A Paradigm Shift in Evaluating and Investigating the Etiology of Bloating

Visceral hypersensitivity

Visceral hypersensitivity is explained by an increased perception of gut mechano-chemical stimulation, which typically manifests in an aggravated feeling of pain, nausea, distension, and ABD.¹⁰ In the gut, food particles and gut bacteria and their derived molecules interact with neuroimmune and enteroendocrine cells causing visceral sensitivity by the proximity of gut’s neurons to immune cells activated by them and leading to inflammatory reactions (Figure 1).

^{Dr. Singh and Dr. Moshiree}

Figure 1. Proposed pathophysiological mechanisms underlying abdominal bloating/distension.

Pelvic floor dysfunction

Patients with anorectal motor dysfunction often experience difficulty in effectively evacuating both gas and stool, leading to ABD.¹² Impaired ability to expel gas and stool results in prolonged balloon expulsion times, which correlates with symptoms of distention in patients with constipation.

^{Atrium Health}

Dr. Baharak Moshiree

Abdominophrenic dyssynergia

Abdominophrenic dyssynergia is characterized as a paradoxical viscerosomatic reflex response to minimal gaseous distention in individuals with FABD.¹³ In this condition, the diaphragm contracts (descends), and the anterior abdominal wall muscles relax in response to the presence of gas. This response is opposite to the normal physiological response to increased intraluminal gas, where the diaphragm relaxes and the anterior abdominal muscles contract to increase the craniocaudal capacity of the abdominal cavity without causing abdominal protrusion.¹³ Patients with FABD exhibit significant abdominal wall protrusion and diaphragmatic descent even with relatively small increases in intraluminal gas.¹¹ Understanding the role of abdominophrenic dyssynergia in abdominal bloating and distention is essential for effective diagnosis and management of the patients.

Gut dysmotility

Gut dysmotility is a crucial factor that can contribute to FABD. Gut dysmotility affects the movement of contents through the GI tract, accumulating gas and stool, directly contributing to bloating and distention. A prospective study involving over 2000 patients with functional constipation and constipation predominant-IBS (IBS-C) found that more than 90% of these patients reported symptoms of bloating.¹⁴ Furthermore, in IBS-C patients, those with prolonged colonic transit exhibited greater abdominal distention compared to those with normal gut transit times. In patients with gastroparesis, delayed gastric emptying resulting in prolonged retention of stomach contents is the main factor in the generation of bloating symptoms.⁴

Small intestinal bacterial overgrowth (SIBO)

SIBO is overrepresented in various conditions, including IBS, FD, diabetes, gastrointestinal (GI) surgery patients and obesity, and can play an important role in generating ABD. Excess bacteria in the small intestine ferment carbohydrates, producing gas that stretches and distends the small intestine, leading to these symptoms. Additionally, altered sensation and abnormal viscerosomatic reflexes may contribute to SIBO-related bloating.⁴ One recent study noted decreased duodenal phylogenetic diversity in individuals who developed postprandial bloating.¹⁵ Increased methane levels caused by intestinal methanogen overgrowth, primarily the archaea Methanobrevibacter smithii, is possibly responsible for ABD in patients with IBS-C.¹⁶ Testing for SIBO in patients with ABD is generally only recommended if there are clear risk factors or severe symptoms warranting a test-and-treat approach.