AJP - Heart and Circulatory Physiology, Vol 246, Issue 4 585-H591, Copyright © 1984 by American Physiological Society
Synchronization of automatic cells in S-A node during vagal stimulation in dogs
T. Yang, M. D. Jacobstein and M. N. Levy
In anesthetized, open-chest dogs, one burst of stimuli was delivered to the
left or right vagus nerve each cardiac cycle. The timing of the stimulus
bursts relative to the cardiac cycle was varied by a constant, small amount
on successive cardiac cycles, until the entire cardiac cycle was scanned.
The level of vagal activity was changed by varying the number of stimulus
pulses in each burst; two levels of activity were used in each experiment.
For a given level of vagal activity, the mean cardiac cycle length and the
amplitude of the phase-response curve were significantly greater during
right than during left vagal stimulation. These response characteristics
increased as the level of vagal activity was augmented. The
minimum-to-maximum phase differences of the phase-response curve were less
during right than during left vagal stimulation and when the level of vagal
activity was increased. The disparities between the minimum-to-maximum
phase differences for the right and left vagi are probably ascribable to
the associated differences in the overall magnitudes of the chronotropic
responses, rather than to any fundamental difference in the innervation of
the effector cells by nerve fibers originating from the right and left
sides.
