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Heterogeneity indices derived from the multiple breath nitrogen washout technique are strongly associated with AHR in asthma
Airway hyperresponsiveness (AHR), inflammation and heterogeneity in airway constriction and ventilation within the airway tree are fundamental features of asthma.1 Heterogeneity in ventilation is relevant not only because it affects gas exchange efficiency (ventilation/perfusion in asthma), but also because it can theoretically magnify the degree of mechanical obstruction2 which could affect the degree of AHR. By thickening of airway walls, increasing airway secretions and releasing mediators, inflammation could also be linked to ventilation heterogeneity and AHR in asthma.3,4 Indeed, the exhaled nitric oxide concentration (FeNO) is substantially increased by inflammation in asthma and has been proposed as a non-invasive biological marker to guide treatment.5
In this issue of Thorax, Downie and coworkers6 present convincing evidence that ventilation heterogeneity is strongly associated with AHR in patients with asthma, regardless of the level of inflammation (see page 684). In a group of subjects with a wide range of asthma severity, the authors measured, among other parameters, the heterogeneity of the conducting airways by multiple breath nitrogen washout (Scond) and FeNO with AHR to methacholine. A subgroup of patients with poorly controlled symptoms was also studied after 3 months of …
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