A system for contact free energy expenditure assessment under free-living conditions: monitoring metabolism for weight loss using carbon dioxide emission

Abstract

Weight disorders are strikingly prevalent globally and can contribute to a wide array of potentially fatal diseases spanning from type II diabetes to coronary heart disease. These disorders have a common cause: poor calorie balance. Since energy expenditure (EE) (kcal d−1) constitutes one half of the calorie balance equation (the other half being food intake), its measurement could be of great value to those suffering from weight disorders. A technique for contact free assessment of EE is presented, which only relies on CO2 concentration monitoring within a sealed office space, and assessment of carbon dioxide production rate (VCO2). Twenty healthy subjects were tested in a cross-sectional study to evaluate the performance of the aforementioned technique in measuring both resting EE (REE) and exercise EE using the proposed system (the ‘SmartPad’) and a U.S. Food and Drug Administration (FDA) cleared gold standard reference instrument for EE measurement. For VCO2 and EE measurements, the method showed a correlation slope of 1.00 and 1.03 with regression coefficients of 0.99 and 0.99, respectively, and Bland–Altman plots with a mean bias = −0.232% with respect to the reference instrument. Furthermore, two subjects were also tested as part of a proof-of-concept longitudinal study where EE patterns were simultaneously tracked with body weight, sleep, stress, and step counts using a smartwatch over the course of a month, to determine correlation between the aforementioned parameters and EE. Analysis revealed moderately high correlation coefficients (Pearson’s r) for stress (r average = 0.609) and body weight (r average = 0.597) for the two subjects. The new SmartPad method was demonstrated to be a promising technique for EE measurement under free-living conditions.

A Smart System for the Contactless Measurement of Energy Expenditure

“…In this work we focus on assessing λ Acc with high accuracy so that we can formally study the correlation of λ Acc vs. λ o and λ Acc vs. VCO 2 (k gen ). In order to do this, we build upon the previous work [ 26 ] in which λ Acc was assessed using a reference instrument. Here, we build upon that work by using a reference instrument to provide a high-accuracy value of λ Acc (using k gen derived from an FDA 510(k)-cleared device’s VCO 2 measure) and λ 0 from CO 2 decay in the exact same environment following the subject’s departure.…”

“…Previous findings [ 26 ] suggested that k gen was correlated to the actual k gen ′ via an environmental correction factor (CF env ) of 1.143, an empirical constant determined to correct for mean error bias originating from any source not accounted for in the “ideal model” used in Equation (1), e.g., imperfect mixing, CO 2 sensor response time, etc., and is used in the model as follows: …”

“…The Smart Pad’s room conditioning involves the connection of the inlet and/or outlet ventilation fan/s to the Smart Pad actuator (see details below). A previous work [ 26 ] reports on the analytical accuracy of the Smart Pad system in one simple configuration within a clinical setting and performing measurements on 20 subjects using a reference instrument for EE measurement in parallel with the Smart Pad. This manuscript builds upon that work by optimizing the operating parameter of EE measurement resolution while also maximizing measurement accuracy.…”

“…Recently, λ values obtained from decay modelling have been applied to CO 2 accumulation data for determination of human CO 2 production rate (VCO 2 ) in cognitively stressed subjects [ 48 ]. Our previous study [ 26 ] accounted for λ by calibration with a reference instrument’s VCO 2 measurements during CO 2 accumulation in an 8 m 3 sized room and the technique was shown to be accurate for assessment of an individual’s VCO 2 . Here, we implemented this EE assessment technique by utilizing a fully developed and automated Smart Pad system while investigating two methods of assessing λ values: Method A, named “λ Acc ”, with λ values assessed from CO 2 accumulation data collected in presence of a subject of known VCO 2 ; and Method B, named “λ o ”, with λ values assessed from CO 2 decay data collected in the absence of the subject.…”

“…Both methods were carried out in a medium-sized test room. Additionally, a strong correlation between λ Acc and VCO 2 was observed, which led to the development of a novel model for VCO 2 and REE assessment within an occupied room that does not rely directly on λ calibration using a reference instrument [ 26 ] or λ assessment from CO 2 decay rate [ 46 ]. The model shows good agreement for REE assessment when compared to independent measurements from a reference instrument.…”