`The terms ``Respiratory Exchange Ratio`` (RER) and ``Respiratory Quotient`` (RQ) are very similar - but they are different.  In my experience with graduate and undergraduate students, most students (and many other scholars) believe these terms to be synonymous.  The distinction is the way in which each is measured.  Respiratory Exchange Ratio is measured using indirect calorimetry, that is the amount of oxygen consumed and the amount of carbon dioxide produced.  The respiratory quotient can be measured across a capillary bed of a particular organ or even a collection of cells in vitro.  Most of the time RER and RQ are the same value, however, during a metabolic or respiratory acidosis/alkalosis RER and RQ do not have to be the same value.`