ESOPHAGEAL MYOELECTRIC RESPONSES TO MAGNETIC STIMULATION OF THE HUMANCORTEX AND THE EXTRACRANIAL VAGUE NERVE

Esophageal myoelectric responses to magnetic stimulation of the human cortex and the extracranial vagus nerve. Am, J. Physiol. 267 (Gastroin test. Liver Physiol. 30): G827-G835, 1994.-We describe the use of magn etic stimulation of the human motor cortex and the extracranial vagus nerve in the neck to study human esophageal electromyographic (EMG) re sponses. Diffuse cortical stimulation produced both an early and a lat e EMG response in the proximal esophagus with latencies of 10.9 +/- 0. 5 and 43.4 +/- 4.3 ms, respectively. Increasing the stimulation intens ity increased the amplitude and duration, but reduced the latency, of the early response (P < 0.01), whereas the late response remained unch anged. The early response, but not the late response, was facilitated when cortical stimulation was performed during valsalva maneuver. Maxi mal early response amplitudes were obtained by focal stimulation of ei ther hemisphere 4-8 cm lateral to the vertex. Stimulation of the neck over the extracranial vagus nerve at the angle of the jaw also produce d an early and a late EMG response in the proximal esophagus with late ncies of 4.3 +/- 0.4 and 56.8 +/- 14.5 ms, respectively. Early respons es were also recorded in the midesophagus and distal esophagus from ei ther cortical or vagal stimulation, but amplitudes were smaller and ri se times were longer, suggesting passive ''volume conduction'' from th e proximal esophagus. Comparison of laryngeal, pharyngeal, and esophag eal early EMG responses showed similar amplitudes and rise times, sugg esting that the action potentials were generated locally at each site and that true esophageal responses were being detected.