Are Bloating and Abdominal Distention Attributed to Gas Production and Visceral Sensitivity in Irritable Bowel Syndrome? (Am J Gastroenterol 2013;108:1516-1525)

Bloating and abdominal distension are common symptoms in patients with irritable bowel syndrome (IBS). Bloating is considered as a subjective sensation and abdominal distention as an objective sign, i.e., the visible increase in abdominal girth.1,2 They can be related to each other or not. Recently, Zhu et al3 evaluated the effects of dietary factors on abdominal bloating and distention and the underlying pathophysiology in IBS. More specifically, they assessed the effects of gas production and visceral hypersensitivity on gastrointestinal (GI) symptoms after lactose ingestion in a population with lactase deficiency. IBS patients (n = 277) and healthy controls (HCs, n = 64) underwent a 20 g lactose hydrogen breath test (LHBT) for evaluation of hydrogen gas production and lactose intolerance (LI) symptoms. Cumulative breath hydrogen excretion was quantified by measuring areas under the curve during LHBT. Five digestive symptoms characteristic of LI (bloating, borborygmi, nausea, pain and diarrhea) were recorded at 15-minute intervals on a scale of 0-4 for 3 hours. Subjects who reported more than one point rise in LI symptoms during the LHBT were diagnosed as LI. Abdominal girth (199 IBS, 40 HCs) was measured in the standing and supine position, before and after LHBT, to evaluate the abdominal distension, using an inextensible metric tape measure over the umbilicus. Abdominal distention was defined to be increased by a minimum distention level of ≥ 0.5 cm. Rectal sensitivity (74 IBS, 64 HCs) was assessed by barostat studies and visceral hypersensitivity was defined as below the 5.0 percentile limit for sensory threshold to discomfort/pain obtained from HCs. In the results, cumulative hydrogen excretion (AUC) during LHBT showed no difference between the groups (P = 0.485) and the prevalence of abdominal distention after lactose ingestion (standing: 58% vs. 72.5%, P = 0.083; supine: 65% vs. 75%, P = 0.213) was similar. In contrast, LI was more frequent in IBS (53.8 vs. 28.1%, P < 0.001), especially bloating (39.0 vs. 14.1%, P < 0.001) and borborygmi (39.0 vs. 21.9 %, P = 0.010). Only 59.0% of patients with bloating had distention. Hydrogen production as well as bloating score was not associated with girth increment. In the multivariate analysis for the factors associated with LI symptom severity, hydrogen production increased bloating (odds ratio [OR], 2.19; 95% confidence interval [CI], 1.09-4.39; P = 0.028) and borborygmi (OR, 12.37; 95% CI, 3.34-45.83; P < 0.001) but not distention (P = 0.673). Visceral hypersensitivity was associated with bloating (OR, 6.61; 95% CI, 1.75-25.00; P = 0.005) and total symptom score (OR, 3.78; 95% CI, 1.30-10.99; P = 0.014). The authors concluded that hydrogen gas production and visceral hypersensitivity both contribute to bloating and borborygmi, in IBS patients after lactose ingestion. Objective abdominal distention is not correlated with subjective bloating as well as gas production.