青藏高原因其高海拔和独特的地理环境而闻名于世，然而，其独特之处也带来了一系列特殊的生态和气候挑战。其中，缺氧环境是青藏高原面临的重要环境风险问题之一。在青藏高原，由于大气压力和氧气含量的急剧减小，形成了极为严重的缺氧环境，暴露在这样的环境中，很可能导致居民缺氧反应，如头痛、恶心、呼吸急促等症状，严重者可能发展成高原病，影响身体健康甚至生命安全。高原缺氧环境不仅对当地居民的身体健康产生深远影响，更对短期停留的游客、科考、参会人员等短居人口（本文采用旅游人口表示）提出了严峻考验。因此，深入探究高原缺氧对于短居人口生理指标的影响机制，并对短居人口缺氧暴露度进行全面评价，可为这一特殊环境下短居人口提供科学的健康管理建议，有助于更全面地理解高原地区的生态与环境问题，综合评价青藏高原缺氧环境风险，为青藏高原地区的旅游业和生态保护提供有益参考。

本论文在国家“第二次青藏高原综合科学考察研究-人类活动与环境安全-缺氧环境与人畜健康”专题支持下，在对青藏高原缺氧环境整体考察研究基础上，以青海高原的短居人口为研究对象，对高原地区短居人口缺氧暴露度进行综合评估。首先，通过对科考路线和科考定点测量数据的详细分析，拟定了短居人口氧含量风险的分级标准。基于此标准，以青海高原短居人口为例，定量评估了不同县域、不同季节在不同缺氧风险下短居人口的缺氧暴露量。依据对短居人口（科考人员）对低氧（缺氧）响应的定点观测和和控制实验（模式动物为大鼠）数据，拟订以7天为弹性阈值，进一步分析了短居人群缺氧暴露量的时空差异。

本论文的主要结论如下：

（1）在高原低氧环境中，短居人口的生理参数，包括血氧饱和度、心率和血压，受氧含量浓度和低氧暴露时间的显著影响。综合各项生理指标，拟定了适用于高原地区的氧含量风险评价标准。短居人群进入高原后，随着近地表大气氧含量的降低，血氧饱和度显著减小，心率显著增加，而收缩压、舒张压和平均动脉压则显著下降。随着低氧暴露时间的延长，血氧饱和度呈现先下降后逐渐上升的趋势(P < 0.01)，心率呈现先上升后逐渐降低的趋势(P < 0.01)，而血压则呈现先下降后上升的趋势(P < 0.01)。此外，各生理指标的恢复周期随着驻地海拔的增加而显著延长，在海拔3100m的驻地，各生理指标在两周内能够迅速恢复，而在海拔4000m的驻地，各生理指标至两周后仍未完全实现恢复。各生理指标的变化源于机体自身对缺氧环境的调节。近地表大气氧含量减少使得血液中氧气减少，直接影响了机体氧气供应，引发血氧饱和度的下降。为适应低氧环境，机体通过提高心率，促进血液流动，以增加氧气输送速度。同时，受低氧应激影响，机体产生血管舒张反应，提高组织对有限氧气的利用效率。随着低氧暴露时间增长，机体在初期紧急应对后，逐渐建立适应性，各生理指标逐渐回升，反映出对低氧环境的调节（习服）机制。随着驻地海拔增加，外部环境更为恶劣，导致适应过程更为复杂和耗时，从而限制了生理指标的迅速恢复。综合考虑不同生理指标对应的缺氧临界值，本文划分了6个缺氧等级，按照缺氧程度由高到低依次划分为Ⅰ级（危重度缺氧）、Ⅱ级（极重度缺氧）、Ⅲ级（重度缺氧）、Ⅳ级（中度缺氧）、Ⅴ级（轻度缺氧）缺氧区和Ⅵ级（非缺氧区）。其中，非缺氧区：绝对氧含量>168.30 g/m³；轻度缺氧区：氧含量处于142.77-168.30 g/m³；中度缺氧区：氧含量处于132.81-142.77 g/m³；重度缺氧区：氧含量处于128.87-132.81 g/m³；极重度缺氧区：氧含量处于122.76-128.87 g/m³；危重度缺氧区：氧含量<122.76 g/m³。

（2）基于定点科考测量和控制实验（模式动物为大鼠）结果，青海高原短居人群缺氧恢复（弹性）阈值（停留时长）拟定为5.4天-7.0天。基于定点科考测量结果，研究发现贵南组达到显著性差异（P < 0.01）的是：血氧饱和度第10天，收缩压第3天至第14天；达到显著性差异（P < 0.05）的是：舒张压第7天；心率未达到显著性差异。取其血氧饱和度第10天、收缩压第3天、舒张压第7天的均值，达到显著性差异的时间（停留时长）为6.7天。达日组达到显著性差异（P < 0.01）的是：血氧饱和度、心率第1天至第14天；收缩压第7天至第14天；舒张压未达到显著性差异。取其血氧饱和度血氧饱和度与心率第1天、收缩压第7天的均值，达到显著性差异的时间（停留时长）为4.0天。取海拔3100m的达日与4000m的贵南的平均海拔3550米m，拟订达到显著性差异的时间（停留时长）为4.0-6.7天，平均为5.4天。控制实验（模式动物为大鼠）表明：在4200m高原低氧环境暴露3天开始机体会出现相应的缺氧症状，但不会导致组织损伤发生，然而从形态学数据结合生理指标发现与对照组相比，低氧暴露7天时氧分压、氧饱和度、红细胞、白细胞数量以及氧化应激指标显著升高（P < 0.05)，且肺组织出现明显的红细胞和炎性细胞浸润，肺组织细胞凋亡率也显著上升，提示低氧胁迫7天可能会对组织器官造成不同程度的损伤。经过对4 200m低氧胁迫7天的大鼠进行1d、3d、5d、7d的平原复氧后发现，复氧7天后机体基本恢复到正常状态，与400m对照组大鼠的指标无显著差异，适当的低氧刺激后增强机体对缺氧的耐受力，物质代谢更加的充分。长时间暴露在缺氧环境中，特别是超过7天，可能导致各项生理指标难以迅速恢复；同时表明：低海拔平原（500米）复氧7天后，机体基本恢复到正常状态，且一定的低氧刺激后，增强机体对缺氧的耐受力，物质代谢更加充分。据此，我们将5.4天-7.0天作为高原短居人群缺氧恢复（弹性）阈值（停留时长）。

（3）青海高原短居人口在不同季节受到缺氧影响的比例存在明显差异，夏季的缺氧影响较低，而冬季的缺氧影响相对较高，以7天为短居人口缺氧弹性阈值，冬季不可恢复型缺氧暴露人数占比达夏季10倍以上。基于本工作建立的短居人口氧含量风险的分级标准，厘定了2019年青海高原全年受到缺氧影响的短居人数占短居人口总数的22.30%，其中主要表现为轻度（Ⅴ级）缺氧人口。受影响最严重的县分别是河南蒙古族自治县、祁连县、德令哈市、玉树市和格尔木市。在夏季，青海高原受到缺氧影响的短居人数占短居人口总数的11.01%，受影响最严重的县分别是玉树市、德令哈市、格尔木市、河南蒙古族自治县和天峻县；在冬季，青海高原受到缺氧影响的短居人数占短居人口总数的40.85%，受影响最严重的县分别是乌兰县、祁连县、德令哈市、湟源县和河南蒙古族自治县。造成这一季节性差异的主要原因与海拔、气候、植被等地理条件对氧含量的影响、旅游淡旺季等密切相关。寒冷的气温和降雪等恶劣气象条件、冬季植被产氧受限大大降低了高原地区的氧含量。严寒的气候使得人体更易感受到高原低氧环境的影响，进一步加大了短居人口缺氧的程度和范围。这些因素导致选择在冬季进行短居的游客缺氧的人口比例明显增加。考虑到短居人群停留时间对短居人群的健康影响，以7天为弹性阈值测算，2019年青海高原短居人口可恢复型缺氧暴露人数为784.08万人，占全年总短居人口的97.82%，不可恢复型缺氧暴露人数为221.92万人，占全年总短居人口的2.18%。其中，夏季短居人口可恢复型缺氧暴露人数为126.39万人，占夏季总短居人口的99.09%，不可恢复型缺氧暴露人数为35.88万人，占夏季总短居人口的0.91%，；冬季短居人口可恢复型缺氧暴露人数为538.74万人，占冬季总短居人口的90.99%，不可恢复型缺氧暴露人数为152.41万人，占冬季总短居人口的9.01%。

本研究提出了青藏高原短居人口缺氧等级多维度评定指标，综合分析了青藏高原缺氧对短居人口的健康影响，深化了对不同季节青藏高原短居人口缺氧暴露和弹性问题的研究。该工作有望为青藏高原地区短居人口提供科学的缺氧健康风险管理策略和应对措施，同时为青藏高原地区的旅游业可持续发展和生态保护提供理论支持和实践指导。

The Qinghai-Tibetan Plateau region is well known for its high altitude and unique geography; however, its uniqueness also presents a special set of ecological and climatic challenges. Among them, the hypoxic environment is one of the major problems facing the plateau region. Hypoxia refers to an environment where oxygen concentration is lower than normal, and in the plateau region, a more severe hypoxic environment is formed due to the drastic reduction of atmospheric pressure and oxygen content. The hypoxic environment of the plateau not only has far-reaching effects on the health of local residents, but also poses a severe test for short-stay tourists, scientific researchers and other short-stay populations. In the plateau region, oxygen scarcity may lead to hypoxic reactions, such as headache, nausea, shortness of breath, and other symptoms, and in severe cases, may develop into plateau sickness, which affects health and even life safety. Therefore, a comprehensive evaluation of the hypoxia exposure of short-stay populations in the Qinghai-Tibetan Plateau region and an in-depth investigation of the mechanism of plateau hypoxia on the physiological indexes of short-stay populations can provide scientific health management recommendations for short-stay populations in this special environment, which can help to understand the ecological and environmental problems of the plateau region in a more comprehensive manner, and at the same time provide a useful reference for the tourism industry and ecological protection in the Qinghai-Tibetan Plateau region.

Under the support of the "Second Comprehensive Scientific Expedition to the Qinghai-Tibetan Plateau - Human Activities and Environmental Safety - Hypoxic Environment and Human and Animal Health", this thesis is a comprehensive assessment of the hypoxic exposure of the short-dwelling population in the plateau region based on the overall study of the hypoxic environment in the high Tibetan plateau, with the short-dwelling population in the Qinghai Plateau as the target of the study. First, a grading standard for the oxygen risk of the short-dwelling population was formulated through detailed analysis of the measurement data of the scientific research routes and the scientific research fixed points. Based on this standard, the hypoxia exposure of short-dwelling populations in different counties and seasons under different hypoxia risks was quantitatively assessed using the short-dwelling populations in Qinghai Plateau as an example. Based on the data from sentinel observations and controlled experiments (the model animal is rat) on the response of the short-dwelling population (scientific researchers) to hypoxia (oxygen deprivation), an elasticity threshold of 7 days was formulated to further analyze the spatial and temporal variations of hypoxic exposure of the short-dwelling population.

The main conclusions of this thesis are as follows:

(1) Physiological parameters, including pulse oxygen saturation, heart rate and blood pressure, of a short-dwelling population in a plateau hypoxic environment are significantly affected by the concentration of oxygen content and the duration of hypoxic exposure. The physiological indicators were synthesized and the oxygen content risk evaluation criteria applicable to the plateau region were formulated. After entering the plateau, pulse oxygen saturation decreased significantly and heart rate increased significantly, while systolic, diastolic and mean arterial pressures decreased significantly with the decrease of near-surface atmospheric oxygen content in short-dwelling populations. With the prolongation of hypoxic exposure time, pulse oxygen saturation showed a trend of decreasing and then gradually increasing (P < 0.01), heart rate showed a trend of increasing and then gradually decreasing (P < 0.01), while blood pressure showed a trend of decreasing and then increasing (P < 0.01). In addition, the recovery period of each physiological index was significantly prolonged with the increase of the altitude of the station, and the physiological indexes were able to recover rapidly within two weeks in the station at an altitude of 3,100m, while in the station at an altitude of 4,000m, the physiological indexes had not yet fully recovered after two weeks. The changes in the physiological indexes originated from the body's own regulation of the hypoxic environment. The decrease in oxygen content in the near-surface atmosphere reduces the oxygen in the blood, which directly affects the body's oxygen supply and triggers a decrease in blood oxygen saturation. To adapt to the hypoxic environment, the organism promotes blood flow by increasing the heart rate to increase the rate of oxygen delivery. At the same time, affected by hypoxic stress, the organism produces a vasodilatory response to increase the efficiency of tissue utilization of limited oxygen. With the growth of hypoxic exposure time, the body gradually establishes adaptation after the initial emergency response, and various physiological indicators gradually rebound, reflecting the regulation (habituation) mechanism to the hypoxic environment. As the altitude of the site increased, the external environment became harsher, resulting in a more complex and time-consuming adaptation process, thus limiting the rapid recovery of physiological indicators. Considering different physiological indicators corresponding to the critical value of hypoxia, this paper divides six hypoxia grade zone, according to the degree of hypoxia in descending order is divided into Ⅰ (critical hypoxia), Ⅱ (extremely hypoxia), Ⅲ (severe hypoxia), Ⅳ (moderate hypoxia), Ⅴ (mild hypoxia) hypoxia and VI(non-hypoxia) zones. Among them, non-hypoxia area: absolute oxygen content >168.30 g/m³; mild hypoxia area: oxygen content in 142.77-168.30 g/m³; moderate hypoxia area: oxygen content in 132.81-142.77 g/m³; severe hypoxia area: oxygen content in 128.87-132.81 g/m³; extremely hypoxia area: oxygen content in 122.76 -128.87 g/m³; critical hypoxia zone: oxygen level <122.76 g/m³.

(2) Based on the results of the sentinel scientific measurements and controlled experiments (the model animal was rat), the hypoxia recovery (resilience) thresholds (length of stay) for the short-stay population on the Qinghai-Tibetan Plateau were formulated as 5.4-7.0 days. Based on the results of sentinel science measurements, it was found that the Guinan group reached significant differences (P < 0.01) in oxygen saturation on day 10 and systolic blood pressure from day 3 to day 14; diastolic blood pressure on day 7; and heart rate did not reach significance. Taking the mean values of their oxygen saturation on day 10, systolic blood pressure on day 3, and diastolic blood pressure on day 7, the time to reach significant difference (length of stay) was 6.7 days. Significant differences (P < 0.01) were reached in the Darjeeling group for: oxygen saturation, heart rate day 1 to day 14; systolic blood pressure day 7 to day 14; and diastolic blood pressure did not reach significance. The time to reach significant difference (length of stay) was 4.0 days by taking the mean values of their blood oxygen saturation oxygen saturation and heart rate day 1 and systolic blood pressure day 7. Taking the average altitude of 3550 m m of Dari at 3100 m above sea level and Guinan at 4000 m, the time to reach significant difference (length of stay) was formulated to be 4.0-6.7 days, with an average of 5.4 days. Control experiments (the model animal was the rat) showed that exposure to hypoxia at 4200 m plateau for 3 days resulted in the development of hypoxic symptoms, but did not lead to tissue damage, however, morphological data combined with physiological indicators showed that compared with the control group, the partial pressure of oxygen, oxygen saturation, the number of erythrocytes, leukocytes, and indicators of oxidative stress were significantly elevated at 7 days of exposure to hypoxia (P < 0.05), and the lungs and tissues showed marked erythrocytes and inflammation. There were obvious infiltration of erythrocytes and inflammatory cells in the tissues, and the apoptosis rate of lung tissues also increased significantly, suggesting that hypoxic stress for 7 days may cause different degrees of damage to tissues and organs. After 1d, 3d, 5d and 7d of reoxygenation in rats exposed to hypoxia for 7 days at 4,200m, it was found that the organism basically recovered to normal state after 7 days of reoxygenation, and there was no significant difference in the indexes with those of the rats in the control group of 400m. It was interesting to find that appropriate hypoxic stimulation increased the organism's tolerance to hypoxia, and the metabolism of the substances was more adequate. Prolonged exposure to hypoxia, especially for more than 7 days, may lead to the difficulty of rapid recovery of various physiological indicators. Meanwhile, it was shown that the body basically recovered to the normal state after 7 days of reoxygenation in the low altitude plain (500m), and the body's tolerance to hypoxia was enhanced and the metabolism of substances was more adequate after a certain amount of hypoxic stimulation. Accordingly, we take 5.4-7.0 days as the hypoxia recovery (resilience) threshold (length of stay) for the short-dwelling population in the plateau.

(3) The proportion of the short-dwelling population in the Qinghai Plateau affected by hypoxia varies significantly in different seasons, with lower hypoxia impacts in summer and relatively higher hypoxia impacts in winter, and the number of people exposed to irrecoverable hypoxia in winter accounts for more than 10 times the number of people exposed to hypoxia in summer using 7 days as the resilience threshold for hypoxia in the short-dwelling population. Based on the grading criteria for oxygen risk in short-stay populations established in this work, it was determined that the number of short-stay people affected by hypoxia throughout the year in the Qinghai Plateau in 2019 accounted for 22.30% of the total number of short-stay populations, of which the main manifestation was the population with mild (Class V) hypoxia. The most severely affected counties were Henan Mongolian Autonomous County, Qilian County, Delingha City, Yushu City and Golmud City. In summer, the number of short-stayers affected by hypoxia on the Qinghai Plateau accounted for 11.01% of the total number of short-stayers, and the most seriously affected counties were Yushu City, Delingha City, Golmud City, Henan Mongolian Autonomous County and Tianjun County; in winter, the number of short-stayers affected by hypoxia on the Qinghai Plateau accounted for 40.85% of the total number of short-stayers, and the most seriously affected counties were Wulan County, Qilian County and Delingha City, Huangyuan County and Henan Mongolian Autonomous County. The main reasons for this seasonal difference are closely related to the influence of geographical conditions such as altitude, climate and vegetation on oxygen content, and the off-peak season for tourism. Cold temperatures and snowfall and other adverse meteorological conditions, winter vegetation oxygen production is limited greatly reduces the oxygen content of the plateau region. The cold climate makes it easier for the human body to feel the effects of the low oxygen environment of the plateau, further increasing the degree and scope of hypoxia in the short-stay population. These factors lead to a significant increase in the proportion of the population that is hypoxic among visitors who choose to make short stays in the winter. Considering the health impacts of the short-stay population's length of stay on the short-stay population, the number of recoverable hypoxic exposures of the short-stay population in the Qinghai Plateau in 2019 was 7,840,800 people, accounting for 97.82% of the total short-stay population for the year, and the number of non-recoverable hypoxic exposures was 2,219,200 people, accounting for 2.18% of the total short-stay population for the year, as measured by the elasticity threshold of 7 days. Among them, the number of people exposed to recoverable hypoxia in the summer short-stay population was 1,263,900, accounting for 99.09% of the total summer short-stay population, and the number of people exposed to non-recoverable hypoxia was 358,800, accounting for 0.91% of the total summer short-stay population; the number of people exposed to recoverable hypoxia in the winter short-stay population was 5,387,400, accounting for 90.99% of the total winter short-stay population, and the number of people exposed to non-recoverable hypoxia was 1,524,100, accounting for 1.5241 million. The number of people exposed to recoverable hypoxia in the winter short-stay population was 5,387,400, or 90.99% of the total winter short-stay population, and the number of people exposed to non-recoverable hypoxia was 1,524,100, or 9.01% of the total winter short-stay population.

This study proposes a multidimensional index for assessing the hypoxia level of the short-stay population on the Qinghai-Tibetan Plateau, comprehensively analyzes the health impacts of hypoxia on the short-stay population on the Tibetan Plateau, and deepens the research on the exposure and resilience of the short-stay population on the Qinghai-Tibetan Plateau in different seasons. This work is expected to provide scientific hypoxia health risk management strategies and countermeasures for the short-stay population on the Qinghai-Tibetan Plateau, as well as theoretical support and practical guidance for the sustainable development of the tourism industry and ecological conservation on the Qinghai-Tibetan Plateau.