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

Toien O. Automated open flow respirometry in continuous and long-term measurements: design and principles. J Appl Physiol 114: 1094-1107, 2013. First published January 24, 2013; doi:10.1152/japplphysiol.01494.2012.-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 O-2 and CO2 measurements. 2) Use of Nafion tube dryers configured as counter-current moisture exchangers provides maintenance-free drying of gases, with typical outlet dew points at -25 to -38 degrees C and no CO2 adsorption. 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 O-2 and CO2 with both zero-reference and span gas. 4) Burning known amounts of 100% ethanol provides total system verification of both O-2 consumption and respiratory quotient. A calculation method to supply instant CO2 calibration gas from an alcohol burn is presented. 5) Automatic flow switching triggered by low/high O-2 thresholds improves accuracy of measurements and safety for the animals experiencing large ranges of O-2 consumption; this is a special requirement for recording metabolism in small hibernating mammals.