Comparison of Various Methods of 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 expenditure associated with physiological phenomena of short duration. This paper presents several mathematic methods, based either on integration or on derivative approaches, which can be used to calculate the instantaneous rates of gas exchange. The methods were then used to calculate and compare total, daily, lying and standing energy expenditure of a steer with its energy cost of standing. The influence of the measurement frequency (1 vs. 5 min) was also tested. Total daily energy expenditure as well as rates over short periods (lying or standing), calculated on the basis of the integration approach, were influenced by the measurement frequency chosen. Additionally, the various equations derived from the integration approach yielded significantly different results. By contrast, the measurement frequency had little influence on the rate of energy expenditure calculated using the derivative approach. The best agreement between results obtained from the derivative approach 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 measurement frequency on the interpretation of instantaneous rates of energy expenditure and of the calculated energy cost of standing.