Aerosol deposition and flow limitation in a compliant tube

Studies in intact dogs have suggested that aerosol deposition is enhanced in the proximity of a flow-limiting segment (FLS) formed during cough. The mechanism for that observation was investigated using a monodisperse (geometric SD less than or equal to 1.15) fluorescent aerosol produced in a condensation generator. The aerosol was passed through a compliant tube (Penrose) that had been mounted vertically in a two-chamber box. The surrounding pressure (Ps) in the upstream chamber was controlled independent of the surrounding pressure in the downstream chamber, thus allowing development of an FLS near the exit of the upstream chamber. At fixed inlet pressure (P1) and Ps, flow limitation was achieved over a range of 0.1-0.5 l X s-1 by lowering downstream pressure alone (P2). The influence of the FLS cross-sectional geometry on the site of peak deposition was examined because area of an FLS is a function of transmural pressure (Ptm = Px - Ps). For those constriction geometries that did not involve opposing wall contact, the deposition distribution was characterized by a single peak immediately downstream of the constriction. In the most compressed geometries the peak in deposition was diminished and shifted further downstream. Total aerosol deposition was found to be characterized by a dimensionless particle inertia parameter formed as the ratio of particle stopping distance and the minor radius of the elliptical tube cross section. The deposition of small particles with an inertial parameter less than 0.01 was found to be independent of geometry and constriction velocity.(ABSTRACT TRUNCATED AT 250 WORDS)