COPD is incompletely reversible expiratory airflow obstruction attributed to a combination of emphysema and airway disease. CT imaging is increasingly being used to characterize and quantify these processes for genetic, epidemiologic, and therapeutic investigations with the premise that their relative balance may define unique subsets of disease. Although the quantification of emphysema by CT imaging has been well established and now validated in multiple histopathologic investigations, the quantification of airway disease Canadian Heath&Care Pharmacy has proven to be a greater challenge.
It is believed that the site of expiratory airflow obstruction in COPD is the small airways that are < 2 mm in diameter. Although direct examination of these structures is beyond the resolution of clinical CT scanning techniques, work by Nakano and colleagues demonstrated that dimensions of the central airways and their degree of remodeling on CT scan are correlated with the burden of distal small airways disease. It was subsequently discovered that the correlation between FEV1 % predicted and WA% is greater in subsegmental (and more peripheral) airways than in segmental airways. It has since become the standard in quantitative CT image analyses to study the most peripheral airways.
Previously, we and other groups demonstrated that with increasing disease severity and increasing burdens of emphysema, airways become less distensible. There may be several reasons for this observation, including mural fibrosis, which prevents dilation, and the disruption of the airway parenchymal interdependence in emphysematous lungs, which may reduce radial traction on the airway. In either case, an incompletely expanded airway may appear to have an elevated WA% on CT scan that could be falsely attributed to a greater burden of airway disease. Because the increase in WA% beyond the segmental airways is the basis of the increased correlation between lung function and airway disease, it is important to uncover whether this measure is related to emphysema. Using CT imaging, epidemiologic, and functional data from a large cohort of smokers in the COPDGene Study, we aimed to (1) examine the effect of emphysema on the relationship between WA% and FEV1 % predicted and (2) assess the relationships among lobar emphysema, segmental and subsegmental WA%, and total bronchial area (TBA) along six bronchial paths.