Mechanisms of high-frequency electrical stimulation of the stomach in gastroparetic patients.

Previous studies have demonstrated that high frequency and low energy gastric electrical stimulation (GES) reduced nausea and vomiting in gastroparetic patients without improving gastric emptying. The mechanisms of action for this have not been clarified. The aim of our study was to investigate the effects of GES on autonomic function, gastric distention and tone, and central control mechanism in gastroparetics patients. 10 gastroparetic patients refractory to standard medical therapy participated in this study and data were collected at baseline session, within two weeks before surgery for implantation of GES system, and at follow-up sessions between 6 to 12 weeks after GES therapy. In each session, electrocardiogram and gastric barostat measurements were conducted before and after a caloric liquid meal. Positron Emission Tomography (PET) brain scans were performed on a separate day. Analysis of autonomic function was accomplished through power spectral analysis of heart rate variability which revealed that the sympthovagal balance was significantly decreased after GES therapy, indicating a significant increase in vagal activity. Results from gastric barostat measurements demonstrated that during GES there was a significant increase in the discomfort threshold for both pressure and volume. Quantitative analysis of PET imaged cerebral activity showed that chronic GES increased thalamic activity. This study suggests that the symptomatic efficacy achieved by GES may be partly attributed to enhanced vagal autonomic function, decreasing gastric sensitivity to volume distention which simulates a postprandial adaptation and the activation of central control mechanisms for nausea and vomiting through thalamic pathways during GES.