The respiratory quotient (RQ) measures the ratio of oxygen taken in to carbon dioxide eliminated by an organism. It reveals what the body is using for energy and can be used to gather data about someone’s metabolism during a diagnostic evaluation.
The respiratory quotient (RQ) or respiratory coefficient is a measure of the ratio between the oxygen (O2) that an organism takes in and the carbon dioxide (CO2) that the organism eliminates, expressed with the formula “RQ=CO2 eliminated/O2 absorbed”. To measure an organism’s respiratory quotient, a device called a respiration meter must be used to measure the gases that the organism absorbs and expresses. This is commonly done within a chamber, which provides a highly reliable way to monitor gas levels without causing injury.
To generate reliable measurements, comparable units for oxygen and carbon dioxide levels should be used. Otherwise, the ratio will be distorted and consequently less meaningful. Different units of measurement can be used, depending on the organism being studied and the precision of the instruments available. With very fine instrumentation and very small organisms, very accurate readings can be obtained which can be used in respiratory quotient calculations.
This ratio reveals what the body is using for energy. At the cellular level, respiration is used to generate new energy for cells by taking in nutrients that the body has used up and by generating a series of reactions to derive energy from those nutrients so that the cell can function. This also produces waste materials that must be disposed of. A common method for cells to derive energy is aerobic respiration, in which oxygen is used as a catalyst for this process; humans, for example, breathe aerobically and rely on oxygen for cellular function.
In an organism that uses fat for energy, the respiratory quotient is approximately 0.7. Burning protein for energy generates a respiratory quotient of 0.9, while consuming carbohydrates generates a perfect 1.0. If an organism’s respiratory quotient rises above 1.0, it is an indicator that the organism relies on anaerobic respiration for energy.
This information can be used to gather data about someone’s metabolism during a diagnostic evaluation used in medical treatment to gather information about a patient that can be used by a doctor to learn more about why a patient is not feeling well. In a healthcare setting, tests to determine someone’s respiratory quotient may be done for the purpose of calculating basal metabolic rate, which reflects the amount of energy someone uses when at rest. Changes in basal metabolic rate can be used to assess overall health and identify errors in metabolism that could be causing symptoms of ill health.
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