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High Altitude and Man

High Altitude and Man. John B. West and Sukhamay Lahiri, editors. American Physiological Society, Bethesda, 1984. 199 pages, tables, diagrams. $39.00.

Thanks to the American Medical Research Expedition to Everest in 1981, physiologists have turned to the high mountains again to do research. The expedition was an outstanding success on three counts: 1) Everest was climbed and scientific observations were made on the summit; 2) numerous physiological studies were successfully completed; and 3) there were no accidents, injuries, or deaths. One climber developed high altitude pulmonary edema which was promptly recognized and treated. High Altitude and Man consists of 16 brief chapters of research studies presented at a symposium sponsored by the American Physiological Society in La Jolla, California. The book is not a complete summary of all the results of the expedition’s findings and only about half of the chapters report on studies performed on Everest. Each chapter contains clear illustrations and numerous well-selected references.

The sections of greatest interest are those concerned with research studies performed during the expedition. John West’s introduction and first chapter provide a succinct description of the remarkable alterations of blood gases near and on the summit of Everest. It is hard to believe that climbers without oxygen are capable of functioning at all on the summit, when one considers their estimated blood gas values to be: arterial PO2 of 28 mm., an arterial PCO2 of 7.5 mm., and a pH of 7.76. (Normal sea level values are 95 mm., 40 mm., and 7.40 respectively.) Equally fascinating was the discovery that the barometric pressure on the summit was about 17mm. higher than that predicted from standard tables. West’s discussion of barometric pressure fluctuations on Everest makes it clear that the oxygenless climber on Everest is so near his physiologic limits that a small decrease in barometric pressure during bad weather may make the summit impossible to attain. West also points out that the location of Everest near the equator results in a higher barometric pressure than one would expect. If Everest were in the polar region, the summit barometric pressure would be lower. For this reason, a polar Everest probably could never be climbed without oxygen. Robert Schoene’s studies on the ventilatory response to hypoxia indicate that climbers who substantially increase their ventilation while breathing a low oxygen mixture will probably perform better at very high altitudes than those who have a lesser increase in ventilation. The chapter on cerebral function reports that high altitude exposure results in mild deterioration in learning, memory, and expression of verbal material which persists for several days after descent. The observation that a bilateral reduction in motor speed (finger tapping) characterized by rapid muscle fatigue persisted for up to one year after descent was surprising. Jim Milledge presents his studies on the effect of strenuous daily exercise on sodium and water exchange. Hill walking for seven hours a day for five days results in retention of sodium and water, an increase in plasma volume, and systemic edema. A similar effect was seen at high altitude. Stimulation of the renin-aldosterone system is the causative mechanism. The hypoxia of altitude exposure is synergistic to exercise in stimulating renin output. While Milledge speculates that exercise-induced fluid retention may contribute to high altitude pulmonary edema, his speculation would have been stronger if he had demonstrated a substantial decrease in vital capacity after exercise. Studies by the reviewer of vital capacity before and after similar exercise and hemodilution at 12,400 feet in the White Mountains of California revealed no change in vital capacity. Bob Winslow reports his studies on the oxygen dissociation curve and finds that the effect of 2, 3-DPG in modulating oxygen affinity at very high altitude is minimized by the presence of uncompensated respiratory alkalosis. The latter becomes progressively more severe at very high altitude and maintains arterial oxygen content, so that it is possible that arterial oxygen saturation may actually be higher at 28,028 feet (8,848 meters) than at 20,500 feet (6,300 meters). Periodic breathing (Cheyne-Stokes respiration) during sleep was studied in expedition members and Sherpas. All lowlanders, including lowland Sherpas, exhibited periodic breathing during sleep. Typical patterns consisted of 3 or 4 deep forceful breaths for about 10 seconds followed by a complete cessation of breathing for a similar duration. The pattern of breathing was identical to that observed and published by Angelo Mosso in the Alps in 1886. Only high-altitude Sherpas did not exhibit periodic breathing. Lahiri commented on the slightly longer lung-ear circulation time at 5,400 meters compared to sea level. This is not a new observation since Marticorena, in 1970, reported that arm to tongue circulation times were prolonged from 5.4 seconds at sea level to 7.3 seconds at 12,300 feet. A lower cardiac output and an increased intra-thoracic blood pool are the probable mechanisms. The lack of any substantial prolongation of the lung to ear circulation time on the Everest subjects also reinforces the concept that left ventricular failure does not occur at high altitude. Duane Blume reports on metabolic and endocrine changes. He made many measurements, but I failed to detect any new discoveries. Blume’s studies once again confirmed the presence of progessive weight loss at very high altitude due to a decrease in food intake (poor appetite), respiratory water loss, and probably hypoxic intestinal malabsorption. Malabsorption at high altitude has been speculated upon for many years, but proof is lacking. More sophisticated methods than xylose absorption will probably be needed to answer this question.

Nine other chapters do not report research results from the expedition, but present data on breathing during sleep, control of breathing at high altitude, brain blood flow during hypoxia, and a brief review of high altitude polycythemia.

This volume is a valuable source of research data regarding high altitude physiology. The sections of greatest interest are those concerned with work done on the expedition to Everest. The reader should be aware that this book is a collection of presentations at a symposium. Such books have certain built-in disadvantages including: 1) Limited and often unbalanced coverage of the field; 2) The writing style is uneven and organization of the sections varies; 3) Since the symposium audience is usually highly specialized, the presentations will also be specialized. This volume is primarily written by physiologists for physiologists. Despite these minor limitations, this book covers all topics in an excellent manner, thanks to capable editors. High Altitude and Man is worth reading by anyone interested in what happens to man at high altitude. This volume belongs in all physiology and medical libraries.

Herbert N. Hultgren, M.D.