Respiratory Quotient

What is Respiratory Quotient?

Respiratory Quotient is abbreviated as RQ and also known as Respiratory Coefficient or Respiratory Ratio, and it is defined as the ratio of volume of carbon dioxide evolved to the volume of oxygen consumed in respiration per unit time per unit weight at standard temperature and pressure. Therefore, we can represent Respiratory Quotient Formula as follows:

RQ = Volume of Carbon Dioxide / Volume of Oxygen Consumed (per unit time and per unit weight at standard temperature and pressure)


The instrument used for measuring Respiratory Quotient is Respirometer.


RQ for Different Respiratory Substrates

Depending upon the Respiratory Quotient, we can know what kinds of respiratory substrate is used for respiration.


1. RQ for Carbohydrates

(In Aerobic respiration)


\[C_{6}H_{12}O_{6} + 6O_{2} \rightarrow 6CO_{2} + 6H_{2}O.\] 


Thus, the RQ = \[\frac{6CO_{2}}{6O_{2}}\] = 1


(In anaerobic respiration)


\[C_{6}H_{12}O_{6} \rightarrow 2 Ethanol + 2CO_{2},\] RQ = Infinity


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2. RQ of Fats/Lipids 

Similarly, with the help of the formula for respiratory quotient, RQ for triolein, it is calculated as 0.71 and for tripalmitin, RQ=0.7


3. RQ for Organic Acid

Using the formula, we get RQ for malic acid= 1.3


4. For Mixed Diet, RQ value= 0.8


Characteristics of Respiratory Quotient

  • The respiratory coefficients differ in organisms for metabolic balance and it ranges from 1.0 to 0.7 (the former value representing the value for pure carbohydrate oxidation and the latter value expected for pure fat oxidation). 

  • In general, molecules which are more oxidized, for example, glucose, require very less oxygen to be fully metabolized and, therefore, they have higher respiratory quotients. On the other hand, molecules that are less oxidized, for example fatty acids, require more oxygen for their complete metabolism and therefore, they have lower respiratory quotients. 

  • Respiratory Quotient value refers to the caloric value for each liter (L) of Carbon dioxide produced. If Oxygen consumption numbers are available, they are usually used directly, and they are more direct and reliable estimates of energy production.

  • Respiratory Quotient is measured as a contribution from the energy produced from protein. However, due to the complexity of the various ways in which varied amino acids can be metabolized, no single Respiratory Quotient can be assigned to the oxidation of protein in the diet.

  • Insulin, which is known to increase lipid storage and decrease fat oxidation, is thought to be positively associated with increase in the respiratory quotient. A positive energy balance then leads to an increased respiratory quotient.

  • Respiratory Coefficient is a dimensionless number which is used to calculate the basal metabolic rate and it is estimated with the help of the ratio from carbon dioxide production to oxygen absorption.


Terms Related to Respiratory Quotient

1. Cellular Respiration

Cellular respiration is a set of processes and metabolic reactions taking place in the cells of organisms that helps in converting chemical energy from oxygen molecules or nutrients into carbon dioxide, water and waste products with the release of ATP (adenosine triphosphate). It helps in sustaining the lives of living organisms like humans and animals.  

2. Aerobic Respiration

Cellular respiration is the process where cells break down food to use it as an energy. In aerobic cellular respiration, the respiration process makes use of oxygen to yield many more ATP molecules as compared to the anaerobic cellular respiration. It is believed that in terms of efficiency, aerobic metabolism is up to 15 times stronger than anaerobic metabolism

3. Anaerobic Respiration

Here, cellular respiration occurs in the absence of oxygen to yield only two ATP molecules. Instead of oxygen, organic or inorganic molecules are used in the anaerobic respiration for the final electron acceptors. Some of the examples of anaerobic respiration are alcohol fermentation, decomposition of organic matter and fermentation of lactic acid. The equation is represented as: glucose + enzymes = carbon dioxide + lactic acid/ethanol


Application of Respiratory Quotient

  • A major application of the respiratory quotient is found in severe cases of chronic obstructive pulmonary disease.

  • It is used as an indicator for underfeeding or overfeeding.

  • It is used in analysis of the functioning of the liver.

  • It is also used to predict the weight gain in non-insulin-dependent patients suffering from diabetics.

  • It is also used in diagnosing the patients who are suffering from liver cirrhosis and also for non-protein respiratory quotients.

Definition of Respiratory Quotient

Breath by definition depicts it as the demonstration of breathing; the inward breath and exhalation of gases are well acquainted with every single one of us. This time, we adventure across an alternate part of it.

Respiratory Quotient

Oxygen consuming breath is the interaction most living things go through to utilize food energy productively. In this high-impact breath, oxygen is burned-through and carbon dioxide is delivered.

The real proportion of the volume of carbon dioxide dispensed with to the volume of oxygen devoured during the demonstration of cell breath is known as the respiratory quotient. It is likewise alluded as the respiratory proportion and is indicated by RQ.

The respiratory remainder relies upon the kind of respiratory substrate utilized during the demonstration of breath. Also, the respiratory remainder is a dimensionless number utilized in the computations of the basal metabolic rate or BMR when assessed from the carbon dioxide creation. These estimations are types of circuitous calorimetry. It turns out to be estimated utilizing Ganong's respirometer.

At the point when the carbs are totally oxidized which are utilized as a substrate, the respiratory remainder becomes one. Here the equivalent measures of carbon dioxide and oxygen are developed and burned-through, individually.

The RQ for starches is roughly 1.

In any case, right now fats will generally be included in the demonstration of cell breath, the respiratory remainder drops to lower than one.

The RQ for fats is around 0.7.

At the point when proteins are respiratory substrates the proportion would be around 0.9. 

The RQ for protein is around 0.8.

One should perceive that in living creatures the respiratory remainder is seldom one, indeed, most frequently, it turns out to be multiple. Unadulterated proteins and fats are really never utilized as respiratory substrates.

Utilization of Respiratory Quotient

Utilizations of the respiratory remainder can be found in serious instances of constant obstructive pneumonic illness. Different applications include:

  • Utilized as a mark of over or depriving.

  • Utilized for investigating the working of the liver.

  • Used to foresee weight gain in non-insulin-subordinate diabetic patients.

  • Utilized for diagnosing the patient's conditions, who are experiencing liver cirrhosis and non-protein respiratory remainder.

Clinical Significance

some of the clinical significances are as follows:

Persistent Obstructive Pulmonary Disease

Persistent Obstructive Pulmonary Disease (POPD) is a respiratory illness that causes constant check of wind stream. Ongoing irritation of the bronchioles alongside mucous creation makes them become disfigured and tight alongside mucous creation, restricting the wind current as an individual breathes out. Since the patient can't completely breathe out, carbon dioxide stays in the alveoli because of loss of flexibility of the sac. The patients experience the ill effects of windedness, useful hack, respiratory acidosis, and muddled pneumonia.

In 1992, a review showed that sugar rich food builds the creation of CO2, prompting an increment in respiratory rate and in the long run respiratory disappointment. In actuality, fat-rich dinners decline the creation of CO2, prompting diminish alveolar ventilation and minor improvement in breath in patients who at first have a RQ proportion more noteworthy than 0.75.

Non-Insulin Dependent Weight Gain

The respiratory remainder can be utilized to foresee weight gain in non-insulin-subordinate diabetic patients. Typically, a diabetic patient has insulin-safe receptors, which brings about hyperglycemia. This keeps utilization from happening through glycolysis, accordingly, expanding lipolysis. As referenced, an expansion in lipolysis will decrease the creation of CO2. A review done in 1998, showed a backwards relationship be tween’s RQ proportion and serum glucose levels in non-insulin-subordinate diabetes mellitus treated with oral hypoglycemic specialists or insulin. Patients who were on the oral hypoglycemic specialists and had a higher BMI checked that their RQ proportion was a lot higher than those of normal BMI. Subsequent to following them for a year, a weight gain of 3 kg was seen in half of the patients alongside an increment of RQ proportion. This review reasoned that RQ proportion is a legitimate indicator for weight gain in diabetics treated with oral agents.

Sustenance Guide for Sick Patients

Using the backhanded calorimetry and respiratory energy use helps with computing the ideal kcal patients need to burn-through each day, particularly when unfit to assess caloric prerequisites, lacking clinical reaction to an anticipated condition, or clinical indication of over and depriving. Patients who are beyond husky or experiencing sepsis have a change in their VCO2 delivery and VO2 utilization. Hence, day by day RQ and circuitous calorimetry are fundamental to upgrade their eating routine and decrease medical clinic stay.

FAQs (Frequently Asked Questions)

1. Define RQ. What is the Respiratory Quotient of Protein?

RQ stands for respiratory quotient and it is the ratio of the volume of carbon dioxide released to the volume of oxygen used in cellular respiration.  It is estimated per unit time per unit weight at standard temperature and pressure. The respiratory quotient of protein is known to be 0.9. 

2. What is the Importance of Respiratory Coefficient?

Respiratory quotient is also known as the respiratory coefficient and it is a huge contributor in  dealing with animal metabolism as it helps in comparing the volume of oxygen consumed by an organism helps in conveniently gaining information about the source of energy a living organism (human or animal) is using.

3. What is the Range of Respiratory Quotients? How is it Calculated?

Respiratory ratio or respiratory quotient is found to be in the range of 0.7 to 1.0 depending upon the source of energy. The source of energy can be lipids or fats, proteins, organic acids and carbohydrates. It is calculated with the help of a formula


RQ = Volume of carbon dioxide released/ Volume of oxygen consumed