Original Article
European Journal of Clinical Nutrition (2006) 60, 69–76. doi:10.1038/sj.ejcn.1602269; published online 7 September 2005
Comparison of accuracy and precision of heart rate calibration methods to estimate total carbon dioxide production during 13C-breath tests
Guarantor: C Slater.
Contributors: CS performed the study, analysed the data, wrote the first draft and refined the manuscript. TP conceived the original idea, advised on study design and data analysis and critically appraised the manuscript. LTW cosupervised the project, and critically appraised the manuscript.
C Slater1, T Preston2 and L T Weaver1
- 1Division of Developmental Medicine, University of Glasgow, Yorkhill Hospitals, Glasgow, UK
- 2Stable Isotope Biochemistry Laboratory, Scottish Universities Environmental Research Centre, East Kilbride, Glasgow, UK
Correspondence: Dr C Slater, Division of Developmental Medicine, University of Glasgow: Child Health, Yorkhill Hospitals, Glasgow G3 8SJ, UK. E-mail: C.Slater@clinmed.gla.ac.uk
Received 30 December 2004; Revised 9 June 2005; Accepted 8 July 2005; Published online 7 September 2005.
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 (VCO2). A resting value is usually assumed, but this can underestimate VCO2 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 VCO2 during 13C-breath tests.
Objective:
To calibrate a heart rate monitor to continually estimate VCO2 during 13C-breath tests.
Design:
Proof of concept study.
Subjects:
Eight healthy adults, 10 healthy children and six children with cystic fibrosis.
Methods:
Heart rate and VCO2 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 [13C]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 VCO2). Smoothing heart rate gave a more precise estimate of VCO2 and a more accurate estimate of resting energy expenditure (mean bias -0.09, 95% CI -0.22, 0.05 mmol CO2 min-1 m-2 body surface area) than using raw data (mean bias -0.21, 95% CI -0.38, -0.04 mmol CO2 min-1 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.
Conclusion:
Use of smoothed HR with a sigmoid function provides an accurate method of estimating nonresting VCO2 during 13C-breath tests.
Sponsorship:
The work described in this paper was funded by the University of Glasgow and UK Medical Research Council Joint Research Equipment Initiative.
Keywords:
pulmonary gas exchange, CO2 production rate, heart rate, total energy expenditure, physical activity level, breath test
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