Determinants of instantaneous pressure in canine left ventricle. Time and volume specification.

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Abstract
Instantaneous pressure (P) in the canine left ventricle is determined predominantly by the simultaneous volume (V) of the ventricular lumen; the instantaneous P-V relation is reasonably well approximated by a regression line of isochronous pressures from different beats on the simultaneous volume values. The P-V data points from differently loaded contractions slightly scatter around the regression line indicating that V is not the sole determinant of P. To identify the secondary determinants of P at a given V, the ventricle was forced to have a fixed V at a specified time in the cardiac cycle while changing the end-diastolic volume and the velocity of ejection over a wide range under a constant inotropic background. At any specified time and V, P decreased with increases in the simultaneous velocity of ejection (-dV/dt, ml/s), the peak velocity of ejection (peak -dV/dt, ml/s) and the volume ejected by the specified time (.intg. -dV, ml). Multiple regression analysis of the data yielded a formula: %P = 100 -0.14 (-dV/dt) - 0.07 (peak -dV/dt) - 0.54 (.intg. -dV) in which %P denotes P of an ejecting beat in percent of the isovolumic P at the same time and V. All those partial regression coefficients are statistically significant (P < 0.005). The instantaneous ventricular pressure apparently can be reduced from isovolumic pressure by 10-20% if the magnitude of those ejection parameters are near physiological maxima.