Digestive System Research Unit, University Hospital Vall d'Hebron,
Autonomous University of Barcelona
Very little is known about the physiology of gas movement in the human gut and its putative role in the origin of abdominal symptoms. Using a gas challenge test it has been shown that most healthy subjects propulse and evacuate as much gas as infused, whereas a large proportion of patients with the irritable bowel syndrome and functional bloating retain gas and/or present abdominal symptoms. The volume of intestinal gas retention determines objective abdominal distension, but subjective perception is lower when the gut is relaxed or when pooling occurs in large capacitance regions, such as the colon. Normally intestinal gas propulsion is finely controlled by different reflex mechanisms. For instance, intraluminal lipids inhibit, but segmental gut distension accelerates gas transit. Impaired gas handling in IBS is the result of abnormal reflex control. The slowing effect of lipids is up-regulated in these patients, whereas the stimulatory effect of distension is markedly impaired. Using the gas challenge test in patients with IBS and functional bloating it was shown that retention of gas loads was effectively cleared by neostigmine administration, and reduced gas retention was associated to improvement of both abdominal distension and symptom perception. These data suggest that prokinetic, rather than conventional spasmolytic drugs, may be indicated for the treatment of abdominal bloating in patients with intestinal gas retention. In conclusion, gas transit studies in patients with IBS and functional bloating have evidenced impaired gas handling that may play a role in the pathogenesis of their symptoms.