Author(s): Chihara K, Kenyon CM, Macklem PT
In five normal men, we divided the rib cage into lung-apposed [pulmonary rib cage (RCp)] and diaphragm-apposed [abdominal rib cage (RCab)] compartments and calculated their absolute cross-sectional areas (Arc,p and Arc,ab) by anteroposterior and lateral dimensions measured by magnetometry. Distortion was quantified as the displacement of RCp and RCab produced by diaphragmatic twitches away from the relaxed configuration. We measured transdiaphragmatic pressure as the difference between gastric and esophageal pressures. Distortability was expressed as percent distortion per transdiaphragmatic pressure and varied among individuals from 0.02 to 0.23%/cmH2O. The pressure acting to restore the distorted rib cage back to its relaxed shape (Plink) varied from 0.1 to 31.3 cmH2O/%distortion. Distortion correlated positively (r = 0.92) and Plink per percent distortion negatively (r = -0.90) with RCab compliance during the relaxation maneuver (delta Arc, ab/delta gastric pressure). We conclude that rib cage distortability varies widely among normal subjects and is closely linked to RCab compliance.