| Objective: To study (1) the changes with aging of inspiratory and expiratory HRCT lung density parameters in asymptomatic nonsmokers, and the correlation with PFT(pulmonary function test) results;(2) the effect on expiratory HRCT air trapping resulted from aging and the correlation between air trapping and PFT results by quantitatively analyzing the inspiratory and expiratory HRCT mean lung density in different groups of asymptomatic nonsmokers. Materials and Methods: Lung HRCT scans were performed at end inspiratory and end expiratory in 63 subjects, and PFT were performed in 32 of them. All the subjects were divided into 5 groups according to the ages. Changes with aging of lung inspiratory and expiratory HRCT quantitative parameters and the correlation with PFT results were assessed. Air trappings in expiratory HRCT were quantitatively analyzed and the correlation between air trapping and PFT results were assessed. Results: (1) In each age group the mean lung density of inspiratory and expiratory lung HRCT respectively are(HU): 21-30years group respectively are-688.093±29.3875 and -881.375± 28.9531, 31-40 years group -693.805 ±23.3521 and -876.858 + 26.0755, 41-50 years group -706.836± 18.3758 and -873.663±24.2965, 51-60 years group -736.579 ± 21.8974 and -876.734 ± 17.3546 , more than 61 years group -778.672±19.6581 and -866.598 + 20.6975. (2) In each age group the overall mean lung density difference between inspiratory and expiratory HRCT respectively are (HU): 21-30 years group 193.282 ± 53.1184 , 31-40 years group 183.053 + 64.1520, 41-50 years group 166.827±44.6268, 51-60 years group 140.155 + 39.9931, more than 61 years group 87.917 ± 34.6236. With aging, the overall mean lung density difference between inspiratory and expiratory HRCT is on decrease, and the decrease is significantly different (P<0.01).(3)FVC, FEV1, TLC correlate significantly with mean lung density of each lung field and overall lung in inspiratory HRCT(P<0.01), and the correlation parameter (r) between these three results and the mean lung density of overall lung respectively are : FVC= -0.682, FEV1= -0.694, TLC= -0.768 : RV correlates extremely significantly with the middle lung field in inspiratory HRCT(P<0.01), significantly with the upper, lower lung fieldand overall lung(P<0.05), the correlation parameter with the overall lung is -0.565. (4) Air trapping occurred in 39.7% (25/63) subjects, including type I 22.2% (14/63), type II 17.5% (11/63), type III never occurred . In all cases with air trappings ,18 cases predominantly appear as lobular, 9 cases segmental, and none lobar air trapping. (5) The difference of FVC and FEV1/FVC between air trapping group and normal group is significant (P<0.05) : FEV1/FVC significantly correlate with the grade of air trapping especially (r = -0.529, P<0.05). Conclusion: Quantitative parameters of inspiratory and expiratory lung HRCT, especially mean lung density and the density difference changed subsequently with aging in asymptomatic nonsmokers. Air trapping occurred in about 40% asymptomatic nonsmokers and aging maybe one of its causes. Inspiratory and expiratory HRCT may reflect the subtle changes of PFT results within the normal ranges: FVC, FEV1, TLC and RV correlate significantly with inspiratory CT mean lung density. And there is significant correlation between FEV1/FVC and the area grade of air trapping.
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