Limitations and requirements for measuring metabolic rates: a mini review

Abstract

Metabolic measurement of humans and model animals is an important aspect of biomedicine. Particularly, in the case of model animals, the limitations of currently widely used metabolic measurement methods are not widely understood. In this mini-review, I explain the theoretical underpinnings of flow-through respirometry as a linear time-invariant system, and the (usually serious) distortions of metabolic data caused by the interaction of chamber volume and flow rate. These can be ameliorated by increasing the flow rate through the chamber, though this is at the expense of the magnitude of the O 2 depletion and CO 2 enhancement signals from which metabolic rates are calculated. If achieved, however, the improvement in temporal response that follows higher flow rates can be marked, and allows confident and accurate measurement of resting and active energy expenditure. Applications of this approach in multiplexing gas signals from multiple cages, and in human room calorimetry, are also discussed.

Network-Based Selection of Candidate Markers and Assays to Assess the Impact of Oral Immune Interventions on Gut Functions

“…In plasma/blood, levels of vitamins, minerals, iron and lipids can be determined (71), whereas in breath hydrogen (measure for carbohydrate malabsorption as a product of colonic bacterial fermentation) (71) and carbon dioxide (measure for triglyceride uptake) (71) are often used. In addition metabolic chambers (70) are used to measure the ratio of carbon dioxide and oxygen along with nitrogen. Urine is also frequently collected to assess for instance protein oxidation.…”

“…Methods to assess the supply of essential nutrients mostly include absorption assays and metabolic chambers (70). Parathyroid hormones might also be interesting to measure as it is the most important endocrine regulator of calcium and phosphorus concentration in extracellular fluid (99).…”

Disentangling environmental drivers of circadian metabolism in desert-adapted mice

“…We recorded oxygen consumption (VO 2 ), carbon dioxide production (VCO 2 ), and water vapor pressure (WVP, kPa) over 72-hours for an empty baseline chamber (e.g., ambient air) and seven animal chambers with an equivalent volume of 9.5 L. Air was pulled from chambers at a mass flow rate of 1600 ml/min (96 L/hr), multiplexed through the SSI MUXSCAN multiplexer, and sub-sampled at 250 ml/min, per the SSI FMS manual. A flow rate of 1600 ml/min and chamber volume of 9.5 L equate to a time constant of 5.9 minutes to sample and replace the entire container volume (Lighton, 2017). Chamber sampling alternated between a baseline chamber measurement for 120 s followed by a random animal chamber measurement for 120 s each, resulting in approximately two measurements per animal per hour.…”

“…VO 2 was used as a proxy for metabolic rate (MR), per Hulbert and Else (2004). As a measure of metabolic fuel use, the respiratory quotient (RQ, L/hr), also called the respiratory exchange rate (RER), was calculated as the ratio of VCO 2 to VO 2 (Lighton, 2017). Energy expenditure (EE, kcal/hr), or the sum of the basal metabolic rate (BMR), physical activity (typically, 4-16%; Abreu-Vieira et al, 2015), and cold-induced thermogenesis, was calculated as in Lighton (2017, eq. 9.15).…”

Reduced Nonexercise Activity Attenuates Negative Energy Balance in Mice Engaged in Voluntary Exercise

“…There are limited data regarding the contributions of VWR and OWA to EE in mice. This is because VWR and OWA are voluntary and typically are performed at low to moderate intensity, thus requiring sensitive instrumentation to detect an increase in EE (17). Only one report to date (18) has demonstrated an acute (within minutes) effect of VWR on EE and was performed in outbred deer mice.…”