Comparison of Three Metabolic Carts Using a Metabolic Calibrator

Abstract

Previous research has investigated the accuracy and reliability metabolic carts, but most studies used previously “validated” systems as the standard or compared the systems simultaneously. The current investigation utilizes the first commercially available, portable metabolic calibrator which is capable of reproducible ventilation and metabolic values. PURPOSE: To evaluate the accuracy and reliability of three different metabolic carts using the same standard, a metabolic calibrator. METHODS: The mechanical calibrator consisted of a piston pump capable of producing various ventilation frequencies and tidal volumes. The calibrator mixed room air with 21 % CO2 to produce O2 and CO2 values within the physiological range. The same protocol was used for each metabolic cart and consisted of tidal volumes varying from 1 to 3 L, breath frequency from 8–50/min and gas mixtures that resulted in VO2 from 512–3151 ml/min and VCO2 from 522–3210 ml/min. Each metabolic cart investigated was tested twice in succession following calibration instructions provided by the manufacturer. The following metabolic carts were tested: ParvoMedics True Max 2400 (2 different carts); SensorMedics Vmax 29c (2 carts); and VacuMed Vista Mini-CPX silver edition (1 cart). RESULTS: The ParvoMedics systems produced mean errors of 7.2% for VO measurements and 4.5% for VCO2 measurements. The Sensormedics breath-by breath system showed the greatest errors for VO2, with an average underestimation of 13.60% with 3.35% errors for VCO2. Conversely, the Sensormedics mixing chamber system produced the lowest average errors of 1.4% for VO and 1.1% for VCO The VacuMed system averaged 1.1% error in measurements of VO2 and 5.1% error in measurements of VCO2. However, the average errors are misleading because of the drastic changes that were seen between trials and between identical models through the study. CONCLUSION: The most accurate system was the SensorMedics Vmax 29c with the optional 4-liter mixing chamber. Further studies are needed to eliminate some of the calibration complications experienced during these trials and to further investigate the characteristics of other metabolic carts.