Histamine inhalation tests: inhalation of aerosol via a facemask versus a valve box with mouthpiece.

Inhalation tests with histamine or methacholine are useful in clinical practice and research to determine the level of bronchial responsiveness. The factors which influence the dose deposited in the lung must, however, be regulated so that the results can be accuarately interpreted. In the method introduced by DeVries et al' and modified by Cockcroft and coworkers2 the aerosol is generated continuously and inhaled by tidal breathing. The dose deposited in the lung may be influenced by nebuliser output, particle size, the nature of apparatus between the nebuliser and the mouth, the variability of tidal breathing, and the duration of inhalation. The effect of each of these, with the exception of the apparatus between the nebuliser and mouth, has been systematically investigated.3In the method described by Cockcroft2 the aerosol passes through a facemask, which is held loosely over the mouth and clipped nose. It is possible that this might lead to more variation in the dose inhaled than if the aerosol is delivered directly into the mouth via a valve box and mouthpiece. In the present study we have compared responses and reliability with these two methods of aerosol delivery.