Pulmonary gas exchange on Mount Everest
Authors: JB West
Journal: European Respiratory Journal (1997)

The paper by PEACOCK and JONES [1], Gas Exchange at Extreme Altitude: Results from the British 40th Anniversary Expedition, presented in this issue of the Journal, reports fascinating new data recorded at extreme altitudes (up  8,000 m) on Mount Everest. Among the interesting findings, was the fact that, on the South Col (altitude 8000 m), alveolar oxygen tension (PA,O2) (measured with a fuel cell) was about 5.1 kPa (38 torr) and arterial oxygen saturation (Sa,O2) (measured with a pulse oximeter) was about 70%, emphasizing the extraordinary degree of hypoxaemia experienced by climbers at extreme altitudes. The results of the British 40th Anniversary Expedition agree remarkably well with those of the 1981 American Medical Research Expedition  Everest [2, 3]. The most important factor in the process of acclimatization, which helps  maintain the arterial oxygen tension (Pa,O2) and Sa,O2 at viable levels, is extreme hyperventilation. This defends the alveolar PA,O2 in the face of the fall in partial pressure of oxygen (PO2) in the surrounding air. In addition, the reduction in partial pressure of carbon dioxide (PCO2) causes a respiratory alkalosis, which also assists in maintaining Sa,O2 by increasing the oxygen affinity of the haemoglobin. It is interesting that, as shown in the paper by PEACOCK and JONES [1], the values for PA,O2 measured on Operation Everest II were much lower [4], apparently because these subjects were less well acclimatized [5]. One of the most stimulating topics in the area of highaltitude medicine and physiology this century has been the challenge of climbing Mount Everest, especially without supplementary oxygen. In the closing stages of the last century, climbers were very pessimistic about reaching such great altitudes. For example, in 1876, T.W. Hinchliff, President of the (British) Alpine Club, wrote gloomily after visiting Santiago, Chile [6]:  could not repress a strange feeling as I looked at Tupungato (21,550 feet) and Aconcagua (23,080 feet) and reflected that endless successions of men must in all probability be forever debarred from their lofty crests.... Those who, like Major Godwin-Austen, have had all the advantages of experience and acclimatization  aid them in attacks upon the higher Himalayas agree that 21,500 feet (7,050 m) is near the limit at which man ceases  be capable of the slightest further exertion. However, in 1909, an Italian aristocrat, the Duke of the Abruzzi, led an expedition  the Karakorum, which, as the Duke's biographer and physician, DE FILIPPI [7] wrote, was designed to contribute  the solution of the problem as  the greatest height  which man may attain in mountain climbing. The expedition reached 7,500 m and the feat prompted DOUGLAS et al. [8]  argue that the lung must have secreted oxygen. Indeed, during the Pikes Peak expedition of 1911, DOUGLAS et al. [8] believed that they had found strong evidence of oxygen secretion in acclimatized subjects. In 1919, Alexander M. Kellas, a Scottish chemist and physiologist, made an extensive theoretical study of the physiological problems associated with climbing Everest [9], but the work was never published in an accessible form, and most high-altitude physiologists are unaware of it. Kellas concluded that the mountain could be climbed without supplementary oxygen if the technical difficulties were not too great, but he died dramatically when the initial Everest reconnaissance had its first view of Everest in 1921. In 1924, E.F. Norton climbed  within 300 m of the Everest summit without supplementary oxygen, but it was 54 yrs before the last 300 m were eventually conquered! In 1930, the Italian physiologist MARGARIA [10] measured maximal oxygen consumptions at very low barometric pressures in a low-pressure chamber, and concluded that man could not reach the Everest summit without supplementary oxygen. A few years later, HENDERSON [11] came  the same conclusion based on measurements of maximal oxygen consumption made in the field. But by 1958, 5 yrs after Hillary and Tenzing had made the first ascent (with supplementary oxygen), the British physiologist PUGH [12] was less willing  make a categorical statement, and wrote that it was unlikely that the mountain could be climbed without oxygen equipment without serious risk. It was not until 1978 that Reinhold Messner and Peter Habeler astounded both physiologists and mountaineers with their oxygenless ascent of Everest. MESSNER [13] reported his sensations on reaching the summit in lyrical terms: Now, when... I have nothing more  do than breathe, a great peace floods my whole being. I breathe like someone who has run the race of his life and knows that he may now rest for ever... In my state of spiritual abstraction, I no longer belong  myself and  my eyesight. I am nothing more than a single, narrow, gasping lung, floating over the mists and the summits. Some physiologists were reluctant  believe the feat at first (emergency oxygen had been taken), but other oxygenless ascents soon followed, including the spectacular solo ascent by Messner in 1981. This first ascent without supplementary oxygen prompted a theoretical analysis of the most critical factors on the Everest summit [14]. These were: 1) the barometric pressure; 2) the extent of the hyperventilation; and 3) EDITORIAL