Neurocardiac and cerebral responses evoked by esophageal vago-afferent stimulation in humans: effect of varying intensities

Objective: This study was designed to determine whether esophageal vago-aff erent electrostimulation, over a wide range of stimulus intensities, can su stain a cardiac vago-efferent effect by way of central nervous system proce ssing. Methods: Studies were performed in ten healthy male subjects (23.9+/ -6.3 years). Esophageal electrostimulation was carried out using a stimulat ing electrode placed in the distal esophagus. Stimulation of esophageal vag o-afferent fibres was employed using electrical impulses (200 mu s at 0.2 H z x 128 s) varying from 2.7 to 20 mA. Respiratory frequencies, beat-to-beat heart rate autospectra and cerebral evoked potentials were recorded at bas eline and at each stimulus intensity in random order. Results: With esophag eal electrical stimulation, we observed a small non-significant decrease in heart rate. There was a dramatic shift of the instantaneous heart rate pow er spectra towards enhanced cardiac vagal modulation with intensities as lo w as 5 mA. This effect was sustained throughout all intensities with no fur ther change in either the low frequency or high frequency power. Conversely , there was a linear dose response relationship between cerebral evoked pot ential amplitude and stimulus intensity mainly occurring above perception t hreshold (10 mA). Esophageal stimulation had no significant effect on heart rate or respiratory frequency at any stimulus intensity. Conclusions:These results indicate that electrical stimulation of the distal esophagus acros s a wide range of current intensities elicits a reproducible shift in the h eart rate power spectrum towards enhanced vagal modulation. The data sugges t a closed loop afferent/effepent circuitry wherein tonic visceral afferent impulses appear to elicit a phasic or modulatory vago-efferent cardiac res ponse in healthy subjects. (C) 1998 Elsevier Science B.V. All rights reserv ed.