Effect of aging on lung structure in vivo: assessment with densitometric and fractal analysis of high-resolution computed tomography data.

PURPOSE: To test the hypothesis that there is a difference between the lung computed tomography (CT) microstructure of asymptomatic older individuals and that of young individuals as evaluated by objective indices of complexity and density.
MATERIALS AND METHODS: Two study groups of nonsmoking urban-dwelling individuals over 75 years and under 55 years were prospectively identified. Thirty-three consecutive volunteers (21 older than 75 y and 12 less than 55 y) were included, and CTs were performed with concurrent pulmonary function testing. Pulmonary regions of interest (ROIs) were evaluated with fractal dimension (FD) analysis (an index of complexity), mean lung density (MLD), and percentage of pixels with lung density (LD) less than thresholds of -910 HU and -950 HU. The Student t test and the Mann-Whitney test were used to evaluate for differences in mean values between groups. The Pearson correlation coefficient was used to correlate mean FD value and LD data with pulmonary function.
RESULTS: Significant correlations of ROI MLD, LD -910 HU, and LD -950 HU with age and sex were shown (P = 0.029-0.003). The ROI mean FD value was greater in younger individuals compared with older individuals (76.5 ± 1.7 vs. 70.3 ± 1.2; P = 0.004). There was a correlation between Kco (gas-diffusing capacity adjusted for alveolar volume) and mean FD value (P = 0.006) and MLD (P = 0.015).
CONCLUSION: The lung parenchyma of nonsmoking older urban-dwelling asymptomatic individuals has significantly different CT density and complexity compared with younger individuals.