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 (FENO), hyperresponsiveness to methacholine (AHR), and calibre (FEV1 % predicted) in mild-to-moderate asthmatics.

We searched our database for asthmatics who had attended our research department. FEV1 % predicted, FENO, and methacholine PC20 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 FENO: 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 FEV1 % predicted (95% CI 2.6-14.4%; P = 0.002) and a 29% difference in FENO between groups A and C (95% CI 2-48%; P = 0.034). When stratified by FENO, there was a 1.29 doubling dilution difference in methacholine PC20 (95% CI 0.26-2.33; P = 0.009) between groups D and F. There was no difference between FEV1 % predicted when grouped by FENO. 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.