Chang-Hee Park

Development of a magnetically suspended centrifugal pump as a cardiac assist device for long-term application

To overcome problems with the shaft seal in conventional centrifugal pumps, the authors have been developing a magnetically suspended centrifugal pump (MSCP) that operates as a valveless, sealless, and bearingless pump. The prototype of the MSCP was modified with respect to size of the volute diffuser and impeller blade profiles. A hemolysis test in vitro using a new version of the MSCP was performed in comparison with a commercially available centrifugal pump. The test circuit for the hemolysis test comprised a blood reservoir, a pump, and polyvinyl tubes, and was filled with fresh heparinized bovine blood. The pumping conditions were a flow rate of 5 L/min and a pump head afterload of 100 tnmHg. The index of hemolysis in the MSCP was significantly lower than that in the Biomedicus pump (0.0035 ± 0.0025 versus 0.0097 ± 0.0056 g/100 L, p<0.05). Reduction in the platelet count during pumping also was lower in the MSCP compared with the Biomedicus pump at both 6 hrs and 12 hrs of pumping (p<0.01). This MSCP may be advantageous for extended use of assist devices, not only from the theoretical point of view, but in a practical sense after the results of the current hemolysis test.

In vivo testing of a magnetically suspended centrifugal pump designed for long-term use.

The life of currently-available centrifugal pumps is limited to no more than three days. As a magnetically suspended centrifugal pump (MSCP) contains no shaft or seal, it could be expected to have a longer life expectancy. The MSCP was evaluated in a chronic animal model using eight adult sheep. Left ventricular assist with the MSCP was instituted between the left atrium and the descending aorta. The flow rates ranged from 2.5 to 6.0 L/min. The duration of the experiments ranged from 14 to 60 days. No mechanical failure occurred. The plasma free hemoglobin levels remained within an acceptable range (3-19 mg/dL). No reduction in the counts of red blood cells or platelets was observed. Thrombus formation within the MSCP was recognized in one pump. The main reason for termination was thromboembolism derived from the circuits. Three types of regulation methods (constant rotational speed, constant motor current, and controlled motor current) were also investigated. Regulation by a constant motor current mode altered the pressure-flow (P-Q) characteristics, and thereby, a steadier pump flow was obtained compared with regulation in the constant rotational speed mode. Moreover, the controlled motor current mode can change the P-Q relationship. These results demonstrate that the MSCP is a promising device for long-term use.

A magnetically suspended centrifugal pump. In vitro and in vivo assessment.

To overcome problems derived from the shaft within conventional centrifugal pumps, we have developed a new centrifugal pump, the magnetically suspended centrifugal pump (MSCP), which has no shaft and operates as a bearingless centrifugal pump. The impeller is suspended freely and centrally by magnetic force within the pump. Hemolysis tests were performed in comparison with the Biopump. Index of hemolysis and destruction of platelets were significantly lower in the MSCP than in the Biopump. Animal studies were designed to evaluate the durability and antithrombogenicity of the MSCP. Short-term animal studies were performed using two mongrel dogs. Left heart bypass was established with the MSCP. After 3 hr, the layer of thrombus adherent to the surface of the polycarbonate impeller impaired pumping efficiency. However, using the impeller coated with silicone, no thrombus was observed on the impeller after continuous pumping for 24 hr. In addition, long-term animal studies were performed using two sheep. Left heart bypass was established with the MSCP containing an impeller coated with silicone. In one sheep, the MSCP ran for 14 days without problems in pumping performance and showed no thrombus within the pump. In the other sheep, the MSCP ran for 15 days, and showed no thrombus on the impeller. During each experiment, plasma free hemoglobin levels were less than 15 mg/dl. The MSCP induced less hemolysis than did the Biopump, and the MSCP containing an impeller coated with silicone demonstrated the potential to run for 14 days without thrombus formation within the pump.

In Vitro and Preliminary In Vivo Assessment of a New Centrifugal Pump: the Magnetically Suspended Centrifugal Pump

To overcome problems derived from the shaft within conventional centrifugal pumps, we have developed a new centrifugal pump, namely, the magnetically suspended centrifugal pump (MSCP), which has no shaft and operates as a noncontacting and bearingless pump. This impeller is suspended magnetically between the magnetic bearing and the driving motor. Hemolysis tests were performed and results were compaired with those for the Biopump (BP-80; Medtronic Bio-Medicus, Eden Prairie, MN, USA). The test conditions were: 51/min of pumping flow rate, and 150 mmHg pressure. The index of hemolysis was significantly lower for the MSCP than for the Biopump, despite the higher rotation rate of the MSCP. Moreover, in the MSCP, platelets were significantly preserved, and the change in the temperature of the test circuit was significantly lower, indicating the superior pumping efficiency of the MSCP compared to the Biopump. In addition, hemolysis tests were performed by changing the gap between the impeller and the pump housing in the MSCP from 0.15 mm to 0.25 mm to determine the optimal gap. The smaller gap resulted in lower hemolysis and lower destruction of platelets. In studies in dogs, an MSCP with a non-coated impeller developed a layer of white thrombus adherent to the impeller surface of polycarbonate, which impaired the pumping efficiency. However, the MSCP with an impeller coated with silicone to a thickness of 100 A did not show aggregations of platelets or fibrin on the impeller in continuous pumping of 24 h. In conclusion, the MSCP has a more gentle influence on blood cells compared to the Biopump and may be one of the most promising centrifugal pumps for long-term cardiac assist.