Visceral hypersensitivity, is the experience of pain in internal organs (viscera). The pain is usually studied using some variation of balloon distention in the rectum, a procedure in which a balloon is inserted into the rectum and slowly inflated. An overall research trend, IBS sufferers experience discomfort and pain in the rectal area at reduced levels of pressure than non sufferers. This article provides an overview of current research findings regarding IBS and visceral hypersensitivity. Please remember that this is not a personal failing on the part of IBS patients. This hypersensitivity is merely the body’s way of reacting to the experience of intestinal pain.
Healthy volunteers who received glycerol, a type of laxative which triggers rapid bowel emptying, exhibited subsequent hypersensitivity. It thus appears that the experience of unusual pain or irritation can set the stage for the development of visceral hypersensitivity.
The Brain-Gut Connection
It appears likely that the visceral hypersensitivity seen in some IBS patients is a result of changes in nervous system functioning on both the level of the intestines and the brain. At the level of the gut, it seems as if nerve pathways in the gastrointestinal tract become sensitized to stimulation, resulting in over-reactivity and resulting in pain amplification.
As for the brain, brain imaging studies provide even more clues: In comparing healthy individuals with IBS patients, there are significant differences in the parts of the brain that are activated in response to pain. In individuals who do not have IBS, rectal distension triggers a response in parts of the brain that are associated with modulating pain. In IBS patients, this same rectal stimulation triggers a response in the parts of the brain associated with vigilance and anxiety -- parts of the brain that serve to amplify the sensation of pain.
Is Inflammation Involved?
Preliminary research is beginning to point to the existence of a mild inflammatory process, particularly in post-infectious IBS (IBS-PI) cases. The cells involved in this inflammatory process are very close to GI nerve cells and thus may contribute to the sensitization that result in pain amplification. This is a very new, but exciting avenue in IBS research.
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