Disorders of the gastrointestinal system impact a significant portion of the population, yet few diagnostic techniques provide reliable details about underyling physiology .and pathophysiology, which are still not well understood despite recent advances that have elucidated the role of interstitial cells of Cajal as the pacemakers and propagators of gastric electrical activity (GEA). Cutaneous electrogastrography (EGG) represents the only commonly available method to assess GEA noninvasively. Over the past 12years, our group has shown that the magnetogastrogram (MGG) accurately reflects both normal internal GEA and changes to the gastric slow wave caused by abnormal conditions. The MGG avoids many of the problems inherent to the EGG since it measures magnetic fields instead of electric potentials, which are smoothed and attenuated by the abdomen. In addition to signal frequency dynamics, which can be determined from cutaneous EGG, multichannel vector MGG also provides for a spatiotemporal characterization of the propagation of GEA. Studies from our new state-of-the-art clinical facility, the Vanderbilt University Gastrointestinal SQUID Technology (VU-GIST) Laboratory have demonstrated the ability to detect gastric uncoupling associated with diabetic gastroparesis and the spiking electrical response activity (ERA) magnetically. In this proposal, we wish to further investigate the relative ability of the MGG and EGG to assess GEA. We will study (1) the effect of abdominal volume conduction and body mass index (BMI) on the EGG and MGG slow waves, (2) changes in the EGG and MGG resulting from diabetic and idiopathic gastroparesis, (3) the effect of pharmacological agents that both reduce and enhance GEA on the EGG and MGG, and (4) the relative ability of the EGG and MGG to noninvasively detect spiking ERA and the influence of abdominal layers on the detection of spiking ERA. In addition to our external noninvasive measurements of cutaneous EGG and MGG, we will design and construct an intraluminal nasogastric catheter that will allow us to simultaneously measure intraluminal gastric pressure and mucosal electrical activity. These simultaneous measurements will help us correlate events observed in external EGG and MGG with the actual internal electrical and mechanical activities. We expect that the MGG will provide a new, noninvasive method to help characterize a variety of gastric disorders, including diabetic and idiopathic gastroparesis
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