The reduction of sleep time by at least four hours and the total loss of rapid eye movement (REM) sleep both produce an increased sensitivity to pain during the following day, according to a study published in the February 1 issue of the journal Sleep .
Reducing time in bed from eight hours to four hours produces a significant increase in pain sensitivity, and total sleep deprivation further increases the effect. Complete deprivation of REM sleep also significantly increases pain sensitivity compared with control nights of sleep.
“These are the first human data to show that modest sleep-time reductions, as opposed to total deprivation, and specific REM sleep deprivation have a hyperalgesic effect,” the authors write.
Disturbed sleep is often a complaint of people who have acute and chronic pain, according to background information in the article. Studies of postoperative patients consistently report an absence of REM sleep for one to two nights after surgery. Although the specific cause for this loss of REM sleep remains unknown, the authors point out that opiate medications such as morphine and methadone suppress REM sleep.
The researchers measured pain threshold by recording the time in seconds that it took each study subject to withdraw an index finger from a small metal box that periodically emitted varying intensities of radiant heat. Participants were tested at two times during the days after their nights of sleep manipulation.
All of the study subjects were healthy, pain-free, normal sleepers who ranged in age from 18 to 35 years.
The authors remain uncertain how the hyperalgesic effect observed in the study changes over time and how it relates to patients with chronic pain. They conclude, however, that their results have potential clinical significance.
“These findings imply that pharmacologic treatments and clinical conditions that reduce sleep and REM sleep time may increase pain,” the authors write.
Sleep is the official journal of the Associated Professional Sleep Societies, LLC, a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society. Go online to www.journalsleep.org.