Life at the Extremes: The Science of Survival / Edition 1 available in Paperback
|Publisher:||University of California Press|
|Edition description:||First Edition|
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At 8848 metres (29,029 feet), Mount Everest is the highest mountain on Earth. If it were possible to be transported instantaneously from sea-level to the summit of Everest, you would lose consciousness and lapse into a coma within seconds because of lack of oxygen. Yet in 1978, the Austrian climbers Peter Habeler and Reinhold Messner reached the top of Everest without the aid of supplementary oxygen; and ten years later, more than twenty-five others had also done so. What is the explanation for their apparently impossible feat? The scientific detective story of how the answer to this question was unravelled, the twists and turns along the way, the excitements, extraordinary feats of endurance and colourful characters involved are the subject of this chapter.
Mountains have fascinated and challenged people for centuries. Beautiful but forbidding, they were initially believed to be the home of the gods. The Greek Pantheon lived on the summit of Mount Olympus, the highest mountain in Greece; the Indians considered the Himalayas the abode of the gods; and evidence of ancient human sacrifice, probably to mountain gods, has been found in the Andes. Even today, many cultures hold sacred mountains in reverence Tenzing Norgay buried chocolate and biscuits on the summit of Everest during the first successful ascent, as a gift to the gods that live there. Mountains lie shrouded in myth and legends, their peaks and crags imaginatively populated not only with gods, but also by mysterious monsters like the Himalayan Yeti and the trauco of southern Chile (that feeds on human blood). Even their namescause enchantment: 'Chimborazo, Cotopaxi, They had stolen my soul away!' Yet despite, or perhaps because of, these stories, people have always been attracted to mountains, whether for spiritual refreshment, the promise of hidden treasure, a means of escaping oppressive regimes, the thrill of exploring new terrain or, more mundanely, to find a way through to the other side: or simply, in George Mallory's memorable phrase, 'Because it's there'.
As a consequence, mountain sickness has been known for centuries. Its cause remained a mystery to the ancients who considered it due to the presence of the gods (which drove men mad), or the result of poisonous emanations from plants, and led to the early European view of mountains as dangerous and mysterious. Some time around the latter half of the nineteenth century, however, mountain climbing emerged as a sport and men vied with the elements and with each other to be the first to reach the highest peaks. Physiologists became increasingly interested in the effects of altitude on the body, and increasingly knowledgeable about their causes, and their studies contributed greatly to the success of the first expedition to reach the summit of Everest. Yet they have been repeatedly astonished by the ability of mountaineers to ascend higher than their predictions.
High altitude is defined, somewhat arbitrarily, as more than 3000 metres (10,000 feet) above sea level. Many people, probably around 15 million, live above this height in the mountainous areas of the world, with the greatest numbers in the Andes, the Himalayas and the Ethiopian Highlands. Many more people visit altitudes of over 3000 metres each year for skiing, backpacking and tourism. The highest permanent human habitations are mining settlements on Mount Aucanquilcha in the Andes, at an altitude of 5340 metres. Although the sulphur mines are located at 5800 metres, the miners prefer to climb the additional 460 metres to work each day rather than sleep higher up. The Indian army is also reputed to have kept troops at 5490 metres for many months, to guard their border with China, but this is probably the limit at which it is possible for humans to live for an extended period, for life at such altitudes is fraught with difficulties. Chief among these is the reduction in the oxygen concentration of the air, but cold, dehydration and the intense solar radiation are also significant problems.
The decrease in the density of the air at altitude means that it contains less oxygen, which poses a considerable problem for most organisms, including humans, who need to supply oxygen constantly to all their cells. Within each cell, oxygen is burned, together with foods such as carbohydrates, to produce energy. Cells that do large amounts of work, such as muscle cells, need proportionately more oxygen, and exercise further increases their demands. Oxygen was 'discovered' in 1775, as recounted in Chapter Seven, and its beneficial effects were immediately understood. But it was almost another hundred years before it was recognized, by the Frenchman Paul Bert, that it was a lack of oxygen (hypoxia) that was the main cause of mountain sickness. It took even longer for his idea to become widely accepted.
Early Accounts of Mountain Sickness
The Chinese were the first to document the effects of altitude, in a classic text, the Ch'ien Hah Shu, that describes the route between China and what is probably Afghanistan around 37-32 BC: 'Again on passing the Great Headache Mountain, the Little Headache Mountain, the Red Land and the Fever Slope, men's bodies become feverish, they lose colour and are attacked with headache and vomiting; the asses and the cattle all being in like condition.' The eminent Chinese scholar Joseph Needham has suggested that such experiences convinced the Chinese that they were meant to stay within the natural borders of their country. Likewise, the Greeks, who found they became breathless on the top of Mount Olympus (around 2900 metres), assumed that the summit was reserved for the gods and was out of bounds to mere mortals.
One of the first clear descriptions of the effect of acute mountain sickness was published in 1590 by Father Jose de Acosta, a Spanish Jesuit missionary who crossed the Andes and spent some time on the high plateau known as the Altiplano. Many of his party became sick when crossing the high pass at Pariacaca (4800 metres). He himself was 'suddenly surprized with so mortall and strange a pang, that I was ready to fall' and considered that 'the aire is there so subtle and delicate, as it is not proportionable with the breathing of man' He also wrote that at this pass and all along the ridge of the mountains were to be found 'strange intemperatures, yet more in some partes than in others and rather to those which mount from the sea, than from the plaines.' This passage has been taken to indicate that Father Acosta was aware that people who had become acclimatized to high altitude by spending time on the high plains, such as the Altiplano plateau, succumbed less readily to mountain sickness than those who ascended directly from sea-level. Scholars now suggest that this is probably not the case, as the original Spanish text appears to have been incorrectly translated.
The local Inca population, however, were very well aware of the effects of altitude and of how acclimatization took time. They knew that lowlanders died in great numbers if transported to high altitudes to work in the mines and they maintained two armies, one that was kept permanently at high altitude to ensure they were acclimatized, and a second which was used for fighting on the coastal plains. To escape the ravages of the Conquistadores, the Incas retreated higher and higher into the mountains, where the Spanish invaders found it difficult to follow. Although the Spanish eventually established a city at Potosí (4000 metres), it was very much a frontier town and both women and livestock had to return to sea-level to give birth and bring up their offspring for the first year. The fertility and fecundity of the native women was unaffected but Spanish children born at altitude died at birth or within the first two weeks of life. The first child of Spanish descent to survive was not born until fifty-three years after the city was founded, on Christmas Eve 1598, an event that was hailed as the miracle of St Nicholas Tolentino. Sadly, none of the 'miracle's' six children survived to maturity. Nevertheless, the problem resolved itself after two to three generations, probably because of interbreeding with the indigenous Indian population. The cattle and horses remained relatively infertile, however, and as a consequence, the Spanish eventually moved the capital to Lima. Infantile mountain sickness is not simply a problem of the past, for it afflicts the lowland Han Chinese colonists of Tibet today.
As the Incas appreciated, mountain sickness is less severe in people who become accustomed to altitude gradually. The dramatic and often fatal consequences of very rapid ascent to high altitude were first encountered by the early balloonists. The first flight in a hot air balloon was made in 1783 by Jean-François Pilâtre de Rozier and the Marquis d'Arlandes in a balloon made by the Montgolfier brothers, Etienne and Joseph. Later the same year another Frenchman, Jacques Charles, invented the hydrogen balloon and reached 1800 metres on his initial ascent, with no apparent ill effects. Balloons are capable of reaching even greater heights, however, which can have serious consequences.
The symptoms of altitude sickness associated with ballooning were described in a famous report by James Glaischer, a meteorologist who accompanied the balloonist Henry Coxwell on a flight from Wolverhampton in 1862. Within an hour they had ascended to a height at which his barometer read 247 millimetres of mercury around 8850 metres. They continued to rise, but the precise altitude they reached is unclear because above this height Glaischer was no longer able to see the barometer clearly, nor is it certain his barometer was correct; but it is likely to be less than the 11,000 metres he reported. He described vividly how he found his arms and legs were paralysed, he was unable to read his watch or see his companion clearly, he tried to speak but found he could not, and he then became temporarily blind. Finally, he lost consciousness. Fortunately, Coxwell was not completely incapacitated and was able to bring the balloon down, although with great difficulty, by venting hydrogen. Because his arms were paralysed, he had to pull the rope that released the vent valve with his teeth. On the way down, Glaischer recovered consciousness and was able to take notes again at an altitude he calculated as around 8000 metres, which illustrates the rapid recovery that can occur following severe acute hypoxia.
The first fatalities occurred a few years later, in 1875, when three French scientists, Sivel, Tissandier and Croce-Spinelli, ascended to over 8000 metres in the balloon Zenith. Although they had primitive oxygen equipment, the amount of oxygen they carried was small and they agreed not to use it until they felt it was really necessary. Unfortunately, the over-confidence and feeling of well-being characteristic of acute oxygen starvation meant they never used it and they all lost consciousness. Only Tissandier survived. He later related that he tried to use the oxygen equipment but was unable to move his arms. However, far from feeling concerned, he wrote: 'one does not suffer in any way; on the contrary. One feels an inner joy, as if filled with a radiant flood of light. One becomes indifferent and thinks no more of the perilous situation or of the danger'.
The Ascent of Everest
With the advent of mountaineering, the effects of mountain sickness became more widely known and better understood. By the mid-1920s it was appreciated that people could climb as high as 8000 metres and remain there safely for a few days, providing they had spent many weeks at an intermediate altitude gradually acclimatizing. In contrast, when exposed to a similar barometric pressure in a decompression chamber, consciousness was lost within a few minutes.
The 1953 British expedition to Mount Everest, led by Sir John (later Lord) Hunt, was well aware of the importance of acclimatization. The long march from Kathmandu to Khumbu, at the foot of the mountain, took several weeks and imposed an obligatory period of acclimatization because most of the trek is at 1800 metres, rising only occasionally to 3600 metres. A further four weeks was then devoted to acclimatization in the Khumbu district (4000 metres) before attempting to establish camps higher up the mountain. The team also adopted a policy of siting these camps at altitudes at which it was possible to sleep and eat easily, and of going down to lower altitudes for rest periods of a few days to recover, a procedure that is copied by most modern expeditions and, as we shall see, has a sound physiological basis.
For the first time, there was also a comprehensive policy on the use of supplementary oxygen; previously, oxygen was not widely used because most climbers had little confidence in the new-fangled gear and the early equipment was very heavy. Above 6500 metres, the Everest expedition used oxygen, both to assist in sleeping (at a rate of 1 litre per minute) and when climbing (4 litres/minute). Even with this advantage, the effects of altitude caused a gradual physical deterioration and they all lost weight. Sometimes they became severely incapacitated, as graphically described by Hunt:
'Our progress grew slower, more exhausting. Each step was a labour, requiring an effort of will to make. After several steps at a funereal pace, a pause was necessary to regain enough strength to continue. I was already beginning to gasp and fight for breath ... My lungs seemed about to burst; I was groaning and fighting to get enough air; a grim and ghastly experience in which I had no power of self-control.'
The cause of this extreme difficulty was discovered later. The tube connecting Hunt's face-mask to the oxygen bottles was completely blocked with ice so that he received no oxygen; not only was he carrying the heavy oxygen equipment but he was gaining no benefit from it! In his account of the Everest expedition, Hunt later wrote: 'I would single out oxygen for special mention ... only this, in my opinion, was vital for success. But for oxygen, we should certainly have not got to the top.'
News of the conquest of Everest on 29 May 1953 by Edmund Hillary and Sherpa Tenzing Norgay arrived in London on 2 June, just in time for the Coronation of Her Majesty Queen Elizabeth. It was announced over the loudspeakers along the Coronation route and greeted by wild cheering of the crowds. At Base Camp, the successful party were amazed to hear the news of their achievement announced on the All India Radio, as the reporter, James Morris of The Times, had only left Advance Base Camp on 30 May to file his article. To celebrate, they fired twelve mortar bombs, a gift of the Indian army, into the snows.
The use of oxygen to conquer Everest led to the belief that it was not possible to survive on its summit unassisted. Indeed, Dr Griffith Pugh, a physiologist on the first expedition to reach the summit of Everest, claimed that 'only exceptional men can go above 8200 metres without supplementary oxygen' His statement was supported by a number of tragic accidents in which elite mountaineers, climbing unassisted, died, usually from exhaustion brought on by hypoxia that caused them to stagger wildly and slip to their deaths. As has so often been the case with high altitude physiology, however, the resilience and determination of the mountaineers proved the scientists wrong, for in 1978 Peter Habeler and Reinhold Messner climbed Everest without oxygen. Since then their remarkable achievement has been repeated by many others, including, in 1988, the first woman, Lydia Bradey (her claim is disputed, since she climbed alone and thus it could not be proved she actually made it to the top).
It is clear from these accounts that a distinction must be made between the physiological effects of sudden ascent to altitude, such as might occur in a balloon flight or when the cabin pressure of an aircraft is suddenly lost, and the effects of a more gradual ascent, typified by the slow climb to the summit of a mountain, in which time is taken for acclimatization. The effects of life-long residence at high altitude constitute yet a third case.
A Digression on Barometric Pressure
Evangelista Torricelli was the first to conceive that air has weight. In a letter to a colleague dated 1644 he wrote that 'we live submerged at the bottom of an ocean of the element air, which by unquestioned experiments is known to have weight'. A pupil of Galileo, Torricelli is also credited with making the first mercury barometer for measuring atmospheric pressure (the pressure exerted by the weight of the air itself).
The decrease in the density of the air with altitude means that the atmospheric pressure decreases as one ascends higher and higher. This was first shown in 1648 by Blaise Pascal on the Puy de Dome in what he engagingly described as The Great Experiment'. Simply put, the pressure is less the higher one goes because there is less weight of air pressing down on top.
Until very recently, the units used to measure atmospheric pressure (Torr) were named after the Italian Torricelli in recognition of his important contribution. Officially, Torr have now been superseded by a new unit of pressure named after the Frenchman Pascal a change that, as might be imagined, was not without controversy. However, because much of the early literature uses Torr, and many physiologists continue to do so, I have also done so here.
At sea-level, the atmospheric (or barometric) pressure is around 760 Torr (millimetres of mercury). Oxygen makes up 21 per cent of the air, 0.04 per cent is carbon dioxide, and the rest is mostly nitrogen. Thus at sea level the pressure produced by oxygen, known as the partial pressure of oxygen, is 159 Torr (21 per cent of 760 Torr). On the summit of Everest the air contains the same percentage of oxygen, but because the barometric pressure falls to about 250 Torr, the partial pressure of oxygen in the air is reduced proportionately. Moreover, the relative decrease in the partial pressure of oxygen in the lungs is even greater than that in the atmosphere. This rather surprising fact arises because the body produces a significant amount of water vapour. Its presence in the alveoli the small air-sacs where gas exchange between the air in the lungs and that dissolved in the blood takes place limits the space available for oxygen, a fact that becomes increasingly important at altitude.
At any altitude, the air in the lungs is saturated with water vapour produced by the body. This can be seen very clearly on a cold day, when the water vapour you breathe out condenses in the cold air, forming a small cloud. Water vapour has a partial pressure of 47 Torr. This means that when the atmospheric pressure is 47 Torr, which occurs at an altitude of 19,200 metres, the lungs will be entirely occupied by water vapour, leaving no room for oxygen or other gases. The fraction of the gas pressure in the lungs that is due to water vapour thus increases with altitude, rising from 6 per cent at sea-level to 19 per cent on the summit of Everest.
The presence of water vapour in the alveoli helps explain why the partial pressure of oxygen is lower in the air-sacs than in the atmosphere (the fact that oxygen is extracted by the body is also a contributing factor). It also physically limits the altitude to which humans can ascend, even when breathing pure oxygen. The lowest barometric pressure at which the normal oxygen concentration of the lungs (100 Torr) can be maintained when breathing pure oxygen is about 10,400 metres, which is around the cruising altitude of most commercial aircraft. It is possible to survive at higher altitudes because an increase in breathing blows off some of the carbon dioxide in the lungs and so provides more room for oxygen. Above 12,200-13,700 metres, however, insufficient oxygen can be provided and consciousness is lost. Above 18,900 metres, the blood 'boils' (it actually vaporizes) at body temperature. This explains why a pressurized suit or cabin, with a self-contained air supply, is required for very high altitude or space exploration (see Chapter Six).