Closed-system respirometry
This calculator computes rates of oxygen consumption (VO2) and/or carbon dioxide production (VCO2) in air or other breathable gas mixture in a closed system (i.e, the animal is sealed in an air-tight chamber for some time and metabolism is computed by the change in concentration of O2 and CO2 between initial and final gas samples). You need to enter:
  • chamber temperature, pressure, and relative humidity (when sealed, not at the end of measurements).
  • chamber volume
  • elapsed time (between taking the initial and final gas samples)
  • initial fractional concentrations of O2 (FiO2) and CO2 (FiCO2)
  • the change in concentration (in percent) of oxygen and/or CO2, and the respiratory quotient (RQ)
      
If you measure only one of these two gas species, the program will use RQ to estimate the other. If you measure both O2 and CO2 concentration changes, the program will optionally use O2 in the calculation of VCO2. NOTE: it is assumed that sample gas is dried before measurement, and the default settings are:
  • Initial O2 concentration (FiO2) = .2095
  • Initial CO2 concentration (FiCO2) = .0004
  • CO2 is absorbed prior to O2 measurement
  • VCO2 is computed from VO2, if oxygen is measured, or from RQ otherwise

Equations notes:
  • STP = standard temperature and pressure (0°C, 760 torr)
  • Δ[O2] = fractional change in O2 concentration
  • Δ[CO2] = fractional change in CO2 concentration
  • FeO2 = FiO2 - Δ[O2]
  • FeCO2 = FiCO2 + Δ[CO2]
VO2 equations:
  • CO2 is absorbed: VO2 = STP volume * Δ[O2] /(1 - FeO2)
  • CO2 NOT absorbed, compute from Δ[CO2]: VO2 = STP volume * (Δ[O2] - (FeO2 * Δ[CO2])/(1 - FeO2)
  • CO2 NOT absorbed, compute from RQ: VO2 = STP volume * (Δ[O2] /(1 - FeO2 * (1-RQ))
VCO2 equations: NOTE: at typical Δ[CO2], different equations have little effect on calculated VCO2
  • from RQ: VCO2 = STP volume * Δ[CO2]/(1 - FeCO2 * (1-(1/RQ)))
  • from VO2: VCO2 = STP volume * (Δ[CO2] - (FeCO2 * VO2))/(1 - FeCO2)

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