The role of respiratory flow asynchrony on convective mixing in the pulmonary acinus

Fine aerosol transport in the alveolated regions of the lungs is intrinsically coupled to alveolar flow patterns driven by lung breathing motions. Hence, understanding acinar flow characteristics is critical in determining local aerosol deposition sites. To date, inhaled aerosol dynamics have been mainly investigated using self-similar expanding lung models, although it is known that anisotropic lung motions exist and thus, potentially alter flow characteristics and enhance convective mixing. Using both experimental and numerical approaches, we assess here the influence of respiratory flow asynchrony on convective mixing by investigating alveolar flow patterns and massless particle transport for increasing phase lags between local wall motion and acinar ductal flows. Experimental results using a microfluidic platform, as well as numerical simulations, suggest that alveolar flow patterns are time-dependent in contrast to quasi-steady phenomena that pertain under synchronous conditions. To capture statistics of convective mixing, we numerically track massless tracers over multiple breathing cycles using anatomically inspired models of alveolated airways. By systemically probing various degrees of phase lag, our results underline the strong correlation between the magnitude of particle dispersion and flow asynchrony. In particular, we find that the dispersion of massless particles in acinar ducts is dramatically increased under flow asynchrony, relative to local, isolated alveolar cavity mixing. Despite the simplicity of the present models, our work highlights the critical role of respiratory flow asynchrony in governing the fate of fine inhaled particles in the pulmonary acinus.