Use of a modified Swan-Ganz pacing catheter for measuring Pdi and diaphragmatic EMG

Measurements of pressures across the diaphragm (Pdi) and diaphragmatic electromyogram (EMG) have become an integral tool to study respiratory muscle fatigue. To measure Pdi and diaphragmatic EMG, three balloon catheter systems have to be swallowed; two of these measure esophageal and gastric pressures and the third one, usually a Swan-Ganz catheter records diaphragmatic EMG. In the present study we describe how a thermodilution Swan-Ganz pacing catheter can be very simply modified to measure both Pdi and diaphragm EMG. Because only one catheter has to be swallowed, subject's acceptability improves, particularly for repeated measurements in the same subject. We have used such a catheter system for more than 18 months to study respiratory muscle fatigue in man. The measurements of Pdi by the modified Swan-Ganz catheter compare well with those recorded simultaneously with conventional balloons, and in vitro frequency response measurements showed that amplitude responses differed by 2% at 2 1/2 Hz. Phase responses of the esophageal and gastric balloons were linear over the range of frequencies tested.