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.

Background: Many cerebral aneurysms can be treated effectively with intracranial stents.

Ventricular assist devices (VADs) have become a viable option for adult patients with end-stage heart failure during the bridge-to-transplant period and have recently shown promise in aiding in myocardial recovery. Because the number of available organs is insufficient, mechanical circulatory support systems such as VADs are also being developed for use in pediatric patients. During myocardial recovery, the system must be weaned from the patient to prepare for explant; for pulsatile devices, this often includes a reduction in flow rate, which can change the fluid dynamics of the device. These changes in flow need to be monitored because strong diastolic rotational flow, no areas of blood stasis, low blood residence time, and wall shear rates above 500 s, can help prevent thrombus deposition. Particle image velocimetry was used to observe the planar flow patterns and wall shear rates of the 12 cc Penn State Pneumatic Pediatric VAD (PVAD) at a normal operating condition and a reduced beat rate. At the reduced beat rate, the PVAD showed an earlier loss of rotational pattern, increased blood residence time, and an overall reduction in wall shear rate at the outer walls. Because this reduction in flow rate could lead to a possible increase in thrombus deposition, it may be necessary to look into other options for weaning a patient from the PVAD.

Because of the shortage of organs for transplant in pediatric patients with end-stage heart failure, Penn State is developing a pneumatically driven 12 cc pulsatile pediatric ventricular assist device (PVAD). A major concern is the flow field changes related to the volume decrease and its effect on device thrombogenicity. Previous studies of similar devices have shown that changes in the orientation of the inlet valve can lead to improvement in the flow field. Herein, the fluid dynamic effects of orientation changes at both the inlet and outlet valves are studied. Using two-dimensional particle image velocimetry, we examine the flow field in vitro using an acrylic model of the PVAD in a mock circulatory loop. Regardless of valve orientation, the overall flow pattern inside the PVAD remains similar, but important differences were seen locally in the wall shear rates, which is notable because shear rates >500 s may prevent thrombus formation. As the inlet valve was rotated toward the fluid side of the PVAD, we observed an increase in inlet jet velocity and wall shear rates along the inlet port wall. A corresponding rotation of the outlet valve increases the wall shear rate along the outer wall near the device outlet. Wall shear rates were all higher when both valves were rotated toward the fluid side of the device, with the best rates found at orientations of +15 degrees for both the inlet and outlet valves. Overall, orientations of +15 degrees or +30 degrees of both the inlet and outlet valve resulted in an increase in wall shear rates and could aid in the reduction of thrombus formation inside the PVAD.

In order to aid the ongoing concern of limited organ availability for pediatric heart transplants, Penn State has continued development of a pulsatile Pediatric Ventricular Assist Device (PVAD). Initial studies of the PVAD observed an increase in thrombus formation due to differences in flow field physics when compared to adult sized devices, which included a higher degree of threedimensionality. This unique flow field brings into question the use of 2D planar particle image velocimetry (PIV) as a flow visualization technique, however the small size and high curvature of the PVAD make other tools such as stereoscopic PIV impractical. In order to test the reliability of the 2D results, we perform a pseudo-3D PIV study using planes both parallel and normal to the diaphragm employing a mock circulatory loop containing a viscoelastic fluid that mimics 40% hematocrit blood. We find that while the third component of velocity is extremely helpful to a physical understanding of the flow, particularly of the diastolic jet and the development of a desired rotational pattern, the flow data taken parallel to the diaphragm is sufficient to describe the wall shear rates, a critical aspect to the study of thrombosis and design of such pumps.