Experimental Research On The Protection Effect Of Artificial Oxygen Enriched Environment Against Hypoxia Of Emergent Entering High Altitude

With the development of the science and technology as well as the improvement of long distance transport capacity of PLA, the speed that people enter the high altitude has been progressively accelerated, especially those who enter high altitude by air, such as pilots, investigators or travelers, etc., will suddenly expose to the low-pressure and hypoxia environment of high altitude within several hours while have to work immediately or put into flying again next day. To ensure their capacity of work and fighting has become the focus that people pay close attention to. In this situation, the authoritative and traditionary anti-hypoxia methods that laddered high altitude acclimatization and hypoxic training have been already no longer suitable in the case of taking too much time. However, there is a high-efficient and immediate effect anti-hypoxia method that supplying oxygen on high altitude for preventing hypoxia effectively through increasing the oxygen concentration and partial pressure of indoor air, which is suitable for people who enter high altitude emergently. Nowadays, nasal feeding oxygen is the main form of high altitude oxygen supplying for its economy of oxygen and energy. While, the oxygen concentration of inspired air is instable and the stimulant to the mucous membrane of nose is serious, as a result it is so unbearable that people couldn't get to sleep well at night. The oxygen artificial oxygen enriched environment(AOEE) at high altitude can protect people from high altitude hypoxia without any appliance through improving the oxygen concentration of indoor air, which is especially suitable for the people, such as pilots, because they not only need to guarantee the effect of oxygen supply, but also insure the sleep quality and the efficiency of human body for flight security.It is confirmed that supplying oxygen in diffusion way has extensively effected anti-hypoxia, however, there is no authoritative regulation of it, more research on the suitable oxygen concentration and supplying oxygen time are still on the way. Moreover, domestic study usually takes up with the gas cylinders with the high pressure or the liquid oxygen as the oxygen source of the oxygen enriched room, but it is hardly to meet the request of the oxygen enriched room for long-time usage, so the oxygen-supply system that can continually supply a large amount of oxygen is urgently needed. Consequently, according to the request and commission of the development of the diffusion oxygen-supply system of Tibet Autonomous Region and Air Force contribution project of the high altitude oxygen-supply, we have studied the preventing high altitude pulmonary edema (HAPE) effect of oxygen enriched room that had different oxygen concentration and different time to supply oxygen through the animal model of HAPE. According to the results of animal experiment and our experience of aviation medicine study in decades, we have made the preliminary standard that the oxygen concentration of the oxygen enriched room to prevent pilots who enter 3500m high altitude above sea level emergently from high altitude hypoxia should be 25%±0.5%, which is resulted from oxygen partial pressure of inspired air〔(75±2) mmHg〕and physiologically equivalent altitude〔(2200±150)m〕. Meanwhile, based on the technology of pressure swing adsorption oxygen making of molecular sieve, a new high altitude diffusion oxygen-supply system has been developed. Then, the human subjects experimentation in an oxygen enriched room at high altitude has been taken to evaluate anti-hypoxia effect. The results of this study have offered the foundation of the application of the oxygen enriched room as well as the medical experimental basis for the technical evaluation of the diffusion oxygen-supply system of Tibet Autonomous Region and the high altitude oxygen-supply contribution of Air Force.METHODS1. Animal experiment 50 male Wistar rats were randomly divided into five groups, ground contrasted group(C), hypoxia group (H) , rich oxygen group 1(OⅠ), rich oxygen group 2(OⅡ) and rich oxygen group 3(OⅢ), 10 rats of each group, which were raised to 6000m at the speed of 10m/s in the low-pressure rich oxygen experiment chambers, except group C. Meanwhile, group H was supplied with air, group OⅠand OⅡwere supplied with gas that contain 35% and 30% oxygen respectively, group OⅢwas alternatively supplied air or gas that contain 35% oxygen every 4h with the flow rate of 7L/min. The experiment chambers were put down after 24h, and put the rats to death. The left lung was fetched to examine the water ratio of it, the frontal lobe of right lung was used for pathological observing, the middle and posterior lobe of the right lung were used to detect the concentration of endothelin-1(ET-1) and nitricoxide synthase (NOS) vigor respectively. 2. Human subjects experimentation on the high altitude scene At high altitude of 3500m above sea level, the oxygen enriched room with the oxygen concentration of 25.49%±0.26 % (physiologically equivalent altitude about 2100m) was built by utilizing high altitude diffusion oxygen-supply system. 18 plain residents were divide into three groups with 6 people for each, the rich oxygen group (O), hypoxia group (H) and plain group (P). After the group O and group H reached the high altitude by air, the HR and SaO2 were recorded before oxygen was supplied while group P was stay on the plain. From 22:00 to 9:00 of the next day, when group O and group H have a rest at the oxygen enriched room and normal room respectively, SaO2, pulse wave and hand move signals were monitored by the sleep monitors while all data of group P were monitored on the plain. The sleep quality questionnaire of three groups was asked to complete at the morning.RESULTS1. Animal experiment The water ratio of lung among every group presented the remarkable difference. It is the lowest of ground C's (0.80%±0.006%, P <0.01), the water ratio of group H was the highest (0.83%±0.010%, P <0.01) and those of the 3 oxygen supplied groups were between two parties. The water ratio of group OⅡwas 0.81%±0.007%, which was obviously lower than group OⅠand OⅢ(P <0.05). Group C was highest〔(1.49±0.24) U/mgpro, P <0.01〕on the vigor of NOS, the NOS vigor of group H was the lowest〔(0.78±0.28 )U/mgpro, P <0.01〕. Compared with the group H, the NOS vigor of group OⅠand OⅢwere more strengthened〔(1.06±0.17)mgpro, (1.09±0.20) mgpro, P <0.01〕, but there were no significant strength of group OⅡ. The ET-1 concentration among every group was no significant difference. The pathology result showed that the rat lung of all the experiment groups obviously presented different degrees of interstitium pulmonary edema for serious degree to light degree was group H, group OⅡ, group OⅠand group OⅢin sequence.2. Human subjects experimentation on the high altitude scene The SaO2 of group O was 92.3%±1.0% after the oxygen was supplied, which was higher than 82.9%±4.2% that before oxygen was supplied and 79.3%±5.9% (P <0.01 ) of group H, but lower than 97.3%±0.8% (P <0.05 ) of the group P. There was no significant difference of HR before and after oxygen was supplied as well as group H, but the HR of group H and group O was higher than that of group P (P <0.01). There was no significant difference of the sleep structure of group O and group H, but compared with group P, the group H and group O had more light sleep and less deep sleep(P <0.01 ). The result of heart rate variability presented that the LFn and LF/HF of group O and group H were (89.3±2.9) ms2, 9.4±2.8 and (90.2±1.8) ms2, 9.9±1.9 respectively, which was no significant difference but higher than (85.8±2.9) ms2 and 6.4±1.4 of group P (P <0.05 ), and the HFn was significant decreased. The results of questionnaire showed that group P had the best sleep quality and group H had the worst one while group O was ordinary.CONCLUSIONThrough the animal experiment, it was observed that rats stayed at 6000m for 24h got serious HAPE and 35% oxygen concentration of oxygen enriched room with oxygen partial pressure of inspired air 70mmHg, physiologically equivalent altitude of 2500m could effectively prevent the HAPE, but it was not obvious of the protection effect of the oxygen enriched room with 30% oxygen concentration (oxygen partial pressure of inspired air of 56mmHg, physiologically equivalent altitude of 3500m). In addition, intermittent supplying of 35% oxygen every 4h could prevent the HAPE of rat effectively as well. If this conclusion could be verified through further research, it would be the basis to determine how long people who enter high altitude emergently should keep in oxygen enriched room on the first day.According to the human subjects experimentation at the 3500m high altitude, the oxygen enriched room with physiologically equivalent altitude of 2500m was successfully built by utilizing the new-type high altitude diffusion oxygen-supply system. It could protect the people who enter high altitude emergently from serious hypoxia, and effectively improve the sleep quality in the first day. But the HR and the sympathetic nerve excitability were still on relatively high-level, which was proved that the compensation and the acclimatization to high altitude was still taken on the body. According the above, it was supposed that oxygen enriched environment and high altitude acclimatization were not contradictory, so that the oxygen concentration of oxygen enriched room could be adjusted according to different situation of individual in order to assure that both the prevention of high altitude hypoxia and the improvement of high altitude acclimatization were effective.