Evaluation of a canopy system and a simple calorimeter for resting metabolism using a respiratory simulator

The evaluation of energy expenditure is of great importance, not only during health promotion, but also during recovery from disease. The measurement of oxygen uptake is the most reliable method for measuring energy expenditure, but, for estimating resting metabolism, there is still a need for sophisticated equipment. We have developed and evaluated a simple calorimeter and compared it with the flow-through (Canopy) system. A respiratory simulator was used to evaluate oxygen uptake at different flow rates. A known concentration of mixed gases flows into the system via the respiratory simulator and the oxygen concentrations and flow rates were compared. The results indicate that large errors in the measurement of oxygen uptake occurred at low flow rates, but these errors were about 5% under estimated values in the simple calorimeter. The measurement error at low flow rates is about 10% in the Canopy system. From these results, we concluded that the simple calorimeter can be used to measure oxygen uptake under resting conditions; however, the Canopy system would be unsuitable for measurement in a subject with small ventilation, such as an elderly patient. Great attention is needed when these oxygen measurement systems are applied to patients with very low flow rates.