APStracts 3:0220A, 1996.

Pco2 affects tracheal tone during apnea in anesthetized dogs. Dickstein, J., A. Greenberg, J. Kruger, A. Robicsek, J. Silverman, L. Sommer, D. Sommer, G. Volgyesi, S. Iscoe, and J. A. Fisher. Department of Anaesthesia, University of Toronto, Toronto, ON M5G 1X5 CANADA

APStracts 3:0220A, 1996.

We hypothesized that CO2, like hypoxia and withdrawal of pulmonary slowly adapting receptor input, would cause tracheal constriction during neural apnea (absence of phrenic activity). In seven anesthetized, paralyzed dogs ventilated to neural apnea, we increased PaCO2 in steps by adding CO2 to the inspirate while keeping ventilation constant. Increases in PaCO2 caused tracheal constriction during neural apnea in all dogs; 69 +/- 26 (SD)% of the change in tracheal diameter occurred during neural apnea. Average sensitivity of tracheal diameter to CO2 was 0.44 mm/mmHg CO2. Our data suggest that central chemoreceptor inputs to brainstem neurons controlling smooth muscle of the extrathoracic airway bypass central mechanisms generating inspiration.

Received 5 January 1996; accepted in final form 29 March 1996.
APS Manuscript Number A23-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 May 96