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

Abstract

Due to the lack of long-term mechanical circulatory support options for children, Penn State is developing a pneumatically driven 12 cc pulsatile pediatric ventricular assist device (PVAD). The reduction in volume, however, necessary to accommodate pediatric patients leads to changes in the functional fluid mechanics. One area that has not been previously observed is the flow upstream and downstream of the inlet and outlet valves. In particular an area of blockage, that includes a large area of stagnant flow, has been observed upstream of the outlet valve that could cause an increase in blood damage. In order to measure the flow upstream and downstream of the ports, we deploy a 50 mm acrylic valve extension. The outlet valve is moved downstream of the outlet port in an attempt to eliminate a flow blockage region upstream of the valve. We mount the PVAD to a mock circulatory loop that models the systemic circulation under normal physiological conditions, with a 40% hematocrit blood analog as the fluid. Two dimensional particle image velocimetry is used to measure the flow. As expected, the flow patterns in the body of the device remain similar to those without the extension, except near the outlet port. Nonuniform flow is observed upstream of both the inlet and outlet valves and regurgitation is observed upstream of the inlet valve. The relocation of the outlet valve leads to a more uniform outflow and the blockage region is eliminated. The observations of non-uniform flow upstream of the inlet valve are a new and important observation when considering computational models. Also, the new outlet flow pattern associated with the relocation of the outlet valve reduces the potential for blood damage. Studies with a relocated valve in a clinical model are being considered.

Effect of the bileaflet inlet valve angle on the flow of a pediatric ventricular assist device: Experimental analysis

“…17,18 Similarly, for others PVADs, the best angle was 15°. 13,19,20 So far, the fluid dynamics has indicated that the best angles for a bileaflet valve with two major orifices are 0°, 15°, and 30°.…”

“…Previous studies with tilting‐disc valves had shown that 45° (considering the major orifice of the valve facing the outside of the device) was the best choice for adult VADs 17,18 . Similarly, for others PVADs, the best angle was 15° 13,19,20 . So far, the fluid dynamics has indicated that the best angles for a bileaflet valve with two major orifices are 0°, 15°, and 30°.…”

“…In the paper's conclusions, the tilting‐disc led to better fluid structures inside the PVAD. However, tilting‐disc valves are known for their flow blockage, especially in the device outlet 6,20 . Contrariwise, bileaflet valves do not have flow blockages and some studies also find better performance for them when compared to tilting‐disc or porcine valves, 21 especially with small valve diameters (<23 mm) 22 …”