Identification of the optimal parameters for recording cortical potentialsevoked by mechanical stimulation of the human oesophagus

Cortical evoked potentials (CEP) have been recorded in response to both ele ctrical stimulation (ES) and mechanical stimulation (MS) of the oesophagus. While the optimal parameters for recording reproducible oesophageal CEP to ES have recently been established, they have not yet been determined for M S, and reported CEP to MS show considerable variability. This study aimed t o identify the optimal parameters required to record reproducible MS induce d CEP. CEP were recorded from the vertex (Cz) in six subjects (one female; age range 23-47 years). MS was performed 5 cm above the lower oesophageal s phincter by rapidly inflating a 2-cm long silicone balloon at a frequency o f 0.2 Hz. The rise time to maximum inflation was 165 ms. In order to determ ine the minimum number of stimuli required to produce optimal signal-to-noi se quality, we acquired data in runs of 25, 50, 100 and 300 stimuli and to determine the stimulation intensity that produced the shortest latency and the largest amplitude CEP, we averaged four runs of 50 stimuli at five diff erent intensities ranging from sensory threshold to pain. CEP reproducibili ty was then assessed in three subjects on three separate occasions using pa rameters determined from these measurements. We found that optimal signal-t o-noise quality was achieved by averaging four runs of 50 stimuli; that P1 latency was shortest and P1-N1 amplitude largest at intensities of 75% and pain threshold and that highly reproducible CEP were obtained in all indivi duals. We conclude that it is possible to obtain highly reproducible oesoph ageal CEP to MS which can now be compared to those obtained by ES in order to identify which is most suitable for clinical studies.