CHRONIC EXPOSURE TO INSUFFICIENT SLEEP ALTERS PROCESSES OF PAIN HABITUATION AND SENSITIZATION

BACKGROUND & OBJECTIVE

Insufficient sleep is associated with pain in those with chronic conditions and in the general population. It is not clear if sleep patterns can be used to predict persistent pain, or if getting consistently sufficient sleep (7 to 8 hours per night) can be protective against persistent pain. There is a bi-directional relationship between sleep and pain (they can influence each other), but the mechanism remains unclear. Sleep restriction studies have found changes in pain sensitivity and severity. Pain inhibition, descending modulation, and decreased thresholds have all been proposed as possible effects from sleep deprivation studies.

This study examined whether chronic exposure to insufficient sleep is one means by which central pain-modulatory circuits become less functional. The authors wanted to test the hypothesis that if a person is consistently short on sleep, they will be more sensitized and be less able to modulate a pain response (hurt more, more often, with less stimulus needed).

METHODS

Study participants (N=17) underwent variations in their sleep in 2 separate 25-day inpatient settings that were more than 2 months apart (participants served as their own controls). They were randomized to the order of experimental conditions on the first day of the hospitalization. Each stay began with 5 nights of sleep restricted to 4 hours per night followed by 2 nights of 8-hour recovery sleep (to mimic common patterns of work/weekend sleep habits). The final day of the program for both groups was an 8-hour sleep opportunity.

Sleep Control conditions: 3 consecutive weeks of 8 hours/night of sleep opportunity.

Sleep Restriction conditions: Repeated exposure to sleep restriction of 4 hours per night, and two 8-hour days for 3 weeks.

The following data was collected for each participant on 7 of the 25 days:

• Polysomnography
• Blood and urine samples
• Pain Testing:
  1. Warmth detection threshold (associated with changes in pain processing)
  2. Heat pain threshold (a reflection of increased pain sensitivity)
  3. Cold pressor test (used to assess progressive increases in pain perception over time as a measure of temporal summation of pain)

An additional rating of spontaneous pain using VAS every 4 hours was taken during waking periods. Participants rated overall body pain. These scores were aggregated for analysis.

RESULTS

Average ratings of generalized body pain were higher in the sleep restricted condition. The higher reports of pain in the restricted condition did not increase in intensity over the 3 weeks of restricted sleep.

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