Journal of Applied Physiology, Vol 72, Issue 2 568-574, Copyright © 1992 by American Physiological Society
Role of the diaphragm in chest wall mechanics
O. Lichtenstein, S. A. Ben-Haim, G. M. Saidel and U. Dinnar
Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
We analyzed three different assumptions about diaphragm function that
determine the thoracoabdominal interaction. In the simplest case, the
diaphragm is assumed to be a completely flaccid membrane serving only to
partition the thorax and the abdominal cavity. In the second case, it is
assumed to have a finite tension but to maintain a relatively flat surface
at the base of the rib cage (i.e., a negligible zone of apposition). In the
general case, it is assumed that the diaphragm has finite tension and its
position may vary (i.e., permitting a zone of apposition). These possible
modes of behavior are incorporated into a mathematical model of ventilatory
system mechanics that distinguishes the diaphragm, lung, abdomen, and rib
cage. The significance of these modes is examined with respect to data from
human experiments in which gas or liquid is introduced into the pleural or
abdominal spaces, causing a volume change (Vep). We show that the Vep
effect on the thoracic and abdominal volumes is sensitive to diaphragm
mechanics and depends on the nature of the Vep: gastric distension (with
water or air) or pneumothorax. Only the behavior of the general model is
consistent with physiological observations, especially the distribution of
Vep. Our general mathematical model can quantitatively predict this
behavior.
