THE PRIMARY objective of the American Medical Research Expedition to Everest was to obtain information on the function of the human body at extreme altitudes. As such it was unique in the long history of expeditions to Everest. In spite of its ambitious goals, the expedition had considerable success. An extensive scientific program was completed, five people reached the summit, and everybody returned home safely.

The rationale for a medical research expedition to extreme altitudes is that many aspects of how man can tolerate the extreme oxygen deprivation of high mountains are still obscure. Physiologists have always been intrigued by the exploits of mountain climbers because they are exposed to the lowest levels of oxygen by far that normal man ever encounters. For example, the pressure of oxygen in the inspired air on the summit of Everest is about 43 mm mercury whereas the normal value at sea level is about 160. The result is that while the normal pressure of oxygen in the arterial blood at sea level is 90-100, a resting climber who breathes the air on the summit of Everest almost certainly has a pressure of less than 30 mm mercury.

These very low levels of oxygen pose tremendous difficulties for the body to extract enough oxygen from the air to maintain physical activity. Indeed, many physiologists were astonished when Messner and Habeler first reached the summit of Everest without supplementary oxygen in May 1978. This was the culmination of many climbing achievements which successively caused physiologists to revise their views of how much oxygen deprivation could be tolerated. For example, as early as 1909' when the Duke of the Abruzzi reached the extraordinary altitude of 7500 m in the Karakoram mountains without supplementary oxygen, some physiologists concluded that the lung had to actively secrete oxygen into the blood to make such an ascent possible. It is now accepted that the lung does not behave in this way. Nevertheless each subsequent altitude record without supplementary oxygen has posed fresh problems for physiologists to answer. It is noteworthy that Norton climbed to over 8500 m on the north side of Everest in 1924 without using oxygen equipment but that, as indicated above, the summit was not reached without supplementary oxygen until 1978, Thus the last 300 m of altitude took 54 years! This is evidence of how close man is to the limit of human tolerance to hypoxia on the summit of Everest.

A more practical reason for our interest in the oxygen deprivation of extreme altitudes is that many patients with severe lung and heart disease also have low levels of oxygen in their blood. Our hope is that by obtaining a better understanding of how normal man tolerates these extreme degrees of oxygen deprivation of high mountains, we can eventually improve our management of these patients with severe disease.

There have been several notable medical research expeditions to high-altitude during this century. One of the most ambitious was the Himalayan Scientific and Mountaineering Expedition of 1960-61 led by Sir Edmund Hillary with' L. G. C. E. Pugh as scientific director.1 A pre-fabricated' hut was erected at an altitude of 5800 m and several medical doctors spent about 5 months during the winter making a series of physiological measurements. Further research was carried out in the spring when the expedition attempted (unsuccessfully) to climb Makalu (8481 m) without supplementary oxygen. Measurements of maximal work were made using a stationary bicycle up to an altitude of 7440' m, and these remained the highest measurements of this type ever made. Three scientists from that expedition took part in the present expedition and its design was influenced considerably by the experience- gained in 1961.

The organization of the American Medical Research. Expedition to Everest was unusual in keeping with its unusual scientific objectives. First there were six climbers headed by John Evans, deputy leader in charge of climbing. He had been a member of the 1971 International Everest Expedition and therefore had first-hand experience of the initial part of the route. The climbers were David Jones, Chris Kopczynski, Jeff Lowe, Glenn Porzak, and Michael Weis. Next there were 6 'climbing scientists', that is medical doctors with an interest in high-altitude physiology who were all experienced high-altitude climbers. This group comprised Steven Boyer, M.D., David Graber, M.D., Peter Hackett, M.D., Christopher Pizzo, M.D., Frank Sarnquist, M.D., and Robert Schoene, M.D. Finally there was a group of 8 other scientists who worked in the two laboratories at altitudes of 6300 m and 5400 m. They were Duane Blume, Ph.D. (deputy leader in charge of logistics and finance), Sukhamay Lahiri, Ph.D., Karl Maret, M.D., James Milledge, M.D,, Richard Peters, Michele Samaja, Ph.D., John West, M.D., Ph.D. (expedition leader), and Robert Winslow, M.D. There was also a base camp manager, Rodney Korich. The team of 40 high- altitude Sherpas was led by Sirdar Sonam Girme.

The expedition began the trek from Kathmandu on 6 August and base camp was established at the head of the Khumbu valley on 30 August. The condition of the Khumbu icefall was unusually good and a route was found through it by 3 September. However a storm then delayed progress for 6 days, but during this time the base camp laboratory was set up and it was operated non-stop until the end of October. Camp 2 (advance base camp) was established high in the Western Cwm on 15 September at an altitude of 6300 m. This was the site of the major laboratory which was constructed from an aluminum frame covered with fiberglass blankets. The laboratory was kept warm by means of a propane stove, and electrical power for the scientific equipment was provided by gasoline generators and solar panels. The laboratory contained a large amount of sophisticated scientific equipment and was the site of an intensive research program during most of October.

Village in dangerous situation due to flood hazard in Doiling Qu valley.

Village in dangerous situation due to flood hazard in Doiling Qu valley. (Photo: Peter Jackson)

Yangbajarin geothermal field, Tibet.

4. Yangbajarin geothermal field, Tibet. (Photo: Peter Jackson)

Kekar Dzong, now called New Tinggri.

Kekar Dzong, now called New Tinggri. (Photo: Peter Jackson)

Peasants carrying Sophora moorcroftiana bushes dragged out by roots.

Peasants carrying Sophora moorcroftiana bushes dragged out by roots. (Photo: Peter Jackson)

The route chosen by the climbing leader, John Evans, for the ascent of the headwall was slightly to the right of the 1980 Polish Southwest Buttress route. Camps 3 and 4 were on steep snow and ice but with good avalanche protection at altitudes of 7250 and 7500 m respectively. Because of the steepness of the terrain, the tents of Camp 3 were placed on an aluminum frame supported on legs. Camp 5 was established on 11 October at an altitude of 8050 m about 50-100 m above the South Col. However by then temperatures at this altitude were very cold and the winds were fierce, and some of us despaired of the expedition reaching the summit. In fact three potential summit assault teams occupied Camp 5 between 11 and 20 October but they were unable to make much progress above Camp 5 because of the gale-force winds and low temperatures.

Fortunately, on 21 October, Chris Kopczynski and Sherpa Sundare found a break in the weather and they climbed to the summit via the southeast ridge in excellent conditions. Their time of about 4J hours from Camp 5 to the summit was exceptionally fast. However this team was not able to make any scientific measurements above Camp 5 because radio communications with the lower camps were bad and they were unable to find the scientific equipment which was in one of the tents at Camp 5 but covered by snow.

24 October was another fine day and Chris Pizzo, M.D. with Sherpa Yong Tenzing reached the summit at 12.30 p.m. Pizzo carried out an extensive series of physiological measurements including the measurement of barometric pressure and temperature, and the collection of air samples from his lungs on the summit. To do this he breathed out into a special piece of equipment (Photo 7) and then pulled a lever. This opened the valve of the small pre-evacuated aluminium can thus trapping the last exhaled air. The samples were brought back to the University of California San Diego for analysis. Additional measurements were made during the climb from Camp 5 including a continuous electrocardiogram and some measurements of breathing. On the same day Peter Hackett, M.D. also reached the summit at about 4 p.m. He made a solo ascent because his Sherpa companion Nuru Dzambu became too cold to continue. Thus the expedition succeeded in putting 3 Americans and 2 Sherpas on the summit.

The extensive science program is summarized in' Figure 1. Note that measurements were made at 4 sites on the mountain: Base camp 5400 m, Camp 2 6300 m, Camp 5 8050 m, and the summit 8848 m.

In the base camp laboratory, a major study was carried out on the control of breathing. One of the most important changes to occur when man goes to high altitude is an increase in breathing. This was studied both in the westerners and the Sherpas in the awake and sleeping states. An interesting finding was that although all the westerners had marked periodic breathing (alternating episodes of increased and decreased respiration) the Sherpas breathing was uniform. The reasons for this are not fully understood but are probably related to the different response of the Sherpas breathing to low levels of oxygen. Another study in this laboratory was on the effects of hemodilution, that is reducing the concentration of red cells in the blood. Some physicians have advocated this at high-altitude where the thickness and viscosity of the blood increase because of the added number of red cells. We tested this by removing some blood and replacing it with cell-free fluid and measuring the results using the stationary bicycle and tests of mental function. No changes were found and this suggests both that hemodilution under these conditions is probably not useful, and also that the increase in red blood cells that occurs at high altitude may not be beneficial as has often been thought. A third study in the base camp laboratory looked at blood changes in the Sherpas. Previous investigators have suggested that these are different from other permanent residents of high altitude, for example in the South American Andes, but our results showed that the blood pictures of the two groups are similar.

Fig. 1: Diagram to show the Chief Projects of the Medical Research Programme.

Fig. 1: Diagram to show the Chief Projects of the Medical Research Programme.

At the Camp 2 laboratory, a very extensive scientific program was completed and there is not space here to do it justice. Many exercise measurements were made because in the oxygen-deprived state of high altitude, the body's problems are magnified when oxygen demands are increased as during exercise. We found that a man's work capacity at this altitude is reduced to about half the sea-level value. When we stimulated the conditions on the summit by giving the subjects low oxygen concentrations to breathe, we showed that exercise capacity there was reduced to less than one quarter of the sea-level control. Moreover all the high levels of exercise were associated with very low values of oxygen in the arterial blood.

A series of sleep studies were undertaken because the oxygen in the blood falls to its lowest levels during sleep as a result of the depressed breathing. In fact many physicians believe that whether a climber can tolerate these altitudes may depend to a large extent on the oxygen levels in the blood during sleep. We found marked periodic breathing as at base camp, and striking fluctuations in the levels of oxygen in the blood. Changes in the blood constituents including its biochemistry were extensively studied. Many of the measurements were made on frozen plasma samples brought back to the United States. One study showed impaired intestinal absorption which may explain, at least in part, why climbers often develop marked weight loss at high altitudes. A series of psychometric tests were also carried out to determine whether the oxygen deprivation affected the brain. Some reversible changes were seen at extreme altitudes, and in two instances, tests showed reduced function after the expedition members had returned to sea level compared with control measurements made prior to the expedition.

Samples of blood were taken, and sleep electrocardiograms were recorded at Camp 5. However the most ambitious program was that planned for the summit. Fortunately Dr Pizzo was able to get several measurements including the alveolar air samples (Photo 7) and these enable us to put together an integrated picture of how man can tolerate the extreme oxygen deprivation of the Everest summit. It is clear that he does this by an enormous increase in his breathing which increases the level of oxygen in his lungs and also results in making the blood very alkaline. Both of these changes assist in the uptake of oxygen by the lungs. Various scientific papers describing the findings are being written at the present time and will eventually be published in the standard physiological journals.

One group of measurements that we made might be of special interest to Himalayan climbers. These were the careful recordings of barometric pressure at accurately known altitudes.2 It is well known that the relationship between barometric pressure and altitude on Everest does not conform to the standard atmosphere tables. Since there has been some uncertainty about the barometric pressures on Everest, we made careful measurements at base camp, the South Col, and the summit. The results are shown in Figure 2 and this relationship could be used to determine altitude if accurate barometric pressure measurements were available. The relationship is accurate for the months of October and May (the usual climbing months) but the barometric pressures will be lower in the winter.

Naturally this rather prosaic account of what was done omits the human drama which is part of any expedition to extreme altitudes. Perhaps there is space to describe two incidents which indicate how very fortunate we were. On the morning of 24 October when Dr Pizzo left Camp 5 for the summit, he was unable to find his ice-axe. It was in fact at the camp but had been buried by snow and ice in the violent storms of the preceding few days. Having nothing better he picked up a tent pole and started heading for the summit with that. However after ascending several hundred meters, he found an ice-axe lying on top of the ice ! We now know that this belonged to Hannelore Sehmatz who died from exposure on the southeast ridge during the German- Austrian expedition of 1979. This million-to-one chance of finding an ice-axe at such a critical point in the climb was largely responsible for the expedition obtaining the extremely valuable scientific information from the summit measurements.

Fig. 2 : Relationship between barometric pressure and the altitude on Everest. The relationship is accurate for the pre- and post- monsoon climbing months but the pressure in winter will be lower. Torr is the same as mm mercury.

Fig. 2 : Relationship between barometric pressure and the altitude on Everest. The relationship is accurate for the pre- and post- monsoon climbing months but the pressure in winter will be lower. Torr is the same as mm mercury.

The second medical summitter, Dr Peter Hackett, had a remarkable escape. As indicated above, he made a solo ascent because his Sherpa companion became too cold to continue. Hackett reached the summit at about 4 p.m. on 24 October and spent a few minutes there taking photographs. As he was descending in the chimney of the Hillary Step, he encountered soft snow and fell. However instead of ending up in the Western Cwm some 2800 m below, he fell only about 2 m before one of his boots caught on a piece of outcropping rock and he found himself suspended upside down, about 8800 m high, completely alone, and with the afternoon fast fading! After considerable difficulties he eventually managed to extricate himself with the aid of a fixed rope that had been left behind by an unknown previous expedition, and he eventually joined Chris Pizzo who was waiting for him at the old Camp 6 site. The two descended to Camp 5 on a moonless night (they had one headlamp), reaching it at about 8 p.m.

In Summary the expedition was extreamly successful. A very extensive scientific program was completed, and everyone returned home safely. Kopczynski, Pizzo and Hackett were the 9th, 10th and 11th Americans to reach the summit while Sherpa Sundare reached the summit for the second time and, indeed made a third ascent with the Canadians in the autumn of 1982. This makes him the only person to achieve this feat.


  1. Ward, M. P., ‘Himalayan Scientific Expedition, 1960-61’, Alpine Club J. 66 343 -364, 1961.
  2. West, J. B. et al. ‘Barometic pressures at extreme altitudes on Mt. Everest: Physiological Significance’, J. Appl. Physiol.: Respirat. Enviran. Exercise Physiol. (in press).
Chris Pizzo, M.D, taking samples of air from his lungs on the summit of Everest, 24 October 1981.

Chris Pizzo, M.D, taking samples of air from his lungs on the summit of Everest, 24 October 1981.


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