Automated open flow respirometry in continuous and long-term measurements: design and principles

Abstract

Sustaining high-quality respirometry measurements on animals for estimating metabolic rate and fuel use is challenging. I present a general discussion and selected methods for automated measurements spanning over >4 mo with little need for adjustments or maintenance. 1) Lack of compensation for respiratory volume change may cause 6% error in the results on a fasting animal. The Haldane transformation provides the simplest calculation method for both O2and CO2measurements. 2) Use of Nafion tube dryers configured as countercurrent moisture exchangers provides maintenance-free drying of gases, with typical outlet dew points at −25 to −38°C and no CO2adsorption. The accuracy is improved by low dead space, making it feasible to pass gases though the same dryer. 3) A software algorithm employing a triple interpolation technique allows corrections for automated calibrations of O2and CO2with both zero-reference and span gas. 4) Burning known amounts of 100% ethanol provides total system verification of both O2consumption and respiratory quotient. A calculation method to supply instant CO2calibration gas from an alcohol burn is presented. 5) Automatic flow switching triggered by low/high O2thresholds improves accuracy of measurements and safety for the animals experiencing large ranges of O2consumption; this is a special requirement for recording metabolism in small hibernating mammals.