Comparison of two systems of measuring energy expenditure

BACKGROUND: Health care professionals typically use resting metabolic rate (RMR) via indirect calorimetry to determine a person's energy expenditure. Traditional indirect calorimetry measurements involve an expensive, cumbersome piece of equipment that requires careful calibration. The recent development of a handheld indirect calorimeter makes it easier to measure RMR. The purpose of this study was to compare simultaneous measurements of RMR with handheld and traditional indirect calorimeters. METHODS: Healthy, free-living subjects (n = 50) age 18 years and older were tested simultaneously with both indirect calorimeters. All subjects breathed through the handheld device using a mouthpiece while wearing noseclips to prevent leaks. The handheld indirect calorimetry device was placed inside a canopy. The exhaled gas from the handheld was positioned directly over the inlet to the port delivering gases to the traditional device's mixing chamber. The canopy facilitated the simultaneous collection of all expired gases into the traditional device. During the measurement, oxygen consumption and RMR were continuously recorded on a personal computer. RESULTS: Mean oxygen consumption and RMR did not significantly differ between the two devices, with a mean difference of 0.58 +/- 15.33 mL/min (p = .790) and 4.66 +/- 113.39 kcal/day (p = .773) and an absolute difference of 12.3 +/- 8.99 mL/min and 86.58 +/- 72.32 kcal/day, respectively. Correlation coefficients for oxygen consumption and RMR were 0.945 and 0.941, respectively. CONCLUSIONS: No significant difference was found between the measurements of indirect calorimetry with the MedGem (HealtheTech, Golden, CO) device compared with the DeltaTrac device (Datex-Ohmeda, Madison, WI). These findings suggest that the handheld indirect calorimeter may provide an accurate measure of oxygen consumption and RMR measurements for spontaneously breathing subjects.