The diaphragm is the most important muscle of respiration. It is believed that the abdominal contents affect diaphragmatic contraction by helping determine its length tension state and by acting as a fulcrum for this muscle to lift the rib cage and thereby increase lung volume. In support of these concepts we describe a patient with severe chronic obstructive pulmonary disease and a large midline hernia of the abdomen who, when standing, had a gastric pressure (Pg) of 4 cm H2O and a maximal transdiaphragmatic pressure (Pdimax) of 14 cm H2O. This was associated with an O2 saturation of 82%, lower thoracic and upper abdominal paradoxical breathing, and severe dyspnea. Once the hernia was reduced there was a rise in Pg to 12 cm H2O, of Pdimax to 27 cm H2O, and of O2 saturation to 89%. There was normalization of the breathing pattern and a decrease in dyspnea. Reduction of this patient's abdominal hernia resulted in an increase in her exercise tolerance.