Prodromal Physiologic Changes During Copper Sulfate‐Induced Nausea and Vomiting: Potential Use of Intestinal EMG Recordings as a Marker for Nausea

Abstract

Although emetic responses are present during many disease states, there is no consensus regarding the physiologic changes that signal the onset of nausea. In this study, 10 adult felines (6 males and 4 females) were instrumented to chronically record, during the awake state, the electrocardiogram, diaphragm and abdominal muscle electromyographic (EMG) activity, and EMG activity from the stomach and duodenum before and after the gavage or intragastric infusion of saline or copper sulfate (CuSO4, doses ranging from 83 to 322 mg). Intragastric CuSO4 is a prototypical emetic stimulus that triggers emesis primarily by activating a gastrointestinal vagus nerve‐to‐brain pathway. CuSO4 infusion elicited a significant increase in heart rate, decrease in respiratory rate, and a disruption in gastric (baseline~6 CPM, cycles‐per‐minute) and intestinal (baseline~20 CPM) EMG activity several minutes prior to vomiting (see Fig. 1). The change in EMG activity was most consistent in the intestine. Administration of saline did not induce these physiologic changes. Increasing the dose of CuSO4 did not alter the physiologic changes induced by the treatment. In some animals, a second bout of vomiting occurred following the first episode, when prodromal changes of the intestinal EMG were less pronounced. It is postulated that the intestinal EMG activity was related to a retrograde movement of chyme from the intestine to the stomach. These findings suggest that monitoring of intestinal EMG activity may be the best indicator of the onset of nausea following treatments and in disease conditions associated with emesis.