Diaphragmatic EMG and transdiaphragmatic pressure measurements with a single catheter.

A single gastroesophageal catheter was used for simultaneous measurements of diaphragmatic electromyogram (EMGdi), esophageal, and gastric pressures in 10 normal volunteers. The catheter consisted of 2 polyethylene tubes, each with an outer diameter of 1.70 mm and an inner diameter of 1.19 mm, 2 platinum wire coils, and esophageal and gastric latex balloons. In all subjects studied, the increase in EMGdi, quantified as the average rate of rise of inspiratory moving average activity, and transdiaphragmatic pressure (Pdi) were linearly related to the increase in end-tidal PCO2 during CO2 rebreathing (range of r, 0.88 to 0.99 and 0.85 to 0.99, respectively). The relation between changes in EMGdi and that of Pdi, mean inspiratory flow, and occlusion pressure were also linear (range of r, 0.83-0.99, 0.73-0.99, and 0.84-0.99, respectively), indicating reliable recordings of EMGdi and Pdi during CO2 rebreathing in upright normal humans.