AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 3 499-R504, Copyright © 1986 by American Physiological Society

ARTICLES

Regional circulatory responses to hypocapnia and hypercapnia in bar-headed geese

F. M. Faraci and M. R. Fedde

To investigate mechanisms that may allow birds to tolerate extreme high altitude (hypocapnic hypoxia), we examined the effects of severe hypocapnia and moderate hypercapnia on regional blood flow in bar-headed geese (Anser indicus), a species that flies at altitudes up to 9,000 m. Cerebral, coronary, and pectoral muscle blood flows were measured using radioactive microspheres, while arterial CO2 tension (PaCO2) was varied from 7 to 62 Torr in awake normoxic birds. Arterial blood pressure was not affected by hypocapnia but increased slightly during hypercapnia. Heart rate did not change during alterations in PaCO2. Severe hypocapnia did not significantly alter cerebral, coronary, or pectoral muscle blood flow. Hypercapnia markedly increased cerebral and coronary blood flow, but pectoral muscle blood flow was unaffected. The lack of a blood flow reduction during severe hypocapnia may represent an important adaptation in these birds, enabling them to increase O2 delivery to the heart and brain at extreme altitude despite the presence of a very low PaCO2.

This article has been cited by other articles:

				G. R. Scott and W. K. Milsom Control of breathing and adaptation to high altitude in the bar-headed goose Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2007; 293(1): R379 - R391. [Abstract] [Full Text] [PDF]