Journal of Applied Physiology, Vol 67, Issue 5 1785-1790, Copyright © 1989 by American Physiological Society
Mechanical analysis of extrapulmonary volume displacements in the thorax and abdomen
S. A. Ben-Haim, O. Lichtenstein and G. M. Saidel
Department of Physiology and Biophysics, Technion-Israel Institute of Technology, Haifa.
Currently, the effect of intrathoracoabdominal, extrapulmonary volume
displacements (Vep) are not well understood. Various clinical conditions
can lead to volume displacements caused by gas or liquid accumulations. To
analyze the pressure and volume changes that occur by Vep, we used a
mathematical model of chest wall and lung mechanics that accounts for
static changes associated with rib cage, diaphragm, abdomen, and lungs. By
solving the model equations, we obtained simulations of the pleural and
abdominal displacements that clearly differentiate the mechanisms involved.
When abdominal displacement occurs, the reduction in lung volume is less
than that caused by an equal displacement in pleural space. Abdominal
displacement produces an increased pressure that expands the rib cage
significantly, whereas pleural displacement does not produce a comparable
action. Furthermore, our model predicts the conditions under which the work
of inspiration is expected to increase as a consequence of these
displacements. Finally, an important distinction is predicted between
abdominal displacements caused by gas or liquid accumulation. Although an
abdominal gas displacement tends to decrease the resting lung volume, the
weight effect of a liquid displacement tends to increase the resting lung
volume by pulling down the diaphragm.
