Effects of postgastric 13C-acetate processing on measurement of gastric emptying: a systematic investigation in health

P>Uniform postgastric processing of the gastric emptying (GE) marker C-13-acetate (Ac) is an unverified assumption behind its widespread application to measure GE. This study assessed the postgastric processing of Ac administered by intraduodenal (i.d.) infusion simulating different physiological conditions. (CO2)-C-13 in breath was assessed in three groups of six volunteers after i.d. administration of A: Different caloric densities (0.75/1.5/3 kcal min(-1)) in a 200 mL meal at constant 1 mg Ac min(-1) simulating a physiological range of nutrient delivery rates; B: different tracer delivery rates (0.5/1.0/2.5 mg Ac min(-1)) simulating delayed, normal and increased GE; C1: a 500 mL meal resulting in same marker and caloric delivery compared to protocol A; C2: 50 mL water bolus injections of 12.5/25/50/100 mg Ac and C3 bolus injections of 50 mg Ac in 50/100/200 mL water in randomized order. A: (CO2)-C-13 excretion was independent of caloric load (P = 0.59). B: The dynamic of (CO2)-C-13 excretion was modulated by tracer elimination which was in turn dependent on the speed of tracer delivery, i.e. with faster deliveries resulting in lower (CO2)-C-13 recovery during infusion (P < 0.001). C: Increasing Ac doses resulted in decreased (CO2)-C-13 recovery (P < 0.001) over the first hour. (CO2)-C-13 recovery kinetics was independent of the volume delivered. This study shows C-13-acetate absorption and metabolism is independent of the volume and caloric delivery of test meals. The 'lag' in estimates of GE derived from (CO2)-C-13 breath tests is due to a postgastric, dose-dependent delay to (CO2)-C-13 elimination. This can be corrected for in analytical derivations of GE parameters based on C-13-acetate breath test measurements.