Airway bacteria and heart disease in COPD patients

What is it about?

This study looked at whether the bacteria living in the mouth and lower airways are linked to heart disease, in both people with chronic obstructive pulmonary disease (COPD) and healthy controls. The background is that COPD and coronary heart disease (calcium buildup and narrowing in the heart's blood vessels) often occur together, and researchers have long wondered whether inflammation and bacteria in the airways might contribute to heart disease, similar to earlier suggestions that oral bacteria may be connected to atherosclerosis. 228 participants comprising 101 healthy controls and 127 COPD patients underwent a CT scan of the heart to measure calcium buildup in the coronary arteries and check for narrowed blood vessels. Samples were also collected from the mouth (oral wash) and from the lower airways (via bronchoscopy), and the bacterial makeup of these samples was analyzed using gene sequencing. The results showed that bacterial diversity differed between COPD patients and healthy controls, COPD patients had somewhat lower diversity in their oral bacteria. However, when comparing people with and without signs of heart disease, no clear differences in bacterial composition were found, either in the mouth or the lower airways. A handful of rare bacterial types did differ statistically, but these made up less than 1% of all bacteria and have no known link to heart disease. The conclusion is that this study found no convincing evidence that airway bacteria are connected to coronary heart disease, in either COPD patients or healthy people. This is the first study to examine this specific link for the lower airways, and the findings suggest that other factors, such as smoking and inflammation, are likely more important for heart risk in COPD than the airway microbiome itself.

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Photo by Europeana on Unsplash

Photo by Europeana on Unsplash

Why is it important?

No prior study has examined whether the lower airway microbiome is associated with heart disease, most previous oral-cardiovascular microbiome work has stopped at the mouth. There is also a long-standing hypothesis that airway inflammation in COPD "spills over" into the bloodstream and contributes to atherosclerosis. If that were true via a microbial pathway, one would expect to see it most clearly in COPD patients. The fact that no association was found is a meaningful negative result that argues against the microbiome being a direct driver of heart disease risk in COPD patients. Since COPD patients carry a substantially elevated risk for heart disease, understanding which biological pathways do and don't contribute helps prioritize where prevention and research efforts should focus.

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