Dysanapsis, a mismatch between airway-tree caliber and lung size, is associated with an increased risk of chronic obstructive pulmonary disease (COPD) in older adults, according to a retrospective study. "Dysanapsis appears to be a major COPD risk factor," said Dr. Benjamin M. Smith of McGill University, in Montreal, Canada, and Columbia University Irving Medical Center, in New York City. "Understanding the biological basis of dysanapsis may lead to early life interventions to promote the development of healthy and resilient lungs," he told Reuters Health by email. Dysanapsis is believed to arise early in life and is thought to increase susceptibility to obstructive lung disease. CT can be used to quantify dysanapsis. For their study, Dr. Smith and colleagues used data from the Multi-Ethnic Study of Atherosclerosis (MESA), the Canadian Chronic Obstructive Lung Disease (CanCOLD) and the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS). They tested their hypothesis that dysanapsis quantified by CT as the ratio of mean airway lumen diameter to total lung volume (airway-to-lung ratio) would be associated with incident COPD among older adults in the general population. During follow-up, among individuals free of COPD at baseline, 4.3% in the MESA study, 15.0% in the CanCOLD study and 25.4% in the SPIROMICS study developed new COPD, the researchers report in JAMA. Participants in the lowest quartile compared with those in the highest quartile of airway-to-lung ratio had a significantly lower ratio of forced expiratory volume in the first second to forced vital capacity (FEV1:FVC) and significantly higher COPD prevalence in the MESA study (0.69 vs. 0.78 and 11.7% vs. 2.9%, respectively) and in the CanCOLD study (0.61 vs. 0.72 and 18.4% vs. 6.5%). After adjustment for other factors, participants in the lowest quartile of airway-to-lung ratio had an 8.12-fold higher incidence of COPD in the MESA study and a 3.33-fold higher incidence of COPD in the CanCOLD study, both significant increases. The airway-to-lung ratio accounted for 16.7% and 18.5% of the baseline FEV1:FVC variance in the MESA study and the CanCOLD study, respectively. "Airway to lung ratio statistically accounted for a greater proportion of variation in FEV1:FVC than smoking and other COPD risk factors and yielded the highest net reclassification index improvement for incident COPD," the authors note. Among SPIROMICS participants with prevalent COPD, those in the highest quartile of airway-to-lung ratios had a significantly faster decline in FEV1 than did those in the lowest quartile. In contrast, there was no significant difference among SPIROMICS participants without prevalent COPD in the rate of FEV1 decline between those in the lowest and highest quartiles of airway-to-lung ratios. "People with smaller airway trees relative to lung size tended to have lower lung function and higher COPD risk, even among never smokers," Dr. Smith said. "Conversely, lifelong heavy smokers who did not have COPD tended to have larger than expected airway trees relative to lung size." "While the harmful effects of smoking are legion, and reducing smoking is essential to public health, we have to start thinking more broadly about the origins and pathophysiology of COPD if we want to take control of this heterogeneous disease," he said. --Will Boggs MD Source
