Hemolysis is the main complication of blood pump ventricular assist. Aiming at the most widely used rotary blood pump, this paper summarizes and analyzes the main influencing factors of hemolysis: the shear stress and exposure time of red blood cells. In addition, local negative pressure, temperature and other factors will also affect hemolysis. And then this paper summarizes the research progress of prediction and improvement methods of hemolysis performance: different combinations of hemolysis prediction model and empirical constant will cause different differences in prediction results. Compared with the power law model, the OPO model can consider the complexity of turbulence more. The research on improving the hemolysis performance mainly focuses on the optimization of the blood pump structure (such as pump clearance, impeller, guide vane, etc.). A few scholars have also studied the hemolysis performance of the blood pump through the reasonable selection of the speed control mode of the blood pump and the blood compatibility materials. Finally, the paper discusses the limitations of current hemolysis research and prospects for future research.
Regurgitation is an abnormal condition happens when left ventricular assist devices (LVADs) operated at a low speed, which causes LVAD to fail to assist natural blood-pumping by heart and thus affects patients’ health. According to the degree of regurgitation, three LVAD’s regurgitation states were identified in this paper: no regurgitation, slight regurgitation and severe regurgitation. Regurgitation index (RI), which is presented based on the theory of dynamic closed cavity, is used to grade the regurgitation of LVAD. Numerical results showed that when patients are in exercising, resting and sleeping state, the critical speed between slight regurgitation and no regurgitation are 6 650 r/min, 7 000 r/min and 7 250 r/min, respectively, with corresponding RI of 0.401, 0.300 and 0.238, respectively. And the critical speed between slight regurgitation and severe regurgitation are 5 500 r/min, 6 000 r/min and 6 450 r/min, with corresponding RI of 0.488, 0.359 and 0.284 respectively. In addition, there is a negative relation correction between RI and rotational speed, so that grading the LVAD’s regurgitation can be achieved by determining the corresponding critical speed. Therefore, the detective parameter RI based on the signal of flow is proved to be able to grade LVAD’s regurgitation states effectively and contribute to the detection of LVAD’s regurgitation, which provides theoretical basis and technology support for developing a LVADs controlling system with high reliability.
Right ventricular (RV) failure has become a deadly complication of left ventricular assist device (LVAD) implantation, for which desynchrony in bi-ventricular pulse resulting from a LVAD is among the important factor. This paper investigated how different control modes affect the synchronization of pulse between LV (left ventricular) and RV by numerical method. The numerical results showed that the systolic duration between LV and RV did not significantly differ at baseline (LVAD off and cannula clamped) (48.52% vs. 51.77%, respectively). The systolic period was significantly shorter than the RV systolic period in the continuous-flow mode (LV vs. RV: 24.38% vs. 49.16%) and the LV systolic period at baseline. The LV systolic duration was significantly shorter than the RV systolic duration in the pulse mode (LV vs. RV: 28.38% vs. 50.41%), but longer than the LV systolic duration in the continuous-flow mode. There was no significant difference between the LV and RV systolic periods in the counter-pulse mode (LV vs. RV: 43.13% vs. 49.23%). However, the LV systolic periods was shorter than the no-pump mode and much longer than the continuous-flow mode. Compared with continuous-flow and pulse mode, the reduction in rotational speed (RS) brought out by counter-pulse mode significantly corrected the duration of LV systolic phase. The shortened duration of systolic phase in the continuous-flow mode was corrected as re-synchronization in the counter-pulse mode between LV and RV. Hence, we postulated that the beneficial effects on RV function were due to re-synchronizing of RV and LV contraction. In conclusion, decreased RS delivered during the systolic phase using the counter-pulse mode holds promise for the clinical correction of desynchrony in bi-ventricular pulse resulting from a LVAD and confers a benefit on RV function.