Effects of REM sleep on the ventilatory response to airway occlusion in the dog.

We determined the effects of sleep state on the ventilatory response following transient airway occlusion and on the response to vagal blockade in the unanesthetized sleeping dog. Three tracheotomized dogs underwent repeated occlusions (159 trials) during rapid eye movement (REM) and nonrapid eye movement (NREM) sleep. In all sleep states we found significant but variable transient hyperventilation following release of occlusion. In NREM sleep, a significant central apnea [expiratory time (TE) prolonged 2-10 times control] followed the hyperpneic response, so long as the increase in tidal volume (VT) during the hyperpnea exceeded three times control VT, that is, a volume-dependent apneic threshold. In REM sleep with maintained levels of eye movement density, hyperventilation commonly followed release of obstruction but only very rarely did VT exceed the volume threshold, and central apnea was rare. Cervical vagal blockade was used to show that significant inhibitory pulmonary stretch receptor reflexes were present in both NREM and REM sleep, although the strength of the reflex was diminished in REM. We postulate that the phasic events of REM sleep inhibit the increase in VT in response to the chemical stimuli accumulated during airway occlusion and also interfere with the prolongation of TE in response to lung stretch and/or transient hypocapnia. The result is that central apnea occurs only very rarely in REM sleep.