Vagal stimulation decreases rate of left ventricular relaxation
Henning, R.J.; Cheng, J.; Levy, M.N.
American Journal of Physiology 256(2 Pt 2): H428-H433
1989
ISSN/ISBN: 0002-9513 PMID: 2916675 Document Number: 336323
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 9%. Thus vagal stimulation significantly decreased the rate of left ventricular relaxation and had a greater depressant effect on ventricular relaxation than on contraction.