Physiology, Respiratory Quotient

Abstract

Respiration is the process by which the respiratory substrate is broken down to release energy. The two main operating factors of cell respiration are aerobic and anaerobic respiration, where aerobic respiration requires the presence of oxygen and anaerobic respiration does not. The most common respiratory substrate is glucose, which has a 6-carbon compound. The substrate is metabolized through glycolysis, TCA cycle, electron transport chain, and oxidative phosphorylation. Through these cycles, cells are able to produce and store ATP, and carbon dioxide is produced as a by-product. It is important to understand the levels of carbon dioxide produced from different substrates because toxic levels can be destructive to the body. Healthcare professionals can recommend that a patient alter his or her diet, particularly for those with pulmonary and liver conditions, to increase the release of CO2 and avoid respiratory fatigue and utilize it as a prognostic factor, respectively.Respiratory quotient, also known as the respiratory ratio (RQ), is defined as the volume of carbon dioxide released over the volume of oxygen absorbed during respiration. It is a dimensionless number used in a calculation for basal metabolic rate when estimated from carbon dioxide production to oxygen absorption. Uptake of oxygen is a form of indirect calorimetry and is measured by a respirometer directly at the tissue or mouth. Respiratory Ratio RQ = Vol CO2 released/Vol O2 absorbedIt is calculated for a particular substrate i.e., carbohydrates, organic acid, fat, and protein. Carbohydrates are oxidized through aerobic respiration resulting in an equal ratio of CO2 release and oxygen consumption. Subsequently, the RQ for fat, protein, and anaerobe is 0.7, 0.8, and 0 respectively. If a mixture of the substrates is consumed, then the RQ ratio collectively is 0.8.