Rotary blood pump flow spontaneously increases during exercise under constant pump speed: Results of a chronic study

Many types of rotary blood pumps and pump control methods have recently been developed with the goal of clinical use. From experiments, we know that pump flow spontaneously increases during exercise without changing pump control parameters. The purpose of this study was to determine the hemodynamics associated with the long-term observation of calves implanted with centrifugal blood pumps (EVAHEART, Sun Medical Technology Research Corporation, Nagano, Japan). Two healthy female Jersey calves were implanted with devices in the left thoracic cavity. A total of 22 treadmill exercise tests were performed after the 50th postoperative day. During exercise, the following parameters were compared with conditions at rest: heart rate, blood pressure, central venous oxygen saturation (SvO₂), pump speed, and pump flow. The pump flow in a cardiac cycle was analyzed by separating the systole and diastole. Compared to the base data, statistically significant differences were found in the following interrelated parameters: the heart rate (66.8 ± 5.2 vs. 106 ± 9.7 bpm), mean pump flow (4.8 ± 0.2 vs. 7.0 ± 0.3 L/min), and volume of pump flow in diastole (26.0 ±1.8 vs. 13.5 ± 2.5 ml). During exercise, the volume of pump flow in systole was 3 times larger than that measured in diastole. Blood pressure, SvO₂, and pump speed did not change significantly from rest to exercise. These results suggested that the mean pump flow depends on the systolic pump flow. Therefore, the increase in the mean pump flow during exercise under constant pump speed was caused by an increase in the heart rate.