In patients with obstructive sleep apnea and associated rapideye-movement (REM) sleep deprivation and disruption, the first night of nasal continuous positive airway pressure (CPAP) is often associated with increases in REM sleep time and REM density (REM rebound). The amount of REM rebound, however, varies considerably. We sought to characterize the magnitude of REM rebound and to determine what factors determine individual differences in REM rebound with initial CP AP treatment. Twenty-six

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... ients with sleep apnea had a baseline nocturnal polysomnogram and a second night with a trial of CPAP. REM sleep time increased by 69% with CPAP, REM density increased by 73%, and REM activity by 169%. REM density was highest in the second REM period. Improvement in respiratory disturbance index with CP AP correlated significantly with increased minutes of REM sleep with CPAP. Of polysomnographic measures on the baseline night, change in minutes of REM sleep with CPAP correlated best with minimum oxygen saturation and to a lesser degree with respiratory disturbance index, and minutes of Stage 1 sleep. One possible explanation for the effect of hypoxemia on subsequent REM rebound is that some physiological functions of REM sleep may fail when oxygen saturation falls below a certain level. Key Words: Sleep apnea-Sleep-REM sleep-CP AP-REM activity. In patients with obstructive sleep apnea (OSA), rapid-eye-movement (REM) sleep is usually diminished and fragmented by repeated arousals from apneas. Successful treatment with nasal continuous positive airway pressure (CPAP) allows extended continuous periods of REM sleep. The REM pressure built up from the accumulated REM deprivation leads to a transient increase in REM sleep (REM rebound) (1).