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Title: Light and diurnal cycle affect autonomic cardiac balance in human; possible role for the biological clock
Author(s): F.A. Scheer, L.J. Van Doornen and R.M. Buijs
Journal: Auton.Neurosci.
Year: 2004
Volume: 110
Issue: 1
Pages: 44--48
Publisher address: Project Group Hypothalamic Integration Mechanisms, Netherlands Institute for Brain Research, Amsterdam, The Netherlands.
File URL: vuams-pubs/Scheer_2004.pdf
Keywords: Adult, Affect, Biological Clocks, Circadian Rhythm, Female, Heart, Heart Rate, Humans, innervation, Light, Male, Netherlands, Photic Stimulation, Photoperiod, physiology, radiation effects, Sympathetic Nervous System, Time, Vagus Nerve
Abstract: The morning shift in cardiac sympatho-vagal balance seems involved in the increased risk of cardiovascular incidents at that time. To investigate the contribution of the biological clock in autonomic cardiac control, we investigated the presence of a diurnal rhythm independent of external factors, and of a circadian phase-dependent effect of moderate light in healthy volunteers. Recordings of heart rate (HR) and vagal and sympathetic cardiac tone were performed at different times over the day-night cycle during supine, awake, resting conditions, during exposure to different light intensities. The similarity between the diurnal rhythm in resting HR and that during previous constant routine conditions, demonstrated that our setup allowed accurate estimation of the endogenous circadian rhythm in HR. The present study suggests that, while a circadian rhythm in vagal cardiac tone is the main cause for the circadian rhythm in resting heart rate, the increase in sympathetic cardiac tone participates in the HR increase caused by early morning light

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