The Study On Effects Of Acute Exposure To High Altitude Hypoxia On Cognitive Function In Lowlanders

Background:China’s territory is largely occupied by high-altitude regions,with the plateau region≥3000m covering up to 26.8%.The plateau environment has unique climatic characteristics that lead to reduced oxygen concentration at higher altitudes.As a result,the oxygen partial pressure drops in both inhaled and blood gases,increasing the risk of hypoxemia,which can cause disordered organ functions,especially in the brain.The brain is known to be the most sensitive organ to hypoxia,and thus deterioration in some brain functions can be expected,if not dysfunctions.This harm is potentially more significant for permanent residents in plain regions due to the sudden elevation and slow adaptation.Therefore,in this study,we aim to explore the underlying links between sudden elevation to high altitude zones and brain functions,with a focus on cognitive aspects.Previous research has made significant progress in this field,actively studying the impact of high plateau-specific environments on human cognitive function.However,no firm conclusions were made due to insufficient objective or unified cognitive assessments.The current limitations may include:1.Plateau simulation research that favors convenient and easy-to-implement strategies,introducing too many confounding factors that are hard to rule out in data analysis.2.No studies have investigated a complete set of cognitive functions.3.Learning effects are hard to rule out in repeated cognitive tests during cognitive function assessments.Thus,a more objective and comprehensive cognitive assessment method is needed for systematic research.Rigorous experimental design and standardized testing procedures should be encouraged.Therefore,in this research,we introduce a systematic procedure that controls the learning effect by adopting a plain group.We employ cognition-related measurements,considering 12 different components,and test scores that are more standardized using professional computer testing software.Statistical standardizations and different analysis methods are used to adjust for learning effects and draw associations between high altitude and cognitive impairment.Objective:The purpose of this study is to investigate the impact of rapid elevation to 3,800meters on the cognitive function of low-altitude residents through a plateau field and plain control study.We will comprehensively and systematically evaluate 12 cognitive indicators using CNS Vital Signs cognitive function evaluation software.Our goal is to identify the main types of cognitive function impaired in acute exposure to high-altitude plateau,observe the change trend of various cognitive function indicators from impairment to recovery,and explore the objective indicators related to the impaired cognitive function.Additionally,we will collect and analyze EEG data to explore its value in early warning and assessment of the cognitive function state of the plateau population.By conducting this research,we aim to better understand the relationship between plateau hypoxia and cognitive function changes,identify objective indicators that can be used for early warning of cognitive function impairment,and ultimately protect the combat effectiveness of troops rushing into the plateau and the health and safety of Tibetan people.Methods:We recruited 43 healthy young people residing in Xi’an,Shaanxi Province（400 meters above sea level）who met our inclusion and exclusion criteria.Participants were divided into two groups:the plateau group（N=20）and the plain group（N=23）.We collected baseline data one week before the plateau group rushed to the plateau.Participants wore32 humidification EEG caps to collect 10-minute resting EEG signals.Then,we collected baseline cognitive data using CNS Vital Signs software,measured physiological parameters,and had participants fill out various scales.One week later,the plateau group flew to the test destination（Chengduo County,Yushu Tibetan Autonomous Prefecture,Qinghai Province,at an altitude of 3,800 meters）,and we repeated the above data collection at the same time on day 1（3-5 hours after arrival）,day 2,day 3,day 5,and day 7 after entering the plateau.The plain group was studied in Xi’an（400 m above sea level）according to the same test plan.By analyzing the cognitive data of the plateau group and the plain group,we aim to identify the main damaged cognitive function,the recovery trend of cognitive function during the period of the plateau,and physiological prediction index.Additionally,we will explore the characteristics of EEG changes before and after the plateau group by analyzing the EEG frequency domain and functional connectivity state.Our goal is to find effective EEG indicators that can be used to predict the impairment of cognitive function.Result:1.Cognitive impairment after an altitude of 3,800 metersWithin 2 days of the 3800-meter elevation,almost all cognitive indicators（including memory,movement speed,psychomotor speed,executive function,complex attention,etc.）were impaired.2.The changing trend of cognitive function in plateau environmentThe change trend of cognitive function during the period of rapid progression showed that the cognitive function was damaged on the first 2 days of rapid progression,gradually recovered from the third day,and basically recovered to the plain level on the fifth to seventh day.3.Associated risk factors for cognitive declineBy establishing the MMSE weighted linear model,it is found that SpO2（saturation of peripheral oxygen）is low,LLS(Louise lake score,Subjects with higher Lake Louise scores and insomnia severity index（ISI）scores were more likely to experience cognitive decline after a steep plateau.4.Changes of resting EEG frequency after rushing into plateauThe delta,theta and alpha bands have the most obvious changes after the plateau.Among them,the relative power of delta band in frontal and parietal regions decreased significantly at D7 compared with D0,while the relative power of theta band in frontal and parietal regions and alpha band in whole brain increased significantly at D7 compared with D0.5.Correlation analysis between EEG features and changes in cognitive functionThe relative power in Delta band was negatively correlated with cognitive function except simple attention,the relative power in theta and beta bands was positively correlated with cognitive function except simple attention,and the relative power in alpha band was positively correlated with cognitive function except reaction time.The gamma-band relative power in the central frontal and occipital regions was positively correlated with memory function and motor speed.Conclusion:1.Most cognitive functions decreased in the first 72 hours after a 3800-meter plateau,and gradually recovered on day 5 after environmental adaptation and returned to baseline level on day 7;2.The resting EEG power changes after entering plateau environment,the most obvious is D7.The power of delta band decreases,while the power of theta band and alpha band increases;3.Low SpO₂,high LLS and high ISI scores,increased relative power in delta band,and decreased relative power in theta,alpha and beta bands were risk factors for most cognitive function decline or impairment.