High-frequency operation of pulsatile ventricular assist devices: A computational study on circular and elliptically shaped pumps

Abstract

Pulsatile positive displacement pumps as ventricular assist devices were gradually replaced by rotary devices due to their large volume and high adverse event rates. Nevertheless, pulsatile ventricular assist devices might be beneficial with regard to gastrointestinal bleeding and cardiac recovery. Therefore, aim of this study was to investigate the flow field in new pulsatile ventricular assist devices concepts with an increased pump frequency, which would allow lower stroke volumes to reduce the pump size. We developed a novel elliptically shaped pulsatile ventricular assist devices, which we compared to a design based on a circular shape. The pump size was adjusted to deliver similar flow rates at pump frequencies of 80, 160, and 240 bpm. Through a computational fluid dynamics study, we investigated flow patterns, residence times, and wall shear stresses for different frequencies and pump sizes. A pump size reduction by almost 50% is possible when using a threefold pump frequency. We show that flow patterns inside the circular pump are frequency dependent, while they remain similar for the elliptic pump. With slightly increased wall shear stresses for higher frequencies, maximum wall shear stresses on the pump housing are higher for the circular design (42.2 Pa vs 18.4 Pa). The calculated blood residence times within the pump decrease significantly with increasing pump rates. A smaller pump size leads to a slight increase of wall shear stresses and a significant improvement of residence times. Hence, high-frequency operation of pulsatile ventricular assist devices, especially in combination with an elliptical shape, might be a feasible mean to reduce the size, without any expectable disadvantages in terms of hemocompatibility.

A Novel Hybrid Membrane VAD as First Step Toward Hemocompatible Blood Propulsion

“…The flow conditions in the pump were analyzed for different operating conditions in Refs. 18 and 20 and compared with those of a conventional circularly shaped pump chamber indicating improved conditions of WSS for the present elliptical design. Figure 2 shows examples of streamlines obtained from the integration of the corresponding velocity fields during the diastolic phase.…”

“…Upon actuation, the central region of the membrane is cyclically exposed to high levels of WSS (up to 15 Pa) and WD (up to 16% areal strain range), see Refs. 18 and 20 . This demanding interface was therefore selected as benchmark to test endothelialization performance.…”

“…The numerical analysis was applied to estimate mechanical strain and fluid stress during pump operation. 20 Particle tracking velocimetry (PTV) measurements were performed to validate the predicted velocity fields (Fig. 3 ) as previously reported.…”

“…[18][19][20] The WSS at the contacting surface was investigated by performing a non-steady state CFD study of the pump at two operation frequencies of 120 bpm and 240 bpm with a stroke volume of 30 mL. 20 The results of these calculations, along with those of corresponding finite element simulations of the membrane deformation (see Supplementary Methods) were used to select the portion of the membrane to be covered with endothelial cells. The initial membrane shape was assumed to be flat in order to reduce the complexity of the CFD model.…”

Short‐term physiological response to high‐frequency‐actuated pVAD support

“…Figure shows an exploded view of the 3D‐printed pVAD prototype used. The design is based on the CFD studies by Loosli et al and features in‐ and outlet valves situated coaxially and an elliptical membrane with corrugations designed to increase the displacement volume for a given strain limit. The pump housing is shaped such as to reduce the WSS and to improve blood flow conditions for endothelialization.…”