Figure 3 presents plots of pressure rise vs. pump flow relationship under various pump speeds. The reproducibility of DexAide pump performance and the interchangeability of the three main pump components were demonstrated by the small standard deviation in pump performance for the 5 combinations. The pressure rise and pump flow exhibit an inverse relationship as commonly observed with rotary blood pumps. The shaded area shows our target operating range of 2 to 6 L/min pump flow and 20 to 60 mm Hg pressure rise. This range was covered with pump speeds between 1,800 and 3,200 rpm. The nominal design point of 4 L/min and 40 mm Hg pressure rise was met at 2,450 ± 70 rpm.
The corresponding pump power vs. pump flow plots are presented in Figure 4. Power consumption increased linearly with increasing pump flow, and the slope of the relationship is higher at higher pump speed. Power consumption was 1.6 ± 0.1 watts at the minimum operating condition of 2 L/min and 20 mm Hg pressure rise and 5.1 ± 0.3 watts at the maximum operating condition of 6 L/min and 60 mm Hg pressure rise. Power consumption at the design point of 4 L/min and 40 mm Hg pressure rise was 3.0 ± 0.2 watts. The normalized pump power vs. pump flow relationship is shown in Figure 5. The linear relationships are almost identical in various pump speeds except for those at 1,800 rpm.
As shown in Figure 6, the reduced impeller size resulted in reduced efficiency. Overall pump efficiency at the nominal design condition was about 10% in the DexAide, compared to 20% for the CorAide. This reduction in efficiency occurs because the pump losses (bearing, secondary impeller, rotating assembly windage) are nearly the same as for the CorAide LVAD while the nominal hydraulic output is about one third of the LVAD’s.
Figure 7 shows the instantaneous relationship between pressure rise vs. pump flow in the pulsatile mock circulatory system for three cardiac cycles of the pneumatic, pulsatile VAD at a beat rate of 70 bpm with the DexAide pump speed set at 2,400 rpm. Although the data showed some hysteresis (thin line), both the maximum flow data point (ejection phase of the pneumatic VAD) and minimum flow data point (filling phase of the pneumatic VAD) were the same as that was obtained in the nonpulsatile circulatory system (thick line). Furthermore, the mean pressure rise vs. mean pump flow for the three pulsatile cardiac cycles (a closed circle) was almost on the line that was obtained in the nonpulsatile circulatory system.Figure 8 shows similar data but with a pneumatic VAD beat rate set at 120 bpm. Again, the data obtained from the pulsatile mock circulatory system were very similar to those obtained in the nonpulsatile circulatory system. The swing of the pump flow (between 4.6 L/min and 6.5 L/min) during the cardiac cycles of the pneumatic, pulsatile VAD was much less than that observed with the VAD at a beat rate of 70 bpm (between 2.7 L/min and 7.0 L/min).