Measurement of gastric and diaphragmatic height during slow breathing maneuvers.

Changes in height of the gastric air bubble can be inferred, in theory, from the difference between gastric pressures measured with water- and air-filled balloon-catheter systems. We describe an apparatus that satisfactorily measures changes in height of gastric balloons in vitro. During slow breathing maneuvers in standing subjects, the apparatus measured changes in height of the balloons in the stomach that were consistent with expected changes in height of the diaphragmatic dome. In four subjects, balloon movements were nearly always less than movements of the costal margin of the diaphragmatic dome observed by ultrasonography; the average ratio of height changes was 0.73. We conclude that changes in height of the diaphragmatic dome can be measured with this method during slow breathing maneuvers in upright subjects.