Emphysema index in a cohort of patients with no recognizable lung disease: influence of age.

OBJECTIVE

To investigate the effects of age on pulmonary emphysema, based on the values of the emphysema index (EI) in a cohort of patients who had never smoked and who had no recognizable lung disease.

METHODS

We reviewed the CT scans, reported as normal, of 315 patients. Exclusion criteria were a history of smoking, cardiorespiratory disease, and exposure to drugs that could cause lung disease. From this cohort, we selected 32 patients (16 men and 16 women), matched for gender and body mass index, who were divided equally into two groups by age (< 50 years and > 50 years). We quantified emphysema using a computer program specific to that task. The EI was calculated with a threshold of -950 HU. We also evaluated total lung volume (TLV) and mean lung density (MLD).

RESULTS

The overall means for TLV, MLD, and EI were 5,027 mL, -827 HU, and 2.54%, respectively. Mean values in the older and younger groups, respectively, were as follows: for TLV, 5,229 mL vs. 4,824 mL (p > 0.05); for MLD, -846 HU vs. -813 HU (p < 0.04); and for EI, 3.30% vs. 1.28% (p < 0.001). Significant correlations were found between EI and age (r = 0.66; p = 0.001), EI and TLV (r = 0.58; p = 0.001), and EI and MLD (r = -0.67; p < 0.001). The predicted EI per age was defined by the regression equation (r² = 0.43): p50(EI) = 0.049 × age - 0.5353.

CONCLUSIONS

It is important to consider the influence of age when quantifying emphysema in patients over 50 years of age. Based on the regression analysis, EI values of 2.6%, 3.5%, and 4.5% can be considered normal for patients 30, 50, and 70 years of age, respectively.