AN APPARATUS TO ATTAIN AND MAINTAIN TARGET END TIDAL PARTIAL PRESSURE OF A GAS

A method of controlling an amount of gas X in a subject's lung using a sequential gas delivery circuit to attain a targeted end tidal partial pressure of gas X, the method comprising: obtaining input of a concentration of gas X in the mixed venous blood entering the subject's pulmonary circulation for gas exchange in one or more respective breaths [i] (CMVX[i]); obtaining input of a logistically attainable end tidal partial pressure of gas X (PetX[i]T) for a respective breath [i]; obtaining input of a prospective computation of an amount of gas X required to be inspired by the subject in an inspired gas to target the PetX[i]T for a respective breath [i] using inputs required to compute a mass balance equation including CMVX[i] and values to compute the contribution of one or more discrete volumetric components of breath [i] to the concentration of gas X in the subject's alveoli, wherein one or more values required to control the amount of gas X in a volume of gas delivered to the subject is output from the mass balance equation; and optionally controlling the amount gas X in a volume of gas delivered to the subject by the sequential gas delivery circuit in a respective breath [i] to target the respective PetX[i] based on the prospective computation.