Mechanics of vomiting: a minireview

Abstract

In a cineradiographic analysis of the vomiting reflex in response to i.v. administration of an emetic drag (lanatoside C, 12 mg/kg) in cats, it was shown that the vomiting act is preceded by cyclic periods of abnormal peristaltic activity of the small bowel and inhibition of gastric peristalsis. It was further observed that massive antiperistalsis of the upper small bowel with reflux into the stomach is a common occurrence in the period immediately preceding vomiting. The emetic act itself is composed of phases of esophageal dilation, gastric emptying, gastric reflux, and esophageal collapse in cyclic repetition. The response of the esophagus and the stomach during emesis is passive, with external pressures and forces apparently providing the expulsive forces, the gastric bolus being contained by contraction of the pylorus and probably an upper esophageal or pharyngeal barrier. Earlier studies were conducted in cats in which observations were made on changes in thoracic venous pressure, abdominal venous pressure, and arterial blood pressure associated with vomiting induced by Veratrum alkaloids. Retching was characterized by a growing series of brief negative inthrathoracic pressure pulses mirrored by positive pressure pulses in the abdomen. Expulsion then occurred and was followed with a sudden reversal of intrathoracic pressure from negative to positive. Expulsion involved a more sustained abdominal contraction, but both retching and expulsion were brought about by the same set of muscles, according to their EMG profiles. From results observed following phrenicotomy and spinal cord section at T5, it was concluded that the diaphragm, acting together with the inspiratory muscles against a closed glottis, is responsible for the negative intrathoracic pressure that occurs in retching. It was also concluded that the abdominal musculature is responsible for the positive pressure generated in the abdomen during retching and expulsion, and which in the latter phase is transmitted into the thorax by an upward shift of the diaphragm.Key words: emesis, cineradiography, peristalsis, motility, tachyarrythmia.