John Kolbe, MD, PhD, is a respiratory physician at Auckland City Hospital and professor of medicine and head of the Department of Medicine at the University of Auckland, New Zealand.
Should we provide any additional testing in a “typical” patient with chronic obstructive pulmonary disease (COPD) and mild bronchiectasis accidentally detected on computed tomography (CT)?
There are undoubtedly some patients who have chronic obstructive pulmonary disease (COPD) and bona fide bronchiectasis, and the management of those patients should be the management of their COPD alongside the management of their bronchiectasis. But if you look at the literature, up to 60% of patients with COPD and a high proportion of patients with chronic asthma are reported to have bronchiectasis. And this is on the basis of the appearances on high-resolution computed tomography (HRCT) scans.
Bronchiectasis is diagnosed by demonstrating a dilated bronchus in association with the size of the accompanying branch of the pulmonary artery. And that’s the so-called BA ratio, bronchial-to-arterial ratio, of >1. Now, as I’ve just implied, in bronchiectasis, the BA ratio is increased because the diameter of the airway is increased.
Theoretically, a BA ratio can be increased if the airway size is normal but the caliber of the pulmonary artery branch is reduced. And there are a number of quite sophisticated studies of CT scans demonstrating that this does occur, that there are patients in whom the bronchial diameter is normal, but the pulmonary artery is reduced. And the likelihood of this is inversely proportional to forced expiratory volume in 1 second (FEV1), so it is more likely to occur in people with severe airflow obstruction, and it’s thought that this is due to a regional hypoxic vasoconstriction.
Therefore, this is an explanation for at least, I think, some of the reported bronchiectasis in COPD. These patients are often reported as having thin-walled, cylindrical bronchiectasis involving the basal segments of the lower lobes. And very often that is of no clinical significance and therefore can probably be ignored.