Long-term ex vivo bovine experiments with the Gyro C1E3 centrifugal blood pump.

Centrifugal blood pumps are used widely for cardiopulmonary bypass, as ventricular assist devices, and for extracorporeal membrane oxygenation (ECMO). However, there is no centrifugal blood pump that is suitable for long-term ECMO. The authors developed the Gyro C1E3 centrifugal blood pump (Kyocera Corporation, Kyoto, Japan), which has superior antithrombogenic, antitraumatic, and hydraulic features in comparison with the conventional centrifugal blood pumps. Five ex vivo long-term durability tests of the Gyro C1E3 were performed using healthy miniature calves. The ECMO circuit was composed of a prototype hollow fiber silicone membrane oxygenator and a Gyro C1E3 pump. Venous blood was drained from the left jugular vein of a calf, passed through the oxygenator and infused into the left carotid artery using a Gyro C1E3. Ex vivo studies were performed from 7 to 15 days at a blood flow rate of 1 L/min. During this period, the Gyro C1E3 demonstrated a stable performance without exchanging the pump. Bleeding complications were the major reason for termination of each experiment. Rotational speed was maintained around 2,000 rpm. All five calves demonstrated neither abnormal signs nor abnormal blood examination data throughout the experiment. Neither clot nor thrombus formations were found during the necropsy in the cannula or pump nor were infarctions observed in any of the major organs. In conclusion, the Gyro C1E3 showed a stable and reliable performance during long-term ex vivo bovine experiments under the conditions tested.

Inlet port positioning for a miniaturized centrifugal blood pump.

We are developing the Baylor-Kyocera KP implantable centrifugal blood pump for small sized adult and pediatric patients. This pump eccentrically positions the inlet port, which eliminates flow stagnation around the top pivot bearing. The inlet port design is important because it may vary the inlet orifice pressure on the top housing and change hydraulic performance and hemolytic characteristics. The pressure distribution inside the KP pump was assessed by a computational fluid dynamic (CFD) analysis with 2.7 x 10(5) elements and 3.16 x 10(5) nodes. Hydraulic performance and hemolysis were evaluated with 3 different pump housings, which had 3.8, 4.5, and 6.1 mm offset inlet ports from the center in a mock circuit. The CFD analysis revealed that the pressure gradually increased from the center toward the peripheral. The pressure difference between the 3.8 to 6.1 mm offsets was less than 600 Pa. The hydraulic performance did not drastically change at 3.8, 4.5, and 6.1 mm offset from the center. However, the hemolysis increased with the increase of the port offset from 0.0080+/- 0.0048 to 0.054 +/- 0.028 g/100 L. The inlet port positioning is important to attain less blood trauma in this small Gyro centrifugal blood pump. The preferable position of the inlet port is less than 4.5 mm offset from the center.

Impeller inner diameter in a miniaturized centrifugal blood pump.

To design a miniaturized centrifugal blood pump, the impeller internal diameter (ID), which is a circle diameter on the inner edge of the vane, is considered one of the important aspects. Hydraulic performance, hemolysis, and thrombogenicity were evaluated with different impeller IDs. Two impellers were fabricated with an outer diameter of 35 mm, of which 1 had an 8 mm ID impeller and the other had a 12 mm ID. These impellers were combined with 2 different housings in which the inlet port was eccentrically positioned 3.8 and 4.5 mm offset from the center. The hydraulic performance and hemolysis were evaluated in a mock circuit, and thrombogenicity was evaluated in a 2 day ex vivo study with each impeller housing combination. Both impellers required 3,000 rpm in the 3.8 mm offset inlet to attain 5 L/min against 100 mm Hg (left ventricular assist device condition). The 8 mm ID impeller required 3,200 rpm, and the 12 mm ID impeller required 3,100 rpm in the 4.5 mm offset housing. The normalized index of hemolysis was 0.0080 +/- 0.0048 g/100 L in the 8 mm ID impeller with the 3.8 mm offset and 0.022 +/- 0.018 g/100 L with 4.5 mm offset. The 12 mm ID impeller had 0.068 +/- 0.028 g/100 L with the 3.8 mm offset and 0.010 +/- 0.002 g/100 L with the 4.5 mm offset. After the 2 day ex vivo study, no blood clot was formed around the top bearing in all the pump heads. The 8 mm ID impeller with 3.8 mm offset inlet and the 12 mm ID impeller with the 4.5 mm offset had less hemolysis compared to the other pump heads that were subjected to 14 day ex vivo and 10 day in vivo studies. The 8 mm ID impeller with the 3.8 mm offset inlet had a blood clot around the top bearing after the 14 day ex vivo study. No thrombus was found around the top bearing of the 12 mm ID impeller with the 4.5 mm offset in the 10 day in vivo study. These results suggest that the ID does not greatly change the hydraulic performance of a small centrifugal blood pump. The proper combination of the impeller ID and inlet port offset obtains less hemolysis. The larger impeller ID is considered to have less thrombogenicity around the top bearing.

Development of a Pivot Bearing Supported Sealless Centrifugal Pump for Ventricular Assist.

Since 1991, in our laboratory, a pivot bearing-supported, sealless, centrifugal pump has been developed as an implantable ventricular assist device (VAD). For this application, the configuration of the total pump system should be relatively small. The C1E3 pump developed for this purpose was anatomically compatible with the small-sized patient population. To evaluate an-tithrombogenicity, ex vivo 2-week screening studies were conducted instead of studies involving an intracorpore-ally implanted VADs using calves. Five paracorporeal LVAD studies were performed using calves for longer than 2 weeks. The activated clotting time (ACT) was maintained at approximately 250 s using heparin. All of the devices demonstrated trouble-free performances over 2 weeks. Among these 5 studies, 3 implantations were subjected to 1-month system validation studies. There were no device-induced thrombus formations inside the pump housing, and plasma-free hemoglobin levels in calves were within the normal range throughout the experiment (35, 34, and 31 days). There were no incidents of system malfunction. Subsequently, the mass production model was fabricated and yielded a normalized index of hemolysis of 0.0014, which was comparable to that of clinically available pumps. The wear life of the impeller bearings was estimated at longer than 8 years. In the next series of in vivo studies, an implantable model of the C1E3 pump will be fabricated for longer term implantation. The pump-actuator will be implanted inside the body; thus the design calls for substituting plastic for metallic parts.

New Method of Evaluating Sublethal Damage to Erythrocytes by Blood Pumps.

We recently proposed a new concept, the total destruction time of erythrocytes, to indicate sublethal damage to erythrocytes by blood pumps. In this article, results of additional experiments concerning this new concept are reported. Five paired in vitro hemolysis tests with bovine blood were conducted using a cone-type centrifugal pump (Group A) and an impeller-type pump (Group B). A total pressure head of 100 mm Hg was applied. The factors evaluated were the normalized index of hemolysis and the total destruction time, or the pumping duration, required to raise the level of the plasma-free hemoglobin to 50% of the total hemoglobin. The morphologic change of the erythrocytes also was analyzed. The percentage of crenated cells was calculated from blood smear specimens 1 min after starting the pumps and 2 h before the total destruction time of Group A in each experiment. Although there was no statistical difference in the normalized index of hemolysis between the two groups, the total destruction time of Group A erythrocytes was significantly shorter than that of Group B (18.9 ± 4.5 h and 33.7 ± 9.9 h in Group A and group B, respectively; p < 2). The rate of crenated erythrocytes was higher in Group A than in Group B at a point 2 h before the total destruction time of Group A. The total destruction time values seem to define a good method for establishing sublethal traumatic damage to erythrocytes in blood pumps.