Severe sleep apnea reduces nightmare recall frequency

'Sleep apnea' being monitored at a Sleep Lab in Thiruvananthapuram. Sleep apnea is a condition where breathing is interrupted, causing disturbances in sleep. Photo: P.V. Sivakumar

Patients with severe obstructive sleep apnea (OSA) report a significantly lower frequency of nightmares than patients with mild or no sleep apnea, indicating that OSA suppresses the cognitive experience of nightmare recall, say researchers.

The study has been published in the Feb. 15 issue of the Journal of Clinical Sleep Medicine.

Results show that the percent of participants with frequent nightmare recall decreased linearly as sleep apnea severity increased. Frequent nightmare recall, occurring at least weekly, was reported by 71.4 percent of people who did not have OSA and 43.2 percent of patients with mild OSA, which was defined as an apnea—hypopnea index (AHI) of five to less than 15 breathing pauses per hour of sleep. The rate of frequent nightmare recall decreased to 29.9 percent in patients with moderate OSA (AHI of 15 to less than 30) and 20.6 percent in patients with severe OSA (AHI of 30 or more). Sleep apnea severity in people who reported infrequent nightmare recall (mean AHI of 40.3) was significantly higher than in those who frequently recalled nightmares (mean AHI of 24.6).

According to principal investigator Jim Pagel, M.S., M.D., associate clinical professor at the University of Colorado Medical School system and director of the Sleep Disorders Centre of Southern Colorado in Pueblo, the decline in frequency of nightmare recall may be attributed to the sleep fragmentation that is caused by OSA. This leads to a reduction in the amount of rapid eye movement (REM) sleep, which is the sleep stage when nightmares generally occur.

“The results were somewhat surprising, since nightmares are frequently reported by patients with sleep apnea,” said Pagel. “It is plausible that patients who successfully utilize continuous positive airway pressure (CPAP) therapy see an increase in the frequency of nightmares, as treatment increases the amount of REM sleep per night.” The retrospective study involved 393 consecutive patients who were evaluated by overnight polysomnography at the Sleep Disorders Centre of Southern Colorado over a two-year period.