Design, calibration and calculation for flow-through respirometry systems

Flow-through respirometry systems that measure oxygen consumption ((V) over dot(O2)), carbon dioxide production ((V) over dot(CO2)) and evaporative water loss (EWL) require the accurate calibration of the flow meter and three separate analysers (O-2, CO2 and H2O vapour). Correct measurement of (V) over dot(O2), (V) over dot(CO2) and EWL depends on the incurrent air flow ((V) over dot(I)) and its condition (e.g. dry, CO2-free), and the excurrent air flow ((V) over dot(E)) and its condition (e.g. dry, CO2-free), which can differ in different parts of the excurrent circuit. Usually either (V) over dot(I) or (V) over dot(E) is measured and the other is calculated from the gas composition. I describe here a procedure for precise calibration of CO2 and H2O analysers in a flow-through respirometry system by reference to a calibrated O-2 analyser, using a small gas flame. Generic equations are derived for calculation of (V) over dot(O2), (V) over dot(CO2) and EWL with a variety of configurations for a flow-through respirometry system. Procedures for selection of data from continuous records of (V) over dot(O2), (V) over dot(CO2) and EWL for calculation of minimal (basal or standard) values are briefly described. Finally, the importance of the correct order of data treatment prior to calculation is described.