Effect of varying inspired O₂ tension on alveolar-arterial O₂ tension difference in man

¹ Department of Medicine, University of Birmingham, Queen Elizabeth Hospital, Birmingham, England

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 (Pa_OO2) 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 Pa_OO2, respectively, and 14.1, 44.5, and 21.3 mm Hg, respectively, among the older group. At the two lower levels of Pa_OO2 results were in general agreement with those of previous workers, but a significant decrease in A-aD was observed when Pa_OO2 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.

Submitted on April 23, 1963