The small airways in asthma-silent no longer
Published Online: December 22, 2011
The small airways are pathologically abnormal in mild and severe asthma. However, the contribution of small airway function to asthma symptoms is largely unknown. Understanding the role of the small airways in the manifestation of day-to-day symptoms and the effect of inhaled corticosteroid treatment on this relationship could have implications for the development of therapies that specifically target the small airways and may lead to improved patient outcomes.
In a recent issue of The Journal of Allergy and Clinical Immunology (JACI), Farah et al report on the relationship between asthma symptoms and the degree of ventilation heterogeneity (the difference in how much air passes between areas of the lungs), as a measure of small airway function, before and after treatment with inhaled corticosteroids. Asthma control and lung function was measured in 105 patients at baseline and again in a subgroup of 50 patients after treatment with inhaled corticosteroids for 2 months.
The researchers examined the relationship between symptom control at baseline and a range of physiological parameters including spirometry, airway hyperresponsiveness, inflammatory surrogate markers and ventilation heterogeneity. In the treatment subgroup, correlations between the change in symptom control and changes in the physiological parameters were analyzed.
The authors found that ventilation heterogeneity in the small airways was worse in patients with poor asthma control. The change in symptoms following inhaled corticosteroid treatment correlated with changes in airway inflammation and ventilation heterogeneity but not spirometry. However, the change in ventilation heterogeneity was the only physiological measurement that independently contributed to the change in symptom control.
Although once regarded as the “silent zone” in the lungs, the current findings demonstrate that the small airways contribute to the expression of asthma symptoms. These results provide a better understanding of the physiological determinants of patient symptoms and suggest therapies that target abnormalities in the small airways may improve asthma outcomes.
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.