Objective  To explore the dynamic changes and significance of heart rate variability (HRV) during the initial phase after acute exposure to Tibet plateau by combining time

frequency domain and non-linear analysis.   Methods  Eighty-six healthy young men of Han nationality underwent short-term (5 min) heart rate variability (HRV) monitoring at 560 meter above sea level (plain)

then were transported to Tibet plateau (3675 meter above sea level) by airplane. There

all subjects were divided into 3 groups

and A gorup (n=12) underwent HRV monitoring on the 2nd day after arrival

B group (n=48) on the 3rd day

  C gr

oup (n=26) on the 4th day.   Results  Compared with the data obtained at plain

the standard deviation of normal to normal intervals (SDNN)

high frequency (HF) and total power (TP) decreased significantly (P0.01)

and root mean square of delta RR (rMSSD)

percentage of delta RR50 ms (PNN

50

) and normalized high frequency (HFnu) also decreased obviously (P0.05)

but the normalized low frequency (LFnu) and LF/HF increased significantly (P0.01) in the 2nd day HRV detection at Tibet. During the 3-4 days after arrival at Tibet

SDNN

rMSSD

HF

TP and HFnu gradually increased

while LFnu and LF/HF tended to decrease toward plain values. However

fractal dimension (FD) within the 2-4 days after arrival kept lower than that at plain.   Conclusion  During initial phase of acute exposure to plateau

HRV decreases

and the modulation function of autonomic nervous system is generally blunted

then the function of autonomic nervous system recovers gradually toward plain values.