| Summary: | Many patients with chronic pain complain of sleep problems. However, the
relationship between sleep and pain in these patients is still not fully understood.
Experimental models are used to understand the interaction between pain and
sleep, but up until now all such models have been of short duration and assessed
different end-points of sleep disruption. The aim of the study is to develop a
longer-acting model to mimic the muscle pain seen in patients with chronic pain,
assess whether the end-point of sleep disruption is constant over subjects and
assess whether the disruption is dependent on length of stimulation and/or the
sleep stage involved. Twelve healthy male subjects participated in the study. They
were exposed to multiple hypertonic and isotonic saline infusions, for a duration
of ten minutes, both while awake and during all stages of sleep. The muscle pain
intensity and quality during wakefulness were assessed using the Visual Analogue
Scale (VAS) and McGill Pain Questionnaire. Polysomnographic signals were
recorded to score sleep changes during all sleep stages. During wakefulness
hypertonic saline infusions produce significantly greater VAS Scores than
isotonic saline infusions. Differences between the VAS scores from evening to
morning were non-significant, therefore implying that there was no overnight
hyperalgesia after any of the experimental stimulations. When compared to the
isotonic saline infusions, the noxious hypertonic saline infusions triggered
significantly more microarousals during REM (67% of subjects); more sleep stage
shifts in SWS (42% of subjects) and more full arousals during stage 2 (83% of
subjects), SWS (67% of subjects) and REM (67% of subjects) sleep. The data
suggests that pain during sleep triggers multiple different end-points of sleep disruption during sleep and the specific end-points may be determined by the
sleep stage involved. The sleep disturbances found in our model of experimental
pain may be similar to those found in patients with chronic muscle pain.
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