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 humidities. The significant effect of ambient relative humidity can be an important consideration for clinical settings and for in vivo measurements of lung deposition.