In The Field

Everest: The rest before the final push.

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.

Having completed our week long research programme at Camp 2 on Mount Everest (6,400m) the climbers have decided to come down low for some well earned rest. The remainder of the Caudwell Xtreme Everest (CXE) investigators continue to work testing all the trekkers that come through the four laboratories in Nepal (Kathmandu, Namche Bazaar, Pheriche and Everest Base Camp).

We are over half way through testing the trekking groups now and data collection has gone extremely well thanks to the effort of the teams at each laboratory. Altitude illness has been minimal on account of the slow ascent profile the trekkers take which means we have been able to test nearly every subject on the cardiopulmonary exercise (CPX) system. The volume of data from the 200 volunteer trekkers and our group of 24 investigator/subjects will be vast. I foresee a busy time ahead analysing the data, a task that will no doubt take a number of years to complete.


Why descend to low altitude in order to rest? Climbing up and down the mountain has taken its toll on many of the team. Some of the men in the group have lost over ten kilograms in the space of six weeks and as a consequence are beginning to feel weak.

High altitude weight loss is a well documented but poorly understood phenomenon. It is one of the consequences of high altitude travel which we shall be investigating whilst here. Above 5,000m despite what seems like an adequate diet people begin to lose weight at an alarming rate. It seems to affect men more than women, and perhaps most disturbingly the weight loss is due not only to fat loss but muscle wasting.

Loss of muscle mass is the last thing one needs when trying to climb the highest mountain in the world. So we have walked down the valley to a village called Dingboche at an altitude a little over 4,000m in order to relax and try and put some weight back on! It certainly is a strange sight in the lodge: a group of undernourished bearded climbers trying to eat as much as they possibly can before returning to base camp! This will be our last chance to rest before the final push up the mountain so we are trying to make the most of it.

When we return to the mountain we have one more laboratory to set up – the South Col laboratory. At 8,000m this will be the highest laboratory in the world. Although on previous expeditions we have taken blood at higher altitudes we have never attempted to set up a powered laboratory and investigate subjects as they pass through on their way to the summit. We plan to perform CPX, spirometry (lung function), transcranial Doppler (ultrasound of blood flow to the brain), sidestream darkfield imaging (a method of imaging blood flow under the tongue) and arterial blood gas analysis whilst there. If successful this will be the highest that any of these techniques have been performed and will provide unique data about human physiology at extreme altitudes.

Hopefully we will all muster the enthusiasm to return to base camp soon and the weather improves sufficiently for us to begin our journey towards the summit.

Dan Martin

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