A vasovagal response can occur with any unpleasant external stimulus. It is the same thing that makes people pass out when they see blood, get a shot, have emotional stress, fear, or many other things. The vagus nerve is one of 12 major nerves (cranial nerves) that come directly off the brain. It is the 10th one. It provides sensory function to the thoracic and abdominal organs and motor function for speech, swallowing, and the muscles of the thoracic/abdominal organs. It also carries sympathetic and parasympathetic outflow to these organs. Sympathetic and parasympathetic nervous function is involuntary (ie. you cannot control it), and causes things like sweating, goose bumps, changes in blood pressure, heart rate, movement of the bowels, and abdominal organ function. The vasovagal response is a very complex response, but in a nutshell, sudden stimulation of the sympathetic and parasympathetic portions of the nerve causes an episode of low blood pressure, low heart rate, and sweating (often preceded by high blood pressure, higher heart rate, and feeling hot), that makes you feel as if you are going to pass out. Actually, most people do pass out. Stimulation of the sympathic/parasympathetic system is very commonly seen with sudden severe pain and is a very common finding during myelograms. If you want more information, look up the terms vasodepressor, vasovagal, or neurocardiogenic syncope in a medical text or website. I hope that helps.
From thy aching doctor,
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