Muscle nerve sympathetic activity during sleep and its change with arousal response.

Muscle nerve sympathetic activity (MSA) was recorded from the peroneal nerve during wakefulness and in different sleep states in healthy young adults. The burst rate (BR) of MSA significantly decreased in NREM, but not in REM sleep, compared with that during wakefulness. Transient increases of MSA frequently appeared in association with rapid eye movements during REM sleep. K-complexes in Stage 2 were almost always accompanied by a burst of MSA, and were followed by a transient elevation of arterial blood pressure. Auditory stimuli applied in sleep induced a burst of MSA followed by a transient increase of arterial blood pressure, only when they elicited an arousal response in the EEG, such as a K-complex, transient EEG desynchronization, or a short train of alpha waves. The same stimuli applied during wakefulness did not induce such changes in MSA and in arterial blood pressure.