New technique for determining instantaneous myocardial force-velocity relations in the intact heart

A new technique is described for the instantaneous determination of myocardial force-velocity relationships. The method employs electronic differentiation of the logarithm of intraventricular pressure, which yields a continuous on-line record of (dP/dt)P -1 (the ratio of the rate of rise of ventricular pressure [dP/dt] to the simultaneous ventricular pressure [P]). A further technique is described for the automatic projection of force-velocity vector loops, displaying (dP/dt)P -1 on the ordinate against ventricular pressure on the abscissa in a beat-to-beat fashion. An excellent correlation ( r =0.982) was demonstrated between (dP/dt)P -1 determined by conventional methods and that derived electronically by use of the logarithmic amplifier circuit. Experimental studies are described which document the responsiveness of (dP/dt)P -1 determined by the present method to interventions known to affect myocardial contractility. An increase in (dP/dt)P -1 was observed following infusions of CaCl 2 , norepinephrine, and glucagon, and a decrease following pentobarbital. Insofar as (dP/dt)P -1 is a valid index of myocardial contractility, the present method permits on-line, beat-to-beat evaluation of changes in ventricular function under a variety of circumstances.