Relationships between airway hyperresponsiveness, inflammation, and calibre in asthma

Previous studies have focused upon the relationship between airway inflammation and hyperresponsiveness with different conclusions. We re-examined the relationship between airway inflammation (FE(NO)), hyperresponsiveness to methacholine (AHR), and calibre (FEV(1) % predicted) in mild-to-moderate asthmatics.

We searched our database for asthmatics who had attended our research department. FEV(1) % predicted, FE(NO), and methacholine PC(20) were collected. Patients were divided into groups based upon AHR as follows: severe (<0.5 mg/ml, group A), moderate (>0.5-2 mg/ml, group B), and mild (>2-8 mg/ml, group C), and upon FE(NO): low (<25 ppb, group D), medium (25-50 ppb, group E), and high (>50 ppb, group F).

In 208 asthmatics, when stratified by AHR, there was an 8.5% difference in FEV(1) % predicted (95% CI 2.6-14.4%; P = 0.002) and a 29% difference in FE(NO) between groups A and C (95% CI 2-48%; P = 0.034). When stratified by FE(NO,) there was a 1.29 doubling dilution difference in methacholine PC(20) (95% CI 0.26-2.33; P = 0.009) between groups D and F. There was no difference between FEV(1) % predicted when grouped by FE(NO). Multivariate regression analysis with covariates, including inhaled corticosteroids, supported our findings from categorical analysis.

We found no relationship between airway inflammation and calibre, whilst showing significant relationships between AHR and airway calibre and AHR and airway inflammation. Whilst relationships exist, the lack of complete concordance highlights the important role each contributes to the assessment of the asthmatic individual.