Mucus transport by cough.

Experiments are described in which a cough is simulated by blowing Newtonian and non-Newtonian liquids out of a straight tube by a turbulent gas flow. Analysis of these experiments indicates that during the flow a steady state balance exists between the shear force exerted on the flowing liquid layer by the flowing gas and the shear force required to maintain the liquid layer in steady laminar flow along the tube wall. By using this steady state shear force balance, quantitative estimates are obtained for the serous layer velocities induced by a cough in various generations of the bronchial tree. These are compared to normal ciliary mucus velocities and are seen to be significant down to about the 12th generation for a cough in a healthy individual. The magnitude of cough-induced serous layer velocities is seen to be strongly dependent on the serous layer thickness, ls, and viscosity, mu s, and increase linearly with ls over mu s.