16 October 2018
How do acute, subacute and repeated exposures to high altitude affect cognition?
Can you tell us more about your research group?
At the Laboratory of Human Cerebrovascular Physiology we investigate human integrative physiology, disease mechanisms, and healthy aging. Our current research focus is on the effects of acute, subacute and repeated exposures to very high altitude on neurocognitive functions, sleep-disordered breathing, and cardiovascular consequences.
Our high altitude field studies include South American Andes, mountains in Kyrgyzstan and the Nepal Himalayas.
What is the rationale behind your study?
Hypoxia associated with high altitude exposure (>2500m) has detrimental effects on human health. The brain is highly sensitive to hypoxia, and higher elevations can impair cognitive and psychomotor performance.
Hundreds of scientists, technicians and support staff work at a very high altitude station (5050m) in the Atacama Large Millimeter/submillimeter Array (ALMA) Observatory in Chile. These workers follow a unique schedule in which they work at 5050m during the day, sleep at the ALMA Observatory Support Facility (AOSF) at 2900m, and spend every other week at near-sea-level (520m) to recover. Due to this unique schedule, the workers at ALMA are acutely exposed (within 2-3 days) to very high altitude upon arrival at the Observatory station.
The ALMA workers are immediately involved in tasks that require highly technical and intellectual skills. The adverse effects of hypoxia with consequent subtle changes in dexterity, attention and reaction times could result in costly consequences. The neurocognitive consequences of such acute exposure to high altitude, and re-exposure after a week at near-sea level, have not been previously explored.
To answer our research questions, we investigated the neurocognitive effects of this particular exposure schedule in altitude-naïve individuals compared to control subjects who performed the same battery of cognitive tests without being exposed to high altitude.
The study design helped us to investigate the effects of very high altitude on the altitude naïve individuals while being able to control a variety of confounding factors such as years of experience at altitude, age, sex, education, ethnicity and smoking. Further, we were able to mimic the schedule followed by the ALMA workers but at the same time implement a stricter experimental design with the use of a matched control group.
Which methods did you use?
In this study, we brought twenty-one young healthy altitude-naïve individuals to the ALMA Observatory in Chile, and implemented a schedule similar to the one followed by the ALMA workers.
In the first week, participants were acutely exposed to very high altitude (5050m) every day to reproduce the workers first work-shift cycle. They then spent a week a near sea-level in Santiago (520m) and went back at high altitude during the third week (repeated exposure). Measurements were taken at near sea-level (baseline), during the first day of the week at high altitude (acute exposure to altitude) and at the end of the work-week at high altitude (acclimatization exposure). The same protocol was followed during the re-exposure week (third week).
Seventeen participants matched for age, sex, and education composed the control group and were tested following the same protocol as the expedition group but they were tested at constant altitude (Calgary, 1103m, altitude of residence).
To assess cognitive function, we used a custom Cambridge Neuropsychological Test Automated Battery (CANTAB®, Cognitive Assessment Software). We assessed processing speed with the Reaction Times task (RTI), sustained attention with attention switching tasks and the Rapid Visual Processing task (RVP), and executive function with the One Touch Stockings of Cambridge task (OTS).
What are your key findings?
During the acute high altitude exposure i.e. first day at ALMA Observatory (5050m), the cognitive functions were adversely affected by the altitude exposure. The most affected cognitive abilities were the ones involved in tasks that need focus and a high level of precision, such as sustained attention.
The acclimatization following repeated exposure at 5050m (ALMA Observatory) for six days with sleep at 2900m (AOSF) had restorative effects on cognitive function, manifested by a lower decline in performance on the last day at altitude.
However, the cognitive improvements gained with acclimatization in one cycle (first week), did not carry-over during re-exposure on the third week, after a week of rest at the near sea-level (Santiago, 520m).
The changes in cognitive functions during both acute and acclimatization exposure were partially explained by blood oxygen saturation (SpO2) and severity of Acute Mountain Sickness (AMS) as assessed by the Lake Louise Score (LLS).
What are the implications of your study?
Our study provides insight into the cognitive effects of acute altitude exposure, the benefits of acclimatization with repeated exposures over a week, and the effects on retention during re-exposure after a week of rest at low altitude. The lack of retention for the cognitive benefits achieved during acclimatization in subsequent re-exposures to high altitude highlights the urgent need to revisit the re-exposure schedule.
Ultimately, these results will be helpful to devise schedules that will ensure safety, reduce health hazards, as well as optimize the performance of the ALMA Observatory workers. Similarly, this can also be extended to other high altitude workers such as the South American mining industry employees who follow a similar pattern of high altitude exposure. This is especially critical for those workers who are engaged in highly sophisticated work such as astronomical observation, engineering, scientific reporting, and operation of heavy-duty equipment.
The concerned government bodies, associated organizations and industrial partners may also use these findings as evidence to change policies concerning the health and safety of high altitude workers.
Why did you choose CANTAB?
This is the first time that a CANTAB battery was used in high altitude research. Firstly, we chose CANTAB for its flexibility and customizability; the CANTAB batteries are portable, wireless, touchscreen device friendly. The use of iPads to administer the battery, and the ability to store the data when internet access is not available, makes the battery a perfect choice to be used in remote settings. Furthermore, CANTAB can be administered in different languages making it suitable to test participants with different native languages.
What are the next steps for your research?
The next step is to use the same custom CANTAB battery for workers at the ALMA observatory. It will be interesting to study the cognitive effects of high altitude exposure for thse workers, controlling for other factors such as years of work at high-altitude, sex, education, smoking and cardiovascular status.
In future studies we will also specifically investigate other cognitive domains such as learning and declarative memory. Another important future direction will be to assess the differential effects of high altitude exposure on cognitive function among altitude naïve and high altitude shift-workers with and without oxygen supplementation. We would like to test the hypothesis of “oxygen conditioning”, and provide a proof-of-concept that hypoxia leads to impaired cognitive function at very high altitude, meaning that oxygen supplementation may be of benefit.
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Matiram Pun and Veronica Guadagni are Postdoctoral Research Fellows at the Laboratory of Human Cerebrovascular Physiology (PI: Prof Dr Marc J Poulin), Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
Matiram, from Nepal, has a medical degree and is a high altitude clinician. Veronica, from Italy, has a doctoral degree in Cognitive Neurosciences and is currently working on healthy brain aging, sleep disorders and cognitive decline in older adults. Both share a fond love for the mountains!
Find out more about the publication: Effects on Cognitive Functioning of Acute, Subacute and Repeated Exposures to High Altitude