Quantification of the hemodynamics inside a novel Synchronized Therapeutic Cardiac Assist Device for Chronic Heart Failure

摘要

A physiological cardiac assist device (PCAD) utilizing a single cannula, that works in synchrony with the heartbeat, was developed to assist the left ventricle (LV) in chronic heart failure. The cannula is inserted through the apex of the beating LV, using a specially designed device in less than a minute. The inflow from the PCAD to the LV occurs during ejection, thereby augmenting stroke volume and stroke work. The PCAD withdraws blood from the LV through the same cannula during diastole. The study evaluates PCAD model using a computational fluid dynamics method to quantify the PCAD's four hemodynamic aspects: blood mixing inside the chamber, pressure regime in the flow field, forces on the piston (motor) and shear stresses. Simulations were performed by numerically solving the continuity and the Navier-Stokes equations, using a finite volume solver (FLUENT). The analyses were time-dependent and three-dimensional with moving boundaries. The blood was assumed incompressible and Newtonian, with laminar flow. The imposed boundary conditions were fixed pressure of 100 mmHg at the cannula inlet/outlet (LV pressure), and the piston displaced 16 ml within 0.3 sec during the systole, at heart rate of 70 bpm. Good hemodynamic performances were obtained. Low shear stress (35 Pa) with a shear stress-time product smaller than 0.35 Pa-sec (smaller by one order of magnitude than the threshold for platelets activation). Good washout properties and remnant fraction of 1% after 7 cycles were observed. The good agreement of our results with these predicted values confirms the ideal mixing assumption. Pressure gradients of less than 20 mmHg (i.e., no cavitations) with no permanent stagnation regions were found. The forces on the piston were relatively low (20 N). The results strongly suggest that there is low probability of hemolysis or thrombosis inside this novel physiological device.