Fig. 6

Stimulation-induced Pdi as a function of the esophageal stimulation level around rib 1 (orange shades) and C6 (green), and the electrode spacing (10–40 mm) with a stimulation intensity of 40 mA. The horizontal dashed line indicates phrenic nerve capture with the punctured needle electrode placed at rib 1. The zero level, aligned accordingly to rib 1 or C6, is depicted by a vertical line. A significantly higher Pdi is generated at the stimulation position of rib 1 than at the level of C6. Furthermore, a gain in Pdi can be observed by the best aligned directed electrode as compared to the omnidirectional electrode