Chest wall mechanics: effects of acute and chronic lung disease.

Data from the literature show that lung tissue properties affect the chest wall compliance, Ccw, which is the change in lung volume, Vl, with respect to the pleural pressure, Ppl. to analyze the difference between acute and chronic lung tissue changes, we used a mathematical model that describes the static, nonlinear mechanics of the ventilatory system in terms of its major elements: rib cage; abdomen; diaphragm and lung. With this model we derived the relationship between chest wall, rib-cage and diaphragm compliances. Although the Vl-Ppl relation is independent of lung mechanics, the volume operating point (FRC) of the ventilatory system depends on lung tissue properties. This accounts for the effect of acute lung abnormalities. In the presence of chronic lung abnormalities, the properties of the rib-cage are changed which shifts the entire Vl-Ppl curve. In general, valid comparisons of (extra-pulmonary) chest wall mechanics can only be made using the entire Vl-Ppl relation, or at least a sufficiently large part of the relation about FRC. Differentiation of the rib-cage and diaphragm mechanics requires additional measurements of the rib-cage A-P distance and the relative position of the diaphragm.