Changes in airway dead space in response to methacholine provocation in normal subjects

Measurements of bronchial hyper-responsiveness rely on sensitive techniques for measurement of bronchoconstriction, ideally based on tidal breathing A potentially useful technique is measurement of airway dead space (V(D)aw), which reflects the volume of the conducting airways. The aim of this study was to evaluate measurements of V(D)aw with the single breath test for CO2 (SBT-CO2), compared to spirometric measurements, as a method of measuring bronchial response to methacholine challenge. Nineteen healthy adults were studied. Dosimetric methacholine challenge tests were performed on two stud y days. Forced expirations or the SBT-CO2 were used to assess the response. There were dose-dependent reductions in the spirometric measurements, with a 10 +/- 10% reduction from the baseline value of forced expiratory volume at the highest dose of methacholine. There was a dose-dependent reduction from the baseline value of V(D)aw by 19 +/- 9% at the highest dose. There w as also a dose-dependent increase in the slope of the alveolar plateau of t he SBT-CO2. This study provides support for measurement of V(D)aw as a mean s of evaluating bronchial responsiveness after methacholine challenge. In a group of healthy adults, this method shows a greater response but with sim ilar dispersion as measurement of forced expiratory volume after methacholi ne challenge.