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 pa thway in health and disease. However, in order to maximize the potential of this technique it is essential that the optimal parameters for recording o esophageal CEP are established. The aim was to determine the optimal parame ters required to record reproducible CEP. CEP were recorded from the vertex in eight subjects (age range 23-44 years). Electrical stimulation was perf ormed 5 cm above the lower oesophageal sphincter. using a bipolar ring elec trode at 0.2 Hz. Protocol 1: to determine the stimulation intensity which g enerates the largest amplitude and shortest latency, two runs of 50 stimuli were applied at increasing intensities. Protocol 2: to determine the numbe r of stimuli for optimal signal to noise ratio, 10 runs of 50 stimuli were recorded. Individual runs were averaged. Protocol 3: to determine the optim al interrun interval, CEP evoked by 200 stimuli were averaged using randoml y chosen inter-run intervals. Protocol 4: CEP reproducibility using paramet ers determined from Protocols 1-3 was assessed in three subjects on three s eparate 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 o f 50 stimuli. Protocol 3; the optimal interstudy interval was 10 min. Proto col 4; highly reproducible CEP were obtained in an individuals. Using these optimal parameters, it is possible to obtain highly reproducible oesophage al CEP to ES which can now be used for clinical study.