Effect of colonic fermentation on respiratory gas exchanges measured in the postabsorptive state

To assess the effect of colonic fermentation on respiratory gas exchanges, six methane-nonproducing healthy volunteers ingested in the postabsorptive state 1 wk apart either 90 mL lactulose syrup containing 60 g lactulose, 4 g lactose, and 7 g galactose or the same solution but without lactulose (control solution). Six patients with short bowel and remnant colon (SBS) also ingested 90 mL lactulose syrup. Carbon dioxide production (VCO 2 ), oxygen consumption (VO 2 ), respiratory quotient (RQ), and hydrogen excreted in breath were measured basally and for 4 h after the ingestion of solutions. In healthy volunteers within 4 h after ingestion of the control solution, VCO 2 and the RQ decreased whereas VO 2 remained unchanged. In contrast, in healthy volunteers and patients with SBS, VCO 2 and the RQ increased after lactulose ingestion, whereas VO 2 did not change. The increase in VCO 2 appeared to be accounted for mainly by bacterial production of carbon dioxide and was significantly related to breath-hydrogen concentration (r = 0.56, P < 0.02 for healthy subjects ; r = 0.59, P < 0.01 for SBS subjects). A breath-hydrogen test should be performed in conjunction with indirect calorimetry to determine whether colonic fermentation is taking place and, if so, to correct appropriately the VCO 2 value in calorimetric xequations.