Investigation on the origin of far field short latency potentials evoked from auricular acupuncture points

 

Bianca Leutzow ,Gibb Andreas, Lange Joern, Schroeder Henry, Wendt Michael, Usichenko Taras, Department of Anesthesiology and Intensive Care Medicine, Ernst Moritz Arndt, University of Greifswald, Germany.

 

Purpose

Averaged EEG-like scalp responses to electrical stimulation from the inner side of the tragus within 10 msec after stimuli application, are suggested to be far field potentials, generated in the vagal system – Vagal Sensory Evoked Potentials (VSEP) (1). Our purpose was to study VSEP response, elicited during stimulation of ear areas, ascribed to be auricular acupuncture (AA) points (2) and to clarify the mechanism of these VSEP responses.

 

Methods

Ten healthy volunteers and 12 patients (ASA I–II) scheduled for elective low-back and extremities surgery in general anesthesia (GA) with trachea intubation were included. Stimulation was applied to triangular fossa (AA point 55), concha (AA point 101), inner side of the tragus (AA point 15) and to non-acupuncture points of the auricular helix and lobule. Stimulation consisted of 100 square impulses of 0.1 ms duration with a frequency of 0.5 Hz and an intensity of 8 mA. EEG responses were recorded from positions C4-F4 and T4-O2, with impedances below 2 kΩ, using a Nihon Kohden MEB 9400. In healthy volunteers, VSEP responses were registered before and after subcutaneous infiltration of stimulated areas with the local anesthetic lidocaine 2%. In patients, VSEP acquisitions were made before and after induction of GA, during the maximal effect of non-depolarizing muscle relaxing agent cis-atracurium 0.1 mg/kg (C-AR) and after recovery from C-AR under GA.

 

Results

In healthy volunteers, responses with previously described latencies could be reproduced only during stimulation of the ear areas with AA points 15, 55 and 101, but not from non-acupuncture points. These responses disappeared after administration of lidocaine. In all patients the responses could be reproduced before and after anesthesia induction. The responses completely disappeared during the C-AR action and re-appeared after recovery from C-AR under GA. In some patients a stimulation-synchronous twitching of scalp muscles was observed.

 

Conclusion

Electrical stimulation of the external ear, leading to scalp responses, starts with excitation of afferent nerves, which can be blocked by a local anesthetic. The disappearance of the responses to electrical stimulation of the auricle under neuromuscular block strongly suggests a muscular origin of these potentials. Even if some final details of the mechanism still should be experimentally clarified, this method can be used to study the site specificity of auricular acupuncture.

 

 

  1. (1) Fallgatter et al. Far field potentials from the brainstem after transcutaneous vagus nerve stimulation.     J NeuralTransm 2003.
  2. (2) Nogier PMF. Über die Akupunktur der Ohrmuschel. Dt Ztschr Akup 1957.