Effect Of Hypoxic Training On Reducing Acute Mountain Sickness Symptoms

BackgroundAs people increasingly frequent high altitude activities, prevention and treatment of acute mountain sickness (AMS) is an important research topic. For the pathogenesis of AMS is not clear, so lack of reliable prediction, evaluation of clinical indicators and alleviation measures of AMS currently. Many studies showed that the hypoxia rather than the hypobaria is the causes of AMS, and AMS often occurred in 6-96 h after reaching altitude. Thus, the experimental results provide an important theoretical basis and experimental evidence that we might carry out the related researches of AMS in the normobaric hypoxia environment.ObjectiveThe previous study is aim to evaluate the impact of exposure to hypoxia on the participants. And research in acute rest hypoxic exposure and exercise in hypoxia from the perspectives of nervous system, respiratory system, vascular system and the endocrine system-related indicators and the link between AMS, trying to find a reliable prediction and (or) evaluation indicators of AMS; and on the basis of fact that hypobaric hypoxia can improve hypoxic tolerance, develop 3 weeks stepwise hypoxic training programs and observe the changes from the nervous system, respiratory system, vascular and endocrine systems, evaluation of hypoxic training reduce the AMS symptoms.MethodsAfter testing the baseline value, participant exposure in the hypoxia chamber (simulated altitude of～4800 m, FIO2 10.4-10.8%) for 6 hours. according to participants’ AMS score at the end of 6 h, divided into AMS Group (AMS score≥3 points and with a headache symptoms) and nonAMS group. Test AMS score and pulmonary function at subjects were exposed to hypoxia chamber 0.5,2,4 and 6 hours after they enter into the chamber. And record dynamic electromyography, heart rate variability (HRV), ventilation markers, heart rate, arterial oxygen saturation (SpO2) and dynamic blood pressure every 5 min when participant supine resting 5 min and supine pedaling exercise with constant load of 80 W (60 rpm) for 20 min. Also, test pulmonary function before and after exercise immediately. And after 3 weeks of hypoxia training, participants rest for 1 week, and then repeat the 6 h exposure to acute hypoxia chamber and acute hypoxia exercise. In addition, participants were drawn vein blood 4 times [in the normoxic resting (NM I), the first 6 h of acute exposure to the end of hypoxia (HY I), the resting after 3 weeks hypoxia training program (NM II) and second acute hypoxic exposure 6 h (HY II)] for analysis of atrial natriuretic peptide (ANP) and angiotensin-convertion enzyme (ACE).Results1) The AMS scores of AMS group and nonAMS group were 3.4±1 and 1.2±0.9, respectively (AMS incidence is 56%). After 3 weeks of hypoxia training, AMS scores of AMS group and nonAMS group are 2±1.8 and 0.8±1, respectively. And prevalence of AMS was only 10%;2) At acute hypoxia 5 min, RMSSD of AMS group was significantly lower than nonAMS group (P=0.05). The AMS group’s LFnu and lnLF/HF was significantly higher than nonAMS group’s, however, we observed crossover phenomenon after participants exercised 10 min (exercise 10 min-20 min AMS Group’s LFnu and lnLF/HF were higher than nonAMS group, but there were no significant differences). Three weeks after hypoxic training, the aforementioned three HRV markers were no significant differences between AMS group and nonAMS;3) SpO2 of AMS group was significantly lower than nonAMS group in the resting hypoxia exposure (75.6±5.0 and 78.6±3.4, P=0.024); And SpO2 of AMS group was significantly lower than nonAMS group in hypoxic exercise. Although AMS and nonAMS group’s SpO2 were significant increased, however, after 3 weeks of hypoxia training, there was no significant difference between the two groups. Only when exercise 5 min time point, AMS group’s SpO2 was significantly lower than nonAMS group;4) There were no significant difference of ANP between AMS and nonAMS group in NM I (P=0.47). Although the two groups’ ANP were significantly decreased at the end of both of HY I and HY II, there were no significant differences between the two groups;5) For the HY I, AMS group’s ACE change volume is significant higher than nonAMS group’s (7.1±8.9 and -11.0±14.8, P=0.02). And there were no significantly difference at NM II (P=0.092). Interestingly, however, at HY II, the two groups have lower ACE activity, and AMS group is significantly higher than nonAMS group (6.9±13.6 and -61.6±17.4, P<0.05).Conclusions1) In the previous study, the 6 h model of acute hypoxic exposure (simulated～4800 m, FIO2 10.4%-10.8%) can be used to research the AMS, and the three weeks of stepwise hypoxia training program can effectively reduce symptoms of AMS;2) During acute hypoxia exercise, the lnLF and lnLF/HF of HRV index can be used to predict AMS, suggesting that hypoxia tolerance is related to ANS dysfunction during acute hypoxia exercise; and 3 weeks stepwise hypoxic training by strengthening the autonomic nervous system, "Vagus-sympathetic" bi-direction regulation, and improve the ANS balance, and thus play a role in alleviating AMS; 3) The Change of SpO2 can be regarded as an effective prediction and (or) evaluation marker during acute hypoxic exposure and acute hypoxia exercise, indicating arterial hypoxemia is an important factor inducing AMS;4) The results from the present study, ANP does not apply to the predict and (or) evaluate the AMS, the mechanisms are still unclear; but it may be used as a hypoxic effect evaluation marker.5) The results from the present study, ACE activity has relationship with hypoxia tolerance:ACE decreased is represent participant has good hypoxia tolerance. However, ACE activity is not sensitive to hypoxia training; it is unclear which means lead to regulating the ACE activity slow down after hypoxia training.