Abstract
This study was designed to investigate specificity and sensitivity of respiratory resistance (Rrs) during methacholine challenge testing (MCh) compared to FEV1 change.
214 subjects (82 male, 132 female; 14 - 77 y) were recruited for MCh. All had a FEV1 ≥70% pred. Asthma treatment mediction was withdrawn.
Baseline forced spirometry (ATS/ERS 2005) data were collected (MasterScreen PFT, CareFusion, Hoechberg, Germany) prior to MCh. Airway hyper responsiveness (AHR) was measured with Astograph J-21 (Chest, Tokyo, Japan). Respiratory resistance (Rrs) is measured continuously through forced oscillation technique (FOT, 3 Hz) during stepwise 1 min. inhalations of doubling MCh (0.049 - 25 mg/mL), until Rrs doubled.
AHR is calculated as cumulative dose of MCh inducing doubling Rrs (Dmin). Dmin = 1 min inhalation MCh at 1.0 mg/mL. Subjects without doubling Rrs are counted as negative Astograph responders.
FEV1 measured after MCh is compared to baseline (FEV1ch). FEV1ch ≥20% and <20% is correlated with Dmin:
1. Dmin ≤3 shows a specificity of 82.2%, with a sensitivity of 60.8%.
2. Dmin ≤10 and Dmin >0.049 ranges showed both good sensitivity but poor specificity.
3. Dmin in relation to FEV1ch had a weak negative correlation: r=0.071.
Cut off point for Dmin ≤3 U for Astograph MCh is a good standard for the clinical diagnosis of asthma with acceptable specificity and sensitivity to detect AHR.
- © 2011 ERS