PROPORTIONALITY BETWEEN CHEST-WALL RESISTANCE AND ELASTANCE

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 (> 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. One implication of these results is that hysteretic "matching" of chest wall components enhances uniformity of regional displacement.