Respiratory mechanics and timing during sleep in occlusive sleep apnea.

Six human obese subjects with the sleep apnea hypersomnolence syndrome associated with upper airway occlusion (UAO) were studied during sleep to characterize respiration. Measurements included the timing components of ventilation, pulmonary resistance, flow, and esophageal and gastric pressures before and during UAOs. During the period between UAOs, the resistance progressively increased (9.4-18.1 cmH2O/l(-1) . s, P less than 0.05) as the ventilation decreased (1.82-0.77 l/s, P less than 0.05), but without changes in esophageal pressure swings. During this period, inspiratory time-to-total cycle time decreased (0.42-0.25 s, P less than 0.05) due to expiratory phase prolongation. The apnea began after expiration and terminated on inspiration with the maximal swings in esophageal and gastric pressure near the termination. During the UAO, the respiratory cycle time decreased slightly, but the expiratory pause time was significantly shortened immediately before ventilation. We suggest that the UAO is but one aspect of this syndrome and that a decrease in central nervous system activity diminishes the respiratory drive before the onset of the UAO.