Alveolar-arterial difference in oxygen tension (A-aD) and physiological dead space/tidal volume ratio (Vd/Vt) were measured in normal subjects aged 17–66 years, in the supine and sitting postures. Paoo2 decreased and A-aD increased with age. A-aD was not affected by posture, but increased with Paoo2. Regression equations relating Paoo2 and A-aD to age, and Paoo2 were calculated. Vd/Vt increased with age in the supine position, but when sitting the increase with age was small and barely significant. Consequently, although Vd/Vt was greater when sitting than when supine in young subjects, there was no such difference in the older subjects. Possible reasons for the effect of age and body position are discussed.
Submitted on August 6, 1962
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