Journal of Applied Physiology, Vol 61, Issue 4 1340-1345, Copyright © 1986 by American Physiological Society
Cardiorespiratory responses to hypoxia in intact and bilaterally vagotomized pigeons
G. M. Barnas, M. Gleeson and W. Rautenberg
Bilateral, cervical vagotomy in birds denervates, among other receptors,
the carotid bodies. To test whether such neural section removes sensitivity
to hypoxia, we measured respiratory, cardiovascular, and blood gas
responses to hypoxia at 84-, 70-, and 49-Torr inspiratory O2 partial
pressure (PIO2) in five pigeons with intact vagi and in five bilaterally,
cervically vagotomized pigeons. Normoxic respiratory frequency (fresp) and
expiratory flow rate (VE) were decreased after vagotomy. Intact pigeons
showed large increases in VE in response to hypoxia, effected mostly by
increases in fresp. VE also increased greatly in response to hypoxia in
vagotomized pigeons, but increases were largely the result of tidal volume.
O2 consumption, CO2 production, and respiratory exchange ratio increased
slightly in all pigeons during hypoxia. Normoxic heart rate was greater
after vagotomy; cardiac output increased in all pigeons in response to
hypoxia, but stroke volume increased only in intact pigeons. During
normoxia, arterial and mixed venous O2 partial pressure, O2 concentration,
and pH were lower and arterial and mixed venous CO2 partial pressure was
higher, after vagotomy. In all pigeons during hypoxia, arterial and mixed
venous O2 and CO2 partial pressure and O2 concentration decreased and
arterial and mixed venous pH increased; changes were roughly parallel in
intact and vagotomized pigeons. The arteriovenous O2 concentration
differences during normoxia and hypoxia were similar in all pigeons. We
conclude that bilateral, cervical vagotomy in the pigeon causes
hypoventilation and tachycardia during normoxia, but strong respiratory and
cardiovascular responses to hypoxia are still present.
