AJP - Heart and Circulatory Physiology, Vol 253, Issue 3 512-H518, Copyright © 1987 by American Physiological Society
Relaxation time constant of isolated rabbit left ventricle
P. Schiereck, J. H. Nieuwenhuijs, E. L. de Beer, M. W. van Hessen, F. A. van Kaam and A. Crowe
Experiments were performed on isolated rabbit left ventricles. Controlled
ejections during otherwise isovolumic contractions were studied. The time
constant of relaxation was defined as the slope of the linear approximation
of the ln(P)-t relation over a 40-ms period starting 20 ms after the
minimum of the first time derivative of left ventricular pressure (dP/dt)
of the isovolumic contraction. Variations in time of ejection, its
amplitude, and velocity are applied independently. No direct effect of the
variations in time and velocity of the ejection on the time constant of
relaxation was found. This is in conflict with the findings of Hori et al.
(Circ. Res. 55: 31-38, 1984). The difference is due to the influence of the
recovery of pressure directly after the end of ejection in their study.
This effect is present especially when ejection was timed to take place
late in the contraction phase. The effect of the variation of the amplitude
of the ejection on the time constant was similar to the effect of the
end-diastolic pressure on the end-diastolic volume. It is concluded that
the time constant of relaxation depends linearly on the same processes that
are responsible for the height of the end-diastolic pressure.
