Diagnostic accuracy of methacholine challenge tests assessing airway hyperreactivity in asthmatic patients - a...

There are few studies comparing diagnostic accuracy of different lung function parameters evaluating dose-response characteristics of methacholine (MCH) challenge tests (MCT) as quantitative outcome of airway hyperreactivity (AHR) in asthmatic patients. The aim of this retrospectively analysis of our database (Clinic Barmelweid, Switzerland) was, to assess diagnostic accuracy of several lung function parameters quantitating AHR by dose-response characteristics.

Changes in effective specific airway conductance (sG_eff) as estimate of the degree of bronchial obstruction were compared with concomitantly measured forced expiratory volume in 1 s (FEV₁) and forced expiratory flows at 50% forced vital capacity (FEF₅₀). According to the GINA Guidelines the patients (n = 484) were classified into asthmatic patients (n = 337) and non-asthmatic subjects (n = 147). Whole-body plethysmography (CareFusion, Würzburg, Germany) was performed using ATS-ERS criteria, and for the MCTs a standardised computer controlled protocol with 3 consecutive cumulative provocation doses (PD₁: 0.2 mg; PD₂: 1.0 mg; PD₃: 2.2 mg) was used. Break off criterion for the MCTs were when a decrease in FEV₁ of 20% was reached or respiratory symptoms occurred.

In the assessment of AHR, whole-body plethysmography offers in addition to spirometry indices of airways conductance and thoracic lung volumes, which are incorporated in the parameter sG_eff, derived from spontaneous tidal breathing. The cumulative percent dose-responses at each provocation step were at the 1^st level step (0.2 mg MCH) 3.7 times, at the 2^nd level step (1 mg MCH) 2.4 times, and at the 3^rd level step (2.2 mg MCH) 2.0 times more pronounced for sG_eff, compared to FEV₁. A much better diagnostic odds ratio of sG_eff (7.855) over FEV₁ (6.893) and FEF₅₀ (4.001) could be found. Moreover, the so-called dysanapsis, and changes of end-expiratory lung volume were found to be important determinants of AHR.

Applying plethysmographic tidal breathing analysis in addition to spirometry in MCTs provides relevant advantages. The absence of deep and maximal inhalations and forced expiratory manoeuvres improve the subject's cooperation and coordination, and provide sensitive and differentiated test results, improving diagnostic accuracy. Moreover, by the combined assessment, pulmonary hyperinflation and dysanapsis can be respected in the differentiation between "asthmatics" and "non-asthmatics".