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Instantaneous pressure (P) in the canine left ventricle is determined predominantly by the simultaneous volume (V) of the ventricular lumen; that is, the instantaneous P-V relation is reasonably well approximated by a regression line of isochronous pressures from different beats on the simultaneous volume values. Strictly speaking, however, 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, we forced the ventricle 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. We found that, at any specified time and V, P decreased with increases in the simultaneous velocity of ejection (-dV/dt, ml/sec), the peak velocity of ejection (peak-dV/dt, ml/sec), and the volume ejected by the specified time (/−dV, ml). Multiple regression analysis of the data yielded a formula: %P = 100-0.14 (-dV/dt)-0.07 (peak -dV/dt)-0.54 (J-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 results indicate that the instantaneous ventricular pressure can be reduced from isovolumic pressure by 10-20% if the magnitude of those ejection parameters are near physiological maxima. Circ Res 46: 256-263, 1980

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