Method and apparatus for estimating reliability of cardiac output measurements

Abstract

According to one aspect, there is provided a method of estimating the reliability of a cardiac output, CO, measurement obtained for a subject using an arterial waveform analysis, AWA, technique. The AWA technique is calibrated using a CO measurement obtained using a thermodilution CO measurement technique. The method comprises: (a) during a first time period in which a first CO measurement is obtained for the subject using the thermodilution CO measurement technique: (i) initiating (203) inflation of a cuff at a first location on the subject; (ii) obtaining (205) a first cuff pressure signal comprising measurements of pressure inside the cuff during inflation; (iii) analysing (207) the first cuff pressure signal to derive a relationship between oscillations in the volume of an artery under the cuff and pressure in the artery; and (iv) estimating (209) a first arterial compliance of the artery for a range of cuff pressures based on the determined relationship; (b) during a second time period after the first time period, repeating (211) steps (i)-(iv) to estimate a second arterial compliance of the artery; and (c) using (213) the results of a comparison of the first arterial compliance and the second arterial compliance to determine the reliability of a CO measurement obtained during the second time period using the AWA technique.

Description

Technical Field

[0001] This disclosure relates to methods and apparatus for estimating the reliability of cardiac output (CO) measurements for a subject, and more particularly, to estimating the reliability of CO measurements obtained using arterial waveform analysis (AWA) techniques. Background Technology

[0002] Cardiac output (CO) is a key hemodynamic parameter measured in critical care. CO is the volume of blood pumped by the heart per unit time. CO is related to heart rate (HR) and stroke volume (SV), which is the volume of blood pumped by the heart during each stroke. Due to the correlation of CO, several methods can be used for CO measurement, with varying degrees of invasiveness and reliability. For example, techniques include intermittent thermodilution via pulmonary artery catheter or through invasive access to venous and arterial sites, continuous arterial waveform analysis (AWA) of pressure waveforms measured invasively (with or without thermodilution calibration), esophageal Doppler, suprasternal Doppler, echocardiography, bioimpedance / resistance, and partial carbon dioxide (CO2) rebreathing.

[0003] A calibrated AWA can measure CO continuously and accurately with minimal additional training for care providers such as physicians and nurses. However, for accurate measurements, the AWA requires repeated calibration for another type of CO measurement (typically thermodilution).

[0004] The basic methods for inferring AWA can be discussed using a simple model of arterial networks, such as... Figure 1 As shown. Figure 1 It can also be found in X. Aubert and J. Muehlsteff, “Non-Invasive Cuff-less Measurements of the Arterial Blood Pressure: What does Pulse-Transit-Time tell us all about?” (Proc. European Study Group on Cardiovascular Oscillations, pp. 211-214, 2006). Mathematically, CO can be determined based on the measured pressure (which in AWA comes from the invasive blood pressure waveform) and parameters of the arterial network (e.g., aortic resistance (in...). Figure 1 The system resistance (represented by a resistor with resistance R0) is... Figure 1 The effective compliance of the arterial network (C) is estimated using a resistor (represented by R0) and the resistance of the resistor. Based on this model, cardiac output (referred to as Q) is... a It can be given by the following formula:

[0005]

[0006] Where, p a It is arterial pressure and p s It's system pressure.

[0007] Currently, these parameters cannot be measured or are not easily measured in clinical practice. As practical methods, C, R0, and R... s Therefore, it is considered an open parameter, which is "calibrated" via intermittent thermodilution that provides a reference CO measurement result, and the parameter then remains constant. In thermodilution measurements, a heated or cooled fluid is introduced into the bloodstream, and the temperature (fluid temperature) is measured at different sites in the circulatory system. In transpulmonary thermodilution measurements, the temperature change between the central venous line and the central arterial line can be measured. Summary of the Invention

[0008] Therefore, once determined via calibration (e.g., thermal dilution measurement), then the parameters C, R0, and R... s Maintaining constant values ​​is crucial. However, there is a risk of unidentified physiological changes in the subjects, which would invalidate CO inferences based on these parameters, and thus, a limitation of current hemodynamic monitoring practices is the difficulty in obtaining reliable estimates of cardiac output between intermittent thermodilution measurements. In particular, changes in arterial compliance (C) from the time a thermodilution calibration measurement is made can lead to incorrect interpretation of arterial pressure waveforms and therefore incorrect estimates of cardiac output, as illustrated in Jean-Louis Vincent Andrew Rhodes, Azriel Perel, Greg S Martin, Giorgio Della Rocca, Benoit Vallet, Michael R Pinsky, Christoph K Hofer, Jean-Louis Teboul, Willem-Pieter de Boode, Sabino Scolletta, Antoine Vieillard-Baron, Daniel De Backer, Keith R Walley, Marco Maggiorini, and Mervyn Singer's "Clinical review: Update on hemodynamic monitoring - a consensus of 16". There is no direct modality of clinical realization for identifying changes in arterial compliance, and therefore there is uncertainty regarding the reliability of waveform-based CO measurements.

[0009] In typical clinical practice, intermittent thermodilution calibration is recommended every few hours. This is problematic because time-based recalibration ignores the physiological changes that can occur between calibrations, and the human body continuously regulates CO on smaller timescales. Therefore, the accuracy of CO obtained through AWA is often limited, leading to incorrect diagnosis, decision-making, and treatment, and ultimately impaired patient outcomes.

[0010] Therefore, it is desirable to provide a technique for estimating the reliability of CO measurement results obtained using AWA technology.

[0011] According to a first specific aspect, a method is provided for estimating the reliability of cardiac output (CO) measurements of an object obtained using an arterial waveform analysis (AWA) technique. The AWA technique is calibrated using CO measurement results obtained using a thermodilution CO measurement technique. The method includes (a) during a first time period (wherein, a first CO measurement result for the object is obtained using a thermodilution CO measurement technique): (i) initiating cuff inflation at a first position on the object; (ii) acquiring a first cuff pressure signal during inflation, including a measurement of the pressure within the cuff; (iii) analyzing the first cuff pressure signal to derive a relationship between oscillations in the arterial volume beneath the cuff and the pressure in the artery; and (iv) estimating a first arterial compliance for a range of cuff pressures based on the determined relationship; (b) repeating steps (i)-(iv) during a second time period following the first time period to estimate a second arterial compliance; and (c) using the result of a comparison between the first and second arterial compliance to determine the reliability of the CO measurement results obtained using the AWA technique during the second time period.

[0012] In some embodiments, if the CO measurement results obtained using the AWA technique during the second time period are determined to be reliable, the method may further include (d) repeating steps (i)-(iv) during a third time period following the second time period to estimate the third arterial compliance; and (e) repeating step (c) using the second and third arterial compliance. In this way, the reliability of the CO measurement results can be assessed continuously or periodically.

[0013] In some embodiments, if the CO measurement result obtained using the AWA technique during the second time period is determined to be unreliable, the method may further include one or more of the following: initiating a thermal dilution CO measurement technique to obtain a second CO measurement result and calibrating the AWA technique using the second CO measurement result; informing the user of the unreliability of the measurement result obtained using the AWA technique; and determining an adjustment to the value of the arterial compliance parameter used in the AWA technique based on the comparison result. In the first case, a recalibration may be automatically triggered when the CO measurement result is determined to be unreliable. In the second case, the user may be notified when the CO measurement result is determined to be unreliable, and the user may manually trigger a recalibration. In the third case, the recalibration process may be avoided by adjusting the arterial compliance parameter used in the AWA technique.

[0014] In some embodiments, the method further includes using AWA technology to determine one or more CO measurement results.

[0015] In some embodiments, the method further includes: obtaining photoplethysmography (PPG) signals and / or electrocardiogram (ECG) signals for the subject while performing steps (i) and (ii); and analyzing the PPG signals and / or ECG signals to determine a first pulse arrival time (PAT) and / or a first pulse wave velocity (PWV) for the subject. Step (iv) includes estimating a first arterial compliance for a range of cuff pressures based on the determined relationship and the first PAT and / or the first PWV. This embodiment provides an improved estimate of the first arterial compliance. In these embodiments, the method may further include: after step (iv), obtaining additional PPG signals and / or additional ECG signals for the subject; analyzing the additional PPG signals and / or additional ECG signals to determine a second PAT for the subject; comparing the second PAT with the first PAT; and determining whether to perform step (b) based on the result of the comparison of the second PAT with the first PAT. These embodiments provide a simple way to monitor a subject to determine when arterial compliance may have changed, and can be used to trigger a more accurate measurement of arterial compliance using a cuff. In these embodiments, the step of determining whether to perform step (b) can include determining to perform step (b) if the difference between the second PAT and the first PAT is greater than a threshold, and otherwise determining not to perform step (b).

[0016] In an alternative embodiment, the second time period is a predefined time following the first time period. In this way, arterial compliance testing using a cuff is performed periodically, enabling the detection of changes in arterial compliance.

[0017] In an alternative embodiment, the method further includes: obtaining a PPG signal for the subject while performing steps (i) and (ii); analyzing the PPG signal to determine a first PPG morphology; after step (iv), obtaining another PPG signal for the subject; analyzing the other PPG signal to determine a second PPG morphology; comparing the second PPG morphology with the first PPG morphology; and determining whether to perform step (b) based on the result of the comparison between the second PPG morphology and the first PPG morphology. These embodiments provide another simple way to monitor a subject to determine when arterial compliance may have changed; and it can be used to trigger a more accurate measurement of arterial compliance using a cuff.

[0018] In some embodiments, the method further includes: obtaining an arterial pressure AP signal representing the AP of the object when performing steps (i) and (ii); and step (iii) includes analyzing the first cuff pressure signal and the AP signal to derive a relationship between oscillations in the arterial volume under the cuff and pressure in the artery. The use of the AP measurement results improves the accuracy of the estimated relationship. In these embodiments, the cuff is capable of being worn on the object's first arm, and the AP signal is obtained from the same arm of the object.

[0019] According to a second aspect, a computer program product including a computer-readable medium is provided, on which computer-readable code is implemented, the computer-readable code being configured such that, when run by a suitable computer or processor, it causes the computer or processor to perform the method according to the first aspect or any embodiment thereof.

[0020] In some embodiments, the suitable computer or processor is configured to: connect to a pump associated with the cuff; connect to a noninvasive blood pressure measurement device including the cuff; and connect to a cuff pressure sensor that outputs a first cuff pressure signal. In other embodiments, the suitable computer or processor can be configured to: connect to a PPG sensor; and connect to an ECG sensor.

[0021] According to a third specific aspect, an apparatus is provided for estimating the reliability of CO measurement results for a subject obtained using an AWA technique. The AWA technique is calibrated using CO measurement results obtained using a thermal dilution CO measurement technique. The apparatus includes: a processing unit configured to (a) during a first time period (wherein, a first CO measurement result for a subject is obtained using a thermal dilution CO measurement technique): (i) initiate inflation of a cuff at a first location on the subject; (ii) acquire a first cuff pressure signal during inflation, including a measurement result of the pressure inside the cuff; (iii) analyze the first cuff pressure signal to derive a relationship between oscillations in the arterial volume under the cuff and the pressure in the artery; and (iv) estimate a first arterial compliance of the artery for a range of cuff pressures based on the determined relationship; (b) repeat functions (i)-(iv) during a second time period following the first time period to estimate a second arterial compliance of the artery; and (c) use the result of a comparison between the first and second arterial compliance to determine the reliability of the CO measurement results obtained using the AWA technique during the second time period.

[0022] In some embodiments, the processing unit is further configured to: (d) repeat function (i)-(iv) during a third time period after the second time period to estimate the third arterial compliance if the CO measurement result obtained using the AWA technique during the second time period is determined to be reliable; and (e) repeat function (c) using the second and third arterial compliance. In this way, the reliability of the CO measurement result can be evaluated continuously or periodically.

[0023] In some embodiments, the processing unit is further configured to: if the CO measurement result obtained using the AWA technique during the second time period is determined to be unreliable, perform one or more of the following: initiate a thermal dilution CO measurement technique to obtain a second CO measurement result and use the second CO measurement result to calibrate the AWA technique; indicate to the user the unreliability of the measurement result obtained using the AWA technique; and determine, based on the comparison result, an adjustment to the value of the arterial compliance parameter used in the AWA technique. In the first case, recalibration can be automatically triggered when the CO measurement result is determined to be unreliable. In the second case, the user can be notified when the CO measurement result is determined to be unreliable, and the user can manually trigger recalibration. In the third case, the recalibration process can be avoided by adjusting the arterial compliance parameter used in the AWA technique.

[0024] In some embodiments, the processing unit is further configured to use AWA technology to determine one or more CO measurement results.

[0025] In some embodiments, the processing unit is further configured to: acquire a PPG signal and / or an ECG signal for the subject when performing functions (i) and (ii); and analyze the PPG signal and / or ECG signal to determine a first PAT and / or a first PWV for the subject. Function (iv) includes estimating a first arterial compliance for a range of cuff pressures based on the determined relationship and the first PAT and / or the first PWV. This embodiment provides an improved estimate of the first arterial compliance. In these embodiments, the processing unit is further configured to: acquire additional PPG signals and / or additional ECG signals for the subject after function (iv); analyze the additional PPG signals and / or the additional ECG signals to determine a second PAT for the subject; compare the second PAT with the first PAT; and determine whether to perform function (b) based on the result of the comparison between the second PAT and the first PAT. These embodiments provide a simple way to monitor a subject to determine when arterial compliance may have changed, and can be used to trigger a more accurate measurement of arterial compliance using a cuff. In these embodiments, the processing unit can be configured to determine to execute function (b) if the difference between the second PAT and the first PAT is greater than a threshold, and otherwise determine not to execute function (b).

[0026] In an alternative embodiment, the second time period is a predefined time following the first time period. In this way, arterial compliance testing using a cuff is performed periodically, enabling the detection of changes in arterial compliance.

[0027] In an alternative embodiment, the processing unit is further configured to: acquire a PPG signal for the subject when functions (i) and (ii) are performed; analyze the PPG signal to determine a first PPG morphology; acquire another PPG signal for the subject after function (iv); analyze the other PPG signal to determine a second PPG morphology; compare the second PPG morphology with the first PPG morphology; and determine whether to perform function (b) based on the result of the comparison between the second PPG morphology and the first PPG morphology. These embodiments provide another simple way to monitor a subject to determine when arterial compliance may have changed; and it can be used to trigger a more accurate measurement of arterial compliance using a cuff.

[0028] In some embodiments, the processing unit is further configured to: obtain an object-specific AP signal representing the AP of the object when performing functions (i) and (ii); and step (iii) includes analyzing the first cuff pressure signal and the AP signal to derive the relationship between oscillations in the arterial volume under the cuff and pressure in the artery. The use of the AP measurement results improves the accuracy of the estimated relationship. In these embodiments, the cuff is capable of being worn on the object's first arm, and the AP signal is obtained from the same arm of the object.

[0029] In some embodiments, the device further includes or contains one or more interfaces to enable connection to one or more of the following: the cuff, a pump for the cuff, and a cuff pressure sensor that measures the pressure in the cuff and outputs the first cuff pressure signal.

[0030] According to a fourth specific aspect, a system is provided for estimating the reliability of CO measurement results for an object obtained using AWA technology. The system includes an apparatus according to a third aspect or any embodiment thereof, and one or more of the following: the cuff, a pump for the cuff, and a cuff pressure sensor that measures the pressure in the cuff and outputs a first cuff pressure signal.

[0031] These and other aspects will become apparent from the embodiments described below, and will be illustrated with reference to the embodiments described below. Attached Figure Description

[0032] Exemplary embodiments will now be described by way of example only with reference to the following figures, in which:

[0033] Figure 1 It is a model of an arterial network;

[0034] Figure 2 It is a block diagram of a device that can be used to implement the techniques described herein;

[0035] Figure 3 This is an illustration of an exemplary measurement setup on an object according to an embodiment, wherein there is invasive access to arteries on different parts of the body where a cuff is placed;

[0036] Figure 4 This is a flowchart illustrating a method for determining the reliability of AWA CO measurement results according to a first specific embodiment;

[0037] Figure 5 It is a graph illustrating the arterial compliance values ​​across a range of wall pressures during the calibration process;

[0038] Figure 6 This is a graph comparing newly acquired arterial compliance values ​​with those measured during the calibration process.

[0039] Figure 7 This is a graph illustrating arterial compliance versus transmural pressure.

[0040] Figure 8 This is an illustration of an exemplary measurement setup on an object according to an embodiment, wherein an invasive artery access is performed on the same arm in which a cuff is placed; and

[0041] Figure 9 This is a flowchart illustrating a method for estimating the reliability of AWA CO measurement results according to a general embodiment. Detailed Implementation

[0042] As noted, the technique is provided for estimating the reliability of cardiac output (CO) measurements obtained using the AWA technique. Specifically, the technique aims to identify when a change in the subject's arterial compliance (C) has occurred since the calibration measurement was made, as changes in arterial compliance are identified as a primary cause of CO calibration drift (e.g., as described in "Clinicalreview: Update on hemodynamic monitoring - a consensus of 16"). These changes can lead to incorrect interpretation of arterial pressure waveforms and, consequently, incorrect estimates of cardiac output. Changes in arterial compliance provide an indication of the reliability of CO measurements obtained using the AWA technique. For example, if arterial compliance has not changed, or has not changed beyond a threshold amount, then CO measurements obtained using the AWA can be considered reliable or sufficiently reliable, and / or if arterial compliance has changed or has changed beyond a threshold amount, then CO measurements obtained using the AWA can be considered unreliable. This indication of the reliability of CO measurements obtained using the AWA can be used to determine whether a new calibration measurement should be made using the thermodilution technique. Alternatively (or additionally), and especially in the case of minor changes in arterial compliance, the reliability of CO measurements obtained by AWA can be used to determine the adjustment of the value of C (arterial compliance) used in the AWA model.

[0043] In this disclosure, the term "calibration procedure" refers to a procedure in which a measurement of cardiac output of an object is obtained using a measurement technique other than AWA (such as thermodilution) and is used to calibrate (i.e., determine) parameters used in a model for AWA-based measurements of CO. The CO measurement obtained using the calibration procedure is referred to herein as a "calibrated CO measurement result." The preferred measurement technique used for the calibration procedure is thermodilution, but other techniques, such as measuring CO via dye solution, echo, or carbon dioxide (CO2) rebreathing, can be used. The term "thermally diluted CO measurement result" refers to a CO measurement result obtained using thermodilution. The term "AWA CO measurement result" is used herein to refer to a measurement of cardiac output obtained using the AWA technique, wherein the AWA model has been calibrated using the calibration procedure. Those skilled in the art will appreciate the details of the AWA technique; for example, further details can be found in the Pulse Contour Cardiac Output (PICCO) Learning Package (2016), at: https: / / www.aci.health.nsw.gov.au / __data / assets / pdf_file / 0005 / 306590 / Pulse_Contour_Cardiac_Output_Learning_Package.pdf.

[0044] This document presents various embodiments to enable the estimation of the reliability of CO measurements obtained using AWA technology. Specifically, cuff-based noninvasive blood pressure (NIBP) measurement devices (or at least one cuff and a sensor for measuring pressure oscillations in the cuff) are used to obtain information about arterial compliance during (i.e., concurrently with) the calibration process. The use of a cuff enables the estimation of arterial compliance (which yields the effective transmural pressure applied to the artery) to be obtained from information about arterial volume versus applied cuff pressure. According to various embodiments, changes in arterial compliance can then be identified by evaluating additional pressure oscillation signals and / or measurement signals from one or more other types of sensors, such as photoplethysmography (PPG) sensors (or other types of pulse oximetry sensors), electrocardiogram (ECG) sensors, and / or (invasive) arterial pressure (AP) sensors. These types of sensors are generally applied to, or at least can be used for, CO measurements that have undergone thermodilution, as thermodilution measurements are typically performed in clinical settings. In embodiments where PPG and / or ECG sensors are present, these sensors can be used to derive or determine pulse arrival time (PAT), which is related to pulse wave velocity (PWV) and is itself related to arterial compliance.

[0045] NIBP measurement devices can be set to automatically acquire cuff-based blood pressure (BP) measurements, for example, every 5 to 60 minutes, and a PPG or ECG sensor can provide a pulse-to-pulse waveform. Therefore, it is possible to detect changes in arterial compliance on relatively short timescales, such as on the order of minutes.

[0046] If a significant change in arterial compliance is detected (indicating that the AWA CO measurement results may be unreliable), one or more actions can be taken. One action is to flag the potential change in arterial compliance to the care provider (e.g., via a display or other user interface component on the patient monitor), which can prompt the care provider to perform or trigger a calibration procedure. Another action is to automatically trigger the calibration procedure, and yet another is to correct or adjust the arterial compliance parameter values ​​in the AWA model based on the detected change in arterial compliance.

[0047] Figure 2 This is a block diagram of a system 2 for estimating the reliability of cardiac output measurements of a target obtained using AWA, according to various embodiments.

[0048] System 2 includes a cuff 4, a pump 6 connected to the cuff 4 (e.g., via a connecting tube 7), and a cuff pressure sensor 8 for measuring pressure in the cuff 4. The cuff 4 is to be placed around a body part of the subject of interest, such as around a limb like an arm or leg. The pump 6 is controllable to selectively inflate the cuff 4. The pump 6 may also be able to selectively deflate the cuff 4, and / or may provide a valve (not shown) to allow deflation of the cuff 4. The cuff pressure sensor 8 measures the pressure in the cuff 4 at least when a defined stimulus is applied to an artery located beneath the cuff 4 (this may be during inflation, deflation, or while the pressure in the cuff 4 is maintained at a specific level). The cuff pressure sensor 8 outputs a cuff pressure signal representing or relating to the pressure in the cuff 4 over time. The cuff 4, pump 6, and cuff pressure sensor 8 may be part of NIBP measurement device 10 and may include one or more additional components configured to process the signal from the cuff pressure sensor 8 to determine the subject's blood pressure. Alternatively, System 2 may not include NIBP measuring device 10, while cuff 4, pump 6 and cuff pressure sensor 8 may be specifically provided for use by System 2 in determining the reliability of CO measurement results obtained using AWA.

[0049] System 2 also includes a device 12, which operates according to the techniques described herein to determine the reliability of CO measurement results obtained using AWA. Device 12 is configured to receive cuff pressure measurement signals from cuff pressure sensor 8. In some embodiments, device 12 is configured to control the operation of pump 6, thereby initiating inflation of cuff 4 for an appropriate period.

[0050] In some embodiments, in addition to estimating the reliability of AWA CO measurement results, device 12 may also be configured to determine AWA CO measurement results. Therefore, in some embodiments, device 12 is configured to implement conventional AWA-based CO measurement techniques to determine WA CO measurement results.

[0051] Device 12 may take the form of or be part of the following: computing devices, such as servers, desktop computers, laptops, tablets, smartphones, smartwatches, etc.; or other types of devices commonly found in clinical settings, such as patient monitoring devices (e.g., monitoring devices located at the patient's bedside in a clinical setting) used to monitor (and optionally display) various physiological characteristics of the subject / patient.

[0052] In embodiments where the cuff 4, pump 6, and cuff pressure sensor 8 are specifically provided for use by the system 2 in determining the reliability of AWA CO measurements, the device 12 may also be configured to process signals from the cuff pressure sensor 8 to determine the subject's blood pressure.

[0053] System 2 may also include a thermodilution measurement device 14 for obtaining and using measurements of the subject's cardiac output during the calibration process. The thermodilution measurement device 14 may be or may include one or more temperature sensors positioned at appropriate sites in the subject's arterial and / or venous systems to measure the regional temperature of the blood at these sites over time. The thermodilution measurement device 14 may also include mechanisms for controllably introducing heated or cooled fluid into the subject's bloodstream. The thermodilution measurement device 14 may include one or more additional components configured to process signals from one or more temperature sensors to determine CO measurement results (i.e., calibration CO measurement results). Alternatively, signals from one or more temperature sensors may be provided to device 12, and device 12 may determine CO measurement results by analyzing the temperature signals.

[0054] In some embodiments, system 2 may include one or more additional sensors for measuring the physiological characteristics of the subject / patient.

[0055] One or more additional sensors may include one or more PPG sensors 16, which are to be placed on the body of an object and output a PPG signal relating to the volume of blood passing through that body part. As known to those skilled in the art, the PPG sensor 16 includes a light sensor and typically includes one or more light sources. The PPG signal output by the one or more PPG sensors 16 may be a raw measurement signal from the light sensor (e.g., the PPG signal may be a signal representing the light intensity over time), or the one or more PPG sensors 16 may perform some processing on the light intensity signal to determine the value of one or more physiological characteristics, such as heart rate, oxygen saturation, etc. In this case, the PPG signal is a time series of the measurement results of that / those physiological characteristics.

[0056] One or more additional sensors may include an ECG sensor 18, which is to be placed on the subject's body and outputs an ECG signal relating to the electrical activity of the subject's heart. As known to those skilled in the art, the ECG sensor 18 includes multiple electrodes placed at different points on the body, and the ECG signal may include one or more signals representing voltages measured by the electrodes over time. The ECG signal output by the ECG sensor 18 may be a raw measurement signal from one or more electrodes, or the ECG sensor 18 may perform some processing on the voltage measurement results to determine values ​​of one or more physiological characteristics such as heart rate, heart rate variability, etc. In this case, the ECG signal is a time series of measurements of that / those physiological characteristics.

[0057] In cases where system 2 or device 12 is primarily for determining AWA CO measurements, one or more additional sensors may include an arterial pressure (AP) sensor 20. The AP sensor 20 is an invasive sensor (i.e., used within an artery, or otherwise requiring access to an artery), and therefore the AP sensor 20 is placed at the measurement site in the arterial system of the subject's body. The AP sensor 20 measures arterial pressure and outputs an AP signal relating to the pressure of the blood in the artery at the measurement site. The AP signal output by the AP sensor 20 may be a raw measurement signal representing the arterial pressure waveform over time. In embodiments where system 2 or device 12 determines AWA CO measurements, system 2 or device 12 analyzes the AP signal according to AWA technology to determine CO.

[0058] The device 12 includes a processing unit 22 that controls the operation of the device 12 and can be configured to run or perform the methods described herein. The processing unit 22 can be implemented in a variety of ways, via software and / or hardware, to perform the various functions described herein. The processing unit 22 may include one or more microprocessors or digital signal processors (DSPs) that can be programmed using software or computer program code to perform desired functions and / or control components of the processing unit 22 to achieve desired functions. The processing unit 22 may be implemented as a combination of dedicated hardware performing some functions (e.g., amplifiers, preamplifiers, analog-to-digital converters (ADCs) and / or digital-to-analog converters (DACs)) and processors performing other functions (e.g., one or more programmable microprocessors, controllers, DSPs, and associated circuitry). Examples of components that may be employed in various embodiments of this disclosure include, but are not limited to, conventional microprocessors, DSPs, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), hardware for implementing neural networks, and / or so-called artificial intelligence (AI) hardware accelerators (i.e., one or more processors or other hardware specifically designed for AI applications that can be used with a main processor).

[0059] Processing unit 22 is connected to memory unit 24, which can store data, information, and / or signals used by processing unit 22 during the operation of control device 12 and / or the execution of the methods described herein. In some embodiments, memory unit 24 stores computer-readable code that can be executed by processing unit 22, causing processing unit 22 to perform one or more functions, including the methods described herein. In specific embodiments, the program code may take the form of an application for a smartwatch, smartphone, tablet, laptop, or computer. Memory unit 24 may include any type of non-transient machine-readable medium, such as cache or system memory, including volatile and non-volatile computer memory, such as random access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), and electrically erasable PROM (EEPROM), and memory unit 24 may be in the form of memory chips, optical discs (such as disks (CD), digital versatile optical discs (DVD), or Blu-ray discs), hard disks, magnetic tape storage solutions, or solid-state drives (SSDs), memory cards, etc.

[0060] In some embodiments, device 12 includes a user interface 26, which includes one or more components that enable a user of device 12 to input information, data, and / or commands into device 12, and / or enable device 12 to output information or data to the user of device 12. Information that can be output by user interface 26 may include any of the following: an indication of the reliability of AWACO measurement results, AWACO measurement results, an indication of arterial compliance, or an indication of changes in arterial compliance since the last calibration procedure, an indication that a calibration procedure should be performed to obtain new calibrated CO measurement results, and calibrated CO measurement results. User interface 26 may include one or more of any suitable input components, including but not limited to a keyboard, keypad, one or more buttons, switches or dials, mouse, trackpad, touchscreen, stylus, camera, microphone, etc., and / or user interface 26 may include one or more of any suitable output components, including but not limited to a display screen, one or more lamps or light elements, one or more speakers, vibration elements, etc.

[0061] It will be appreciated that actual implementations of device 12 may include Figure 2 Additional components as shown. For example, device 12 may also include a power source such as a battery, or components for enabling device 12 to be connected to a mains power source. Device 12 may also include interface circuitry for enabling data to be connected to and / or exchanged with other devices, including any one or more of NIBP measurement device 10 (or separate cuff pressure sensor 8), sensors 16, 18, 20, servers, databases, and user equipment.

[0062] Figure 3 Exemplary measurement setups on an object according to a first set of exemplary embodiments are shown. In this set of embodiments, the reliability of AWA CO measurement results is estimated without utilizing invasively obtained arterial pressure measurement results (e.g., without utilizing the AP signal from AP sensor 20). In these embodiments, the arterial access site for thermodilution measurement and AP sensor 20 are typically not on the same limb (e.g., arm) as cuff 4. However, it will be appreciated that in some embodiments of the first set of embodiments, the arterial access site for thermodilution measurement may be on the same limb as cuff 4, but the arterial pressure measurement results are not used to estimate the reliability of AWA CO measurement results.

[0063] Figure 3 The image shows object 30, to which thermodilution CO measurement was performed via invasive access to arterial site 32 and venous site 34. The arterial access can be located anywhere in the femoral artery, axillary, brachial artery, or radial artery, and... Figure 3The access site for the middle jiao artery is shown as location 32, located at the femoral artery access site. The access site for the vein can also be any of the following: femoral vein, axillary vein, brachial vein, or radial vein. Figure 3 In the diagram, the venous access site is shown as axillary venous access site 34. Temperature sensors (e.g., thermistors) are typically present at each site to enable thermodilution measurements. More specifically, in thermodilution measurements, a cold saline solution is injected into the body via a central venous line, and temperature changes can be measured distally via an arterial line catheter equipped with a thermistor or other temperature sensor. Although not shown in the diagram... Figure 3 As shown, but the AP sensor 20 is typically located at the same arterial access site used for thermal dilution (e.g., Figure 3 The femoral portion 32 is located in the arterial system, but it can be located in different parts of the arterial system. The AP sensor 20 measures arterial pressure and outputs an AP signal, also known as an arterial blood pressure (ABP) waveform.

[0064] The cuff 4 was placed on the left arm 36 of the object 30, and Figure 3 A PGG sensor 16 is also shown placed on the left hand (or one or more fingers of the left hand) of the subject 30, and an ECG sensor 18 is placed in the heart region of the subject 30 (in a manner typical for ECG sensors). The PPG sensor 16 should be present on the same limb as the cuff 4. As noted below, in some embodiments, the PPG sensor 16 and / or ECG sensor 18 are not required.

[0065] In a first specific embodiment, the reliability of the AWA CO measurement results for object 30 is estimated using the measurement results of pressure oscillations in cuff 4 and one or both of the PPG signal from PPG sensor 16 and the ECG signal from ECG sensor 18. Figure 4 An exemplary method according to this embodiment is shown in the figure. Figure 4 One or more of the steps in the process can be performed by system 2, device 12 and / or processing unit 22.

[0066] In step 101, a calibration procedure is performed to determine the calibration CO measurement results for the AWA technique used to calibrate subject 30. Specifically, a thermodilution-based calibration procedure is performed to obtain one or more measurements of cardiac output of subject 30. The calibration CO measurement results are used to determine the values ​​of parameters used in the AWA model, and in particular, the value of arterial compliance C. This calibration step is performed in a conventional manner.

[0067] During the thermal dilution CO measurement procedure (e.g., simultaneously or during the thermal dilution CO measurement procedure), the cuff 4 is inflated, causing it to apply pressure to the limb (e.g., arm 36). This is shown as step 103. During the inflation of the cuff 4 (and optionally also during subsequent inflation), the cuff pressure sensor 8 measures pressure oscillations in the cuff 4 and outputs a cuff pressure signal. The PPG sensor 16 and / or the ECG sensor 18 also operate during the inflation of the cuff 4 and output corresponding signals related to the duration of the cuff inflation.

[0068] The cuff pressure signal was analyzed to obtain information about arterial size / volume via transmural pressure across a range of arterial walls, which varies with cuff inflation and / or deflation.4 The cuff pressure signal was also processed to determine the blood pressure measurement of subject 30. This yielded the relationship between the oscillation of arterial volume under the cuff and the derived arterial pressure.

[0069] The PPG and / or ECG signals (if appropriate) acquired during step 103 are analyzed to estimate the pulse arrival time (PAT) of subject 30. The estimated PAT provides an indication of the pulse wave velocity (PWV) across a range of arterial walls (e.g., applied by cuff 4) along an artery in the limb to which PPG sensor 16 is attached. In addition to or instead of PAT, pulse transit time (PTT) can be determined by using PPG and ECG signals, ECG and AP signals, or PPG and AP signals.

[0070] In step 105, the relationship between the derived arterial volume and arterial pressure oscillations and the estimated pulse wave velocity can be analyzed to obtain an estimate of arterial compliance across a range of transmural pressures for subject 30. This estimate of arterial compliance is considered the “baseline arterial compliance” because it is the estimate of arterial compliance performed during the calibration procedure. Figure 5 The graph in the figure illustrates the arterial compliance values ​​of transmural pressure across a range during the calibration procedure.

[0071] Those skilled in the art will appreciate the various different methods by which arterial compliance can be noninvasively estimated using oscillation assays (i.e., measurements of arterial pressure oscillations) and / or PWV derived from PAT, which are not provided in further detail herein. However, some exemplary techniques that can be used are described in WO 2020 / 126576 and International (PCT) Patent Application No. PCT / EP2020 / 068331.

[0072] Following the thermodilution calibration procedure, the AP sensor 20 is used to measure arterial pressure over time, and the AP signal is evaluated using a calibrated AWA model to determine the CO measurement result. As previously mentioned, arterial compliance may change during this time period, which could cause the AWA CO measurement result to become unreliable.

[0073] Therefore, in this embodiment, to identify when arterial compliance may change, after estimating baseline arterial compliance in step 105, the PPG sensor 16 and / or ECG sensor 18 continue to measure their respective parameters over time and output measurement signals (step 107). These measurement signals are analyzed to determine the PAT of the object 30. In some embodiments, the PAT of the object 30 may be determined on a frame-by-frame basis. Changes in PAT may (but are not necessarily) be due to changes in arterial compliance.

[0074] Therefore, in step 109, the PAT of object 30 determined in step 107 is compared with the PAT determined in steps 103 / 105. If the PAT has not changed, or the difference between the PAT estimates is within an acceptable margin (e.g., the magnitude of the difference is less than a threshold amount, or the percentage change is less than a threshold amount), then it is considered that there is no change in arterial compliance that would make the AWACO measurement unreliable, and the method returns to step 107 and is repeated.

[0075] However, if PAT has changed, or the difference between PAT estimates is greater than an acceptable margin (e.g., the magnitude of the difference is greater than a threshold amount, or the percentage change is greater than a threshold amount), then it is possible that arterial compliance has changed in a way that makes the AWA CO measurement unreliable. However, although changes in arterial compliance lead to changes in PAT, not all changes in PAT are due to changes in arterial compliance, and therefore pulsatile to pulsatile PAT is not sufficient to indicate a change in arterial compliance. This is because changes in PAT can occur due to changes in arterial smooth muscle tone, but can also be due to changes in blood pressure or pre-ejection phase of the heart. Therefore, when a change or sufficient change in PAT is detected in step 109, it is necessary to use the oscillation measurement signal from cuff pressure sensor 8 to determine another estimate of arterial compliance. Therefore, when a change or sufficient change in PAT is detected in step 109, a cuff inflation procedure similar to steps 103 and 105 is performed to obtain an additional estimate of arterial compliance (steps 111 and 113). As in step 105, step 113 provides a further estimate of arterial compliance with transmural pressure across a range for subject 30.

[0076] In step 115, an additional estimate of arterial compliance determined in step 113 can be compared with the baseline arterial compliance determined in step 105 to confirm whether the PAT change is due to a change in arterial compliance. As in steps 103 and 105, the new estimate of arterial compliance is based on the oscillatory measurement signal obtained from cuff pressure sensor 8 and the PWV derived from PAT from simultaneously acquired transmural pressures across a range of arterial walls. Figure 6 The graph in the figure illustrates a comparison between the newly acquired arterial compliance values ​​(referred to as P_tm) for a range of transmural pressures (from step 113) and the arterial compliance measured during the calibration procedure. Figure 6 Line 60 represents the baseline arterial compliance value for a range of transmural pressures, and line 62 represents a newly acquired arterial compliance value for said range of transmural pressures. In some embodiments, the comparison in step 115 may indicate a change in PAT due to a change in arterial compliance if, at any transmural pressure, the newly acquired arterial compliance value differs from the arterial compliance measured during the calibration procedure by more than a threshold amount (e.g., 10%, although other values ​​may be used). Alternatively, the comparison in step 115 may involve determining the absolute difference or ratio of the measured arterial compliance and optionally integrating these differences to obtain a aggregated value for transmural pressures across a range.

[0077] If arterial compliance has changed from baseline arterial compliance estimates, then current and future AWA CO measurements should be considered unreliable.

[0078] In some embodiments, the unreliability of the AWA CO measurement result can be flagged or indicated to the care provider. For example, visual and / or auditory indications of this unreliability can be provided by device 12 (e.g., a label on the screen of a patient monitoring device). Upon observation of an indication of unreliability, the care provider can initiate an additional calibration procedure (e.g., thermal dilution) to determine a new calibrated CO measurement result. In this case, the method is repeated from step 101.

[0079] In some embodiments, an indication of the unreliability of the AWA CO measurement results can be used to trigger or initiate a new calibration procedure (e.g., a thermal dilution procedure). In this case, the method can return to step 101 and repeat to obtain new calibrated CO measurements and an estimate of baseline arterial compliance.

[0080] Alternatively (or additionally), and especially in cases of small changes in arterial compliance (e.g., changes less than a threshold), newly acquired arterial compliance values ​​can be used to determine the adjustment of the C (arterial compliance) value used in the AWA model. Figure 7This is a graph illustrating arterial compliance versus transmural pressure, and provides examples of arterial compliance values ​​obtainable at the brachial artery site. Since these values ​​only represent the nature of the arterial segment below cuff 4 (the size of the arterial segment is determined by the size of the cuff itself; for example, the cuff may cover approximately 14 cm of artery), this data can then be used to scale previously obtained C values ​​obtained through thermodilution. Scaling of C can be done by increasing or decreasing it proportionally, for example, by considering the entire length of the arterial tree, and / or by considering other patient-specific characteristics such as body mass index (BMI) or body length (height).

[0081] Figure 7 It also shows how arterial compliance information can be obtained across a wider range of transmural pressure values, thus allowing the derivation of the relationship between blood pressure and arterial compliance. This is useful for more accurate CO estimation in the case of BP changes, since the C parameter in Equation (1) depends on BP. The cuff 4 applies external pressure to the arm 36, and the transmural pressure (P) on the arterial wall is... tm ) is defined as:

[0082] P tm =P art –P 袖带 (2)

[0083] Among them, P art It is the arterial pressure that varies between systolic and diastolic blood pressure, and P 袖带 This is the pressure inside the cuff 4. Therefore, P 袖带 Changes can alter P tm It also "simulates" changes in blood pressure. This allows C to be inferred within that range, and values ​​can be stored, for example, in a lookup table.

[0084] Figure 7 An example of arterial compliance values ​​is shown, which can be measured over gradual inflation of the cuff up to systolic pressure. However, this full inflation of the cuff is unnecessary because blood pressure is unlikely to change by more than 20-40 mmHg under typical patient conditions in a nursing setting. This is in Figure 7 The area shown is designated as the "operation area" 70. For this reason, the cuff 4 can only be inflated to the mean arterial pressure (e.g., or possibly lower). In this case, the systolic and diastolic blood pressure values ​​can be obtained through an invasive arterial site 32.

[0085] Therefore, the above method will enable more accurate estimation of CO using AWA than currently available techniques. This is because arterial compliance can be used across a range of pressures, whereas currently only point calibration at the blood pressure at the time of obtaining calibrated CO measurements is considered. In particular, by obtaining arterial compliance values ​​across a range of blood pressures, it is possible to adjust the arterial compliance parameters in the AWA CO inference process based on the measured pressure. For example, using AWA technology to process an unaltered (unprocessed) AP waveform to estimate CO, for example at a mean arterial pressure of 100 mmHg, results in a mean transmural pressure of 100 mmHg across the arterial wall. The transmural pressure across the arterial wall can be altered using cuff 4. If the AP waveform is recorded while the cuff pressure is kept at a plateau (e.g., cuff pressure = 20 mmHg, resulting in a mean transmural pressure of 80 mmHg), a different waveform will be obtained. Subsequently, if the blood pressure drops from a mean pressure of 100 mmHg to a mean pressure of 80 mmHg, the AWA CO technology can be adjusted during calibration based on a previous CO measurement performed at a cuff pressure of 20 mmHg.

[0086] In the second specific embodiment, the reliability of the AWACO measurement of object 30 is estimated using only the measurement of pressure oscillations in cuff 4. That is, unlike the first embodiment described above, neither the PPG sensor 16 nor the ECG sensor 18 is present or used. In this second embodiment, steps 101 and 103 are performed as described above, except that no PPG or ECG signals are obtained. In step 105, baseline arterial compliance is estimated by analyzing the cuff pressure signal obtained during the calibration procedure. Simply put, the obtained cuff pressure oscillations are converted into changes in arm volume, and then the changes in arterial volume are quantified, thereby inferring arterial compliance. Those skilled in the art will understand various techniques for estimating arterial compliance based on cuff pressure signals obtained during the calibration procedure. For example, suitable techniques are described in “A modelling framework for assessment of arterial compliance by fusion of oscillometry and pulse wavevelocity information” (Computer Methods and Programs in Biomedicine, 196, 2020) by Bogatu, LI, Turco, S., Mischi, M., Woerlee, P., Bouwman, A., Korsten, EHHM, & Muehlsteff, J. Other suitable techniques can be found in WO 2020 / 126576 and international (PCT) patent application PCT / EP2020 / 068331.

[0087] Steps 107 and 109 are omitted, and after the calibration procedure (step 101), cuff pressure signals continue to be acquired, for example continuously, or preferably intermittently (because it requires inflation of cuff 4, which may be inconvenient for subject 30). This typically corresponds to step 111, and the cuff pressure signals analyzed in step 113 to estimate arterial compliance. Step 115 compares the baseline estimate of arterial compliance with the newly determined estimate to determine whether the AWA CO measurement results are still reliable.

[0088] In a third embodiment, potential changes in arterial compliance since the calibration procedure has been performed can be inferred by analyzing the morphology (e.g., shape) of the PPG signal from the PPG sensor 16. As in the first and second embodiments, cuff pressure signals are acquired and used to estimate arterial compliance.

[0089] In this third embodiment, steps 101 and 103 are performed as described above, including acquiring the PPG signal during the calibration procedure. However, instead of determining the PAT or PWV, the morphology of the PPG signal can be analyzed to provide a baseline morphology (i.e., the morphology corresponding to when the calibration procedure is performed). Morphological aspects that can be considered include decomposition into positive and reflected waves, or using higher-order derivatives from which the pulse transit time (PTT) can be derived. Other aspects include, on a beat-to-beat basis, the ratio of the PPG amplitude to the arterial pulse pressure (PPG). amp / PP, such as the corresponding vascular compliance) versus total peripheral resistance (TCR) and Winkssel compliance (Cwk) obtained from the model flow CO algorithm (as described in Wook-Jong Kim et al., “The photoplethysmographic amplitude to pulse pressure ratio can track sudden changes in vascular compliance and resistance during liver graft reperfusion” (Medicine (Baltimore), July 2, 2017, Vol. 96, No. 22, e7045).

[0090] In step 105, baseline arterial compliance is estimated by analyzing the cuff pressure signal obtained during the calibration procedure. This can be performed in a manner similar to that described in the second specific embodiment above.

[0091] In this third embodiment, steps 107 and 109 include acquiring the PPG signal and analyzing its morphology to determine whether the morphology has changed since the self-calibration process. If a change in morphology is identified in step 109, steps 111 and 113 can be performed to re-estimate arterial compliance. Step 115 compares the baseline estimate of arterial compliance with the newly determined estimate to determine whether the AWA CO measurement results are still reliable, as in the first embodiment.

[0092] It will be appreciated that the analysis of PPG signal morphology can also be used in the first specific embodiment, as well as the estimation of PAT and PWV.

[0093] Figure 8 The illustration shows an exemplary measurement setup on an object according to a second set of exemplary embodiments. In this set of embodiments, the reliability of the AWA CO measurement results is estimated by taking into account invasively obtained arterial pressure measurements. This can improve the estimation of arterial compliance. In these embodiments, the arterial access site for thermodilution measurements and the AP sensor 20 need to be located on the same limb (e.g., the arm) as the cuff 4.

[0094] Figure 8 Subject 80 is shown, for which a thermodilution CO measurement was performed via invasive access to arterial site 82 and venous site 84. As noted, the arterial access site should be located on the same limb as the cuff, and the arterial access site / AP sensor 20 should be located distally relative to the cuff 4. Figure 8 In this diagram, the arterial access site is shown as the radial artery access site 82 on the left arm 86 of the subject 80, with the cuff 4 on the upper arm, although the brachial artery access site can be used alternatively (assuming the cuff 4 is high enough on the arm). Venous access can be any central venous site. Figure 8 In the diagram, vein access 84 is shown as a vein access site 84 located in the axillary region. Temperature sensors are typically present at each site to enable thermal dilution measurements. Although not shown in... Figure 8 As shown, but the AP sensor 20 is typically located at the same arterial access site used for thermal dilution (e.g., Figure 8 Artery access site 82).

[0095] The cuff 4 is placed on the same arm as the artery access site 82, and thus the cuff 4 is placed on the left arm 86 of the object 80. Figure 8A PGG sensor 16 is also shown placed on the left hand (or one or more fingers of the left hand) of the subject 80, while an ECG sensor 18 is placed in the area of ​​the heart of the subject 80 (in a manner typical for ECG sensors). The PPG sensor 16 should be present on the same limb as the cuff 4. As noted below, in some embodiments, the PPG sensor 16 and / or ECG sensor 18 are not required.

[0096] In a first specific embodiment of the second set of embodiments, the reliability of the AWA CO measurement results of the object 30 is estimated using the measurement results of pressure oscillations in the cuff 4, the measurement results of arterial pressure (AP) obtained from the AP sensor 20, and one or both of the PPG signal from the PPG sensor 16 or the ECG signal from the ECG sensor 18. The exemplary method according to this embodiment is similar to... Figure 4 The method shown is as described. However, during the calibration process (step 101), and especially in step 103 when the cuff 4 is inflated, and in step 111 when the cuff 4 is inflated, the AP measurement results are obtained by the AP sensor 20.

[0097] Entering the arterial line at the brachial / radial artery site (e.g., site 82) improves the accuracy of arterial compliance estimation in steps 105 and 113. Having the AP signal allows the entire pressure and volume waveform to be considered when estimating arterial compliance, rather than relying solely on the oscillation amplitude (i.e., from the cuff pressure signal). Therefore, steps 105 and 113 also consider the AP measurement results for arterial compliance estimation, and since the non-invasive measurement results (cuff pressure signal) are supplemented by the invasive measurement results (AP signal), a more accurate arterial compliance estimation is achieved.

[0098] This method is based on estimating arterial compliance via formula (3):

[0099]

[0100] If the arterial volume V a and pressure wave P a If available, arterial compliance can be obtained. In OR and ICU settings, arterial pressure wave P a Blood pressure (BP) is typically obtained via an invasive arterial line. For redundancy, non-invasive cuff-based oscillation measurement is also used. Vessel wall oscillations are detected as pressure oscillations within the cuff. If cuff compliance (the conversion from pressure to volume change within the cuff) is known, information about arterial volume (V) can be obtained. a Information regarding synchronicity. By appropriately processing the signal regarding synchronicity, arterial compliance can be derived from the following equation:

[0101]

[0102] In practical implementations, the acquired and synchronized low-noise derivatives need to be calculated and divided.

[0103] In a second specific embodiment of the second set of embodiments, simultaneous recording of AP measurements, ECG signals, and PPG signals during cuff inflation can be used to distinguish between central and peripheral changes in arterial compliance. These types of changes in arterial compliance are described in W. Zong, G. Moody, and R. Mark’s “Effects of vasoactive drugs on the relationship between ECG-pulse wave delay time and arterial blood pressure in ICU patients” (Computers in Cardiology 1998, Vol. 25) and Jani, B., and C. Rajkumar’s “Ageing and vascular ageing” (Postgraduate medical journal, Vol. 82968, 2006, pp. 357-362).

[0104] Therefore, in steps 105 and 113, peripheral arterial compliance can be estimated using PAT measurements derived from ABP and PPG, while central arterial compliance can be estimated using ECG and PAT and oscillation measurements (i.e., cuff pressure signals). Differences in these estimated arterial compliance can be used to determine the reliability of AWA CO measurements. For example, the reliability of AWA CO measurements can be determined by comparing peripheral arterial compliance (because peripheral arterial compliance is more easily altered) or by comparing more central arterial compliance. Alternatively, a baseline relationship between peripheral and central arterial compliance can be derived, and the presence of the same relationship in subsequent measurements can be examined.

[0105] The general method according to the technique described in this article is as follows: Figure 9 As shown. Figure 9 One or more steps in the process can be performed by system 2, device 12 and / or processing unit 22.

[0106] In step 203, inflation of the cuff 4 begins at a first location on the object (e.g., around a limb such as an arm).

[0107] Next, in step 205, which occurs during the inflation of the cuff 4, a pressure signal of the cuff 4 is obtained, including a pressure measurement inside the cuff 4 during inflation. Steps 203 and 205 generally correspond to step 103 in the specific embodiment described above.

[0108] In step 207, the cuff pressure signal was analyzed to derive the relationship between the oscillation of the arterial volume under cuff 4 and the pressure in the artery.

[0109] In step 209, arterial compliance is estimated for a range of cuff pressures (transmural pressure). Arterial compliance is estimated based on the relationship determined in step 207. Steps 207 and 209 are generally described above with reference to step 105 of the specific embodiment described above.

[0110] The “first round” of steps 203-209 is performed during a first time period when calibrated CO measurement results are obtained for the object using the thermal dilution CO measurement technique. Therefore, the AWA technique is calibrated using the thermal dilution CO measurement results obtained during the first time period. This “round” can be referred to as the “calibration round” when steps 203-209 are performed while calibrating CO measurements are being obtained. Optionally, step 201 (which is performed before or concurrently with step 203) marks the beginning of the thermal dilution calibration procedure. Step 201 can generally correspond to step 101 in the specific embodiment described above. In this first round of steps 203-209, the output of step 209 is referred to as “first arterial compliance,” and as indicated, represents arterial compliance for an artery with a range of transmural pressures. Therefore, the first time period is the time period for measuring first arterial compliance and the time period for obtaining calibrated CO measurement results for calibrating the AWA technique. Therefore, first arterial compliance is typically measured at the same time as direct CO measurement, for example, using thermal dilution.

[0111] In embodiments where the method is implemented by system 2, device 12, and / or processing unit 22, processing unit 22 can be manually controlled to perform the first round of steps 203-209 when a thermally diluted CO measurement result is obtained. Alternatively, (e.g., in response to receiving a control signal from the thermally diluted CO measuring device) processing unit 22 can be automatically controlled to perform the first round of steps 203-209 when a thermally diluted CO measurement is obtained. Alternatively, processing unit 22 can be automatically controlled to perform the first round of steps 203-209 at a desired time (e.g., according to a schedule) and to initiate thermally diluted CO measurement. In any of these ways, first arterial compliance will be measured during the time period in which the thermally diluted CO measurement result is obtained.

[0112] Subsequently, in step 211, i.e., in the second time period following the first time period, a second round of steps 203-209 is triggered, wherein steps 203-209 are repeated to provide an additional estimate of the arterial compliance. This additional estimate is referred to as "second arterial compliance." As previously stated, "second arterial compliance" refers to the arterial compliance of an artery with respect to a range of transmural pressures. The repetition of steps 203-209 triggered by step 211 can generally correspond to steps 111 and 113 of the specific embodiment described above.

[0113] Once the repetition of steps 203-209, triggered by step 211, is completed, the method proceeds to step 213. In step 213, first arterial compliance and second arterial compliance are compared, and the result of the comparison between the first arterial compliance and the second arterial compliance (e.g., difference) is used to determine the reliability of the CO measurement results obtained using the AWA technique.

[0114] In some embodiments, if the AWA CO measurement is deemed reliable, the method may return to step 203 at some subsequent third time interval and perform another round of steps 203-209. If the AWA CO measurement is deemed unreliable, a new calibration CO measurement may be required. In this case, the method may return to step 201 to automatically initiate a new thermodilution CO measurement and calibration of the AWA model. Alternatively, the method may also include informing a user of device 12 or system 2 (e.g., via a display screen or other user interface component of device 12 or system 2) of the unreliability of the AWA CO measurement, and the care provider may manually initiate a new thermodilution measurement in step 201. As another alternative, if the measured value of AWA CO is deemed unreliable, an adjustment to the value of the arterial compliance parameter (C) in the AWA model may be determined instead of obtaining a new calibration CO measurement. This adjustment may be determined as a function of a second arterial compliance and / or based on the difference between the first and second arterial compliance. For example, the newly measured arterial compliance may be input into the Windkessel model to output a more accurate estimate of CO. Alternatively, the output CO can be scaled relative to the ratio of arterial compliance at calibration (compliance 1) to the current arterial compliance (compliance 2). In embodiments where the adjustment of C in the AWA model has been determined, the method can return to step 203 at a subsequent time interval.

[0115] In some embodiments, step 213 may include comparing the result of the comparison to a threshold. The result of the comparison may be a difference, the magnitude of the difference, or a fractional or percentage change in arterial compliance. If the difference, the magnitude of the difference, or the fractional or percentage change (if appropriate) is above the threshold, then the AWA CO measurement result may be considered unreliable, and otherwise reliable. In the case of a fractional or percentage change, a 10% threshold may be appropriate. In the case of a difference or a significant difference, an appropriate threshold may be set around 10% of a typical arterial compliance value.

[0116] In some embodiments, the method performed by system 2 or device 12 may further include obtaining one or more AWACO measurements. This step may be performed continuously, periodically, or when CO measurements are required. This step includes obtaining an arterial pressure (AP) signal representing the arterial pressure over time and processing the AP signal using an AWA model to determine cardiac output.

[0117] In some embodiments where the AP signal used by the AWA model is obtained from the same limb around which the cuff 4 is placed, the AP signal may be obtained during steps 203 and 205, and step 207 may include analyzing the first cuff pressure signal and the AP signal to derive the relationship between the oscillation of the arterial volume under the cuff 4 and the pressure of the artery.

[0118] In some embodiments, when steps 203 and 205 are performed, one or both of a PPG signal and an ECG signal are obtained. This or these signals are analyzed in step 207 to determine the object's PAT and / or PWV, and in step 209, the PAT and / or PWV, along with the relationship determined in step 207, are used to estimate the first arterial compliance.

[0119] In another embodiment, when the PAT is determined in the calibration rounds of steps 203-209, once the calibration rounds are complete, PPG and / or ECG signals can continue to be acquired and analyzed to determine the PAT for the target. This or these PAT values ​​can be compared with the PAT values ​​determined in the calibration rounds, and the result of the comparison can be used to determine whether step 211 should be performed and a second arterial compliance estimate should be made. In particular, as noted above, changes in PAT can (but do not necessarily) indicate changes in arterial compliance, and therefore monitoring changes in PAT can provide an indication of whether arterial compliance may have changed. Therefore, if the comparison indicates that the PAT has changed by a sufficient amount (e.g., 10%, but other values ​​may be used), step 211 can be performed. If the comparison indicates that the PAT has not changed by a sufficient amount, then the CO measurement results obtained using the AWA technique can continue to be considered reliable.

[0120] In embodiments where PPG and ECG signals are unavailable (e.g., because system 2 does not include PPG sensor 16 and ECG sensor 18), then in step 209, the first arterial compliance can be estimated based solely on the first cuff pressure signal. In these embodiments, step (b) can be repeated intermittently or periodically, i.e., the second time period in step (b) is a predefined time following the first time period. In some embodiments, step (b) can be performed every X minutes, where X can be a value in the range of 5 to 60.

[0121] In embodiments where PPG signals are available, changes in arterial compliance can be inferred from changes in PPG signal morphology. Therefore, in some embodiments, PPG signals are obtained when steps 203 and 205 are performed, and the PPG signals are analyzed to determine a first PPG morphology. After step 209, further PPG signals of the object are obtained, and these additional PPG signals are analyzed to determine a second PPG morphology. Based on a comparison between the second and first PPG morphologies, the comparison is used to determine whether to perform step 211.

[0122] Therefore, a method, apparatus, and system are provided for estimating the reliability of CO measurement results obtained using AWA technology.

[0123] It will be appreciated that the techniques described herein can be implemented by a computer program, particularly a computer program on or within a carrier. This program can take the form of source code, object code, code between source and object code, such as partially compiled code, or any other form suitable for use in implementations of the methods described herein. It will also be appreciated that such programs can have many different architectural designs. For example, program code implementing the functions of the methods, apparatus, or systems described herein can be subdivided into one or more subroutines. Many different ways of distributing functionality among these subroutines will be apparent to those skilled in the art. Subroutines can be stored together in an executable file to form a self-contained program. Such an executable file can include computer-executable instructions, such as processor instructions and / or interpreter instructions (e.g., Java interpreter instructions). Alternatively, one or more subroutines can be stored in at least one external library file and linked statically or dynamically (e.g., at runtime) to a main program. The main program contains at least one call to at least one of the subroutines. Subroutines can also include function calls to each other. Embodiments relating to computer program products include computer-executable instructions corresponding to each processing stage of at least one method of the methods set forth herein. These instructions may be subdivided into subroutines and / or stored in one or more files that can be statically or dynamically linked. Another embodiment relating to a computer program product includes computer-executable instructions corresponding to each module of at least one of the apparatuses, systems, and / or products described herein. These instructions may be subdivided into subroutines and / or stored in one or more files that can be statically or dynamically linked.

[0124] The carrier of a computer program can be any entity or device capable of carrying the program. For example, the carrier can include data storage devices such as ROM, for example, CD ROM or semiconductor ROM, or magnetic recording media, such as hard disk. Furthermore, the carrier can be a transmissible carrier, such as electrical or optical signals, which can be transmitted via cables or optical fibers or through radio or other modules. When the program is implemented with such signals, the carrier can be constituted by such cables or other devices or modules. Alternatively, the carrier can be an integrated circuit in which a program is embedded, adapted to perform the relevant method or be used in the performance of the relevant method.

[0125] Those skilled in the art, through studying the accompanying drawings, the disclosure, and the appended claims, can understand and implement variations of the disclosed embodiments in practice with respect to the principles and techniques described herein. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality. A single processor or other unit can perform the functions of several items recited in the claims. Although specific measures are recited in dissimilar dependent claims, this does not imply that combinations of these measures cannot be advantageously used. Computer programs may be stored / distributed on suitable media, such as optical storage media or solid-state media provided with or as part of other hardware, but computer programs may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A computer program product comprising a computer-readable medium, wherein computer-readable code is implemented on the computer-readable medium, the computer-readable code being configured to, when run by a suitable computer or processor, cause the computer or processor to perform a method for estimating the reliability of cardiac output (CO) measurements obtained using arterial waveform analysis (AWA) technology for a subject, wherein... The AWA technique is calibrated using CO measurement results obtained through thermal dilution CO measurement technology, and the method includes: (a) During a first time period when the AWA technique is calibrated using a first CO measurement result obtained using the thermal dilution CO measurement technique: (i) Begin (203) inflating the cuff at a first position on the object; (ii) Obtain (205) a first cuff pressure signal including a measurement of the pressure inside the cuff during inflation; (iii) Analyze (207) the first cuff pressure signal to derive the relationship between the oscillations in the arterial volume under the cuff and the pressure in the artery; and (iv) Estimate (209) the first arterial compliance of the artery for a range of cuff pressures based on the determined relationship; (b) During a second time period following the first time period, repeat steps (i)-(iv) of (211) to estimate the second arterial compliance of the artery; and (c) The reliability of the CO measurement results obtained using the AWA technique during the second time period is determined by using the result of the comparison between the first arterial compliance and the second arterial compliance in (213).

2. The computer program product according to claim 1, wherein, If the CO measurement results obtained using the AWA technique during the second time period are determined to be reliable, the method further includes: (d) Repeat steps (i)-(iv) during a third time period following the second time period to estimate the third arterial compliance of the artery; and (e) Repeat step (c) using the second arterial compliance and the third arterial compliance.

3. The computer program product according to claim 1 or 2, wherein, If the CO measurement result obtained using the AWA technique during the second time period is determined to be unreliable, the method further includes one or more of the following: The thermal dilution CO measurement technique is initiated to obtain a second CO measurement result, and the second CO measurement result is used to calibrate the AWA technique; Inform the user of the unreliability of the measurement results obtained using the AWA technology; and The results of the comparison are used to determine the adjustment of the values ​​of the arterial compliance parameters used in the AWA technique.

4. The computer program product according to claim 1 or 2, wherein, The method further includes: When steps (i) and (ii) are performed, photoplethysmography (PPG) signals and / or electrocardiogram (ECG) signals for the object are obtained; and Analyze the PPG signal and / or the ECG signal to determine the first pulse arrival time (PAT) and / or the first pulse wave velocity (PWV) for the subject; Step (iv) includes estimating (209) the first arterial compliance of the artery for the range of cuff pressures based on the determined relationship and the first PAT and / or the first PWV.

5. The computer program product according to claim 4, wherein, The method further includes: After step (iv), additional PPG signals and / or additional ECG signals for the object are obtained; Analyze the additional PPG signal and / or the additional ECG signal to determine a second PAT for the object; Compare the second PAT with the first PAT; and The decision to perform step (b) is made based on the result of the comparison between the second PAT and the first PAT.

6. The computer program product according to claim 1 or 2, wherein, The second time period is a predefined time following the first time period.

7. The computer program product according to claim 1 or 2, wherein, The method further includes: When steps (i) and (ii) are performed, a photoelectric volumetric (PPG) signal for the object is obtained; Analyze the PPG signal to determine the first PPG morphology; After step (iv), another PPG signal for the object is obtained; Analyze the additional PPG signal to determine the second PPG morphology; Compare the second PPG morphology with the first PPG morphology; and The decision to perform step (b) is made based on the result of the comparison between the second PPG form and the first PPG form.

8. The computer program product according to any one of claims 1, 2, and 5, wherein, The method further includes: When steps (i) and (ii) are performed, an AP signal representing the arterial pressure AP of the object is obtained; Step (iii) includes analyzing (207) the first cuff pressure signal and the AP signal to derive the relationship between the oscillations in the arterial volume under the cuff and the pressure in the artery.

9. An apparatus (12) for estimating the reliability of cardiac output (CO) measurements of a subject obtained using arterial waveform analysis (AWA) technology, wherein, The AWA technology is calibrated using CO measurement results obtained using thermal dilution CO measurement technology. The device (12) includes a processing unit (22) configured to: (a) During a first time period when the AWA technique is calibrated using a first CO measurement result obtained using the thermal dilution CO measurement technique: (i) Begin inflating the cuff (4) at the first position on the object; (ii) Obtain a first cuff pressure signal, which includes a measurement of the pressure inside the cuff (4) during inflation; (iii) Analyze the pressure signal of the first cuff to derive the relationship between the oscillation in the arterial volume under the cuff (4) and the pressure in the artery; and (iv) Estimate the first arterial compliance of the artery for a range of cuff pressures based on the determined relationship; (b) During a second time period following the first time period, repeat functions (i)-(iv) to estimate the second arterial compliance of the artery; and (c) The reliability of the CO measurement results obtained using the AWA technique during the second time period is determined by using the result of the comparison between the first arterial compliance and the second arterial compliance.

10. The apparatus (12) according to claim 9, wherein, The processing unit (22) is further configured to: When functions (i) and (ii) are performed, photoplethysmography (PPG) signals and / or electrocardiogram (ECG) signals for the object are obtained; and Analyze the PPG signal and / or the ECG signal to determine the first pulse arrival time (PAT) and / or the first pulse wave velocity (PWV) for the subject; Specifically, function (iv) includes estimating the first arterial compliance of the artery for the range of cuff pressure based on the determined relationship and the first PAT and / or the first PWV.

11. The apparatus (12) according to claim 10, wherein, The processing unit (22) is further configured to: Following function (iv), additional PPG signals and / or additional ECG signals are obtained for the object; Analyze the additional PPG signal and / or the additional ECG signal to determine a second PAT for the object; Compare the second PAT with the first PAT; and The decision to execute function (b) is made based on the result of the comparison between the second PAT and the first PAT.

12. The apparatus (12) according to claim 9, wherein, The second time period is a predefined time following the first time period.

13. The apparatus (12) according to claim 9, wherein, The processing unit (22) is further configured to: When functions (i) and (ii) are performed, a photoelectric volumetric (PPG) signal for the object is obtained; Analyze the PPG signal to determine the first PPG morphology; Following function (iv), an additional PPG signal for the object is obtained; Analyze the additional PPG signal to determine the second PPG morphology; Compare the second PPG morphology with the first PPG morphology; and Whether to execute the function (b) is determined based on the result of the comparison between the second PPG configuration and the first PPG configuration.

14. The apparatus (12) according to any one of claims 9-13, wherein, The processing unit (22) is further configured to: When functions (i) and (ii) are executed, an AP signal representing the arterial pressure AP of the object is obtained; Function (iii) includes analyzing the first cuff pressure signal and the AP signal to derive the relationship between the oscillations in the arterial volume under the cuff (4) and the pressure in the artery.

15. A system for estimating the reliability of cardiac output (CO) measurements of a subject obtained using arterial waveform analysis (AWA) technology, the system comprising: The apparatus according to any one of claims 9-14; as well as One or more of the following: The cuff; Pump for the cuff; and A cuff pressure sensor measures the pressure in the cuff and outputs the first cuff pressure signal.

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