Small airways, big role in asthma control and patients’ physical activity

Published online: September 1, 2021

Asthma is common respiratory problem affecting nearly 8% of the population of the United States. Asthma triggers, such as airborne allergens, cause chronic inflammation in the airways that eventually leads to interruptions of the normal lung physiology and function. Therefore, the clinical assessment of asthma typically involves lung function testing; that is routinely done by using a spirometry or, for self-monitoring, a peak flow meter. Despite the fact that these commonly used conventional techniques are the mainstream of lung function testing in asthma, they have a very limited capacity in the assessment of small airway function. As a consequence, the diagnosis of function abnormalities in the small airways (with a diameter < 2mm) i.e small airway dysfunction, is not usually a part of the routine clinical assessment of asthma, and data regarding its relationship with asthma triggers, clinical features, and treatment outcomes are still limited.

In a  recent issue of The Journal of Allergy and Clinical Immunology: In Practice, Abdo et al performed sophisticated lung function assessment in a cohort of asthma patients and healthy subjects to study the prevalence of small airway dysfunction in asthma and its association with disease severity, symptom frequency, and the objectively measured physical activity, as well as common risk factors of  poor asthma control such as older age, obesity, smoking, and a frequent type of airway inflammation in asthma i.e  eosinophilic airway inflammation. The authors applied advanced statistical models to disentangle the complex relationships between all these clinical asthma features.

The authors reported high prevalence of small airway dysfunction in asthma (up to 90%) that increased with the increase in asthma severity. Severe small airway dysfunction was associated with frequent daily symptoms, higher risk of acute asthma exacerbation, and low levels of physical activity (<5000 steps/day). The article also described small airway dysfunction as a spectrum of connected distal lung function abnormalities including limitation of the air flow in the small airways, increased small airway resistance, and, as a result, air trapping in the peripheral parts of the lung and decreased airway elasticity. These diverse small airway abnormalities were a result of mainly older age, obesity, obesity-related systemic inflammation, eosinophilic airway inflammations, and smoking. The authors also suggested that these risk factors of asthma lead to frequent daily symptom and low physical activity mainly through their contribution to small airway dysfunction. Interestingly, the authors demonstrated that higher physical activity might improve small airway dysfunction and asthma symptoms. In summary, the authors defined small airway dysfunction as a prevalent feature of asthma that strongly affects patients’ physical activity and quality of life and that can potentially be treated by reducing airway inflammation through weight loss and by increasing physical activity.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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