Evaluation of mixing chamber systems for low respiratory rate using a respiratory simulator

The measurement of oxygen (O₂) uptake is the most reliable method for measuring energy expenditure, but, for estimating resting metabolism with low respiratory rates, there is still a need for sophisticated equipment. We have evaluated two commercial mixing chamber type that recommend measuring resting metabolism using a respiratory simulator at different flow rates. The results indicated that large errors of O₂ uptake occurred at low flow rates, but these errors were less than 5% at over 5 l/min in the calorimeter used rotameter. While the device used Pitot flowmeter could not detect the flow rate under the condition of 2.59 l/min. However, the error in O₂ uptake using both devices showed less than 5%. We concluded that the both mixing chamber systems seem to be used to measure O₂ uptake under resting normal conditions.