Shear-augmented dispersion in the respiratory system.
Biological systems contain numerous examples of shear-augmented dispersion in which gradients in the velocity profile act in concert with lateral mixing or molecular diffusion to cause materials to disperse at an enhanced rate. Some of the better known examples are found in the respiratory or cardiovascular systems, but other applications include the dispersal of pollutants discharged into a flowing stream, the mixing of contaminants in groundwater flows and the possibility of enhanced transport rates through tissues subjected to transient loads. This review focuses on two examples in the respiratory system, bolus dispersion and high-frequency ventilation, that draw upon a broad range of fundamental studies in shear-augmented dispersion. Simple examples are considered which contain specific features of the considerably more complex real situations. These features include, for example, the effects of turbulence, secondary flows, absorption by the walls, aerosol deposition, complex geometries and oscillatory flow. A scaling analysis is presented that yields the approximate dependence of effective diffusivities associated with shear-augmented dispersion when more detailed analyses are either not warranted or too complex to be tractable.
Kamm
R D
RD
Department of Mechanical Engineering, Masschusetts Institute of Technology, Cambridge, USA.
D000818:Animals; D001692:Biological Transport; D004058:Diffusion; D008433:Mathematics; D008954:Models, Biological; D012123:Pulmonary Ventilation / Q000502:physiology; D012143:Respiratory Physiological Phenomena