Figure 36-5 Bymixer. This compartment, placed in the expiratory limb of a circle system, provides a mixing chamber through which a portion of the exhaled gas flows. Mixing of gas within this chamber provides constant mixed expired O₂ and CO₂ concentrations, from which V̇O₂ , V̇CO₂ , and dead space can be calculated. (Adapted from Breen PH, Serina ER: Bymixer provides on-line calibration of measurement of CO₂ volume exhaled per breath. Ann Biomed Eng 25:164, 1997.)