Pulmonary gas exchange in elderly subjects

Although important alterations in structure and function develop with age, the hypothesis that the lungs are capable of maintaining adequate gas exchange for the maximum human life span is generally accepted. This hypothesis was examined by measuring arterial oxygen and carbon dioxide tension (Pa,O2 and Pa,CO2) alveolo-arterial differences in oxygen and carbon dioxide tension (PA-a,O2 and Pa-A,CO2), steady state transfer capacity of the lung for carbon monoxide (TL,CO,ss) as well as the gas exchange ratio (R) in a series of 74 healthy subjects aged more than 68 yrs (69-104 yrs). In addition, Pa,O2 and Pa,CO2 were measured in a series of 55 young healthy subjects, who acted as controls. In the elderly subjects, except for TL,CO,ss, there was no significant correlation between any of the other variables and age. However, for a given Pa,CO2, Pa,O2 was always lower in the group of elderly subjects than in the group of young control subjects. TL,CO,ss, as well as TL,CO,ss/minute ventilation (V'k) ratio, was correlated with age, according to the following regression equations: TL,CO,ss (mL.min-1.kPa-1) = 126-0.90 x age (yrs), and TL,CO,ss/V'k (kPa-1 x 10(3)) = 13.5-0.085 x age, respectively. These results show that arterial oxygen tension did not decrease with age in this series of elderly subjects. However, the decrease in steady-state transfer capacity of the lungs for carbon monoxide with age indicates that oxygen transport could be diffusion-limited in elderly subjects, at least when oxygen consumption is increased.

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