Cardiac activation during arousal in humans: further evidence for hierarchy in the arousal response

Objectives: One major subject of discussion in sleep studies is whether bur sts of K-complexes (K-bursts) and delta waves (D-bursts), expressions of a subcortical arousal, truly reflect an arousal response during sleep. To add ress this question we studied the changes in heart rate (HR) during spontan eous arousals in healthy subjects. Methods: Twenty-seven healthy adults were examined. Arousals were graded in 4 levels, including the standard definition of a micro arousal (MA), phase s of transitory activation (FAT), D-bursts and K-bursts. HR was analyzed fo r 10 brats before and 20 beats during arousal. EEG spectral analysis was pe rformed for all types of arousals, including in the analysis the 20 s perio d preceding the actual event. Results: Each type of arousal was associated with HR changes consisting of a tachycardia followed by a bradycardia. Changes were more pronounced durin g MA and FAT. Detailed analysis of the HR response showed that HR always in creased before MA and PAT onset, associated with a rise in delta, theta and Fast EEG activities, and suggesting a cerebral activation. Conclusions: Our data suggest that such subcortical arousals represent a re al arousal response inducing cardiac activation similar to that found durin g MA acid PAT. During MA and PAT, a rise in HR appears before the onset of the actual arousal associated with an increase in EEG slow and fast activit y. The link between EEG and HR variation during MA and PAT and the fluctuat ions in HR during subcortical arousal suggest a continuous spectrum in the arousal mechanisms, starting at the brainstem level and progressing to cort ical areas. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.