Cascaded constant flow pulses as a tool for analyzing ventricular mechanics

Cascaded constant flow pulses (CFPs) were applied to the isolated rabbit left ventricle. During cascaded CFPs, flow is stepwise changed, and the influence of flow changes on left ventricular pressure can be measured separately from other effects like volume and time. It is found that pressure before and during cascaded flow pulses with a stepwise increase in flow during ejection could be described by a three-element model consisting of an elastance, series-elastance, and a resistance (all time-varying). However, when flow during ejection was stepwise decreased, after the flow change an additional deactivation effect (time-varying) had to be incorporated into the model. After ejection a deactivation effect always was present. With a decreasing flow during ejection, the deactivation effect after ejection was enhanced. It is concluded that deactivation only is generated when flow decreases, and that it can be represented by a decreased ventricular elastance