Method and apparatus to attain and maintain target arterial blood gas concentrations using ramp sequences

An apparatus for controlling an amount of at least one gas X in a subject's lung to attain a targeted end tidal partial pressure of the at least one gas X (PetXT), the apparatus comprising:

• (1) a gas delivery device;
• (2) a control system for controlling the gas delivery device, wherein the control system is adapted to target a PETXT value with a respective breath [i], the PETXT value comprising either a PETXT increment or a PETXTdecrement, the control system configured to:
• a. Obtain input of a logistically attainable PETXT value for the respective breath [i];
• b. Perform a prospective computation of an amount of gas X required to be inspired by the subject in an inspired gas to target the PETXT for the respective breath [i] the performing comprising:
• i. Computing a tidal model of the subject's lung including input of the concentration of gas X in the mixed venous blood entering the subject's pulmonary circulation for gas exchange in the respective breath [i] (CMVX[i]);
• and
• ii. Outputting one or more values required to control the amount of gas X in a volume of gas delivered to the subject, based on the tidal model of the subject's lung;
• and
• c. Control the amount of gas X in a volume of gas delivered to the subject in the respective breath [i] (FIX) to target the respective PETXT for the breath [i].

The apparatus of claim 4 wherein tuning the estimated value of the functional residual capacity comprises:

• changing the targeted end tidal partial pressure of gas X between a tuning breath [i+x] and a previous tuning breath [i+x−1];
• comparing the magnitude of the difference between the targeted end tidal partial pressure of gas X for said tuning breaths [i+x] and [i+x−1] with the magnitude of the difference between the measured end tidal partial pressure of gas X for the same tuning breaths to quantify any discrepancy in relative magnitude;
• and
• adjusting the estimated value of the functional residual capacity in proportion to the discrepancy to reduce the discrepancy in any subsequent prospective computing of F/X

The apparatus of claim 4 wherein tuning the estimated value of the functional residual capacity comprises:

• obtaining input of a measured baseline steady state value of PETX[i] for computing FIX at the start of a sequence;
• selecting a target end tidal partial pressure of gas X (PETX[i]T) for at least one tuning breath [i+x] wherein PETX[i+x]T differs from PETX[i+x−1]T;
• comparing the magnitude of the difference between the targeted end tidal partial pressure of gas X for said tuning breaths [i+x] and [i+x−1] with the magnitude of the difference between the measured end tidal partial pressure of gas X for the same tuning breaths to quantify any discrepancy in relative magnitude;
• and
• adjusting the estimated value of the functional residual capacity in proportion to any discrepancy in magnitude to reduce the discrepancy in a subsequent prospective computation of F/X including in any subsequent corresponding tuning breaths [i+x−1] and [i+x] forming part of an iteration of the sequence.

A computer program product for use in conjunction with a gas delivery device to control an amount of at least one gas X in a subject's lung to attain a target end tidal partial pressure of the at least one gas X (PETXT), the computer program comprising program code for:

• a. obtaining input of a logistically attainable end tidal partial pressure of gas X (PETXT) for a respective breath [i];
• and
• b. performing a prospective computation to obtain input of an amount of gas X required to be inspired by the subject in an inspired gas to target the PETXTfor the respective breath [i] (F/X), the performing comprising:
• i. computing a tidal model of the subject's lung including input of the concentration of gas X in the mixed venous blood entering the subject's pulmonary circulation for gas exchange in the respective breath [i] (CMVX[i]);
• and
• ii. outputting one or more values required to control FIX, based on tidal model of the subject's lung.

A method for controlling an amount of at least one gas X in a subject's lung to attain a targeted end tidal partial pressure of at least one gas X (PETXT), the method comprising:

• a. obtaining input of a logistically attainable PETXTvalue for a respective breath
• [i] comprising either a PETXT increment or a PETXTdecrement;
• and
• b. performing a prospective computation of an amount of gas X required to be inspired by the subject in an inspired gas to target the respective PETXTfor the respective breath [i] (F/X), the performing comprising:
• i. computing a tidal model of the subject's lung including input of the concentration of gas X in the mixed venous blood entering the subject's pulmonary circulation for gas exchange in the respective breath [i] (CMVX[i]);
• and
• ii. ii. outputting one or more values required to control the amount of gas X in a volume of gas delivered to the subject, based on the tidal model of the subject's lung.

The method of claim 14 wherein tuning the estimation of the functional residual capacity comprises:

• changing the targeted end tidal partial pressure of gas X between a tuning breath [i+x] and a previous tuning breath [i+x−1];
• comparing the magnitude of the difference between the targeted end tidal partial pressure of gas X for said tuning breaths [i+x] and [i+x−1] with the magnitude of the difference between the measured end tidal partial pressure of gas X for the same tuning breaths to quantify any discrepancy in relative magnitude;
• and
• adjusting the estimated value of the functional residual capacity in proportion to the discrepancy to reduce the discrepancy in any subsequent prospective computing of F/X

The method of claim 14 wherein tuning the estimation of the functional residual capacity comprises:

• obtaining input of a measured baseline steady state value of PETX[i] for computing FIX at the start of a sequence;
• selecting a target end tidal partial pressure of gas X (PETX[i]T) for at least one tuning breath [i+x} wherein PETX[i+x]T differs from PETX[i+x−1]T;
• comparing the magnitude of the difference between the targeted end tidal partial pressure of gas X for said tuning breaths [i+x] and [i+x−1] with the magnitude of the difference between the measured end tidal partial pressure of gas X for the same tuning breaths to quantify any discrepancy in relative magnitude;
• and
• adjusting the estimated value of the functional residual capacity in proportion to any discrepancy in magnitude to reduce the discrepancy in a subsequent prospective computation of F/X including in any subsequent corresponding tuning breaths [i+x−1] and [i+x] forming part of an iteration of the sequence.