Respirometry measures gas exchange associated with metabolism, commonly oxygen consumption or carbon-dioxide production. In a closed chamber, the change in gas amount over time can estimate a rate after correcting for chamber volume, background and temperature. Flow systems instead compare incoming and outgoing gas. A measured oxygen flux reports aggregate oxidative activity under the stated conditions; it does not uniquely identify which fuel or individual reaction produced it. [ref]
Respiratory enzymes in oxidative phosphorylation. I. Kinetics of oxygen utilization by Britton Chance and G. R. Williams. 1955, recording oxygen utilization and respiratory states
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