Factors influencing pulmonary methane excretion in man. An indirect method of studying the in situ metabolism of the methane-producing colonic bacteria.

Measurements of pulmonary excretion of methane (CH(4)) were used to obtain information on the CH(4)-producing bacteria in man. Preliminary studies indicated that (a) all CH(4) excreted by man is produced by colonic bacteria, (b) there is no appreciable utilization of CH(4) by man, and (c) breath CH(4) can serve as a relatively accurate indicator of CH(4) production in the intestine. The rate of pulmonary CH(4) excretion varied enormously, ranging from undetectable (<5 x 10(-6) ml/min) to 0.66 ml/minute. In general, the CH(4) excretion rate for subjects was consistently very low (nonproducers) or relatively large (producers). 33.6% of the adult population were producers of CH(4). Whereas diet, age over 10 yr, and sex did not influence the rate of CH(4) production, some familial factor appeared to play an important role. 84% of siblings of CH(4) producers also were producers, while only 18% of the siblings of nonproducers were found to be CH(4) producers. This familial tendency appeared to be determined by early environmental rather than genetic factors. These studies of CH(4) excretion demonstrate that the exposure of individuals to intestinal bacterial metabolites may differ markedly and that these differences may be chronic and determined by familial factors.

Effect of dietary fiber on intestinal gas production and small bowel transit time in man.

The influence of dietary fiber on intestinal gas production and on small bowel transit time was studied in eight healthy subjects using breath H2 excretion as an indicator of colonic gas production. Hydrogen excretion following ingestion of bran was substantially less than that following ingestion of lactulose, a nonabsorbable fermentable sugar. Likewise, human fecal homogenates produced only about 10% as much H2 and CO2 during incubation with bran as with glucose or lactulose. Thus, the polysaccharides in bran appear to be relatively poor substrate for colonic bacterial gas production, and reported gas-related symptoms after bran ingestion may be due to some other mechanism. The small bowel transit time of bran was greater than that of lactulose; however, addition of bran to lactulose did not slow lactulose transit.

Quantitative measurement of lactose absorption.

The quantity of lactose not absorbed by 4 normal and 6 lactase-deficient subjects was determined by three indirect methods which involved: (1) measurement of pulmonary hydrogen (H2) excretion, (2) pulmonary (14)CO2 excretion, and (3) stool (14)C excretion, after ingestion of 12.5 g of 1-(14)C-lactose and 4 g of polyethylene glycol (PEG). Results were compared with absorption determined directly from the (14)C:PEG ratio of multiple terminal ileal aspirates. The fraction of lactose not absorbed determined by ileal aspiration ranged from 0 to 8% in normals and 42 to 75% in mild-intolerant subjects. Whereas all three indirect methods were useful in qualitatively separating normal from deficient subjects, the quantity of lactose absorbed as determined by H2 excretion correlated most closely with ileal measurements (r = 0.94). Pulmonary (14)CO2 excretion for 24 hr after (14)C-lactose ingestion did not distinguish normal (17 +/- 4% (SEM) of ingested (14)C per 24 hr) from lactase-deficient subjects (21.1 +/- 3%). Likewise, stool (14)C:PEG ratios grossly underestimated malabsorption with less than one-quarter of the nonabsorbed (14)C appearing in the stool. This study suggests that individual differences in susceptibility to diarrhea after milk ingestion by lactase-deficient subjects may be due to differences in the quantity of lactose not absorbed and/or differences in the rate of bacterial metabolism of lactose in the colon. Analysis of ileal fluid collected during passage of the lactose meal indicated that about two-thirds of the osmotic load delivered to the colon consists of endogenous electrolytes. Thus the water load delivered to the colon is about 3 times that calculated to be osmotically held by the nonabsorbed sugar.

Investigation of small bowel transit time in man utilizing pulmonary hydrogen (H2) measurements.

Pulmonary H2 excretion was used to quantitate the small bowel transit time in man. This technique is based on the observation that H2 is produced when carbohydrate is fermented by colonic bacteria and that this H2 production is reflected by a concomitant increase in breath H2 excretion. The time, therefore, between ingestion of the unabsorbable disaccharide, lactulose, and the rise in breath H2 represents the small intestinal transit time of the head of the lactulose load as it passes through the gut. Following ingestion of a mixture of polyethylene glycol (PEG) and lactulose by 9 subjects, transit time measured by H2 excretion correlated closely with the simultaneously determined time for PEG to reach the distal ileum (r equals 0.97). The ileal appearance of PEG preceded the rise in H2 excretion by a mean of 7.6 minutes. Transit time of 19 Gm. of lactulose in 40 healthy subjects averaged 72 minutes (range 25 to 118). Studies repeated 3 to 5 times in 6 subjects showed good individual reproducibility with subsequent measurements differing from initial by a mean of plus or minus 14 per cent. There was an inverse relation between transit time and dose of lactulose ingested by 9 subjects with 5, 10 and 20 Gm. of lactulose having mean transit times of 128 plus or minus 19, 94 plus or minus 15, and 40 plus or minus 8 (S$M.) minutes, respectively. This technique appears to provide a simple, safe, and noninvasive means of studying small bowel transit time in man.

Colonic concentrations of hydrogen and methane following colonoscopic preparation with an oral lavage solution.

Explosions are a rare complication of electrocautery in the colon. The cause of these explosions is ignition of gas containing hydrogen (greater than 4%) or methane (greater than 5%), and oxygen. Hydrogen and methane are products of colonic bacterial metabolism. Oral solutions used for colonoscopy preparation are designed to cleanse the colonic lumen but provide no substrate for fermentation reactions. In 52 patients undergoing colonoscopy, gas samples were collected from the right, transverse, and left colon and analyzed for hydrogen, methane, oxygen, and carbon dioxide. The highest hydrogen and methane concentrations were 0.6% and 0.7%, respectively, less than 16% of the explosive level. Oxygen and carbon dioxide concentrations were close to those of air, suggesting that the bulk of colonic gas was air infused during the procedure. We conclude that the concentrations of explosive gases are well below the hazardous levels when oral colonic cleansing solutions and standard colonoscopic procedures are employed.

Colonic conservation of malabsorbed carbohydrate.

[14C]Sucrose absorption was studied in 4 healthy controls and 4 patients after jejunoileal bypass using an ileal perfusion technique which made it possible to distinguish 14C-absorption in the small bowel from that occurring in the colon. Healthy controls failed to absorb 2--4% of a 50-g dose of [14C]sucrose in the small bowel; however, virtually none of the [14C] appeared in feces in a dialyzable form with appreciable osmotic activity. In bypass patients, the small bowel failed to absorb 29--84% of the 50-g dose of [14C]sucrose. Approximately two-thirds of the nonabsorbed [14C] was in the form of sucrose and the remainder was nearly all present as monosaccharides. A mean of only 42% of the [14C] Not absorbed in the small bowel appeared in the feces and only about one-third of this fecal [14C] was in a dialyzable form with appreciable osmotic activity. Thus, the colon plays an important role in carbohydrate malabsorption by salvaging carbohydrate and reducing osmotic activity of the nonabsorbed sugar. This conlonic function appears to depend upon bacterial metabolism of the carbohydrate, and individual variations in diarrhea and weight loss associated with carbohydrate malabsorption could reflect individual differences in the bacterial flora of the colon.