Aim: 

Fluctuation in autonomic cardiovascular regulation during exposure to altitude can increase sleep disruption and the risk of heart attack. The aim of this study was to evaluate heart rate variability (HVR) in mountain marathon runners during sleep and after 30–41 hours of acclimatisation at 3480 m above sea level.

Methods: 

The study population was five adult mountain marathon runners (age range, 38–41 years). Polysomnography was carried out on the subjects during sleep at 122 m and after an acclimatisation period of 30–32 or 38–41 hours after reaching 3480 m. The polysomnographic records containing the ECG signals were scored and analyzed with automatic HRV Somnological 3 software (Embla®) following the guidelines (1996) of the Task Force of the European Society of Cardiology and North American Society of Pacing Electrophysiology.

Results: 

A significant decrease (P < 0.05) in the average mean RR intervals was observed during the awakening period, during sleep, and during stages S1 + S2 and S3 + S4 of Non-REM sleep and REM sleep. The averages of the mean total power of the high-frequency (HF) signals recorded during stages S3 + S4 (P < 0.01) of NREM sleep and during REM (P < 0.02) sleep at 3480 m differed significantly from those observed at 122 m.

Conclusions: 

The study results showed significantly diminished RR intervals in a sample of mountain marathon runners during sleep, indicating that decreased RR intervals could prolong the period of acclimatisation necessary to reduce sympathetic tone and cardiovascular stress during athletic performance at high altitude.

Sponsor FSA-SKY-ORG-FIRST 2007