Changes in the single-breath nitrogen washout curve on exposure to 17,600 ft

Abstract

Seventeen volunteers were exposed to 17,600 ft after an acclimatization period, at 9,800 ft. Single-breath nitrogen washout curves were done at base camp (2,600 ft), on days 2 and 4 at 9,800 ft, and on days 1, 2,3 4, and 7 at 17,600 ft. There was a significant 39% increase in the slope of phase III on day 2 at 9,800 ft, accompanied by a 125 ml mean increase in anatomic dead space (Vd) and a marked decrease in cardiac oscillations. By day 4 at 9,800 ft phase III slopes were reduced and were not significantly different from base-line controls, while cardiac oscillations were increased and Vd decreased from day 2. Subsequent exposure to 17,600 ft produced another significant increase in phase III slope to 87% above control, which by day 7 had decreased significantly to 63% above control. Cardiac oscillations were again diminished and Vd increased. These changes cannot be accounted for by changes in gas density, nor by the decrease in PIOO2 per se, since this alone would decrease the range of PaNN2. They suggest a pathophysiologic lung lesion which impairs gas mixing and increases asynchronous emptying during early altitude exposure. high-altitude pulmonary edema; gas-mixing impairment at altitude Submitted on November 7, 1974