Errors in regional lung deposition predictions of nebulized salbutamol sulphate due to neglect or partial inclusion of hygroscopic effects

Regional lung deposition predictions from a stable particle model and a conventional, one-way hygroscopic model (Stapleton, K.W., Finlay, W.H. and Zuberbuhler, P., An in vitro method for determining regional dosages delivered by jet nebulizers. J. Aerosol Med., 7 (1994) 325-344) are compared with results from a more general, fully two-way coupled hygroscopic model (Finlay, W.H. and Stapleton, K.W., The effect on deposition of coupled heat and mass transfer between hygroscopic droplets and their surrounding phase. J. Aerosol Sci. 26, (1995) 137-145) for actual nebulized aerosols characterized experimentally. Data is obtained for Ventolin(R) (2.5 ml nebule, 1 mg/ml salbutamol sulphate in normal saline) with ambient conditions of 50% RH and six nebulizer brands, and for 15% RH and 90% RH for three nebulizer brands, all at room temperature. This data is entered into a deposition model with the three hygroscopic models for an inhalation flow rate of 300 ml/s and tidal volume of 750 ml. The results indicate that errors in regional dosages of less than 14% of the two-way coupled value occur when using either a stable particle model or a one-way coupled hygrosopic model at 90% RH. Similarly small errors occur at all humidities tested with the stable particle model for the nebulizer brands having high number density; however, for the other nebulizer brands, errors up to 19% in extrathoracic deposition and 35% in alveolar deposition occur at 15% RH and 50% RH. The one-way coupled model gives significant errors (up to 48%) in alveolar and extrathoracic deposition at these two lower humidities for most nebulizer brands tested. (C) 1997 Elsevier Science B.V.