Ventilatory and Arousal Responses to Added Inspiratory Resistance during Sleep

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Abstract
Airway resistance increases during sleep. We have determined the ventilatory and arousal responses to the addition of inspiratory resistance of 4,7, or 10 cmH2O/L/s during sleep in 10 normal men who slept wearing valved face masks. Insufficent ventilatory response data were obtained during rapid eye movement (REM) sleep to allow adequate analysis. The immediate responses to loading were decreases in tidal volume (Vt), breathing frequency (f), and minute ventilation ( e), with no difference between wakefulness and Stage 2 and Stage 3/4 sleep in the effects of loading on Vt and e, but f fell more during wakefulness than during sleep (p < 0.05) because of a greater lengthening of inspired time (Ti) (p < 0.05). During the first 10 breaths, occlusion pressure (P0.1) increased similarly in all EEG stages. Averaging responses during the 2-min periods when resistances were applied, the only variable to differ between EEG stages was Ti, which increased more in wakefulness than in Stage 2 or Stage 3/4 sleep (p < 0.01). Arousal within 2 min of application of resistance occurred less frequently from Stage 3/4 sleep than from Stage 2 or REM sleep (p < 0.02). The study demonstrates that sleep modifies the changes in respiratory timing produced by resistive loading without having a major effect on ventilation or P0.1 responses. The low frequency of arousal from Stage 3/4 sleep with loading may explain why asthmatics rarely awaken from this stage with wheeze.