Flow Modulation Algorithms for Continuous Flow Left Ventricular Assist Devices to Increase Vascular Pulsatility: A Computer Simulation Study

Abstract

Continuous flow (CF) left ventricular assist devices (LVAD) support diminishes vascular pressure pulsatility. Despite its recent clinical success CF LVAD support has been associated with a higher incidence of gastrointestinal bleeding, aortic valve dysfunction and hemorrhagic strokes. To overcome this limitation, we are developing algorithms to provide vascular pulsatility using a CF LVAD. The effects of timing and synchronizing the CF LVAD flow modulation to the native myocardium, modulation amplitude, and modulation widths were studied on the native ventricle and vasculature using a computer simulation model of the circulatory system simulating heart failure. A total of over 150 combinations of varying pulse widths, beat frequencies, time shifts, and amplitudes to modulate CF LVAD flow were tested. All control algorithms maintained a mean CF LVAD flow of 5.0 ± 0.1 L/min (full support) or 2.5 ± 0.1 L/min (partial support). These algorithms resulted in an increased arterial pressure pulsatility of up to 59 mmHg, reduced left ventricular external work (LVEW) by 10-75%, and increased myocardial perfusion by up to 44% from baseline heart failure condition. Importantly, reduction in LVEW and increase in pulsatility may be adjusted to userdefined values while maintaining the same average CF LVAD flow rate. These methods of CF LVAD flow modulation may enable tailored unloading of the native ventricle to provide rest and rehabilitation (maximal unloading to rest followed by gradual reloading to wean), which may promote sustainable myocardial recovery. Further, these LVAD flow modulation patterns may reduce the incidence of adverse events associated with the CF LVAD therapy by increasing vascular pulsatility.

RPM and flow modulation for a continuous flow left ventricular assist device to increase vascular pulsatility : a computer simulation, mock circulation, and in-vivo animal study.

“…The effects of synchronizing and timing of the modulation of LVAD motor speeds/flow to the native myocardium, modulation amplitude, and modulation width have only recently been reported as a byproduct of this thesis work [44].…”

Development of a physiologic ex vivo vessel perfusion system.

“…A 'full flow' VAD condition set at 3800 rpm was added in an attempt to significantly reduce any remaining pulse pressure and completely unload the ventricle. Prior to the administration of pulsatile flow algorithms, a modified heart failure condition was created to match the exact parameters used in previous work 84 . Pulsatile flow algorithms at 2900 +/-1100 rpm and 3200 +/-800 rpm were then added.…”

“…Pulsatile flow algorithms at 2900 +/-1100 rpm and 3200 +/-800 rpm were then added. As detailed previously 85 , the first condition allowed for the maximum rpm modulation, while the second condition provided full unloading of the ventricle. These two conditions were run both asynchronously at periods of 0.4, 0.5, 0.8, and 1.6 seconds and synchronously.…”

“…The data was analyzed using the HEART program, an automated beat-to-beat cardiovascular analysis package using Matlab 86 , along with additional custom Matlab programs developed for the analysis of pulsatile VAD waveforms 85 . This beat analysis allowed for the calibration of data channels, the calculation of various peaks, averages, and pulses, and the creation of data plots.…”

“…However, they still remained slightly higher than the pulse pressures that have been As one of the primary advantages of this system is its ability to create a multitude of VAD-specific waveforms, a laptop fitted with a VAD pulsatility program was then connected to the system as the VAD controller. Prior to the VAD pulsation data sets, an altered heart failure state was created to match the state established by Ising in previous research 85 . As detailed in the previous section, the VAD was pulsed asynchronously and synchronously at varying time periods and levels of rpm modulation.…”