The Effect of Ambient Relative Humidity on Regional Dosages Delivered by a Jet Nebulizer

ABSTRACT In this study, the output of DeVilbiss Pulmo-Neb® disposable jet nebulizers driven by a DeVilbiss Pulmo-Aide® compressor to nebulize 2.5 ml nebules of 1 mg/ml Ventolin® was measured at five ambient relative humidities ranging from 3% to 95%. It was found that as the humidity was increased from 3% to 95%, the mass median diameter of the aerosol increased by 14% while the concentration of the nebulizer solution at the end of the nebulization period decreased by 19%. Calculations using the procedure of Stapleton, Finlay, and Zuberbuhler (J. Aerosol Med., 7:325-344, 1994) predict that as the ambient relative humidity is increased from 3% to 95%, there is a 100% increase in extrathoracic dosage, a 9% increase in bronchial dosage, and a 63% decrease in pulmonary dosage. The major source of this effect is the hygroscopic shrinkage of the particles as they are inhaled with low humidity ambient air, although there is a minor effect due to changes in initial particle size distribution at different humiditi...