Members of the Caudwell Xtreme Everest expedition, testing human adaptation to hypoxia on the roof of the world, write a diary blog for Nature from 30 March, 2007.
We have now completed our trek to the base camp of Mount Everest at 5,300m above sea level. It is a harsh environment in which to live, let alone carry out complicated physiological protocols. During the day the temperature reaches about 20 oC yet at night it falls below -10 oC. This means that there are huge temperature fluctuations within our tented laboratories. Needless to say, the sensitive equipment we are using to study our subjects does not appreciate this daily freeze-thaw cycle. Keeping the equipment happy in this environment is a full time job!
So why are we here? The majority of clinicians involved in this project care for critically ill patients on intensive care units. These patients tend to be the most unwell in the hospital and are universally hypoxic (they don’t get enough oxygen). Unlikely though it may seem, we noticed a remarkable similarity between critically ill patients and lowlanders venturing to high altitude. Amongst both of these groups there are those that cope well with hypoxia and those that do not. Admittedly this is hardly a Nobel Prize winning discovery. What is interesting, however, is that we seem to have no real ability to predict which path any one individual may follow when exposed to hypoxia. Despite advances in technology and a better understanding of human physiology, our ability to predict who will survive adult respiratory distress syndrome on an intensive care unit and who will make it to the top of Mount Everest is limited.
Studies designed to investigate the isolated effect of hypoxia in the critically ill are fraught with difficulty. Different underlying pathologies and treatment strategies cloud any potential data derived from this population. There are a number of strategies which could be employed to overcome these confounding issues. Animal studies and cellular models are two such examples but both have their limitations when trying to investigate the interaction of multiple human physiological systems. The model we have therefore chosen is the gradual exposure of human volunteers to increasing degrees of hypoxia. And the manner in which we shall induce hypoxia is by slow ascent to high altitude, allowing ample time for adequate acclimatisation. Although not a perfect model (if such a thing exists) it does remove many of the confounding factors experienced in critically ill patients.
[Editor’s note: You might be wondering why they don’t just put people in pressure chambers. But this presents difficulties too: it’s expensive, there aren’t enough such chambers in the UK for this experiment, and volunteers would probably be slightly less willing to sit in an uncomfortable room than to climb a mountain. Certainly the view isn’t as good.]
To accomplish our aims we have created a large observational healthy volunteer study composed of two distinct components. The first and certainly most important of these seeks to study a group of 200 subjects first at sea level, then as they ascend slowly to Everest Base Camp (5,300m). The subjects will journey in small groups throughout the trekking season and pass through the four laboratories we are currently setting up. They will spend twice the standard number of days resting as they ascend in order to aid their physiological acclimatisation to high altitude. This is because it is our intention to study successful adaptation to hypoxia as opposed to altitude illness in our subjects.
The second component of the study is a much more in-depth look at a small group of 24 subjects, who are all people involved in the running of the project. This group will perform the same tests as the large trekking group but in addition will endure some rather less pleasant studies, which we felt the general public may not be so keen on! Members of this smaller group will remain above 5,000m for the duration of the season in order for us to look at the long term changes associated with living at high altitude. Some of the members of this group will be climbing Mount Everest where more research will be carried out in the Western Cwm (6,400m), on the South Col (8,000m) and hopefully on the summit (8,848m).
The first of the trekking groups has now arrived in Kathmandu and they will be studied in the laboratory there before they start to follow us up the Khumbu Valley towards base camp. By next week I’ll be able to tell you what it is like to live at 5,300m and discuss in more detail some of the studies which the volunteers and investigators will be taking part in.
Nigel Hart, one of the medical team, celebrates easter.
Pic credit: Caudwell Xtreme Everest