The effect of interference source proximity on cuff imbalance.

The presence of cuff imbalance degrades the signal-to-interference (ENG/EMG) ratio in tripolar nerve cuff electrode recordings. Known causes of cuff imbalance include inhomogeneous tissue growth after cuff implantation and cuff manufacturing tolerances. In this paper, we report on an additional contribution to cuff imbalance that stems from variations in orientation and distance of the tripolar cuff relative to the external interference source. The latter is represented here by a dipole. Interference amplitude is also shown to depend on orientation and distance variations, here both factors included in the term "proximity." The study was conducted using field simulations and saline-bath experiments.