The 12cc Penn State Pulsatile Pediatric Ventricular Assist Device: Fluid Dynamics Associated With Valve Selection

Abstract

The mortality rate for infants awaiting a heart transplant is 40% because of the extremely limited number of donor organs. Ventricular assist devices (VADs), a common bridge-to-transplant solution in adults, are becoming a viable option for pediatric patients. A major obstacle faced by VAD designers is thromboembolism. Previous studies have shown that the interrelated flow characteristics necessary for the prevention of thrombosis in a pulsatile VAD are a strong inlet jet, a late diastolic recirculating flow, and a wall shear rate greater than 500 s(-1). Particle image velocimetry was used to compare the flow fields in the chamber of the 12 cc Penn State pediatric pulsatile VAD using two mechanical heart valves: Bjork-Shiley monostrut (BSM) tilting disk valves and CarboMedics (CM) bileaflet valves. In conjunction with the flow evaluation, wall shear data were calculated and analyzed to help quantify wall washing. The major orifice inlet jet of the device containing BSM valves was more intense, which led to better recirculation and wall washing than the three jets produced by the CM valves. Regurgitation through the CM valve served as a significant hindrance to the development of the rotational flow.

Flow Visualization of the Penn State Pulsatile Pediatric Ventricular Assist Device Cannulae and Change in Outlet Valve Placement

“…Previous PVAD studies by Cooper et al 7 and Roszelle et al 18,19 describe the PIV technique used in the study extensively. The images were acquired with a pulse delay of 200 ls and a resolution between 35 and 45 lm/pixel depending on the plane.…”

“…These include flow characterization, valve selection, valve orientation, device three-dimensionality, and most recently the effect of varying clinical conditions on the flow field. 7,8,15,[18][19][20] Overall, we have found that the PVAD has a flow field with adequate wall washing under normal operating conditions. The reduced volume of the PVAD makes the flow in the body of the pump more sensitive, so that changes in the valve position and inflow and outflow cannulae affect the device flow field.…”

“…14 As studies of the PVAD progressed, we tried to better control the clinical filling and timing conditions of the device. In a valve selection study by Cooper et al, 7 we set a standard operating condition, to be used with the PVAD mock circulatory loop, as 75 bpm while maintaining complete filling and ejection of the pump. While Cooper et al 7 still observed the blockage during late systole; its size was reduced, as was the length of time it was observed during the cardiac cycle.…”

“…In a valve selection study by Cooper et al, 7 we set a standard operating condition, to be used with the PVAD mock circulatory loop, as 75 bpm while maintaining complete filling and ejection of the pump. While Cooper et al 7 still observed the blockage during late systole; its size was reduced, as was the length of time it was observed during the cardiac cycle. The persistence of the blockage, however, led us to consider moving the valve further downstream, to provide a smoother outflow.…”

A Fluid Dynamics Study in a 50 cc Pulsatile Ventricular Assist Device: Influence of Heart Rate Variability

“…Previous studies, examining wall location definition, have shown the ability to locate the wall to within a half a pixel and a thorough error analysis was carried out as was detailed in Ref. [21]. From this, the error in the projected vectorto-wall distance is 6 17.5 lm at the low magnification, and 6 6 lm at the high magnification.…”