Dynamic properties of left ventricular response to changes in coronary perfusion

To determine the dynamic property of cardiac function response to alterations in coronary perfusion, we varied coronary arterial pressure (CAP) sinusoidally around one of four mean CAP levels with a constant amplitude at several frequencies in isolated, isovolumically contracting canine heart preparations. From the frequency spectrum of the peak left ventricular pressure (PLVP) response, we arrived at a phenomenological model with two components coupled in parallel and estimated the parameter values. One component is a first-order delay system having a short time constant (~1 s) and a small gain (range 0.08-0.16); it probably represents a hydraulic effect of coronary perfusion. The other component is a second-order delay system with longer time constants (~15 and 6 s) and a larger gain (range 0.14-0.69); this probably represents a metabolic effect. The gain value of the slow component varied inversely with the mean CAP level, and studies with adenosine suggested that this dependence was due to the coronary autoregulation. The model prediction of the transient responses of PLVP to step changes in CAP agreed reasonably well with those experimental data of transient responses obtained in the identical hearts but not used to determine the model parameter values.