Influence of left ventricular assist device pressure-flow characteristic on exercise physiology: Assessment with a verified numerical model

Abstract

Current left ventricular assist devices are designed to reestablish patient’s hemodynamics at rest but they lack the suitability to sustain the heart adequately during physical exercise. Aim of this work is to assess the performance during exercise of a left ventricular assist device with flatter pump pressure-flow characteristic and increased pressure sensitivity (left ventricular assist device 1) and to compare it to the performance of a left ventricular assist device with a steeper characteristic (left ventricular assist device 2). The two left ventricular assist devices were tested at constant rotational speed with a verified computational cardiorespiratory simulator reproducing an average left ventricular assist device patient response to exercise (EXE↑) and a left ventricular assist device patient with no chronotropic and inotropic response (EXE→). According to the results, left ventricular assist device 1 pumps a higher flow than left ventricular assist device 2 both at EXE↑ (6.3 vs 5.6 L/min) and at EXE→ (6.7 vs 6.1 L/min), thus it better unloads the left ventricle. Left ventricular assist device 1 increases the power delivered to the circulation from 0.63 W at rest to 0.67 W at EXE↑ and 0.82 W at EXE→, while left ventricular assist device 2 power shows even a minimal decrease. Left ventricular assist device 1 better sustains exercise hemodynamics and can provide benefits in terms of exercise performance, especially for patients with a poor residual left ventricular function, for whom the heart can hardly accommodate an increase of cardiac output.

Hemodynamic exercise responses with a continuous-flow left ventricular assist device: Comparison of patients’ response and cardiorespiratory simulations

“…The model of the LVAD was implemented according to the in-vitro measurements with a HVAD pump reported in [16] and connected between the left ventricle and the aorta (see Fig 2) [ [20][21][22].…”

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

“…16. For the pump a second‐order polynomial equation was used to reproduce the pressure‐flow characteristics, in line with the in vitro measurements reported in Ref. 17.…”

“…The model included an inflow cannula (diameter 1.9 cm and length 2.5 cm) and outflow graft (diameter 0.9 cm and length 20 cm), each modeled with an inertance and a resistance as reported in Ref. 16. For the pump a second‐order polynomial equation was used to reproduce the pressure‐flow characteristics, in line with the in vitro measurements reported in Ref.…”

Pressure, Flow Rate and Operating Speed Characteristics of a Continuous Flow Left Ventricular Assist Device During Varying Speed Support

“…Therefore, CF-LVAD Q-n and H-n characteristics need to be considered as well for the proposed varying speed CF-LVAD support modes to estimate the pump variables. Another study by Graefe et al [25] found that CF-LVAD H-Q characteristics play a role on the unloading of the left ventricle during exercise, therefore, sustaining exercise capacity of a failing heart also depends on the CF-LVAD H-Q characteristics under constant speed pump support. CF-LVAD pressure sensitivity also plays a role on the left ventricular unloading, thus afterload of the right ventricle [26].…”