Indirect calorimetry

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Indirect calorimetry metabolic cart measuring oxygen uptake (O2) and carbon dioxide production (CO2) of a spontaneously breathing subject (dilution method with canopy hood). Indirect calorimetry laboratory with canopy hood.jpg
Indirect calorimetry metabolic cart measuring oxygen uptake (O2) and carbon dioxide production (CO2) of a spontaneously breathing subject (dilution method with canopy hood).

Indirect calorimetry calculates heat that living organisms produce by measuring either their production of carbon dioxide and nitrogen waste (frequently ammonia in aquatic organisms, or urea in terrestrial ones), or from their consumption of oxygen. Indirect calorimetry estimates the type and rate of substrate utilization and energy metabolism in vivo starting from gas exchange measurements (oxygen consumption and carbon dioxide production during rest and steady-state exercise). This technique provides unique information, is noninvasive, and can be advantageously combined with other experimental methods to investigate numerous aspects of nutrient assimilation, thermogenesis, the energetics of physical exercise, and the pathogenesis of metabolic diseases. [1]

Contents

Scientific background

Indirect calorimetry measures O2 consumption and CO2 production. On the assumption that all the oxygen is used to oxidize degradable fuels and all the CO2 thereby evolved is recovered, it is possible to estimate the total amount of energy produced from the chemical energy of nutrients and converted into the chemical energy of ATP, with some loss of energy during the oxidation process. [1] Respiratory indirect calorimetry (IC) is a noninvasive and highly accurate method of metabolic rate, which has an error of less than 1%. [2] It has high reproducibility and has been considered a gold standard method. [3] This method allows estimating BEE and REE as well as identification of energy substrates that are predominantly metabolized by the body at a specific moment. It is based on the indirect measurement of the heat produced by oxidation of macronutrients, which is estimated by monitoring O2 consumption and CO2 production for a certain period of time. [2] The calorimeter has a gas collector that adapts to the subject and through a unidirectional valve minute by minute collects and quantifies the volume and concentration of O2 inspired and CO2 expired by the subject. After a volume is met, Resting Energy Expenditure is calculated by the Weir formula and results are displayed in software attached to the system. [2] Another formula used is: [4]

where RQ is the respiratory quotient (ratio of volume CO2 produced to volume of O2 consumed), is 21.13 kilojoules (5.05 kcal), the heat released per litre of oxygen by the oxidation of carbohydrate, and is 19.62 kilojoules (4.69 kcal), the value for fat. This gives the same result as the Weir formula at RQ = 1 (burning only carbohydrates), and almost the same value at RQ = 0.7 (burning only fat).

History

Antoine Lavoisier noted in 1780 that heat production, in some cases, can be predicted from oxygen consumption[ citation needed ], using multiple regression. Indirect calorimetry, as we know it, was developed around 1900 as an application of thermodynamics to animal life. [5] Although the development of indirect calorimetry dates back over 200 years, its greatest use has been in the last two decades with the development of total parenteral nutrition, interdisciplinary nutrition support teams, and the production of portable, reliable, relatively inexpensive calorimeters. [6]

Collection methods

Four different gas collection and measurement techniques can be used to perform this test:

Applications

Indirect calorimetry provides at least two pieces of information: a measure of energy expenditure or 24-hour caloric requirements as reflected by the Resting Energy Expenditure (REE) and a measure of substrate utilization as reflected in the Respiratory Quotient (RQ). Knowledge of the many factors that affect these values has led to a much broader range of applications. Studies of indirect calorimetry over the past 20 years have led to the characterization of the hypermetabolic stress response to injury and the design of nutritional regimens whose substrates are most efficiently assimilated in different disease processes and organ failure states. Indirect calorimetry has influenced everyday practices of medical and surgical care, such as the warming of burn unit and surgical suites and the weaning of patients from ventilators. [6]

References

  1. 1 2 Ferrannini, E. (1988). "The theoretical bases of indirect calorimetry: A review". Metabolism: Clinical and Experimental. 37 (3): 287–301. doi:10.1016/0026-0495(88)90110-2. PMID   3278194.
  2. 1 2 3 Pinheiro Volp, A. C.; Esteves De Oliveira, F. C.; Duarte Moreira Alves, R.; Esteves, E. A.; Bressan, J. (2011). "Energy expenditure: Components and evaluation methods". Nutricion Hospitalaria. 26 (3): 430–440. doi:10.1590/S0212-16112011000300002 (inactive 18 July 2025). PMID   21892558.{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)
  3. 1 2 Haugen, H. A.; Chan, L. N.; Li, F. (2007). "Indirect calorimetry: A practical guide for clinicians". Nutrition in Clinical Practice. Vol. 22. pp. 377–388. doi:10.1177/0115426507022004377. PMID   17644692.{{cite book}}: |journal= ignored (help)
  4. A.R. Bain; et al. (Jun 2012). "Body heat storage during physical activity is lower with hot fluid ingestion under conditions that permit full evaporation Authors". Acta Physiologica . 206 (2): 98–108. doi:10.1111/j.1748-1716.2012.02452.x. PMID   22574769. S2CID   23682662. citing Nishi, Y. (1981). "Measurement of thermal balance in man". In K. Cena & J. Clark (ed.). Bioengineering, Thermal Physiology and Comfort . Elsevier. pp.  29–39.
  5. Atwater WO, et al. "Description of neo respiration calorimeter and experiments on the conservation of energy in the human body." US Department Agriculture, Off Exp Sta Bull 63, 1899
  6. 1 2 McClave, S. A.; Snider, H. L. (1992). "Use of indirect calorimetry in clinical nutrition". Nutrition in Clinical Practice. 7 (5): 207–221. doi:10.1177/0115426592007005207. PMID   1289691.
  7. Douglas, C. Gordon (18 March 1911). "A method for determining the total respiratory exchange in man". Proceedings of the Physiological Society. doi:10.1113/jphysiol.1911.sp001452 . Retrieved 10 September 2024. (Douglas Bag)
  8. Academy of Nutrition and Dietetics "Measuring RMR with Indirect Calorimetry (IC)." Nutr Clin Pract. 2007 Aug;22(4):377-88.