Biocompatible Flow Chamber to Study the Hemodynamic Performance of Prosthetic Heart Valves

Abstract

Heart valve diseases claim more than 250,000 victims each year in the United States. One option to treat a diseased heart valve is to replace it with a prosthetic heart valve. There are two main types of prosthetic heart valves, mechanical heart valves and bioprosthetic heart valves. The goal of this study was to build a biocompatible flow chamber (following the design of a left ventricular assist device) to study the hemodynamic performance of prosthetic heart valves. The flow chamber consists of two fluid chambers separated by a flexible latex diaphragm. One chamber is filled with water (water chamber) and connected to a Harvard reciprocating pump, which drives the diaphragm to move up and down and causes fluid in the other chamber (testing fluid chamber) to circulate through two heart valves. The biocompatibility of this flow chamber towards blood platelets and red blood cells were tested under static and dynamic conditions. For static testing, washed platelets were placed in the testing fluid chamber for up to 5 hours. Samples were taken out every hour and platelet surface P-selectin expression was measured using flow cytometry. To investigate the effect of the chamber on red blood cells, whole blood was placed in the test chamber for up to 6 hours. Hemolysis was measured every hour (at 540 nm). For dynamic testing, two St. Jude bileaflet mechanical heart valves were placed into the testing fluid chamber to control the flow direction. The flow rate of the system was fixed at 5 L/min with a stroke volume of 80mL and stroke rate of 72 min-1. The systolic /diastolic ratio was 0.375. Washed platelets were circulated in the chamber for 90 minutes and platelet surface P-selectin expression was examined every 15 minutes. For hemolysis measurement, whole blood was circulated through the two heart valves for 90 minutes and blood samples were taken every 15 minutes. The results demonstrated that the flow chamber did not induce hemolysis and platelet activation under static or dynamic conditions, with or without the St. Jude bileaflet mechanical heart valves. In parallel, a 3D computational fluid dynamics model was built to study the flow conditions in the flow chamber. The results indicated that the design of the flow chamber did not induce any turbulence in the testing fluid chamber (maximum Reynolds number was ~2100), which is desirable to study cellular functions. These results demonstrated the feasibility of using this flow chamber to study the hemodynamic performance of prosthetic heart valves.