Load compensation as a function of state during sleep onset

Ventilation decreases and airway resistanceincreases with the loss of electroencephalogram alpha activity at sleeponset. The aim of this study was to determine whether reflexive load compensation is lost immediately on the loss of alpha activity. Sixhealthy male subjects were studied under two conditions (load andcontrol-no load), in three states (continuous alpha, continuous theta,and immediately after a transition from alpha to theta), and in twophases (early and late sleep onset). Ventilation and respiratory timingwere measured. A comparison of loaded with control conditions indicatedthat loading had no effect on inspiratory minute ventilation duringcontinuous alpha (differential effect of 0.00 l/min) and only a small,nonsignificant effect in theta immediately after phase2 transitions (0.31 l/min), indicating a preservationof load compensation at these times. However, there were significantdecreases in inspiratory minute ventilation on loaded trials duringcontinuous theta in phase 2 (0.77 l/min) and phase 3 (1.15 l/min) andduring theta immediately after a transition in phase3 (0.87 l/min), indicating a lack of reflexive loadcompensation. The results indicate that, because reflex load compensation is state dependent, state-related changes in airway resistance contribute to state-related changes in ventilation duringsleep onset. However, this effect was slightly delayed with transitionsinto theta early in sleep.