The effect of hypertonic saline infusion on sleep architecture in humans

Abstract

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.