Indirect calorimetry laboratory with canopy hood

Indirect calorimetry calculates

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

that

living organisms In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fun ...

produce by measuring either their production of

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

and nitrogen waste (frequently

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

in aquatic organisms, or

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...

in terrestrial ones), or from their consumption of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

. Indirect calorimetry estimates the type and rate of substrate utilization and energy metabolism in vivo starting from

gas exchange Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a ...

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 Thermogenesis is the process of heat production in organisms. It occurs in all warm-blooded animals, and also in a few species of thermogenic plants such as the Eastern skunk cabbage, the Voodoo lily ('' Sauromatum venosum''), and the giant w ...

, the energetics of physical exercise, and the pathogenesis of metabolic diseases.Ferrannini
"The theoretical bases of indirect calorimetry: a review."
Metabolism. 1988 Mar;37(3):287-301.

Scientific background

Indirect calorimetry measures O₂ consumption and CO₂ production. On the assumption that all the oxygen is used to

oxidize Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...

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. Respiratory indirect

calorimetry In chemistry and thermodynamics, calorimetry () is the science or act of measuring changes in ''state variables'' of a body for the purpose of deriving the heat transfer associated with changes of its state due, for example, to chemical re ...

(IC) is a noninvasive and highly accurate method of

metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

, which has an error of less than 1%.Marson F, et al
"Correlation between oxygen consumption calculated using Fick's method and measured with indirect calorimetry in critically ill patients."
Arq Bras Cardiol. 2004 Jan;82(1):77-81, 72-6. Epub 2004 Feb 12. It has high reproducibility and has been considered a gold standard method.Haugen HA, et al
"Indirect calorimetry: a practical guide for clinicians."
Nutr Clin Pract. 2007 Aug;22(4):377-88. This method allows estimating

BEE Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfami ...

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.Pinheiro Volp AC, et al
"Energy expenditure: components and evaluation methods."
Nutr Hosp. 2011 May-Jun;26(3):430-40. doi: 10.1590/S0212-16112011000300002. 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 Resting metabolic rate (RMR) is whole-body mammal (and other vertebrate) metabolism during a time period of strict and steady ''resting conditions'' that are defined by a combination of assumptions of physiological homeostasis and biological equili ...

is calculated by the

Weir formula The Weir formula is a formula used in indirect calorimetry, relating metabolic rate to oxygen consumption Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table ...

and results are displayed in software attached to the system. Another formula used is: :

M=VO_2\left(\frace_c+\frace_f\right)

where RQ is the respiratory quotient (ratio of volume CO₂ produced to volume of O₂ consumed),

e_c

is , the heat released per litre of oxygen by the oxidation of carbohydrate, and

e_f

is , 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). ⊅Σ′

History

Antoine Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS (

thermodynamics Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws ...

to animal life.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 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 Parenteral nutrition (PN) is the feeding of nutritional products to a person intravenously, bypassing the usual process of eating and digestion. The products are made by pharmaceutical compounding companies. The person receives a nutritional mi ...

, interdisciplinary nutrition support teams, and the production of portable, reliable, relatively inexpensive calorimeters.McClave SA, et al
"Use of indirect calorimetry in clinical nutrition."
Nutr Clin Pract. 1992 Oct;7(5):207-21.

Collection methods

Four different gas collection and measurement techniques can be used to perform this test: *Douglas Bag: Expired respiratory gases are collected on an inflatable airtight bag. (Douglas Bag) After completion of any test using Douglas Bags, gas collected must be analysed for volume and composition. *Canopy (dilution): The dilution technique is considered the gold standard technology for Resting Energy Expenditure measurement in clinical nutrition. The test lasts just few minutes and consists of making a patient lie down relaxed on a bed or on a comfortable couch, with the head under a transparent hood connected to a pump, which applies an adjustable ventilation through it. Exhaled gas dilutes with the fresh air ventilated under the hood and a sample of this mixture is conveyed to the analysers, through a capillary tube and analysed. Ambient and diluted fractions of O₂ and CO₂ are measured for a known ventilation rate, and O₂ consumption and CO₂ production are determined and converted into Resting Energy Expenditure.Academy of Nutrition and Dietetic
"Measuring RMR with Indirect Calorimetry (IC)."
Nutr Clin Pract. 2007 Aug;22(4):377-88. *Face mask (breath by breath): Indirect calorimetry tests are also often performed with a face mask, which is used to convey exhaled and inhaled gas through a turbine flowmeter able to measure the patient's breath by breath minute ventilation, at the same time a sample of gas is conveyed to the analyser and VO₂ and VCO₂ are measured and converted in energy expenditure. *Interface with a Ventilator (

Intensive Care Intensive care medicine, also called critical care medicine, is a medical specialty that deals with seriously or critically ill patients who have, are at risk of, or are recovering from conditions that may be life-threatening. It includes pro ...

settings): In case the patient is mechanically ventilated, an indirect calorimeter can still measure breath by breath inhaled/exhaled O₂ and CO₂ if interfaced with the ventilator through the

endotracheal tube A tracheal tube is a catheter that is inserted into the trachea for the primary purpose of establishing and maintaining a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide. Many different types of tracheal tubes ar ...

Applications

Indirect calorimetry provides at least two pieces of information: a measure of energy expenditure or 24-hour caloric requirements as reflected by the

(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.

Scientific background

History

Collection methods

Applications

References

See also