Journal of Applied Physiology, Vol 64, Issue 4 1387-1396, Copyright © 1988 by American Physiological Society
Site of airway obstruction: effects on the acoustic impedance of excised pig lungs
F. Feihl, N. Simon, C. Jaeggi, C. Depeursinge and C. Perret
Institut de Physiopathologie, Centre Hospitalier, Universitaire Vaudois, Lausanne, Switzerland.
We investigated the relationship between the site of airway obstruction and
the frequency dependence (FD) of lung acoustic impedance (ZL). The real
(RL) and imaginary (XL) parts of ZL were measured by forced random noise in
excised left pig lungs, before (base line) and after 1) no airway
obstruction (controls, n = 10), 2) insufflation of 1-mm (B1, n = 5) or 2-mm
(B2, n = 7) beads, and 3) partial reversible obstruction of lower lobar
(LL) and then main-stem (MS) bronchus (n = 4). The beads caused both
partial and total obstruction of airways with internal diameters of 2 mm
(B1) and 2-6 mm (B2). Compared with base line, a negative FD of RL appeared
from 4 to 10 Hz in LL, B1, and B2 obstructions. The FD of XL greater than
20 Hz increased in MS and LL obstruction exclusively and was the ZL feature
that most clearly differentiated central from peripheral obstruction. In
this experimental model, the anatomic limit distal from which obstruction
no longer causes the "central" type of ZL change lies in airways with
internal diameters notably greater than 2 mm.
