DEVELOPMENT OF MOCK CIRCULATION MODELS FOR THE ASSESSMENT OF COUNTERPULSATION SYSTEMS

Study objective -This study entailed the development of mock circulation models to assess and compare the haemodynamic efficacy of extra-aortic counterpulsation (using trained skeletal muscle wrapped around the proximal descending aorta) and conventional intra-aortic balloon counterpulsation. Design and experimental materials - Hydraulic Windkessel type lumped parameter models were used either in conjunction with native skeletal muscle or as a dynamic simulation of counterpulsation. The haemodynamic performance of the wrapped latissimus dorsi muscle of the normal sheep was assessed using an artificial load to simulate the pressurised proximal descending aorta. Mock circulation models of counterpulsation comprised Windkessel compliance chambers, laminar flow resistors, a blood analogue, a prosthetic blood pump, and a purpose made hydraulic counterpulsator. Measurements and main results - An electrically stimulated muscle wrap, 5 cm in length, previously trained for 2 weeks at 3 V and 35 Hz, was assessed for haemodynamic performance in a mock circulation: volume of fluid displaced = 14.1(SD 1.8) ml; pressure increase from 100 mm Hg = 14.9(2.1) mm Hg; external work per contraction cycle = 180(70) mJ; external mean power = 800(100) mW. In a simulation of intra-aortic balloon counterpulsation, haemodynamic benefit (ie, an increase in proximal flow rate and endocardial viability ratio and a reduction in left ventricular stroke power) was assessed with respect to defined parameters. Conclusions - This paper demonstrates the potential of the mock circulation models both for the investigation of muscle wrap performance and for the comparison of extra-aortic muscle with intra. aortic balloon counterpulsation.