Heart rate changes during sleep in response to experimental thermal (nociceptive) stimulations in healthy subjects

Objective: During wakefulness, nociceptive thermal stimulation can trigger a rapid and transient rise in heart rate (HR). During sleep, HR variations are different across sleep stages; HR is more variable in stage 2 and in REM than in stages 3 and 4. The aim of this study was to assess the HR response to experimental thermal stimulation during different sleep stages. Methods: Eight young subjects free of sleep and pain problems, underwent a night of polysomnographic recording during which experimental thermal stimulations were applied. During all sleep stages (St), a series of cold, warm/control and heat pain stimulations were applied over the shoulder skin by means of a water-driven system. Variation of HR interval was measured for 6 s before and for 6 s during the thermal stimulation. Results: In comparison to control warm stimulation, experimental nociceptive thermal stimulation induced a significant rise in HR during sleep; HR increased by 7% in St 2, 5.4% in St 3&4, and by 4.3% in REM sleep. Conclusion: The brief increase in cardiac activity with experimental nociceptive stimulation suggests that during sleep, the autonomic-cardiac nervous system remains reactive to external sensory inputs and is part of the physiological response to preserve body safety and sleep integrity in the face of potentially harmful stimulation.