Laryngeal and diaphragmatic responses to airway occlusion in sleep and wakefulness.

Under anesthesia, electrodes were implanted in 5 adult cats for chronically recording sleep parameters. In the same operation, a tracheal fistula was created that allowed tracheal intubations for recordings of breathing (pneumotachography) and tracheal occlusions in subsequent experiments conducted during the spontaneous sleep-waking cycle. After a recovery period of at least 3 months, electrodes were placed, under ether anesthesia, in the laryngeal abductors. Two days later, electrodes were inserted into the diaphragm, and the responses of the diaphragm and laryngeal abductor muscles to airway occlusion in sleep and wakefulness were studied. Total airway occlusion at end-expiration in NREM sleep caused a progressive augmentation of both laryngeal adductor and diaphragmatic activity. Increases in laryngeal abductor activity exceeded for increases in diaphragmatic activity. The greatest augmentations between one breath and the next were seen when occluded breath "n" occurred in sleep and occluded breath "n + 1" occurred in wakefulness. This augmentation of activity at the transition from sleep to wakefulness was greater for the laryngeal abductors than for the diaphragm, and it signifies an immediate wakefulness stimulus to the response to an occlusion. Occlusions in REM sleep caused a variable augmentation in laryngeal inspiratory activity, but, across animals, there was no clear augmentation of either tonic (expiratory) laryngeal abductor or diaphragmatic activity. In addition, arousal in response to occulusion was delayed in REM sleep.