Respiration at High Altitudes *

It has been clearly recognized that a low barometric pressure, when first encountered, may interfere with the normal workings of the human machine, but that later by compensatory responses the body may become adapted to the new conditions. The outstanding variable encountered in ascents to high altitudes by airplane, dirigible, free balloon, or mountaineering is the tenuousness of the atmospheric oxygen. Most of the bodily changes observed at high altitudes can be directly or indirectly attributed to the relative shortage of oxygen. Mankind differs greatly in sensitivity, and in ability to adjust, to the variations in the oxygen content of air caused by increasing altitude. The degree of disturbance and the extent of the compensatory adjustments depend upon four conditions: (1) the speed of the ascent; (2) the height attained; (3) the length of the sojourn; and (4) to some extent, upon the physical condition of the individual. A few individuals fail to make any adjustments and so find themselves unable to tolerate even moderate heights. Others begin to make adjustive responses at altitudes as low as 3000 and 4000 feet; these gradually augment as the ascent is continued and so maintain mental and physical efficiency to altitudes of 20,000 feet and more. There are certain responses to altitude which, even though immediately brought into action, are to be regarded as only temporary compensations. These may be looked upon as emergency adjustments, since they are the effect of the direct action of oxygen want on the nervous system, and since they subside during or very soon after descent from high altitudes. When a residence is maintained at a high altitude more enduring compensatory adjustments are made which adapt the body to the new environment. These permanent adjustments not only give acclimatization but are of a kind that persist for days and weeks after descent. The altitude changes that have been observed occur in the blood, and in the circulatory and the respiratory systems. This paper is confined to a discussion of the respiratory changes. These have been investigated by a reduction of barometric pressure in a low-pressure