COMPARISON OF VARIOUS METHODS FOR CALCULATING THE INSTANTANEOUS RESPIRATORY GASEOUS EXCHANGES FROM DISCRETE MEASUREMENTS IN RESPIRATION CHAMBERS

Whole body respiration chambers are characterized by a relatively low turnover rate of air which is a handicap for measuring the energy expe nditure associated with physiological phenomena of short duration. Thi s paper presents several mathematical methods, based either on integra tion or on derivative approaches, which can be used to calculate the i nstantaneous rates of gas exchange. The methods were then used to calc ulate and compare total, daily, lying and standing energy expenditure of a steer with its energy cost of standing. The influence of the meas urement frequency (1 vs. 5 min) was also tested. Total daily energy ex penditure as well as rates over short periods (lying or standing), cal culated on the basis of the integration approach, were influenced by t he measurement frequency chosen. Additionally, the various equations d erived from the integration approach yielded significantly different r esults. By contrast, the measurement frequency had little influence on the rates of energy expenditure calculated using the derivative appro ach. The best agreement between results obtained from the derivative a pproach was achieved at the 1 min measurement frequency, in particular with the higher order equations. This study showed the importance of the mathematical treatment of indirect calorimetry data and of the mea surement frequency on the interpretation of instantaneous rates of ene rgy expenditure and of the calculated energy cost of standing. (C) 199 7 Academic Press Limited.