Abnormal airway branching in the lung increases risk for COPD

Chronic obstructive pulmonary disease (COPD) is a chronic lung disease that results in damage to the airways (Bronchitis) and destruction of the small air sacs, called alveoli (Emphysema). Traditionally considered a smoker’s disease, COPD can also appear in people exposed to indoor air pollution (wood burning stoves) and air pollution. Not everyone who smokes will get COPD and people who have never smoked before could still develop the disease. This suggests that there are other factors that impact a person’s risk for developing the disease. Differences in lung structure could predispose certain people to developing COPD but to date we have had no strong evidence to suggest that this could be the case. Now, a team of researchers from McGill University and Columbia University has data that suggests people who have altered airway branching are at increased risk of developing COPD later in life.

To understand this work you first need to appreciate some intricacies of the lungs structure. Your lung contains many airways which help conduct air to the alveoli which transfer oxygen to the blood stream. These airways branch, much like the branches on a tree, and get progressively smaller as you go further down the paths. Starting at the trachea, two bronchi branch off leading to either lung (the left and the right). These two bronchi further branch into two more airways and each of them into two more. Simplistically, each airway gives rise to two more, getting smaller and smaller until they reach the alveoli. Typically, it has been thought that the branching of the airways is similar in the majority of people, that is to say they have a similar branching pattern and number of airways. The work by Smith and colleagues has identified differences in the airway branching of 26.5% of the people in their study. This was broken down to two major types of differences, either an extra airway branch (called the accessory subsuperior airway) or a missing airway branch (called the absent right medial-basal airway). With these difference branching patterns in mind, the investigators where able to assess differences in disease risk between groups of people.

First, they noticed that people with the extra airway had a 31% greater chance of developing COPD whether or not they smoked in the past. This appeared to be due to an enlargement of the alveolar sacs in these patients which would predisposes them to emphysema. People who smoked and were missing an airway branch were 50% more likely to go on to develop COPD. This appeared to be caused by having overall smaller airways then those with the normal branching pattern.

This research identifies one of the factors that can modify your risk for COPD whether you smoke or not. This doesn’t mean that smoking isn’t a significant risk factor for COPD, indeed it is far an away the largest risk factor, way more than any risk factor associated with lung structure. Approximately 50% of patients who are lifelong smokers will develop COPD. This study also suggests that factors affecting lung growth and development, including those in early life, may be important determinants of COPD risk and certainly warrant more research. Perhaps if we know what causes these changes in lung branching that predisposes someone to COPD, we can prevent it from happening in the first place. Speaking of prevention, the simplest way to decrease your risk for COPD is to not smoke or quit as soon as you can.

Image Credit: By Centre for Research Collections University of Edinburgh – Casts of lungs, Marco resin, 1951, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=46647752

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