A longitudinal study of pulmonary distensibility in healthy adults.

To assess changes in pulmonary distensibility with age in a longitudinal study, 34 healthy non-smoking adults were examined on two or more occasions over an interval of 6.0 +/- 1.8 yr (mean +/- SD). Exponential analysis of static pressure-volume data obtained during deflation of the lungs gave the exponent, K, an index of distensibility. Total lung capacity (TLC) was measured in a body plethysmograph and increased over the interval of study. The results were compared with findings in a previous cross-sectional study of 124 subjects. At entry into the longitudinal study, mean values for K and static recoil pressure were similar to those obtained for subjects in the cross-sectional study. Over the interval of study, K increased more in subjects with higher values for K (older subjects) supporting the use of a logarithmic analysis of K on age. Using a statistical model which allowed for a variable number of observations and for variance of K between subjects, the increase in ln K with age was similar to that found in the cross-sectional study. From the relationship between K and the average size of airspaces (mean linear intercept, Lm) demonstrated previously in excised lungs, it is shown that the reported increase in Lm with age suffices to explain the increase in K with age in intact subjects.