Airway inhomogeneities contribute to apparent lung tissue mechanics
during constriction.
Lutchen, Kenneth R., Zoltn Hantos, Ferenc Pet0k, Agnes Adamicza,
B[acute]ela Suki.
Department of Biomedical Engineering, Boston University, Boston,
MA, epartment of Medical Informatics and Engineering, Albert Szent
-Gy[diaeresis]orgyi Medical University, Szeged, Hungary, Department of
Experimental Surgery, Albert Szent-Gy[diaeresis]orgyi Medical
University, Szeged, Hungary
APStracts 3:0117A, 1996.
Recent studies have suggested that part of the measured increase in
lung tissue resistance after bronchoconstriction is an artifact due
to increased airway inhomogeneities. To resolve this issue, we
measured lung impedance (ZL) in 7 open-chest rats, with the lungs
equilibrated on room air and then on a mixture of neon-oxygen (NeOx).
The rats were placed in a body box, with the tracheal tube leading
through the wall of the box to either atmosphere or NeOx mixture. A
broadband flow signal was delivered to the box. The signal contained
7 oscillation frequencies in the 0.234-12.07 Hz range, which were
combined to produce tidal ventilation. The ZL was measured before and
during steady-state bronchoconstriction caused by infusion of
methacholine (Mch). Partitioning of airway and tissue properties was
achieved by fitting ZL with a model including airway resistance
(Raw), airway inertance, tissue damping (G), and tissue elastance
(H). We hypothesized that if inhomogeneities were not significant,
the apparent tissue properties would be independent of the resident
gas, while Raw would scale as the ratio of viscosities. Indeed,
during control the NeOx-to-air Raw ratio (RawN/RawA) was 1.25 +/-
0.10, while the GN/GA and HN/HA ratios were both 1.03 +/- 0.04. Also,
there was a small increase in lung elastance (EL) between 0.234 and 4
Hz which was similar on air and NeOx. During Mch infusion, Raw and G
increased markedly (45-65%), but the increase in H was relatively
small (<13%). Moreover, RawN/RawA and HN/HA remained the same
(1.27 +/- 0.04 and 1.03 +/- 0.05, respectively), whereas GN/GA
increased to 1.19 +/- 0.07 (P<0.01); the increase in EL with
frequency was now marked and dependent on the resident gas. These
results provide direct evidence that for a healthy rat lung, airway
inhomogeneities do not significantly influence the lung resistance
(RL) and EL vs. frequency data. However, during Mch-induced
constriction a large portion of the increase in tissue resistance and
the altered frequency dependence of EL are virtual and a consequence
of the augmented airway inhomogeneities. Our data also show that
alternative inferences would have been drawn from single frequency
data at or above 1 Hz.
Received 21 August 1995; accepted in final form 4 January 1995.
APS Manuscript Number A914-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96