State of vigilance, oestrogen replacement therapy, and lipid profile as modifiers of nocturnal movement-induced heart rate responses.

Study Objectives: To investigate the body movement-associated heart rate responses during sleep in postmenopausal women and to evaluate the possible effect of transdermal oestrogen replacement therapy and metabolic factors on these responses.

Design: A prospective double-blind cross-over placebo-controlled trial.

Setting: A university sleep research unit.

Patients: Seventy-one healthy postmenopausal women.

Methods: The subjects underwent a whole-night polysomnography including an electrocardiogram (ECG) and a sensitive whole-body movement sensor channel. Body movements of 2-15 s duration with an artefact-free ECG were identified and heart rate was automatically analysed for 30 s before and 60 s after movement. The movement-induced reflex tachycardia and the following rebound bradycardia were measured for the awake state, non-rapid eye movement (REM) sleep and REM sleep. Indices of the heart rate response correlated with age, body mass index (BMI) and high-density lipoprotein (HDL)/low-density lipoprotein (LDL) cholesterol ratio.

Results: The tachycardia response to a body movement was stronger during sleep than in the awake state, being strongest in REM sleep. The rebound bradycardia following a tachycardia response was relatively similar in REM and in the awake states, but attenuated in non-REM sleep. Oestrogen did not influence the heart rate response. Increasing age and BMI attenuated the response, while an increase in the HDL/LDL cholesterol ratio enhanced the rebound bradycardia response.

Conclusions: Sleep powerfully modulates the rapid cardiac autonomic responses to internal stressors. Postmenopausal hormone replacement therapy does not influence these responses, but they are strongly modulated by lipid metabolism and closely correlated with age and BMI.