Abstract
An indirect measurement of the maximum rate of rise of left ventricular pressure (dP/dt Max.) was derived by dividing aortic diastolic pressure (Pd) by the interval between the first rapid vibration of the first sound and the beginning of ventricular ejection (S 1X), using appropriate recordings of aortic and ventricular pressures and external phonocardiograms from intact anesthetized dogs. A very close correlation of Pd/S 1X with the direct measurement of dP/dt Max. was found (R = 0.92) under a variety of experimental conditions designed to alter aortic pressure and ventricular filling pressure, output and contractile capacity. Pd/S 1X, the interval S 1X, and the mean systolic ejection rate (MSER) were compared as indices of ventricular contractile capacity under various experimental circumstances. All indices reflected the inotropic effects of epinephrine and hypocalcemia, but S 1X and MSER were more misleading than Pd/S 1X when the circulatory alteration included a change of aortic diastolic pressure.
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