Description and Validation of Flow-Through Chambers of Respirometry for Measuring Gas Exchange in Animal Trials

Abstract

Indirect calorimetry (IC) is a widely used method to study animal energy metabolism by measuring gas exchange. The accuracy of IC depends on detecting variations in signals reflecting the metabolic response, which can be challenging due to measurement noise and external factors. This study proposes a methodology to validate IC systems, including an easy-to-use spreadsheet for data computing, to verify accuracy and detect whole-system leaks. We conducted a recovery test using a simulation of CO₂ dynamics in MS Excel and injecting a known CO₂ concentration into four respirometry chambers. The thought flow rate of CO₂ was observed and compared to the expected rate from the simulation. Data filtering and computing, including a detailed calculation of signals calibration, Bartholomew transformation, and noise reduction, was developed to obtain the gas exchange and heat production parameters using an open-circuit IC system. The results from the recovery test in our system show that the proposed methodology is accurate and precise. The proposed methodology and recovery test can be used to standardize the validation of IC systems together with adequate data computing, providing accurate measurements of animal energy metabolism in different environmental conditions and energy utilization from feeds.

Keywords: energy expenditure; farm animals; gas exchange; metabolic rate; respirometric chambers.

Figure 1

Scheme of multiple flow-through respirometry systems and coupling to the gas for injection test. Fin: ingoing flow. Fout: outgoing flow. Finj: injection flow. CH_i: chambers (i = 1, 2, 3, 4). WVP: water vapor pressure analyzer. The arrows represent the airflow direction (→). Data transference line (●---●).

Figure 2

(A). Illustrative scheme of the recovery procedure with an injection of a known gas concentration (65% CO₂). Fin: ingoing flow. Fout: outgoing flow. Finj: pure gas injection flow. V_CH: chamber volume. Vbag: volume of the bag that contains tested gas. → airflow direction. (B). Phases of CO₂ recovery test and CO₂out behavior defined by the simulation. The tinj differentiates the injection and washing phases.

Figure 3

Example of recording, transforming, and filtering the gas concentration (O₂—oxygen and CO₂—dioxyde of carbon) sequence in a multi-chamber IC system. The black dashed line represents the recording time limit between chambers and the baseline.

Figure 4

Dynamic (per minute) of the injection of known concentration of CO₂ injected on each chamber and description of parameters of CO₂out(ti), ΔVCO₂, or Cumulative ΔVCO₂, and the error calculated for each time. Each line represents the behavior of each chamber (CHn, where n refers to different chambers). The shadow line describes the expected results per unit of time according to the simulation.

Figure 5

The curve of recorded signal (A) calibration and Bartholomew transformation applied to individual data (B) and filtered data with moving average (C) of the fractional concentration of CO₂. In the same way, it was applied to O₂.