LOS ANGELES, Feb. 15 (Xinhua) -- Patients with severe obstructive sleep apnea (OSA) are more likely to have a significantly lower frequency of nightmares than patients with mild or no sleep apnea, a new study shows.
The findings indicate that OSA suppresses the cognitive experience of nightmare recall, according to the study published in the Feb. 15 issue of the Journal of Clinical Sleep Medicine.
This is the first large study to address both reported dream and nightmare recall frequency in a clinically evaluated sample of patients with a high frequency of severe OSA, said researchers at the University of Colorado Medical School.
This retrospective study involved 393 consecutive patients who were evaluated by overnight polysomnography over a two-year period. Their mean age was 50.5 years with a range of 13 to 82 years, and 67 percent of participants were male.
The 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).
The authors noted that the study clearly demonstrates that increasingly severe OSA has a much greater negative effect on reported nightmare recall frequency than it does on reported dream recall.
The decline in frequency of nightmare recall may be attributed to the sleep fragmentation that is caused by OSA, leading to a reduction in the amount of rapid eye movement (REM) sleep, which is the sleep stage when nightmares generally occur, according to the study.
