Mechanical unloading with a miniaturized axial flow pump (hemopump): an experimental study

Modelling in the study of interaction of Hemopump device and artificial ventilation

The aim of this work is to evaluate in different ventricular conditions the influence of joint mechanical ventilation (MV) and Hemopump assistance. To perform this study, we used a computer simulator of human cardiovascular system where the influence of MV was introduced changing thoracic pressure to positive values. The simulation confirmed that haemodynamic variables are highly sensitive to thoracic pressure changes. On the other hand, Hemopump assistance raises, among the others, mean aortic pressure, total cardiac output (left ventricular output flow plus Hemopump flow) and coronary flow. The simulation showed that the joint action of Hemopump and positive thoracic pressure diminishes these effects.

Simulation study of the Hemopump as a cardiac assist device

A dynamic model was developed for a Hemopump that withdraws blood from the left ventricle and discharges it to the aorta through a miniature axial-flow pump. Incorporation of the Hemopump model in a previously established model for the canine circulatory system enabled the effects of the Hemopump on various haemodynamic variables of the circulatory system to be studied, and the benefit of the Hemopump to the failing heart was investigated. In addition, the influence of the physiological status of the right ventricle on the Hemopump performances was examined, and the synchronous and non-synchronous operations of the Hemopump were compared. Results verified that the Hemopump assists the failing heart by increasing the oxygen supply, while reducing the oxygen consumption of the heart through a reduction in the workload of the left ventricle. These beneficial effects were enhanced when the pump's rotation speed was increased. When pump speed was increased from 17,000 to 23,000 revolutions min-1, the oxygen supply increased 101%, and the oxygen consumption decreased 60%. However, when the pump rotation speed was too high, the inflow to the pump could be impaired and the pump performance could be negatively affected. Predications from the model were in good agreement with the results previously obtained in animal experiments and in vitro measurements.

Centrifugal pumps as left ventricular assist for coronary revascularization on a beating heart

During recent years, coronary bypass surgery has progressed toward minimizing invasiveness. One important feature of this approach is performing surgery on a beating heart. During the crucial phase of such surgery, the mechanical support of the heart with a left ventricular assist device (LVAD) is a possible option. During the period from October 1, 1994 until June 30, 1997, we employed a centrifugal pump system in 118 cases of coronary artery bypass graft (CABG) procedures with LVAD support (mechanically supported CABG [SUPPCAB]). A total of 179 distal anastomoses with an average of 1.5 +/- 0.5 coronary anastomoses per patient was performed. Three types of pumps were used: 23 BioPump, 87 Isoflow, and 8 Capiox systems. The median time on mechanical support was 44 min (range, 16-116 min). The mean flow rate during support time was 3.5 +/- 0.8 L/min, which results in a calculated flow of 1.7 +/- 0.6 L/min/m2 body surface area (BSA). The average flow was 3.2 +/- 0.8 L/min with the BioPump and 3.7 +/- 0.8 L/min with the Isoflow pump, respectively (p < 0.01). The mean arterial pressure during mechanical support was 75 +/- 12 mm Hg. In 2 patients, the pump system was kept running postoperatively in the ICU. Eight of the patients received operations under resuscitation or in cardiogenic shock. Nine (7.9%) of the patients did not survive the early postoperative phase. For coronary revascularization of the anterolateral and diaphragmatic parts of the heart, the SUPPCAB procedure is feasible with excellent mechanical support of the heart by centrifugal pumps. Especially in high risk cases, this procedure can be recommended.