Journal of Applied Physiology, Vol 59, Issue 4 1304-1312, Copyright © 1985 by American Physiological Society
Wall motion in expiratory flow limitation: choke and flutter
P. M. Webster, R. P. Sawatzky, V. Hoffstein, R. Leblanc, M. J. Hinchey and P. A. Sullivan
Limitation of expiratory airflow from mammalian airways is currently
understood to be due to choking at wave speed (S. V. Dawson and E. A.
Elliott. J. Appl. Physiol. 43: 498-515, 1977). A critical weakness of the
theory is the lack of a mechanism for the dissipation of energy when effort
exceeds that needed for maximal flow. We have observed substantial wall
motion with flow limitation in a physical model of a trachea. Therefore we
have examined a simple two-dimensional mathematical model, designed to
approximate the behavior of the physical model of the trachea, to try to
identify a relationship between flow limitation and wall oscillation. The
model matches wave-speed predictions when only long waves are considered.
The model predicts that aerodynamic flutter will occur in the zone of
supercritical flow described in wave-speed theory. Aerodynamic flutter in
the zone of supercritical flow provides a potential mechanism for the
energy dissipation necessary for transition from supercritical to
subcritical flow and explains the high-frequency pure tone heard with flow
limitation.
