Changes in airway resistance during sleep onset.

Ventilation is lower during sleep than wakefulness. An increase in airway resistance has been proposed as the critical factor. As the change in ventilation has been shown to occur abruptly at transitions between alpha and theta electroencephalogram activity, it was of interest to determine whether the increase in airway resistance between wakefulness and sleep also occurs at these transitions. Three young healthy male subjects were run for an average of 15 sleep onsets in each of three conditions. The three conditions were 1) an esophageal balloon was put in place to allow the measurement of airway resistance, 2) in addition to an esophageal balloon the nose was occluded, and 3) there was no esophageal balloon and the nose was not occluded. Ventilation and airway resistance were measured during sleep onset and analyzed as a function of arousal state. In those conditions of the experiment in which airway resistance was affected by state, the changes, like those in ventilation, occurred at transitions between alpha and theta electroencephalogram activity. However, in the three subjects studied, the magnitude of ventilatory changes at alpha-theta transitions and the extent to which changes in ventilation were associated with changes in airway resistance differed between subjects. It was concluded that although inspiratory airway resistance is a major component affecting the state-related changes in ventilation at sleep onset, the degree of its contribution may vary over individuals.