Kazumi Mizuguchi

The Baylor total artificial heart. Flow visualization studies.

To analyze the flow patterns of the left blood chamber of the Baylor total artificial heart (TAH) and to evaluate influences of the inflow valve angle to the flow patterns, flow visualization studies were performed. The inflow valve angle of the left housing was changed by 20 degrees orthogonal to the inflow tube, and comparison studies of the modified and unmodified models were made. For evaluating sectional flow patterns, a laser light was used, the clear transparent housing was scanned segmentally, and flow patterns were recorded on high contrast film for measuring flow velocities. A signal was used that synchronized the timing of the camera shutter to the pusher-plate movement signal. With the modified 20 degree inflow valve direction, there were better closing characteristics of the inflow valve leaflets. At the same time, we could successfully reduce the vortex formation at the inflow port, which may cause thrombus formation. We also have improved the washout during the diastolic phase in not only the bottom area, but in the entire pumping chamber. This flow visualization setup is simple and inexpensive. It is useful not only for validation of global flow patterns, but also for validation of local flow velocities of various blood pumps.

The Baylor-ABI Electromechanical Total Artificial Heart: Accelerated Endurance Testing

To test the durability of each part or assembled component of the Baylor-ABI total artificial heart (TAH), the authors performed an endurance test under severe conditions. The TAH was immersed in a saline bath at 42 degrees C, which is 4-5 degrees C higher than normal body temperature. This is an accelerated endurance test because of the elevated temperatures. In this accelerated endurance test loop, the 42 degrees C heated saline was circulated not only in the pump but also outside the pump. During pumping, temperatures of the motor and outside surface of the centerpiece were continuously measured. This testing showed that during almost 4 months of pumping no electromechanical troubles were observed. Both inside (motor) and outside temperatures were stable and the differences in both temperatures were only 3-4 degrees C, demonstrating that heat generation is not a problem. The voltage and current required in this system remained constant, indicating stable and reliable performance. Based on these results, this pump is expected to run continuously over a long duration in a normal physiologic environment. This accelerated endurance test system is very suitable for estimating the influence of heat generation by the actuator of blood pumps. It is also quite useful in validating the durability of various cardiac prosthesis.

Phase 1 Ex Vivo Studies of the Baylor/NASA Axial Flow Ventricular Assist Device

The Baylor/NASA ventricular assist device (VAD) is a small, electrically driven, valveless axial flow pump that is implantable inside the chest cavity. It is intended to assist a diseased heart. In the phase 1 study of this pump development program, the 2-day pump is intended to produce an assist device for cardiopulmonary bypass (CPB) application. The main focus of this phase of the program was to develop a pump which produced minimum blood trauma. Antithrombogenic features are planned to be incorporated into the phase 2 pump. In this phase 1 study, eight pumps were implanted paracorporeally in two calves as LVADs to assess hemolysis, pump performance, efficiency, and stability, the goal for this study being a 2-day implantation. The pump running times ranged from 18 to 203 (78.1 ± 23.7; mean ± SE) h. Plasma free hemoglobin levels were below 13.7 mg/di, except for one case complicated by inflow cannula obstruction due to pannus formation. Pump speed was maintained between 10100 and 11400rpm. Pump output ranged from 3.6 to 5.11/min. The electrical power required by the system ranged from 10.5 to 12.8W. No detectable organ dysfunction was noted and postmortem evaluations demonstrated no pump-related adverse effects in any of the calves. Thrombus deposition was observed mainly at the hub area and flow straightener. For the next series of experiments (phase 2), the thrombogenic regions in these subacute experiments should be eliminated.