Local Blood Residence Times in the Penn State Artificial Heart

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Abstract
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 (10‐6–10‐4M of fluorescein sodium) were easily discernible. The washout process was characterized by an exponential decay with a time constant T. For all positions and operating conditions tested, T values were between 1–2 beats. In all cases tested, values of T in the valve regions were significantly longer (8.9–31.6%; p ≥ 0.0075) than in the chamber proper. At every position T 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 T 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.