Design of a rotary control valve for an electrohydraulic ventricular assist device

Mechanical circulatory assist devices are grouped in two major classes: pulsatile, in which the blood flow rate is unsteady and similar to the natural circulatory system, and non-pulsatile, in which the blood is pumped at a steady flow rate. Ventricular assist devices or VADs assist the natural heart in pumping the blood and are therefore often pulsatile. One possibility in designing such a device is to create the pulsatile flow by alternately emptying and filling a chamber in a manner similar to the function of the natural heart. This thesis examines the design of a rotary valve intended for use in hydraulically actuated VADs that will create an oscillating flow to empty and fill the VAD chamber from a unidirectional hydraulic pump. Note that in these devices the hydraulic fluid and the blood are separated by a flexible membrane. The valve contains a rotating element whose angular velocity is determined by the speed of the axial flow pump and appropriately sized annular gaps. This rotating element is then used to switch the flow between two sets of inlet and exit ports on the valve, one set causes the hydraulic fluid to fill the VAD chamber and the second causes the chamber to empty. Important aspects of the design include its energy efficiency, its simplicity and reliability, and a reduction in the number of parts exposed to alternating mechanical loads. A prototype of the design is described and preliminary tests described in the thesis show promising performance. The prototype was constructed to test both the feasibility of the concept and the feasibility of implementing the valve under the size and other constraints used in the design of VADs at the Cardiovascular Devices Division of the University of Ottawa Heart Institute. (Abstract shortened by UMI.)...