Caudwell Xtreme Everest Expedition – Altitude Research

West Face of Everest

In mountaineering news this week, are the preliminary results from the Caudwell Xtreme Everest Expedition. In this ground breaking piece of applied research which took measurements from over 200 people on the trek to Everest base camp, rather than the usual technique of making subjects endure hours and weeks of confinement in a hypobaric chamber to simulate the effects of high altitude and the associated physiological adaptations. Alongside this larger test, a smaller group of people were tested progressively higher on the mountain and have shown that some people are capable of withstanding the lowest ever levels of blood oxygen ever seen in conscious humans.

One of the reasons for the Caudwell Xtreme Everest Expedition was to try and find a reason for the difference in people abilities to adapt. “The findings suggest that the amount of oxygen alone isn’t the secret to physiological success. Other factors could be how much oxygen a person’s haemoglobin can carry, or the efficiency of the cellular factories known as mitochondria, which use the oxygen.”

A further arm of the research is the genetic factors of adaptation, that follows on from Cynthia bealls work on looking at the DNA of Tibetans and other highland dwellers that points towards a major gene being responsible for the amount of oxygen a single red blood cell can transport around the body.

Despite all this research it is likely that the whole process will be multi-faceted, and whilst genetics may well make up a part of the acclimatisation progress, in terms of mountaineering where anything except the highest mountains are attainable by the majority of climbers, all this research might do is help us understand the mechanisms behind these individual differences. To examine this we need to look at how humans adapt to altitude.

The reason we have to adapt, the graph showing the reduction in the partial pressure of Oxygen with height gain

To understand the extreme adaptation to altitude you have to follow the series of physiological events that happen as we lose the levels of oxygen we experience at sea level. The first sign of hypoxia (lack of oxygen) is a change in the acidity of our blood. When this change in pH is detected the initial response is to increase our breathing and heart rate to counteract it. If a few hours down the line your body is still under stress from low oxygen levels, and the associated elevated level of blood acidosis level then a bicarbonate feedback loop in the kidneys known as the renal response kicks in and we start to get rid of blood plasma to concentrate the haemoglobin (Red Blood Cells that transports oxygen) in the blood.

In terms of how each person differs then things like the tidal volume of the lungs (The amount of air we take in with each breathe), our VO2Max (general fitness level) or maximum heart rate will potentially add variation to the speed and level of adaptation. Also people differ in their levels of red blood cells (haemoglobin) at sea level which of course will effect us when at altitude.

Our bodies go on changing and in an attempt to maintain cerebral function blood flow is increased to the brain, this leads to the swelling of the brain and in extreme situations the onset of High Altitude Cerebral Oedema (HACE). There is research to show that some people are more likely to suffer from cerebral or pulmonary oedema, if they have had it before. In fact modern randomly controlled trials have included people with medically diagnose HAPE being given medication to combat it and then fired up to altitude to see how effect the drugs are. This research has lead to showing that Diamox, Dexamethazone and Nifedipine can be used as a prophylactic against Acute Mountain Sickness and HAPE.

The next adjustment we make with altitude is a metabolic response where we realise Erythropiotin or EPO from the kidneys. Now EPO is the drug that Tour de France cyclist use to increase there red blood cell count, along with the chance of having a stroke, without the need to train at altitude. It is virtually impossible to trace as it is naturally occurring, the only way it can be detected is by measuring the red blood cell count, above a certain level and an individual is deemed to be cheating. At altitude this is perhaps my favourite piece of the acclimatisation process, as it shows how marvellous we as humans are at adapting, as not only does the kidney release the EPO the bone marrow has moved EPO receptors to the surface of the cells in anticipation. As a result the body starts to produce more and more haemoglobin, increasing the efficiency of moving oxygen around the body.

If the exposure to altitude is prolonged then a our muscles can lose up to 20% of their mass. There is a thought that if the majority of the muscle loss occurs between the capillary and the mitrochrondria, then by reducing the distance between the oxygen rich red blood cell and the part of the muscles where it is needed, the mitrochrondria then the exchange of oxygen is far more efficient.

Graph showing the increase of efficiency of gaseous exchange in the bodies acclimatized at 5800m and subjects at sea level

It is only after all these changes occur in the body that we are fully adapted to our new rarefied air environment, and people like the subjects on the Caudwell Xtreme Everest Expedition can record the lowest blood oxygen level ever. It has been hypothesis that if you were to be dropped off on the summit of Everest from a pressurised helicopter, you’d be unconscious very rapidly and dead in minutes.

Photo copyright: Leo Houlding: Sunrise on Everest

What some of the altitude research might show rather facetiously is that the majority of people who summit the highest mountains do so by forms of cheating, if you are to look at how World Anti-Doping Agency defines erogenic aids (drugs to aid performance). In my limited research the best effort I have seen to date was by Reinhold Messner and Peter Habeler who summited Everest without the use of Supplemental Oxygen, Diamox or other drugs that have been shown to give you an unfair advantage at extreme altitudes.

However in an email from a friend of one of these ascentionist I got news that they had used Aspirin and Sleeping pills, so there is still a very limited potential to improve on the style of ascent. Although it has to be said that although aspirin thins the blood, and helps people perform at moderate altitudes it has no proven significant physiological effect.

It should be noted though that there is a cost to not using these enhancements that was established by R.B. Huey through research into climbers of Everest and K2, in a which it states “Individual mountaineers not using supplemental oxygen had a significantly higher death rates during descents than did those using supplemental oxygen (p<.001). This pattern is especially evident on K2, where approximately 1 in 5 climbers not using supplemental oxygen died during descent.”

There is a wealth of research that looks into altitude, the Caudwell Xtreme Everest Expedition is one of the more well known through the TV documentary about the efforts they made, not to mention the size of the sample they had, will undoubtedly lead to a stream of papers the first of which was published back in 2007 in a Critical Care Journal. Similarly small research expedition like the one from the Bangor’s School of Sport Health and Exercise Science have the potential to unearth just as much interesting research albeit in a less public fashion.

Leave a Reply

Your email address will not be published. Required fields are marked *