Sleep deprivation can induce or worsen nocturnal respiratory disturbances. In patients with sleep apnea hypopnea, sleep abnormalities consist of repetitive episodes of arousals and awakenings that lead to sleep fragmentation. Because the propensity for upper airway collapse is increased in these patients, we wondered if sleep fragmentation could increase upper airway collapsibility and contribute to the pathogenesis of this disease. In eight normal subjects, upper airway collapsibility was assessed during sleep by progressively decreasing the pressure in a nasal mask while recording airflow, mask, and esophageal pressures. The critical pressure was determined by the relationship between breath-by-breath values of maximal inspiratory airflow of each flow-limited inspiratory cycle and the corresponding mask pressure. Critical pressure was measured twice in each subject: after one night of total sleep deprivation and after one night of sleep fragmentation using auditory stimuli. The two measures were done in random order 1 wk apart. A polysomnographic recording was obtained the night after each measurement of critical pressure. Sleep architecture was identical after sleep deprivation and fragmentation. Sleep-related breathing abnormalities were more frequent after sleep fragmentation than after sleep deprivation. Critical pressure was -17.1 +/- 6.8 cm H2O (mean +/- SEM) after sleep deprivation, and -12.3 +/- 6.3 cm H2O after sleep fragmentation (p < 0.05), corresponding to an earlier closing of the upper airway. We conclude that sleep fragmentation leads to a higher upper airway collapsibility than does sleep deprivation.