APStracts 3:0429A, 1996.

Effects of carotid body hypocapnia during ventilatory acclimatization to hypoxia. Dwinell, M. R., P. L. Janssen, J. Pizarro, and G. E. Bisgard. Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive West, Madison, WI 53706

APStracts 3:0429A, 1996.

Hypoxic ventilatory sensitivity is increased during ventilatory acclimatization to hypoxia (VAH) in awake goats, resulting in a time -dependent increase in ventilation (E). The objectives of this study were to determine whether the increased CB hypoxic sensitivity is dependent on the level of CB CO2 and if the CB CO2 gain is changed during VAH. Studies were carried out in adult goats with CB blood gases controlled by an extracorporeal circuit while systemic (CNS) blood gases were regulated independently by the level of inhaled gases. Acute E responses to CB hypoxia (PcbO2 40 Torr) and CB hypercapnia (PcbCO2 50 and 60 Torr) were measured while maintaining systemic normoxia and isocapnia. CB PO2 was then lowered to 40 Torr for 4 hours while the systemic blood gases were kept normoxic and normocapnic. During the 4 hour CB hypoxia, E increased in a time -dependent manner. Thirty minutes after return to normoxia, the ventilatory response to CB hypoxia was significantly increased compared to the initial response. The slope of the CB CO2 response was also elevated following VAH. An additional group of goats (n=7) was studied with a similar protocol, except that PcbCO2 was lowered throughout the 4 hour hypoxic exposure to prevent reflex hyperventilation. Carotid body PCO2 was progressively lowered throughout the 4 hour CB hypoxic period to maintain E at the control level. Following the 4 h CB hypoxic exposure, the ventilatory response to hypoxia was also significantly elevated. However, the slope of the CB CO2 response was not elevated following the 4 hour hypoxic exposure. These results suggest that CB sensitivity to both O2 and CO2 are increased following 4 hours of CB hypoxia with systemic isocapnia. The increase in CB hypoxic sensitivity is not dependent on the level of CB CO2 maintained during the 4 hour hypoxic period.

Received 10 June 1996; accepted in final form 9 September 1996.
APS Manuscript Number A539-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996