Abstract
Background: Methacholine challenge (MCh) test is the standard method used to unravel bronchial hyperresponsiveness. Airways resistance (Raw) is commonly measured with body- plethysmograph in addition to FEV1. The test is considered positive when a 20% decrease in FEV1 (provocative dose, PD20) is reached. We aimed at investigating whether respiratory impedance (Zrs) provides more sensible indexes, compared to Raw in detecting changes in bronchomotor tone.
Methods: 20 subjects underwent saline aerosol bolus (baseline) followed by MCh (50 up to 2400 μg). After each dose we measured: 1) respiratory impedance (Zrs, at impulse frequency from 1 to 35 Hz) and corresponding values of respiratory resistance (Rrs) and reactance (Xrs); 2) Raw and FEV1.
Results: Fig. 1A shows that Xrs decreased at all frequencies at the methacholine dose preceding PD20 and even more at a dose higher than PD20. Due to the change in Xrs at low frequencies and to the increase in resonance frequency (fres), we considered the so called area of reactance (AXrs) as defined in Fig. 1B. We found that AXrs correlates significantly with Raw through an exponential function (Y= 0.1e3.4X), indicating that the growth in AXrs is larger than that of Raw, on increasing MCh.
Conclusion: Determination of AXrs through impulse oscillometry is more sensible than Raw and FEV1 to assess the increase in airway resistance during MCh.
- © 2011 ERS