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Representative tidal, regionial and maximal flow–volume curves at baseline in a subject with low forced expiratory volume in step one s (FEV1)/vital capacity ratio and normal FEV1. ——: 40% forced vital capacity indicating the point where instantaneous maximal and partial expiratory flows were measured.
An SBN2). After at least four regular breaths, the subjects were asked to fully expire to RV and then to take an IVC of 100% oxygen. This was followed, without breath-hold, by a full expiration to RV at a rate of 0.30–0.50 L·s ?1 . Expiratory nitrogen concentration was plotted against VC and the slope of nitrogen alveolar plateau (phase III) calculated by drawing the best-fit line. The first departure from this straight line exceeding cardiogenic oscillations was taken as the onset of phase IV. The open capacity (OC) was calculated as the difference between TLC and the volume at which phase IV (closing capacity) began 26. The slope of phase III and OC were measured at least in triplicate, and the mean value retained for analysis. The results were expressed as % predicted (% pred) 25.
Aerosols of MCh chloride solutions (0.2%, 1% and 6%) were delivered via a DeVilbiss 646 nebuliser attached to a KoKo (Rosenthal–French) breath-activated dosimeter (Ferraris, Louisville, CO, USA). Aerosols were inhaled during quiet tidal breathing in the sitting position 27. Increasing doses of MCh from 40 to 4,800 ?g were inhaled until a decrease of FEV1 ?20% from control was achieved. FVC, FEV1, V?max and V?part were measured only once at each step to avoid the effects of full lung inflation on airway calibre. The provocative dose of MCh causing an FEV1 decrease of 20% (PD20) was determined by interpolating between two adjacent points of the log dose–response curve.