AJP - Heart and Circulatory Physiology, Vol 256, Issue 2 428-H433, Copyright © 1989 by American Physiological Society
Vagal stimulation decreases rate of left ventricular relaxation
R. J. Henning, J. Cheng and M. N. Levy
Division of Investigative Medicine, Mt. Sinai Medical Center, Cleveland, Ohio.
We determined the effects of vagal stimulation on the time constant (tau)
of left ventricular isovolumic pressure decay and on the maximum rates of
left ventricular pressure change (dP/dt) during contraction and relaxation
in anesthetized dogs. In each dog, the atria were paced at a constant rate
of 150 beats/min. We recorded left ventricular pressure waveforms in the
absence (control) and in the presence of vagal stimulation at frequencies
of 1, 2, and 3 Hz. During the control periods and during vagal stimulation
at each frequency, we determined tau, the maximal rate of contraction, and
the maximal rate of relaxation from left ventricular pressure waveforms
recorded at medium (100 mmHg), high (130 mmHg), and low (73 mmHg)
afterloads. Vagal stimulation at a frequency of 3 Hz increased tau by 23%.
This effect of vagal stimulation on tau was most pronounced at the high
afterload. Vagal stimulation at 3 Hz decreased the maximal rate of
relaxation by 19%, but it decreased the maximal rate of contraction by only
8%. Thus vagal stimulation significantly decreased the rate of left
ventricular relaxation and had a greater depressant effect on ventricular
relaxation than on contraction.
