Journal of Applied Physiology, Vol 76, Issue 6 2428-2436, Copyright © 1994 by American Physiological Society
Shunt properties of large intrathoracic airways
M. Cauberghs, E. Verbeken and K. P. Van de Woestijne
Labortorium voor Pneumologie, Universitair Ziekenhuis Gasthuisberg, Leuven, Belgium.
The impedance of the wall of human intrathoracic trachea and central
airways was measured by submitting preparations of excised airways to
forced oscillations at various frequencies from 2 to 32 Hz. Both real
(resistance) and imaginary (reactance) parts of wall impedance demonstrate
a marked frequency dependence, varying with transmural pressure. These
variations of resistance and reactance are related and are linked to the
static elastic properties of the airways. The data allow us to calculate
the total shunt impedance of the central intrathoracic airways. When the
latter shunt values are used to correct measurements of impedance values of
excised emphysematous lungs, it turns out that the shunt does not modify
markedly the observed frequency dependence of resistance and compliance of
those lungs, at least at transpulmonary pressures > 0.2 kPa. A model
study suggests, in addition, that the latter frequency characteristics
cannot be explained satisfactorily by parallel mechanical inhomogeneities.
We submit that the frequency dependence of resistance and compliance of
excised emphysematous lungs is determined mainly by the visco- and/or
plastoelastic properties of lung tissue itself.
