DISTURBED SLEEP IS A FREQUENT COMPLAINT OF PEO- PLE EXPERIENCING ACUTE AND CHRONIC PAIN. OBJEC- TIVE ELECTROPHYSIOLOGIC STUDIES OF sleep in surgery

DISTURBED SLEEP IS A FREQUENT COMPLAINT OF PEOPLE EXPERIENCING ACUTE AND CHRONIC PAIN. OBJECTIVE ELECTROPHYSIOLOGIC STUDIES OF sleep in surgery patients with acute pain have documented reductions in sleep and rapid eye movement (REM) sleep time, frequent brief arousals, and also longer awakenings during 1 to 6 days of postsurgical recovery.1-7 Any number of confounding factors, including the sleep environment and the hormonal-biochemical response to the surgical insult, limit the ability to attribute the observed sleep disturbance to the pain in postsurgical recovery. Similarly, disturbed sleep has been reported in electrophysiologic studies of patients with various chronic pain disorders.8-12 Again, much of this literature is limited due to inadequate diagnostic rigor, including the comorbidity of depression and anxiety disorders, and of primary sleep disorders. An important observation arising from these studies, even with their limitations, is the bidirectionality in the pain-sleep relation (i.e., pain disturbs sleep and disturbed or shortened sleep enhances pain). One approach to avoiding the various confounds inherent in clinical studies is assessing pain sensitivity in healthy, pain-free adults after sleep manipulations. An early total sleep deprivation study conducted by Nathaniel Kleitman and his students reported “cutaneous sensitivity to touch remained unchanged,” whereas “that to pain showed a progressive increase during the period of deprivation.”13 The pain-threshold reduction began to emerge after an initial 8 hours of sleep loss. While reported anecdotally in sleep-deprivation studies, over all these years, only a few studies have directly assessed pain during sleep deprivation. The few modern studies indicate that total sleep deprivation has a hyperalgesic effect.14 However, in clinical conditions with acute or chronic pain, sleep is never totally absent. Sleep time is merely reduced or its staging disrupted. Thus, we first tested the hypothesis that reduced sleep time would have a hyperalgesic effect. While there are no systematic studies of sleep-time reductions, as opposed to total deprivation, several studies have assessed the hyperalgesic effects of selective sleep-stage deprivation. Due to the description of the alpha-delta sleep anomaly (i.e., an admixture of electroencephalogram [EEG] alpha and delta frequencies) in fibromyalgia patients and patients with chronic pain, the sleepstage deprivation studies have focused on slow-wave sleep.10 The results have been inconsistent, although they do suggest that when stage 3-4 sleep deprivation has hyperalgesic effects, it occurs with concomitant reductions of sleep time.15-17 We have therefore used a novel radiant heat stimulation methodology to assess pain sensitivity following modest sleep loss and sleep-stage specific loss of REM sleep. We chose to focus on REM sleep because of some intriguing conflicting information. On the one hand, opioid analgesics have been shown to suppress acetylcholine release and REM sleep when administered to brain Sleep Loss and REM Sleep Loss are Hyperalgesic