Mechanics of vomiting: a minireview

Area of Science:

• Gastroenterology
• Physiology
• Pharmacology

Background:

• Vomiting is a complex reflex with poorly understood mechanisms.
• Previous studies explored pressure changes during vomiting but lacked detailed kinematic analysis.

Purpose of the Study:

• To elucidate the kinematic and dynamic aspects of the vomiting reflex in cats.
• To analyze the role of gastrointestinal motility and pressure changes during emesis.

Main Methods:

• Cineradiographic analysis of vomiting induced by intravenous lanatoside C in cats.
• Electromyography (EMG) of muscles involved in retching and expulsion.
• Investigation of the effects of phrenicotomy and spinal cord section.

Main Results:

• Vomiting is preceded by abnormal small bowel peristalsis and inhibited gastric peristalsis.
• Massive antiperistalsis of the upper small bowel with gastric reflux is observed before vomiting.
• The emetic act involves cyclic phases of esophageal dilation, gastric emptying, gastric reflux, and esophageal collapse.
• External pressures, not intrinsic esophageal/gastric forces, drive expulsion, with pyloric and pharyngeal barriers containing the gastric bolus.
• Retching involves negative intrathoracic and positive abdominal pressure pulses; expulsion shows a positive intrathoracic pressure shift.
• The diaphragm and inspiratory muscles against a closed glottis generate negative intrathoracic pressure during retching.

Conclusions:

• The vomiting reflex is a coordinated act involving specific patterns of gastrointestinal motility and pressure dynamics.
• The diaphragm plays a crucial role in generating the negative intrathoracic pressure characteristic of retching.