Cardiac autonomic nervous activity during ascent from sea level to 3000m in 10 minutes and then back to sea level using the same time

This study was aimed to assess the responses of cardiac autonomic nerve during the simulated altitude ascending from sea level to 3000m in 10 minutes, and then returning to sea level using the same time. R-R interval (RRI) series were analyzed continuously by wavelet packet transform followed by Hilbert transform to assess the amplitudes of modified total (TPmod: 0–0.4375 Hz), low (LFmod: 0.0625–0.1875 Hz) and high (HFmod: 0.1875–0.4375 Hz) frequency component, as well as the ratio of LFmod/ HFmod in every one minute. The results suggested that the autonomic heart rate control was gradually attenuated in the process of ascent, and was progressively enhanced during descent. The balance of sym-pathovagal shifted to sympathetic dominance during the study. Monitoring cardiac autonomic nervous responses in the process of ascent and descent would be an effective way to evaluate the regulatory mechanism for acclimatization to hypoxia.