| Effective volume
To generate a washout curve, set up the respirometry system as it is normally used (but without an animal) at the flow rate used for measurements. Make a recording of gas concentration, starting at equilibrium levels. After establishing a baseline, deflect concentration by rapidly exhaling into the incurrent flow upstream from the chamber (or quickly inject a bolus of some gas with different concentration than reference gas). Continue recording as gas concentration rapidly peaks, slowly declines, and eventually returns to equilibrium concentration. Save the data. In LabAnalyst, correct the baseline to zero, even for oxygen files (it will probably help to smooth the data also). Mark a block in the washout curve as it returns to equilibrium. Usually it is best to select from the middle of the washout curve. Then select the effective volume option. LabAnalyst will request the flow rate and compute effective volume.