Resistive work of breathing (sWOB) as target parameter evaluating methacholine challenge to assess airway hyperreactivity (AHR) in comparison to other lung function parameters

Abstract

Rational: Effective specific airway conductance (sG eff = 1/sR eff ) features a sensitive target parameter differentiating severity of AHR, performed by methacholine (MCH) challenge tests using a plethysmograph. sG eff is computed as ratio between the integral of the tidal flow/volume loop , and the integral of the resistive work of breathing (sWOB). Aim: AHR assessed by sWOB in comparison to sG eff , FEV 1 and MEF 50 , computing sensitivity and specificity (http://www.roccet.ca) Method: From our database 348 subjects (141 males; 207 females; aged 14.7 to 88.4 ys) were selected, in order to differentiate asthmatic patients (121, 34.8%) from non-asthmatic subjects (227, 65.2%). MCH (5%) was administered as aerosol in 3 consecutive cumulative provocation levels (P1: 0.2 mg; P2: 1.0 mg; P3: 2.2 mg), using the Jaeger aerosol provocation system (APS), Provocation doses (PD) were calculated for each parameter specifically (PD 150 sWOB, PD 40 sG eff , PD 20 FEV 1 , PD 20 MEF 50 ). Results: Best sensitivity ( s ) and corresponding PD for MCH was found for PD 150 sWOB ( s =85.9% at 1.26 mg), followed by PD 40 sG eff ( s =79.7% at PD 0.64 mg), PD 20 FEV 1 ( s =70.9% at 1.42 mg), and PD 20 MEF 50 ( s =65.2% at 0.52 mg). Noteworthy, lowest PD were need for PD 20 MEF 50 , highest for PD 20 FEV 1 . Best response to MCH, and hence discrimination between mild, moderate or severe AHR, was detected by PD 40 sG eff (67.2%), followed by PD 20 MEF 50 (51.4%), PD 150 sWOB (47.7%), and PD 20 FEV 1 (25.8%) Conclusions: sWOB feathers a highly sensitive, and discriminating parameter in the assessment of AHR. It offers insight into underlying mechanisms of lung physiology of MCH challenge tests.