title: Percent relative cumulative frequency analysis in indirect calorimetry: application to studies of transgenic mice.
abstract: Indirect calorimetry is commonly used in research and clinical settings to assess characteristics of energy expenditure. Respiration chambers in indirect calorimetry allow measurements over long periods of time (e.g., hours to days) and thus the collection of large sets of data. Current methods of data analysis usually involve the extraction of only a selected small proportion of data, most commonly the data that reflects resting metabolic rate. Here, we describe a simple quantitative approach for the analysis of large data sets that is capable of detecting small differences in energy metabolism. We refer to it as the percent relative cumulative frequency (PRCF) approach and have applied it to the study of uncoupling protein-1 (UCP1) deficient and control mice. The approach involves sorting data in ascending order, calculating their cumulative frequency, and expressing the frequencies in the form of percentile curves. Results demonstrate the sensitivity of the PRCF approach for analyses of oxygen consumption (.VO2) as well as respiratory exchange ratio data. Statistical comparisons of PRCF curves are based on the 50th percentile values and curve slopes (H values). The application of the PRCF approach revealed that energy expenditure in UCP1-deficient mice housed and studied at room temperature (24 degrees C) is on average 10% lower (p < 0.0001) than in littermate controls. The gradual acclimation of mice to 12 degrees C caused a near-doubling of .VO2 in both UCP1-deficient and control mice. At this lower environmental temperature, there were no differences in .VO2 between groups. The latter is likely due to augmented shivering thermogenesis in UCP1-deficient mice compared with controls. With the increased availability of murine models of metabolic disease, indirect calorimetry is increasingly used, and the PRCF approach provides a novel and powerful means for data analysis.
authors.affiliation: Department of Biochemistry, Microbiology, and Immunology, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ontario K1H 8M5, Canada.
authors.forename: Marc
authors.initials: M
authors.lastname: Riachi
authors.forename: Jean
authors.initials: J
authors.lastname: Himms-Hagen
authors.forename: Mary-Ellen
authors.initials: ME
authors.lastname: Harper
mesh_terms: D000064:Acclimatization; D000818:Animals; D002153:Calorimetry, Indirect / Q000379:methods*; D002352:Carrier Proteins; D003080:Cold Temperature; D003627:Data Interpretation, Statistical; D004734:Energy Metabolism / Q000502:physiology*; D007473:Ion Channels; D008565:Membrane Proteins / Q000172:deficiency; D051379:Mice; D008822:Mice, Transgenic / Q000502:physiology*; D024101:Mitochondrial Proteins; D010101:Oxygen Consumption / Q000502:physiology; D000071256:Uncoupling Protein 1
chemical_list: D002352:Carrier Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; C000604372:Ucp1 protein, mouse; D000071256:Uncoupling Protein 1