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ISSN: 2165-7904
Journal of Obesity & Weight Loss Therapy
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Indirect Calorimetry: From Expired CO2 Production, Inspired O2 Consumption to Energy Equivalent

Priscila Giacomo Fassini, José Henrique Silvah*, Cristiane Maria Mártires Lima, Camila Fernanda Costa Cunha, Moraes Brandão, Lauro Wichert-Ana, Júlio Sérgio Marchini and Vivian Miguel Marques Suen
Ribeirão Preto School of Medicine, University of São Paulo, Brazil
Corresponding Author : José Henrique Silvah
Avenida Bandeirantes, 3900
Bairro Monte Alegre, Departamento de
Clínica Médica, 6º andar do HC
CEP: 14049-900, Ribeirão Preto, São Paulo, Brazil
Tel: 551636023375
Fax: 551636020229
E-mail: [email protected]
Received: May 15, 2015 Accepted: July 16, 2015 Published: July 30, 2015
Citation: Fassini PG, Silvah JH, Lima CMM, Cunha CFC, Brandão M, et al. (2015) Indirect Calorimetry: From Expired CO2 Production, Inspired O2 Consumption to Energy Equivalent. J Obes Weight Loss Ther S5:001. doi:10.4172/2165-7904.S5-001
Copyright: © 2015 Fassini PG, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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This paper emphasizes the methodology of data collection of indirect calorimetry, including establishment of steady state conditions and the standards in which the values are presented. It also aims to describe in details the calculations of VO2, VCO2, Resting Energy Expenditure (REE) and Respiratory Quotient (RQ). The trial is registered with number NCT02072694.


This paper emphasizes the methodology of data collection of indirect calorimetry, including establishment of steady state conditions and the standards in which the values are presented. It also aims to describe in details the calculations of VO2, VCO2, Resting Energy Expenditure (REE) and Respiratory Quotient (RQ). The trial is registered with number NCT02072694.

Indirect calorimetry; Energy expenditure; Oxygen consumption; Calibration; Respiration; Metabolism

The indirect calorimetry can be understood as a non-invasive measurement of energy produced by the organism through quantifying the volumes of consumed oxygen and produced carbon dioxide (Vo2 and Vco2, respectively) by the oxidation of substrates [1].

The calorimeters commercially available calculate Vo2 and Vco2 through equations using concentrations of O2 and CO2 concentrations in the inhaled air (FIO2 and FICO2) and exhaled air (FEO2 and FECO2), respectively, and the inhaled (VI) and exhaled (VE) lung volumes of air per minute [2,3].

While the software acquired with the calorimeter provides all results, understanding how the calculations from which the values of Vo2, Vco2 and Resting Energy Expenditure (REE) are obtained could be challenging even for experts in this field. Therefore, this report shows how the data provided by the calorimeter could be used to compute those values, since the establishment of steady state conditions, once seldom papers clearly demonstrate it.
Materials and Methods


A 34 years-old healthy female volunteer, BMI 18.7 kg/m2, underwent an indirect calorimetry test. The subject was a participant of a study approved by the ethical review board of Ribeirão Preto Medical School of São Paulo University, which is registered with number NCT02072694.
Experimental design

According to the manufacturer recommendations, the calorimeter Quark RMR® (Cosmed, Rome, Italy) was turned on 45 minutes before calibration [4] in 3 steps: 1) Ambient air; 2) standard mixture composed of CO2, O2 and N2 in the concentrations of 5%, 16% and 79%, respectively and 3) Validation of the bidirectional digital turbine ?owmeter, performed using a certi?ed 3 L calibration syringe [5]. The IC test was performed as suggested by Compher et al. [6] and Suen et al. [7], with canopy, being the flow rate regularly adjusted to maintain a constant FECO2 through all the time.

Before the acquisition of data, the participant was asked to remain quiet, awake, with a regular respiratory pattern, avoiding yawning, coughing, speaking and sighing. After emptying of the bladder, her height and weight were measured; the volunteer layed down on supine position with her head elevated 30 degrees, extended limbs and opened eyes in a silent room at 23°C [7].

The indirect calorimetry test lasted approximately 15 minutes, in which was assured that all recommendations were followed.

Establishment of steady state conditions and data analysis

Initially, the obtained data was exported from Cosmed 10.0a software to a spreadsheet of Microsoft Excel 2007® and the first 5 minutes were not taken into account. In the graphic plotted with the variations of Vo2 and Vco2 along the remaining 10 minutes, a 5-minute period with steady state conditions was chosen. In this interval, the coefficients of variation of the observed Vo2 and Vco2 were respectively 4.8 and 4.7 [5] (Figure 1). The mean values of VE, FEO2 and FECO2 were calculated and used in the equations to obtain the Vo2, Vco2, REE and RQ. The volume of VE was provided by the calorimeter in L/min BTPS, which means the volume of a gas at body temperature (37°C), ambient pressure and saturated with water vapor at the subject’s body temperature [8].

Calculating Vco2

From the steady state interval, the means found were: VE=26.59 L/min (BTPS); FEO2=19.92%; FECO2=0.83%. The means of FIO2 and FICO2 were 20.89% and 0.08%, respectively. The value of VI was obtained using Haldane’s transformation [2]. The calculations are described below:







VI=(0.7925x26.59)/0.7903→VI=26.66 L/min


Vco2=(26.59x0.0083)-(26.66x0.0008)(x1000 to convert to mL/min)

Vco2(BTPS)=199.37 L/min

The Vco2, adjusted to Standard Temperature, Pressure and Ambience Dryness (STPD), which was 0.7681 (provided by the calorimeter) is:

Vco2=199.37 x 0.7681→Vco2 (STPD) = 153.13 mL/min

Calculating Vo2

To calculate the Vo2, an equation from Haldane’s transformation was employed [2], as follow:



Vo2(BTPS)=258.15 mL/min

Adjusting to STPD: Vo2=258.15x0.7681

Vo2(STPD)=198.28 mL/min

Calculating both REE and RQ

The Weir equation [9] was used to compute the REE


REE=((3.941x198.28)+(1.11x153.14))x1.44→REE=1370 kcal/day

The RQ is obtained by the ratio Vco2/Vo2


The indirect calorimetry has been used as a research and clinical practice tool [10]. Usually, the software provided with the available calorimeters processes the collected data and summarizes it in reports or spreadsheets containing the values of REE, Vo2, Vco2, RQ and others.

Nevertheless, sometimes the researcher wishes to understand how this software computes the aforementioned values. Once, in the literature, there are discrepancies among the equations used [9,11], some difficulties arise at this point. Moreover, researchers must attempt to not only describe the values given by the calorimeter software, but also to report the methods to obtain it in order to assure the quality of collected data. Therefore, it is important to disclose all equations used, how steady state conditions were established; the standard of the values (BTPS or STPD) and under which conditions the test was executed.

The value of VE given by the calorimeter and the VI, in this case, calculated through Haldane’s transformation are expressed in BTPS. However, the values of Vo2 and Vco2 are usually expressed in STPD, which is the volume of a gas under standard conditions of temperature (0°C), barometric pressure (760 mmHg) and humidity (partial pressure of water, 0 mmHg) [8]. Therefore, it is necessary to adjust the Vo2 and Vco2 to STPD.

Because detailed reports about the calculations related to indirect calorimetry are commonly not found, this paper illustrates all the steps involved, since the arrangements for test execution, the establishment of a steady state interval, the calculations of the values of the Vo2, Vco2, REE and RQ. In addition, it emphasizes the adjustment of values to STPD.

Thanks to Neusa Aparecida Brasão Santos Carlos and Maria do Rosário Del Lama de Unamuno for the technical support. The trial was supported by Fundação de Amparo à Pesquisa de São Paulo-FAPESP, scholarships 2012/21579-4, 2012/21626-2 and 2012/22543-3.

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  8. American Thoracic Society; American College of Chest Physicians (2003) ATS/ACCP Statement on cardiopulmonary exercise testing. Am J RespirCrit Care Med 167: 211-277.

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