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 NEWS  5th Sep 2006

Why Everest and not an Altitude Chamber?


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We have been asked why we are going to all the effort of going to Everest and not conducting studies in altitude chambers.

It is largely a matter of statistics and practicality.

Statistics:
Everyone is different. When looking at particular biological factors these potential differences have to be catered for. The larger the number of test subjects involved, the smaller the effect of clinical ?odd balls?. This applies across the board in medical research, whether it is for testing new drugs, looking at trends in population change or the effect of environmental factors on a group.

On Caudwell Xtreme Everest in the spring of 2007 we had 204 healthy volunteer trekkers, 40 plus scientists and technicians at labs from Kathmandu to Everest Base Camp and 15 climbing doctors out of which 8 reached the summit. That is a lot of people. This is on top of a ?sea level? study at the Archway Campus in London. This has involved hundreds of volunteers undertaking a similar bike test to that which was used on the mountain. Each of these volunteers has also had blood samples taken and swabs to determine their genotype. This large-scale effort has taken a long time and will provide an important baseline against which the results from the mountain can be compared.

One of the fundamental themes behind Caudwell Xtreme Everest is how the body adapts and why some people do so more readily. This process takes time, especially if it is to be done safely. Any chamber study would require that volunteers live in a chamber continuously for weeks at a time, which is where we come to the other issue ? practicality.


Compact and bijou
Practicality:
We have been very lucky to already use altitude chambers. One of them belonged to the Royal Air Force, Centre of Aviation Medicine (CAM) at RAF Henlow in Bedfordshire. What we have used them for, however, is the testing of equipment.

At CAM they have four chambers and their primary function is aircrew training. It is important that aircrew can identify the symptoms that come with the onset of hypoxia. This will prompt them to sort out their air supply while they still can. Left unattended hypoxia can quickly put an aircrew in a position where they are beyond logical reasoning and really don?t care!

One of the chambers does have a secondary role for research. This includes the testing and qualification of new equipment such as masks, regulators, helmet integration and other life support systems. All of this individual equipment has to perform to the high standards set by the military and it also has to be compatible with all the other equipment worn by modern aircrew.

Each of the four chambers has the same layout ? a main compartment with eight seats and a smaller connecting compartment with two seats. Each compartment can be controlled independently, which means that is possible to create an airlock to get in an out of the main chamber without altering its effective altitude.

If we were to assume that we had eight volunteers. What would it be like? There is not enough room for everyone to sleep, no washing, cooking or sanitary facilities. A portaloo in the small compartment would be the only option. They would have to make room for an exercise bike, be regularly wired up for clinical measurement and when someone is exercising it would get very warm. Also, should you become frustrated with your fellow guinea pigs, there isn?t exactly anywhere to go. All in all, as a study it would probably be of more use to psychiatrists than for the needs of Caudwell Xtreme Everest.


Flow meter testing
How the chambers were used:
We needed to be sure that our medical analysis equipment performed accurately in the rarefied atmosphere of the mountain. The ability to accurately select any altitude and control the rate of ascent and descent meant that we had complete control over the test environment.

An example of this testing was for the gas analysis equipment provided by Cortex. This is used to monitor the composition of the air breathed in and out by a test subject. Before any live experiment it has to go through a calibration procedure and we needed to be sure that its altitude compensation feature worked at levels far higher than originally intended. A flow of a controlled composition of gas was fed from outside the chamber to the equipment inside. The effective altitude was increased in stages, and at each stage the equipment went though its self-calibration routine. After a few runs we had solid data on how the well the equipment performed.

Another aspect of the Cortex equipment is a flow meter which records how heavily a test subject is breathing during exercise. At very high altitudes the thin air means that there are significantly fewer air molecules available for the flow meter to measure. In this case we were able to put the Cortex meter in series with a proven RAF one, attach both to a mechanical ventilator, and see how the readings compared.

The Doctors and staff at the RAF Centre of Aviation Medicine have been extremely helpful in the support of Caudwell Xtreme Everest.

Story by Steve Holland 


Steve Holland

Related Images
10/09/06: Why Everest and not an Altitude Chamber
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