Cigarette smoking and airway wall thickness on CT scan in a multi-ethnic cohort: the MESA Lung Study

Abstract

Background: Autopsy studies show that smoking contributes to airway wall hyperplasia and narrowing of the airway lumen. Studies of smoking and airway measures on computed tomography (CT) scan are limited to case-control studies of measures that combine airway lumen and wall thickness.

Objectives: We hypothesized that cumulative cigarette smoking would be associated with increased airway wall thickness in a large, population-based cohort.

Methods: The Multi-Ethnic Study of Atherosclerosis enrolled participants age 45-84 years from the general population. Smoking history was assessed via standardized questionnaire items; current smoking was confirmed in half the cohort with cotinine. Airway lumen and wall thickness were measured in two dimensions in posterior basal segmental bronchi on cardiac-gated CT scans. Analyses were adjusted for age, gender, genetic ancestry, education, height, weight, asthma history, particulate matter, scanner type, and scanner current.

Results: Half of the 7898 participants had smoked and 14% were current smokers. Pack-years of smoking were associated with thicker airway walls (mean increase 0.002 mm per ten pack-years [95% CI: 0.00002, 0.004] p = 0.03). Current smoking was associated with narrower airway lumens (mean decrease -0.11 mm [95% CI: -0.2, -0.02] p = 0.02). There was no evidence that either association was modified by genetic ancestry, and findings persisted among participants without clinical disease.

Conclusions: Long-term cigarette smoking was associated with subclinical increases in wall thickness of sub-segmental airways whereas current smoking was associated with narrower airway lumen diameters. Smoking may contribute to airway wall thickening prior to the development of overt chronic obstructive pulmonary disease.

Figure 1

Participant in the Multi-Ethnic Study of Atherosclerosis (MESA) studies included in the analysis.

Figure 2. Airway measurements on CT scan

Upon locating an airway perpendicular to the plane, a centroid was placed in the center of the airway, from which the Pulmonary Analysis Software Suite generated rays and inner and outer airway diameters. If a ray extended into adjacent tissue the analyst would manually exclude it and the PASS system would regenerate the inner and outer diameter to better conform to the shape of the airway. The remaining rays were averaged to calculate airway wall thickness and lumen diameter.

Figure 3. Continuous relationships of cigarette pack years to airway measures

a. Wall thickness b. Lumen diameter The plots show the smoothed association for airway dimensions per ten pack years for mean levels of other covariates from a multivariable generalized additive model using repeated measures assuming compound symmetric covariance within MESA family units. Never-smokers were coded as having zero pack years.