Restoring pulsatility and peakVO<sub>2</sub> in the era of continuous flow, fixed pump speed, left ventricular assist devices: ‘A hypothesis of pump's or patient's speed?’

Laoutaris, Ioannis D.

doi:10.1177/2047487319856448

Cited by 6 publications

(6 citation statements)

References 66 publications

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“…An overview on the effect of LVAD speed increase on peak exercise was reported by Laoutaris . In two studies a positive increase in peak oxygen consumption was found, 11 studies reported moderate increase within the range of 7–9%, two studies reported little or no effect on TCO and five studies did not observe significant differences in oxygen consumption at peak exercise.…”

Section: Effects Of Lvad Speed Increase In Different Exercise Profilesmentioning

confidence: 95%

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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Section: Effects Of Lvad Speed Increase In Different Exercise Profilesmentioning

confidence: 95%

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

et al. 2019

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“…Due to the still unclear picture of maximal and submaximal exercise tests, pre-and/or post-LVAD implantation, further studies have been conducted (34,39,40). Exercise test results and their potential for risk stratification would provide important clinical insights (17,21,41).…”

Section: Submaximal Vs Maximal Exercisementioning

confidence: 99%

Exercise physiology in left ventricular assist device patients: insights from hemodynamic simulations

Fresiello

Gross

Jacobs

2021

Ann Cardiothorac Surg

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Left ventricular assist devices (LVADs) assure longer survival to patients, but exercise capacity is limited compared to normal values. Overall, LVAD patients show high wedge pressure and low cardiac output during maximal exercise, a phenomenon hinting at the need for increased LVAD support. Clinical studies investigating the hemodynamic benefits of an LVAD speed increase during exercise, ended in inhomogeneous and sometimes contradictory results. The native ventricle-LVAD interaction changes between rest and exercise, and this evolution is complex, multifactorial and patient-specific. The aim of this paper is to provide a comprehensive overview on the patient-LVAD interaction during exercise and to delineate possible therapeutic strategies for the future. A computational cardiorespiratory model was used to simulate the hemodynamics of peak bicycle exercise in LVAD patients. The simulator included the main cardiovascular and respiratory impairments commonly observed in LVAD patients, so as to represent an average hemodynamic response to exercise. In addition, other exercise responses were simulated, by tuning the chronotropic, inotropic and vascular functions, and implementing aortic regurgitation and stenosis in the simulator. These profiles were tested under different LVAD speeds and LVAD pressure-flow characteristics.Simulations output showed consistency with clinical data from the literature. The simulator allowed the working condition of the assisted ventricle at exercise to be investigated, clarifying the reasons behind the high wedge pressure and poor cardiac output observed in the clinics. Patients with poorer inotropic, chronotropic and vascular functions, are likely to benefit more from an LVAD speed increase during exercise.Similarly, for these patients, a flatter LVAD pressure-flow characteristic can assure better hemodynamic support under physical exertion. Overall, the study evidenced the need for a patient-specific approach on supporting exercise hemodynamics. In this frame, a complex simulator can constitute a valuable tool to define and test personalized speed control algorithms and strategies.

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“…This objective constitutes a compromise function that aims for ventricular unloading and ensures the opening of the aortic valve. A permanent closure of the aortic valve may lead to fusion of the aortic valvular cusps and a resulting thrombus formation [10]. By ventricular unloading we refer to reducing the hydraulic work that the LV has to perform in order to provide sufficient perfusion.…”

Section: Optimal Control Problem Formulationmentioning

confidence: 99%

A Personalized Switched Systems Approach for the Optimal Control of Ventricular Assist Devices based on Atrioventricular Plane Displacement

Zeile

Rauwolf

Schmeißer

et al. 2020

Preprint

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Objective: A promising treatment for congestive heart failure is the implementation of a left ventricular assist device (LVAD) that works as a mechanical pump. Modern LVADs work with adjustable constant rotor speed and provide therefore continuous blood flow; however, recently undertaken efforts try to mimic pulsatile blood flow by oscillating the pump speed. This work proposes an algorithmic framework to construct and evaluate optimal pump speed policies. Methods: We use a model that captures the atrioventricular plane displacement, which is a physiological indicator for heart failure. We employ mathematical optimization to adapt this model to patient specific data and to find optimal pump speed policies with respect to ventricular unloading and aortic valve opening. To this end, we reformulate the cardiovascular dynamics into a switched system and thereby reduce nonlinearities. We consider system switches that stem from varying the constant pump speed and that are state dependent such as valve opening or closing. Results: As a proof of concept study, we personalize the model to a selected patient with respect to ventricular pressure. The model fitting results in a root-mean-square deviation of about 6 mmHg. Optimized constant and piecewise constant rotor speed profiles improve the default initialized solution by 31% and 68% respectively. Conclusion: These in silico findings demonstrate the potential of personalized hemodynamical optimization for the LVAD therapy. Significance: LVADs and their optimal configuration are active research fields. Mathematical optimization enhances our understanding of how LVADs should provide pulsatility.

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Restoring pulsatility and peakVO₂ in the era of continuous flow, fixed pump speed, left ventricular assist devices: ‘A hypothesis of pump's or patient's speed?’

Cited by 6 publications

References 66 publications

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

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

Exercise physiology in left ventricular assist device patients: insights from hemodynamic simulations

A Personalized Switched Systems Approach for the Optimal Control of Ventricular Assist Devices based on Atrioventricular Plane Displacement

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Restoring pulsatility and peakVO2 in the era of continuous flow, fixed pump speed, left ventricular assist devices: ‘A hypothesis of pump's or patient's speed?’

Cited by 6 publications

References 66 publications

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

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

Exercise physiology in left ventricular assist device patients: insights from hemodynamic simulations

A Personalized Switched Systems Approach for the Optimal Control of Ventricular Assist Devices based on Atrioventricular Plane Displacement

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Restoring pulsatility and peakVO₂ in the era of continuous flow, fixed pump speed, left ventricular assist devices: ‘A hypothesis of pump's or patient's speed?’