Michael Ash BSc(Hons).DO. ND. FDipION reviews the current understanding behind bloating and distension.
The unpleasant symptoms of bloating and abdominal distension are common and bothersome, affecting up to 96% of patients with functional gastrointestinal disorders (such as IBS) and an estimated 30% of the general population. Clear pathophysiologic explanations have been lacking and available treatment options can appear contradictory and ineffective. Treatments will be explored in a follow up review.
Bloating refers to the subjective sensation of abdominal swelling, whereas visible abdominal distension refers to an actual increase in abdominal girth. For a long time, these have been poorly understood symptoms, but recent studies, have shed some light on the different mechanisms involved in the generation of these symptoms and summarised in this review.,
Specialised measuring devices called abdominal inductance plethysmography (a test used to measure changes in blood flow or air volume in different parts of the body) and computed tomography ((CT) A diagnostic technique in which x-rays are taken in many different directions. A computer synthesises the x-rays to generate cross-sectional and other images of the body) have convincingly demonstrated that distension of the abdomen is a real event with some patients exhibiting as much as a 12cm increase in abdominal girth.
However, bloating and distension are not always present at the same time. In IBS studies only half of ‘bloated patients’ also have visible distension. This sub group of ‘bloated and distended’ patients tend to present with constipation and visceral hyposensitivity, whereas the simply ‘bloated’ group present more frequently with diahorrea and visceral hypersensitivity.
The more severe the bloating the greater the change in rectal perception (The lower threshold for pain or discomfort in response to distension). It may well be that bloating and distension have a mix of common and uncommon causes.
Click on the image below to see an enlarged model of possible causes and exacerbating factors in the development of bloating and distension. This diagram was extracted from: Gastroenterology. Volume 136, Issue 5, May 2009, Pages 1487-1490
- ‘Too much gas’. Despite the immediate instinctive sense that this must be correct, detailed studies have failed to demonstrate this as a substantive cause.
- Abnormal colonic fermentation has been suggested in some studies.
- Defective handling of exogenous gas loads within the GI tract in patients with bloating has been convincingly identified in several studies of patients with IBS complaining of bloating. Especially in terms of transit of gas and tolerance (pain) of it.
- Mechanistically, an altered GI reflex activity and enhanced sensitivity to nutrients (intolerances) have been found to be important factors involved in the impaired gas transit in these patients, as well as in symptom perception., These symptoms mostly emanate from the small rather than the more logical large intestine.
- These studies suggest that IBS patients do not necessarily have to produce more ‘gas’ to have ‘gas-related’ symptoms, instead these may be due to motor dysfunction, producing a transport problem, and enhanced visceral sensitivity.
- Another possibility is focal gas pooling which may release abnormal viscerosomatic (a muscular response to stimulation of a nerve-receptor organ in a visceral organ) responses, resulting in bloating and visible abdominal distension.of the diaphragm.
- Excess lumbar lordosis, (forward curvature of the spine, producing a hollow in the back) weak abdominal musculature, and voluntary protrusion of the abdomen have been suggested to be of importance in the generation of bloating and abdominal distension, but none of these alterations could be confirmed by a CT study.
- However, a number of other careful studies comparing healthy volunteers and patients, have provided important explanations of abdominal distension in patients with functional GI disorders. They show that abdominal accommodation to volume loads is an active process involving local muscular response and that patients with IBS and bloating have impaired viscerosomatic reflexes and abdominal wall muscular control. In patients with bloating, abdominal perception and distension in response to intra-abdominal volume increments are exaggerated markedly and associated with muscular dystony (a disorder characterised by unusual or involuntary movements or muscular spasms) of the abdominal wall.,
- Comparing two different groups of patients with bloating revealed two different mechanisms:
- Group 1: IBS patients with bloating,
- Group 2: Intestinal dysmotility (Food fails to move normally through the stomach and intestines, there often is distension of the stomach and intestines as fluid collects, and is frequently painful) and bloating.
Both sets were scanned with CT at ease and during bloating. At ease they were the same but once bloated there were differences:
- Patients with intestinal dysmotility demonstrated a true increase in total abdominal volume with upward movement of their diaphragm.
- IBS patients had a very modest increment of the abdominal volume; instead the abdominal distension was related to downward movement of the diaphragm, placing stress on the phrenic nerve (this innervates the diaphragm and controls breathing), resulting in forward (distension) redistribution of abdominal contents.
Other less well-established/studied factors of potential importance are:
- Abnormal mucosal immune activation. A large subset of IBS patients show gender-dependent mucosal infiltration of white blood cells and histamine correlating with abdominal bloating and dysmotility-like dyspepsia (Chronic or recurrent pain in the upper abdomen) ,
- Altered bacterial flora, investigations using sophisticated measuring techniques have revealed that the faecal flora in patients with IBS is different from healthy controls. If this is a trigger rather than a result, changing the floral balance may provide therapeutic outcomes with little risk if probiotics rather than antibiotics are used.,,,,
- Sex hormones in which changes in the production of female related oestrogen and progesterone influence IBS, bloating and bowel function.
- Psychological factors, including somatisation (The presence of real and significant physical symptoms that cannot be explained by a medical condition, but are instead a manifestation of anxiety or other mental distress).
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