A Model of the Cardiorespiratory Response to Aerobic Exercise in Healthy and Heart Failure Conditions

Patients with a Ventricular Assist Device (VAD) are hemodynamically stable but show an impaired exercise capacity. Aim of this work is to identify and to describe the limiting factors of exercise physiology with a VAD. We searched for data concerning exercise in heart failure condition and after VAD implantation from the literature. Data were analyzed by using a cardiorespiratory simulator that worked as a collector of inputs coming from different papers. As a preliminary step the simulator was used to reproduce the evolution of hemodynamics from rest to peak exercise (ergometer cycling) in heart failure condition. Results evidence an increase of cardiac output of +2.8 l/min and a heart rate increase to 67% of the expected value. Then, we simulated the effect of a continuous-flow VAD at both rest and exercise. Total cardiac output increases of +3.0 l/min (+0.9 l/min due to the VAD and +2.1 l/min to the native ventricle). Since the left ventricle works in a non-linear portion of the diastolic stiffness line, we observed a consistent increase of pulmonary capillary wedge pressure (from 14 to 20 mmHg) for a relatively small increase of end-diastolic volume (from 182 to 189 cm3). We finally increased VAD speed during exercise to the maximum possible value and we observed a reduction of wedge pressure (-4.5 mmHg), a slight improvement of cardiac output (8.0 l/min) and a complete unloading of the native ventricle. The VAD can assure a proper hemodynamics at rest, but provides an insufficient unloading of the left ventricle and does not prevent wedge pressure from rising during exercise. Neither the VAD provides major benefits during exercise in terms of total cardiac output, which increases to a similar extend to an unassisted heart failure condition. VAD speed modulation can contribute to better unload the ventricle but the maximal flow reachable with the current devices is below the cardiac output observed in a healthy heart.

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“…A complete description of the model is provided in [8]. A schematic representation of the model structure is provided in Fig 1 for clarity.…”

Section: Methodsmentioning

confidence: 99%

Exercise physiology with a left ventricular assist device: Analysis of heart-pump interaction with a computational simulator

et al. 2017

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“…What is observed in Fig. 7 is a phenomenon common to different types of assistance, for example, in the case of physical exercise (17): changing the VAD flow (in our case by changing VADR) causes a redistribution of flows between the ventricle and the VAD. COt is anyway lower in the case of Lower Rrs.…”

Section: Discussionmentioning

confidence: 67%

“…The normalization factors are LVV and RVV in the basal conditions. 7 is a phenomenon common to different types of assistance, for example, in the case of physical exercise (17): changing the VAD flow (in our case by changing VADR) causes a redistribution of flows between the ventricle and the VAD. This is of course true in the hypothesis that no change occurs in right/left ventricular contractility or in circulatory conditions.…”

Section: Discussionmentioning

confidence: 94%

Control of a Pediatric Pulsatile Ventricular Assist Device: A Hybrid Cardiovascular Model Study

et al. 2017

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The aim of this work is to study pediatric pneumatic ventricle (PVAD) performance, versus VAD rate (VADR) and native heart rate (HR) ratio Rr (VADR/HR). The study uses a hybrid model of the cardiovascular system (HCS). HCS consists of a computational part (a lumped parameter model including left and right ventricles, systemic and pulmonary arterial and venous circulation) interfaced to a physical part. This permits the connection of a VAD (15 mL PVAD). Echocardiographic and hemodynamic data of a pediatric patient (average weight 14.3 kg, HR 100 bpm, systemic pressure 75/44 mm Hg, CO 1.5 L/min) assisted apically with asynchronous PVAD were used to set up a basal condition in the model. After model tuning, the assistance was started, setting VAD parameters (ejection and filling pressures, systole duration) to completely fill and empty the PVAD. The study was conducted with constant HR and variable VADR (50-120, step 10, bpm). Experiments were repeated for two additional patients' HRs, 90 and 110 bpm and for two values of systemic arterial resistance (R ) and E . Experimental data were collected and stored on disk. Analyzed data include average left and right ventricular volumes (LVV, RVV), left ventricular flow (LVF), VAD flow (VADF), and total cardiac output (COt). Data were analyzed versus Rr. LVV and RVV are sensitive to Rr and a left ventricular unloading corresponds in general to a right ventricular loading. In the case of asynchronous assistance, frequency beats are always present and the beat rate is equal to the difference between HR and VADR. In the case of pulsatile asynchronous LVAD assistance, VADR should be chosen to minimize frequency beat effects and right ventricular loading and to maximize left ventricular unloading.

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“…A general overview of the simulator is reported in Figure , more information about its components and its validation are reported in Refs. 14,15. The cardiovascular model included a time varying elastance model for the representation of the atria and ventricles, contracting in diastole and systole, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…A general overview of the simulator is reported in Figure 1, more information about its components and its validation are reported in Refs. 14 and pulmonary circulations, baroreflex and metabolic peripheral controls. The respiratory model includes ventilation mechanics, gas exchange, and ventilation control.…”

Section: Cardiorespiratory Simulatormentioning

confidence: 99%

LVAD speed increase during exercise, which patients would benefit the most? A simulation study

et al. 2019

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Patients supported with a left ventricular assist device (LVAD) have impaired cardiovascular adaptations during exercise, resulting in reduced total cardiac output and exercise intolerance. The aim of this study is to report associations among these impaired cardiovascular parameters and exercise hemodynamics, and to identify in which conditions an LVAD speed increase can provide substantial benefits to exercise. A cardiorespiratory simulator was used to reproduce the average hemodynamics of LVAD patients at exercise. Then, a sensitivity study was conducted where cardiovascular parameters were changed individually ±20% of their baseline value at exercise (heart rate, left/right ventricular contractility, total peripheral resistance, and valve pathologies). Simulations were performed at a baseline LVAD speed of 2700 rpm and repeated at 3500 rpm to evaluate the benefits of a higher LVAD support on hemodynamics. Total cardiac output (TCO) was mostly impaired by a poor left ventricular contractility or vasodilation at exercise (−0.6 L/min), followed by a poor chronotropic response (−0.3 L/min) and by a poor right ventricular contractility (−0.2 L/min). LVAD speed increase better unloads the left ventricle and improves total cardiac output in all the simulated conditions. The most substantial benefits from LVAD speed increase were observed in case of poor left ventricular contractility (TCO + 1.6 L/min) and vascular dysfunction (TCO + 1.4 L/min) followed by lower heart rate (TCO + 1.3 L/min) and impaired right ventricular contractility (TCO + 1.1 L/min). Despite the presence of the LVAD, exercise hemodynamic is strongly depending on the ability of the cardiovascular system to adapt to exercise. A poor left ventricular inotropic response and a poor vascular function can strongly impair cardiac output at exercise. In these conditions, LVAD speed increase can be an effective strategy to augment total cardiac output and unload the left ventricle. These results evidence the need to design a physiological LVAD speed controller, tailored on specific patient’s needs.

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A Model of the Cardiorespiratory Response to Aerobic Exercise in Healthy and Heart Failure Conditions

Cited by 28 publications

References 38 publications

Exercise physiology with a left ventricular assist device: Analysis of heart-pump interaction with a computational simulator

Exercise physiology with a left ventricular assist device: Analysis of heart-pump interaction with a computational simulator

Control of a Pediatric Pulsatile Ventricular Assist Device: A Hybrid Cardiovascular Model Study

LVAD speed increase during exercise, which patients would benefit the most? A simulation study

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