Journal of Behavioral and Brain Science, 2013, 3, 26-48 http://dx.doi.org/10.4236/jbbs.2013.31004 Published Online February 2013 (http://www.scirp.org/journal/jbbs)

Heart Rate Variability, Standard of Measurement, Physiological Interpretation and Clinical Use in Mountain Marathon Runners during Sleep and after Acclimatization at 3480 m Ivana Gritti1*, Stefano Defendi1, Clara Mauri1, Giuseppe Banfi1, Piergiorgio Duca1, Giulio Sergio Roi2

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Department of Biomedical and Clinical Science Luigi Sacco, University of Milan, Milan, Italy 2 Education and Research Department Isokinetic, Bologna, Italy * Email: [email protected], [email protected], [email protected] Received November 19, 2012; revised December 20, 2012; accepted December 27, 2012

ABSTRACT Fluctuations in autonomic cardiovascular regulation during exposure to high altitude may increase the risk of heart attack during waking and sleep. This study compared heart rate variability (HVR) and its components during sleep at low altitude and after 30 - 41 hours of acclimatization at high altitude (3480 m) in five mountain marathon runners controlled for diet, drugs, light-dark cycle and jet lag. In comparison to sea level, RR-intervals during sleep at high altitude decreased significantly (P < 0.001). The significant increase in sympathetic autonomic cardiovascular modulation at high altitude protects against excessive oxygen deprivation during sleep. Increases in R-R intervals can require longer periods of acclimatization at 3480 m to mitigate the effects of altitude/hypoxia on sympathetic tone, thus reducing cardiovascular distress at rest during waking and sleep and probably before during and after athletic performance at altitude. Keywords: Heart Rate Variability; Very Low Frequency Fluctuation (VLF,