Respiratory quotient

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The respiratory quotient (or RQ or respiratory coefficient), is a dimensionless 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 a respirometer.

It can be used in the alveolar gas equation.

Calculation[edit]

The respiratory quotient (RQ) is the ratio:

RQ = CO2 eliminated / O2 consumed

where the term "eliminated" refers to carbon dioxide (CO2) removed ("eliminated") from the body.

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.

Many metabolized substances are compounds containing only the elements carbon, hydrogen, and oxygen. Examples include fatty acids, glycerol, carbohydrates, deamination products, and ethanol. For complete oxidation of such compounds, the chemical equation is

CxHyOz + (x + y/4 - z/2) O2 → x CO2 + (y/2) H2O

and thus metabolism of this compound gives an RQ of x/(x + y/4 - z/2).

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). In general, molecules that are more oxidized (e.g., glucose) require less oxygen to be fully metabolized and, therefore, have higher respiratory quotients. Conversely, molecules that are less oxidized (e.g., fatty acids) require more oxygen for their complete metabolism and have lower respiratory quotients. 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).[citation needed]

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

Applications[edit]

Practical applications of the respiratory quotient can be found in severe cases of chronic obstructive pulmonary disease, in which patients spend a significant amount of energy on respiratory effort. By increasing the proportion of fats in the diet, the respiratory quotient is driven down, causing a relative decrease in the amount of CO2 produced. This reduces the respiratory burden to eliminate CO2, thereby reducing the amount of energy spent on respirations.[1]

Respiratory quotients of some substances[edit]

Reference[2]

Name of the substance Respiratory Quotient
Carbohydrates 1
Proteins 0.8 - 0.9
Ketones (eucaloric) 0.73[3]
Ketones (hypocaloric) 0.66[4][5][6]
Triolein (Fat) 0.7
Oleic Acid (Fat) 0.71
Tripalmitin (Fat) 0.7
Malic acid 1.33
Tartaric acid 1.6
Oxalic acid 4.0

See also[edit]

Respiratory Exchange Ratio

References[edit]

  1. ^ Kuo, C. D.; Shiao, G. M.; Lee, J. D. (1993-07-01). "The effects of high-fat and high-carbohydrate diet loads on gas exchange and ventilation in COPD patients and normal subjects". Chest 104 (1): 189–196. ISSN 0012-3692. PMID 8325067. 
  2. ^ Telugu Academi, Botany text book, 2007 Version[verification needed]
  3. ^ Mosek, Amnon; Natour, Haitham; Neufeld, Miri Y.; Shiff, Yaffa; Vaisman, Nachum (2009). "Ketogenic diet treatment in adults with refractory epilepsy: A prospective pilot study". Seizure 18 (1): 30–3. doi:10.1016/j.seizure.2008.06.001. PMID 18675556. 
  4. ^ Johnston, Carol S; Tjonn, Sherrie L; Swan, Pamela D; White, Andrea; Hutchins, Heather; Sears, Barry (2006). "Ketogenic low-carbohydrate diets have no metabolic advantage over nonketogenic low-carbohydrate diets". The American Journal of Clinical Nutrition 83 (5): 1055–61. PMID 16685046. 
  5. ^ Phinney, Stephen D.; Horton, Edward S.; Sims, Ethan A. H.; Hanson, John S.; Danforth, Elliot; Lagrange, Betty M. (1980). "Capacity for Moderate Exercise in Obese Subjects after Adaptation to a Hypocaloric, Ketogenic Diet". Journal of Clinical Investigation 66 (5): 1152–61. doi:10.1172/JCI109945. PMC 371554. PMID 7000826. 
  6. ^ Owen, O. E.; Morgan, A. P.; Kemp, H. G.; Sullivan, J. M.; Herrera, M. G.; Cahill, G. F. (1967). "Brain Metabolism during Fasting*". Journal of Clinical Investigation 46 (10): 1589–95. doi:10.1172/JCI105650. PMC 292907. PMID 6061736. 

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