Ventilatory effects of specific carotid body hypocapnia in the dog during wakefulness and sleep . Smith, Curtis A., Kurt W. Saupe, Kathleen S. Henderson, and Jerome A. Dempsey. The John Rankin Laboratory of Pulmonary Medicine, Department of Preventive Medicine, University of Wisconsin, Madison, 504 N. Walnut Street, Madison, WI 53705-2368
APStracts 2:0181A, 1995.
We used extracorporeal perfusion of the vascularly-isolated carotid sinus region to determine the effects of specific carotid body chemoreceptor hypocapnia/alkalosis on ventilatory control in the unanesthetized dog. Eight female dogs were studied during wakefulness, non-rapid eye movement sleep (Non-REM), and rapid eye movement (REM) sleep. Carotid body perfusions lasted from 1 to 2 minutes and each trial was preceded by a 1 minute control period. Two levels of carotid body hypocapnia were employed, approximately 7 and 14 Torr below eupneic levels in a given dog. We found: 1) During wakefulness and Non-REM sleep carotid body hypocapnia caused reduced tidal volume (VT) but not apnea or expiratory time (TE) prolongation. 2) The inhibition of ventilation in response to carotid body hypocapnia was graded below normocapnia, showing the highest sensitivity at carotid body PCO2s (PCBCO2) near 7 Torr below eupneic values. Inhibition reached a maximum near 14 Torr below the eupneic level; VT, I, and VT/TI fell 31, 23 and 27% in wakefulness and 30, 23 and 30% in Non-REM sleep. 3) Reductions in ventilation in response to carotid body hypocapnia are lessened but still persist throughout perfusion (up to at least 130 seconds) despite significant systemic hypercapnia. 4) During REM sleep carotid body hypocapnia had no consistent inhibitory effect on ventilation until PCBCO2 was reduced to values near 14 Torr below the eupneic level at which point ventilation was similar to wakefulness and Non-REM. 5) Moderate carotid body hypocapnia was as effective as carotid body hyperoxia in reducing VT and I. We conclude that carotid body hypocapnia/alkalosis can significantly inhibit eupneic VT and ventilation during wakefulness and Non-REM sleep and, if the hypocapnia is severe enough, during REM sleep. 

Received 19 December 1994; accepted in final form 24 April 1995.
APS Manuscript Number A1282-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  9 May 1995.