Key result
Vagal stimulation at 3 Hz increased the time constant of left ventricular pressure decay by 23% and decreased the maximal rate of relaxation by 19% in anesthetized dogs.
Why the study?
Does vagal stimulation affect the rate of left ventricular relaxation and contraction in anesthetized dogs?
Does vagal stimulation affect the rate of left ventricular relaxation and contraction in anesthetized dogs?
Vagal stimulation significantly decreases the rate of left ventricular relaxation, with a greater depressant effect on relaxation than on contraction in a canine model.
Answers are grounded in this paper and cite their sources.
Vagal stimulation effects in anesthetized dogs warrant no clinical application; leaves open translation to human cardiac function and conscious models.
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.
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Henning et al. (1989) studied this question. Vagal stimulation vs. Absence of vagal stimulation (control) was evaluated on Time constant (tau) of left ventricular isovolumic pressure decay and maximum rates of left ventricular pressure change (dP/dt) during contraction and relaxation. Vagal stimulation at 3 Hz increased the time constant of left ventricular pressure decay by 23% and decreased the maximal rate of relaxation by 19% in anesthetized dogs.
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