System and method for wearable patient monitoring

Abstract

One of the side-effects of decompensation in heart failure is excessive accumulation of interstitial fluid. Systems and methods are provided for measuring the edema using near infrared (NIR) light, in the tissue at the periphery of a patient with heart failure. This edema value, calculated from the water fraction in the tissue at the periphery, is used to determine if the patient is at risk of decompensation. If the patients is at risk of decompensation, the system includes a user interface such as a display, a speaker, or a haptic feedback device, to alert the patient to seek medical intervention.

Description

SYSTEM AND METHOD FOR WEARABLE PATIENT MONITORINGCROSS REFERENCE TO RELATED APPLICATION

[0001] The present application is based on and claims priority to US Provisional Application Serial No. 63 / 625,898, filed January 26, 2024, and incorporated herein by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable.BACKGROUND

[0003] Heart failure (HF) is a chronic condition affecting millions of people annually. It is a condition in which the heart’s ability to pump blood is impaired due to a variety causes. More than 26 million people worldwide, including approximately 6 million in the U.S., are affected and its prevalence is increasing. Despite advances in treatment and prevention of heart failure, even successfully treated patients are at risk for decompensation for the rest of their life.

[0004] That is, heart failure is a chronic disease. After a patient has recovered from the acute phase of heart failure and leaves the hospital, the patient is still susceptible to episodes of acute decompensation. Detecting decompensation is difficult. Invasive monitoring systems usually require a surgically implanted device to monitor pulmonary artery (PA) pressure. Monitoring a PA pressure device typically requires a clinician to read the output and analyze the data. This can lead to delays in detecting decompensation. Missing the early signs of decompensation can lead to re-hospitalization which in turn correlates with increased risk of poor outcomes.

[0005] In this context, significant effort has been directed towards the development of remote monitoring technologies for HF patients and in particular on the development of dedicated devices to capture alterations in physiological parameters as decompensation progresses. Invasive devices, such as the CardioMEMS HF system, which monitors the pulmonary artery (PA) pressure, have been shown to reduce re-hospitalization rates. Bymonitoring the elevation of PA pressures, which occurs several weeks before acute HF events, the CardioMEMS device was able to provide an early warning of decompensation and helped reduce HF-related hospitalization by 37% in monitored New York Heart Association (NYHA) class III patients vs. control during a 15-18 month follow-up period (CHAMPION trial). These benefits were confirmed in a 2 year post FDA-approval study. Still, the widespread adoption of CardioMEMS continues to face substantial limitations due to the need for an invasive procedure for its placement and the related costs, including the potential need for recalibration.

[0006] Thus, there is a need for new systems and methods to assist for the extended treatment or monitoring of patients experiencing heart failure.SUMMARY OF THE INVENTION

[0007] The present disclosure overcomes the aforementioned drawbacks by providing systems and methods for extended monitoring of a patient experiencing heart failure using a wearable monitor. In one configuration, the wearable monitor is non-invasive and may be worn on a periphery of the patient, such as a leg or, more particularly, a calf or shin of the patient. The monitor may include an optical sensor configured to determine a condition of the patient proximate the monitor. In one configuration, the monitor may determine one or more parameters of the patient and, based thereon, determine the potential and / or send alerts regarding the condition of the patient, for example, relative to heart failure monitoring. In one non-limiting example, the monitor mayo be able to determine a condition that may include edema, such that the monitor is configured to detect edema in a patient’s extremities. The monitor may include a near-infrared spectroscopy (NIRS) sensor and processor to determine an amount of edema present in the patient’s extremities. The amount of edema present can be used to determine if the patient is in danger of decompensation. If this amount of edema is above a threshold value or changes in values over time that exceed a threshold, an alarm can be raised indicating the patient may be in danger of decompensation and preventative care can be sought.

[0008] In one aspect, the present disclosure provides a wearable system for monitoring a patient with heart failure. The system includes a near-infrared spectroscopy (NIRS) source, and a sensor configured to deliver multi-wavelength near-infrared light to tissue of the patient with heart failure. The system comprises a mounting system that is configured to position the NIRS source and sensor on the patient with heart failure to acquire NIRS data from the patient with heart failure. A processor is configured to receive the NIRS data from the sensor and determine a tissue water fraction using the NIRS data. The system generates a report including an indication of potential forthe decompensation in the patient based on the determined water fraction.

[0009] In accordance with another aspect of the disclosure, a method is provided for determining the edema in a tissue located at the periphery of a patient, that is indicative of an unsafe condition. This method uses a light source to deliver light to the tissue located at the periphery of the patient, and a sensor that receives light that interacts with the tissue located at the periphery of the patient, to generate optical data. The processor uses the optical data to calculate an absorption coefficient of the tissue located at the periphery of the patient. Using the processor and the absorption coefficient, contributions to absorption of at least one of oxy hemoglobin (HbO), deoxy (HbR) hemoglobin, water, lipids, or scattering are estimated. The processor uses the contributions to absorption to determine the edema in the tissue located at the periphery of the patient. The processor determines whether the edema in the tissue located at the periphery of the patient indicates an unsafe condition, and using the processor, generates an alert reporting the unsafe condition.

[0010] In accordance with another aspect of the disclosure, a method is provided for monitoring a patient with heart failure. The method comprises securing a near-infrared spectroscopy (NIRS) source and a sensor to the patient to deliver multi-wavelength nearinfrared (NIR) light to the tissue of a patient with heart failure. The NIRS data is received from the sensor with a processor. The processor is used to determine a tissue water fraction using the NIRS data. The processor generates a report including an indication of the potential for decompensation in the patient, based on the determined tissue water fraction.

[0011] In accordance with another aspect of the disclosure, a system is provided for determining the edema in tissue located at the periphery of a patient. This edema is indicative of an unsafe condition. The system comprises a light source configured to deliver light to tissue located at the periphery of the patient, and a sensor configured to receive light that interacts with the tissue located at the periphery of the patient. The system also comprises a processor configured to receive the optical data, use the optical data to calculate an absorption coefficient of the tissue located at the periphery of the patient, use the absorption coefficient to estimate contributions to absorption of at least one of oxy hemoglobin (HbO), deoxy (HbR) hemoglobin, water, lipids, or scattering, and use the contributions to absorption to determine the edema in the tissue located at the periphery of the patient. The system further comprises a user interface that is configured to generate an alert reporting an unsafe condition.

[0012] The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference us made to the accompanying drawings that form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention.BRIEF DESCRIPTION OF DRAWINGS

[0013] Fig. 1 is a schematic diagram of a person with the wearable system of the present disclosure, located at a plurality of peripheries of the patient.

[0014] Fig. 2 is a block diagram of the system of the present disclosure.

[0015] Fig. 3 is a flow chart setting forth some examples of the non-limiting steps of a method of evaluating the edema in the tissue located at the periphery of the patient.

[0016] Fig. 4A is a graph of recovered water while varying lipid concentration from optical data acquired in accordance with the present disclosure.

[0017] Fig. 4B is a graph of recovered water while varying total hemoglobin concentration from optical data acquired in accordance with the present disclosure.

[0018] Fig. 4C is a graph of recovered water while varying tissue oxygen saturation from optical data acquired in accordance with the present disclosure.

[0019] Fig. 4D is a graph of recovered water while varying scattering coefficients in optical data acquired in accordance with the present disclosure.

[0020] Fig. 5A is a graph of recovered water fraction for a first subject acquired using a full spectrum and a limited spectrum.

[0021] Fig. 5B is a graph of recovered water fraction for a second subject acquired using a full spectrum and a limited spectrum.DETAILED DESCRIPTION

[0022] As discussed, HF is a chronic disease and acute decompensation episodes lead to high re-admission rates to hospital, and increased mortality. The present disclosure recognizes that a major side-effect of decompensation in HF is the development of edema (excessive accumulation of interstitial fluid). This edema can take multiple forms including pulmonary edema, ascites (abdominal fluid), and peripheral edema, especially in the lower extremities.

[0023] Attempts at non-invasive monitoring has primarily addressed the detection of volume overload caused by decompensating HF manifested through tissue edema. The primary approach has been to use whole body bioimpedance analyzers (BIA), and correlations have been seen between fluid overload by BIA and subsequent hospitalization. Yet, these studies were conducted with hospital grade devices and have not been replicated using at home monitoring. A stringent need remains for at home monitoring devices that can detect decompensation in HF patients early enough to allow titration of medications and other preventive measures to be taken while the patient is still at home so patients can avoid the development of acute HF and re-hospitalization.

[0024] The present disclosure provides systems and methods for monitoring a patient over time for conditions of HF. More particularly, systems and methods are provided to monitor for potential decompensation in people in HF. In one, non-limiting example, a multiparametric sensor band is provided that can be worn by a patient in HF to allow for ongoingmonitoring, even when outside the oversight of clinicians or healthcare facilities. As will be described, the present disclosure provides systems and methods that can utilize optical data, such as using near-infrared spectroscopy, which takes advantage of low tissue absorption in the 700- 1100 nm region, to quantify tissue water content, and provides hemodynamic status assessment by measuring tissue hemoglobin concentration and hemoglobin oxygen saturation.

[0025] Referring to Fig. 1 , in one, non-limiting example a patient 100 in HF may wear a monitor system 102. The monitor system may be designed to be positioned on a periphery of the patient 100. More particularly, the monitor system 102 may be incorporated into and / or may include a system configured to be mounted to a periphery of the patient 100. For example, a mounting system 104a may be configured to be positioned on or about a calf of the patient 100. Additionally or alternatively, a mounting system 104b may be configured to be positioned about another part of a leg of the patient 100. Additionally or alternatively, a mounting system 104c may be configured to be positioned about an arm of the patient 100. Additionally or alternatively, a mounting system 104d may be configured to be positioned about a head of the patient 100. Additionally or alternatively, a mounting system 104e may be configured to be positioned about a neck of the patient 100.

[0026] Regardless of the particular position of the monitoring system 102 or the configuration of the associated mounting system 104a-104e, the monitoring system 102 may be configured to communicate, as indicated by signal 106. As will be described, the signal 106 may be a wireless communication signal, for example, designed to be received by a computer 108 or personal computing device (including a phone or other device) 110, whether communicated locally or over a wide area network (including the Internet) 112. Additionally or alternatively, the signal 106 may be an auditory, visual, or vibrational alarm communicated locally from the monitoring system 102.

[0027] Referring now to Fig. 2, the monitor system 102 and mounting system 104a-104e of Fig. 1 may include a housing 200 coupled to the mounting system 104a-104e. As illustrated in the mounting system 104a-104e may include elastic and / or extendable straps or other components configured to secure the monitoring system 102 to the patient. The housing200 may surround a plurality of monitoring components. In one non-limiting example, such components may include any of an excitation source 202, a sensor(s) 204, a processor 206, memory 208, an energy storage device 210, and / or a communications device 212.

[0028] The excitation source 202 may be a light source. In one, non-limiting example, the excitation source 202 may include a light source configured for near-infrared spectroscopy (NIRS). The excitation source 202 may be designed to non-invasively probe a peripheral volume of the patient to, as will be described, allow the system 102 to monitor for overload and hemodynamics in patients with heart failure. Thus, the mounting system 104a-104e may form or include a wearable strap configured to arrange the excitation source 202 on a periphery of the patientto achieve such probing. As one non-limiting example, the mounting system 104a-104e may be designed to arrange the excitation source 202 on or about the patient’s calf, shin, or ankle area, or other areas, as described above. The housing and surrounding components may be flexible to adapt to the contours of the patient where the system 102 is mounted or secured.

[0029] The sensor 204 may be configured to acquire data from the patient using the excitation source 202. For example, the sensor 204 may be a NIRS sensor. In one, nonlimiting example, one or more of the excitation source 202 and the sensor 204 may be configured as a FlexNIRS system, such as described in Wu, K.-C. et al. Open-source FlexNIRS: A low-cost, wireless and wearable cerebral health tracker. Neuroimage 256, 119216 (2022)., which is incorporated herein by reference in its entirety.

[0030] The sensor 204 produces data that is provided to the processor 206. The processor 206 is configured to access a non-transitory storage medium or memory 208 that includes instructions for the processor to operate as will be described. That is, as will be described, the processor 206 is configured to analyze data acquired by the sensor 204 and communicate via the communications device 212. The communications device 212 may be or include a display, a speaker, or a haptic feedback system for local communications, and / or may be designed for wired or wireless communication, as described with respect to Fig. 1. Wireless communication may include cellular protocols, Bluetooth protocols, WiFi protocols, or other short or long range communications protocols or mechanisms.

[0031] In one, non-limiting example, the housing 200 may include a flexible printed circuit board. The processor 206 and communications device 212, and / or other components, may be joined to the source 202 and sensor 204 by a flexible PCB bridge. In one, particular and non-limiting example the housing 200 may be formed from a NinjaFlex rubber. A magnetic connector may be used to connect the energy storage device 210. In a further non-limiting example, if based on the FlexNIRS system, the Tl AFE4900 may be upgraded to the Tl AFE4460, which allows control of up to 32 LEDs in the source 202 and functioning in 16 measurement phases, and the sensor 204 can read up to 4 photodiodes, with an automatic, no illumination phase for background light subtraction. In a non-limiting example, the processor 206, memory 208, and communications device 212 can include a Silicon Labs BGM121 system-in-package module, which embeds an AMR-Cortex-M4 microcontroller with a Bluetooth low-energy (BLE) module. The latter has a transmission power of up to 8 dBm, receiving sensitivity of -90 dBm and can work at a ranges beyond 20 m in open space, and has been tested to operate without errors up to 10 m in a complex, hospital-like environment. The sensor 204 can also include or be coupled other sensors 204a. In one non-limiting example, the system 102 may include an accelerometer and / or gyroscope. As one, non-limiting example, the other sensors 204a may include an inertial module, which may include a low power MEMS 3-axis accelerometer and 3-axis gyroscope used to detect movement and remove motion artifacts.

[0032] The processor 206, as well as the source 202, sensor 204, and communications device 212 may receive operational power from the energy storage device 210, which may be or may include a battery that is rechargeable or replaceable. In one, non-limiting example, a small and lightweight lithium-ion polymer battery may be used. For example, such a battery may have a capacity of 600 mAh, which is sufficient for a wireless communications from the wearable device, while recording data for up to 20+ hours at full sampling rate.

[0033] The source 202 and sensor 204 may, together, form a probe 214. The probe 214 may be configured in an in-line design meant to be positioned vertically aligned with the axis of the patient, such as on the leg. The sensor 204 may include photodiodes at 1 .5, 2, 2.5, and3 cm away from the source 202. Both 8 LED (1 modules) and 16 LED (2 modules) version can be used. Also, individual LEDs can be used, in any number or combination. In one nonlimiting example, 8 wavelength modules (COB-8040-MGH-X-8) from Marubeni Corp, can be used to that can be operated to deliver up to 16 distinct illumination wavelengths. In one, non-limiting example, wavelengths may be between 600 and 1100 nm. In one, particular and non-limiting example, the probe may include e a nine wavelength LED grouping as a light source (740, 760, 780, 810, 850, 910, 940 and 1050). Regardless of the particular configuration, the entire system 102 (except the battery) can be embedded in a 3D printed rubber sleeve that can be inserted into an adjustable, flexible strap 104a-104e, which will also contain a battery holder, in some configurations.

[0034] In operation, the source 202 provide excitation light to the patient that results in optical data that is acquired by the sensor 204. The optical data is then provided to the processor to analyze the condition of the patient wearing the system 102 and then generate and / or communicate a report using the communication device 212. In one non-limiting example, the processor 206 is able to model emitter and receiver characteristics (including but not limited to spectral emission profiles and spectral detector efficiency profiles) light interaction with tissue to obtain metrics of tissue physiology including water fraction, lipid fraction, hemoglobin content and oxygen saturation as well as tissue optical scattering. That is, the system 102 is able to determine tissue water fraction (fwater) and other metrics related to blood perfusion adequacy (tissue hemoglobin oxygen saturation - StO2and total hemoglobin concentration - HbT, proportional to the tissue blood volume fraction) and provide assessments of cardiovascular function, such as heart-rate variability (HRV) and the photo-plethysmographic pulsatile waveform (PPG-WF). In this way, the system 102 is able to detect peripheral edema formation in patients with chronic heart failure and provide at home monitoringto reduce the chance of rehospitalization.

[0035] Referring to Fig. 3, a process 300 in accordance with the present disclosure, which may use the system 102 such as described with respect Figs. 1 and 2 may begin at process block 302 with the acquisition of optical data. In one, non-limiting example, a source may generate near-infrared (NIR) light at a plurality of wavelengths and deliver it to tissue locatedat the periphery of the patient. The sensor collects the reflected light to acquire optical data. At process block 304 , the optical data is processed. In one, non-limiting example, the optical data may be processed to determine an absorption coefficient of the tissue that was excited. For example, the absorption coefficient may be determined as the sum of contributions from oxy (HbO) and deoxy (HbR) hemoglobin, water, lipids, and scattering. In one, non-limiting example, the effective attenuation coefficient at each wavelength can be determined, which is the slope of the linear equation:where p is the distance between the source and the sensor, and / (p,A) is the measured intensity with a source (e.g., LED) at a given sensor (e.g., photodiode). Using the following equations, the absorption coefficient can calculated:As such, the HbO, HbR, water, lipids, and scattering coefficients, a and b, can be determined. Optical data may be linked to the concentration of tissue absorbers (including but not limited to oxy, deoxy-Hb, water, lipids) as well as optical scattering by other mechanisms, including, but not limited to analytical solutions to the diffusion approximation in the semi-infinite geometry, finite element modeling and stochastic light transport models.

[0036] Simulation approaches and tests in phantoms and in vivo may be used to optimize the choice of light emitters and detectors. In one particular, non-limiting example, realistic measurements may be simulated for various sets of available light emitters and stability and accuracy of tissue absorber concentration and scattering property recovery in the presence of noise may be evaluated.

[0037] Referring to process block 306, patient properties can be determined. As one nonlimiting example, the tissue water fraction and / or other properties, as described above, canbe determined. Then, at process block 308, the patient properties determined at process block 306 can be used to determine a patient condition. As one non-limiting example, the patient properties may include water fraction and the patient condition may include edema.

[0038] Referring to Figs. 4A-4D, the present disclosure recognizes a connection between the optical data that can be acquired, the tissue water fraction, and the presence of edema. Fig. 4A shows a correlation between the lipid concentration in tissue and the tissue water fraction. Fig. 4B shows a correlation between the total hemoglobin concentration and the tissue water fraction. Fig. 4C shows a correlation between tissue oxygen saturation and the tissue water fraction. Fig. 4D shows a correlation between the absorption coefficient b, and the tissue water fraction.

[0039] Thus, referring again to Fig. 3, the above described optical data can be used to determine patient properties, including water fraction. The present disclosure then recognizes that water fraction and changes in water fraction across time can be used to identify or predict a patient condition, such as edema. In this regard, the water fraction or changes in water fraction over time, determined as described above, when considering a patient condition such as edema, can be compared to an absolute threshold or a threshold of change at decision block 310. That is, a threshold is selected for use at decision block 310 that is specific to the patient condition that is selected for assessment at process block 308. In the non-limiting example of using a patient property of water fraction to assess a patient condition of edema, the threshold used at decision block 310 may include values between 5 and 50% or between 30 and 50%, or increments of 1 % therebetween. As another example, a particular rate of change may be used as a threshold. As one non-limiting example, a rate of change per day may be selected. As a further, non-limiting example, a threshold of 1%, 2%, 3%, 4% 5%, 6%, 7%, 8%, 9%, 10%, or greater per day . The present disclosure also recognizes that a correlation exists between volume overload and decompensating HF manifested through tissue edema. The water fraction in tissue is an indication of the volume overload. Additionally or alternatively, different or multiple thresholds may be utilized. For example, as described above, edema can be a leading indicator or associated with decompensation for patients in HF. Thus, decision block 310may not just review water fraction or other patient parameters to assess edema as a condition, but may assess edema or other indicators or conditions relative to further conditions, such as decompensation. For example, changes overtime and value or absolute value can be used for assessment. Thus, the threshold(s) may be selected to identify patients at greater risk of developing the acute phenotypes with worse prognosis to prioritize intervention. Thus, reporting or alarms may extend to include prioritization or other indicators. Also, due to the high signal quality of system, heart rate (HR) and heart rate variability (HRV) can also be characterized. Both elevations in resting HR and decrease in HRV imply higher risk of death and hospitalization. Further, the peripheral photoplethysmography waveform is impacted by changes in vascular impedance due to congestion and may contain additional signature of decompensation. Thus, further processing and thresholds or layers of processing and thresholds may be used.

[0040] Regardless of the particular condition or selected threshold(s), if not over the threshold, the process can loop to carry on continued or continuous monitoring. However, if over the threshold, a report may be generated at process block 312. In one non-limiting example, the report may indicate that changes in water fraction are indicative of a condition such as edema, and / or can indicate edema or predicted edema has been determined in the tissue at the periphery of the patient. Additionally or alternatively, the report may further consider the determination that the patient is showing signs of decompensation.

[0041] In one non-limiting example, the processor may compare an edema value with a threshold value and determines if the patient is experiencing the early signs of decompensation. If the edema value and / or the rate of change is at or above the threshold value, then the report may be formed as an alarm that is generated. In one non-limiting example, this alarm may include the potential for decompensation in the patient. In another non-limiting example, in the event of an alarm signal, the processor signals a user interface. This interface can be a display, a speaker, a haptic feedback device, and / or send alerts or reports to clinicians that are present or remote.

[0042] EXAMPLE

[0043] The above-described systems and methods were tested and studied using one, nonlimiting example implementation. A system consistent with the above description was constructed. The prototype used hardware from the FlexNIRS cerebral oximeter described in Wu, K.-C. et al. Open-source FlexNIRS: A low-cost, wireless and wearable cerebral health tracker. Neuroimage 256, 119216 (2022). The FlexNIRS is a low-cost wearable device (<$100 for all components) that integrates two dual-LED light sources (735 and 850 nm) and 3 photodiode detectors together with a high-performance analog front end from Texas Instruments (AFE4900) and a Bluetooth Low Energy (BLE) enabled micro-controller on a flexible printed circuit board (PCB) powered by a re-chargeable LiPo battery. The entire device was housed in 3D printed jacket using NinjaFlex rubberfor comfort and attached to a strap. Characterization tests in phantoms and human subjects demonstrated very low noise (NEP of 70 fW Hz, a state-of-the-art performance in the NIRS field) and robustness of tissue hemoglobin oxygen saturation quantification in vivo (±6% accuracy). The excellent noise performance allowed for acquisition rates as high as 266 Hz, resolving fine features of the pulsatile waveform and their changes during physiological challenges. Compared to the original FlexNIRS, the multi-wavelength (MW) NIRS sensor created in this prototype replaced the light sources with custom 8 wavelength LED packages (COB-8040-MGH-X, Marubeni America Corporation, covering the 700 to 1000 nm range), the analog front-end was upgraded to the Tl AFE4460 that can control up to 32 laser sources and 4 photodetectors and the device geometry was modified to use source-detector separations from 1 .5 to 3 cm allowing the use of multi-distance measurements to avoid the need for light source intensity calibration and permitting the recovery optical properties and thus tissue functional parameters. Thus, a prototype MW-FlexNIRS system was created that realized a multiparametric decompensation early warning monitor that is user friendly and comfortable to wear, allowing therapeutic interventions to be initiated remotely through a telehealth platform.

[0044] To explore a different geometry and extend the number of wavelengths used in GS- FlexNIRS measurements, another prototype was also created. The additional prototype was a linear prototype using Marubeni EDCC LEDs at 740, 760, 780, 810, 850, 890, 910, 940, and1050 nm and Vishay Semiconductor VEMD5080X01 photodiode detectors at 4 sourcedetector separation groups. This probe is fabricated on a 2-layer flexible circuit board and integrates with the control module of the modular GS-FlexNIRS system, minimizing both design costs and turnaround times.

[0045] The system will utilizes nine LED sources selected from the following ten purchased EDCC LEDs at wavelengths: 740, 760, 780, 810, 850, 890, 910, 940, 970, and 1050 nm. Light is detected at three source-detector separations (nominal distances from the center of the source assembly) of 34.5 mm, 29 mm, and 23.5 mm, with an additional short-separation measurement at 6.7 mm (nominal). The detector employed is the same as that used in preliminary characterizations with a self-calibrating geometry and four wavelengths: the VEMD5080X01.

[0046] The probe is compatible with the previously developed Bluetooth control / acquisition unit, using the same 26-pin flat cable. The control / acquisition unit firmware can be easily modified to sequentially cycle through the nine LEDs. The 16 programmable stages optimize light output at lower power levels, as was achieved with the four-wavelength configuration. While this geometry does not support self-calibration, the three source-detector separations enable concentration change measurements using a pre-calibrated multidistance approach. The inclusion of nine wavelengths enhances spectral discrimination, particularly for detecting changes in water fraction, compared to the original four- wavelength design. Sufficient light was collected at 1050 nm, despite the 50% reduction in detector efficiency at that wavelength.

[0047] Studies showed the light intensity of each LED, as measured by the detectors at the longest source-detector separation (3.3-3.5 cm). Data was acquired at 100 Hz and smoothed using a 5-point moving average. Pulsatile signals were visible at all wavelengths indicating high signal to noise ratio.

[0048] Tissue water fraction measurement in heart failure patients

[0049] While the development of edema is a marker of decompensation, others have not recognized water fraction as a patient parameter that can be used to determine or predict edema and, therethrough, determine or predict decompensation. That is, while in vivotissue water fraction assessment with NIRS has been extensively demonstrated and validated against MRI21 in the breast optical imagingfield, the present disclosure recognizes the use of multi-wavelength NIRS measurements to obtain tissue water fraction in HF patients as a toolto determine edema and / or decompensation.

[0050] The ability to monitor hemoglobin concentration and oxygen saturation in addition to edema using the prototype FlexNIRS devices provides not only an additional marker of decompensation, but also identify the patients more at risk of developing the acute phenotypes with worse prognosis to prioritize intervention. Thus, reporting or alarms may extend to include prioritization or other indicators.

[0051] Heart Rate Variability and Pulsatile Waveforms

[0052] Due to the high signal quality of the FlexNIRS platform (demonstrated up to 266 Hz in its original configuration), the system can also characterize HRV. Both elevations in resting HR and decrease in HRV imply higher risk of death and hospitalization. Further, the peripheral photoplethysmography waveform, though less studied, is impacted by changes in vascular impedance due to congestion and may contain additional signature of decompensation.

[0053] The FlexNIRS-MW sensor prototype was sensitive to both decompensation and recovery from acute HF and can effectively probe these parameters. The creation of a low- cost wearable able to provide multi-parametric monitoring of cardiovascular physiology in HF patients provides a meaningful improvement in outcomes for the HF population that is not being served by CardioMEMS and other devices.

[0054] MW-FlexNIRS hardware development

[0055] Electro-optic design

[0056] The MW-FlexNIRS was constructed based on a modification of the FlexNIRS device that places the analog front end on the same flexible PCB as the controller and Bluetooth module. The control section is joined to the probe section by a flexible PCB bridge, and featured a magnetic connector for the battery cable. The system used theTI AFE4460, which allows control of up to 32 LEDs in 16 measurement phases, and can read up to 4 photodiodes, with an automatic no illumination phase for background light subtraction. TheSi Licon Labs BGM121 system-in-package module was used, which embeds an AMR-Cortex- M4 microcontroller with a Bluetooth low-energy (BLE) module. The latter has a transmission power of up to 8 dBm, receiving sensitivity of -90 dBm and can work at a ranges beyond 20 m in open space, and has been tested to operate without errors up to 10 m in a complex, hospital-like environment. An inertial module (LSM6DSO32) containing a low power MEMS 3-axis accelerometer and 3-axis gyroscope was included to detect movement and remove motion artifacts.

[0057] Finally, a small and lightweight Lithium-ion Polymer battery (LP503040JH) with a capacity of 600 mAh enabled the prototype to be a wireless, wearable device, while recording data for up to 20+ hours at full sampling rate. The probe component featured an in-line design configured to be positioned vertically aligned with the axis of the leg, with photodiodes at 1 .5, 2, 2.5 and 3 cm away from the source. Both 8 LED (1 modules) and 16 LED (2 modules) version were made using custom designed 8 wavelength modules (COB- 8040-MGH-X-8) from Marubeni Corp, to allow up to 16 distinct illumination wavelengths to be used. The entire device (except the battery) was embedded in a 3D printed rubber sleeve that will be inserted into an adjustable, flexible strap which will also contain a battery holder.

[0058] LED wavelength selection was guided by measuring tissue optical properties. The inline probe design allowed multi-distance measurements to be obtained, while avoiding the need to calibrate source intensity.

[0059] The absorption coefficient was determined as the sum of contributions from oxy (HbO) and deoxy (HbR) hemoglobin, water and lipids, the scattering follow an inverse power law with wavelength, and the diffusion approximation for light propagation holds. The system measured the effective attenuation coefficient at each wavelength, derived from the last equation above as the slope of ln[p l(p,A)] for each wavelength vs distance p, where l(p,A) is the measured intensity with a given LED on at the four photodiodes. From the data, a non-linear optimization was performed to retrieve HbO, HbR, water, lipids and scattering a and b coefficients. The conditioning of this inversion was used to select preferred wavelengths including 660, 680, 700, 760, 810, 830, 940 and 980 nm as a primary set, augmented by 630, 720, 735, 780, 850, 870, 890 and 910 nm. Alternative analyses usingrealistic LED emission profiles, detector spectral sensitivity, and realistic noise, further indicated 740, 760, 810,850, 890, 910, 940 and 1050 nm as potentially desirable wavelengths.

[0060] In simulation, the true water fraction was recovered within 5% of the actual value, and no significant cross-talk was detected from other tissue components using the proposed probe configuration. This was done with a 5% standard deviation in the optode coupling, and an expected minimum 40 dB SNR at the largest separation.

[0061] In Vivo Test Data

[0062] Referring to Figs. 5A and 5B, graphs are provided showing a comparison of full spectrum (720-1020 nm) vs. limited wavelength set (735 760 780 810 850 910 940 990) in actual in vivo measurements acquired using the systems and methods described herein. The data showthat the use of a limited wavelength set achievable in a wearable device offers very similar readings to the output of a full spectral fit in terms of water fraction and measurements are repeatable over time.

[0063] Data Collection

[0064] The systems and methods described herein provide an optical sensing wearable for cardiac failure patient monitoring and provide a unique combination of parameters that can provide an early warning of decompensation. For example, an optical wearable is provided for the measurement of peripheral edema in heart failure patients. The system provides for multi-parametric monitoring of edema, blood perfusion, heart rate variability and pulsatile waveforms. Dynamic measurements allow the assessment of response to challenges as well, such as orthostatic changes and physical exertion. Being sensitive to hemoglobin, the systems and methods can also be used to assess capillary refill together with either manual pressure application or cuff inflation over the device.

[0065] It is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosed systems and methods are capable of other configurations and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

[0066] Similarly, unless otherwise limited or defined, “or” indicates a non-exclusive list of components or operations that can be present in any variety of combinations, ratherthan an exclusive list of components that can be present only as alternatives to each other. For example, a list of “A, B, or C” indicates options of: A; B; C; A and B; A and C; B and C; and A, B, and C. Correspondingly, the term “or” as used herein is intended to indicate exclusive alternatives only when preceded by terms of exclusivity, such as “only one of,” or “exactly one of.” For example, a list of “only one of A, B, or C” indicates options of: A, but not B and C; B, but not A and C; and C, but not A and B. In contrast, a list preceded by “one or more” (and variations thereon) and including “or” to separate listed elements indicates options of one or more of any or all the listed elements. For example, the phrases “one or more of A, B, or C” and “at least one of A, B, or C” indicate options of: one or more A; one or more B; one or more C; one or more A and one or more B; one or more B and one or more C; one or more A and one or more C; and one or more A, one or more B, and one or more C. Similarly, a list preceded by “a plurality of” (and variations thereon) and including “or” to separate listed elements indicates options of one or more of each of multiple of the listed elements. For example, the phrases “a plurality of A, B, or C” and “two or more of A, B, or C” indicate options of: one or more A and one or more B; one or more B and one or more C; one or more A and one or more C; and one or more A, one or more B, and one or more C.

[0067] Also as used herein, unless otherwise limited or defined, the terms “about” and “approximately” refer to a range of values ± 5% of the numeric value that the term precedes. As a default the terms “about” and “approximately” are inclusive to the endpoints of the relevant range, but disclosure of ranges exclusive to the endpoints is also intended.

[0068] The discussion presented herein is to enable a person skilled in the art to make and use the present disclosure. Various modifications to the illustrated description will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other configurations and applications without departing from the disclosure. Thus, the disclosure is not intended to be limited to configurations shown but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected configurations and are not intended to limit the scope of the disclosure. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of the disclosure.

[0069] The present invention has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variation, and modifications, aside from those expressly stated, are possible and within the scope of the invention.

Claims

CLAIMS1 . A wearable system for monitoring a patient with heart failure, comprising: a near-infrared spectroscopy (NIRS) source and sensor configured to deliver multiwavelength near-infrared (NIR) light to tissue of a patient with heart failure; a mounting system configured to position the NIRS source and sensor on the patient with heart failure to acquire NIRS data from the patient with heart failure; a processor configured to receive the NIRS data from the sensor and determine a tissue water fraction using the NIRS data; and generating a report including an indication of potential for decompensation in the patient based on the determined tissue water fraction.

2. The system of claim 1 , wherein the report includes an alarm when the indication of potential for decompensation in the patient with heart failure is above a threshold.

3. The system of claim 1 , wherein the NIRS sensor includes a light source configured to emit the NIR light at multiple wavelengths between 600 nm and 1100 nm.

4. The system of claim 1 , wherein the mounting system is configured to couple the NIRS sensor to a periphery of the patient.

5. The system of claim 1 , wherein the report further includes an indication of peripheral volume overload and hemodynamics in the patient with heart failure.

6. The system of claim 1 , wherein the report includes blood perfusion metrics.

7. The system of claim 1 , wherein the blood perfusion metrics include calculating total hemoglobin concentration (HbT) and hemoglobin oxygen saturation (StO2).

8. The system of claim 1 , wherein the report includes an assessments of cardiovascular function including heart-rate variability (HRV) or a photoplethysmographic pulsatile waveform (PPG-WF).

9. The system of claim 1 , wherein the processor is configured to determine absorption coefficient as a sum of contributions from oxy (HbO) hemoglobin, deoxy (HbR) hemoglobin, water, lipids, and scattering based on an inverse power law with wavelength, and a diffusion approximation for light propagation.

10. The system of claim 1 , wherein the processor is configured to determine an effective attenuation coefficient at each wavelength, derived as a slope of ln[p2l(p,A)] for each wavelength versus distance p, where l(p,A) is a measured intensity derived from the NIRS data.

11. A method for determining a edema in tissue located at a periphery of a patient that is indicative of an unsafe condition, the method comprising: using a light source, delivering light to the tissue located at the periphery of the patient; using a sensor, receiving light that interacts with the tissue located at the periphery of the patient to generate optical data; using a processor and the optical data, calculating an absorption coefficient of the tissue located at the periphery of the patient; using the processor and the absorption coefficient, estimating contributions to absorption of at least one of oxy hemoglobin (HbO), deoxy (HbR) hemoglobin, water, lipids, or scattering; using the processor and the contributions to absorption, determining the edema in the tissue located at the periphery of the patient; usingthe processor, determiningthatthe edema in the tissue located at the periphery of the patient indicates an unsafe condition; andusing the processor, generating an alert reporting the unsafe condition.

12. The method of claim 11 , wherein determining the absorption coefficient includes using an inverse power law with wavelength and a diffusion approximation for light propagation.

13. The method of claim 11 , wherein the determining that the edema in the tissue located at the periphery of the patient indicates an unsafe condition includes comparing estimated contributions to decompensation metrics.

14. The method of claim 13, wherein determining that the edema in the tissue located at the periphery of the patient indicates an unsafe condition includes gradingthe edema.

15. The method of claim 11 , wherein the light source includes a near-infrared spectroscopy (NIRS) source configured to deliver multi-wavelength near-infrared (NIR) light16. The method of claim 11 , wherein estimating the contributions includes determining a tissue water fraction and determining that the edema in the tissue located at the periphery of the patient indicates an unsafe condition includes determining a potential for decompensation in the patient based on the determined tissue water fraction.

17. The method of claim 16, wherein the alert includes a report indicating of potential for decompensation in the patient.

18. A method for monitoring a patient with heart failure, comprising: securing a near-infrared spectroscopy (NIRS) source and sensor to the patient to deliver multi-wavelength near-infrared (NIR) light to tissue of a patient with heart failure; receiving the NIRS data from the sensor with a processor; using the processor to determine a tissue water fraction using the NIRS data; andusing the processor, generating a report including an indication of potential for decompensation in the patient based on the determined tissue water fraction.

19. The method of claim 1 , wherein the report includes an alarm when the indication of potential for decompensation in the patient with heart failure is above a threshold.

20. A system for determining a edema in tissue located at a periphery of a patient that is indicative of an unsafe condition, the system comprising: a light source configured to deliver light to the tissue located at the periphery of the patient; a sensor configured to receive light that interacts with the tissue located at the periphery of the patient to generate optical data; a processor configured to: receive the optical data; usingthe optical data, calculate an absorption coefficient of the tissue located at the periphery of the patient; using the absorption coefficient, estimate contributions to absorption of at least one of oxy hemoglobin (HbO), deoxy (HbR) hemoglobin, water, lipids, or scattering; using the contributions to absorption, determine the edema in the tissue located at the periphery of the patient; determine that the edema in the tissue located at the periphery of the patient indicates an unsafe condition; and a user interface configured to generate an alert reportingthe unsafe condition.

21. The system of claim 1 , wherein the user interface includes one of a display, a speaker, or a haptic feedback device.

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