Local Blood Residence Times in the Penn State Artificial Heart

Thrombus formation associated with cardiac assist devices is a major concern in their application. Thrombogenesis is thought to be a function of, among other things, fluid shear stress and blood residence time. In the current study, a fiber-optic probe was developed and employed in conjunction with indicator dilution techniques to evaluate the local near-wall fluid residence times at a number of locations inside the Penn State 70 cc parallel port and 100 cc angle port left ventricular assist devices (LVADs). In this in vitro study, both 50% and 30% systolic duration regimes were investigated for each chamber. Using a relatively inexpensive optical arrangement, two decades of dye concentration (10(-6)-10(-4) M of fluorescein sodium) were easily discernible. The washout process was characterized by an exponential decay with a time constant tau. For all positions and operating conditions tested, tau values were between 1-2 beats. In all cases tested, values of tau in the valve regions were significantly longer (8.9-31.6%; p less than or equal to 0.0075) than in the chamber proper. At every position tau was substantially lower in the 70 cc chamber than in the larger pump (17.8-27.4%). Systolic duration appeared to have no significant effect on tau at the majority of investigated sites. The results indicate that the valve regions, which are known to have greater shear stresses, are also in contact with a volume element of blood for a longer time than is the rest of the chamber. This combination may be detrimental to fragile blood components.