HUMAN RIB CAGE DISTORTABILITY

In five normal men, we divided the rib cage into lung-apposed [pulmona ry rib cage (RCp)] and diaphragm-apposed [abdominal rib cage (RCab)] c ompartments and calculated their absolute cross-sectional areas (Arc,p and Arc,ab) by anteroposterior and lateral dimensions measured by mag netometry. Distortion was quantified as the displacement of RCp and RC ab produced by diaphragmatic twitches away from the relaxed configurat ion. We measured transdiaphragmatic pressure as the difference between gastric and esophageal pressures. Distortability was expressed as per cent distortion per transdiaphragmatic pressure and varied among indiv iduals from 0.02 to 0.23%/cmH(2)O. The pressure acting to restore the distorted rib cage back to its relaxed shape (Plink) varied from 0.1 t o 31.3 cmH(2)O/%distortion. Distortion correlated positively (r = 0.92 ) and Plink per percent distortion negatively (r = -0.90)with RCab com pliance during the relaxation maneuver (Delta Arc,ab/Delta gastric pre ssure). We conclude that rib cage distortability varies widely among n ormal subjects and is closely linked to RCab compliance.