[This article is, in fact, one of the chapters in the book Doctor on Everest by the author and published by Hodder & Stoughton Ltd. to whom the editor acknowledges with thanks the permission to reprint. See also the review of this book, printed later in this issue.]

'The harm comes from the quality of the air one breathes in and out since it is so extremely thin and delicate', wrote Fra Joseph da Costa in 1608 about the high mountains of the South American Andes. The thinness of the air he described affects mountaineers at altitude in all parts of the world. I will try to explain how the mountaineer is affected in language someone who is not a specialist can follow and so I hope to enable him to understand some of the problems we met on Everest.

The air we breathe at sea level is composed of four parts nitrogen and one part oxygen and although this ratio does not change with increasing altitude the density or quantity of these gases becomes less. As the atmospheric pressure falls with increasing altitude so the pressure exerted by its constituent gases, oxygen and nitrogen, also diminishes; so that at 18,000 feet (Base Camp) the oxygen pressure is half of that at sea level and on the summit of Everest at 29,028 feet it is less than one-third. An ordinary weather barometer can, for this reason, be used as an altimeter. The higher one climbs the thinner the air becomes, and life would not be possible if the body did not make adjustments to compensate for the lack of pressure to force oxygen into the tissues, especially those of the brain. A pressure is needed to force the oxygen across the delicate membranes in the lungs into the blood where the red cells carry it to distant parts of the body, in the same way as a fireman requires not only large amounts of water but also a pump to deliver it at high pressure. Oxygen is released to the tissues and becomes the essential fuel for the normal function of every type of cell; when it is burnt up by cell metabolism it forms a waste product, carbon dioxide, which is breathed to the outside air.

As the mountaineer climbs higher and higher, so the air he breathes contains oxygen at lower and lower pressure and the time will come when this pressure is no longer adequate to force oxygen in sufficient quantities to the tissues ; if the brain is totally deprived for more than a few minutes the person dies rapidly.

Men who are short of oxygen for long periods of time could theoretically suffer from brain damage. But all the four men who went to 28,000 feet on Everest in 1933 subsequently had distinguished careers. A recent television interview with three octogenarian Everesters, Odell, Somervell and John Noel, only serves to advertise the healthy life in the cold thin air up high.

Oxygen lack is observed first at about 5,000 feet and with increasing altitude the thinness of the air causes troublesome headaches, difficulty in sleeping and a nasal quality in the speech. Because of the diminished air resistance it gives some advantage to sprinters and short distance runners, as was shown in the Olympic Games held at Mexico City (2,254 m.) in 1968. If the body made no adjustments life would be insupportable above 7,000 feet. Acclimatization is the process by which the body learns to cope with the situation of living under diminished oxygen pressure.

The first known facts about acclimatization were learnt in the South American Andes. The Incas of Peru in the sixteenth century had laws which prevented slaves being moved from the sea coast up to sulphur mines in the mountains and working alongside men who had lived all their lives at these altitudes and were naturally acclimatized.

Auconquilcha, the highest sulphur mine in Chile, lies at 19,000 feet and the present-day Indians who work there prefer to live in quarters at 17,500 feet and travel up and down daily, which suggests that the critical height for permanent acclimatization is around 18,000 feet. The speed of acclimatization varies between mountaineers and may explain why some are able to tolerate very high altitudes. In the eighteenth century scientists did not believe that man could stay alive on the high peaks of the Alps, yet in 1786 the village doctor from Chamonix, Michael Gabriel Paccard, as a result of a challenge from Monsieur H. B. de Saussure, climbed to the summit of Mont Blanc and returned (it and well to tell the tale.

On Mount Everest in 1924 Noel Odell spent eleven nights consecutively at over 23,000 feet without oxygen while searching for the missing climbers Mallory and Irvine. During this time he climbed six times up and down between Camp III (21,000 feet) and Camp IV (23,000 feet), once from the north col to Camp V (25,000 feet) and twice within four days to 27,000 feet.) Of this unprecedented feat Odell said, ‘Our evidence has shown his emphatically that one can live and feel fit for an indefinite period at 23 000 feet... there seems no reason at all to suppose that this important physiological capability other things being equal, should not be possible as an an altitude equivalent to that of the top of Mount Everest. But Odell had extraordinary physique and was described by Norton deputy leader of the expedition, as 'a climber of unequalled endurance and toughness'. In 1933 Frank Smythe spent three nights at 27,400 feet without oxygen. Over twenty ascents to 28 000 feet without the use of additional oxygen are now recorded

In 1875 Tissandier and two colleagues ascended to 29,000 feet in a balloon and two of them died. Part of the explanation or these contrasting experiences lies in the speed of ascent to altitude. In the early Everest expeditions the route through Tibet was long and involved crossing several high passes so acclimatization was well under way by the time the climbers were at risk. Because balloonists and aircraft pilots reach high altitude before acclimatization has started they must use oxygen above 10,000 feet, not only to survive but to be able to fly their machines safely.

The physiological process of acclimatization is central to the whole question of high altitude mountaineering. Oxygen is essential for the life and function of all cells in the body and the more sensitive the cell the greater is its demand for oxygen. If deprived of oxygen the brain cells will die m less than four minutes while the heart, the cells of which are not so delicate, may go on beating for much longer. All the physiological processes in acclimatization are ultimately directed to one end: to keep the body adequately supplied with oxygen The first and rapid phase of acclimatization starts at about 5,000 feet, the reduction of oxygen pressure in the atmosphere, in the lungs and in the blood is first detected by small receptor organs placed in the main arteries to the brain.

These receptors cause the respiratory centres in the brain to be stimulated and as a result the depth and frequency of breathing increase, which may be the first thing the mountaineer notices. With deeper breathing carbon dioxide, which dilutes oxygen in the lungs is removed more rapidly and its concentration in the blood is reduced. Although the pressure of oxygen in the atmosphere falls the effect is mitigated by the lowering of carbon dioxide so that oxygen pressure in blood and tissues does not fall greatly.

Cheyne-Stokes or cyclical, periodic breathing that is common to every person on arrival at altitude and is particularly noticeable and worrying at night. A pattern is established of a gradual increase in the depth of breathing which rises to a peak, then falls off slowly and finally ceases for several seconds. This period of quiet may be most alarming. The reason for Cheyne- Stokes breathing is not understood. The carbon dioxide in the blood builds up as it is not being blown off in the usual way and when it reaches sufficient concentration it stimulates the respiratory centre and breathing restarts. The carbon dioxide is then blown off, the stimulus lessens and breathing comes to a standstill. With acclimatization this abnormal behaviour of the respiratory centre ceases and it settles down to a new level of stimulation.

Stimulation of the oxygen receptors also causes two other important effects. At about 18,000 feet there is a clear increase in the speed and force of the heart's contraction, which the climber senses as palpitations. As a consequence the volume of blood circulating each minute increases and as no extra oxygen is extracted with each circulation, the pressure of oxygen in the tissues is higher than it would have been. In addition, the low oxygen causes an increase in the rate of production of red blood cells which may take four to six weeks to complete. At altitude blood can carry up to a third more oxygen than at sea level but unfortunately at the same time it becomes thicker and more viscous.

The blood is made even thicker because the volume of plasma, which suspends the red cells, decreases due to the lack of oxygen stimulating the sympathetic nerves to constrict the walls of the veins and so eliminate the normal pool of blood in the periphery of the body.

The consequence of this abnormal stickiness of the blood is twofold. The heart is put under more strain by the increased work required to pump the thick blood through it, and there is more danger of small vessels forming clots which cause blockages or thromboses. In 1933 on Everest Eric Shipton lost his speech for a short while presumably due to a small stroke affecting the speech centre in his brain. Edmund Hillary had a more severe but temporary stroke climbing Makalu in 1960.

The thickness of the blood may be further accentuated by loss of body water with dehydration. Heavy breathing in the cold dry atmosphere on the high mountain together with sweating due to heavy work wearing insulated clothes causes the loss of much body water. Between five and seven litres of fluid per day should be drunk at altitudes over 20,000 feet.

All these points indicate that the various parts of the acclimatization process start at different altitude levels and proceed at different rates. Some people are never troubled by altitude provided they ascend slowly enough, while others for no obvious physical reason can never acclimatize properly however long they remain high. This feature of altitude is very individual and idiosyncratic. Inronically acclimatization is not continuing process. Deterioration starts after about one month at high altitude but this time varies markedly with different men. The climber's capacity for work falls off and he suffers from poor appetite, loss of weight and he cannot sleep properly. He may also experience hallucinations as Smythe did in 1933 when he was descending alone to Camp VI. He was so convinced that he was roped to some invisible companion that he turned and offered the mythical figure half his Kendal mint-cake; he also saw two hovering pulsating kite balloons m the sky. If the mountaineer is going to be able to reach altitude of more than 20,000 feet and also to perform the had work of climbing and carrying loads, the lower part of the climb should be as leisurely as possible. It is also probable that acclimatization alone cannot sustain life and heavy work at high altitude, and oxygen may have to be added from cylinders carried on the back. This is a problem which has been debated with intensity ever since the first attempts to climb Everest.

In 1922 when the oxygen cylinders were heavy, bulky and cumbersome Mallory wrote, 'For my part, I don’t think it impossible to get up without oxygen...nothing in the experience of the first attempt has led me to suppose that those last 2,000 feet cannot be climbed in a day.'

Dr T Howard Somervell wrote of the 1922 expedition, ‘... it seems that the chances of climbing the mountain are probably greater if oxygen be not used. an attempt without oxygen only three or four coolies are required for the camping equipment and the food at the highest camp. It were better to prepare for a number of attempts each by a small but acclimatized party rather than to stake all on one or two highly organized endeavours, in which oxygen, and a large number of coolies are used.'

Norton in 1924 says, ' I still believe that there is nothing in the atmospheric conditions even between 28,000 and 29,000 feet to prevent a fresh and fit party from reaching the top without oxygen.' Odell reports his own experience at about 26,000 feet thus: '... oxygen gave so little effect and the apparatus proved such an irksome load that I was glad to hand the outfit over to a porter to carry ..., '—and again, on my second ascent to that altitude (27,000 feet) I used oxygen from Camp V at 25,000 feet but at rather over 26,000 feet I felt I was deriving so little benefit from it that I turned it off and did not use the gas again... I felt able to progress altogether better than when I had been breathing oxygen... without the bulk and awkwardness of the apparatus.'

Ruttlege summarizes the experiences of the 1933 expedition thus, ‘... a climber will receive little or no benefit from the use of oxygen at an altitude to which he has acclimatized himself in the natural way.' And Raymond Greene, the doctor of the party, said, ‘The condition of the climbers at 28,000 feet was so good that there is little doubt of their capacity, in good condition, to climb Everest without oxygen.'

But George Finch, the designer of the oxygen system in 1922 and its greatest exponent, was still adamant many years after. 'The climbing of Mount Everest is... very close to the limit of human endeavour. As such it calls for the exercise of every advantage that the wit of man can devise. 'Tilman in 1938 reverts to the common view, I am not convinced on this year s showing that the advantages conferred by using oxygen out weigh the ethical objections to its use.'

No one has yet climbed Everest without oxygen. However, Edmund Hillary was able to do enough mental arithmetic on the final part of the climb to work out how much oxygen he had left in his cylinders and when he reached the summit he removed his mask for ten minutes and took many excellent photographs. In 1963 four men, Willi Unsoeld, Tom Hornbein, Barry Bishop and Lute Jerstad, were forced to bivouac in the open air above 28,000 feet on the way down from the summit of Everest. Their oxygen had run out and although frost-bitten they survived the night, that by a miracle was windless. Don Whillans and Dougal Haston on their ascent of the south face of Annapurna were doing difficult Alpine standard climbing up to 26,000 feet only using oxygen for sleeping.

The foregoing paragraphs give the views and experiences of some great men about Everest. On our expedition three hundred bottles of oxygen were brought to the mountain under the supervision of Dr. Duane Blume, a high altitude physiologist, who was responsible for the design of the oxygen system which was an improvement on the Hornbein system used with success by the Americans in 1963.

The oxygen content should be the same for each breath regardless of the rate of breathing. Thus when doing a short burst of hard work when they might double their normal number of breaths per minute the supply would adjust to keep pace with the demand. The tanks held 1,180 litres of oxygen at a pressure of 3,000 pounds per square inch and when full weighed a little over sixteen pounds. Attached to the cylinder was an on/off valve that reduced the pressure in the tank to 60 p.s.i. betore it entered the tubing; without this reducing valve the pressure coming direct from the tank would be far too high.

A novel feature-the real clockwork of the system, was a neat little diluter-demand regulator unit the size of a fist which was attached to the oxygen cylinder by polyurethane tubing and worn strung round the neck. A dial with four settings that could easily be changed by hand, adjusted the mixing of outside atmospheric air with oxygen from the tank to dilute he oxygen concentration in the inspired air to an equivalent height of 17.500 feet. Dial number 1 was used from 23,000 to 25,000 feet dial 2 to 27,000 feet, dial 3 to the summit and dial 4 if a high concentration of oxygen was required for a particular effort of work. The system like all clever inventions was simple in design and easy to understand.

Corrugated rubber tubing connected the diluter demand valve by a simple fitting to the rubber face mask of standard U.S. Air Force design. Made of rubber it could easily be crushed in the hand to break up any ice that formed by moisture freezing on the outlet valve. The mask was clipped on to a cloth helmet by two simple wire catches lying over the cheeks.

The Blume system is an open circuit apparatus; the person breathes a mixture of air and added oxygen and exhales to the atmosphere outside. In a closed circuit system, as used by Evans and Bourdillon on Everest in 1953, the person inhales a high concentration of oxygen from a breathing bag and exhales through a canister of soda lime, which absorbs the carbon dioxide produced in the lungs. The exhaled gas returns to the breathing bag and is used again many times. In theory, this system is ideal but the soda lime absorbers are bulky and the apparatus is very hot to wear.

In order to do hard climbing on Everest a reliable system is needed: this one fulfilled the requirements well.

Thanks are due to Dr. M. Purves for his help in compiling this chapter.

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