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A new mock circulatory loop was developed for hemolysis studies associated with the Penn State electric ventricular assist device (EVAD). This flow loop has several advantages over previously designed loops. It is small enough to accommodate experiments in which only single units of blood are available, it is made out of biocompatible materials, it incorporates good geometry, and it provides normal physiological pressures and flows to both the aortic outlet and the venous inlet of the pumping device. Experiments with reduced aortic pressure but normal cardiac output showed that hemolysis in a loop with normal aortic blood pressure was significantly higher than that in a loop with lowered aortic pressure, thereby illustrating the importance of maintaining loop pressures as close as possible to those found in vivo. This data also imply that blood traveling through the left ventricle in an artificial heart may be subject to higher hemolysis rates than that traversing the right ventricle. Another set of experiments to determine the effects of 4 hemolysis or drag-reducing agents (Pluronic F-68, Dextran-40, Polyox WSR-301, and Praestol 2273TR) on blood trauma due to the EVAD and associated valves was performed. Results indicated that none of the additives significantly reduced hemolysis under the conditions found in the mock loop. Finally, a compilation of data gathered in these experiments showed that the index of hemolysis (IH) is dependent on hematocrit (HCT), which suggests that another parameter, IH/HCT, may be more suited to the quantification of hemolysis.

A volume compensation chamber is a device used to reduce large pressure fluctuations created in electric ventricular assist devices during the emptying and filling of the blood sac. In this study, the effect of motor casing pressure variation (pressure swing) on the performance of the Penn State electric ventricular assist device (EVAD) was investigated. Design criteria were established for the maximum pressure swing tolerated by the EVAD and the optimal mean chamber pressure at which to operate. At the chosen mean chamber pressure of -15 mm Hg, it was found that pressure swing should be maintained below 45 mm Hg. A two-phase fluid volume compensation chamber was developed that reduced the pressure swing enough to ensure adequate pump performance. The device consists of a metal chamber with a high-heat-flux porous coating applied to the inside surface. The chamber uses Freon as the working fluid and is isolated from the EVAD by a metal bellows. It was found that the high-flux coating significantly reduces the pressure swing, in some cases by as much as 50% when compared with an identical chamber with no coating. In the coated chamber the pressure swing was maintained between 22 and 30 mm Hg at a beat rate of 60 beats/min, for a wide range of Freon volumes (4-38 ml). Even at 100 beats/min the pressure swings obtained with the coated chamber are well within an acceptable range.

A method for real-time in vitro observation of cavitation on a prosthetic heart valve has been developed. Cavitation of four blood analog fluids (distilled water, aqueous glycerin, aqueous polyacrylamide, and aqueous xanthan gum) has been documented for a Medtronic/Hall™ prosthetic heart valve. This method employed a Penn State Electrical Ventricular Assist Device in a mock circulatory loop that was operated in a partial filling mode associated with reduced atrial filling pressure. The observations were made on a valve that was located in the mitral position, with the cavitation occurring on the inlet side after valve closure on every cycle. Stroboscopic videography was used to document the cavity life cycle. Bubble cavitation was observed on the valve occluder face. Vortex cavitation was observed at two locations in the vicinity of the valve occluder and housing. For each fluid, cavity growth and collapse occurred in less than one millisecond, which provides strong evidence that the cavitation is vaporous rather than gaseous. The cavity duration time was found to decrease with increasing atrial pressure at constant aortic pressure and beat rate. The area of cavitation was found to decrease with increasing delay time at a constant aortic pressure, atrial pressure, and beat rate. Cavitation was found to occur in each of the fluids, with the most cavitation seen in the Newtonian fluids (distilled water and aqueous glycerin).