Fluid dynamics of a pediatric ventricular assist device

The number of pediatric patients requiring some form of mechanical circulat ory assistance is growing throughout the world because of new surgical proc edures and the success of pediatric cardiac transplantation. However, the s alvage rate for those patients requiring circulatory support may be as low as 25%. Despite the fact that Penn State's 70 cc pneumatic ventricular assi st device has been used with a success rate of over 90% in more than 250 pa tients worldwide, efforts to scale down the pump have encountered difficult ies. Animal experiments with a 15 cc version were unsuccessful, with explan ted pumps showing extensive thrombus deposition within the pumping chamber. The materials used to fabricate the smaller pump as well as the basic oper ating principles are identical to the successful adult-sized version. It is therefore believed that reducing the size of the pump altered the internal flow field, and that fluid dynamic factors were responsible for the high d egree of thrombus observed with the implanted devices. A dimensional analys is was conducted that revealed significant differences in both Reynolds (Re ) and Strouhal (St) numbers between the successful and unsuccessful pumps. Two component laser Doppler velocimetry was then used to characterize the i nternal flow field quantitatively. Comparison with data from the 70 cc pump showed a reduction in wall shear stress and turbulence levels in the 15 cc pump that would yield an environment conducive to clot formation.