What is a Metabolic Cart?
A Metabolic Cart measures:
- Pulmonary Ventilation of every breath
- Oxygen concentration – both inspiratory and expiratory
- Carbon Dioxide concentration – again both inspiratory and expiratory
- Also ambient Temperature, Pressure, & Humidity. Temperature, Pressure, & Humidity are used to convert the metabolic data from Atmospheric conditions to Standard Temperature, Pressure and Dry conditions, or STPD.
- Finally, this measurement data is used to calculate O2 Consumption and CO2 Production and other Metabolic Data.
There are 2 types of Metabolic Carts:
- The Breath-by-Breath System. In the Breath-by-Breath System the gas sample is drawn directly from the Subject’s mouth to be analyzed by the Gas Analyzers.
- The Mixing Chamber System. Mixing Chamber Systems typically adds 2 additional components: a Non-rebreathing Valve and a Mixing Chamber. The Non-rebreathing Valve allows only Expiratory Air into the Mixing Chamber. The Mixing Chamber mixes the Expiratory Air for a more homogeneous sample. The gas sample is then drawn directly from the Mixing Chamber to be analyzed by the Gas Analyzers.
BOTH System types have their respective advantages and disadvantages. However, AEI and many researchers believe that Mixing Chamber Systems advantages far outweigh the disadvantages and are more accurate in determining VO2 and VCO2.