Validation of an indirect calorimeter using n-of-1 methodology

Summary Background Validation data for currently available indirect calorimeters is limited. The purpose of this investigation was to validate a newer indirect calorimeter system (Vmax Encore) against a criterion device (Deltatrac Metabolic Monitor) in spontaneously breathing mode. Materials and methods An n-of-1 methodology was used in which both indirect calorimeters were employed in the same subject repeatedly until 15 measurement pairs were generated for oxygen consumption (VO 2 ), carbon dioxide production (VCO 2 ), resting metabolic rate (RMR), and respiratory quotient (RQ). Bias was defined as a 95% confidence interval of differences between devices that excluded zero. A set of intradevice measurement pairs was also obtained to analyze the precision of the Vmax and Deltatrac (precision defined as not more than 5% of measurements being ≥5% different). Results Both Vmax and Deltatrac precisely measured VO 2 and RMR. The largest intradevice difference for RMR in the Deltatrac was 4.7% (one of 20 pairs) and in the Vmax 4.8%. On the other hand, VCO 2 and RQ were not measured precisely by either device, with 10% or more of the measurement pairs differing by ≥ 5%. The Vmax was biased toward low measurement of VO 2 and RMR relative to the Deltatrac. Oxygen consumption was on average 4.5 ± 2.4% lower for the Vmax device compared to Deltatrac while RMR was lower by an average of 4.1 ± 2.2%. Conclusions The Vmax Encore indirect calorimeter is a precise instrument for measuring VO 2 and RMR in spontaneously breathing individuals, but it is biased toward lower values compared to the Deltatrac.