Numerical Study On Blood Damage Of Two-Stage Axial Blood Pump Pulsating During Heart Failure

Heart failure now is one of the highest mortality possibility among the cardiovascular disease. Heart transplantation became the only therapy to save the lives of these patients who have the end-stage heart failure. However, lacking of donors to heart transplantation, most of patients will go to die in the period of waiting for donors. Therefore, the axial blood pump was designed to support the patients with end-stage heart failure for maintaining the normal blood perfusion and cardiovascular circulation, to delay the patients’ lifetime.The high impeller rotation speed generated high shear stress, and damaged the blood in the axial blood pump with high damage degree. The miniatured axial blood pump used as percutaneous implantation has the strict restrictions in radial dimension, and small size limitation in axial direction. So the paper reduced the rotation speed by increasing the impeller stage, in order to seek the probability of decreasing blood damage within reaching assistance requirement. Simultaneously, as the left ventricle contracts and relaxes periodically, the cyclic pressure and flow in the inlet of the blood pump which made the blood pump operating in the pulsatile state and blood damage were unknown.In summary, this paper developed the evaluation method of the blood damage by combing the mathematical models of hemolysis with thrombosis. Otherwise, CFD calculations was used to explore the blood damage values of two-stage axial blood pump under the pulsatile state during heart failure. This paper mainly studied the two aspects as following:(1)The two-stage axial pump has been designed in two different diameter sizes, and subdivided into three kinds of combinations according to the different first level head. The single stage axial blood pump was used to compare the blood damage in the two stage ones. In the condition of inlet flow was 5 L/min and outlet pressure was 100 mmHg, we carried out the numerical simulation of those two styles of axial blood pumps. As a results, the blood damage of the two-stage axial blood pumps was worse than that of the single one when the diameter was14 mm; in the 8 mm diameter series, the hemolysis and of two-stage axial blood pump was better than the single one, but the platelet activation was worse. Compared the three different head combination in axial blood pumps, on the index of hemolysis level and platelet activation state, the design of the two-stage pump with the low and high-head impeller combination wasbetter than the two-stage pump with the equal heads, and the high and low-head impeller combination.(2) To understand the blood damage in a pulsatile flow caused by the blood pump, we established the multi-scale model of the blood pump with cardiovascular circulatory system.The cardiovascular circulation was simplified into a lumped parameter model of zero-dimensional scale, and the flow in the axial blood pump was modeled as a distributed parameter model of three-dimensional scale which combined these two models into a“multi-scale model”. MATLAB simulation of multi-scale model was used to obtain the transient pressure and flow during a cardiac cycle with the pump working under the condition of heart failure. According to internal blood pump hemodynamic characteristics,we divided the transient flow into multiple quasi-steady flows and used the quasi-steady flow to compute the hemolysis and platelet activation value based on a common used model. Finally, we calculated time-weighted average on hemolysis and platelet activation value of steady states to obtain the average hemolysis and platelet activation value in one cardiac cycle. The study showed that the method of multi-scale model can be used to estimate the average hemolysis and platelet activation value of the blood pump supporting patient with heart failure.