Structural airway remodeling features are differentially associated with the presence of chronic bronchitis (CB) and its persistence over time, regardless of any changes in an individual’s smoking status. Results of the study were published in the journal Thorax.
Recognizing that CB is strongly linked to cigarette smoking but that not all smokers develop CB, the investigators sought to evaluate whether measures of structural airway disease on computed tomography (CT) scans are differentially linked to CB. Adults enrolled in the large multicenter Genetic Epidemiology of COPD (COPDGene) cohort study were included in the current analysis of this topic. The study defined CB using the classic definition—that is, the presence of cough and phlegm for ≥3 months per year for ≥2 consecutive years. Additionally, CB was defined using the responses to the chronic cough-related questions on the St. George’s Respiratory Questionnaire (SGRQ). The SGRQ-based definition classifies more individuals as having CB than does the classic definition, with comparable associations with airway disease and symptoms, but recognizes more individuals at risk for future exacerbations than does the classic definition.
Volumetric CT scans were required at study enrollment. Airway disease on CT was quantified by the following: (1) wall area percent (WA%) of segmental airways; (2) Pi10—that is, the square root of the wall area of a hypothetical airway with a 10-mm internal perimeter; (3) total airway count (TAC); and (4) airway fractal dimension (AFD).
Data were analyzed from participants with Global Initiative for Obstructive Lung Disease (GOLD) stages 0 through 4. Participants with forced expiratory volume in
1 second (FEV1)/forced vital capacity (FVC) of ≥0.70 and FEV1 percent predicted of ≥80 but with respiratory symptoms were classified as GOLD 0. All of the participants had a smoking burden of ≥10 pack-years.
At baseline, a total of 8917 participants were included in the study, with follow-up data available for 5517 of them at the 5-year visit. Overall, 4407 of the participants had GOLD stage 0 disease, 791 had GOLD stage 1 disease, 1935 had GOLD stage 2 disease, 1175 had GOLD stage 3 disease, and 609 had GOLD stage 4 chronic obstructive pulmonary disease. The mean smoking pack-years was 44.5 ± 25.1. In total, 4341 of the participants were active smokers.
Of the 8917 study participants, 1734 had CB at baseline. Results of the study showed that all of the airway measures were significantly worse in those with CB than in those without CB: (1) WA%: 54.5 ± 8.8 vs 49.8 ± 8.3, respectively; (2) Pi10: 2.58 ± 0.67 mm vs
2.28 ± 0.59 mm, respectively; (3) TAC: 156.7 ± 81.6 vs 177.8 ± 91.1, respectively; and (4) AFD: 1.477 ± 0.091 vs 1.497 ± 0.092, respectively (P <.001 for all airway measures).
Per multivariable logistic regression with adjustment for age, gender, race, change in smoking status, pack-years of smoking, change in FEV1 and CT scanner type, WA% (adjusted odds ratio [aOR], 1.75; 95% CI, 1.56 to 1,97; P <.001), Pi10 (aOR, 1.66; 95% CI, 1.48 to 1.86; P <.001), TAC (aOR, 0.69; 95% CI, 0.60 to 0.80; P <.001), and AFD (aOR, 0.76; 95% CI, 0.67 to 0.86; P <.001) were all significantly associated with persistent CB.
Limitations of the study includes that persistence of CB was defined using participant responses 5 years apart, there was no information on when participants quit smoking, and COPDGene included non-Hispanic Whites and African Americans.
The investigators concluded that in a cohort of current and former smokers, higher TAC and AFD appear to confer a reserve against persistent CB. The structural risk factors evaluated may help to identify those individuals at differential risk for CB, and thus target personalized preventive and therapeutic interventions.
Bhatt SP, Bodduluri S, Kizhakke Puliyakote AS, et al. Structural airway imaging metrics are differentially associated with persistent chronic bronchitis. Thorax. Published online January 6, 2021. doi:10.1136/thoraxjnl-2020-215853