Volume of carbon dioxide produced per unit time, measured by open-flow respirometry, used with VO₂ to derive substrate use and energy expenditure.
Use VCO₂ alongside VO₂ — on its own it is rarely the endpoint of interest. The pair gives the respiratory exchange ratio (VCO₂/VO₂) and, with it, fuel selection and energy expenditure. VCO₂ is sensitive to acid–base state and hyperventilation, so interpret it next to VO₂ rather than in isolation.
| Primary value | Carbon dioxide produced per unit time, from outflow–inflow CO₂ difference × flow |
|---|---|
| Common units | ml CO₂/min (whole animal); ml CO₂/kg/min (normalized) |
| Compatible assays | Home-cage metabolic chamber, resting metabolic rate, graded treadmill exercise |
| Required boundary | Gas flow set to animal size and CO₂ sensor calibrated to standard gas and fresh air |
| Do not infer alone | Substrate use or energy expenditure without the paired VO₂ |
Record VCO₂ on the same flow and timeline as VO₂ so RER is computed from synchronized samples. Calibrate the CO₂ analyzer to a standard gas and fresh air, and watch for transient VCO₂ spikes from hyperventilation or buffering that do not reflect steady-state oxidation.
VCO₂ tracks oxidative metabolism, but it can transiently exceed metabolic CO₂ during hyperventilation, acid buffering, or high-intensity exercise, and it lags VO₂ during rapid transitions. Read it with VO₂ and over a defined steady-state window.
Store animal ID, body mass, ambient temperature, gas flow rate, inflow and outflow CO₂ fraction, sampling interval, activity state, VCO₂ per minute, normalized VCO₂, paired VO₂, calibration record, and instrument or software version.
Endpoint pages should cite the method literature behind the scored value and keep high-specificity protocol claims qualified unless the source supports them.
Endpoint articles link to adjacent products, software workflows, and sibling endpoints where the connection is useful and already routable.
