Transport and deposition of inhaled fine particles within the lung (such as bacteria, airborne pollutants and aerosolized drugs) has important clinical implications and is determined by the interaction of inhaled and residual alveolar gas. In 23 July Proceedings of the National Academy of Sciences, Akira Tsuda and colleagues at Harvard University, Massachusetts, US, show that chaotic acinar flow may be the origin of substantial mixing and transport of fine aerosols deep in the lung (Proc Natl Acad Sci USA 2002, 99:10173-10178).

Tsuda et al. performed direct observations of flow patterns in freshly excised lungs and found that acinar flows are neither simple nor reversible. Instead, they observed substantial alveolar flow irreversibility with stretched and folded fractal patterns, leading to a sudden increase in mixing.

"This finding suggests that aerosol transport and deposition in the pulmonary acinus are governed by entirely different dynamics than processes based...