An increase in afterload augments ventricular relaxation rate in isolated perfused canine hearts

The afterload dependency of relaxation rate was reappraised in isolated canine hearts both in isovolumic and isobaric contractions by using the reliable exponential method in which the asymptote LV pressure (P chi) is variable. This method provided a closer correlation (r = 0.999 +/- 0.001) between the measured LV pressure decay and the model estimate than the semilogarithmic method assuming P chi = 0 (r = 0.992 +/- 0.001). Time constants of isovolumic LV pressure decay obtained by the exponential method demonstrated a significant (p less than 0.01) decrease during volume loading both in isovolumic and isobaric contractions, indicating that the relaxation rate is augmented as afterload increases. In contrast, if we assume P chi = 0, the time constant of LV pressure decay was independent of peak LV pressure as previously reported. Thus, we conclude that the load insensitive relaxation rate implied by the semilogarithmic method (P chi = 0) may be erroneous due to an invalid assumption, ie, P chi = 0, but the relaxation rate is augmented as afterload increases both in isovolumically contracting and isobarically ejecting isolated canine hearts.