Hypovolemia does not affect speed of isovolumic left ventricular contraction and relaxation in excised canine heart.

摘要

Hypovolemia results in hypotension due to a decrease in left ventricular (LV) stroke volume. We have showed a logistic relaxation time constant (tauL) that is a superior lusitropic index during the LV pressure (LVP) falling phase independent of LV preload compared with the conventional monoexponential relaxation time constant (tauE). In the present study, we investigated the effect of decreasing LV preload on tauL and tauE during the LV contraction and other relaxation phases. The isovolumic LVP curve was analyzed at LV Volumes (LVVs) of 18, 14, and 10 mL during 2-Hz pacing in seven excised, cross-circulated canine hearts. TauL and tauE were evaluated using logistic and monoexponential analyses of the four phases of the cardiac cycle: the period from the onset to the maximum time derivative of LVP (LV dP/dtmax), from LV dP/dtmax to peak LVP, from peak LVP to the minimum time derivative of LVP (LV dP/dtmin), and from LV dP/dtmin to LV end-diastolic pressure. TauL and tauE during the four phases did not change significantly with the decrease in LVV. During the change in LVV, the logistic function always fit significantly better compared with the monoexponential function. In conclusion, hypovolemia does not affect the speed of isovolumic LV contraction and relaxation. Each phase of the LVP curve is of a logistic nature. TauL is as a useful index for estimation of the speed of alteration during each phase of cardiac systole and diastole.