Improving temporal accuracy of human metabolic chambers for dynamic metabolic studies

Abstract

Metabolic chambers are powerful tools for assessing human energy expenditure, providing flexibility and comfort for the subjects in a near free-living environment. However, the flexibility offered by the large living room size creates challenges in the assessment of dynamic human metabolic signals—such as those generated during high-intensity interval training and short-term involuntary physical activities—with sufficient temporal accuracy. Therefore, this paper presents methods to improve the temporal accuracy of metabolic chambers. The proposed methods include 1) adopting a shortest possible step size, here one minute, to compute the finite derivative terms for the metabolic rate calculation, and 2) applying a robust noise reduction method—total variation denoising—to minimize the large noise generated by the short derivative term whilst preserving the transient edges of the dynamic metabolic signals. Validated against 24-hour gas infusion tests, the proposed method reconstructs dynamic metabolic signals with the best temporal accuracy among state-of-the-art approaches, achieving a root mean square error of 0.27 kcal/min (18.8 J/s), while maintaining a low cumulative error in 24-hour total energy expenditure of less than 45 kcal/day (188280 J/day). When applied to a human exercise session, the proposed methods also show the best performance in terms of recovering the dynamics of exercise energy expenditure. Overall, the proposed methods improve the temporal resolution of the chamber system, enabling metabolic studies involving dynamic signals such as short interval exercises to carry out the metabolic chambers.

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

“…Figure 2 illustrates that our AMR protocol and the previously-validated method for improving the temporal resolution of the WRICs 3 were successful in capturing the fast-changing dynamics of exercise MR in the WRICs. The steady states at the three intensity levels were clearly delineated by the 10-min rest intervals using our previously published methods 3 . Comparisons of the agreement between instruments at each exercise level are listed in Table 3, and illustrated by the Bland-Altman plots in Supplementary Information Figure S5.…”

“…All gas samples during the studies were dried below 1,000 ppm using a gas sample dryer (manufactured by Perma Pure LLC, Lakewood, NJ). Other operational details of the WRICs have previously been published 3 .…”

“…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.…”

“…Although WRICs provide researchers with more flexibility to study the effects of sedentary behavior 33 and various activity types and intensities on total MR 34 – 38 , the “dilution effect” caused by the room size of the WRICs 3 limits their temporal resolution, which has traditionally hindered their use in short-interval exercise studies. To remedy the long delay imposed by the room size of WRICs, we have recently devised a method to improve the temporal resolution of WRICs and validated our system against 22 sessions of 24-h gas infusion studies of dynamic metabolic profiles 3 . Here, we further evaluate our system using data collected from 29 human subjects under both resting and exercising conditions, investigate the biases between instruments, and quantify the sources of variation in the MR mesurements.…”

Combination Therapy for Hypothyroidism: Rationale, Therapeutic Goals, and Design

“…Moreover, these systems do not capture all the components of energy expenditure. A more comprehensive strategy would be using extended recordings in whole room indirect calorimeters ( 51 ), but only few institutions have these instruments. One can envision, though, their use in proof of concept studies or in a nested study in the context of a large multicenter trial.…”