Respiratory deposition patterns of salbutamol pMDI with CFC and HFA-134a formulations in a human airway replica

This paper describes a technique that uses a well-defined human airway repl ica and gamma counting as a standard method for evaluating and comparing th e performance of medical inhalers and spacers. High-fidelity replicas repro duced as needed from master casts made from human cadavers include the orop haryngeal cavity, larynx, trachea, and five to nine generations of bronchi. Deposition in the small airways and alveoli region of the cast is simulate d by material that passes through the upstream airways and is collected on foam filters. Deposition patterns in the respiratory tract replica were obt ained by using radiolabel in the medical inhaler and by gamma scintigraphy. This technique was used to determine respiratory deposition patterns of sa lbutamol in a pressurized metered dose inhaler (pMDI) with chlorofluorocarb on (CFC, in-house formulation) and HFA-134 formulations (Proventil hydroflu oroalkane [HFA]). At an inspiration flow of 30 L/min, patterns in the salbu tamol/CFC formula showed a high deposition in the oropharyngeal airway (78% ) and a 16% deposition in the lung, similar to in vivo measurements reporte d in the literature. However, the salbutamol/HFA formula showed lower oral deposition (56%) but higher lung deposition (24%). The difference in the or al deposition patterns may be attributed to lower initial spray velocity, i nitial droplet evaporation rate, and possibly initial droplet sizes of Prov entil HFA. The small orifice diameter (0.25 mm) of the Proventil HFA actuat or produced a softer plume with a smaller impact force, resulting in lower oropharyngeal deposition. Cascade impactor measurements showed similar aero dynamic particle size distribution of the CFC and HFA formulations. We also showed that using spacers in the Proventil HFA resulted in a lower orophar yngeal. deposition and higher lung deposition, indicating beneficial effect s. Comparison of oropharyngeal deposition and those predicted by artificial throats used in the impactor measurements showed that, in general, the art ificial throat predicted a lower deposition.