Oxygen delivery

Given adequate time during a slow climb to high altitude, most of us adapt to the low levels of oxygen and can continue to function unhindered (a process known as acclimatisation). Research into acclimatisation has revealed that if given enough time, the body adapts to maintain an adequate delivery of oxygen to all its cells. This mainly occurs by increases in breathing, heart rate and the number of circulating red blood cells (which carry oxygen).

We want to know how well the human body can adapt to low levels of oxygen at the extremes of human survival. We sought to answer this question by taking blood from climbers on the Balcony, below the summit of Mount Everest, in order to see how much blood was being delivered to their cells. This had never been attempted before and was the result of years of planning and rehearsal to ensure a safe and accurate way of obtaining the results.

Other studies at Everest Base Camp looked at where blood and oxygen is directed within the body when it is subjected to exercise at high altitude. We believe that organs such as the gut suffer a lack of blood flow as blood is directed towards higher priority organs such as the exercising muscles.

Efficiency of oxygen use

The well accepted explanation above of how improvements in oxygen delivery lead to acclimatisation may not, however, be the full story. The way in which cells use oxygen may change as a result of its reduced availability. Tiny structures within our cells called mitochondria use the oxygen we breathe to create energy. It is possible that mitochondria become more efficient over time as the amount of oxygen delivered to them steadily decreases. Furthermore, some people may adapt better than others to high altitude and become more efficient at coping with low levels of oxygen. The reason for some people being more efficient than others is likely to lie within the genes that they are born with and carry throughout their life.

We investigated these ideas by studying how a group of over two hundred people perform at high altitude using an exercise testing system called cardiopulmonary exercise testing (CPX). This is a system we now use to determine patients? fitness for surgery in hospital. CPX works by analyzing a person's breathing as they exercise. It gives us information about how efficiently they are using the oxygen that they breathe.

We performed CPX tests on people at various stages along the trail to Everest Base Camp and will use the data collected with information about their specific genes. In this way, we hope to be able to answer important questions about whether our genes control how efficiently we adapt to low levels of oxygen.

In some of the climbers on the mountain, we took samples of blood and muscle to look in great detail at the mitochondria and how they were functioning. Such experiments have never been performed at high altitude before and will provide us with invaluable information about how mitochondria work when starved of oxygen.