Effect of nebulised aerosol size on lung deposition in patients with mild asthma.

A radioaerosol technique has been used to investigate whether the size distribution of aerosols released from a jet nebuliser affects the amount of aerosol delivered to the lungs. Six subjects with mild asthma (FEV1 81% of predicted) were studied on three occasions. On each visit they received one of three aerosols tagged with technetium-99m in 0.9% saline. The aerosols were generated by either (A) a Turret nebuliser operated at 8 l min-1 (mass median diameter (MMD) 1.8 micron); (B) an Upmist nebuliser operated at 6 l min-1 (MMD 4.6 microns); or (C) an Inspiron Mini-neb operated at 4 l min-1 (MMD 10.3 microns). The aerosols were given in a randomised single blind manner and inhaled under identical conditions of inspiratory volume and frequency. The mean (SD) percentage of aerosols A, B, C released from the nebulisers during inhalation that was recovered in an expiratory filter was 23 (6), 25 (4), and 24 (4) respectively. Of the aerosols released from the nebuliser and deposited in the body, the percentage deposited in the lung was 79 (3) for aerosol A, 59 (4) for aerosol B, and 44 (5) for aerosol C. The remaining aerosol was deposited in the oropharynx and swallowed. It is concluded that small nebulised aerosols (MMD less than 2 microns) deliver a larger dose to the lungs and should be used to maximise lung deposition.