title: The carbon dioxide production rate assumption biases gastric emptying parameters in healthy adults.
abstract: BACKGROUND
  An altered gastric emptying (GE) rate has been implicated in the aetiology of obesity. The (13)C-octanoic acid breath test (OBT) is frequently used to measure GE, and the cumulative percentage of (13)C recovered (cPDR) is a common outcome measure. However, true cPDR in breath is dependent on accurate measurement of carbon dioxide production rate (VCO(2)). The current study aimed to quantify differences in the (13)C OBT results obtained using directly measured VCO(2) (VCO(2DM)) compared with (i) predicted from resting VCO(2) (VCO(2PR)) and (ii) predicted from body surface area VCO(2) (VCO(2BSA)).
  
  
  METHODS
  The GE rate of a high-fat test meal was assessed in 27 lean subjects using the OBT. Breath samples were gathered during the fasted state and at regular intervals throughout the 6-h postprandial period for determination of (13)C-isotopic enrichment by continuous-flow isotope-ratio mass spectrometry. The VCO(2) was measured directly from exhaled air samples and the PDR calculated by three methods. The bias and the limits of agreement were calculated using Bland-Altman plots.
  
  
  RESULTS
  Compared with the VCO(2DM), the cPDR was underestimated by VCO(2PR) (4.8%; p = 0.0001) and VCO(2BSA) (2.7%; p = 0.02). The GE T(half) was underestimated by VCO(2PR) (13 min; p = 0.0001) and VCO(2BSA) (10 min; p = 0.01), compared with VCO(2DM).
  
  
  CONCLUSIONS
  The findings highlight the importance of directly measuring VCO(2)production rates throughout the (13)C OBT and could partly explain the conflicting evidence regarding the effect of obesity on GE rates.
authors: Hugh Sinclair Unit of Human Nutrition and Institute for Cardiovascular and Metabolic Research, Department of Food and Nutritional Sciences, University of Reading, Whiteknights Campus, Reading, UK.
authors: Oonagh
authors: O
authors: Markey
authors: Amir
authors: A
authors: Shafat
mesh_terms: D000328:Adult; D001944:Breath Tests / Q000379:methods*; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D003627:Data Interpretation, Statistical; D005260:Female; D005746:Gastric Emptying / Q000502:physiology*; D006801:Humans; D008297:Male
chemical_list: D002245:Carbon Dioxide