Chest wall configuration assessed at total lung capacity during acute asthma and after recovery.

During acute asthma reversible increase in lung compliance and total lung capacity (TLC) have been observed. The magnitude of the increase in TLC, however, was found to be relatively small when TLC was measured radiographically. We wondered if structural distortion of the respiratory bellows develops during acute asthma attacks, accounting for the limited increase in TLC. We analyzed the chest wall dimensions using chest roentgenograms obtained in 32 patients who had previously participated in the study of radiographic evaluation of TLC. We found that the dimensional changes accompanying the small increase in TLC during acute asthma were nonuniform, consisting of mainly an increase in lung height (0.45 +/- 0.15 cm) with limited coordinated expansion of other dimensions and a small but significant distortional contraction of lung width at the lowest portion of the rib cage (-0.25 +/- 0.12 cm). These findings were interpreted to mean that in response to the decrease in elastic lung recoil (internal load) occurring during acute asthma, the diaphragm makes limited but effective further caudad descent without provoking serious structural distortion and that rib cage muscles, working at mechanical disadvantage at high lung volume, act largely as fixators.