Nausea and vomiting occur from a large variety of causes and diseases involving several systems, including some neurologic disorders. The mechanisms of nausea and vomiting, which are often used as a basis for development of drugs to counteract the nausea and vomiting associated with surgery, chemotherapy, and radiation, are described in this article. Severe and prolonged vomiting can also produce neurologic disturbances.
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• Vomiting can be the initial manifestation of a neurologic disorder such as raised intracranial pressure.
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• Investigation of vomiting includes consideration of neurologic and gastrointestinal disorders as well as system diseases or the action of drugs or toxins.
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• Vomiting is under the control of a "vomiting center" in the reticular formation, and a chemoreceptor trigger zone in the area postrema of the floor of the fourth ventricle.
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• Several methods of treatment are available for the control of nausea and vomiting.
Historical note and terminology
Although nausea and vomiting may occur independently of each other, nausea frequently precedes vomiting, and both are likely mediated by the same neural pathways. Nausea is an imminent desire to vomit, whereas vomiting is the oral expulsion of gastric contents. Nausea may or may not proceed vomiting. Vomiting is a synonym for emesis but is distinguishable from retching, rumination, and regurgitation. Retching is the rhythmic contraction of abdominal and respiratory muscles, which accompanies vomiting; if the stomach is empty, the whole process may consist of retching only. Rumination is the effortless regurgitation of undigested food within minutes of a meal accompanied by intra-abdominal muscle contraction and relaxation of the lower esophagus. Vomiting is distinguished from regurgitation, which is the expulsion of food without nausea or contraction of abdominal or diaphragmatic muscles. It is usually seen with gastroesophageal reflux disease due to incompetence of the lower esophageal sphincter.
Historically, nausea and vomiting have been recognized as symptoms of systemic and gastrointestinal diseases. Vomiting was described as a manifestation of neurologic disorders such as migraine. In the second century, Galen thought there was a connection between the stomach and the brain because of the nausea and vomiting that would accompany an attack of migraine. Area postrema was first described anatomically in 1896, but no function was assigned to it (26). In 1951 area postrema was identified as a chemoreceptor trigger zone in vomiting responses (03). Since then, the chemoreceptor zone has been described as participating in a range of functions other than emesis: water and electrolyte balance, drinking, sleep wakefulness cycles, osmoreceptor cardiovascular responses to angiotensin II, and neurosecretion.
Patients with nausea and vomiting are seen both by neurologists and gastroenterologists, as well as several other specialties. Investigation of chronic nausea and vomiting now falls in the realm of the emerging field of neurogastroenterology, which studies the disorders of the enteric nervous system.