Asia Pac Allergy.  2013 Oct;3(4):224-230. 10.5415/apallergy.2013.3.4.224.

Measuring and imaging small airways dysfunction in asthma

• Thien F

• KMID: 2397299
• DOI: http://doi.org/10.5415/apallergy.2013.3.4.224

Abstract

Asthma is a chronic inflammatory disorder of the airways causing typical symptoms, and the diagnosis is supported by evidence of airflow obstruction which is variable, reversible or inducible. However, standard assessment of lung function with spirometry does not measure dysfunction in small airways which are < 2 mm in diameter towards the periphery of the lung. These airways make only a small contribution to airway resistance under normal circumstances. Nevertheless, there is mounting evidence that pathology and dysfunction in these small airways are implicated in the pathogenesis and natural history of asthma. Using forced oscillation and the multibreath nitrogen washout techniques, uneven ventilation (ventilation heterogeneity) due to small airways dysfunction has been shown to be an important marker of asthma disease activity, even in the absence of abnormalities in standard spirometric measurements. Recent advances in imaging research, particularly with hyperpolarised gas magnetic resonance imaging, have also given insights into the significance and dynamic nature of ventilation heterogeneity in asthma. The challenge is to integrate these new physiological and imaging insights to further our understanding of asthma and facilitate potential new treatments.

Keyword

Asthma; Small airways; Forced oscillation technique; Multibreath nitrogen washout; Xenon computed tomography; Hyperpolarised gas lung imaging

MeSH Terms

Airway Resistance
Asthma*
Diagnosis
Lung
Magnetic Resonance Imaging
Natural History
Nitrogen
Pathology
Population Characteristics
Spirometry
Ventilation
Nitrogen

Figure

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  Fig. 1 Relationship between airway generation and resistance to airflow.

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  Fig. 2 Relationship between airway generation, airflow and volume of airways.

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  Fig. 3 Hyperpolarised helium-3 magnetic resonance lung imaging in a healthy normal volunteer (A) and in patients with mild (FEV1 of 132% of predicted value, B), moderate (FEV1 of 83% of predicted value, C), and severe (FEV1 of 34% of predicted value, D) asthma. Reproduced from Samee et al. [31] with permission of Elsevier. FEV1, forced expiratory volume in 1 second.

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  Fig. 4 Premethacholine (left) and postmethacholine (right) images from separate days on the same patient, with baseline day 1 are on top and day 2 (17 days later) at bottom. Two defects in the same location are observed in the left lung at baseline on both days. On day 1, the one large defect resolved (curved arrow) after methacholine, another decreased (straight arrow), and small new defects developed (one marked by arrowhead). On day 2, the two defects in the left lung remained unchanged after methacholine. A large new defect (short thick arrow) developed on the right and a small defect (open arrow) occurred close to the one marked by the arrowhead on day 1. Reproduced from de Lange et al. [33] with permission of Elsevier.

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