Small Airway Dysfunction and Asthma Management

Small airway dysfunction refers to impaired ventilation and inflammatory changes occurring in airways with an internal diameter of less than 2 mm. In asthma, this dysfunction arises from distal airway inflammation, mucus plugging and structural remodelling, leading to increased resistance, ventilation heterogeneity and exercise- or allergen-induced bronchoconstriction. Conventional spirometry often fails to detect early small airway involvement, as measures such as FEV₁ and FEV₁/FVC provide only indirect indices of distal obstruction. In response, more sensitive techniques—including oscillometric methods, multiple breath nitrogen washout and high-resolution imaging—have been adopted to quantify peripheral airway resistance, ventilation distribution and regional lung volumes. Recognition of small airway involvement has refined asthma phenotyping, identified patients at risk of poor control and exacerbations, and prompted the development of inhaled formulations with reduced particle size to enhance peripheral deposition. Extrafine inhaled corticosteroid–long-acting β₂-agonist combinations, targeted biological therapies and personalised follow-up using small-airway biomarkers now underpin a more precise approach to asthma management.

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Small Airway Dysfunction and Asthma Management publication trend

The graph below shows the total number of articles in small airway dysfunction and asthma management across all publications each year (not limited to Nature Index journals).

Technical terms

Small airways: Bronchioles with an internal diameter under 2 mm that contribute little to total airway resistance until diseased.

Impulse oscillometry (IOS): A noninvasive technique measuring airway resistance and reactance by superimposing pressure oscillations during tidal breathing.

Multiple breath nitrogen washout (MBNW): A lung function test that assesses ventilation distribution and closing volume by analysing dilution of resident nitrogen during tidal breathing.

FEF25-75 (Forced Expiratory Flow mid-volume): The average flow rate between 25 % and 75 % of forced vital capacity, serving as a surrogate marker of small airway patency.

Extrafine inhaled formulation: Aerosol particles <2 µm in diameter engineered to enhance deposition in distal airways and improve therapeutic targeting.

References

1. Small airways in asthma: Pathophysiology, identification and management. Chinese Medical Journal - Pulmonary and Critical Care Medicine (2023).
2. Small airway dysfunction and poor asthma control: a dangerous liaison. Clinical and Molecular Allergy (2021).
3. Small airway dysfunction is associated to excessive bronchoconstriction in asthmatic patients. Respiratory Research (2014).
4. Asthma control in patients receiving inhaled corticosteroid and long-acting beta2-agonist fixed combinations. A real-life study comparing dry powder inhalers and a pressurized metered dose inhaler extrafine formulation. BMC Pulmonary Medicine (2011).
5. Recent Advances in Inflammation and Treatment of Small Airways in Asthma. International Journal of Molecular Sciences (2019).