Journal of Applied Physiology, Vol 68, Issue 3 1024-1032, Copyright © 1990 by American Physiological Society
Respiratory muscle electromyogram responses to acute hypoxia in awake ponies
A. G. Brice, H. V. Forster, L. G. Pan, T. F. Lowry and C. L. Murphy
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
We determined the effect of acute hypoxia on the ventilatory (VE) and
electromyogram (EMG) responses of inspiratory (diaphragm) and expiratory
(transversus abdominis) muscles in awake spontaneously breathing ponies.
Eleven carotid body-intact (CBI) and six chronic carotid body-denervated
(CBD) ponies were studied during normoxia (fractional inspired O2 concn
[FIO2] = 0.21) and two levels of hypoxia (FIO2 approximately 0.15 and 0.12;
6-10 min/period). Four CBI and five CBD ponies were also hilar nerve
(pulmonary vagal) denervated. Mean VE responses to hypoxia were greater in
CBI ponies (delta arterial PCO2 = -4 and -7 Torr in CBI during hypoxic
periods; -1 and -2 Torr in CBD). Hypoxia increased the rate of rise and
mean activity of integrated diaphragm EMG in CBI (P less than 0.05) and CBD
(P greater than 0.05) ponies relative to normoxia. Duration of diaphragm
activity was reduced in CBI (P less than 0.05) but unchanged in CBD ponies.
During hypoxia in both groups of ponies, total and mean activities per
breath of transversus abdominis were reduced (P less than 0.05) without a
decrease in rate of rise in activity. Time to peak and total duration of
transversus abdominis activity were markedly reduced by hypoxia in CBI and
CBD ponies (P less than 0.05). Hilar nerve denervation did not alter the
EMG responses to hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)
