Increased lung deposition and biological effect of methacholine by use of a drying device for bronchial provocation tests

A simple device aiming to increase deposition of nebulized methacholine in the lower airway was studied. The device controlled inspiratory flow and volume and dried the aerosol. The effect of drying on deposition in the throat and lower airways was studied in six subjects given an aerosol of 99mTechnetium-diethylenetriamine pentaacetate (DTPA) in saline with the device and with a reference device giving the same inspiratory flow and volume but no drying. Drying reduced throat deposition from 46 (range 26-61) to 13 (range 6-22)% (p less than 0.05) of the inhaled and retained dose. The effect of drying on the biological effect of nebulized methacholine was studied in 21 subjects who underwent three provocation tests on different days with doubling concentrations of methacholine from 0.5 to a maximum of 64 mg.ml-1, one with the reference device and two with the drying device. The percentage change in forced expiratory volume in one second (%FEV1) per cumulative dose of methacholine changed from -1.0 (2.6) %FEV1.mumol-1 (geom. mean and SD) with the reference device to -1.6 (3.6) with the drying device p less than 0.02. In an additional study 20 subjects underwent four provocation tests on different days, two with a different version of the drying device and two with the reference device. The slope changed from -1.1 (3.1) to -1.6 (3.3), p less than 0.02. The reproducibility of duplicate measurements did not improve with the drying device. Thus, the drying device decreased throat deposition and increased the biological effect of nebulized methacholine.

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