Factors limiting depth of a maximal inspiration in human subjects

Abstract

Simultaneous measurements of esophageal and gastric pressure during the performance of vital capacity maneuvers were made in trained and untrained normal adult subjects. The changes in transdiaphragmatic pressure from functional residual capacity to total lung capacity were found to result largely from changes in intraesophageal pressure, gastric pressure changing substantially in only two of the untrained subjects. In addition, six of the individuals were subjected to oscillating pressures during vital capacity maneuvers. Oscillatory flow at the mouth continued at maximum inspiratory levels in five of the subjects. It was concluded from these two sets of observations that antagonistic action of abdominal muscles and/or glottic closure does not limit lung expansion in most trained subjects; in these the limitations to further expansion appear to arise from the elastic recoil of the respiratory system and the diminishing effectiveness of the inspiratory muscles at high lung volumes. Submitted on July 19, 1962