Researchers from the Sleep Disorders Center of Southern Colorado in Pueblo found that 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.
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% of people who did not have OSA and 43.2% 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% in patients with moderate OSA (AHI of 15 to less than 30) and 20.6% 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, MS, MD, associate clinical professor at the University of Colorado Medical School system and director of the Sleep Disorders Center 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 study was published in the February 15 issue of the Journal of Clinical Sleep Medicine.