ESTIMATING CARDIAC PARAMETERS WHEN PERFORMING AN ACTIVITY USING A PERSONALIZED CARDIOVASCULAR HEMODYNAMIC MODEL

The present disclosure enables personalized cardiac rehabilitation guidance and care continuum using a personalized cardiovascular hemodynamic model that effectively simulates cardiac parameters when the patient performs an activity using a wearable device like a digital watch that can help capture Electrocardiogram (ECG) signal, Photoplethysmogram (PPG) signal and accelerometer signal. The cardiovascular hemodynamic models of the art are not personalized and cannot be input with real time parameters from the subject being monitored. Input parameters including Systemic Vascular Resistance (SVR) using Metabolic EquivalenT (MET) levels associated with an activity level of the subject, unstressed blood volume using an autoregulation method, total blood volume in a body of the subject, and heart rate of the subject are estimated and input to the personalized cardiovascular hemodynamic model to estimate cardiac parameters including cardiac output, ejection fraction and mean arterial pressure.

PRIORITY CLAIM

This U.S. patent application claims priority under 35 U.S.C. § 119 to: Indian Patent Application No. 202121010972, filed on 15 Mar., 2021. The entire contents of the aforementioned application are incorporated herein by reference.

TECHNICAL FIELD

The disclosure herein generally relates to the field of computer assisted modeling of hemodynamic patterns of physiologic blood flow, and, more particularly, to systems and methods for estimating cardiac parameters when performing an activity using a personalized cardiovascular hemodynamic model.

BACKGROUND

Cardiovascular disease (CVD) is one of the main causes of deaths in the world today. With advancing age, the risk of CVD increases significantly. To reduce the effect of CVDs, it has been a well-established fact that the higher levels of regular physical exercises would reduce cardiovascular events and modality. According to medical literature and guidelines, increasing levels of physical activity are the first-line approaches for preventing and treating vascular dysfunction and cardio-metabolic diseases. Moreover, during post-operative recovery of a patient who had suffered a cardiovascular surgery recently, performing prescribed exercises during the recovery phase is always recommended. However, unless the patient diligently and periodically consults a caregiver, it is challenging to gauge whether the prescribed exercises are yielding a desired outcome, or any change is required in the planned therapy.

SUMMARY

In an aspect, there is provided a processor implemented method comprising the steps of: estimating, via one or more hardware processors, a plurality of input parameters for a personalized cardiovascular hemodynamic model associated with a subject being monitored, the plurality of input parameters comprising (i) Systemic Vascular Resistance (SVR), (ii) unstressed blood volume, (iii) total blood volume in a body of the subject, and (iv) heart rate of the subject, the step of estimating comprises: estimating the SVR using Metabolic EquivalenT (MET) levels associated with an activity level of the subject; and updating the unstressed blood volume estimated when the subject is at rest, using an autoregulation method, when an activity is performed by the subject, wherein the autoregulation method comprises: sensing aortic pressure by baroreceptors located at carotid sinus and aortic arch; converting the sensed aortic pressure into a neural firing frequency via afferent sympathetic pathways; generating sympathetic and parasympathetic nervous activities via a central nervous system and efferent pathway depending on the neural firing frequency; and updating an additional blood demand representing the unstressed blood volume during the activity using the generated sympathetic and parasympathetic nervous activities; and estimating, via the personalized cardiovascular hemodynamic model, cardiac parameters including cardiac output, ejection fraction and mean arterial pressure, using the estimated plurality of input parameters.

In another aspect, there is provided a system comprising: one or more data storage devices operatively coupled to one or more hardware processors and configured to store instructions configured for execution via the one or more hardware processors to: estimate a plurality of input parameters for a personalized cardiovascular hemodynamic model associated with a subject being monitored, the plurality of input parameters comprising (i) Systemic Vascular Resistance (SVR), (ii) unstressed blood volume, (iii) total blood volume in a body of the subject, and (iv) heart rate of the subject, wherein estimating the plurality of input parameters comprises: estimating the SVR using Metabolic EquivalenT (MET) levels associated with an activity level of the subject; and updating the unstressed blood volume estimated when the subject is at rest, using an autoregulation method, when an activity is performed by the subject, wherein the autoregulation method comprises: sensing aortic pressure by baroreceptors located at carotid sinus and aortic arch; converting the sensed aortic pressure into a neural firing frequency via afferent sympathetic pathways; generating sympathetic and parasympathetic nervous activities via a central nervous system and efferent pathway depending on the neural firing frequency; and updating an additional blood demand representing the unstressed blood volume during the activity using the generated sympathetic and parasympathetic nervous activities; and estimate cardiac parameters including cardiac output, ejection fraction and mean arterial pressure, using the estimated plurality of input parameters.

In yet another aspect, there is provided a computer program product comprising a non-transitory computer readable medium having a computer readable program embodied therein, wherein the computer readable program, when executed on a computing device, causes the computing device to: estimate a plurality of input parameters for a personalized cardiovascular hemodynamic model associated with a subject being monitored, the plurality of input parameters comprising (i) Systemic Vascular Resistance (SVR), (ii) unstressed blood volume, (iii) total blood volume in a body of the subject, and (iv) heart rate of the subject, wherein estimating the plurality of input parameters comprises: estimating the SVR using Metabolic EquivalenT (MET) levels associated with an activity level of the subject; and updating the unstressed blood volume estimated when the subject is at rest, using an autoregulation method, when an activity is performed by the subject, wherein the autoregulation method comprises: sensing aortic pressure by baroreceptors located at carotid sinus and aortic arch; converting the sensed aortic pressure into a neural firing frequency via afferent sympathetic pathways; generating sympathetic and parasympathetic nervous activities via a central nervous system and efferent pathway depending on the neural firing frequency; and updating an additional blood demand representing the unstressed blood volume during the activity using the generated sympathetic and parasympathetic nervous activities; and estimate cardiac parameters including cardiac output, ejection fraction and mean arterial pressure, using the estimated plurality of input parameters.

In accordance with an embodiment of the present disclosure, the one or more hardware processors are configured to personalize a cardiovascular hemodynamic model to obtain the personalized cardiovascular hemodynamic model, prior to estimating the plurality of input parameters, based on one or more of (i) cardiac parameters obtained from an echocardiogram, (ii) ECG signal obtained from a wearable device worn by the subject when performing the activity and (iii) metadata of the subject including height and weight associated thereof.

In accordance with an embodiment of the present disclosure, the one or more hardware processors are configured to perform sequential activation of a right atrium ra, a left atrium la, a right ventricle rv and a left ventricle lv of the personalized cardiovascular hemodynamic model using compliance functions Cra(t), Cla(t), Crv(t) and Clv(t) respectively, the compliance functions being defined as:(i) the compliance function to actuate ra,

and Cmax,raare the minimum and maximum values of the ra compliance, u(t) is the activation function, time t is considered over a complete cardiac cycle, Tais the start of the activation of ra and T is the end of the cardiac cycle;(ii) the compliance function to actuate la, Cla(t)+Cmin,la+0.5×Cmax,la−Cmin,la)u(t−dla), wherein Cmin,laand Cmax,laare the minimum and maximum values of the la compliance and dlarepresents a time delay between activation of the ra and the la; and(iii) the compliance functions to actuate rv and lv are represented as

In accordance with an embodiment of the present disclosure, the one or more hardware processors are configured to estimate the total blood volume using height and weight of the subject.

In accordance with an embodiment of the present disclosure, the one or more hardware processors are configured to estimate the SVR based on

wherein Rs(0) represents the SVR at rest, MET(t) represents a metabolic equivalent of the activity performed at the tthtime, and τ is a time constant, and wherein the SVR corresponds to a section of the body of the subject depending on the activity being performed, while the SVR of remaining sections are considered constant or modulated by the autoregulation method, the section of the body being an upper body, a middle body or a lower body of the subject.

In accordance with an embodiment of the present disclosure, the one or more hardware processors are configured to estimate the heart rate of the subject using (i) a Photoplethysmogram (PPG) signal and an accelerometer signal or (ii) an Electrocardiogram (ECG) signal, from a wearable device worn by the subject when performing the activity.

DETAILED DESCRIPTION

Considering the risks posed by Cardiovascular disease (CVD), it is very important to periodically monitor a patient's cardiac parameters to assess effects of prescribed exercises on the cardiac parameters of the patient. Unless the patient diligently visits a caregiver, say during a post-operative period, assessing cardiovascular conditions for recovery is challenging. A lapse on the part of the patient may be detrimental to the patient's health. The present disclosure enables personalized cardiac rehabilitation guidance and care continuum using a personalized cardiovascular hemodynamic model that effectively simulates cardiac parameters when the patient performs an activity using a wearable device like a digital watch that can help capture Electrocardiogram (ECG) signal, Photoplethysmogram (PPG) Signal and accelerometer signal. In the context of the present disclosure, the expression ‘patient’ may interchangeably be referred as a ‘subject’.

FIG. 1illustrates an exemplary block diagram of a system100for estimating cardiac parameters when performing an activity using a personalized cardiovascular hemodynamic model, in accordance with some embodiments of the present disclosure. In an embodiment, the system100includes one or more hardware processors104, communication interface device(s) or input/output (I/O) interface(s)106, and one or more data storage devices or memory102operatively coupled to the one or more hardware processors104. The one or more hardware processors104can be implemented as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, graphics controllers, logic circuitries, and/or any devices that manipulate signals based on operational instructions. Among other capabilities, the processor(s) are configured to fetch and execute computer-readable instructions stored in the memory. In the context of the present disclosure, the expressions ‘processors’ and ‘hardware processors’ may be used interchangeably. In an embodiment, the system100can be implemented in a variety of computing systems, such as laptop computers, notebooks, hand-held devices, workstations, mainframe computers, servers, a network cloud and the like.

The memory102may include any computer-readable medium known in the art including, for example, volatile memory, such as static random access memory (SRAM) and dynamic random access memory (DRAM), and/or non-volatile memory, such as read only memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes. In an embodiment, one or more modules (not shown) of the system100can be stored in the memory102.

FIG. 2illustrates an exemplary block diagram of a cardiovascular hemodynamic model triggered via activity related data, in accordance with some embodiments of the present disclosure. Heart is a muscular organ in which each half is composed of a pair of atria and a pair of ventricles serving like a pulsatile pump. A left heart chamber, comprising a left ventricle (lv) and a left atrium (la), pumps oxygenated blood to all tissues of the body. This specific circulation is called systemic circulation. On the other hand, a right heart, comprising a right ventricle (rv) and a right atrium (ra), drives deoxygenated blood to the lungs forming a pulmonic circulation. In addition, there are four cardiac valves namely, mitral (mi) and aortic (ao) valves in the left heart and tricuspid (tr) and pulmonic (pu) valves in the right heart respectively. These valves synchronously open and dose based on a pressure difference within the cardiac chambers and ensures rhythmic unidirectional flow through the heart.

In accordance with the present disclosure, following assumptions have been considered to describe the hemodynamics of the cardiac system.

Assumption 1: Each of the cardiac chambers is triggered by an autonomous compliance function (C(t)), due to the elasticity of the cardiac wads. So, the volume (V(t)), at time t, across any cardiac chamber is defined as V(t)=C(t)×P(t)+Vs; where P(t) is the pressure at the tthtime and Vs is the unstressed volume of that particular chamber.
Assumption 2: The cardiac chambers are considered compliance vessels. Hence, the rate of change of volume across a cardiac chamber at time t, is defined as a difference between an inflow Q1(t) and an outflow Q2(t), so, dV/dt (t)=Q1(t)−Q2(t).
Assumption 3: Each vessel is considered a resistive vessel, as the blood flow is impeded due to frictional forces, depending on viscosity of blood, diameter of the blood vessels, etc. Thus, a flow across a resistive vessel is Q(t)=ΔP(t)/R; where ΔP(t) is a pressure difference in successive compartments of the vessel, at time t and R is the vascular resistance of that vessel.

Based on the three assumptions provided herein above, pressure dynamics of a cardiovascular hemodynamic model is analytically defined as:

where {dot over (P)}la, {dot over (P)}lv, {dot over (P)}sa, {dot over (P)}ra, {dot over (P)}rv, and {dot over (P)}paare pressure variables in the la, lv, systemic arteries sa, ra, rv and pulmonary arteries pa respectively, having initial conditions of pla0, plv0, psa0, pra0, prv0and ppa0. The valvular resistance across the mitral, aortic, tricuspid and pulmonic valves are Rmi, Rao, Rtrand Rpurespectively. The vascular resistance and compliance pair, across the pulmonic and systemic vessels are Rp, Cpaand Rs, Csarespectively.

Ui; ∀i {,i, ao, tr, pu} are inputs for opening and closing of the heart valves as mentioned in equation (2) below.

where δmi, δao, δtr, and δpudefine regurgitation effect of the cardiovascular system.

As per the assumption 1, the cardiac chambers are activated sequentially, in a synchronized manner, by time-varying compliance functions. Typically, this activation starts from a sinoatrial node, which is located inside ra, then, it traverses to the la with a time delay of dla, causing them to contract for pumping the blood into the ventricles. After that, the activation traverses from the atrium to the ventricles via an atrioventricular node with a time delay of d, allowing the ventricles to fill with blood. In accordance with the present disclosure, the compliance functions Cra(t), Cla, Clv(t) and Crv(t) to sequentially actuate ra, la, rv and lv are defined as given in equation (3), equation (4) and equation (5) respectively.

where Cmin,raand Cmax,raare the minimum and maximum values of the ra compliance and u(t) is the activation function. The time t is considered over a complete cardiac cycle. Tais the start of the activation of ra and T is the end of the cardiac cycle.

Similarly, in accordance with the present disclosure, the compliance function to actuate la is modeled using equation (3), where Cmin,laand Cmax,laare the minimum and maximum values of the la compliance, u(t) is the activation function of la and dlarepresent a delay in activation of la with respect to ra.

Likewise, in accordance with the present disclosure, the compliance functions to actuate rv and lv are represented by equation (5) below, where Ci; i ∈{lv,rv} is the systolic compliance across lv or rv and is estimated as a ratio of R-peak and T-peak of the ECG signal, uv(t) is the activation function, and d represents the delay in activation of lv or rv from ra. T1and T2are the systolic and diastolic activation time instances of the cardiac cycle respectively.

In accordance with the present disclosure, depending on pressure variations in the cardiac chambers, blood circulates as shown inFIG. 3. Based on the circulation, the volume across the cardiac chambers also get developed as per assumption 2 mentioned above. The rate of change of volume across the cardiac chambers is measured as given in equation (6) below.

Similarly, the rate of change of volume across the systemic and pulmonary arteries is evaluated using equation (7) below,

The overall blood volume using equations (6) and (7) above is represented by equation (8) below.

FIG. 3AthroughFIG. 3Billustrate an exemplary flow diagram of a computer implemented method300for estimating cardiac parameters when performing an activity using a personalized cardiovascular hemodynamic model, in accordance with some embodiments of the present disclosure. In an embodiment, the system100includes one or more data storage devices or memory102operatively coupled to the one or more hardware processors104and is configured to store instructions configured for execution of steps of the method200by the one or more hardware processors104. The steps of the method300will now be explained in detail with reference to the components of the system100ofFIG. 1. Although process steps, method steps, techniques or the like may be described in a sequential order, such processes, methods and techniques may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of processes described herein may be performed in any order practical. Further, some steps may be performed simultaneously.

Accordingly, in an embodiment of the present disclosure, the one or more hardware processors104, are configured to estimate, at step302, a plurality of input parameters for a personalized cardiovascular hemodynamic model associated with a subject being monitored, In an embodiment, the plurality of input parameters comprises (i) Systemic Vascular Resistance (SVR), (ii) unstressed blood volume, (iii) total blood volume in a body of the subject, and (iv) heart rate of the subject.

When the subject performs any activity like say physical exercise, the amount of blood flowing through skeletal muscles is significantly increased and it is solely dependent on the intensity of the activity. In accordance with the present disclosure, systemic vessels are considered as resistive vessels. Therefore, to accommodate increasing blood flow across the systemic vessels, the vessel resistivity requires to be reduced that significantly reduces the resistance across the systemic vessels. In accordance with the present disclosure, to estimate how much the vessel resistivity needs to be changed and how it is correlated with the level of exercise, the metabolic rate of the subject (which defines the rate of change energy expended per unit time) is considered as it is tightly coupled with vessel conductance.

For a specific activity, the metabolic rate is measured by a metabolic equivalent of task or Metabolic EquivalenT (MET) levels. The MET is defined as the ratio of an exercise metabolic rate to a resting metabolic rate. Thus, for a given activity, the MET value has been considered a constant. For example, in light intensive activities, such as walking slowly, the MET level is consider to be less than 3, in moderate intensive activities (walking at say 4.5 km/hr) the MET level is considered between 3 and 6 and for intensive exercises, such as jogging at say 11 km/hr, the MET level is greater than 6.

Thus, in accordance with the present disclosure, the one or more hardware processors104, are configured to estimate, at step302a, the SVR using the MET levels associated with an activity level of the subject. In an embodiment, the SVR is represented as given in equation (9) below.

In order to simulate the effect of the activity with the variation of systemic resistance, the systemic circulation part in a body is subdivided into three generic sections such as an upper body, a middle body and a lower body as shown inFIG. 2. Depending on the activity performed by the subject, the SVR across the section is modulated based on the MET level as described above, and the SVR in the other sections are assumed to be constant or modulated by an autoregulation method described hereinafter.

Unstressed blood volume (or dead volume) is defined as the maximum volume of blood that can be placed inside a capacitive vessel without raising its effective pressure above 0 mmHg. As per literature, in normal cardiac condition (resting state), the unstressed blood volume is approximated as shown in equation (10) below.

Therefore, in a resting state around 40% of the total blood volume (Vtotal) is stressed volume (effectively participate in hemodynamics) and the rest is unstressed volume. When the subject performs an activity, or during an exercise condition because of the increasing demand of blood, a portion of the unstressed blood is added into the stressed volume. Baroreflex regulates the effect of unstressed blood volume while enhancing the venous return of blood during a ventricular systolic phase.FIG. 4illustrates an exemplary block diagram of the autoregulation method for estimating unstressed blood volume, in accordance with some embodiments of the present disclosure. In an embodiment of the present disclosure, the one or more hardware processors104, are configured to update, at step302b, the unstressed blood volume estimated at rest (from the total blood volume—refer equation 10) using the autoregulation method, when an activity is performed by the subject. As seen inFIG. 4, four subsystems, viz., an afferent sympathetic pathway, central nervous system, efferent pathway and unstressed blood volume regulator cooperate to enable autoregulation.

The effect of baroreflex starts from sensing of aortic pressure by baroreceptors located at carotid sinus and aortic arch. Accordingly, in an embodiment of the present disclosure, the autoregulation method comprises sensing aortic pressure by baroreceptors located at carotid sinus and aortic arch, at step302b-1. The sensed aortic pressure is converted into a neural firing frequency faff(P) via afferent sympathetic pathways, at step302b-2. Analytically, this functionality is defined as shown in equation (11) below.

Sympathetic and parasympathetic nervous activities are then generated via the central nervous system and efferent pathway, depending on the neural firing frequency, at step302b-3. The sympathetic activity fsais defined as shown in equation (12) below.

The Parasympathetic activity fpsais defined as shown in equation (13) below.

Based on the generated sympathetic and parasympathetic nervous activities, the additional blood volume requirement during an exercise needs to be regulated. Autoregulation of the unstressed blood volume via the unstressed blood volume regulator is analytically represented as shown in equation (14) below.

The governing equations of ΔVssa(t) and ΔVspsa(t) are defined as given in equations (15) and (16) below.

where K is a constant, and τsa, τpsaare the time constant of the sympathetic and parasympathetic activities respectively.

An additional blood demand representing the unstressed blood volume during the activity, is then updated using the generated sympathetic and parasympathetic nervous activities, at step302b-4.

In accordance with the present disclosure, the total blood volume which is part of the plurality of input parameters is estimated using height and weight of the subject. As per medical literature, the total blood volume across a healthy human body (who does not have any kind diseases) is closely related with Body-Surface-Area (BSA), and the BSA correlates with the height h and the weight w of the subject. Accordingly, the total blood volume is defined as shown in equation (17) below.

The heart rate is an important parameter that dynamically changes during exercise. Hence, creating a model of heart rate based on a specific physical activity is very difficult to achieve. In accordance with the present disclosure, the personalized cardiovascular hemodynamic model is executed considering the heart rate is continuously monitored when the subject performs an activity. In accordance with the present disclosure, the heart rate of the subject, which is part of the plurality of input parameters, is estimated using (i) a Photoplethysmogram (PPG) signal and an accelerometer signal or (ii) an ECG signal, from a wearable device, such as a digital watch, worn by the subject when performing the activity. As per literature, noise effect of an ECG signal during activities is less than the PPG signal, Hence, if the ECG signal is available, the heart rate is easily measured continuously using detected peaks. If only the PPG signal is available, then the heart rate for each cycle may not be obtained. Hence, the heart rate for a specific time-window is estimated by employing noise cancellation technique using the accelerometer signal. In an embodiment, the accelerometer signal is a 3-axis accelerometer signal, also captured continuously via the wearable device.FIG. 5illustrates heart rate estimation from a PPG signal and an accelerometer signal, in accordance with some embodiments of the present disclosure. Fast Fourier transform is performed on the PPG signal and the accelerometer signal in parallel for the same duration. Heart rate is estimated based on peaks available in the PPG signal after discarding the peaks (representing noise) obtained from the accelerometer signal.

In an embodiment, the step of estimating a plurality of input parameters is preceded by personalizing a cardiovascular hemodynamic model to obtain the personalized cardiovascular hemodynamic model. In an embodiment, the personalizing is based on one or more of (i) cardiac parameters obtained from an echocardiogram such as valvular area, (ii) ECG signal obtained from a wearable device worn by the subject when performing the activity, and (iii) metadata of the subject including height and weight associated thereof. In accordance with the present disclosure, the cardiovascular hemodynamic model is configured with the compliance functions Cra(t), Cla(t), Clv(t) and Crv(t) to sequentially actuate ra, la, rv and lv as explained above. Echocardiography information of the subject helps to derive constant parameters in equation (1) above. For instance, the mitral valve resistance Rmi, the aortic valve resistance Rao, the tricuspid valve resistance Rtrand the pulmonic valve resistance Rpumay be accurately calculated from the echocardiography information, more specifically from information pertaining to valvular diameter of the subject, thereby personalizing the cardiovascular hemodynamic model. Again, the parameters δmi, δao, δtr, and δpuin equation (2) above, that define the regurgitation effect may be estimated from the echocardiography information. Furthermore, the parameters T and Tain equation (3) above, and T1, T2and d in equation (5) above may be estimated based on an ECG signal from the subject obtained using a wearable device. Metadata pertaining to the subject such as the height and the weight of the subject may be used to compute the total blood volume using equation (17) above.

In an embodiment of the present disclosure, at step304, cardiac parameters are estimated via the personalized cardiovascular hemodynamic model, using the estimated plurality of input parameters estimated at step302. In an embodiment, the cardiac parameters include cardiac output, ejection fraction and mean arterial pressure.FIG. 6illustrates an input-output relation of the personalized cardiovascular hemodynamic model, when an activity is performed by the subject, in accordance with some embodiments of the present disclosure.

Simulation Results and Discussion

Experiment 1: Publicly available Troika dataset was used. In these experiments, 12 subjects in the age group 18 years to 35 years were asked to run on a treadmill with changing speeds. The speed-variations are defined as follows.

Rest for 30sec→6-8 km/hr for 1 min→12-15 km/hr for 1 min→6-8 km/hr for 1 min→12-15 km/hr for 1 min→Rest for 30 sec.
While performing exercises on the treadmill, two-channel PPG signals, three-axis acceleration signals, and one-channel ECG signals were simultaneously recorded from each subject. For each subject, the PPG signals were recorded from the wrist by two pulse oximeters with green LEDs (wavelength: 515 nm), Their distance (from center to center) was 2 cm. The acceleration signal was also recorded from the wrist by a three-axis accelerometer. Both the pulse oximeter and the accelerometer were embedded in a wristband, worn by the subjects. The ECG signal was recorded simultaneously from the chest using wet ECG sensors. All signals were sampled at 125 Hz and sent to a computer via Bluetooth.

The cardiovascular hemodynamic model of the present disclosure was provided with the plurality of input parameters as described hereinafter. Total blood volume: Subject specific metadata in the form of height and weight is not available in the Troika dataset. Hence, it was assumed that all the subjects are healthy, and the total blood volume was assumed to be 5 liters for each subject.

SVR during exercise: In the Troika dataset, the level of exercise has been clearly mentioned; hence, the respective MET levels (value) were predicted accurately from the MET table. The MET values for the respective activity duration are tabulated below in Table 1.

TABLE 1MET table with respect to speed variationActivity durationRunning Speed(sec)(km/hr)MET Value0-30Rest231-906-8891-15012-1515151-2106-88211-27012-1515271-300Rest2

Depending on the MET values, the estimated SVR across the lower body was estimated using equation (9) above.FIG. 7illustrates estimation of the SVR of the lower body of a subject, based on MET levels, in accordance with some embodiments of the present disclosure. In this simulation, the value of Rs(0) which defines the SVR at the resting state, was chosen as 0.05 mmHgsec/mL and the time constant τ was 0.5 sec.

Heart rate estimation from ECG signal: In the Troika dataset, as the ECG signal has been captured during the physical activities, by filtering and detecting the ECG peaks, the continuous heart rate was estimated.FIG. 8illustrates estimated heart rate from a raw ECG signal for a subject 11 (of the 11 subjects considered, the ECG signal from the 12thsubject being erroneous), in accordance with some embodiments of the present disclosure. Unstressed blood volume is approximated using the autoregulation method.

By inputting the plurality of input parameters mentioned above into the cardiovascular hemodynamic model of the present disclosure, the cardiac parameters such as the cardiac output, the ejection fraction and the mean arterial pressure were estimated.FIG. 9illustrates heart rate in the form of a box plot for the subject 11, in accordance with some embodiments of the present disclosure, wherein the heart rate was estimated using the ECG signal. Similar box plots were derived for all the 11 subjects considered. Table 2 below provides a comparison of the estimated heart rate at different levels of physical activities for the 11 subjects.

FIG. 10illustrates cardiac output in the form of a box plots for the subject 11, in accordance with some embodiments of the present disclosure. Similar box plots were derived for all the 11 subjects considered, Table 3 below provides a comparison of the estimated cardiac output at different levels of physical activities for the 11 subjects.

FIG. 11illustrates ejection fraction in the form of a box plot for the subject 11, in accordance with some embodiments of the present disclosure. Similar box plots were derived for all the 11 subjects considered, Table 4 below provides a comparison of the estimated ejection fraction at different levels of physical activities for the 11 subjects.

FIG. 12illustrates mean arterial pressure in the form of a box plot for the subject 11, in accordance with some embodiments of the present disclosure. Similar box plots were derived for all the 11 subjects considered.

Table 5 below provides a comparison of the estimated mean arterial pressure at different levels of physical activities for the 11 subjects.

Experiment 2: As the Troika dataset does not contain metadata such as the height, weight and age of the subjects, another experiment was conducted inhouse, where the subjects were asked to perform the following sequence of activities in an office environment.

1. Rest: The subject had to sit on a chair in relaxed position at a given cubicle of the work environment at the 4th floor, for 1 min duration.
2. Walk: After the resting period, the subject was required to walk to the staircase of the building.
3. Climbing stairs: As soon as the subject reached the stairs, he/she had to climb the stairs as fast as he could, leading to using a lot of energy and resulting in higher heart beats. This activity was continued till the subject reached 8th floor (i.e. climbs 4 floors).
4. Walk: Once the subject reached the 8th floor, he/she had to walk through the corridor for approaching the destination.
5. Rest: At the destination the subject had to sit on a chair in a relaxed position for 1 min duration.
During the above sequence of activities, a wearable device, Samsung Gear S2™ classic Smart watch had been used for logging data from a tri-axis accelerometer sensor, and a PPG sensor. Inside the watch, a custom application had been executed for logging the data and sharing with a host machine over Wi-fi. All the signals were sampled at 100 Hz. The cardiovascular hemodynamic model of the present disclosure was provided with the plurality of input parameters as described hereinafter.

Total blood volume: In this dataset, the height and weight of all the subjects had been noted before the experiment. Depending on this, the total blood volume, in accordance with equation (17) was calculated and tabulated as shown below.

TABLE 6Total blood volume based on subject metadataTotal BloodSubjectHeightWeightVolumeBMINo(cm)(Kg)Age(Liter)(kg/m2)116972235.325.212162.575365.328.383152.453234.1722.824160.0272414.6628.125165.165264.9223.856167.6470285.1325.68

SVR during exercise: In this experiment, it was observed that when a subject is climbing upward on the stairs, the speed of movement varies from subject to subject making it difficult to estimate a specific MET level for the entire experiment. Therefore, an evaluation of the SVR during the exercise became difficult to estimate. To approximate the SVR, a vertical accelerometer signal was employed to estimate the MET, and then from the MET, the SVR was estimated in accordance with equation (9) above. The corresponding procedure is described below.

A collected vertical (z-axis) acceleration signal was initially passed through a low-pass filter in order to eliminate high frequency noise signals. Let us assume that the filtered vertical signal is zf. Heart-rate reserve (% HRR) was calculated as

where HRactis the measured heart rate as obtained from the watch during the activities and HRrestis the mean value of the heart rate.

The maximum heart rate HRmaxwas calculated as

The MET level was estimated as

where a, b and c are constants. In the cardiovascular hemodynamic model of the present disclosure used for the experiment, the values of the constants used were a=0.0034. b=0.038, c=3.37.

FIG. 13illustrates the estimated MET using a vertical accelerometer signal for a subject 2, andFIG. 14illustrates the estimated SVR using the estimated MET for the subject 2, in accordance with some embodiment of the present disclosure.

Heart rate estimation from PPG signal: During the exercise condition, the signal quality of PPG is very poor. To overcome this challenge, a time-window of 10 sec was selected and the heart rate was estimated by comparing with the accelerometer signal as described previously.FIG. 15illustrates the estimated heart rate from PPG signal for the subject 2, in accordance with some embodiment of the present disclosure. During the simulation, the unstressed volume is approximated using the autoregulation method,FIG. 16illustrates estimated unstressed blood volume based on the autoregulation method for the subject 2, in accordance with some embodiment of the present disclosure.

By inputting the plurality of input parameters mentioned above from experiment 2 into the cardiovascular hemodynamic model of the present disclosure, the cardiac parameters such as the cardiac output, the ejection fraction and the mean arterial pressure were estimated.

FIG. 17illustrates estimated heart rate from PPG signal in the form of a box plot for the subject 2, in accordance with some embodiments of the present disclosure. Similar box plots were derived for all the 6 subjects considered. Table 7 below provides a comparison of the estimated heart rate at different levels of physical activities for the 6 subjects.

FIG. 18illustrates estimated cardiac output in the form of a box plot for the subject 2, in accordance with some embodiments of the present disclosure. Similar box plots were derived for all the 6 subjects considered. Table 8 below provides a comparison of the estimated cardiac output at different levels of physical activities for the 6 subjects.

FIG. 19illustrates estimated ejection fraction in the form of a box plot for the subject 2, in accordance with some embodiments of the present disclosure. Similar box plots were derived for all the 6 subjects considered.

Table 9 below provides a comparison of the estimated ejection fraction at different levels of physical activities for the 6 subjects.

FIG. 20illustrates estimated mean arterial pressure in the form of a box plot for the subject 2, in accordance with some embodiments of the present disclosure. Similar box plots were derived for all the 6 subjects considered. Table 10 below provides a comparison of the estimated mean arterial pressure at different levels of physical activities for the 6 subjects.

As part of a post-operative monitoring process, during therapy planning, a care giver simulates different heart rate conditions along with post-operative valvular conditions and selects different exercise levels, linked with MET value. Depending upon the selected heart rate, MET, subject metadata and underlying cardiac pathology emulated in the personalized cardiovascular hemodynamic model for the subject being monitored, cardiac parameters like cardiac output, ejection fraction and mean arterial pressure are generated by the personalized cardiovascular hemodynamic model. The simulated cardiac output provides a baseline activity response based on which, the caregiver may plan daily ambulatory activities and therapy. The method and system of the present disclosure thus overcome the challenges of the art wherein firstly cardiovascular hemodynamic models used were not personalized for the subject being monitored. Secondly, the input parameters for the personalized hemodynamic mod& of the present disclosure is estimated using output of wearable devices, thereby facilitating personalized cardiac rehabilitation guidance and care continuum.

The illustrated steps are set out to explain the exemplary embodiments shown, and it should be anticipated that ongoing technological development will change the manner in which particular functions are performed. These examples are presented herein for purposes of illustration, and not limitation. Further, the boundaries of the functional building blocks have been arbitrarily defined herein for the convenience of the description.