Therespiratory quotient(orRQorrespiratory coefficient), is adimensionless numberused in calculations ofbasal metabolic rate(BMR) when estimated from carbon dioxide production. It is calculated from the ratio of carbon dioxide produced by the body to oxygen consumed by the body. Such measurements, like measurements of oxygen uptake, are forms of indirectcalorimetry. It is measured using arespirometer. The Respiratory Quotient value indicates which macronutrients are being metabolized, as different energy pathways are used for fats, carbohydrates, and proteins.A value of 0.7 indicates that lipids are being metabolized, 0.8 for proteins, and 1.0 for carbohydrates. The approximate respiratory quotient of a mixed diet is 0.8.Some of the other factors that may affect the respiratory quotient are energy balance, circulating insulin, and insulin sensitivity.
It can be used in thealveolar gas equation. Respiratory quotient is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed in respiration over a period of time. Its value can be one, zero, more than 1 or less than one. RQ = Volume of C02evolved/Volume of 02absorbed RQ Equal to Unity: Respiratory quotient is equal to unity if carbohydrates are the respiratory substrate and the respiration is aerobic. C6H1206+ 602→ 6C02+ 6H20 RQ = 6C02/602= 1