Reference values of arterial oxygen tension in the middle-aged and elderly

The lack of available reference values of arterial PO₂, particularly for elderly persons, led us to study a sample of 194 normal nonsmoking subjects, equally distributed over all age ranges from 40 to 90 yr. The radial artery was punctured and blood samples were taken and analyzed on an automated, computerized gas-analyzer. The trend of the mean values of PaO₂ in the 5-yr class intervals of age showed a clear decline up to the 70- to 74-yr class, and then an inversion. The two regression lines intersecting at this point provided a better fit to the data than did a single regression line (R₂ ² - R₁ ² = 0.918 - 0.678 = 0.24; F = 20.49, p = 0.0027). The relationship of PaO₂ with age was thus subsequently considered for the two subgroups (40 to 74 yr; ≥ 75 yr) identified on the basis of this cutoff. Because of the significant influence on PaO₂ of age, body-mass index (BMI), and PaCO₂ in the group 40 to 74 yr of age, the following reference equation was constructed: PaO₂ (mm Hg) = 143.6 - (0.39 · age) -(0.56 - BMI) - (0.57. PaCO₂); R² = 0.28; SEE = 7.48; p <0.0001. For subjects ≥ 75 yr old, for whom there was no correlation with age, BMI, or PaCO₂, only the mean ± SD and 5th percentile of PaO₂ were reported (83.4 ± 9.15 mm Hg and 68.4 mm Hg, respectively). PaCO₂ values were not correlated with either age or BMI; the mean ± SD was 35.79 ± 3.87 mm Hg. Our study yields appropriate reference values of PaO₂, including the lower and upper limits for subjects aged 40 to 90 yr, that can be used routinely in pulmonary function laboratories.