When climbing a mountain as high as Everest most climbers need extra (supplemental) oxygen to help them, as there is so little oxygen in the air around them. Most traditional breathing systems ('open systems') deliver a continuous flow of oxygen into a mask which the climber breathes in, then breathes out, into the surrounding air. The system is fairly wasteful of oxygen requiring the climber to carry reserve bottles.
Members of the Caudwell Xtreme Everest team are developing an alternative system known as a 'closed circuit'. This system recycles the air that the climber breathes out by removing carbon dioxide (our waste gas) and adding a small amount of extra oxygen. The system is far more efficient that the traditional open system so climbers do not need to carry extra cylinders of oxygen.
The closed circuit is not a new idea; in 1953 during the successful British expedition to Mount Everest two climbers got within 90m of the summit using a 'closed circuit' oxygen system. With it they were able to climb at a speed of more than 250m/hr during their summit attempt - the fastest in more than 80 years of climbing on Mount Everest. Sadly the system failed these two climbers; close to the summit, they encountered difficulties while trying to change the filter canisters attached to their tanks. The canisters and valves froze and the climbers had to abort their ascent. Since this time there has been little interest in the development of a modern closed circuit system.
There is potential for it to benefit more than just climbers, however. Nearer to sea level, many thousands of people depend upon supplemental oxygen to overcome a range of lung and heart conditions. Developing a lightweight, efficient and reliable oxygen circuit would allow patients to venture outside their homes and enjoy what most of us take for granted.