A recent study comparing computed tomography (CT) scan data found that smokers with bronchiectasis have a greater loss of blood vessels in the lungs, a process known as vascular pruning. Vascular pruning was further associated with reduced lung function and exercise capacity.
The study, “Pulmonary vascular pruning in smokers with bronchiectasis” was published in the European Respiratory Journal.
Bronchiectasis is usually a consequence of different medical conditions, including chronic obstructive pulmonary disease (COPD), that result in damage to the airways. While its effects on airways are well-established, little is known about the effects of bronchiectasis on blood circulation in the lungs. A better understanding of this could improve the ability to identify bronchiectasis in the clinic, and to quantify its severity.
Researchers have now analyzed baseline data from a large, multi-center COPDGene study, containing genetic and epidemiological COPD determinants from 10,000 smokers. Researchers studied CT scan data to measure and compare blood vessel composition in subjects with or without bronchiectasis.
Vascular pruning was assessed by calculating the ratio of blood volume in vessels measuring less than 5 mm2 and total blood vessel volume, according to data from CT scans. Lower values of this ratio indicated more vascular pruning.
Of the 486 smokers analyzed in the study, 155 had bronchiectasis, which was on average mild in severity. Most were women (68%), and were on average older than non-bronchiectasis subjects (64 versus 60). Most of the bronchiectasis subjects had two or more lung lobes affected (60%).
Results showed that COPD patients with bronchiectasis had more vascular pruning in the left and right lower lobes of the lungs, compared with non-bronchiectasis subjects.
The team then investigated the effect of vascular pruning on clinical features such as lung function and exercise capacity. While lung function was measured through forced expiratory volume in one second (FEV1; the volume of air one can exhale in one second after a deep breath), exercise capacity was assessed through the six-minute walk test (distance walked in six minutes).
Bronchiectasis patients with vascular pruning had significantly worse lung function (1.70 L versus 2.24 L) and exercise capacity (361 versus 441 meters) than subjects with bronchiectasis but no vascular pruning.
Because emphysema (overinflation of the air sacs in the lung) is normally associated with vascular pruning, researchers performed further analyses to test its possible influence on the results. However, no influence of emphysema on the existing data was observed, confirming the direct association between bronchiectasis and vascular pruning.
“In summary, we have demonstrated that subjects with bronchiectasis have injury beyond the airways, as demonstrated by intraparenchymal pulmonary vascular pruning,” the team stated, adding that “subjects with bronchiectasis and vascular pruning have impaired expiratory airflows and exercise capacity.”
Researchers noted that the study population was heavy smokers with COPD, and therefore does not represent all smokers or bronchiectasis patients in general. Still, the team said, the findings highlight the effects of bronchiectasis on the vascular system, adding to its already-known effects on the airways.