Recirculating flow in an expanding alveolar model: Experimental evidence of flow-induced mixing of aerosols in the pulmonary acinus

Mixing processes of aerosol particles in the pulmonary acinus by rhythmic e xpansion of alveolar walls have recently been simulated within a realistic geometric model of the alveolar duct (Tsuda et al., 1995). We studied the v elocity fields in an expanding large-scaled silicone copy of this alveolar model applying particle-image-velocimetry. Without wall expansion the flow fields are characterized by a large recirculation region within the alveola r sac and a separation streamline separating this region from the duct Row. With wall expansion, the topology of the Row entirely changed. A separatio n streamline at the alveolar opening disappeared. There was convective flow exchange between duct and alveolus. Large recirculation hows were often ob served in the expanding alveolus, indicating the occurrence of stagnation s addle point in the alveolar flow field. Such singularity point is character istic for the occurrence of chaotic Row mixing, which in turn leads to sign ificant increase in deposition of fine aerosols in the pulmonary acinus. (C ) 2000 Elsevier Science Ltd. All rights reserved.