An appraisal of whole-room indirect calorimeters and a metabolic cart for measuring resting and active metabolic rates

Abstract

Whole-room indirect calorimeters (WRICs) have traditionally been used for real-time resting metabolic rate (RMR) measurements, while metabolic rate (MR) during short-interval exercises has commonly been measured by metabolic carts (MCs). This study aims to investigate the feasibility of incorporating short-interval exercises into WRIC study protocols by comparing the performance of WRICs and an MC. We assessed the 40-min RMR of 15 subjects with 2-day repeats and the 10-15 min activity MR (AMR) of 14 subjects at three intensities, using a large WRIC, a small WRIC, and an MC. We evaluated the biases between the instruments and quantified sources of variation using variance component analysis. All three instruments showed good agreement for both RMR (maximum bias = 0.07 kcal/ min) and AMR assessment (maximum bias = 0.53 kcal/min). Moreover, the majority of the variability was between-subject and between-intensity variation, whereas the types of instrument contributed only a small amount to total variation in RMR (2%) and AMR (0.2%) data. In Conclusion, the good reproducibility among the instruments indicates that they may be used interchangeably in welldesigned studies. Overall, WRICs can serve as an accurate and versatile means of assessing MR, capable of integrating RMR and short-interval AMR assessments into a single protocol. Whole-room indirect calorimeters (WRICs) have been used to assess various metabolic states in both healthy subjects and subjects affected by pathologies 1,2. A WRIC, an isolated room with a known volume and a controlled air inflow rate, provides minute-by-minute measurements of the subject's O 2 consumption and CO 2 production from breaths, via the continuous measurement of O 2 and CO 2 concentrations in inflow air and outflow air. These data enable precise calculations of metabolic rate (MR, unit: kcal/min) for prolonged periods allowing for activities of daily living 3 , and energy expenditure (EE, unit: kcal), which is the cumulative MR over time. Hence, MR and EE in the general sense are used interchangeably in the medical literature and in this paper. Human EE is comprised of various components and is influenced by many factors. The largest component of human EE is resting EE, which is the energy required to carry out fundamental physiological functions, contributing 60-80% of the total daily EE 4. RMR is influenced by various physiological characteristics, including gender 5 , ethnicity 6 , age 7, 8 , body composition 9,10 , various metabolic syndromes 11-16 , and gene variations 17. Additionally, resting MR (RMR) responds to environmental stimuli, such as cold temperatures 18,19 , food intake and dietary composition 20-24. Moreover, RMR drops significantly during sleep 25 and varies by circadian phase 26. A smaller, yet important component of human MR is activity-induced MR (AMR) 27. Activities can be subdivided into two categories: non-exercise activity thermogenesis (NEAT) and volitional exercise 28,29. NEAT includes occupational and leisure activities and any spontaneous activitie...

Validity and reproducibility of a whole‐room indirect calorimeter for the estimation of VO2, VCO2, and resting metabolic rate

“…Although this observation may be due to differences in protocol, sample size, and instrumentation, smaller WRICs have shorter response times and require smaller correction factors for room volume during short-term measurements, possibly increasing precision (Chen, Smith, et al, 2020). Related to this, a study comparing 40-min measurements of RMR in one large (26,000 L) and one small (5500 L) WRIC observed a relative difference of ~4% between the two measurements (Chen, Scott, et al, 2020), possibly due to the difference in response time.…”

Acute Effects of Liothyronine Administration on Cardiovascular System and Energy Metabolism in Healthy Volunteers

“…This WRIC system allows for accurate and fast measure of energy expenditure (EE) with an error of ±45kcal/day (0.03 kcal/min on average). This error range means that a meaningful effect size in EE is above 0.06 kcal/min ( 2 , 3 ). Throughout the recording the study participants were seated on a phlebotomy chair in resting position.…”

“…This is commonly achieved with levothyroxine (LT4) which is relatively inexpensive, available in multiple strengths and administered in single dose. This strategy relies on the conversion of the prodrug LT4 into its active metabolite T3 to correct the lack of endogenous T3 production (estimated as 15% of the total circulating pool) from the thyroid gland ( 3 ). Experimental data ( 4 , 5 ) indicate that LT4 alone is not sufficient to restore tissue euthyroidism, and clinical observations ( 6 ) demonstrate that circulating levels of T3 are reduced in patients receiving LT4 therapy.…”