Partitioning of airway and lung tissue properties: comparison of in
situ and open chest conditions.
Suki, B[acute]ela, Ferenc Pet[acute]ak, Agnes Adamicza, Zolt[acute]an
Hantos, and Kenneth R. Lutchen.
Department of Biomedical Engineering, Boston University, Boston,
MA, USA, Departments of Medical Informatics and Experimental Surgery,
Albert Szent-Gy[diaeresis]orgyi Medical University, Szeged,
Hungary
APStracts 2:0159A, 1995.
The purpose of this study was to investigate under physiological
breathing conditions whether airway and lung tissue properties are
different in situ and in open chest conditions. We measured lung
input impedance (ZL) in dogs from 0.2 to 8 Hz with an optimal
ventilator waveform at four tidal volumes (VT from 75 to 450 ml) in
intact animals using an esophageal balloon as well as after opening
the chest. The ZL from both conditions was partitioned to airway and
tissue compartments as characterized by airway resistance (Raw) and
inertance (Iaw) and tissue damping (G) and elastance (H),
respectively. All parameters, except Iaw, depended to some extent on
VT. The in situ tissue G and H slightly decreased with VT while in
the open chest condition, G decreased and H slightly increased with
VT. We found small but significant differences between the mechanical
properties of the airways and lung tissues in situ and in open chest
condition. Over the total population, the G, Raw and Iaw parameters
were 13% (non significant), 35% (p<0.001) and 31% (p<0.001)
smaller, respectively, in situ than in open chest condition. However,
the H was 15% larger (p<0.001), respectively, in situ. While we
cannot completely rule out certain artifacts, these differences most
likely reflect real alterations in the lung due to the different
configurations and possible differences in the distribution of
pleural pressures in the two conditions. The G being smaller and H
being larger in situ resulted in hysteresivities (_=G/H) 36% smaller
(p<0.001) in situ. Consequently, energy dissipation in the lung
tissues relative to energy storage as characterized by _ is somewhat
increased in the open chest configuration. This may be anticipated
since the mechanical efficiency of the lungs is expected to be better
in its natural state than in any artificially maintained condition
which was the end result of an invasive intervention.
Received 12 December 1994; accepted in final form 3 April 1995.
APS Manuscript Number A1263-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.