EFFECT OF ALTITUDE ON RESPIRATORY FLOW PATTERNS

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Abstract
Data on breath velocities in O2 at ground level and at 30,000 ft. simulated altitude at rest and following exercises are shown with statistical treatment of variation in a group of 32 young men. A stretched wire gas velocity apparatus was adapted to a closed circuit for recording instantaneous breath velocity patterns. Decrease in population density of the respired gas molecules causes an increase in velocity of all phases of the breath pattern and induces a marked post-expiratory pause in enough individuals to show a highly significant mean change in the whole group. More marked effects are obtained with arbitrarily imposed inspir-atory airway restriction both at rest and in exercise. In some individuals during unrestricted breathing, post-expiratory pauses are interposed even following exercises. Respiratory rate was not essentially altered by "ascent" in oxygen to 30,000 ft. It is deduced that, in rarefied O2, ventilation is more expeditiously carried out than at ground level and thus a pause following expiration is interposed until CO2 accumulates at the usual rate to a critical level in the circulatory blood. A post-expiratory pause, when present at ground level, is lengthened at altitude and, in some individuals not having pauses at ground level, it is induced at altitude. This suggests that for every individual there is a specific density of the respired gases which will induce a post-expiratory pause. In individuals not normally having a pause, lower density will induce a pause; in those individuals having a pause normally, lower density will lengthen the pause, and higher density reduce or eliminate it. The use of density as an unbiased index of venti-latory ability is pointed out.

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