The gas recovery test of respiratory chambers

Respiratory Chambers (RCs) were originally constructed with the purpose to study heat production from animals by quantifying oxygen (O2) consumption and carbon dioxide (CO2) production (initially detailed in the 18th century by Lavoisier and Leplace; for the history of calorimetry, see McLean and Tobin [1]. Enteric methane (CH4) is measured in calorimetry studies, as CH4 is an energy loss [2], [3]. The RC can therefore be used to quantify the CH4 production from animals, and many new RC units have been constructed during the last decades with the main aim of measuring CH4. The constructed RCs in research institutes differ in the design or material; however, their principles remain relatively similar. There are both hypobaric (= pull type) and hyperbaric (= push type) RCs, respectively, controlling air pressure below and above atmospheric pressure, depending on the position of the pumping system [4]. The majority of chambers is designed so that the air is sucked through the chamber (pull type/under-pressure), which requires more effort in terms of maintenance and calibration requirement for the gas meters than in push-type systems, where dust and NH3 loads are much less abundant. For all types of chambers, continuous measuring of all gasses of outside air content is essential as there might be contaminant levels, which should not be neglected. A recent ring-test study in the UK revealed that different RC installments are at risk of producing data that is of poorer accuracy than is ideally required [5]. This risk can be avoided through adoption of appropriate calibration regimes for all sensors within a RC system. Finally, proper validation of chambers is necessary for better comparison of gas production from cattle between facilities. Although calibration of different compartments of the RC is essential, particularly in identifying the source of errors, validating the whole system is without a doubt the most crucial of all in establishing the overall performance assessment. A set of tests needs to be established and implemented in order to identify and quantify different systemic and random uncertainties of the RC system. Knowledge about these types of uncertainties is vital for rapid elimination or appropriate correction of data, which in turn improves the accuracy of the gas exchange measurement.