A respiratory metabolic simulator includes a cell that produces CO2 and depletes O2, e.g., a direct methanol fuel cell having an external electrical circuit. An electric load is applied to the external electrical circuit of the direct methanol fuel cell to vary the electrical load applied to the external electrical circuit of the direct methanol fuel cell to produce carbon dioxide. The carbon dioxide generated by the direct methanol fuel cell is supplied to respiration gases produced by the respiratory metabolic simulator. The direct methanol fuel cell is also used to remove oxygen from the respiration gases prior to mixing the respiration gases and the carbon dioxide.
