Effects Of Acute Mid-altitude Exposure On Human Cognitive Ability

BackgroundHuman cognitive ability change in response to hypoxia has been the focus of investigation. High-altitude plateau exposure is accompanied with hypoxia, low pressure, coldness and radiation, which triggers human body protective compensatory reaction through breathing, blood vessels, and metabolic regulation to maintain homeostasis of inner environment. However, human body could not compensate the damage caused by high-altitude exposure or long-time exposure that leads not only to a series of non-specific clinical syndromes such as headache, insomnia, life-threatening high altitude pulmonary edema(HAPE) and high altitude cerebral edema(HACE), but also the emotional and cognitive neuromotor functional damage. Moreover, high-altitude exposure also causes dysfunctional brain metabolism, cerebral vascular regulation and CNS neurons, which further results in the damage of the white matter microstructural integrity and affects human cognitive ability.Human activities except extreme sports and special tasks in the plateau mostly remain in the mid-altitude area(from 2,438 to 4,572 m), with increasing people traveling, living and working there. During an emergency task such as disaster relief and military activities, high-altitude exposure can reduce the cognitive capacity of the rescue-workers and military personnel, and affect the completion of military task and disaster rescue, resulting in potential disastrous consequence. It is well known that high altitude plateau exposure can cause cognitive impairment. However, there is no large-scale field study on mid-altitude exposure, and the effects of mid-altitude acute exposure on human cognitive ability are controversial likely due to the difference among the research methods, altitudes, exposure rates, with or without supplemental oxygen, and the learning effect of repeated testing in the studies. Therefore, there is an urgent need for a large-scale prospective cohort field study toassess the impact of acute mid-altitude exposure on human emotional, cognitive and behavioral ability.High-altitude headache(HAH) is the most common symptom of acute high altitude exposure and the most important symptom of acute mountain sickness(AMS). Cerebral vascular dilation and imbalanced contraction, and metabolic disorders induced by high altitude hypoxia are the common pathophysiological mechanisms of HAH and the major pathogenic factors of cognitive changes after acute high-altitude exposure. We speculate that HAH has a close relationship with mental and neurological behavior. Thus, we performed a large-scale field study to investigate the associations between HAH clinical features and psychological capacity of human subjects in order to provide fundamental information for the prevention and reduction of AMS and high altitude cognitive impairment.Pre-exposure is currently the main approach to prevent high altitude sickness. Pre-exposure to a mid-altitude for a period of time can reduce the incidence of cognitive damage and mitigate AMS upon the exposure to high altitude. However, prolonged plateau pre-exposure could decrease the cognitive ability and compromise the benefits of pre-exposure. Until now, there is little investigation on the optimal time of pre-exposure. In this study, we designed a prospective large-scale cohort field study to compare the effects of short-term mid-altitude pre-exposure and long-term pre-exposure on the emotion and cognitive changes in response to higher altitude exposure, and analyze the potential risk factors.AimsThis large-scale cohort field study intends to assess the effects of acute mid-altitude pre-exposure on the human emotion, behavioral and cognitive abilities. We examined whether HAH affected cognitive ability and whether cognitive capability was an independent risk factor and an independent predictor for HAH. We also investigated the impact of mid-altitude pre-exposure duration on human cognitive ability before exposure to high altitude.Materials and Methods1. Assessments of effects of acute mid-altitude(3,700m) pre-exposure on human cognitive ability.Total 200 young healthy plain male residents were recruited and divided into two groups: the control group(N=50) and the experimental group(N=150). The control group stayed in plain(500m altitude), and the experimental group stationed in mid-altitude plateau(3,700m). Cognitive ability and neurobehavioral ability including emotion, responsiveness, short-term listen and memory ability, motion-sensing ability, attention and movement stability in two groups were assessed at day 0, 1 and 15 respectively. The demographic data and AMS symptom score, the heart rate, blood pressure, and Sp O2 measurements of the subjects were collected and analyzed.2. Idenfied cognitive ability as a potential independent risk factor and an independent predictor for HAH in mid-altitude(3,700m).Total 163 young healthy plain male residents were transported to mid-altitude(3,700m) by airplane within 2 hours. Cognitive ability and neurobehavioral ability including emotion, responsiveness, short-term listening and memory ability, motion-sensing ability, attention and movement stability of the subjects were measured within 24 hours after arrival. Demographic information, HAH symptom, heart rate, blood pressure and Sp O2 measurements of the subjects were collected and analyzed based on the presence of absence of headache.3. Examined the effect of mid-altitude pre-exposureon cognitive ability after exposure to high altitude.Total 111(9 follow-ups were lost) young healthy male plain residents were recruited and divided into two groups: the short-termpre-exposure group(N=57) and the long-term pre-exposure(3 months) group(N=54). Subjects in the short-term pre-exposure group were stayed for 4 days at 3,700 m altitude, and then transported into high altitude(4,400m) by airplane. Subjects in the long-term pre-exposure group were stayed for 3 months at 3700 m altitude, and thentransported into high altitude(4,400m). Cognitive ability and neurobehavioral ability including emotion, responsiveness, short-term listenand memory ability, motion-sensing ability, attention and movement stability of the subjects were assessed at the end of pre-exposure at 3,700 m altitude and on the 10 th day of 4,400 m exposure. Demographic information, AMS symptom score, heart rate, blood pressure, and Sp O2 measurementsof the subjects were collected and analyzed.Results1. Effect of acute mid-altitude(3,700m) exposure on human cognitive abilityMid-altitude exposure significantly decreased the negative emotion(P <0.05), which remained constant when the exposure time was longer. Listen and memory ability, movement stability, motion-sensing ability on day 1 after acute mid-altitude exposure were significantly increased(P<0.05). The increase of responsiveness and movement stability were sustainedonto day 15(P<0.05).However, listen and memory ability, and motion-sensing ability significantly declined after 15-day exposure, to the plain level(500m)(P<0.05). Mid-altitude exposure did not significantly change the attention ability(P>0.05). Cognitive ability change after acute mid-altitude exposure was not associated with the characteristics, AMS incidence, and AMS severity of the subjects.2. Cognitive ability as an independent risk factor and independent predictor for HAHHAH beforepre-exposure had positive correlations with baseline anxiety(R=0.212, P=0.009), anger(R=0.198, P=0.015), depression(R=0.164, P=0.045), fear(R=0.194, P =0.017), confusion(R=0.105, P=0.044), and had no correlation with neurobehavioral ability. After 3,700 m mid-altitude exposure, HAH-positive group had significantly increased negative-mood scores(P<0.05), decreased activity scores(P=0.031) in comparison with HAH- negative group. There was no significant difference in neurobehavioral ability between HAH-positive group and HAH-negative group. After exposure(3,700m), HAH had positive correlation with anxiety(R=0.350, P<0.001), anger(R=0.296, P<0.001), depression(R=0.263, P<0.001), fear(R=0.373, P<0.001), confusion(R=0.298, P<0.001), but had negative correlation with activity(R =-0.212, P=0.009). In cognitive ability, only movement stability was negatively correlated with HAH(R=-0.161, P=0.047). Regression analysis showed that negative emotion in plain area was a risk factor for HAH, and confusion mood was an independent risk factor for HAH. After exposure, heart rate, lack of energy, and confusion emotion were independent risk factors for HAH.3. Effect of mid-altitude pre-exposureon cognitive ability after exposure to high altitude.Pre-exposuretomid-altitude(3,700m) and after exposure to high altitude(4,400m), the short-term(4 days) pre-exposure group had less negative emotion, higher motion-sensing ability, better attention and movement stability, and less AMS incidence in comparison with the long-term(3 months) pre-exposure group.Conclusion1. Acute plateau(3,700m) exposure led to a significant decrease of negative emotion, which became unchanged when the exposure time extended. Neurobehavioral ability transiently increased after acute mid-altitude exposure, and decreased to / below the level at the plain as the exposure duration lasts;2. HAH affects emotion, but had no significant effect on neurobehavioral ability. Higher heart rate, emotional confusion and lack of energy were independent risk factors for HAH. Emotion confusion is an independent predictor for HAH;3. Exposure to high altitude(4,400m), the short-term(4 days) mid-altitude pre-exposure hadless negative emotion, and better neurobehavioral ability.