Diffusing capacity of the lung for carbon monoxide at high altitude

¹ Himalayan Scientific and Mountaineering Expedition 1960–61; and Division of Human Physiology, Medical Research Council Laboratories, London, England

Diffusing capacity of the lung for carbon monoxide (Dl) was measured in London (Pb approx. 750 mm Hg), at 15,300 ft (4,700 m; Pb approx. 440 mm Hg), and at 19,000 ft (5,800 m; Pb approx. 380 mm Hg) on seven members of the Himalayan Scientific and Mountaineering Expedition, 1960–61. At each altitude Dl was measured at two work levels (300 and 900 kg-m/min) and at three different inspired oxygen tensions in order to separate membrane and blood components of the diffusing barrier. A steady state method was used with mixed expired gas analysis; dead space-to-tidal volume ratio was assumed but calculated Dl was insensitive to this. There was no consistent change in Dl at 15,300 ft (subjects breathing ambient air) compared with sea level, but Dl was significantly increased after 7–10 weeks at 19,000 ft (mean changes of 15 and 19% for work levels of 300 and 900 kg-m/min, respectively). However, this small change in Dl can be wholly accounted for by the increased rate of reaction of carbon monoxide with hemoglobin due to hypoxia and by the increased blood hemoglobin concentration.

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