These oligosaccharides pass through the small intestine largely unchanged, and when they reach the large intestine, bacteria ferment them, producing copious amounts of flatus.When excessive or malodorous, flatus can be a sign of a health disorder, such as irritable bowel syndrome, celiac disease, non-celiac gluten sensitivity or lactose intolerance. It can also be caused by certain medicines, such as ibuprofen, laxatives, antifungal medicines or statins. Some infections, such as giardiasis, are also associated with flatulence.Interest in the causes of flatulence was spurred by high-altitude flight and human spaceflight; the low atmospheric pressure, confined conditions, and stresses peculiar to those endeavours were cause for concern. In the field of mountaineering, the phenomenon of high altitude flatus expulsion was first recorded over two hundred years ago. Mechanism
Production, composition, and odor
Flatus (intestinal gas) is mostly produced as a byproduct of bacterial fermentation in the gastrointestinal (GI) tract, especially the colon. There are reports of aerophagia (excessive air swallowing) causing excessive intestinal gas, but this is considered rare.Over 99% of the volume of flatus is composed of odorless gases. These include oxygen, nitrogen, carbon dioxide, hydrogen and methane. Nitrogen is not produced in the gut, but a component of environmental air. Patients who have excessive intestinal gas that is mostly composed of nitrogen have aerophagia. Hydrogen, carbon dioxide and methane are all produced in the gut and contribute 74% of the volume of flatus in normal subjects.
A polymerase chain reaction for tuberculous DNA may be done, or adenosine deaminase or interferon gamma levels may also be checked.The most common causes of exudative pleural effusions are bacterial pneumonia, cancer (with lung cancer, breast cancer, and lymphoma causing approximately 75% of all malignant pleural effusions), viral infection, and pulmonary embolism. Another common cause is after heart surgery when incompletely drained blood can lead to an inflammatory response that causes exudative pleural fluid. Conditions associated with exudative pleural effusions:
Parapneumonic effusion due to pneumonia
Malignancy (either lung cancer or metastases to the pleura from elsewhere)
Infection (empyema due to bacterial pneumonia)
Trauma
Pulmonary infarction
Pulmonary embolism
Autoimmune disorders
Pancreatitis
Ruptured esophagus (Boerhaaves syndrome)
Rheumatoid pleurisy
Drug-induced lupus

Other/ungrouped
Other causes of pleural effusion include tuberculosis (though stains of pleural fluid are only rarely positive for acid-fast bacilli, this is the most common cause of pleural effusions in some developing countries), autoimmune disease such as systemic lupus erythematosus, bleeding (often due to chest trauma), chylothorax (most commonly caused by trauma), and accidental infusion of fluids. Less common causes include esophageal rupture or pancreatic disease, intra-abdominal abscesses, rheumatoid arthritis, asbestos pleural effusion, mesothelioma, Meigss syndrome (ascites and pleural effusion due to a benign ovarian tumor), and ovarian hyperstimulation syndrome.Pleural effusions may also occur through medical or surgical interventions, including the use of medications (pleural fluid is usually eosinophilic), coronary artery bypass surgery, abdominal surgery, endoscopic variceal sclerotherapy, radiation therapy, liver or lung transplantation, insertion of ventricular shunt as a treatment method of hydrocephalus, and intra- or extravascular insertion of central lines.