Measurement of twitch transdiaphragmatic pressure: surface versus needle electrode stimulation.

The transdiaphragmatic pressure (Pdi) generated during bilateral supramaximal phrenic nerve stimulation at 1 Hz from surface stimulating electrodes was compared with pressures obtained from needle electrodes inserted under local anaesthesia. Surface electrodes were used to obtain diaphragmatic electromyograms and magnetometers to monitor rib cage and abdominal configuration. Twitch Pdi was recorded at functional residual capacity in three normal subjects. Mean (SD) twitch Pdi in the three subjects during stimulation with surface electrodes was 19.4 (1.8), 22.5 (1.1), and 29.3 (2.2) cm H2O compared with 12.9 (1.5), 17:4 (1.3), and 22.6 (3.0) cm H2O with needle stimulating electrodes. Thus phrenic nerve stimulation with needle electrodes was more complicated and more invasive than stimulation with surface electrodes and resulted in lower transdiaphragmatic pressures.