Ventilatory adaptations to resistive loading during wakefulness and non-REM sleep

Ventilatory and timing responses to repetitive and sustained inspiratory resistive loading were assessed in six naive male subjects during wakefulness (AW) and non-REM sleep (NREM). In five of six subjects, tidal volume (VT) was maintained or increased with repetitive five-breath loading periods during wakefulness. In these five subjects, mouth occlusion pressure (P₁₀₀) increased with loading during AWS (1.8 ± 0.5 control vs. 2.2 ± 0.4 cmH₂O loaded, P<0.05), but not during NREM (2.1 ± 1.5 control vs. 2.1 ± 1.5 cmH₂O loaded). For each state, VT and frequency (f) responses to sustained loads were similar to responses to five-breath loads. During sustained loading: a) VT increased 35% during AW, decreased 28% during NREM, b) f decreased 35% during AW, increased 6% during NREM, c) minute ventilation (V̇) decreased 12% during AW, decreased 23% during NREM. Ventilatory responses persisted until arousal (0.4-1.7 min) in NREM. With repetitive loading: a) inspiratory duration (TI) increased during AW but did not change during NREM, b) uty cycle(TI/TT) increased with loading in both states. These findings suggest that a) NREM abolished between-breath augmentations in P₁₀₀, b) within-breath load compensation is operant during both AW (preserved VT) and NREM (failure of predicted TI prolongation) by differing mechanisms, c) arousal may be a ventilatory compensation to inspiratory resistive loading in NREM.