Pectus excavatum is generally regarded as a cosmetic deformity; however, some children with pectus excavatum complain of chest pain and exercise limitation. Physiologic studies sometimes show mild restrictive changes and suggest an increased oxygen cost of breathing. Limitation of rib cage mobility related to the deformity may explain these findings. If rib cage mobility is limited, the ability of the actively inspiring rib cage to lower abdominal pressure would be decreased. If this were so, increased swings in abdominal pressure would be seen during the respiratory cycle, especially at times of stress such as during exercise. To test the hypothesis that pectus excavatum is associated with decreased rib cage mobility, we studied 11 patients with pectus excavatum and 11 control subjects. Four control subjects were also studied with rib cage mobility restricted by chest wall strapping sufficient to decrease vital capacity by 5, 10, and 40%. Gastric pressure was measured using balloon catheters and was used as an index of abdominal pressure. Flow at the mouth was recorded and integrated to give volume. Measurements were made at rest, immediately after exercise, and during graded voluntary inspiration to total lung capacity. Gastric pressure was related to tidal volume, and pressure-volume loops were constructed. There were no differences in abdominal pressure swings during respiration between the patients with pectus excavatum and the control subjects. Both groups showed moderate increase in gastric pressure during inspiration at rest and smaller increases or even decreases in abdominal pressure at end inspiration after exercise and at total lung capacity.(ABSTRACT TRUNCATED AT 250 WORDS)