SHUNT PROPERTIES OF LARGE INTRATHORACIC AIRWAYS

The impedance of the wall of human intrathoracic trachea and central a irways was measured by submitting preparations of excised airways to f orced oscillations at various frequencies from 2 to 32 Hz. Both real ( resistance) and imaginary (reactance) parts of wall impedance demonstr ate a marked frequency dependence, varying with transmural pressure. T hese 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 airw ays. 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 r esistance and compliance of those lungs, at least at transpulmonary pr essures >0.2 kPa. A model study suggests, in addition, that the latter frequency characteristics cannot be explained satisfactorily by paral lel mechanical inhomogeneities. We submit that the frequency dependenc e of resistance and compliance of excised emphysematous lungs is deter mined mainly by the visco- and/or plastoelastic properties of lung tis sue itself.