Relationship of blood pressure and pump flow in an implantable centrifugalblood pump during hypertension

The purpose of this study was to evaluate the real time relationship betwee n pump flow and pump differential pressure (D-P) during experimentally indu ced hypertension (HT). Two calves (80 and 68 kg) were implanted with the EV A-HEART centrifugal blood pump (SunMedical Technology Research Corp., Nagan o, Japan) under general anesthesia. Blood pressure (BP) in diastole was inc reased to 100 mm Hg by norepinephrine to simulate HT. Pump flow, D-P, EGG, and BP were measured at pump speeds of 1,800, 2,100, and 2,300 rpm. All dat a were separated into systole and diastole, and pump flow during HT was com pared with normotensive (NT) conditions at respective pump speeds. Diastoli c BP was increased to 99.3 +/- 4.1 mm Hg from 66.5 +/- 4.4mm Hg (p < 0.01). D-P in systole was under 40 mm Hg (range of change was 10 to 40 mm Hg) eve n during HT. During NT, the average systolic pump flow volume was 60% of th e total pump flow. However, during HT, the average systolic pump flow was 1 00% of total pump flow volume, although the pump flow volume in systole dur ing HT decreased (33.1 +/- 5.7 vs 25.9 +/- 4.0 ml/systole, p < 0.01). In di astole, the average flow volume through the pump was 19.6 +/- 6.9 ml/diasto le during NT and -2.2 +/- 11.1 ml/diastole during HT (p < 0.01). The change in pump flow volume due to HT, in diastole, was greater than the change in pump flow in systole at each pump speed (p < 0.001). This study suggests t hat the decrease of mean pump flow during HT is mainly due to the decrease of the diastolic pump flow and, to a much lesser degree, systolic pump flow .