Journal of Applied Physiology, Vol 70, Issue 2 511-515, Copyright © 1991 by American Physiological Society
Proportionality between chest wall resistance and elastance
G. M. Barnas, D. Stamenovic and J. J. Fredberg
Department of Anesthesiology, University of Maryland, Baltimore 21201.
Fredberg and Stamenovic (J. Appl. Physiol. 67: 2408-2419, 1989)
demonstrated a relatively robust phenomenological relationship between
resistance (R) and elastance (E) of lung tissue during external forcing.
The relationship can be expressed as omega R = eta E, where omega = 2 pi
times forcing frequency and eta is hysteresivity; they found eta to be
remarkably invariant under a wide range of circumstances. From data
gathered in previous experiments, we have tested the adequacy and utility
of this phenomenological description for the chest wall (eta w) and its
major compartments, the rib cage (eta rc), diaphragm-abdomen (eta d-a), and
belly wall (eta bw+). For forcing frequencies and tidal volumes within the
normal range of breathing, we found that eta w remained in a relatively
narrow range (0.27-0.37) and that neither eta w nor the compartmental eta's
changed much with frequency or tidal volume. Compared with eta w, eta rc
tended to be slightly low, whereas eta d-a tended to be slightly higher
than eta w. However, at higher frequencies (greater than 1 Hz) all eta's
increased appreciably with frequency. During various static nonrespiratory
maneuvers involving use of respiratory muscles, eta w increased up to
twofold. We conclude that in the normal ranges of breathing frequency and
tidal volume 1) elastic and dissipative processes within the chest wall
appear to be coupled, 2) eta's of the various component parts of the chest
wall are well matched, 3) respiratory muscle contraction increases the
ratio of cyclic dissipative losses to energy storage, and 4) R of the
relaxed chest wall can be estimated from E.(ABSTRACT TRUNCATED AT 250
WORDS)
