[Method for the immediate measurement of myocardial pressure velocity relationships in situ]

A method for instantaneous measurements and representations of myocardial pressure-velocity relations permitting the analysis of various contractility parameters is described. Basing on a modified two-element model of cardiac muscle the measurement of the relative shortening velocity vce = dp/dt(p) of the contractile elements is carried out by a special analog computer, which calculates the quotient (dp/dt) to the simultaneous left ventricular pressure p. Electronic differentiation of the logarithm of pressure-proportional input voltages is used. The p-v-diagram can be displayed on x-y-oscilloscopes. Over an input voltage range of 20 mV---20V the quotient can be measured within the range of 20 sec-1---250 sec-1. Output voltages can be calibrated automatically. Between (dp/dt)p-1 determined by conventional methods and the dlnp/dt calcuated electronically there exists a correlation gamma = 0.995. An additional electronic circuit which permits the determination of a contractility parameter indicates the point of (dp/dt)max on the p-v-relation display. The application of the method in experimental studies under inotropic changes in the rabbit heart in situ following beta-receptor blockade is demonstrated.