Assessment of airway hyperresponsiveness: comparison of spirometry and body plethysmography

While methacholine (MCH) testing is commonly used in the clinical diagnosis of asthma, the detection of airway narrowing often relies on either spirometry or body plethysmography, however comparative studies are rare. In this study we performed MCH testing in 37 patients with variable shortness of breath at work and in 37 patients with no history of airway disease. The inclusion criteria were: no acute respiratory infection within 6 weeks, no severe diseases, normal baseline specific airway resistance (sR(aw)), normal baseline forced expiratory volume in 1 s (FEV(1)), Tiffeneau index >70%, no previous treatment with steroids within 14 days and no short acting bronchodilators within 24 h. Cumulative doses of 0.003, 0.014, 0.059, 0.239 and 0.959 mg MCH were inhaled by a dosimeter method. A FEV(1) decrease of ≥20% from baseline and a 100% increase of sR(aw) to ≥2.0 kPa/s was defined as end-of-test-criterion. Provocation doses were calculated by interpolation. Performance of lung function parameters was compared using receiver-operating-characteristic (ROC) analysis. ROC analysis resulted in an area under the ROC curve (AUC) of 0.74 for FEV(1) vs. 0.82 for sR(aw). The corresponding Youden Indices (J) were 0.46 for FEV(1) and 0.57 for sR(aw). The Youden Index of sR(aw) was higher and sensitivity and specificity (73%/84%) were rather well-balanced, in contrast to FEV(1) (54%/92%). In conclusion, in cumulative MCH challenges sR(aw) was found to be the overall most useful parameter for the detection of bronchial hyperresponsiveness. Body plethysmography yielded a balanced sensitivity-specificity ratio with higher sensitivity than spirometry, but comparable specificity.