Objectives: A hierarchy in arousal response has been proposed for spontaneous arousal by analyzing the temporal changes in heart rate (HR) and electroencephalographic (EEG) activity. To address the question as to whether the same continuum may be proposed in sleep disorders, we performed temporal spectral EEG and HR analyses during periodic leg movements (PLM) associated or not with microarousal (MA).
Methods: Data were obtained in 12 patients with restless leg syndrome and/or PLM syndrome. PLMs were classified into 3 types including PLM associated with MA, PLM without MA, and PLM associated with delta or K-complex bursts. HR and EEG spectral analyses were done for 10s before and 10s after the PLM onset.
Results: Each type of PLM was associated with a typical EEG and autonomic pattern consisting of an increase in HR and delta band activity before the PLM, regardless of the presence or absence of MA. Thereafter, a rise in delta, alpha and beta(2) activity was noted associated with tachycardia. This was greater when MA or bursts of slow wave activity were present. In the period following the PLM, HR, delta and alpha power showed a long-lasting decrease with values significantly below the baseline.
Conclusions: From these data, we can conclude that: (1) cardiac and cerebral changes occur in association with PLM even when MA cannot be detected; (2) the combined increase in delta activity and HR before the onset of PLM suggests that these changes are part of the arousal response during PLM; (3) the graded arousal response during PLM confirms that the human arousal response involves a progression of central nervous system activation from brainstem to cortical level.