REFERENCE VALUES OF ARTERIAL OXYGEN-TENSION IN THE MIDDLE-AGED AND ELDERLY

The lack of available reference values of arterial PO2, particularly f or elderly persons, led us to study a sample of 194 normal nonsmoking subjects, equally distributed over all age ranges from 40 to 90 yr. Th e radial artery was punctured and blood samples were taken and analyze d on an automated, computerized gas-analyzer. The trend of the mean va lues of Pa-O2 in the 5-yr class intervals of age showed a clear declin e up to the 70- to 74-yr class, and then an inversion, The two regress ion lines intersecting at this point provided a better fit to the data than did a single regression line (R(2)(2) - R(1)(2) = 0.918 - 0.678 = 0.24; F = 20.49, p = 0.0027). The relationship of Pa-O2 with age was thus subsequently considered for the two subgroups (40 to 74 yr; grea ter than or equal to 75 yr) identified on the basis of this cutoff. Be cause of the significant influence on Pa-O2 of age, body-mass index (B MI), and Pa(CO2)in the group 40 to 74 yr of age, the following referen ce equation was constructed: Pa-O2 (mm Hg) = 143.6 - (0.39 . age) (0.5 6 . BMI) - (0.57 . PaCO2); R(2) = 0.28; SEE = 7.48; p < 0.0001. For su bjects greater than or equal to 75 yr old, for whom there was no corre lation with age, BMI, or Pa-CO2, only the mean +/- SD and 5th percenti le of Pa-O2 were reported (83.4 +/- 9.15 mm Hg and 68.4 mm Hg, respect ively). Pa-CO2 values were not correlated with either age or BMI; the mean +/- SD was 35.79 +/- 3.87 mm Hg. Our study yields appropriate ref erence values of Pa-O2, including the lower and upper limits for subje cts aged 40 to 90 yr, that can be used routinely in pulmonary function laboratories.