EFFECT OF COLONIC FERMENTATION ON RESPIRATORY GAS EXCHANGES MEASURED IN THE POSTABSORPTIVE STATE

To assess the effect of colonic fermentation on respiratory gas exchan ges, six methane-nonproducing healthy volunteers ingested in the posta bsorptive 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 w ithout lactulose (control solution). Six patients with short bowel and remnant colon (SBS) also ingested 90 mL lactulose syrup. Carbon dioxi de production (VCO2), oxygen consumption (VO2), 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 af ter ingestion of the control solution, VCO2 and the RQ decreased where as VO2 remained unchanged. In contrast, in healthy volunteers and pati ents with SBS, VCO2 and the RQ increased after lactulose ingestion, wh ereas VO2 did not change. The increase in VCO2 appeared to be accounte d for mainly by bacterial production of carbon dioxide and was signifi cantly related to breath-hydrogen concentration (r = 0.56, P < 0.02 fo r healthy subjects; r = 0.59, P < 0.01 for SBS subjects). A breath-hyd rogen test should be performed in conjunction with indirect calorimetr y to determine whether colonic fermentation is taking place and, if so , to correct appropriately the VCO2 value in calorimetric equations.