Journal of Applied Physiology, Vol 54, Issue 2 502-507, Copyright © 1983 by American Physiological Society
Effects of high-frequency oscillatory ventilation on vagal and phrenic nerve activities
G. C. Man, S. F. Man and C. T. Kappagoda
This study was undertaken to define the mechanism for the respiratory
inhibition observed during high-frequency oscillatory ventilation (HFOV).
The effects of HFOV on the activities of single units in the vagus (Vna)
and phrenic nerves (Pna) were examined in pentobarbital-anesthetized dogs.
The animals were either ventilated by intermittent positive-pressure
ventilation (IPPV) with and without positive end-expiratory pressure
(PEEP), or by HFOV at a frequency of 25 Hz and pump displacement volume of
3 ml/kg. In 13 vagal units the Vna was much higher during HFOV than during
IPPV or airway occlusion at a matched airway pressure. Ten units in the
phrenic nerves were examined, and Pna (expressed as bursts/min) was
attenuated by HFOV in all of them. In four of them, the effect of cooling
the vagi to 8-10 degrees C on Pna was examined, and it was found that HFOV
failed to alter the Pna. We conclude that 1) HFOV stimulates the pulmonary
vagal afferent fibers continuously and to a degree greater than that due to
static lung inflation and increased airway pressure and 2) the increased
vagal activity during HFOV probably causes phrenic nerve activity
inhibition.
