MODULE SUPPLEMENT: PULMONARY SYSTEM
Component 3: Transport Of O2 and CO2 in the Blood and Body Fluids

Based on the changes that occur in V/Q matching and in diffusing capacity you would expect changes in arterial blood gases with age.

The partial pressure of oxygen (PaO₂) decreases in older adults. An often used formula for the expected PaO₂ from healthy non-smoking supine subjects ranging in age from 14-84 has been derived, although it's important to keep in mind that these are old data (e.g., the formula is from about 1968):

PaO₂ = 109-0.43 (age) +/- 4

Others have used 100.1-0.323(age)--there's a very slight difference in the results.

However, these formulas need to be viewed with some caution. They alert us to the potential vulnerability of older adults to lower levels of tissue oxygenation, but they tend to assume an on-going linear decline. Some data suggest a plateauing at about age 75 or even before. Enright (1999) suggests that PaO₂ decreases until age 60-65 and then plateaues from 65-90 at ~83mmHg. More research is needed in this area.

Adapted from: Enright, P.L. (1999). Aging of the Respiratory System.
In Hazzard, W.R., et al. Principles of gerontology and geriatrics, 4^th ed., McGraw-Hill, p. 724.