title: Comparison of accuracy and precision of heart rate calibration methods to estimate total carbon dioxide production during 13C-breath tests.
abstract: BACKGROUND
  13C-breath tests are noninvasive tools to measure gastrointestinal function and nutritional interventions. Calculation of percentage dose recovered of 13C in exhaled breath requires knowledge of CO2 production rate (VC02). A resting value is usually assumed, but this can underestimate VC02 because subjects are unlikely to remain at rest during tests that last for many hours. There is a need for a method to estimate nonresting VC02 during 13C-breath tests.
  
  
  OBJECTIVE
  To calibrate a heart rate monitor to continually estimate VC02 during 13C-breath tests.
  
  
  METHODS
  Proof of concept study.
  
  
  METHODS
  Eight healthy adults, 10 healthy children and six children with cystic fibrosis.
  
  
  METHODS
  Heart rate and VC02 were measured simultaneously at resting and nonresting levels. A new calibration method (smoothing heart rate and fitting a sigmoid function) was compared with published methods. A [ 3C]acetate breath test was used to demonstrate the range of physical activity during breath tests.
  
  
  RESULTS
  The new calibration method was more accurate than existing methods (mean bias -0.0002%, 95% confidence interval (CI) -0.0007, 0.0003% of the mean measured VC02). Smoothing heart rate gave a more precise estimate of VC02 and a more accurate estimate of resting energy expenditure (mean bias -0.09, 95% Cl -0.22, 0.05 mmol CO2 min-' m-2 body surface area) than using raw data (mean bias -0.21, 95% Cl -0.38, -0.04 mmol CO2 min' m-2 body surface area). Physical activity level ranged from 1.0 to 2.5 in children, and 1.0 to 1.5 in adults.
  
  
  CONCLUSIONS
  Use of smoothed HR with a sigmoid function provides an accurate method of estimating nonresting VC02 during 13C-breath tests.
authors.affiliation: Division of Developmental Medicine, University of Glasgow, Yorkhill Hospitals, Glasgow, UK. C.Slater@clinmed.gla.ac.uk
authors.forename: C
authors.initials: C
authors.lastname: Slater
authors.forename: T
authors.initials: T
authors.lastname: Preston
authors.forename: L T
authors.initials: LT
authors.lastname: Weaver
mesh_terms: D000293:Adolescent; D000328:Adult; D001481:Basal Metabolism / Q000502:physiology; D001944:Breath Tests; D002138:Calibration; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D002247:Carbon Isotopes; D002648:Child; D002675:Child, Preschool; D003550:Cystic Fibrosis / Q000378:metabolism* / Q000503:physiopathology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide