What is the Respiratory Quotient

Respiration is the process of breaking down the respiratory substrate to release energy. The two main operating factors of cell respiration are aerobic and anaerobic respiration, with aerobic respiration requiring the presence of oxygen and anaerobic respiration not. The most common respiratory substrate is glucose, a 6-carbon compound. The substrate is broken down using glycolysis, the TCA cycle, the electron transport chain, and oxidative phosphorylation. Through these cycles, cells can produce and store ATP, and carbon dioxide is produced as a by-product.

Respiratory quotient:

The respiratory quotient (RQ) is calculated by dividing the volume of carbon dioxide released by the volume of oxygen absorbed during respiration. It is a dimensionless number used in calculating basal metabolic rate when calculated from carbon dioxide production to oxygen absorption. The uptake of oxygen is a type of indirect calorimetry that is measured with a respirometer directly at the tissue or mouth.

The processed substrate determines the respiratory quotient. This is because the ratio is defined as the number of CO2 molecules ejected divided by the number of O2 molecules consumed. RQ for carbohydrates is one because the amount of carbon dioxide released equals the amount of oxygen consumed. When the respiratory substrate is only partially oxidised, R.Q. = 0. Organic acids have an R.Q. value greater than one, whereas fats have a lower R.Q. value. Proteins have an R.Q that is less than one. During aerobic respiration, 02 is consumed and C02 is released. The respiratory quotient is the proportion of CO2 evolved to CO2 consumed during respiration (RQ). The type of respiration substrate used determines the RQ’s value. Carbohydrates are commonly used as substrates for respiration. Complete oxidation of carbohydrates consumes 02 and releases C02 in equal amounts during aerobic respiration.

Significance of Respiratory quotient

The respiratory quotient (RQ or respiratory coefficient) is a dimensionless number used to calculate the basal metabolic rate (BMR) from carbon dioxide production. It is calculated using the ratio of carbon dioxide produced by the body to oxygen consumed by the body. Such measurements are examples of indirect calorimetry, as are oxygen uptake measurements. It is measured using a respirometer. Because fats, carbohydrates, and proteins use different energy pathways, the respiratory quotient value indicates which macronutrients are being metabolised. The respiratory quotient for lipid metabolism is approximately 0.7, the respiratory quotient for proteins is approximately 0.8, and the respiratory quotient for carbohydrates is approximately 1.0. However, the majority of the time, energy is derived from both fats and carbohydrates. A mixed diet has a respiratory quotient of about 0.8. Other factors that may influence the respiratory quotient include energy balance, circulating insulin, and insulin sensitivity.

The specific fatty acids are present to determine the RQ for fats. Among the commonly stored fatty acids in vertebrates, RQ ranges from 0.692 (stearic acid) to 0.759 (oleic acid) (docosahexaenoic acid). Historically, it was assumed that ‘average fat’ had an RQ of 0.71, and this remains true for the majority of mammals, including humans. According to a recent study, aquatic animals, particularly fish, have fat that should yield higher RQs on oxidation, reaching as high as 0.73 due to high levels of docosahexaenoic acid.

Respiratory coefficients for organisms in metabolic balance typically range from 1.0 (representing the value expected for pure carbohydrate oxidation) to 0.7. (the value expected for pure fat oxidation). More oxidised molecules (such as glucose) require less oxygen to fully metabolise, resulting in higher respiratory quotients. Less oxidised molecules, on the other hand, require more oxygen to complete their metabolism and have lower respiratory quotients. See BMR for more information on how these figures are calculated. The RQ value corresponds to a caloric value for each litre (L) of CO2 produced, and a mixed diet of fat and carbohydrate yields an average value between these two numbers. If O2 consumption data is available, it is usually used directly because it provides a more direct and reliable estimate of energy production. Protein-energy contributes to RQ in the sense that it is measured. However, due to the complexities of the various ways in which different amino acids can be metabolised, no single RQ can be assigned to protein oxidation in the diet. Insulin, which promotes lipid storage while inhibiting fat oxidation, is associated with an increase in the respiratory quotient. A positive energy balance also results in an increased respiratory quotient.

Conclusion:

The respiratory quotient (RQ) is calculated by dividing the volume of carbon dioxide released by the volume of oxygen absorbed during respiration. It is a dimensionless number used in calculating basal metabolic rate when calculated from carbon dioxide production to oxygen absorption. During aerobic respiration, 02 is consumed and C02 is released. The respiratory quotient is the proportion of CO2 evolved to CO2 consumed during respiration (RQ). The type of respiration substrate used determines the RQ’s value. Carbohydrates are commonly used as substrates for respiration. Complete oxidation of carbohydrates consumes 02 and releases C02 in equal amounts during aerobic respiration.