Greater consideration of small airways dysfunction warranted in asthma management
medwireNews: Small airways dysfunction (SAD) occurs across all degrees of asthma severity but has the highest prevalence among individuals with the most severe disease, suggest baseline findings from the ATLANTIS study.
As reported in The Lancet Respiratory Medicine, the study included 773 people with asthma from 29 centres in nine countries, 91% of whom were found to have SAD, defined as any abnormal measure on physiological tests including spirometry, body plethysmography, impulse oscillometry and multiple breath nitrogen washout.
Dirkje Postma (Groningen Research Institute for Asthma and COPD, the Netherlands) and study co-authors demonstrated that individuals with the most severe asthma according to their Global Initiative for Asthma (GINA) score had the highest prevalence of SAD regardless of the measure used, whereas lower rates were seen in those with less severe disease.
For example, the prevalence of SAD as defined by a reduction from baseline in forced vital capacity (FVC) was 84% in the 46 participants with the most severe asthma (GINA stage 5) compared with 72% in the 135 with the least severe disease (GINA stage 1). And when acinar airway ventilation heterogeneity (Sacin) as determined by breath nitrogen washout was used to define SAD, the prevalence was 41% in the GINA stage 5 group compared with just 12% in the GINA stage 1 group.
The greater prevalence of SAD in more severe asthma may be due to “structural lung changes that are not responsive to the use of oral corticosteroids, high-dose inhaled corticosteroids, or both”, hypothesise the researchers.
Postma et al stress that the “prevalence of SAD in asthma was dependent on the measure used”. The overall prevalence was lowest, at 19%, when Sacin was used to define SAD, while the prevalence was highest, at 73%, when FVC decline was used.
Sacin reflects “dysfunction of the most peripheral small airways”, whereas FVC “probably [reflects] obstruction in more small-sized to mid-sized airways”, they explain.
The ATLANTIS (Assessment of Small Airways Involvement In Asthma) investigators also used a structural equation modelling approach to generate a clinical SAD score, with higher scores indicating more severe disease. They demonstrated that higher scores correlated with longer asthma duration, greater severity and number of exacerbations, as well as with poorer disease control.
Moreover, they defined two SAD severity groups based on clinical scores. Participants in the more severe SAD group had abnormal Sacin measurements whereas those in the less severe group did not, and the difference in SAD severity between the two groups “was particularly clear” with measures related to spirometry and impulse oscillometry. Individuals in the more severe SAD group also had higher GINA stage, worse asthma control and more frequent healthcare use, and were more likely to use long-acting β-adrenoceptor agonists and inhaled corticosteroids, than those in the less severe SAD group.
“In summary, we can detect asthma subtypes on the basis of the presence and extent of SAD, which can be measured with easy-to-use, clinically applicable approaches”, write the researchers.
“Therefore, this aspect of asthma needs further consideration in the management of the disease”, they add.
Discussing these findings in an accompanying comment, Carrie Pistenmaa Aaron (Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA) says that “[t]he ATLANTIS study adds substantially to our knowledge on the involvement of the small airways in asthma.”
She notes, however, that the study “is limited by the absence of a gold standard measure of small airway obstruction to classify an individual patient as having small airways involvement or not.”
And Aaron concludes that “an important next step is to determine which small airways measure, or collection of measures, best identifies obstruction in the [small airways].”
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