For 5 weeks, five international research teams will conduct a scientific expedition in Nepal, in the heart of the Himalayas, close to the summit of Mount Manaslu (8,156 m). The French component of the expedition, coordinated by a researcher from Inserm (Unit 1042, “Hypoxia and Cardiovascular and Respiratory Pathophysiologies,” Inserm/Université Joseph Fourier), will conduct an original project on the impact of altitude on the brain and heart, and on sleep disturbances induced by altitude.
Altitude is known to profoundly disrupt sleep and induce central sleep apnea. From an altitude of 2,500 m, a moderate reduction and cyclic oscillations are observed in blood oxygenation. The development of these disorders is also accompanied by a reduction in sleep efficiency, an increase in the time it takes to fall asleep, a shortening in the duration of phases of deep sleep, and a substantial increase in intrasleep awakenings. The quantification of these disorders was for a long time limited to the analysis of oscillations in arterial O2 saturation.
However, at the present time, one question has not had a clear answer: Is central apnea a marker of bad or good adaptation of the body to altitude? This question is important because there are large intersubject variations in the intensity of sleep disturbances induced by altitude exposure. It was recently shown in the laboratory directed by Samuel Vergès that individuals with severe symptoms of high altitude intolerance (in the course of 1 night in an altitude simulation laboratory) have less sleep apnea than comparable individuals who tolerate high altitude well. However, this remains to be established in the field at high altitude.
Study of this question should improve understanding of the mechanisms of adaptation to altitude, and influence the advice and assessments offered to people traveling to high altitude.
The study proposed by the French group within the scientific expedition therefore has the following objectives:
- To assess the effects of the expiratory resistance mask (ventilation with PEP) on arterial and tissue oxygenation, on pulmonary extravascular leakage, and on symptoms of acute mountain sickness during a period at high altitude for a large sample of volunteers.
- To study, on the basis of new technologies (near-infrared spectroscopy Speckle Tracking echocardiography), the changes to the brain and heart induced by lack of oxygen (hypoxia) at high altitude, and to assess their reversibility through wearing the mask.
- To compare altitude-induced sleep modifications in trekkers who adapt well to altitude compared to those who show symptoms of acute mountain sickness.
The researchers’ study of the effects of lack of oxygen on the healthy body at high altitude should enable a better understanding of the consequences of lack of oxygen on some patients at normal altitudes, for example those with respiratory diseases. The high altitude is thus a real open-air laboratory, constituting an original study model for the adaptive abilities and limitations of the human body.
Initial Phase of Study at Normal Altitude
All participants in the trek and Manaslu climb made themselves available in February for a battery of scientific and medical assessments at sea level in Wales (Bangor University). All measurements that will be done at high altitude were carried out at sea level, thus enabling reference values to be obtained for every subject, for comparison with measurements taken at high altitude.
The phase of testing at normal altitude was an opportunity to address technical and logistic issues that needed to be resolved so that the tests can be repeated under the best possible conditions at high altitude at reduced atmospheric pressure (which strongly affects equipment), in the cold (down to -20°C), and when the bodies of both the researchers and volunteer subjects will be severely affected by the altitude.
Science Lab at 5,000 Meters
Five groups of 10 people will leave Kathmandu at intervals of 1 day each to spread the measurements. It will take 10 days to reach the destination. The five international research teams will set up their laboratory and all the necessary logistics (tents, production of solar and wind energy, etc) slightly above the Manaslu base camp, at a little over 5,000 m altitude. Most of the high altitude measurements will be performed on all those participating in the trek, who will arrive day after day. Other measurements will be performed during the trek and during the Manaslu climb (8,156 m). The entire expedition will last 5 weeks, from March 21 to April 26.
As with assessments carried out at normal altitude, assessments will involve measuring the pulmonary extravascular fluid by pleuropulmonary ultrasound, cerebral perfusion by transcranial Doppler, cerebral oxygenation by near-red spectroscopy, and cardiac function by Speckle Tracking echocardiography, before and during ventilation under positive expiratory pressure. Symptoms will be assessed by questionnaire. Finally, sleep will be assessed during nights spent in tents at the Manaslu base camp, by placement of various sensors that enable identification of the quality of sleep, and the occurrence of sleep apnea associated with a drop in blood oxygenation, such as is frequently observed at high altitude.
Following 4 days of acclimatization at 5,000 meters, this battery of tests will be repeated in order to observe the adaptations of the human body to this high altitude. All participants will spend 10 days at base camp, and the team will then complete the Manaslu circuit with a 3-day descent to Beshisahar.
The participants in this trek show a classic profile of populations taking part in treks at high altitude, aged from 22 to 65 years, with relatively varied levels of physical fitness and altitude experience. They have volunteered to complete a trek of several weeks around Manaslu and have also volunteered to participate in scientific experiments in this context, including 5 consecutive days at the camp located at the highest point in the Manaslu circuit, where the laboratories will be installed.
To bring a scientific expedition to life for Internet users, Inserm is doing all it can to follow the expedition. Enriched content (photos or videos) will be posted daily on @Insermlive and on the Institute’s Facebook page. Internet users will also be able to follow this expedition in real time on the social networks using the hashtag #scienceausommet.