Investigation of the Characteristics of HeartWare HVAD and Thoratec HeartMate II Under Steady and Pulsatile Flow Conditions

Abstract

The aim of this study was to elucidate the dynamic characteristics of the Thoratec HeartMate II (HMII) and the HeartWare HVAD (HVAD) left ventricular assist devices (LVADs) under clinically representative in vitro operating conditions. The performance of the two LVADs were compared in a normothermic, human blood-filled mock circulation model under conditions of steady (nonpulsatile) flow and under simulated physiologic conditions. These experiments were repeated using 5% dextrose in order to determine its suitability as a blood analog. Under steady flow conditions, for the HMII, approximately linear inverse LVAD differential pressure (H) versus flow (Q) relationships were observed with good correspondence between the results of blood and 5% dextrose under all conditions except at a pump speed of 9000 rpm. For the HVAD, the corresponding relationships were inverse curvilinear and with good correspondence between the blood-derived and 5% dextrose-derived relationships in the flow rate range of 2-6 L/min and at pump speeds up to 3000 rpm. Under pulsatile operating conditions, for each LVAD operating at a particular pump speed, an counterclockwise loop was inscribed in the HQ domain during a simulated cardiac cycle (HQ loop); this showed that there was a variable phase relationship between LVAD differential pressure and LVAD flow. For both the HMII and HVAD, increasing pump speed was associated with a right-hand and upward shift of the HQ loop and simulation of impairment of left ventricular function was associated with a decrease in loop area. During clinical use, not only does the pressure differential across the LVAD and its flow rate vary continuously, but their phase relationship is variable. This behavior is inadequately described by the widely accepted representation of a plot of pressure differential versus flow derived under steady conditions. We conclude that the dynamic HQ loop is a more meaningful representation of clinical operating conditions than the widely accepted steady flow HQ curve.

Influence of Impeller Speed Patterns on Hemodynamic Characteristics and Hemolysis of the Blood Pump

“…Compared with the steady-state H-Q curve, the H-Q curve corresponding to the three speed patterns could display the hemodynamic changes in the blood pump in the real situation more The relationship between the pressure head and the flow rate of the blood pump was different from that in the steady state. In the transient state, the H-Q curve between the pressure head and the flow rate was a closed loop, consistent with the results of previous studies [24]. The pressure head generated by the blood pump varied counterclockwise with the flow rate.…”

Flow features and device‐induced blood trauma in CF‐VADs under a pulsatile blood flow condition: A CFD comparative study

“…A larger pressure difference (~350 mmHg) was predicted for the extracorporeal CentVAD2, which is likely due to the higher resistance of the long tubing in an extracorporeal circuit. The time average values of the simulated pressure difference also closely matched the pressure difference values of the pressure head ( H ) and flow rate ( Q ) curves of the corresponding VADs at the flow rate of 4.5 L/min for the simulated pump speeds …”

“…The time average values of the simulated pressure difference also closely matched the pressure difference values of the pressure head (H) and flow rate (Q) curves of the corresponding VADs at the flow rate of 4.5 L/min for the simulated pump speeds. 17,26,27…”

HVAD Flow Waveform Morphologies: Theoretical Foundation and Implications for Clinical Practice

“…The rate of blood flow (Q) through any cfVAD (be it an axial or a centrifugal flow pump) is dictated by the pressure gradient (H) between the inlet and outlet ports and the rotational speed (revolutions per minute [RPMs]) of its impeller. 8 , 9 These relationships are depicted by “HQ curves”; HQ curves representative of the HVAD device are shown in Figure 1 . At a given RPM, flow decreases as the pressure gradient increases.…”