Identification of the optimal parameters for recording cortical evoked potentials to human oesophageal electrical stimulation.

Cortical evoked potentials in response to stimulation of the oesophagus may prove to be a powerful technique for assessing the oesophageal afferent pathway in health and disease. However, in order to maximize the potential of this technique it is essential that the optimal parameters for recording oesophageal CEP are established. The aim was to determine the optimal parameters required to record reproducible CEP. CEP were recorded from the vertex in eight subjects (age range 23-44 years). Electrical stimulation was performed 5 cm above the lower oesophageal sphincter using a bipolar ring electrode at 0.2 Hz. Protocol 1: to determine the stimulation intensity which generates the largest amplitude and shortest latency, two runs of 50 stimuli were applied at increasing intensities. Protocol 2: to determine the number of stimuli for optimal signal to noise ratio, 10 runs of 50 stimuli were recorded. Individual runs were averaged. Protocol 3: to determine the optimal inter-run interval, CEP evoked by 200 stimuli were averaged using randomly chosen inter-run intervals. Protocol 4: CEP reproducibility using parameters determined from Protocols 1-3 was assessed in three subjects on three separate occasions. The results were as follows: Protocol 1; P1 latency was shortest and P1-N1 amplitude largest at an intensity of 75% above threshold. Protocol 2; optimal signal-to-noise was achieved by averaging four runs of 50 stimuli. Protocol 3; the optimal interstudy interval was 10 min. Protocol 4; highly reproducible CEP were obtained in all individuals. Using these optimal parameters, it is possible to obtain highly reproducible oesophageal CEP to ES which can now be used for clinical study.