Prosthetic valve function under simulated low cardiac output conditions: preliminary observations

An experimental protocol was developed and a series of laboratory experiments started to assess the function and behaviour of replacement valves under simulated low cardiac output, that is low flow and low pressure conditions. The Helmholtz Institute's pulse duplicator (1) and instrumentation were carefully tuned in order to achieve accurate and reproducible delivery of the required extremely small stroke volumes. A pilot study was completed with 27 mm St. Jude Medical and CarboMedics bileaflet valves and Wessex porcine bioprostheses, three each, in the simulated aortic position. The results of these experiments suggest that the performances of the two bileaflet prostheses are inadequate if the flow is less than 2.0 l/min; the porcine bioprosthesis needs relatively low flow to start proper function, but its stenotic nature soon becomes apparent; increase in pressure without a corresponding increase in flow has a deleterious effect on valve performances by increasing regurgitation; increasing pulse rate is inversely correlated with valve efficiency; and there is no "all-or-none" cut off point between functional and non-functional situation for the tested devices; there is a semilogarithmic relation between increasing flow and valve performance. The clinical consequences are manifold and may be related both to the stabilization of circulation and to the increased thromboembolic risk during the early postoperative period.