REM Sleep Deprivation May Increase Sensitivity to Acute Pain

Yael Waknine

June 27, 2005

June 27, 2005 — Rapid eye movement (REM) sleep deprivation may cause increased sensitivity to acute pain, according to the results of a small prospective study presented at the Associated Professional Sleep Societies 19th Annual Meeting in Denver, Colorado.

In a previous study, investigators found that healthy, pain-free individuals demonstrated an enhanced sensitivity to acute pain following a four-hour general sleep restriction that included a 2/3 decrease in REM sleep.

"Such findings suggest that the relationship between disturbed sleep and pain is bidimensionsal— not only does pain disrupt sleep, but disrupted sleep may enhance pain," Timothy A Roehrs, PhD, lead investigator, told Medscape. "We were interested in determining whether loss of REM sleep itself is hyperalgesic."

Dr. Roehrs is the director of research at the Henry Ford Hospital Sleep Disorders and Research Center in Detroit, Michigan.

In the current study, six healthy adults aged 18 to 35 years with no history of psychiatric disease, primary sleep disorders, or drug abuse underwent two-night sessions of uninterrupted time in bed (TIB) for eight hours (T8), two hours uninterrupted TIB (T2), 9.5 hours TIB with REM deprivation (RD), and 9.5 hours TIB with yoked non-REM (NR) awakenings.

During REM deprivation, subjects were awakened on initiation of REM sleep and required to remain awake for 15 minutes before returning to bed; subjects were awakened at corresponding times during the NR session.

Pain threshold was assessed at 10:30 and 14:30 hours via index finger withdrawal latency (FWL) time in response to radiant heat stimulation applied at five randomized intensities. As a behavioral method of measuring reaction to pain, FWL eliminates the response bias inherent in self-assessment techniques.

Results showed that mean total sleep times were similar in the RD and NR conditions, and both were of shorter duration than in the T8 condition (5.3 and 5.2 vs 6.7 hours). The percentage of REM sleep during RD was significantly decreased compared with NR (3.68% vs 14.33%; P < .01). Also, the percentage of REM sleep during NR was significantly decreased compared with T8 (14.33% vs 21.72%; P < .02).

A significant correlation was found between treatment and morning pain testing (P < .003). REM sleep deprivation was associated with a significant decrease in mean FWL (7.76 seconds; P < .025), relative to T8 and NR conditions that yielded similar mean FWLs (11.36 and 10.05 second, respectively). The T2 FWL also differed from the T8 and NR conditions (7.23 seconds; P < .022) and was similar to that of the RD condition.

"Sleep disruptions were similar in the NR and RD conditions, but did not involve REM sleep; the effects on pain threshold observed in the RD condition were therefore due specifically to the loss of REM sleep, not to the disruption of sleep per se," noted Dr. Roehrs. "We found that REM loss itself was hyperalgesic."

According to Dr. Roehrs, the finding is significant in that analgesic medications have an acute REM-suppressing effect, and their efficacy may be potentially compromised by increased sensitivity to pain during the night.

"Physicians should be aware that in an acute pain situation, patients may experience increased pain due to sleep disturbances, and this preliminary association between REM loss and hyperalgesia suggests that improving patient sleep may be an important aspect of pain management," concluded Dr. Roehrs, noting that as with any small study, further research is necessary to confirm these findings and their clinical significance in a larger population.

The study was supported by the Fund for Henry Ford Hospital.

APSS 19th Annual Meeting: Abstract 0377. Presented June 23, 2005.

Reviewed by Gary D. Vogin, MD

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