Validity Test of a New Open-Circuit Indirect Calorimeter

Indirect calorimetry is an accurate way to measure resting metabolic rate. The Deltatrac Metabolic Monitor is considered a criterion standard but is no longer manufactured. New-generation indirect calorimeters have been introduced, but there are limited published validation data comparing these devices to criterion instruments.

A prospective, observational, N-of-1 trial was conducted to validate a new-generation indirect calorimeter against a gold standard device. This design was chosen to minimize and define the degree of biological variation, thus focusing on variation due to the devices. Measurements of gas exchange using both indirect calorimeters were conducted daily for 10 consecutive days. Another set of measurement pairs was conducted using just the criterion device for 10 days. Ninety-five percent confidence intervals of differences were used to test for bias. Precision was defined as repeat measures with one device falling within 5% of the other at least 90% of the time.

There were no statistically significant differences between the devices for any measured or calculated parameter. Interdevice differences were no larger than intradevice differences using the criterion instrument. The values obtained from the new device were precise and unbiased compared with the values obtained from the gold standard device.

The new indirect calorimeter measures gas exchange in a reliable and accurate manner compared with a gold standard device. The two devices are equivalent.