APStracts 8:0025A, 2001.

Selected Contribution: Chemoreflex responses to CO2 before and after an 8-h exposure to hypoxia in humans. Fatemian, Marzieh, and Peter A. Robbins. University Laboratory of Physiology, University of Oxford, Oxford OX1 3PT, United Kingdom

APStracts 8:0025A, 2001.

The ventilatory sensitivity to CO2, in hyperoxia, is increased after an 8-h exposure to hypoxia. The purpose of the present study was to determine whether this increase arises through an increase in peripheral or central chemosensitivity. Ten healthy volunteers each underwent 8-h exposures to 1) isocapnic hypoxia, with end-tidal Po2 (Ťpeto2ť) = 55 Torr and end-tidal Pco2 (Ťpetco2ť) = eucapnia; 2) poikilocapnic hypoxia, with Ťpeto2ť = 55 Torr and Ťpetco2ť = uncontrolled; and 3) air-breathing control. The ventilatory response to CO2 was measured before and after each exposure with the use of a multifrequency binary sequence with two levels of Ťpetco2ť: 1.5 and 10 Torr above the normal resting value. Ťpeto2ť was held at 250 Torr. The peripheral (Gp) and the central (Gc) sensitivities were calculated by fitting the ventilatory data to a two-compartment model. There were increases in combined Gp + Gc (26%, P < 0.05), Gp (33%, P < 0.01), and Gc (23%, P = not significant) after exposure to hypoxia. There were no significant differences between isocapnic and poikilocapnic hypoxia. We conclude that sustained hypoxia induces a significant increase in chemosensitivity to CO2 within the peripheral chemoreflex.

Received 12 September 2000; accepted in final form 1 December 2000
APS Manuscript Number A917-0.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 January 2001