Respiratory quotient

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The respiratory quotient (or RQ or respiratory coefficient), is a unitless number used in calculations of basal metabolic rate (BMR) when estimated from carbon dioxide production. Such measurements, like measurements of oxygen uptake, are forms of indirect calorimetry. It is measured using Ganong's Respirometer.

It can be used in the alveolar gas equation.

## Contents

* 1 Calculation
* 2 Respiratory Quotients of Some Substances
* 3 External links
* 4 References

## Calculation

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The respiratory quotient (RQ) is calculated from the ratio:

RQ = CO2 produced / O2 consumed

In this calculation, the CO2 and O2 must be given in the same units, and in quantities proportional to the number of molecules. Acceptable inputs would be either moles, or else volumes of gas at standard temperature and pressure (time units may be included, but they cancel out since they must be the same in numerator and denominator).

The range of respiratory coefficients for organisms in metabolic balance usually ranges from 1.0 (representing the value expected for pure carbohydrate oxidation) to ~0.7 (the value expected for pure fat oxidation). See BMR for a discussion of how these numbers are derived. A mixed diet of fat and carbohydrate results in an average value between these numbers. An RQ may rise above 1.0 for an organism burning carbohydrate to produce or "lay down" fat (for example, a bear preparing for hibernation).

RQ value corresponds to a caloric value for each liter (L) of CO2 produced. If O2 consumption numbers are available, they are usually used directly, since they are more direct and reliable estimates of energy production.

RQ as measured includes a contribution from the energy produced from protein. However, due to the complexity of the various ways in which different amino acids can be metabolized, no single RQ can be assigned to the oxidation of protein in the diet.

## Respiratory Quotients of Some Substances

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Reference [1]

Name of the substance  | Respiratory Quotient

|

Carbohydrates | 1
Triolein (Fat)  | 0.7
Oleic Acid (Fat)  | 0.71
Tripalmitin (Fat)  | 0.7
Proteins | 0.8 - 0.9
Malic acid | 1.33
Tartaric acid | 1.6
Oxalic Acid | 4.0

## External links

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* Template:GPnotebook
* Template:EMedicineDictionary

## References

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1. ↑ Telugu Academi, Botany text book, 2007 Version

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Respiratory system, physiology: respiratory physiology

Lung volumes|

VC * FRC * Vt * dead space * CC

calculations: respiratory minute volume * FEV1/FVC ratio

devices: spirometry * body plethysmography * peak flow meter

Airways/
ventilation (V)|

positive pressure ventilation * breath (inhalation, exhalation) * respiratory rate * respirometer * pulmonary surfactant * compliance * hysteresivity * airway resistance * bronchial hyperresponsiveness * bronchial challenge test * bronchoconstriction/bronchodilation

Blood/
perfusion (Q)|

pulmonary circulation * hypoxic pulmonary vasoconstriction * pulmonary shunt

Interactions/
ventilation/perfusion ratio (V/Q)|

ventilation/perfusion scan * zones of the lung * gas exchange * pulmonary gas pressures * alveolar gas equation * alveolar-arterial gradient * hemoglobin * oxygen-haemoglobin dissociation curve (2,3-DPG, Bohr effect, Haldane effect) * carbonic anhydrase (chloride shift) * oxyhemoglobin * respiratory quotient * arterial blood gas * diffusion capacity * DLCO

Control of respiration|

pons (pneumotaxic center, apneustic center) * medulla (dorsal respiratory group, ventral respiratory group) * chemoreceptors (central, peripheral) * pulmonary stretch receptors (Hering-Breuer reflex)

Insufficiency|

high altitude * oxygen toxicity * hypoxia

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