The Science of the Summits

A report on the research conducted by the Hypoxia Physiopathology laboratory in Grenoble. Destination Aiguille du Midi for a better understanding of how the body works at nearly 13,000 feet of altitude...

Suspended in a cable car 230 feet from the ground, Alexis is en route to an unusual experiment: he has volunteered to participate in a scientific study conducted at Aiguille du Midi, in the Alps, at 12,605 feet of altitude! Surrounding him are Petit Dru, the Aiguilles, and Mont Blanc – the roof of western Europe at 15,778 feet above sea level. A landscape that will take your breath away… but not just because of its beauty! Here the effects of altitude are already making themselves felt. Pressure here is lower than at sea level, meaning that each intake of air contains less oxygen (O2). To compensate this, the respiratory rate increases, causing breathlessness. A phenomenon referred to by specialists as hypoxia.

  • Montagnes
    At 2 o'clock in the morning, mountaineers are already tackling the slopes of Mont Blanc du Tacul followed by those of Mont Maudit, which is one of the ways of reaching Mont Blanc. A morning departure is essential when embarking on long expeditions and to avoid the bad weather typically encountered late in the day in the mountains.
    © Inserm/François Guénet
  • Enregistrement du sommeil sur un volontaire
    The Aiguille du Midi, with its 12,605 feet of altitude, provides conditions close to those experienced by the mountaineers spending the night in a refuge or bivouac. Alexis took a sleeping pill at bedtime and then was woken up in the middle of the night, in the same way as a climber tackling a summit.
    © Inserm/François Guénet
  • Boîte d'hypnotiques
    The hypnotic used for the study is zolpidem, a benzodiazepine commonly taken by mountaineers during their nights at high altitude. Each volunteer is evaluated over a period of 4 nights: two at low altitude in Grenoble, and two at high altitude at Aiguille du Midi, during which they are administered either the hypnotic or placebo.
    © Inserm/François Guénet
  • Prise de sang sur un volontaire
    On waking, a blood sample is taken to determine the residual quantity of the hypnotic in the body. Samples are taken from everyone, regardless of whether the active substance or placebo was administered, because neither the investigator nor the volunteers must know who took what.
    © Inserm/François Guénet
  • Un des investigateurs de l’étude, évalue l’équilibre postural du volontaire grâce à une plateforme de force
    First experiment: Guillaume Séchaud (on the left), one of the study investigators, evaluates the postural balance of the volunteer using a force platform. Postural balance is an essential aptitude for mountaineers walking on the crests of mountain peaks.
    © Inserm/François Guénet
  • Volontaire remplissant un questionnaire.
    Sensation on waking, quality of sleep, etc.: the volunteer is then required to complete a questionnaire to evaluate his level of alertness and the presence of symptoms of altitude sickness, which include headache, nausea and vomiting.
    © Inserm/François Guénet
  • volontaire équipé d’un sac à dos de 10 kg
    The force platform is packed with sensors. The volunteer, wearing a rucksack like a mountaineer would, is asked to remain as stable as possible while the pressure exerted by his feet at various points is recorded in real time, transmitted to a computer and visualized on screen.
    © Inserm/François Guénet
  • réalisation de la "tâche cognitive" au repos puis en activité, en pédalant sur un vélo
    Now we get to the heart of the study: the performance of a "Simon task" at rest and while pedaling a bike. This exercise is used to evaluate the additional time required to inhibit an incorrect response. For mountaineers, this would involve reacting to a misstep or wrong move…
    © Inserm/François Guénet
  • Appareil de test pour tâche cognitive
    For the volunteer, this task consists of pressing these response buttons, on the left or right, depending on the color of the point that appears on the screen in front of him. Which is not as easy as it looks. Regardless of their color, the points can appear on the left or right of the screen, complicating the work of the brain and forcing it to inhibit any hasty or incorrect responses!
    © Inserm/François Guénet
  • Oxymètre
    During the exercises, this device, called an oxymeter, is used to measure oxygen saturation, i.e. the level of oxygen in the red blood cells. This can rapidly drop at altitude, which can bring on altitude sickness. This parameter is useful for the researchers to understand the physical condition of the participants after their night at high altitude, having taken a hypnotic. And, ultimately, to better understand the effects of this practice on the health of mountaineers.
    © Inserm/François Guénet

Each individual, irrespective of their condition, tolerates altitude differently. Every year, thousands of mountaineers develop altitude sickness, which can sometimes be fatal. Hypoxia can also affect sleep: breathing, qualified as periodic, is interspersed with apnea and micro-awakenings. For a better night’s sleep, some mountaineers take sleeping pills. But what are the effects of these medicines on their cognitive and physical capacities when they set off several hours later to climb the peaks – an activity which requires optimal alertness and physical fitness? By studying the sleep of 24 volunteers at high altitude from July to October 2016, the experiment conducted by the Hypoxia Physiopathology laboratory in Grenoble and led by Samuel Vergès, Inserm researcher, and Pierre Bouzat, physician at the University Hospital of Grenoble, attempts to provide some responses.

Find the report in issue 33 of Science&Santé magazine (in French)