Design, calibration and calculation for flow-through respirometry systems

Abstract

Flow-through respirometry systems that measure oxygen consumption (VO₂), carbon dioxide production (VCO₂) and evaporative water loss (EWL) require the accurate calibration of the flow meter and three separate analysers (O₂, CO₂ and H₂O vapour). Correct measurement of VO₂, VCO₂ and EWL depends on the incurrent air flow (V_I) and its condition (e.g. dry, CO₂-free), and the excurrent air flow (V_E) and its condition (e.g. dry, CO₂-free), which can differ in different parts of the excurrent circuit. Usually either V_I or V_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 O₂ analyser, using a small gas flame. Generic equations are derived for calculation of VO₂, VO₂ and EWL with a variety of configurations for a flow-through respirometry system. Procedures for selection of data from continuous records of VO₂, VCO₂ 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.