Ventilation during sleep onset.

There is now considerable evidence which indicates that respiratory activity is different during sleep compared with wakefulness. However, there has been little work on respiratory changes during the transitional period from wakefulness to sleep. The present study was concerned with the quantitative and temporal properties of ventilation during sleep onset. Sleep onsets were studied in five young male adults in a series of single-subject designs in which sleep onsets were replications. The results indicated that during sleep onset the loss of alpha-activity in the electroencephalogram was associated with a substantial, rapid, and highly predictable reduction in ventilation. The change in ventilation was typically due to a reduction in tidal volume and was, in part, secondary to a reduction in metabolic rate. We speculate that the nonmetabolic component may reflect the loss of waking neural drive to respiration, though the present study did not eliminate a variety of other interpretations.