. As such, the non-invasive monitoring device 100 may transmit arterial measurement waves into the patient’s radial arteries at the arterial measurement transmitter in the monitoring unit 104 and receive arterial measurement waves transmitted through the patient’s radial arteries at the arterial measurement receiver in the band 900. In embodiments, the monitoring unit 104 may also include an arterial measurement receiver so that the non-invasive monitoring device 100 can receive both transmitted arterial measurement waves and reflected / scattered arterial measurement waves.

[0155] The monitoring unit 104 generates arterial measurement signals corresponding to the one or more arteries using the reflected and / or transmitted arterial measurement waves at step 1106. In implementations, the monitoring unit 104 may include arterial measurement circuitry configured to generate the arterial measurement signals. As an example, the monitoring unit 104 may includeRF circuitry, for instance, implemented using the RF circuit 612 and the FPGA 614 shown in FIG.7. The RF circuit 612 and the FPGA 614 may generate RF signals from reflected / scattered RF waves as described above with reference to FIGS. 7 and 8.

[0156] In implementations, the non-invasive monitoring device 100 proceeds to carry out sample process 1200, discussed below with reference to FIG. 14, locally at step 1108. For example, the one or more processors of the monitoring unit 104 may carry out sample process 1200. As another example, alternatively or additionally, one or more processors of the portable gateway 108 may carry out sample process 1200. To illustrate, the monitoring unit 104 may transmit the arterial measurement signals (e.g., RF signals) to the portable gateway 108 using the processed described above with reference to FIG. 1. The monitoring unit 104 may include, for instance, a network interface (e.g., configured as the wireless communications circuit 502 shown in FIG. 7) configured to communicate with the portable gateway 108 and transmit the arterial measurement signals (e.g., among other signals, such as ECG signals and / or accelerometer signals) to the portable gateway 108. The portable gateway 108 may then execute sample process 1200.

[0157] In implementations, the monitoring unit 104 may transmit the arterial measurement signals to a remote server at step 1110. As an example, the monitoring unit 104 may include a network interface (e.g., configured as the wireless communications circuit 502 shown in FIG. 7) configured to communicate with a remote server, such as the remote server 102 shown in FIG. 1. Using the network interface, the monitoring unit 104 may transmit the arterial measurement signals (e.g., RF signals and / or among other signals, such as ECG signals and / or accelerometer signals) to the remote server 102, as discussed with reference to FIG. 1. In illustrations, the monitoring unit 104 may transmit the arterial measurement signals to the remote server 102 directly or via the portable gateway 108, as further described with reference to FIG. 1. The remote server 102 may then carry out sample process 1200.

[0158] In implementations, the non-invasive monitoring device 100 may carry out steps 1108 and 1110. As an illustration, the portable gateway 108 and the remote server 102 may carry out sample process 1200 concurrently. In implementations, the non-invasive monitoring device 100 may carry out only one of steps 1108 and 1110. To illustrate, non-invasive monitoring device 100 may transmit the arterial measurement signals to the remote server 102, which independently carries out sample process 1200. Accordingly, steps 1108 and 1110 are illustrated in FIG. 13 with dashedlines to indicate that the non-invasive monitoring device 100 may carry out one or both of steps 1108 and 1110.

[0159] FIG. 14 illustrates a sample process flow for determining a measurement relating to an output of the patient’s heart. In various embodiments, the sample process 1200 as shown in FIG.14 can be implemented by cardiac output processing circuitry in electronic communication with the arterial measurement circuitry. In implementations, the cardiac output processing circuitry may be located at the monitoring unit 104 shown and described above. For example, one or more processors of the monitoring unit 104 (e.g., the microcontroller 606 shown in FIG. 7) may execute instructions configured to cause the monitoring unit 104 to perform the sample process 1200. The monitoring unit 104 may store the instructions in a non -transitory computer-readable memory (e.g., stored at the microcontroller 606 and / or at a separate memory 608, as shown in FIG. 7). In implementations, cardiac output processing circuitry can be located at the portable gateway 108 shown and described above. One or more processors of the portable gateway 108 may execute instructions configured to cause the portable gateway 108 to perform the sample process 1200, where the portable gateway 108 is configured to store the instructions in a non -transitory computer-readable memory. In instances, the portable gateway 108 may perform the sample process 1200 as part of executing an application related to determining heart output measurements on the portable gateway 108. In implementations, the cardiac output processing circuitry may be located at a remote server, such as the remote server 102 discussed above with reference to FIG.1, in electronic communication with the monitoring unit 104. One or more processors of the remote server 102 may execute instructions configured to cause the remote server 102 to perform the sample process 1200. The remote server 102 may store the instructions in a non -transitory computer-readable memory at the remote server 102.

[0160] The cardiac output processing circuitry is configured to identify an arterial pulse waveform for one or more arteries from arterial measurement signals at step 1202. For example, in implementations, as discussed above, the arterial measurement signals may include RF signals generated by the monitoring unit 104. These RF signals may measure the area or diameter of the one or more arteries. In implementations, the cardiac output processing circuitry may perform at least some analysis and / or signal processing on the RF signals as part of identifying the arterial pulse waveform.

[0161] As an illustration, identifying an arterial pulse waveform from the RF signals may include transforming the RF signals into an arterial pressure wave. For example, for each subject state there is an arterial compliance curve CartPtm) (i.e. , a relation between changes in arterial cross section area and changes in transmural pressure). This compliance curve controls the relationship between blood pressure and pulse wave velocity (PWV), or the velocity of a pressure wave traveling through the patient’s arteries. The compliance curve can be inferred by measuring pulse arrival time (PAT) at multiple cuff pressures, where PAT represents the interval between the R peak of an ECG waveform and the foot of the corresponding systolic pressure waveform.

[0162] In examples, PWV is not measured directly. Instead, the PAT is measured. For example, the cardiac output processing circuitry can determine an ECG waveform for the patient (e.g., as described in further detail below) and identify an R peak in the ECG waveform. The cardiac output processing circuitry can also identify the start of the systolic portion of a corresponding arterial pulse waveform (e.g., as also described in further detail below). The cardiac output processing circuitry can then measure the PAT as the time difference between the R peak and the start of the systolic portion of the corresponding arterial pulse waveform. To illustrate, FIG. 15A depicts an amplitude of an arterial pulse waveform 1400 over time on the same graph as an ECG signal 1350 over time. The cardiac output processing circuitry can identify an R peak 1352, for example, using a feature extractor or the Pan-Tompkins algorithm. The cardiac output processing circuitry can also identify the start of the corresponding individual pulse waveform 1402, for example, as described in further detail below with reference to step 1204. The cardiac output processing circuitry can then determine the PAT as the time difference between points 1352 and 1402. In examples, for the purposes of arterial pulse waveform calibration, the PAT may be measured through an external device, such as a finger probe configured to use photoplethysmography to generate the arterial pulse waveform used for measurement PAT.

[0163] In examples, changes in the PWV can be inferred from changes in PAT (e.g., assuming that the pre-ejection period (PEP), or the time elapsed between the electrical depolarization of the left ventricle and the beginning of the ventricular ejection, remains constant). As such, assuming a blood pressure measurement for PWV (e.g., taking using a sphygmomanometer) coupled with a PAT measurement (both will be referred as reference measurements), the relationship between a reference PAT measurement and a reference PWV measurement can be depicted as follows:LP ATref + PEP (1)PWVrefIn above Equation 1, L represents the length over which the PAT is measured. For example, for a PAT taken using a radial arterial pulse waveform measurement, L may be approximately 70 to 90 cm (e.g., the distance from the patient’s heart to their wrist). As another example, for a PAT taken using an aortic region measurement, L may be approximately 2 to 10 cm. The same relationship holds when evaluating the pressure, as shown by Equation 2 below:L PAT = PTT + PEP = — — + PEP (2)PWV

[0164] From Equations 1 and 2, Equation 3 can be derived, by denoting dPAT as the difference between the above PAT and PATref values:1PWV(P) = dPAT / . 1 / / L+ / PWVrefAdditional relationships can be derived given the description of PWV according to the Bramwell-Hill relation, which is provided below:(Ptm)PWV(Ptm) =t(.Ptm)In this equation, Aart(Ptm) represents the arterial cross-sectional area (or volume per unit length). Additionally, Cart is the arterial compliance per unit length at transmural pressure Ptm, which can be further represented by Equation 5 below.

[0165] Cuff inflation changes the transmural pressure under a sphygmomanometer cuff according to the following equation, where BP represents blood pressure and Pcuff represents the transmural pressure under the cuff:Ptm=BP ~ Pcuff (6)This means that if the functional form of Aart(Ptm) is known, the compliance can be inferred, and from it the PWV under the cuff for each cuff pressure. Assuming the sphygmomanometer cuff does not greatly affect flow, only the PWV change under the cuff affects the change in PAT. As discussed above, the system can determine the PAT as the time difference between points 1352 and 1402.

[0166] For instance, Laura I. Bogatu et. al. (2021), “Modulation of Pulse Propagation and Blood Flow via Cuff Inflation — New Distal Insights”, Sensors 2021, 21, 5593 uses the following functional form, which was previously found by fitting experimental data:In Equation 7, the parameter b is taken as fixed at 3.3. Parameters a and c can be fitted from the cuff inflation data, and d does not affect the PWV. Once a and c are known based on how transmural pressure is related to PWV, blood pressure can be inferred from the PWV, which is calculated from dPAT The reference PWV is calculated from the cuff-measured pressure. As such, using Equations 1 and 7, the RF signal may be transformed into a pressure signal.

[0167] In implementations, the cardiac output processing circuitry may be configured to identify arterial pulse waveforms for the one or more arteries directly from the RF signals. For example, the raw RF signals of amplitude over time (e.g., as shown in FIG. 15A) may show strong correlation with pressure signals. As an illustration, FIGS. 15B and 15C shows graphs 1560 of arterial pulse waveforms from RF signals 1562 (e.g., measured using a radial artery) againstarterial pulse waveforms from pressure signals 1564. The pressure wave signals were generated using an arterial line catheter. For each of the graphs 1560, the RF signal waveforms 1562 and the pressure signal waveforms 1564 are aligned so that their maximum slopes occur at the same time, and each is normalized to the range of 0 to 1. Each line indicates the mean waveform over a minute, and the shaded areas represent the standard deviation of the signals in that minute. As shown, the systolic pressure rise is similar for both the RF signals and the pressure signals, and the dicrotic notch is visible in both and aligns well in time. As such, in implementations, the cardiac output processing circuitry may use the arterial pulse waveforms derived from the raw RF signals, particularly where the systolic portion of the arterial pulse waveform is used to determine the cardiac output as described in further detail below.

[0168] In implementations, as part of step 1202, the cardiac output processing circuitry may identify individual arterial pulse waveforms. For instance, FIG. 15D illustrates example an arterial pulse waveform 1300 produced from the non-invasive monitoring device 100 being using RF to take measurements from the patient’s aortic region. More specifically, FIG. 15D shows the amplitude of the arterial pulse waveform 1300 over time (in seconds). As shown, the larger arterial pulse waveform 1300 is composed of individual arterial pulse waveforms 1302. The cardiac output processing circuitry may thus apply a feature extractor to the arterial pulse waveform 1300 to identify one or more of the individual pulse waveforms 1302 to use in the remainder of the sample process 1200. As an example, the cardiac output processing circuitry may be trained through machine learning to identify a start point 1304 and an end point 1306 for individual arterial pulse waveforms 1302. As another example, the cardiac output processing circuitry may identify the start point 1304 and the end point 1306 based on the points 1304 and 1306 being local minimums. In implementations, the cardiac output processing circuitry may repeat the step 1202 of identifying an arterial pulse waveform to identify a number of individual arterial pulse waveforms.

[0169] In implementations, identifying the arterial pulse waveform as part of step 1202 may include determining a representative arterial pulse waveform. To illustrate, the cardiac output processing circuitry may examine one or more segments of the arterial measurement signals. As an example, the segments may be divided according to time (e.g., one-minute segments, two-minute segments, five-minute segments, and / or the like). As another example, the segments may be segments of the arterial measurement signals transmitted by the non-invasive monitoring device 100 to the remote server 102. As another example, the segments may be portions of the arterialmeasurement signals that the cardiac output processing circuitry determines has noise below a predetermined threshold, were taken according to certain predetermined conditions (e.g., when the patient was stationary, as determined by accelerometer signals from the non-invasive monitoring device 100), and / or the like. The cardiac output processing circuitry may analyze the one or more segments of the arterial measurement signals to identify individual arterial pulse waveforms, like the individual arterial pulse waveform 1302 shown in FIG. 15D, as described above. The cardiac output processing circuitry may further segment these into segmented arterial pulse waveforms. For instance, the cardiac output processing circuitry may identify the start point 1304 and the end point 1306 for a number of individual arterial pulse waveforms 1302 and divide the individual arterial pulse waveforms 1302 into segmented arterial pulse waveforms. The cardiac output processing circuitry may then generate a representative arterial pulse waveform from the segmented arterial pulse waveforms. In examples, the cardiac output processing circuitry may average the segmented arterial pulse waveforms to generate the representative arterial pulse waveform, which serves as an average arterial pulse waveform for the segments of arterial measurement signals analyzed.

[0170] Referring back to FIG. 14, the cardiac output processing circuitry may analyze the arterial pulse waveform to identify one or more arterial pulse landmarks. For example, the cardiac output processing circuitry may identify one or more arterial pulse landmarks in an individual arterial pulse waveform. As another example, the cardiac output processing circuitry may identify one or more arterial pulse landmarks in a representative arterial pulse waveform, as described above.

[0171] In implementations, the one or more arterial pulse landmarks may include at least a beginning and an end of the systolic portion of the arterial pulse waveform. For example, FIG. 16 illustrates the amplitude of the arterial pulse waveform 1400 over time. As shown in FIG. 16, the cardiac output processing circuitry may analyze the arterial pulse waveform 1400 to identify the start of an individual arterial pulse waveform 1402, which also represents the beginning of the systolic portion of the arterial pulse waveform, and the dicrotic notch 1404, which also represents the end or around the end of the systolic portion of the arterial pulse waveform. In implementations, the one or more arterial pulse landmarks may include additional or alternative landmarks. To illustrate, the cardiac output processing circuitry may additionally, or alternatively, identify the systolic peak 1406 and / or the dicrotic peak 1408 of the individual arterial pulse waveform, as further shown in FIG. 16.

[0172] In various embodiments, the cardiac output processing circuitry may identify the one or more arterial pulse landmarks using local minima and / or maxima analysis. For instance, the cardiac output processing circuitry may identify the start point 1402 and the dicrotic notch 1404 using local minima analysis. As another example, the cardiac output processing circuitry may confirm the identification of the start point 1402 and the dicrotic notch 1404 by further identifying the systolic peak and / or the dicrotic peak 1408 using local maxima analysis. To illustrate, by verifying that the systolic peak 1406 lies between the start point 1402 and the dicrotic notch 1404 and / or by verifying that the dicrotic notch 1404 is followed by the dicrotic peak 1408, the cardiac output processing circuitry can confirm that it has correctly identified the start point 1402 and the dicrotic notch 1404. Otherwise, the cardiac output processing circuitry may, in examples, discard the individual arterial pulse waveform as unreliable and move onto analyzing the next individual arterial pulse waveform. In implementations, the cardiac output processing circuitry may use another method of analysis for identifying the arterial pulse landmarks, such as a feature extractor designed to identify the desired arterial pulse landmarks (e.g., the start and end of the systolic portion of the arterial pulse waveform).

[0173] In implementations, the cardiac output processing circuitry may use one or more additional signals to aid in identifying the arterial pulse landmarks. For instance, as discussed above, the monitoring device 100 may include ECG electrodes 114 in various embodiments. The cardiac output processing circuitry may identify features of the ECG signals generated from cardiac activity sensed by the ECG electrodes 114 and use these ECG features in identifying one or more arterial pulse landmarks. To illustrate, the cardiac output processing circuitry may identify R peaks in the ECG signals, such as by using the Pan-Tompkins algorithm or another feature extractor to identify QRS complexes in the ECG signals. As shown in FIG. 15 A, the R peak 1352 of a patient’s ECG signal 1350 may be closely associated with a start point 1402 of a cardiac cycle in an arterial pulse waveform 1400. In use cases, the cardiac output processing circuitry may first identify an R peak 1352 and examine a time period following the R peak 1352 in the arterial pulse waveform 1400 to identify a corresponding start point 1402 of a cardiac cycle. For example, the cardiac output processing circuitry may examine a period of 100 ms, 250 ms, 500 ms, and / or the like after an R peak. Such limited analysis of the arterial pulse waveform 1400 may save processing time, particularly where R peaks may already be identified by the cardiac output processing circuitry for other uses in analyzing the patient’s cardiac health. In use cases, the cardiac output processingcircuitry may use the R peak 1352 as an initial location for identifying the start point 1402 of a cardiac cycle where the start point 1402 is unclear. As an example, if the cardiac output processing circuitry is analyzing an arterial pulse waveform 1400 with a relatively low amplitude and / or a relatively high amount of noise, and the cardiac output processing circuitry cannot identify the start point 1402 with at least a predetermined level of confidence, the cardiac output processing circuitry may identify the R peak 1352 in the ECG signal 1350. The cardiac output processing circuitry may then set the R peak 1352 as the approximate start point 1402. Alternatively, the cardiac output processing circuitry may use the R peak 1352 to narrow the section of the arterial pulse waveform for analysis, such as by applying a more processing-intensive local minima analysis of the section of the arterial waveform 1400 following the R peak.

[0174] As another illustration, the cardiac output processing circuitry may identify T waves in the ECG signals using a feature extractor. With reference to FIG. 15 A, for example, the T wave 1354 may occur before the dicrotic notch 1404, as the T wave 1354 marks the repolarization of the ventricles as the semilunar valves of the heart close, producing the dicrotic notch 1404. As such, similar to the R peak discussed above, the cardiac output processing circuitry may identify the T wave 1354 and use the T wave to identify the dicrotic notch 1404. The cardiac output processing circuitry may use the T wave as a starting point for identifying the dicrotic notch 1404 more generally or, in certain use cases, in response to the cardiac output processing circuitry being unable to identify the dicrotic notch with at least a predetermined level of confidence. In examples, to identify the dicrotic notch, the cardiac output processing circuitry may examine a period of 100 ms, 250 ms, 500 ms, and / or the like in the arterial pulse waveform 1400 after the T wave 1354.

[0175] In implementations, the cardiac output processing circuitry may use other types of signals to identify the arterial pulse landmarks. In examples, the monitoring unit 104 may include a bioacoustics sensor configured to detect bioacoustics markers of the patient’s heart. Such bioacoustics markers may include, for instance, SI markers associated with the closing of the atrioventricular valves during ventricular contraction and S2 marker associated with the closing of the semilunar valves during ventricular diastole. The S2 marker, in particular, may be associated with the dicrotic notch 1404, as the dicrotic notch 1404 is also created by the semilunar valves closing. As such, in various use cases, the cardiac output processing circuitry may identify S2 markers in bioacoustics signals produced by the bioacoustics sensor and examine a time period after or around the S2 markers to identify the dicrotic notch. Similar to the examples of R peaksand T waves discussed above, the cardiac output processing circuitry may use the S2 marker as a starting point for identifying the dicrotic notch 1404 generally or in response to the cardiac output processing circuitry being unable to identify the dicrotic notch with at least a predetermined level of confidence. In examples, the cardiac output processing circuitry may examine a period of 100 ms, 200 ms, 300 ms, 400 ms, 500 ms, and / or the like in the arterial pulse waveform 1400, with this time period either starts after the dicrotic notch or is centered around the dicrotic notch.

[0176] In implementations, the cardiac output processing circuitry may combine steps 1202 and 1204. As such, rather than identifying individual arterial pulse waveforms, the cardiac output circuitry may move straight to identifying systolic portions within a larger arterial pulse waveform. For example, the cardiac output processing circuitry may identify all of the start and end points for systolic portions within the larger arterial pulse waveform.

[0177] Referring back to FIG. 14, the cardiac output processing circuitry determines an area under the arterial pulse waveform using the one or more arterial pulse landmarks at step 1206. In implementations, the cardiac output processing circuitry may integrate the arterial pulse waveform or find a Riemann sum under the arterial pulse waveform between the landmarks identified as part of step 1204. For example, the cardiac output processing circuitry may be configured to find an area of the systolic portion of the arterial pulse waveform at step 1206. As such, the cardiac output processing circuitry may find the area under the arterial pulse waveform between the start and end points of the systolic portion identified at step 1204. To illustrate, the cardiac output processing circuitry may find the area under the arterial pulse waveform between the start point 1402 and the dicrotic notch 1404, shown in FIG. 16.

[0178] The cardiac output processing circuitry calculates a measurement relating to an output of the patient’s heart using the determined area under the arterial pulse waveform at step 1208. For example, the measurement relating to the patient’s heart may be cardiac output, stroke volume, ejection fraction, and / or the like. In implementations, the cardiac output processing circuitry is configured to calculate at least the cardiac output for the patient. The calculation may be represented as the following:Cardiac output « Area under the curve X Heart rate (8)As such, the cardiac output processing circuitry may be configured to further determine the heart rate of the patient as part of calculating the patient’s cardiac output.

[0179] For instance, in embodiments and as discussed above, the non-invasive monitoring device 100 may include ECG electrodes, such as ECG electrodes 114 shown above, configured to sense cardiac electrical activity of the patient. The monitoring device 102 may generate ECG signals for the patient, which the cardiac output processing circuitry may analyze to determine the patient’s heart rate. As an illustration, the cardiac output processing circuitry may use a feature extractor to identify QRS complexes or R waves in particular in the ECG signals. As another example, the cardiac output processing circuitry may use the Pan-Tompkins algorithm to detect QRS complexes in the ECG signals. The cardiac output processing circuitry may then count the number of R waves that occur within a predetermined amount of time to determine the patient’s heart rate. For instance, the cardiac output processing circuitry may determine the number of R waves that occur over the same length of time as the arterial measurement signals used throughout the sample process span. The cardiac output processing circuitry may then divide the number of R waves over the length of time in minutes to determine the patient’s heart rate.

[0180] As another illustration, the cardiac output processing circuitry may be configured to determine the patient’s heart rate using the arterial measurement signals. To illustrate, with reference to FIG. 16, the RF arterial pulse waveform 1400 cycles regularly with the patient’s heartbeat. As such, the cardiac output processing circuitry may identify the number of individual arterial pulse waveforms within a predetermined period of time to determine the patient’s heart rate. For example, the cardiac output processing circuitry may identify the systolic peaks 1406 within a predetermined period of time, count the number of systolic peaks 1406, and divide the number of systolic peaks by the period of time in minutes to determine the patient’s heart rate.

[0181] Referring back to the formula for cardiac output above, the cardiac output processing circuitry may then determine the patient’s cardiac output by multiplying the area under the arterial pulse waveform determined at step 1206 by the patient’s heart rate. In implementations, the cardiac output processing circuitry may include one or more additional terms in the cardiac output calculation. For example, the cardiac output processing circuitry may include terms representing arterial compliance, the shape of the arterial pulse waveform, a calibration factor for the patient, and / or the like. As an illustration the cardiac output processing circuitry may determine the cardiacoutput using the following formula, where CF represents a patient-specific calibration factor, HR represents the heart rate, and APWit) represents the arterial pulse wave over time:Cardiac output = CF X HR X J APW(t)dtsystoleAs another illustration, the cardiac output processing circuitry may determine the cardiac output using a more comprehensive formula, as shown by Equation 10 below, where AC(p) represents the arterial compliance for a given pressure, and dAPW / dt represents the slope of the arterial pulse wave over time:

[0182] In examples, the arterial compliance, represented as AC(p) above, may be a model of the patient’s arterial elasticity, which varies as a function of arterial pressure. As such, the AC(p) term may vary across the systolic time according to the APW(t) term in this equation, which may represent arterial pressure over time. In examples, the slope of the arterial pulse wave over time, represented as dAPW / dt above, may represent the cardiac contractility of the patient’s arteries. The cardiac output processing circuitry may determine the dAPW / dt by finding the derivative of the AP Wit) curve or approximate the derivative by finding rate of change over a small interval between consecutive points of the APWit) curve.

[0183] In implementations, as noted above, the cardiac output processing circuitry may be configured to calibrate the cardiac output relative to a baseline of the patient. For instance, in various embodiments and as noted above, the cardiac output processing circuitry may be configured to determine a patient-specific calibration factor configured to calibrate the cardiac output. In implementations, the baseline of the patient may be or include one or more absolute calibration values for the patient. These absolute calibration values may be configured to allow thecardiac output processing circuitry to output an absolute cardiac output for the patient, rather than a relative cardiac output.

[0184] In examples, the cardiac output processing circuitry may be configured to receive the one or more absolute calibration values for the patient. As an illustration, the cardiac output processing circuitry may receive the one or more absolute calibration values at the time the patient is provided with the non-invasive monitoring device 100. For instance, when the patient receives the non-invasive monitoring device 100, a technician and / or a clinician may take the one or more absolute calibration values. The technician and / or clinician may then input the one or more absolute calibration values to the cardiac output processing circuitry using a technician interface 116 and / or a caregiver interface 118. The cardiac output processing circuitry may then determine the calibration factor using the one or more absolute calibration values.

[0185] In examples, the non-invasive monitoring device 100 may determine the one or more absolute calibration values or be used in determining the one or more absolute calibration values for the patient. To illustrate, as discussed in further detail below, the one or more absolute calibration values may include a blood pressure of the patient. As such, the patient may use several non-invasive monitoring devices 100 along an arterial path of the patient’s body, where the cardiac output processing circuitry can determine the patient’s blood pressure using arterial measurement signals generated by the non-invasive monitoring devices 100. For instance, the patient may use a first non-invasive monitoring device 100 near the patient’s aorta (e.g., as shown in FIG. 9A or 9B) and a second non-invasive monitoring device 100 along the patient’s radial artery (e.g., as shown in FIG. 12). The cardiac output processing circuitry may identify corresponding points on each of the resulting arterial pulse waveforms from the two monitoring devices 100. As an example, the cardiac output processing circuitry may identify a systolic peak on an individual waveform produced by the first non-invasive monitoring device 100 and a systolic peak on a corresponding waveform produced by the second non-invasive monitoring device 100. The cardiac output processing circuitry may then determine a time difference between the two corresponding points as a pulse transit time (PTT).

[0186] Using the PTT, the cardiac output processing circuitry may then determine the patient’s blood pressure. As an illustration, the cardiac output processing circuitry may determine the patient’s pulse wave velocity (PWV) by dividing a distance between the arteries measured by the first non-invasive monitoring device 100 and the second non-invasive monitoring device 100 bythe PTT. In examples, the distance between the monitoring devices 100 may be measured by the technician or a caregiver, may be estimated based on body measurements of the patient (e.g., based on the patient’s height, weight, and / or chest circumference), and / or the like. A patient’s PWV may be represented by the Moens-Korteweg equation:In the Moens-Korteweg equation, h is the artery wall thickness, Eincis the arterial stiffness (e.g., Young’s modulus), p is the blood density, and R is the artery radius. The Moens-Korteweg equation may be modified to provide the equation below that includes the patient’s blood pressure (P):In the above equation, Eo is the arterial elasticity, and Po is a constant to calibrate the blood pressure. As such, the cardiac output processing circuitry may use the PWV calculated for the patient, as well as known constants or constants the cardiac output processing circuitry identifies for the patient (e.g., based on patient measurements, parameters, and / or the like input by a technician or a clinician), to calculate the patient’s blood pressure. The blood pressure then serves as an absolute calibration value for the patient.

[0187] In various implementations, as discussed above, the cardiac output processing circuitry may receive or determine the one or more absolute calibration values when the patient is provided with the non-invasive monitoring device 100. In implementations, the cardiac output processing circuitry may receive or determine updated absolute calibration values after the patient has been using the non-invasive monitoring device 100 for a certain period of time. For example, the cardiac output processing circuitry may receive or determine updated absolute calibration values according to a predetermined schedule. To illustrate, the cardiac output processing circuitry may receive or determine the one or more absolute calibration values once every three days, once every five days,once a week, once every ten days, once every two weeks, and / or the like. The cardiac output processing circuitry may determine the updated absolute calibration values automatically, or the cardiac output processing circuitry may prompt the patient or a caregiver to provide the updated absolute calibration values. As an illustration, the absolute calibration values may include the patient’s blood pressure, and the cardiac output processing circuitry may prompt the patient or a caregiver to take the patient’s blood pressure periodically and input the patient’s blood pressure. The patient or caregiver may input the patient’s blood pressure, for instance, using the portable gateway 108 and / or using a caregiver interface 118. As another example, the cardiac output processing circuitry may receive or determine updated absolute calibration values when the patient goes in for regularly scheduled doctor appointments. For instance, whenever the patient attends a regular checkup, the patient’s clinician may determine one or more updated absolute calibration values and input the one or more updated absolute calibration values to the cardiac output processing circuitry via a caregiver interface 118.

[0188] In examples, the absolute calibration values may include one or more absolute cardiac output values for the patient. As an illustration, a clinician may measure an absolute cardiac output for the patient using echocardiography, as described above. As another illustration, a clinician may measure an absolute cardiac output for the patient using thermodilution, as also described above. In examples, the absolute calibration values may include one or more blood pressure values for the patient. To illustrate, the patient or a caregiver for the patient may measure the patient’s blood pressure using a sphygmomanometer. As another illustration, the cardiac output processing circuitry may determine the patient’s blood pressure using multiple non-invasive monitoring devices 100, an example of which is outlined above.

[0189] Using the one or more absolute calibration values, the cardiac output processing circuitry may determine a calibration factor for the patient. The cardiac output processing circuitry, as part of step 1208, may then calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further using the calibration factor. Such calculated cardiac output may represent an absolute cardiac output for the patient (e.g., as opposed to a relative cardiac output). For example, where the one or more absolute calibration values are or include an absolute cardiac output value for the patient, and referencing Equation 9 for cardiac output provided above, the cardiac output processing circuitry may use the following equation to calculate an uncalibrated cardiac output for the patient:Uncalibrated cardiac output = HR X j APW(t)dt (12) systoleThe cardiac output processing circuitry may then compare the uncalibrated cardiac output to the absolute cardiac output value for the patient and determine the calibration factor accordingly. The cardiac output processing circuitry may then use the calibration factor, for instance, as CF in Equation 9 for cardiac output discussed above.

[0190] As another example, referencing Equation 10 for cardiac output provided above, the cardiac output processing circuitry may use the following formula to calculate an uncalibrated cardiac output for the patient:systoleThe cardiac output processing circuitry may then compare the uncalibrated cardiac output to an absolute cardiac output value for the patient to similarly determine a calibration factor to use as CF part of Equation 10 above.

[0191] As another example, where the one or more absolute calibration values are or include the patient’s blood pressure, the cardiac output processing circuitry may use the patient’s blood pressure to calibrate the arterial pulse waveform, where the arterial pulse waveform represents pressure over time. For instance, the cardiac output processing circuitry may receive or calculate the patient’s actual systolic pressure. The cardiac output processing circuitry may then set the systolic peak of the arterial pulse waveform as the baseline of the patient’s actual systolic pressure and reproportion the scale of the arterial pulse waveform accordingly. The reproportioning of the arterial pulse waveform may use a calibration factor determined from the actual systolic pressure baseline. To illustrate, with reference to FIG. 16, the cardiac output processing circuitry may receive from the patient’s caregiver that the patient has a systolic pressure of 120 mmHg. The cardiac output processing circuitry may then set the systolic peak 1406 to be the received baseline of 120 mmHg and revalue the rest of the amplitude scale shown in FIG. 16 using a calibrationfactor determined from the 120 mmHg baseline. For example, if the systolic peak 1406 represents an amplitude of 255 before renumbering, the cardiac output processing circuitry may divide 120 mmHg by 255 to create a calibration factor of 0.471 mmHg. The cardiac output processing circuitry may then multiply the other points of the arterial pulse waveform by the calibration factor of 0.471 mmHg before determining the area under the arterial pulse waveform at step 1206 of FIG.14. In this way, the calibration factor may be involved in both steps 1206 and 1208 of the sample process 1200. In implementations, the cardiac output processing circuitry may perform this calibration for each individual arterial pulse waveform or for a representative arterial pulse waveform. In implementations, the cardiac output processing circuitry may determine, for instance, all of the systolic peaks in a segment of a larger segment of arterial pulse waveform (e.g., containing a number of individual arterial pulse waveforms), average the systolic peaks, and determine the calibration factor as outlined above according to the average systolic peak for the larger arterial pulse waveform. Additionally, or alternatively, the cardiac output processing circuitry may receive or calculate the patient’s actual diastolic pressure and similarly use the dicrotic peak to calibrate the arterial pulse waveform.

[0192] In implementations where the cardiac output processing circuitry receives or determines updated absolute calibration values over time, the cardiac output processing circuitry may be configured to also determine updated calibration factors over time. For instance, the cardiac output processing circuitry may be configured to receive updated absolute cardiac output values for the patient over time and recalculate the CF calibration factor, as described above. As another example, the cardiac output processing circuitry may be configured to receive updated blood pressure values for the patient over time. The cardiac output processing circuitry may then use the updated blood pressure values for the patient to calibrate the arterial pulse waveforms using the processes described above. For instance, referring to the previous example, if the cardiac output processing circuitry receives that the patient’s systolic pressure is now 110 mmHg, the cardiac output processing circuitry may determine an updated calibration factor of 0.431 mmHg.

[0193] In implementations, the cardiac output processing circuitry may be configured to determine more than one calibration factor for the patient. Such calibration values may be multiplied, divided, added, subtracted, raised to a power, and / or the like to calibrate the patient’s determined cardiac output. For example, the cardiac output processing circuitry may receive or determine multiple absolute cardiac output values for the patient. The cardiac output processing circuitry may use, forinstance, Equation 13 to determine uncalibrated cardiac output values corresponding to the absolute cardiac output values. To illustrate, the cardiac output processing circuitry may receive absolute cardiac output values for the patient for three separate days and determine uncalibrated cardiac output values for the same three days. The cardiac output processing circuitry may then calculate a line of best fit between the absolute cardiac output values and a line of best fit between the uncalibrated cardiac output values and then determine calibration factors that allow the line of best fit for the uncalibrated cardiac output values to be transformed to the line of best fit for the absolute cardiac output values. The calibration factors may take the form, for example, of CFi and CF2 in the equation below, which is modified from Equation 9.Cardiac output = CF1X HR X j APW(t)dt + CF2(14) systole

[0194] In implementations, the cardiac output processing circuitry may be configured to calibrate the cardiac output relative to a baseline of the patient where the baseline is instead a relative, rather than an absolute, baseline. The cardiac output processing circuitry, as an illustration, may determine a baseline cardiac output for the patient and normalize the cardiac output calculated as part of step 1208 of sample process 1200 using the baseline cardiac output. The resulting normalized cardiac output for the patient may thus be a relative cardiac output.

[0195] In examples, the cardiac output processing circuitry may determine a baseline cardiac output for the patient using an initial measurement or set of measurements taking when the patient is provided with the non-invasive monitoring device 100. Accordingly, the cardiac output processing circuitry may determine the baseline cardiac output for the patient using the sample process 1200 discussed above with reference to FIG. 14, where the cardiac output processing circuitry sets the initial set of measurements as calibration measurements. To illustrate, during an initial calibration session, the cardiac output processing circuitry may identify a calibration arterial pulse waveform for one or more arteries of the patient from arterial measurement signals generated by the non-invasive monitoring device 100. The calibration arterial pulse waveform may be generated from the arterial measurement signals captured during the calibration session. The cardiac output processing circuitry may then analyze the calibration arterial pulse waveform to identify one or more calibration arterial pulse landmarks of the calibration arterial pulse waveformand, using the one or more calibration arterial pulse landmarks, determine an area under the calibration arterial pulse waveform. For example, as discussed above with reference to FIG. 14, the cardiac output processing circuitry may determine the start and end points of the systolic portion of the calibration arterial pulse waveform. Next, the cardiac output processing circuitry may determine the area under the calibration arterial pulse waveform between the start and end points of the systolic portion. Finally, the cardiac output processing circuitry may calculate a calibration cardiac output for the patient using the determined area under the calibration arterial pulse waveform. As an example, the cardiac output processing circuitry may calculate the calibration cardiac output as the product of the determined area under the calibration arterial pulse waveform and the patient’s heart rate. The baseline cardiac output may then be based on the calibration cardiac output.

[0196] As an example, the cardiac output processing circuitry may set the baseline cardiac output as the calibration cardiac output. As another example, the cardiac output processing circuitry may repeat identifying the calibration arterial pulse waveform for the one or more arteries of the patient, resulting in a number of calibration arterial pulse waveforms. To illustrate, the cardiac output processing circuitry may identify a number of individual arterial pulse waveforms within a larger calibration arterial pulse waveform recorded during an initial calibration session. The cardiac output processing circuitry may then repeat, for each of the plurality of calibration arterial pulse waveforms, (a) analyzing the calibration arterial pulse waveform to identify one or more calibration arterial pulse landmarks of the calibration arterial pulse waveform, (b) determining the area under the calibration arterial pulse waveform using the one or more calibration arterial pulse landmarks, and (c) calculating the calibration cardiac output for the patient using the determined area under the calibration arterial pulse waveform. By repeating these steps, the cardiac output processing circuitry may produce a number of calibration cardiac outputs, where each of calibration cardiac outputs corresponds to a calibration arterial pulse waveform. The cardiac output processing circuitry may then determine a baseline cardiac output as a statistical output of the calibration arterial pulse waveforms. As an illustration, the cardiac output processing circuitry may determine an average of the calibration cardiac outputs and set the average as the baseline cardiac output. As another illustration, the cardiac output processing circuitry may determine a median of the calibration cardiac outputs, setting the median as the baseline cardiac output.

[0197] In examples, the cardiac output processing circuitry may calculate a baseline cardiac output for the patient using a baseline arterial pulse waveform for the patient. As an example, the cardiac output processing circuitry, for an initial calibration or baselining session, may generate the baseline arterial pulse waveform by identifying a number of segmented baseline arterial pulse waveforms for one or more arteries of the patient from one or more baseline segments of the arterial measurement signals. To illustrate, the cardiac output processing circuitry may set one or more segments of arterial measurement signals generated during an initial baselining session as the baseline segment(s) of the arterial measurement signals. The cardiac output processing circuitry may then identify individual arterial pulse waveforms within the baseline segment(s) and further segment the individual arterial pulse waveforms into segmented baseline arterial pulse waveforms. The cardiac output processing circuitry may generate the baseline arterial pulse waveform for the patient from the segmented baseline arterial pulse waveforms. For instance, the cardiac output processing circuitry may average the segmented baseline arterial pulse waveforms to generate the baseline arterial pulse waveform.

[0198] Using the baseline arterial pulse waveform, the cardiac output processing circuitry may calculate the baseline cardiac output. As an illustration, the cardiac output processing circuitry may apply the sample process 1200 to the baseline arterial pulse waveform. Accordingly, the cardiac output processing circuitry may analyze the baseline arterial pulse waveform to identify one or more baseline arterial pulse landmarks of the baseline arterial pulse waveform and determine an area under the baseline arterial pulse waveform using the one or more arterial pulse landmarks. For instance, the cardiac output processing circuitry may identify the start and end points of the systolic portion of the baseline arterial pulse waveform and determine the area under the baseline arterial pulse waveform between these start and end points. The cardiac output processing circuitry may then calculate the baseline cardiac output for the patient using the determined area under the baseline arterial pulse waveform. As an example, the cardiac output processing circuitry may calculate the baseline cardiac output as the determined area under the baseline arterial pulse waveform multiplied by the patient’s heart rate.

[0199] In examples, the cardiac output processing circuitry may normalize the cardiac output relative to a baseline cardiac output by dividing all cardiac outputs determined subsequent to the baseline cardiac output by the baseline cardiac output. In this way, the cardiac outputs calculated for the patient are normalized to represent a proportion of the baseline cardiac output. Thisrepresentation may be useful for clinicians to see how the patient’s cardiac output is trending over time, where values greater than 1 show that the patient’s cardiac output is increasing, whereas values lower than 1 show that the patient’s cardiac output is decreasing. In examples, the cardiac output processing circuitry may normalize the cardiac output relative to the baseline cardiac output by setting the baseline cardiac output as the initial measurement in any reports provided to the patient’s clinician or other caregivers or the patient themselves. With this presentation, the individual viewing the report can see visually how the patient’s cardiac output has trended over time compared to initial measurements taken for the patient.

[0200] In implementations, as discussed above, the cardiac output processing circuitry may apply sample process 1200 to a representative arterial pulse waveform to produce a representative cardiac output for the patient. In implementations, the cardiac output processing circuitry may alternatively repeat applying sample process 1200 to a number of individual arterial pulse waveforms to produce a number of cardiac outputs. For example, as explained above with reference to step 1202, identifying an arterial pulse waveform may include identifying a number of individual arterial pulse waveforms. These individual arterial pulse waveforms may be from a specific segment of the arterial measurement signals, sampled from a segment of the arterial measurement signals, from a time period where the patient was stationary (e.g., as shown by accelerometer signals), and / or the like. For each individual arterial pulse waveform, the cardiac output processing circuitry may (a) identify one or more arterial pulse landmarks of the given arterial pulse waveform, (b) determine the area under the given arterial pulse waveform using the one or more arterial pulse landmarks, and (c) calculate the cardiac output for the patient using the determined area under the given arterial pulse waveform. The result of this process may be a number of cardiac outputs for a number of individual arterial pulse waveforms. In examples, the cardiac output processing circuitry may determine a representative cardiac output from these cardiac outputs. As an illustration, the cardiac output processing circuitry may determine a statistical measure of the cardiac outputs, such as an average of the cardiac outputs or a median of the cardiac outputs. The average or median cardiac output may thus be the representative cardiac output for the patient.

[0201] As discussed above, in implementations, the cardiac output processing circuitry is configured to provide reports to clinicians, caregivers, and / or the patient themselves. In various embodiments, the reports may include trends for the patient. As such, the cardiac output processingcircuitry may be configured to determine trends of the cardiac output relative to one or more historical cardiac outputs calculated for the patient. The cardiac output processing circuitry may further present the determined trends to a clinician, caregiver, and / or patient. For example, the cardiac output processing circuitry may track each cardiac output determined for the patient. These may include, for instance, a baseline cardiac output and subsequent representative cardiac outputs, where each representative cardiac output is associated with a time period for the patient. Illustrations of time periods include a day, two days, three days, five days, seven days, ten days, fourteen days, and / or the like during which the patient was using the non-invasive monitoring device 100. The cardiac output processing circuitry may plot the cardiac outputs over time and provide the plot of the cardiac outputs to the clinician, caregiver, and / or the patient. As another example, the cardiac output processing circuitry may determine a line of best fit for a plot of the cardiac outputs and provide the slope of the line and / or a visual representation of the line as part of the report.

[0202] As another example, the cardiac output processing circuitry may determine whether a latest cardiac output determined for the patient is above or below an absolute or relative cardiac output value. For instance, a low cardiac output may represent heart failure, especially if compared relative to an initial baseline or calibration cardiac output value. However, a high cardiac output may also represent issues with the patient’s heart or circulatory system, such as anemia. Accordingly, the cardiac output processing circuitry may identify where cardiac output values fall outside of a range for the patient. To illustrate, the cardiac output processing circuitry may determine whether absolute cardiac outputs for the patient are less than around 2.2 to 2.4 L / min / m2. As another illustration, the cardiac output processing circuitry may determine whether relative cardiac outputs for the patient are 20%, 30%, 40%, 50%, and / or the like greater or less than an initial baseline or calibration cardiac output determined for the patient. The cardiac output processing circuitry may highlight cardiac output values falling outside a normal cardiac output range and / or falling outside a predetermined percentage of an initial baseline or calibration cardiac output in a report on the patient.

[0203] In implementations, the cardiac output processing circuitry is further configured to alert a clinician, caregiver, and / or the patient based on the trend of the cardiac output relative to the one or more historical outputs. Examples of alerts include highlighting trends or specific cardiac output values on a patient report dashboard, sending the clinician an email with the trend or a flagged1cardiac output value, sending the clinician a text message indicating that the clinician should check a patient report dashboard, sending the patient or a caregiver of the patient an alert to set up an appointment with the patient’s clinician, and / or the like. As an illustration, the cardiac output processing circuitry may provide an alert on a patient report dashboard if the slope of a line of best fit for the cardiac outputs determined for the patient reaches a predetermined slope, such as a slope of at least -0.20, -0.25, -0.30, -0.35, -0.40, -0.45, -0.50, and / or the like. A continued worsening slope may result in increasingly urgent alerts. For instance, a slope of -0.15 may cause a dashboard alert, but once the slope reaches -0.25, the cardiac output processing circuitry may email the patient’s clinician with a report including the worsening trend. As another illustration, the cardiac output processing circuitry may provide alerts based on an absolute or relative cardiac output value, such as based on the absolute or relative cardiac output value falling outside of a predetermined range as discussed above.

[0204] The above processes are discussed with reference to cardiac outputs. However, the cardiac output processing circuitry may be used to determine another type of measurement relating to an output of the patient’s heart as part of step 1208 of FIG. 14. In examples, the cardiac output processing circuitry may be configured to calculate the stroke volume or ejection fraction for the patient.

[0205] Although the subject matter contained herein has been described in detail for the purpose of illustration, such detail is solely for that purpose and that the present disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present disclosure contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.

[0206] Other examples are within the scope and spirit of the description and claims. Additionally, certain functions described above can be implemented using software, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions can also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

[0207] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantagesdescribed herein, and each of such variations and / or modifications is deemed to be within the scope of the inventive embodiments described herein. Those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be an example and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the inventive teachings is / are used.

[0208] Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

Claims

CLAIMSWhat is claimed is:

1. A non-invasive cardiac monitoring system configured to determine a cardiac output of an ambulatory patient, comprising:a non-invasive wearable monitoring device configured to be worn on a body of an ambulatory patient, comprisinga monitoring unit configured to be disposed on the patient’s body, the monitoring unit comprisingat least one arterial measurement transmitter configured to transmit arterial measurement waves towards one or more arteries of the patient;at least one arterial measurement receiver configured to receive at least one of reflected or transmitted arterial measurement waves from the one or more arteries of the patient; andarterial measurement circuitry configured to generate arterial measurement signals corresponding to the one or more arteries of the patient using the received at least one of reflected or transmitted arterial measurement waves; and cardiac output processing circuitry in electronic communication with the arterial measurement circuitry, wherein the processing circuitry is configured toidentify an arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals,analyze the arterial pulse waveform to identify one or more arterial pulse landmarks of the arterial pulse waveform,determine an area under the arterial pulse waveform using the one or more arterial pulse landmarks, andcalculate a cardiac output for the patient using the determined area under the arterial pulse waveform.

2. The cardiac monitoring system of claim 1 , wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso, wherein the monitoring unit is configured to be disposed on the adhesive patch.

3. The cardiac monitoring system of claim 1, wherein the non- invasive wearable monitoring device further comprises a garment configured to be removably worn around the patient’s torso and wherein the monitoring unit is configured to be disposed on the garment.

4. The cardiac monitoring system of claim 1 , wherein the monitoring unit comprises the cardiac output circuitry.

5. The cardiac monitoring system of claim 1, further comprising a gateway configured to communicate with the monitoring unit and with a remote server.

6. The cardiac monitoring system of claim 5, wherein the gateway comprises the cardiac output processing circuitry.

7. The cardiac monitoring system of claim 6, wherein the monitoring unit comprises a network interface configured to communicate with the gateway and transmit at least the arterial measurement signals to the gateway.

8. The cardiac monitoring system of claim 1, further comprising a remote server in electronic communication with the monitoring unit.

9. The cardiac monitoring system of claim 8, wherein the remote server comprises the cardiac output processing circuitry.

10. The cardiac monitoring system of claim 9, wherein the monitoring unit comprises a network interface configured to communicate with the remote server and transmit at least the arterial measurement signals to the remote server.

11. The cardiac monitoring system of claim 10, further comprising a gateway configured to communicate with the monitoring unit and with the remote server, wherein the network interface of the monitoring unit is configured to communicate with the remote server via the gateway.

12. The cardiac monitoring system of claim 1, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

13. The cardiac monitoring system of claim 1, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

14. The cardiac monitoring system of claim 13, wherein the monitoring unit is configured to be removably attached to an arm of the patient.

15. The cardiac monitoring system of claim 1, wherein the arterial measurement signals comprise radiofrequency (RF) signals.

16. The cardiac monitoring system of claim 15, wherein the at least one arterial measurement transmitter and the at least one arterial measurement receiver comprise at least one RF antenna configured to transmit RF waves towards the one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient; andwherein the arterial measurement circuitry comprises RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

17. The cardiac monitoring system of claim 1, wherein the cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further based on a heart rate of the patient.

18. The cardiac monitoring system of claim 17, wherein the non-invasive wearable monitoring device comprisesone or more electrocardiogram (ECG) electrodes configured to sense cardiac electrical activity of the patient; andECG circuitry configured to generate ECG signals using the sensed cardiac electrical activity of the patient.

19. The cardiac monitoring system of claim 18, wherein the cardiac output processing circuitry is configured to determine the heart rate of the patient using the ECG signals.

20. The cardiac monitoring system of claim 19, wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso, wherein the monitoring unit is configured to be disposed on the adhesive patch.

21. The cardiac monitoring system of claim 19, wherein the monitoring unit comprises the cardiac output circuitry.

22. The cardiac monitoring system of claim 19, further comprising a remote server in electronic communication with the monitoring unit.

23. The cardiac monitoring system of claim 22, wherein the remote server comprises the cardiac output processing circuitry.

24. The cardiac monitoring system of claim 19, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

25. The cardiac monitoring system of claim 19, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

26. The cardiac monitoring system of claim 19, wherein the arterial measurement signals comprise radiofrequency (RF) signals.

27. The cardiac monitoring system of claim 26, wherein the at least one arterial measurement transmitter and the at least one arterial measurement receiver comprise at least one RF antenna configured to transmit RF waves towards the one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient; andwherein the arterial measurement circuitry comprises RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

28. The cardiac monitoring system of claim 17, wherein the cardiac output processing circuitry is configured to determine the heart rate of the patient using the arterial measurement signals.

29. The cardiac monitoring system of claim 1, wherein the wearable monitoring device is configured to be worn on the patient’s skin in an area around a major artery of the patient.

30. The cardiac monitoring system of claim 29, wherein the major artery comprises a radial artery of the patient.

31. The cardiac monitoring system of claim 29, wherein the major artery comprises a brachial artery of the patient.

32. The cardiac monitoring system of claim 29, wherein the major artery comprises a subclavian artery of the patient.

33. The cardiac monitoring system of claim 29, wherein the major artery comprises the patient’s aorta.

34. The cardiac monitoring system of claim 1, wherein the one or more arterial pulse landmarks comprise a beginning and an end of a systolic portion of the arterial pulse waveform.

35. The cardiac monitoring system of claim 34, wherein the one or more arterial pulse landmarks comprises a systolic peak and a dicrotic peak of the arterial pulse waveform.

36. The cardiac monitoring system of claim 35, wherein the cardiac output processing circuitry is configured to analyze the arterial pulse waveform to identify the one or more arterial pulse landmarks using local minima and maxima analysis.

37. The cardiac monitoring system of claim 35, wherein the cardiac output processing circuitry is configured to identify the beginning and the end of the systolic portion of the arterial pulse waveform using the systolic peak and the dicrotic peak of the arterial pulse waveform.

38. The cardiac monitoring system of claim 34, wherein the area under the arterial pulse waveform comprises an area of the systolic portion of the arterial pulse waveform.

39. The cardiac monitoring system of claim 34, wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso, wherein the monitoring unit is configured to be disposed on the adhesive patch.

40. The cardiac monitoring system of claim 34, wherein the monitoring unit comprises the cardiac output circuitry.

41. The cardiac monitoring system of claim 34, further comprising a remote server in electronic communication with the monitoring unit.

42. The cardiac monitoring system of claim 41, wherein the remote server comprises the cardiac output processing circuitry.

43. The cardiac monitoring system of claim 34, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

44. The cardiac monitoring system of claim 34, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

45. The cardiac monitoring system of claim 34, wherein the arterial measurement signals comprise radiofrequency (RF) signals.

46. The cardiac monitoring system of claim 45, wherein the at least one arterial measurement transmitter and the at least one arterial measurement receiver comprise at least one RF antenna configured to transmit RF waves towards the one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient; andwherein the arterial measurement circuitry comprises RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

47. The cardiac monitoring system of claim 1, wherein the arterial pulse waveform comprises a representative arterial pulse waveform.

48. The cardiac monitoring system of claim 47, wherein the cardiac output processing circuitry is further configured toidentify a plurality of segmented arterial pulse waveforms for the one or more arteries of the patient from one or more segments of the arterial measurement signals; andgenerate the representative arterial pulse waveform from the plurality of segmented arterial pulse waveforms.

49. The cardiac monitoring system of claim 48, wherein the cardiac output processing circuitry is configured to generate the representative arterial pulse waveform by averaging the plurality of segmented arterial pulse waveforms.

50. The cardiac monitoring system of claim 1, wherein the cardiac output processing circuitry is further configured to repeat identifying the arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals to identify a plurality of arterial pulse waveforms.

51. The cardiac monitoring system of claim 50, wherein the cardiac output processing circuitry is further configured to repeat, for each of the plurality of arterial pulse waveforms, analyzing the arterial pulse waveform to identify the one or more arterial pulse landmarks of the arterial pulse waveform, determining the area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of arterial pulse waveforms.

52. The cardiac monitoring system of claim 51, wherein the cardiac output processing circuitry is further configured to calculate a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of arterial pulse waveforms.

53. The cardiac monitoring system of claim 52, wherein the representative cardiac output for the patient comprises an average of the plurality of cardiac outputs for the plurality of arterial pulse waveforms.

54. The cardiac monitoring system of claim 52, wherein the representative cardiac output for the patient comprises a median of the plurality of cardiac outputs for the plurality of arterial pulse waveforms.

55. The cardiac monitoring system of claim 1, wherein the cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further using one or more of heart rate, arterial compliance, or slope of the arterial pulse waveform.

56. The cardiac monitoring system of claim 1, wherein the cardiac output processing circuitry is further configured to calibrate the cardiac output relative to a baseline of the patient.

57. The cardiac monitoring system of claim 56, wherein the cardiac output processing circuitry is configured to calibrate the cardiac output relative to the baseline of the patient by determining a calibration factor for the patient.

58. The cardiac monitoring system of claim 57, wherein the cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further using the calibration factor for the patient.

59. The cardiac monitoring system of claim 58, wherein the cardiac output comprises an absolute cardiac output.

60. The cardiac monitoring system of claim 57, wherein the baseline of the patient comprises one or more absolute calibration values for the patient.

61. The cardiac monitoring system of claim 60, wherein the cardiac output processing circuitry is further configured to receive the one or more absolute calibration values for the patient, and wherein determining the calibration factor comprises determining the calibration factor using the one or more absolute calibration values.

62. The cardiac monitoring system of claim 61, wherein the processing circuitry is further configured to periodically receive updated one or more absolute calibration values for the patient, and wherein determining the calibration factor comprises determining the calibration factor using the updated one or more absolute calibration values for the patient.

63. The cardiac monitoring system of claim 61, wherein the one or more absolute calibration values for the patient comprise one or more absolute cardiac output values for the patient.

64. The cardiac monitoring system of claim 63, wherein the one or more absolute cardiac output values for the patient are measured using echocardiography.

65. The cardiac monitoring system of claim 63, wherein the one or more absolute cardiac output values for the patient are measured using thermodilution.

66. The cardiac monitoring system of claim 61, wherein the one or more absolute calibration values for the patient comprise one or more blood pressure values for the patient.

67. The cardiac monitoring system of claim 66, wherein the one or more blood pressure values for the patient are measured using a sphygmomanometer.

68. The cardiac monitoring system of claim 66, wherein the one or more blood pressure values for the patient are measured using a plurality of patch-based monitoring devices worn along a plurality of locations on an artery.

69. The cardiac monitoring system of claim 61, wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached tothe patient’s torso, wherein the monitoring unit is configured to be disposed on the adhesive patch.

70. The cardiac monitoring system of claim 61, wherein the monitoring unit comprises the cardiac output circuitry.

71. The cardiac monitoring system of claim 61, further comprising a remote server in electronic communication with the monitoring unit.

72. The cardiac monitoring system of claim 71, wherein the remote server comprises the cardiac output processing circuitry.

73. The cardiac monitoring system of claim 61, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

74. The cardiac monitoring system of claim 61, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

75. The cardiac monitoring system of claim 61, wherein the arterial measurement signals comprise radiofrequency (RF) signals.

76. The cardiac monitoring system of claim 75, wherein the at least one arterial measurement transmitter and the at least one arterial measurement receiver comprise at least one RF antenna configured to transmit RF waves towards the one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient; andwherein the arterial measurement circuitry comprises RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

77. The cardiac monitoring system of claim 57, wherein determining the calibration factor comprises determining a baseline cardiac output for the patient.

78. The cardiac monitoring system of claim 77, wherein the cardiac output processing circuitry is further configured to calibrate the cardiac output relative to the baseline of the patient by normalizing the cardiac output for the patient using the baseline cardiac output for the patient.

79. The cardiac monitoring system of claim 78, wherein the normalized cardiac output for the patient comprises a relative cardiac output for the patient.

80. The cardiac monitoring system of claim 79, wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso, wherein the monitoring unit is configured to be disposed on the adhesive patch.

81. The cardiac monitoring system of claim 79, wherein the monitoring unit comprises the cardiac output circuitry.

82. The cardiac monitoring system of claim 79, further comprising a remote server in electronic communication with the monitoring unit.

83. The cardiac monitoring system of claim 82, wherein the remote server comprises the cardiac output processing circuitry.

84. The cardiac monitoring system of claim 79, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

85. The cardiac monitoring system of claim 79, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

86. The cardiac monitoring system of claim 79, wherein the arterial measurement signals comprise radiofrequency (RF) signals.

87. The cardiac monitoring system of claim 86, wherein the at least one arterial measurement transmitter and the at least one arterial measurement receiver comprise at least one RF antenna configured to transmit RF waves towards the one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient; andwherein the arterial measurement circuitry comprises RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

88. The cardiac monitoring system of claim 77, wherein the determining the baseline cardiac output for the patient comprisesidentifying a calibration arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals;analyzing the calibration arterial pulse waveform to identify one or more calibration arterial pulse landmarks of the calibration arterial pulse waveform;determining an area under the calibration arterial pulse waveform using the one or more calibration arterial pulse landmarks; andcalculating a calibration cardiac output for the patient using the determined area under the calibration arterial pulse waveform, wherein the baseline cardiac output is based on the calibration cardiac output.

89. The cardiac monitoring system of claim 88, wherein the baseline of the patient comprises the calibration cardiac output.

90. The cardiac monitoring system of claim 88, wherein the cardiac output processing circuitry is further configured to repeat identifying the calibration arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals to identify a plurality of calibration arterial pulse waveforms.

91. The cardiac monitoring system of claim 90, wherein the cardiac output processing circuitry is further configured to repeat, for each of the plurality of calibration arterial pulse waveforms, analyzing the calibration arterial pulse waveform to identify the one or more calibration arterial pulse landmarks of the calibration arterial pulse waveform, determining the area under the calibration arterial pulse waveform using the one or more calibration arterial pulse landmarks, and calculating the calibration cardiac output for the patient using the determined area under the calibration arterial pulse waveform to produce a plurality of calibration cardiac outputs for the plurality of calibration arterial pulse waveforms.

92. The cardiac monitoring system of claim 91, wherein the baseline of the patient comprises a statistical output of the plurality of calibration arterial pulse waveforms.

93. The cardiac monitoring system of claim 92, wherein the statistical output of the plurality of calibration arterial pulse waveforms comprises an average of the calibration arterial pulse waveforms.

94. The cardiac monitoring system of claim 92, wherein the statistical output of the plurality of calibration arterial pulse waveforms comprises a median of the calibration arterial pulse waveforms.

95. The cardiac monitoring system of claim 77, wherein the cardiac output processing circuitry is further configured to generate a baseline arterial pulse waveform for the patient.

96. The cardiac monitoring system of claim 95, wherein the cardiac output processing circuitry is configured to generate the baseline arterial pulse waveform for the patient by identifying a plurality of segmented baseline arterial pulse waveforms for the one or more arteries of the patient from one or more baseline segments of the arterial measurement signals; andgenerating the baseline arterial pulse waveform for the patient from the plurality of segmented baseline arterial pulse waveforms.

97. The cardiac monitoring system of claim 96, wherein generating the baseline arterial pulse waveform comprises averaging the plurality of segmented baseline arterial pulse waveforms.

98. The cardiac monitoring system of claim 95, wherein the cardiac output processing circuitry is further configured to calculate the baseline cardiac output using the baseline arterial pulse waveform.

99. The cardiac monitoring system of claim 98, wherein the cardiac output processing circuitry is configured to calculate the baseline cardiac output byanalyzing the baseline arterial pulse waveform to identify one or more baseline arterial pulse landmarks of the baseline arterial pulse waveform;determining an area under the baseline arterial pulse waveform using the one or more baseline arterial pulse landmarks; andcalculating the baseline cardiac output for the patient using the determined area under the baseline arterial pulse waveform.

100. The cardiac monitoring system of claim 1, wherein the cardiac output circuitry is further configured to determine a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient.

101. The cardiac monitoring system of claim 100, wherein the cardiac output circuitry is further configured to present the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver.

102. The cardiac monitoring system of claim 100, wherein the cardiac output circuitry is further configured to alert a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

103. The cardiac monitoring system of claim 100, wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso, wherein the monitoring unit is configured to be disposed on the adhesive patch.

104. The cardiac monitoring system of claim 100, wherein the monitoring unit comprises the cardiac output circuitry.

105. The cardiac monitoring system of claim 100, further comprising a remote server in electronic communication with the monitoring unit.

106. The cardiac monitoring system of claim 105, wherein the remote server comprises the cardiac output processing circuitry.

107. The cardiac monitoring system of claim 100, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

108. The cardiac monitoring system of claim 100, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

109. The cardiac monitoring system of claim 100, wherein the arterial measurement signals comprise radiofrequency (RF) signals.

110. The cardiac monitoring system of claim 109, wherein the at least one arterial measurement transmitter and the at least one arterial measurement receiver comprise at least one RF antenna configured to transmit RF waves towards the one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient; andwherein the arterial measurement circuitry comprises RF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

111. A method for determining a cardiac output of an ambulatory patient using a non-invasive cardiac monitoring system, comprising:identifying an arterial pulse waveform for one or more arteries of an ambulatory patient from arterial measurement signals corresponding to the one or more arteries of the patient generated by a non-invasive wearable monitoring device, configured to be worn on a body of the ambulatory patient and further configured to transmit arterial measurement waves towards the one or more arteries of the patient, using at least one of reflected or transmitted arterial measurement waves received by the non-invasive wearable monitoring device;analyzing the arterial pulse waveform to identify one or more arterial pulse landmarks of the arterial pulse waveform;determining an area under the arterial pulse waveform using the one or more arterial pulse landmarks; andcalculating a cardiac output for the patient using the determined area under the arterial pulse waveform.

112. The method of claim 111, wherein the non-invasive wearable monitoring device comprises a monitoring unit, comprisingat least one arterial measurement transmitter configured to transmit the arterial measurement waves towards the one or more arteries of the patient;at least one arterial measurement receiver configured to receive the at least one of reflected or transmitted arterial measurement waves from the one or more arteries of the patient; andarterial measurement circuitry configured to generate the arterial measurement signals corresponding to the one or more arteries of the patient using the received at least one of reflected or transmitted arterial measurement waves.

113. The method of claim 112, wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso, wherein the monitoring unit is configured to be disposed on the adhesive patch.

114. The method of claim 112, wherein the non-invasive wearable monitoring device further comprises a garment configured to be removably worn around the patient’s torso and wherein the monitoring unit is configured to be disposed on the garment.

115. The method of claim 111, further comprising receiving at least the arterial measurement signals from the non-invasive wearable monitoring device.

116. The method of claim 111, wherein the arterial measurement signals comprise radiofrequency (RF) signals.

117. The method of claim 111, wherein calculating the cardiac output for the patient comprises calculating the cardiac output for the patient using the determined area under the arterial pulse waveform and further based on a heart rate of the patient.

118. The method of claim 117, further comprising determining the heart rate of the patient.

119. The method of claim 118, wherein determining the heart rate of the patient comprises determining the heart rate of the patient using ECG signals generated from sensed cardiac electrical activity for the patient.

120. The method of claim 118, wherein determining the heart rate of the patient comprises determining the heart rate of the patient using the arterial measurement signals.

121. The method of claim 111, wherein the one or more arteries of the patient comprise a radial artery of the patient.

122. The method of claim 111, wherein the one or more arteries of the patient comprise a brachial artery of the patient.

123. The method of claim 111, wherein the one or more arteries of the patient comprise a subclavian artery of the patient.

124. The method of claim 111, wherein the one or more arteries of the patient comprise the patient’s aorta.

125. The method of claim 111, wherein the one or more arterial pulse landmarks comprise a beginning and an end of a systolic portion of the arterial pulse waveform.

126. The method of claim 125, wherein the one or more arterial pulse landmarks comprises a systolic peak and a dicrotic peak of the arterial pulse waveform.

127. The method of claim 126, wherein the area under the arterial pulse waveform comprises an area of the systolic portion of the arterial pulse waveform.

128. The method of claim 111, wherein the arterial pulse waveform comprises a representative arterial pulse waveform.

129. The method of claim 111, further comprising repeating identifying the arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals to identify a plurality of arterial pulse waveforms.

130. The method of claim 129, further comprising repeating, for each of the plurality of arterial pulse waveforms, analyzing the arterial pulse waveform to identify the one or more arterial pulse landmarks of the arterial pulse waveform, determining the area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of arterial pulse waveforms.

131. The method of claim 130, further comprising calculating a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of arterial pulse waveforms.

132. The method of claim 111, further comprising calibrating the cardiac output relative to a baseline of the patient.

133. The method of claim 132, wherein calibrating the cardiac output relative to the baseline of the patient comprises determining a calibration factor for the patient.

134. The method of claim 133, wherein calculating the cardiac output for the patient comprises calculating the cardiac output for the patient using the determined area under the arterial pulse waveform and further using the calibration factor for the patient.

135. The method of claim 134, wherein the cardiac output comprises an absolute cardiac output.

136. The method of claim 133, wherein the baseline of the patient comprises one or more absolute calibration values for the patient.

137. The method of claim 136, further comprising receiving the one or more absolute calibration values for the patient, wherein determining the calibration factor comprises determining the calibration factor using the one or more absolute calibration values.

138. The method of claim 137 further comprising periodically receiving updated one or more absolute calibration values for the patient, wherein determining the calibration factor comprises determining the calibration factor using the updated one or more absolute calibration values for the patient.

139. The method of claim 137, wherein the one or more absolute calibration values for the patient comprise one or more absolute cardiac output values for the patient.

140. The method of claim 137, wherein the one or more absolute calibration values for the patient comprise one or more blood pressure values for the patient.

141. The method of claim 133, wherein determining the calibration factor comprises determining a baseline cardiac output for the patient.

142. The method of claim 141, wherein calibrating the cardiac output relative to the baseline of the patient further comprises normalizing the cardiac output for the patient using the baseline cardiac output for the patient.

143. The method of claim 142, wherein the normalized cardiac output for the patient comprises a relative cardiac output for the patient.

144. The method of claim 111, further comprising determining a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient.

145. The method of claim 144, further comprising presenting the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver.

146. The method of claim 144, further comprising alerting a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

147. A non-transitory computer-readable medium storing instructions that are configured to, when executed by one or more processors, cause the one or more processors to:identify an arterial pulse waveform for one or more arteries of an ambulatory patient from arterial measurement signals corresponding to the one or more arteries of the patient generated by a non-invasive wearable monitoring device, configured to be worn on a body of the ambulatory patient and further configured to transmit arterial measurement waves towards the one or more arteries of the patient, using at least one of reflected or transmitted arterial measurement waves received by the non-invasive wearable monitoring device;analyze the arterial pulse waveform to identify one or more arterial pulse landmarks of the arterial pulse waveform;determine an area under the arterial pulse waveform using the one or more arterial pulse landmarks; andcalculate a cardiac output for the patient using the determined area under the arterial pulse waveform.

148. The non-transitory computer-readable medium of claim 147, wherein the non-invasive wearable monitoring device comprises a monitoring unit, comprisingat least one arterial measurement transmitter configured to transmit the arterial measurement waves towards the one or more arteries of the patient;at least one arterial measurement receiver configured to receive the at least one of reflected or transmitted arterial measurement waves from the one or more arteries of the patient; andarterial measurement circuitry configured to generate the arterial measurement signals corresponding to the one or more arteries of the patient using the received at least one of reflected or transmitted arterial measurement waves.

149. The non-transitory computer-readable medium of claim 148, wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso, wherein the monitoring unit is configured to be disposed on the adhesive patch.

150. The non-transitory computer-readable medium of claim 148, wherein the non-invasive wearable monitoring device further comprises a garment configured to be removably wornaround the patient’s torso and wherein the monitoring unit is configured to be disposed on the garment.

151. The non-transitory computer-readable medium of claim 147, wherein the instructions are further configured to cause the one or more processors to receive at least the arterial measurement signals from the non-invasive wearable monitoring device.

152. The non-transitory computer-readable medium of claim 147, wherein the arterial measurement signals comprise radiofrequency (RF) signals.

153. The non-transitory computer-readable medium of claim 147, wherein the instructions are configured to cause the one or more processors to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further based on a heart rate of the patient.

154. The non-transitory computer-readable medium of claim 153, wherein the instructions are further configured to cause the one or more processors to determine the heart rate of the patient.

155. The non-transitory computer-readable medium of claim 154, wherein the instructions are configured to cause the one or more processors to determine the heart rate of the patient by determining the heart rate of the patient using ECG signals generated from sensed cardiac electrical activity for the patient.

156. The non-transitory computer-readable medium of claim 154, wherein the instructions are configured to cause the one or more processors to determine the heart rate of the patient using the arterial measurement signals.

157. The non-transitory computer-readable medium of claim 147, wherein the one or more arteries of the patient comprise a radial artery of the patient.

158. The non-transitory computer-readable medium of claim 147, wherein the one or more arteries of the patient comprise a brachial artery of the patient.

159. The non-transitory computer-readable medium of claim 147, wherein the one or more arteries of the patient comprise a subclavian artery of the patient.

160. The non-transitory computer-readable medium of claim 147, wherein the one or more arteries of the patient comprise the patient’s aorta.

161. The non-transitory computer-readable medium of claim 147, wherein the one or more arterial pulse landmarks comprise a beginning and an end of a systolic portion of the arterial pulse waveform.

162. The non-transitory computer-readable medium of claim 161, wherein the one or more arterial pulse landmarks comprises a systolic peak and a dicrotic peak of the arterial pulse waveform.

163. The non-transitory computer-readable medium of claim 162, wherein the area under the arterial pulse waveform comprises an area of the systolic portion of the arterial pulse waveform.

164. The non-transitory computer-readable medium of claim 147, wherein the arterial pulse waveform comprises a representative arterial pulse waveform.

165. The non-transitory computer-readable medium of claim 147, wherein the instructions are further configured to cause the one or more processors to repeat identifying the arterial pulse waveform for the one or more arteries of the patient from the arterial measurement signals to identify a plurality of arterial pulse waveforms.

166. The non-transitory computer-readable medium of claim 165, wherein the instructions are further configured to cause the one or more processors to repeat, for each of the plurality of arterial pulse waveforms, analyzing the arterial pulse waveform to identify the one or more arterial pulse landmarks of the arterial pulse waveform, determining the area under the arterial pulse waveform using the one or more arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of arterial pulse waveforms.

167. The non-transitory computer-readable medium of claim 166, wherein the instructions are further configured to cause the one or more processors to calculate a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of arterial pulse waveforms.

168. The non-transitory computer-readable medium of claim 147, wherein the instructions are further configured to cause the one or more processors to calibrate the cardiac output relative to a baseline of the patient.

169. The non-transitory computer-readable medium of claim 168, wherein the instructions are configured to cause the one or more processors to calibrate the cardiac output relative to the baseline of the patient by determining a calibration factor for the patient.

170. The non-transitory computer-readable medium of claim 169, wherein the instructions are configured to cause the one or more processors to calculate the cardiac output for the patient using the determined area under the arterial pulse waveform and further using the calibration factor for the patient.

171. The non-transitory computer-readable medium of claim 170, wherein the cardiac output comprises an absolute cardiac output.

172. The non-transitory computer-readable medium of claim 169, wherein the baseline of the patient comprises one or more absolute calibration values for the patient.

173. The non-transitory computer-readable medium of claim 172, wherein the instructions are further configured to cause the one or more processors to receive the one or more absolute calibration values for the patient; andwherein the instructions are further configured to cause the one or more processors to determine the calibration factor using the one or more absolute calibration values.

174. The non-transitory computer-readable medium of claim 173, wherein the instructions are further configured to cause the one or more processors to periodically receive updated one or more absolute calibration values for the patient, and wherein determining the calibration factor comprises determining the calibration factor using the updated one or more absolute calibration values for the patient.

175. The non-transitory computer-readable medium of claim 173, wherein the one or more absolute calibration values for the patient comprise one or more absolute cardiac output values for the patient.

176. The non-transitory computer-readable medium of claim 173, wherein the one or more absolute calibration values for the patient comprise one or more blood pressure values for the patient.

177. The non-transitory computer-readable medium of claim 169, wherein determining the calibration factor comprises determining a baseline cardiac output for the patient.

178. The non-transitory computer-readable medium of claim 177, wherein the instructions are configured to cause the one or more processors to calibrate the cardiac output relative to the baseline of the patient further by normalizing the cardiac output for the patient using the baseline cardiac output for the patient.

179. The non-transitory computer-readable medium of claim 178, wherein the normalized cardiac output for the patient comprises a relative cardiac output for the patient.

180. The non-transitory computer-readable medium of claim 147, wherein the instructions are further configured to cause the one or more processors to determine a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient.

181. The non-transitory computer-readable medium of claim 180, wherein the instructions are further configured to cause the one or more processors to present the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver.

182. The non-transitory computer-readable medium of claim 180, wherein the instructions are further configured to cause the one or more processors to alert a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

183. A non-invasive cardiac monitoring system configured to determine a cardiac output of an ambulatory patient, comprising:a non-invasive patch-based monitoring device configured to be worn on a body of an ambulatory patient, comprisingan adhesive patch configured to be removably attached to the patient’s body, and a monitoring unit configured to be disposed on the adhesive patch, the monitoring unit comprisingat least one radiofrequency (RF) antenna configured to transmit RF waves towards one or more arteries of the patient and receive reflected RF waves from the one or more arteries of the patient; andRF circuitry configured to generate RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves; and cardiac output processing circuitry in electronic communication with the RF circuitry, wherein the processing circuitry is configured toidentify an RF arterial pulse waveform for the one or more arteries of the patient from the RF signals,analyze the RF arterial pulse waveform to identify one or more RF arterial pulse landmarks of the RF arterial pulse waveform,determine an area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, andcalculate a cardiac output for the patient using the determined area under the RF arterial pulse waveform.

184. The cardiac monitoring system of claim 183, wherein the monitoring unit comprises the cardiac output processing circuitry.

185. The cardiac monitoring system of claim 183, further comprising a gateway configured to communicate with the monitoring unit and with a remote server.

186. The cardiac monitoring system of claim 185, wherein the gateway comprises the cardiac output processing circuitry.

187. The cardiac monitoring system of claim 186, wherein the monitoring unit comprises a network interface configured to communicate with the gateway and transmit at least the RF signals to the gateway.

188. The cardiac monitoring system of claim 183, further comprising a remote server in electronic communication with the monitoring unit.

189. The cardiac monitoring system of claim 188, wherein the remote server comprises the cardiac output processing circuitry.

190. The cardiac monitoring system of claim 189, wherein the monitoring unit comprises a network interface configured to communicate with the remote server and transmit at least the RF signals to the remote server.

191. The cardiac monitoring system of claim 190, further comprising a gateway configured to communicate with the monitoring unit and with the remote server, wherein the network interface of the monitoring unit is configured to communicate with the remote server via the gateway.

192. The cardiac monitoring system of claim 183, wherein the adhesive patch is configured to be removably attached to the patient’s torso.

193. The cardiac monitoring system of claim 183, wherein the adhesive patch is configured to be removably attached to an extremity of the patient.

194. The cardiac monitoring system of claim 193, wherein the adhesive patch is configured to be removably attached to an arm of the patient.

195. The cardiac monitoring system of claim 183, wherein the cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further based on a heart rate of the patient.

196. The cardiac monitoring system of claim 195, wherein the patch-based monitoring device comprisesone or more electrocardiogram (ECG) electrodes configured to sense cardiac electrical activity of the patient; andECG circuitry configured to generate ECG signals using the sensed cardiac electrical activity of the patient.

197. The cardiac monitoring system of claim 196, wherein the adhesive patch comprises the one or more ECG electrodes.

198. The cardiac monitoring system of claim 196, wherein the cardiac output processing circuitry is configured to determine the heart rate of the patient using the ECG signals.

199. The cardiac monitoring system of claim 198, wherein the monitoring unit comprises the cardiac output circuitry.

200. The cardiac monitoring system of claim 198, further comprising a remote server in electronic communication with the monitoring unit.

201. The cardiac monitoring system of claim 200, wherein the remote server comprises the cardiac output processing circuitry.

202. The cardiac monitoring system of claim 198, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

203. The cardiac monitoring system of claim 198, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

204. The cardiac monitoring system of claim 195, wherein the cardiac output processing circuitry is configured to determine the heart rate of the patient using the RF signals.

205. The cardiac monitoring system of claim 183, wherein the at least one RF antenna is sized for the one or more arteries of the patient to which the at least one RF antenna is configured to transmit the RF waves.

206. The cardiac monitoring system of claim 205, wherein the one or more arteries of the patient comprise a radial artery of the patient.

207. The cardiac monitoring system of claim 205, wherein the at least one RF antenna comprises a surface area no greater than approximately 1.5 x 2.5 cm.

208. The cardiac monitoring system of claim 207, wherein the surface area of the at least one RF antenna is no greater than approximately 1.0 x 2.0 cm.

209. The cardiac monitoring system of claim 183, wherein the patch-based monitoring device is configured to be placed on the patient’s skin in an area around a major artery of the patient.

210. The cardiac monitoring system of claim 209, wherein the major artery comprises a radial artery of the patient.

211. The cardiac monitoring system of claim 209, wherein the major artery comprises a brachial artery of the patient.

212. The cardiac monitoring system of claim 209, wherein the major artery comprises a subclavian artery of the patient.

213. The cardiac monitoring system of claim 209, wherein the major artery comprises the patient’s aorta.

214. The cardiac monitoring system of claim 183, wherein the one or more RF arterial pulse landmarks comprise a beginning and an end of a systolic portion of the RF arterial pulse waveform.

215. The cardiac monitoring system of claim 214, wherein the one or more RF arterial pulse landmarks comprise a systolic peak and a dicrotic peak of the RF arterial pulse waveform.

216. The cardiac monitoring system of claim 215, wherein the cardiac output processing circuitry is configured to analyze the RF arterial pulse waveform to identify the one or more RF arterial pulse landmarks using local minima and maxima analysis.

217. The cardiac monitoring system of claim 215, wherein the cardiac output processing circuitry is configured to identify the beginning and the end of the systolic portion of the RF arterial pulse waveform using the systolic peak and the dicrotic peak of the RF arterial pulse waveform.

218. The cardiac monitoring system of claim 214, wherein the area under the RF arterial pulse waveform comprises an area of the systolic portion of the RF arterial pulse waveform.

219. The cardiac monitoring system of claim 214, wherein the monitoring unit comprises the cardiac output circuitry.

220. The cardiac monitoring system of claim 214, further comprising a remote server in electronic communication with the monitoring unit.

221. The cardiac monitoring system of claim 220, wherein the remote server comprises the cardiac output processing circuitry.

222. The cardiac monitoring system of claim 214, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

223. The cardiac monitoring system of claim 214, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

224. The cardiac monitoring system of claim 183, wherein the RF arterial pulse waveform comprises a representative RF arterial pulse waveform.

225. The cardiac monitoring system of claim 224, wherein the cardiac output processing circuitry is further configured toidentify a plurality of segmented RF arterial pulse waveforms for the one or more arteries of the patient from one or more segments of the RF signals; andgenerate the representative RF arterial pulse waveform from the plurality of segmented RF arterial pulse waveforms.

226. The cardiac monitoring system of claim 225, wherein the cardiac output processing circuitry is configured to generate the representative RF arterial pulse waveform by averaging the plurality of segmented RF arterial pulse waveforms.

227. The cardiac monitoring system of claim 183, wherein the cardiac output processing circuitry is further configured to repeat identifying the RF arterial pulse waveform for the one or more arteries of the patient from the RF signals to identify a plurality of RF arterial pulse waveforms.

228. The cardiac monitoring system of claim 227, wherein the cardiac output processing circuitry is further configured to repeat, for each of the plurality of RF arterial pulse waveforms, analyzing the RF arterial pulse waveform to identify the one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determining the area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

229. The cardiac monitoring system of claim 228, wherein the cardiac output processing circuitry is further configured to calculate a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

230. The cardiac monitoring system of claim 229, wherein the representative cardiac output for the patient comprises an average of the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

231. The cardiac monitoring system of claim 229, wherein the representative cardiac output for the patient comprises a median of the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

232. The cardiac monitoring system of claim 183, wherein the cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further using one or more of heart rate, arterial compliance, or slope of the RF arterial pulse waveform.

233. The cardiac monitoring system of claim 183, wherein the cardiac output processing circuitry is further configured to calibrate the cardiac output relative to a baseline of the patient.

234. The cardiac monitoring system of claim 233, wherein the cardiac output processing circuitry is configured to calibrate the cardiac output relative to the baseline of the patient by determining a calibration factor for the patient.

235. The cardiac monitoring system of claim 234, wherein the cardiac output processing circuitry is configured to calculate the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further using the calibration factor for the patient.

236. The cardiac monitoring system of claim 235, wherein the cardiac output comprises an absolute cardiac output.

237. The cardiac monitoring system of claim 234, wherein the baseline of the patient comprises one or more absolute calibration values for the patient.

238. The cardiac monitoring system of claim 237, wherein the cardiac output processing circuitry is further configured to receive the one or more absolute calibration values for the patient, and wherein determining the calibration factor comprises determining the calibration factor using the one or more absolute calibration values.

239. The cardiac monitoring system of claim 238, wherein the cardiac output processing circuitry is further configured to periodically receive updated one or more absolute calibration values for the patient, and wherein determining the calibration factor comprises determining the calibration factor using the updated one or more absolute calibration values for the patient.

240. The cardiac monitoring system of claim 238, wherein the one or more absolute calibration values for the patient comprise one or more absolute cardiac output values for the patient.

241. The cardiac monitoring system of claim 240, wherein the one or more absolute cardiac output values for the patient are measured using echocardiography.

242. The cardiac monitoring system of claim 240, wherein the one or more absolute cardiac output values for the patient are measured using thermodilution.

243. The cardiac monitoring system of claim 240, wherein the one or more absolute calibration values for the patient comprise one or more blood pressure values for the patient.

244. The cardiac monitoring system of claim 243, wherein the one or more blood pressure values for the patient are measured using a sphygmomanometer.

245. The cardiac monitoring system of claim 243, wherein the one or more blood pressure values for the patient are measured using a plurality of patch-based monitoring devices worn along a plurality of locations on an artery.

246. The cardiac monitoring system of claim 239, wherein the monitoring unit comprises the cardiac output circuitry.

247. The cardiac monitoring system of claim 239, further comprising a remote server in electronic communication with the monitoring unit.

248. The cardiac monitoring system of claim 247, wherein the remote server comprises the cardiac output processing circuitry.

249. The cardiac monitoring system of claim 239, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

250. The cardiac monitoring system of claim 239, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

251. The cardiac monitoring system of claim 234, wherein determining the calibration factor comprises determining a baseline cardiac output for the patient.

252. The cardiac monitoring system of claim 251, wherein the cardiac output processing circuitry is further configured to normalize the cardiac output for the patient using the baseline cardiac output for the patient.

253. The cardiac monitoring system of claim 252, wherein the normalized cardiac output for the patient comprises a relative cardiac output for the patient.

254. The cardiac monitoring system of claim 253, wherein the monitoring unit comprises the cardiac output circuitry.

255. The cardiac monitoring system of claim 253, further comprising a remote server in electronic communication with the monitoring unit.

256. The cardiac monitoring system of claim 255, wherein the remote server comprises the cardiac output processing circuitry.

257. The cardiac monitoring system of claim 253, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

258. The cardiac monitoring system of claim 253, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

259. The cardiac monitoring system of claim 251, wherein the determining the baseline cardiac output for the patient comprisesidentifying a calibration RF arterial pulse waveform for the one or more arteries of the patient from the RF signals;analyzing the calibration RF arterial pulse waveform to identify one or more calibration RF arterial pulse landmarks of the calibration RF arterial pulse waveform;determining an area under the calibration RF arterial pulse waveform using the one or more calibration RF arterial pulse landmarks; andcalculating a calibration cardiac output for the patient using the determined area under the calibration RF arterial pulse waveform, wherein the baseline cardiac output is based on the calibration cardiac output.

260. The cardiac monitoring system of claim 259, wherein the baseline of the patient comprises the calibration cardiac output.

261. The cardiac monitoring system of claim 259, wherein the cardiac output processing circuitry is further configured to repeat identifying the calibration RF arterial pulse waveform for the one or more arteries of the patient from the RF signals to identify a plurality of calibration RF arterial pulse waveforms.

262. The cardiac monitoring system of claim 261, wherein the cardiac output processing circuitry is further configured to repeat, for each of the plurality of calibration RF arterial pulse waveforms, analyzing the calibration RF arterial pulse waveform to identify the one or more calibration RF arterial pulse landmarks of the calibration RF arterial pulse waveform, determining the area under the calibration RF arterial pulse waveform using the one or more calibration RF arterial pulse landmarks, and calculating the calibration cardiac output for the patient using the determined area under the calibration RF arterial pulse waveform to produce a plurality of calibration cardiac outputs for the plurality of calibration RF arterial pulse waveforms.

263. The cardiac monitoring system of claim 262, wherein the baseline cardiac output comprises a statistical output of the plurality of calibration RF arterial pulse waveforms.

264. The cardiac monitoring system of claim 263, wherein the statistical output of the plurality of calibration RF arterial pulse waveforms comprises an average of the calibration RF arterial pulse waveforms.

265. The cardiac monitoring system of claim 263, wherein the statistical output of the plurality of calibration RF arterial pulse waveforms comprises a median of the calibration RF arterial pulse waveforms.

266. The cardiac monitoring system of claim 251, wherein the cardiac output processing circuitry is further configured to generate a baseline RF arterial pulse waveform for the patient.

267. The cardiac monitoring system of claim 266, wherein the cardiac output processing circuitry is configured to generate the baseline RF arterial pulse waveform for the patient by identifying a plurality of segmented baseline RF arterial pulse waveforms for the one or more arteries of the patient from one or more baseline segments of the RF signals; and generating the segmented baseline RF arterial pulse waveform for the patient from the plurality of baseline segment RF arterial pulse waveforms.

268. The cardiac monitoring system of claim 267, wherein generating the baseline RF arterial pulse waveform comprises averaging the plurality of segmented baseline RF arterial pulse waveforms.

269. The cardiac monitoring system of claim 266, wherein the cardiac output processing circuitry is further configured to calculate the baseline cardiac output using the baseline RF arterial pulse waveform.

270. The cardiac monitoring system of claim 269, wherein the cardiac output processing circuitry is configured to calculate the baseline cardiac output byanalyzing the baseline RF arterial pulse waveform to identify one or more baseline RF arterial pulse landmarks of the baseline RF arterial pulse waveform;determining an area under the baseline RF arterial pulse waveform using the one or more baseline RF arterial pulse landmarks; andcalculating the baseline cardiac output for the patient using the determined area under the baseline RF arterial pulse waveform.

271. The cardiac monitoring system of claim 183, wherein the cardiac output circuitry is further configured to determine a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient.

272. The cardiac monitoring system of claim 271, wherein the cardiac output circuitry is further configured to present the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver.

273. The cardiac monitoring system of claim 271, wherein the cardiac output circuitry is further configured to alert a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

274. The cardiac monitoring system of claim 271, wherein the monitoring unit comprises the cardiac output circuitry.

275. The cardiac monitoring system of claim 271, further comprising a remote server in electronic communication with the monitoring unit.

276. The cardiac monitoring system of claim 275, wherein the remote server comprises the cardiac output processing circuitry.

277. The cardiac monitoring system of claim 271, wherein the monitoring unit is configured to be removably attached to the patient’s torso.

278. The cardiac monitoring system of claim 271, wherein the monitoring unit is configured to be removably attached to an extremity of the patient.

279. A method for determining a cardiac output of an ambulatory patient using a non-invasive cardiac monitoring system, comprising:identifying a radiofrequency (RF) arterial pulse waveform for one or more arteries of an ambulatory patient from RF signals corresponding to the one or more arteries of the patient generated by a non-invasive patch-based monitoring device, configured to be worn on a body of the ambulatory patient and further configured to transmit RF waves towards the one or more arteries of the patient, using reflected arterial measurement waves received by the non-invasive patch-based monitoring device;analyzing the RF arterial pulse waveform to identify one or more RF arterial pulse landmarks of the RF arterial pulse waveform;determining an area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks; andcalculating a cardiac output for the patient using the determined area under the RF arterial pulse waveform.

280. The method of claim 279, wherein the non-invasive patch-based monitoring device comprises a monitoring unit, comprisingat least one RF antenna configured to transmit the RF waves towards the one or more arteries of the patient and receive the reflected RF waves from the one or more arteries of the patient; andRF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

281. The method of claim 280, wherein the non-invasive wearable monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso and wherein the monitoring unit is configured to be disposed on the adhesive patch.

282. The method of claim 280, wherein the non-invasive wearable monitoring device further comprises a garment configured to be removably worn around the patient’s torso and wherein the monitoring unit is configured to be disposed on the garment.

283. The method of claim 280, wherein the at least one RF antenna is sized for the one or more arteries of the patient to which the at least one RF antenna is configured to transmit the RF waves.

284. The method of claim 283, wherein the one or more arteries of the patient comprise a radial artery of the patient.

285. The method of claim 283, wherein the at least one RF antenna comprises a surface area no greater than approximately 1.5 x 2.5 cm.

286. The method of claim 285, wherein the surface area of the at least one RF antenna is no greater than approximately 1.0 x 2.0 cm.

287. The method of claim 279, further comprising receiving at least the RF signals from the non-invasive patch-based monitoring device.

288. The method of claim 279, wherein calculating the cardiac output for the patient comprises calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further based on a heart rate of the patient.

289. The method of claim 288, further comprising determining the heart rate of the patient.

290. The method of claim 289, wherein determining the heart rate of the patient comprises determining the heart rate of the patient using ECG signals generated from sensed cardiac electrical activity for the patient.

291. The method of claim 289, wherein determining the heart rate of the patient comprises determining the heart rate of the patient using the RF signals.

292. The method of claim 279, wherein the one or more arteries of the patient comprise a radial artery of the patient.

293. The method of claim 279, wherein the one or more arteries of the patient comprise a brachial artery of the patient.

294. The method of claim 279, wherein the one or more arteries of the patient comprise a subclavian artery of the patient.

295. The method of claim 279, wherein the one or more arteries of the patient comprise the patient’s aorta.

296. The method of claim 279, wherein the one or more RF arterial pulse landmarks comprise a beginning and an end of a systolic portion of the RF arterial pulse waveform.

297. The method of claim 296, wherein the one or more RF arterial pulse landmarks comprises a systolic peak and a dicrotic peak of the RF arterial pulse waveform.

298. The method of claim 297, wherein the area under the RF arterial pulse waveform comprises an area of the systolic portion of the RF arterial pulse waveform.

299. The method of claim 279, wherein the RF arterial pulse waveform comprises a representative RF arterial pulse waveform.

300. The method of claim 299, further comprising repeating identifying the RF arterial pulse waveform for the one or more arteries of the patient from the RF signals to identify a plurality of RF arterial pulse waveforms.

301. The method of claim 300, further comprising repeating, for each of the plurality of RF arterial pulse waveforms, analyzing the RF arterial pulse waveform to identify the one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determining the area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

302. The method of claim 301, further comprising calculating a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

303. The method of claim 279, further comprising calibrating the cardiac output relative to a baseline of the patient.

304. The method of claim 303, wherein calibrating the cardiac output relative to the baseline of the patient comprises determining a calibration factor for the patient.

305. The method of claim 304, wherein calculating the cardiac output for the patient comprises calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform and further using the calibration factor for the patient.

306. The method of claim 305, wherein the cardiac output comprises an absolute cardiac output.

307. The method of claim 304, wherein the baseline of the patient comprises one or more absolute calibration values for the patient.

308. The method of claim 307, further comprising receiving the one or more absolute calibration values for the patient, wherein determining the calibration factor comprises determining the calibration factor using the one or more absolute calibration values.

309. The method of claim 308, further comprising periodically receiving updated one or more absolute calibration values for the patient, wherein determining the calibration factor comprises determining the calibration factor using the updated one or more absolute calibration values for the patient.

310. The method of claim 308, wherein the one or more absolute calibration values for the patient comprise one or more absolute cardiac output values for the patient.

311. The method of claim 308, wherein the one or more absolute calibration values for the patient comprise one or more blood pressure values for the patient.

312. The method of claim 304, wherein determining the calibration factor comprises determining a baseline cardiac output for the patient.

313. The method of claim 312, wherein calibrating the cardiac output relative to the baseline of the patient further comprises normalizing the cardiac output for the patient using the baseline cardiac output for the patient.

314. The method of claim 313, wherein the normalized cardiac output for the patient comprises a relative cardiac output for the patient.

315. The method of claim 279, further comprising determining a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient.

316. The method of claim 315, further comprising presenting the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver.

317. The method of claim 315, further comprising alerting a patient caregiver based on the trend of the cardiac output relative to the one or more historical cardiac outputs.

318. A non-transitory computer-readable medium storing instructions that are configured to, when executed by one or more processors, cause the one or more processors to:identify a radiofrequency (RF) arterial pulse waveform for one or more arteries of an ambulatory patient from RF signals corresponding to the one or more arteries of the patient generated by a non-invasive patch-based monitoring device, configured to be worn on a body of the ambulatory patient and further configured to transmit RF waves towards the one or more arteries of the patient, using reflected RF waves received by the non-invasive patch-based monitoring device;analyze the RF arterial pulse waveform to identify one or more RF arterial pulse landmarks of the RF arterial pulse waveform;determine an area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks; andcalculate a cardiac output for the patient using the determined area under the RF arterial pulse waveform.

319. The non-transitory computer-readable medium of claim 318, wherein the non-invasive patch-based monitoring device comprises a monitoring unit, comprisingat least one RF antenna configured to transmit the RF waves towards the one or more arteries of the patient and receive the reflected RF waves from the one or more arteries of the patient; andRF circuitry configured to generate the RF signals corresponding to the one or more arteries of the patient using the received reflected RF waves.

320. The non-transitory computer-readable medium of claim 319, wherein the non-invasive patch-based monitoring device further comprises an adhesive patch configured to be removably attached to the patient’s torso and wherein the monitoring unit is configured to be disposed on the adhesive patch.

321. The non-transitory computer-readable medium of claim 319, wherein the non-invasive patch-based monitoring device further comprises a garment configured to be removably worn around the patient’s torso and wherein the monitoring unit is configured to be disposed on the garment.

322. The non-transitory computer-readable medium of claim 319, wherein the at least one RF antenna is sized for the one or more arteries of the patient to which the at least one RF antenna is configured to transmit the RF waves.

323. The non-transitory computer-readable medium of claim 322, wherein the one or more arteries of the patient comprise a radial artery of the patient.

324. The non-transitory computer-readable medium of claim 322, wherein the at least one RF antenna comprises a surface area no greater than approximately 1.5 x 2.5 cm.

325. The non-transitory computer-readable medium of claim 324, wherein the surface area of the at least one RF antenna is no greater than approximately 1.0 x 2.0 cm.

326. The non-transitory computer-readable medium of claim 318, wherein the instructions are further configured to cause the one or more processors to receive at least the RF signals from the non-invasive patch-based monitoring device.

327. The non-transitory computer-readable medium of claim 319, wherein the instructions are configured to cause the one or more processors to calculate the cardiac output for the patientusing the determined area under the RF arterial pulse waveform and further based on a heart rate of the patient.

328. The non-transitory computer-readable medium of claim 327, wherein the instructions are further configured to cause the one or more processors to determine the heart rate of the patient.

329. The non-transitory computer-readable medium of claim 328, wherein the instructions are configured to cause the one or more processors to determine the heart rate of the patient by determining the heart rate of the patient using ECG signals generated from sensed cardiac electrical activity for the patient.

330. The non-transitory computer-readable medium of claim 328, wherein the instructions are configured to cause the one or more processors to determine the heart rate of the patient using the RF signals.

331. The non-transitory computer-readable medium of claim 318, wherein the one or more arteries of the patient comprise a radial artery of the patient.

332. The non-transitory computer-readable medium of claim 318, wherein the one or more arteries of the patient comprise a brachial artery of the patient.

333. The non-transitory computer-readable medium of claim 318, wherein the one or more arteries of the patient comprise a subclavian artery of the patient.

334. The non-transitory computer-readable medium of claim 318, wherein the one or more arteries of the patient comprise the patient’s aorta.

335. The non-transitory computer-readable medium of claim 318, wherein the one or more RF arterial pulse landmarks comprise a beginning and an end of a systolic portion of the RF arterial pulse waveform.

336. The non-transitory computer-readable medium of claim 335, wherein the one or more RF arterial pulse landmarks comprises a systolic peak and a dicrotic peak of the RF arterial pulse waveform.

337. The non-transitory computer-readable medium of claim 336, wherein the area under the RF arterial pulse waveform comprises an area of the systolic portion of the RF arterial pulse waveform.

338. The non-transitory computer-readable medium of claim 318, wherein the RF arterial pulse waveform comprises a representative RF arterial pulse waveform.

339. The non-transitory computer-readable medium of claim 338, wherein the instructions are further configured to cause the one or more processors to repeat identifying the RF arterial pulse waveform for the one or more arteries of the patient from the RF signals to identify a plurality of RF arterial pulse waveforms.

340. The non-transitory computer-readable medium of claim 339, wherein the instructions are further configured to cause the one or more processors to repeat, for each of the plurality of RF arterial pulse waveforms, analyzing the RF arterial pulse waveform to identify the one or more RF arterial pulse landmarks of the RF arterial pulse waveform, determining the area under the RF arterial pulse waveform using the one or more RF arterial pulse landmarks, and calculating the cardiac output for the patient using the determined area under the RF arterial pulse waveform to produce a plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

341. The non-transitory computer-readable medium of claim 340, wherein the instructions are further configured to cause the one or more processors to calculate a representative cardiac output for the patient using the plurality of cardiac outputs for the plurality of RF arterial pulse waveforms.

342. The non-transitory computer-readable medium of claim 318, wherein the instructions are further configured to cause the one or more processors to calibrate the cardiac output relative to a baseline of the patient.

343. The non-transitory computer-readable medium of claim 342, wherein the instructions are configured to cause the one or more processors to calibrate the cardiac output relative to the baseline of the patient by determining a calibration factor for the patient.

344. The non-transitory computer-readable medium of claim 343, wherein the instructions are configured to cause the one or more processors to calculate the cardiac output for the patientusing the determined area under the RF arterial pulse waveform and further using the calibration factor for the patient.

345. The non-transitory computer-readable medium of claim 344, wherein the cardiac output comprises an absolute cardiac output.

346. The non-transitory computer-readable medium of claim 343, wherein the baseline of the patient comprises one or more absolute calibration values for the patient.

347. The non-transitory computer-readable medium of claim 346, wherein the instructions are further configured to cause the one or more processors to receive the one or more absolute calibration values for the patient; andwherein the instructions are further configured to cause the one or more processors to determine the calibration factor using the one or more absolute calibration values.

348. The non-transitory computer-readable medium of claim 347, wherein the instructions are further configured to cause the one or more processors to periodically receive updated one or more absolute calibration values for the patient, and wherein determining the calibration factor comprises determining the calibration factor using the updated one or more absolute calibration values for the patient.

349. The non-transitory computer-readable medium of claim 347, wherein the one or more absolute calibration values for the patient comprise one or more absolute cardiac output values for the patient.

350. The non-transitory computer-readable medium of claim 347, wherein the one or more absolute calibration values for the patient comprise one or more blood pressure values for the patient.

351. The non-transitory computer-readable medium of claim 343, wherein determining the calibration factor comprises determining a baseline cardiac output for the patient.

352. The non-transitory computer-readable medium of claim 351, wherein the instructions are configured to cause the one or more processors to calibrate the cardiac output relative to the baseline of the patient further by normalizing the cardiac output for the patient using the baseline cardiac output for the patient.

353. The non-transitory computer-readable medium of claim 352, wherein the normalized cardiac output for the patient comprises a relative cardiac output for the patient.

354. The non-transitory computer-readable medium of claim 318, wherein the instructions are further configured to cause the one or more processors to determine a trend of the cardiac output relative to one or more historical cardiac outputs calculated for the patient.

355. The non-transitory computer-readable medium of claim 354, wherein the instructions are further configured to cause the one or more processors to present the trend of the cardiac output relative to the one or more historical cardiac outputs to a patient caregiver.

356. The non-transitory computer-readable medium of claim 354, wherein the instructions are further configured to cause the one or more processors to alert a patient caregiver based on the trend of the cardiac output

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