Resting Metabolic Rate Values When Measured Using A Ventilated Canopy System Versus A Non-ventilated Silicone Mask

The gold standard for measuring resting metabolic rate (RMR) via indirect calorimetry is using a ventilated canopy system (canopy). Yet, many use a non-ventilated silicone mask (mask) for evaluating RMR. PURPOSE: to methodically compare RMR measurement via indirect calorimetry using a canopy and a mask. METHODS: 44 participants attended the lab following an overnight fast. While supine, RMR was measured for 40 minutes using a canopy or a mask, followed immediately by a second RMR measurement using the opposite mode. The order of canopy vs mask was randomized. VO2, VCO2, RER and RMR were compared between canopy and mask using a paired t-test. Bland-Altman analysis was conducted to determine the limits of agreement (LOA) between canopy and mask RMR. RESULTS: Data are mean ± SEM. Resting VO2, RER and RMR were significantly different between canopy and mask (VO2 = 3.67 ± 0.09 vs 3.47 ± 0.08 l/min; RER = 0.72 ± 0.007 vs 0.78 ± 0.007; RMR = 1740.22 ± 53.86 vs 1694.14 ± 54.85 kcal in canopy vs mask, p < 0.05 for all). Although showing high individual variance (SD = 129.91 kcal), mean RMR difference between canopy and mask was 46.07 ± 19.58 kcal and was significantly different than zero in a one-sample t-test (p = 0.023, 95%CI = 6.58 - 85.57 kcal). Pearson correlation between the canopy and mask was strong (r = 0.935, p < 0.001). Bland-Altman analysis suggest no consistent bias between the measurements, but LOA were large (95% LOA = -300.7 to 208.6 kcal). When analyzing these differences separately based on sex, males (n = 24) had a smaller and females (n = 20) larger difference in RMR between canopy and mask (canopy vs mask difference 39.34 ± 28.73 kcal, p = 0.184 and 54.16 ± 26.53 kcal, p = 0.055, for males and females, respectively). Pearson correlation between canopy and mask was stronger in males and less strong in females (r = 0.931 vs r = 0.772, p < 0.001, for males and females, respectively). CONCLUSION: When measuring RMR via indirect calorimetry, using a non-ventilated silicone mask might be an acceptable alternative to ventilated canopy but the detected bias was non-consistent, and therefore cannot be corrected computationally. It is advisable to compare the 2 modes for every subject. This might result in a significant burden for the researcher and the subject and is a major disadvantage for the use of a silicone mask in the measurement of RMR.