|GRIBOK, ANDREI - University Of Tennessee|
|HOYT, REED - Us Army Medical Research Institute|
|BULLER, MARK - Us Army Medical Research Institute|
Submitted to: Physiological Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2013
Publication Date: 5/29/2013
Citation: Gribok, A., Hoyt, R., Buller, M., Rumpler, W.V. 2013. On the accuracy of instantaneous gas exchange rates, energy expenditure, and respiratory quotient calculations obtained in indirect whole room calorimeter. Physiological Reviews. 34(6):737-755.
Interpretive Summary: Measurement of whole body energy expenditure and fuel usage based on oxygen consumption and carbon dioxide production is inherently noisy over short periods of time and insensitive over longer periods due to the intermittent nature of respiration. Investigations into whole body energy usage by humans have typically examined short periods of time (several minutes to an hour) under restrictive conditions to increase stability of the measures or longer periods (single days to multiple days) under free living conditions or in the semi restrictive environment of a calorimeter to increase the stability of the measures. In this paper we examine a mathematical approach to improve the sensitivity of long term measures and increase the stability of short term measures. The application of this methodology allows investigators to look a short term effects over long periods of time while minimizing the instability of the measurement.
Technical Abstract: This paper analyzes the accuracy of metabolic rate calculations performed in the whole room indirect calorimeter using the molar balance equations. The equations are treated from the point of view of cause-effect relationship where the gaseous exchange rates representing the unknown causes need to be inferred from a known, noisy effect – gaseous concentrations. Two methods of such inference are analyzed. The first method is based on the previously published regularized deconvolution of the molar balance equation and the second one, proposed in this paper, relies on regularized differentiation of gaseous concentrations. It is found that both methods produce similar results for the absolute values of metabolic variables and their accuracy. The uncertainty for O2 consumption rate is found to be 7% and for CO2 production – 3.2%. The uncertainties in gaseous exchange rates do not depend on the absolute values of O2 consumption and CO2 production. In contrast, the absolute uncertainty in RQ is a function of the gaseous exchange rates and varies from 9.4% during the night to 2.3% during moderate exercise. The uncertainty in energy expenditure was found to be 5.9% and independent of the level of gaseous exchange. For both methods, closed form analytical formulas for confidence intervals are provided allowing quantification of uncertainty for four major metabolic variables in real world studies.