What is the formula to determine how PaO2 declines with age?

The correct choice describes the formula used to calculate the decline of arterial oxygen tension (PaO2) as a person ages. The formula, 109 - 0.43 X age, reflects the well-established observation that, generally, as individuals get older, the efficiency of the lungs to oxygenate blood tends to decrease. This decline is a normal physiological change due to factors such as reduced lung elasticity, decreased surface area for gas exchange, and a decline in respiratory muscle function.

By starting from a baseline of 109 mmHg for a young adult, the formula systematically adjusts for age-related decline, where each passing year reduces the expected PaO2 by 0.43 mmHg. This allows healthcare professionals to estimate a patient's oxygen levels based on their age, which can be crucial for assessing pulmonary function and guiding treatment decisions in geriatric patients.

Using this understanding, the chosen formula provides a practical tool for evaluating how aging affects respiratory health, underscoring the significance of monitoring oxygenation in older adults.