Airway tree morphology and blood eosinophil count in past smokers without a history of lung disease: A cross-sectional analysis of lung cancer screening computed tomography.

BACKGROUND

Native airway structures may affect the host immune response to inhaled noxious particles. We hypothesized that a distinct airway tree structure may be associated with a higher blood eosinophil count (BEC) after smoking cessation, even in the absence of lung disease.

METHODS

This cross-sectional study retrospectively evaluated consecutive male nonsmokers and smokers with no history of lung disease or airflow limitation who underwent lung cancer screening computed tomography (CT), spirometry, and BEC measurement. Total airway count (TAC), airway tree surface area-to-volume ratio (SAV), airway-to-lung size ratio (ALR), and segmental airway wall area percentage (WA%) were quantified using computed tomography (CT).

RESULTS

The study included 205 nonsmokers, 123 past smokers, and 133 current smokers. BEC, neutrophil, lymphocyte, monocyte, and basophil counts were higher in current smokers than in past smokers and nonsmokers, but there was no difference between past smokers and nonsmokers. Higher TAC and SAV, but not ALR or WA%, were associated with greater log-transformed BEC in past smokers (r = 0.25, p = 0.005 and r = 0.25, p = 0.005, respectively), but not in current smokers or nonsmokers. These associations in past smokers remained significant after adjusting for age, body size, and pack-years. In contrast, TAC and SAV were not associated with neutrophil, lymphocyte, or monocyte count in past smokers.

CONCLUSION

A higher branch count and surface area-to-volume ratio of the airway tree may be associated with persistent eosinophilic inflammation in past smokers without a history of lung disease.