NEUROCARDIAC RESPONSE TO ESOPHAGEAL ELECTRIC-STIMULATION IN HUMANS - EFFECTS OF VARYING STIMULATION FREQUENCIES

The purpose of this study was to determine if the cardioautonomic resp onses to esophageal electric stimulation were mediated entirely throug h modulation of respiratory frequency or a direct vagal effect. We per formed electric stimulation of the esophagus in 13 healthy male contro ls (24 +/- 6 yr) using a manometric catheter to which a stainless stee l electrode was attached. Stimulation frequencies ranged from 0.1 to 1 Hz and were applied in random fashion. We computed the power spectra of the heart rate variability and respiratory frequency as measures of autonomic function. Electric stimulation of the esophagus produced si gnificant increases in the high-frequency power of the heart rate auto spectrum at all stimulation frequencies (maximal at 0.2 Hz). However, regardless of the frequency of esophageal stimulation, the respiratory rate was not changed from baseline. These studies indicate that enhan cement of cardiac vagal modulation observed in response to esophageal electric stimulation is not primarily due to changes in respiratory fr equency, but rather occurs through a direct, vagally mediated action t hrough sensory neural pathways involving vagal esophageal afferents.