Abstract
Alveolar-arterial oxygen tension difference (A-aD) and physiological dead space were measured in 16 normal men and women selected equally from the age groups 20–29 and 50–59 years, at mean alveolar oxygen tensions (PaOO2) of 107, 291, and 653 mm Hg. Arterial oxygen tension was measured polarographically and arterial carbon dioxide tension by an interpolation method. Values for A-aD were not related to posture but were significantly greater in the older group. Mean values for A-aD in the younger group were 8.7, 23.5, and 6.1 mm Hg at the three levels of PaOO2, respectively, and 14.1, 44.5, and 21.3 mm Hg, respectively, among the older group. At the two lower levels of PaOO2 results were in general agreement with those of previous workers, but a significant decrease in A-aD was observed when PaOO2 was raised to 653 mm Hg. It is suggested that this finding may be due either to change in the effective size of anatomical shunt while breathing 99.5% oxygen, or to a significant distribution component of total A-aD at the intermediate alveolar oxygen tension. effect of posture, age and sex; physiological dead space; veno-arterial shunt Submitted on April 23, 1963
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