Protective effects of electroacupuncture on cardiac function in rats subjected to thoracic surgery trauma.
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)?(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/dtJP" 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/dtJP" 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/dtJP" determined by the present method to interventions known to affect myocardial contractility. An increase in (dP/dt)P" was observed following infusions of CaCl2, norepinephrine, and glucagon, and a decrease following pentobarbital. Insofar as (dP/dtJP" 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.