- Design
- Multicentre cross-sectional observational study
- Population
- 1,169 adults with asthma
- Primary outcome
- Associations of BMI, oscillometry-defined small airway dysfunction and severe exacerbations
- Effect
- SAD–exacerbation aOR 2.01 (1.53–2.65); SAD mediated 26–41% of obesity–exacerbation link
A multicentre observational study in the European Respiratory Journal (25 September) assessed 1,169 adults with asthma using spirometry and impulse oscillometry, which measures small airway function directly.
Oscillometry-defined small airway dysfunction was more common with BMI of 30 or above, and oscillometry values worsened non-linearly with BMI, more steeply beyond about 28–30. Small airway dysfunction was independently associated with obesity (adjusted OR 2.11) and with severe exacerbations in the previous year (adjusted OR 2.01). In mediation analysis it accounted for 26–41% of the link between obesity and exacerbations. Spirometry added little.
This is cross-sectional, so it cannot show that treating small airways reduces attacks. But it offers a plausible, measurable mechanism, and suggests that in patients with obesity and frequent exacerbations, normal spirometry may miss meaningful airway disease.
- Normal spirometry does not exclude small airway dysfunction in asthma with obesity.
- Consider oscillometry, where available, in obese patients with frequent exacerbations.
- Weight reduction remains a reasonable target in asthma with obesity.
- Treatment aimed at small airways is a hypothesis, not yet proven to reduce exacerbations.
Why it matters
It suggests a measurable, potentially treatable link between weight and asthma attacks.
Don't overread it
Cross-sectional associations cannot show that treating small airways reduces exacerbations.
The statistics, in plain English
An adjusted odds ratio of 2.01 means about double the odds of a severe exacerbation with small airway dysfunction. Mediation analysis estimates how much of one association runs through another; 26–41% is a meaningful share but from cross-sectional data.
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