Evaluation of an extremely flatulent patient: case report and proposed diagnostic and therapeutic approach

Reappraisal of H2S/sulfide concentration in vertebrate blood and its potential significance in ischemic preconditioning and vascular signaling

Hydrogen sulfide (H(2)S) is rapidly emerging as a biologically significant signaling molecule. Studies published before 2000 report low or undetectable H(2)S (usually as total sulfide) levels in blood or plasma, whereas recent work has reported sulfide concentrations between 10 and 300 microM, suggesting it acts as a circulating signal. In the first series of experiments, we used a recently developed polarographic sensor to measure the baseline level of endogenous H(2)S gas and turnover of exogenous H(2)S gas in real time in blood from numerous animals, including lamprey, trout, mouse, rat, pig, and cow. We found that, contrary to recent reports, H(2)S gas was essentially undetectable (<100 nM total sulfide) in all animals. Furthermore, exogenous sulfide was rapidly removed from blood, plasma, or 5% bovine serum albumin in vitro and from intact trout in vivo. To determine if blood H(2)S could transiently increase, we measured oxygen-dependent H(2)S production by trout hearts in vitro and in vivo. H(2)S has been shown to mediate ischemic preconditioning (IPC) in mammals. IPC is present in trout and, unlike mammals, the trout myocardium obtains its oxygen from relatively hypoxic systemic venous blood. In vitro, myocardial H(2)S production was inversely related to Po(2), whereas we failed to detect H(2)S in ventral aortic blood from either normoxic or hypoxic fish in vivo. These results provide an autocrine or paracrine mechanism for myocardial coupling of hypoxia to H(2)S in IPC, i.e., oxygen sensing, but they fail to provide any evidence that H(2)S signaling is mediated by the circulation.

Rectal luminal Pr(CO2), measured by automated air tonometry, does not reflect gastric luminal Pr(CO2) in children

Rectal luminal regional P(CO2) (Pr(CO2)) was compared with gastric luminal Pr(CO2) measured by automated air tonometry at intervals of 10 min in 20 children aged 6-16 years scheduled for elective surgery under general anesthesia. In 5 patients, measurement of rectal Pr(CO2) failed because of catheter-related problems. In the remaining 15 children, aged 10.6 +/- 2.5 years, 19 +/- 7 paired rectal and gastric Pr(CO2) values (n total, 241) were measured. Bias and precision for gastric compared to rectal Pr(CO2) was -1.79 kPa and 2.89 kPa. In patients with obvious feces in the rectum, bias (precision) for gastric compared to rectal Pr(CO2) was -2.7 kPa (2.6 kPa) and in those with empty rectum, -0.75 kPa (1.42 kPa; t-test; P < 0.001). Based on our in vivo data, rectal luminal Pr(CO2), measured by automated air tonometry, does not reflect gastric luminal Pr(CO2) in children. Enteral luminal gas production within feces in the rectum seems to be a major source of this disagreement.

Aerophagia and Intestinal Gas

Aerophagia refers to a rather rare disorder that may occur in both children and adults that features repetitive air swallowing and belching and that may result in abdominal distention. There are few, if any, controlled studies to guide therapy, which remains largely supportive but may include behavioral therapy and psychotherapy. Bloating, distention, and other gas-related symptoms are common in functional gastrointestinal disorders, including the irritable bowel syndrome; their pathophysiology remains, for the most part, poorly understood. Two separate phenomena need to be distinguished in these disorders: gas production and gas perception. Thus, whereas gas production, which relates most closely to flatus emissions, is probably within the normal range in most patients with irritable bowel syndrome, gas transport or transit through the gut may be impaired and may lead to the retention of gas within segments of the gut. Visceral hypersensitivity, a common phenomenon in all functional disorders, may exacerbate the sensation of distention and contribute to other "gas-related" symptoms. Few controlled studies have addressed any of these issues. Although, on an empiric basis, dietary therapy may be partially effective in some situations, there is at present no data to support the use of any form of pharmacologic, endoscopic, or surgical therapy for any of these symptoms.