Respiratory oxygen flow is the oxygen consumption per total system, which is an extensive quantity. Oxygen flow or respiration of a cell is distinguished from oxygen flux (oxygen flow divided by the volume or mass of a system). These are different forms of normalization of rate.

Respirometry provides an indirect calorimetric approach to the measurement of metabolic heat changes, by measuring oxygen uptake (and carbon dioxide production and nitrogen excretion in the form of ammonia, urea or uric acid) and converting the oxygen consumed into an enthalpy change, using the oxycaloric equivalent.

The most advanced way to analyze mitochondrial function is by means of high-resolution respirometry with the Oroboros O2k.