According to a new study from the National Heart, Lung, and Blood Institute (NHLBI), people with small airways relative to the size of their lungs may have a lower breathing capacity and an increased risk for chronic obstructive pulmonary disease (COPD), even if they do not smoke or have any other risk factors.

Although COPD often develops as a result of smoking, researchers have long puzzled over why nearly one-third of cases occur in people who never smoked.

“This work, stemming from the careful analysis of lung images of COPD patients, shows that an abnormal lung development may account for a large proportion of COPD risk among older adults,” said James Kiley, PhD, director of NHLBI’s Division of Lung Diseases, in a press release. “More research is needed to understand what drives this occurrence and to devise possible interventions.”

According to a National Institutes of Health press release, when people breathe, they move air through their airways, beginning with the windpipe or trachea, which branches out to smaller airways called the bronchi and bronchioles. Airways are thought to develop in proportion to the lungs, but in some people, the airways grow smaller or larger than expected because of a condition called dysanapsis for reasons that are not clear.

Researchers examined records for more than 6500 older adults participating in 3 studies that included smokers and nonsmokers, with and without COPD, to evaluate whether small airways may be the culprit for COPD in people who do not smoke or have other risk factors.

The Multi-Ethnic Study of Atherosclerosis (MESA) Lung Study, the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS), and the Canadian Cohort of Obstructive Lung Disease (CanCOLD) study all assessed dysanapsis using computed tomography scans of the lungs.

The MESA Lung study included white, African American, Hispanic, and Chinese American people who were 69 years of age on average. Meanwhile, the participants from the CanCOLD study were 67 years of age on average and came from 9 Canadian cities. SPIROMICS was based at 12 US medical centers and included people who were 63 years of age on average and reported 20 or more pack-years of smoking.

Participants with smaller airways relative to lung size were much more likely to develop COPD compared with those with larger airways relative to lung size in both the MESA Lung and CanCOLD studies.

The researchers followed up with a focus on participants from the CanCOLD study who never smoked and heavy smokers from the SPIROMICS study. Those who never smoked and had COPD had much smaller airways relative to lung size, whereas the heavy smokers who did not have COPD had larger than normal airways.

“These results show that small airways relative to lung size are a very strong risk factor for COPD,” Smith said in a press release. “This helps us to understand why 30% of COPD can occur in people who never smoked.”

Further, Smith said that the findings may also help explain why some lifelong heavy smokers do not develop COPD in the press release. People with larger airways relative to lung size may be able to withstand lung damage from smoking and still have enough breathing reserve to prevent them from developing COPD. However, given the multiple health problems caused by tobacco, Smith emphasized that smokers should do their best to quit.

Lung development may explain why some non-smokers get COPD and some heavy smokers do not. NIH. Published June 9, 2020. Accessed June 10, 2020.