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Modulation of pump speed has been proposed and implemented clinically to improve vascular pulsatility in continuous flow ventricular assist device patient. The flow dynamics of the HVAD with a promising asynchronous pump speed modulation and its potential risk for device-induced blood trauma was investigated numerically. The boundary conditions at the pump inlet and outlet were defined using the pressure waveforms adapted from the experimentally recorded ventricular and arterial pressure waveforms in a large animal ischemic heart failure (IHF) model supported by the HVAD operated at constant and modulated pump speeds. Shear stress fields and hemolysis indices were derived from the simulated flow fields. The overall features of the computationally generated flow waveforms at simulated constant and pulse-modulated speed operations matched with those of the experimentally recorded flow waveforms. The simulations showed that the shear stress field and hemolysis index vary throughout the cardiac cycle under the constant speed operation, and also as a function of modulation profile under modulated speed operation. The computational model did not demonstrate any differences in the time average hemolysis index between constant and modulated pump speed operations, thereby predicting pulse-modulated speed operation may help to restore vascular pulsatility without any further increased risk of blood trauma. Graphical abstract The streamline inside the HVAD pump and the wall shear stress distribution on the impeller surface at six discrete time instants over one cardiac cycle under constant speed operation (3000 rpm) (a) and under pulse-modulated speed operation (b). c Computationally predicted flow rate waveform under pulse-modulated speed operation. d Computationally predicted time-varying HI generated by the HVAD pump under the two operation modes constant speed (dash line) and pulse-modulated speed (solid line). These figures indicate that the pulse-modulated speed operation may help to restore vascular pulsatility without any further increased risk of blood trauma.

In this study, the flow features and device-associated blood trauma in 4 clinical ventricular assist devices (VADs; 2 implantable axial VADs, 1 implantable centrifugal VAD, and 1 extracorporeal VAD) were computationally analyzed under clinically relevant pulsatile flow conditions. The 4 VADs were operated at fixed pump speed at a mean rate of 4.5 L/min. Mean pressure difference, wall shear stress, volume distribution of scalar shear stress (SSS), and shear-induced hemolysis index (HI) were derived from the flow field of each VAD and were compared. The computationally predicted mean pressure difference across the 3 implantable VADs was ~70 mmHg, and the extracorporeal VAD was ~345 mmHg, which matched well with their reported pressure-flow curves. The axial VADs had higher mean wall shear stress and SSS compared with the centrifugal VADs. However, the residence time of the centrifugal VADs was much longer compared with the axial VADs because of the large volume of the centrifugal VADs. The highest SSS was observed in one axial VAD, and the longest exposure time was observed in 1 centrifugal VAD. These 2 VADs generated the highest HI. The shear-induced HI varied as a function of flow rate within each cardiac cycle. At fixed pump speed, the HI was greatest at low flow rate due to longer exposure time to shear stress compared with at high flow rate. Subsequently, we hypothesize that to reduce the risk of blood trauma during VAD support, shear stress magnitude and exposure time need to be minimized., (Copyright © 2017 John Wiley & Sons, Ltd.)