A new study using CT scans have revealed significant changes indicating lung destruction in some asthmatics.
Clinicians have long thought that some people with asthma experience declines in their lung function, called fixed airflow obstruction (FAO), due to changes to their airways. In this study published in The Journal of Allergy and Clinical Immunology, researchers have found that this issue could extend to the surrounding lung tissue.
Respirologist Kaoruko Shimizu at Hokkaido University said, “Bronchial asthma is considered to be mainly due to inflammation and remodeling of the larger respiratory airways. But not all asthmatics improve with the typical treatments prescribed to alleviate this condition. We wanted to know if changes to the surrounding lung tissue induced a decline in pulmonary function over time in this subgroup of patients.”
Shimizu and her colleagues applied a novel computer tomography (CT)-based approach to detect changes in lung tissue. In this approach, the scientists examined CT scans employing an index called “exponent D” for areas of reduced lung density with increasing coalescence of neighbouring airspaces, which indicates emphysema, or the destruction of air sacs. Airway obstruction was measured by testing the ability of people with asthma to forcefully exhale air in one second. This ability is reduced when the airways are narrower.
The tests examined around 200 smokers and non-smokers with varying degrees of asthma, who were then followed up annually for five years.
People with asthma who experienced persistent airflow limitation, regardless of the severity of their asthma or their smoking status, exhibited constricted airways and also showed signs of lung tissue destruction, the researchers found.
The observed changes to lung tissue in this subgroup of asthmatic patients were not associated with the typical inflammatory markers linked to bronchial asthma. This is important, because it could explain why conventional anti-inflammatory treatments are not as successful in this group.
Future studies should investigate lung destruction in asthma, enabling more personalised management, said Shimizu.
Source: Hokkaido University
