[Comparison of heart rate variability in healthy young men during exposure to different altitudes].

The characteristics of cardiovascular autonomic nerve system(ANS) modulation during exposure to three different altitudes were compared by time domain, spectral and nonlinear analysis of short-(5 minutes)term heart rate variability (HRV). The standard deviation of all RR intervals (SDNN), the square root of the mean squared differences of successive RR intervals (rMSSD), the percentage of successive interval differences >50 ms (PNN50), low frequency (LF), high frequency power (HF), and total power (TP) at 2800 m were slightly higher than those at 1856 m, but the differences were non-significant statistically. SDNN, rMSSD, LF and HF at 3040 m were significantly lower than those at 1856 m and 2800 m. These results show that parasympathetic nerve activity decreases significantly, and ANS modulation is blunted after exposure to higher altitude. This kind of change of ANS may contribute to further elucidate pathophysiology in body after exposure to high altitude.