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

Abstract

An apparatus and method for controlling the end tidal partial pressure of a gas X in a subject's lung, and to the use of such an apparatus and method for research, diagnostic and therapeutic purposes, wherein the method consists of: -obtaining input of a series of logistically attainable PetX values for a series of respective breaths: -determining an amount of gas X required to be inspired by the subject in an inspired gas to target the PetX for each of said respective breaths; and controlling a gas delivery device to deliver the amount of gas in a volume of gas delivered to the subject in each of said respective breaths to target the respective PetX for that breath.

We claim: 
     
         1 . to  79 . (canceled) 
     
     
         80 . 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 (PetX T ), 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 PETX T  value with a respective breath [i], the PETX T  value comprising either a PETX T  increment or a PETX T decrement, the control system configured to:
 a. Obtain input of a logistically attainable PETX T  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 PETX T  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] (C MV X[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] (F I X) to target the respective PETX T  for the breath [i]. 
   
     
     
         81 . The apparatus of  claim 1 , wherein computing a tidal model of the subject's lung further includes predicting the C MV X[i] by compartmental modelling of gas dynamics. 
     
     
         82 . The apparatus of  claim 1 , wherein computing a tidal model of the subject's lung further includes estimating or measuring the value of at least one parameter selected from a group consisting of: functional residual capacity of the subject's lung, anatomic dead space of the subject's lung, metabolic production of gas X in the respective breath [i], metabolic consumption of gas X in the respective breath [i], and tidal volume of the respective breath [i]. 
     
     
         83 . The apparatus of claim  3 , the control system further configured to tune the estimated value of the functional residual capacity over a series of tuning breaths. 
     
     
         84 . 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 
 
     
     
         85 . 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 P ET X[i] for computing F I X at the start of a sequence; 
 selecting a target end tidal partial pressure of gas X (P ET X[i] T ) for at least one tuning breath [i+x] wherein P ET X[i+x] T  differs from P ET X[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. 
 
     
     
         86 . The apparatus of claim  3 , the control system further configured to tune the estimated value of metabolic consumption of gas X over a series of tuning breaths. 
     
     
         87 . The apparatus of claim  7 , wherein tuning the estimated value of the metabolic production or consumption of gas X comprises targeting a sequence of end tidal partial pressure of gas X, the targeting comprising:
 comparing a targeted end tidal partial pressure of gas X (P ET X [i+x] T ) for the at least one tuning breath [i+x] with a corresponding measured end tidal partial pressure of gas X for the corresponding breath [i+x] to quantify any discrepancy; and   adjusting the estimated value of the total metabolic production or consumption of gas X in proportion to any discrepancy to reduce the discrepancy in any subsequent prospective computation of F I X   
     
     
         88 . The apparatus of claim  7 , wherein tuning the estimated value of the metabolic production or consumption of gas X comprises targeting a sequence of end tidal partial pressure of gas at least once by:
 obtaining input of a measured baseline steady state value for P ET X [i] T  for computing F I X at the start of a sequence; targeting a selected target end tidal partial pressure of gas X (P ET X [i+x] T ) for each of a series of tuning breaths [i+1 . . . i+n], wherein P ET X [i] T  differs from the baseline steady state value for P ET X[i];   comparing the targeted end tidal partial pressure of gas X (P ET X[i+x] T  for at least one tuning breath [i+x] in which the targeted end tidal gas concentration of gas X has been achieved without drift in a plurality of prior breaths [1+−1, 1+x−2 . . . ] with a corresponding measured end tidal partial pressure of gas X for a corresponding breath [i+x] to quantify any discrepancy and adjusting the estimated value of the total metabolic production or consumption of gas X in proportion to the discrepancy to reduce the discrepancy to reduce the discrepancy in a subsequent prospective computation of F / X including in any subsequent corresponding tuning breath [i+x] forming part of an iteration of the sequence.   
     
     
         89 . 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 (P ET X T ), the computer program comprising program code for:
 a. obtaining input of a logistically attainable end tidal partial pressure of gas X (P ET X T ) 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 P ET X T for 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] (C MV X[i]); and 
 ii. outputting one or more values required to control F I X, based on tidal model of the subject's lung. 
   
     
     
         90 . 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 (P ET X T ), the method comprising:
 a. obtaining input of a logistically attainable P ET X T value for a respective breath
 [i] comprising either a P ET X T  increment or a P ET X T decrement; 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 P ETX   T for 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] (C MV X[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. 
   
     
     
         91 . The method of claim  11 , wherein computing a tidal model of the subject's lung further includes predicting the C MV X[i] by compartmental modelling of gas dynamics. 
     
     
         92 . The method of claim  11 , wherein computing a tidal model of the subject's lung further includes estimating or measuring the value of at least one parameter selected from a group consisting of: functional residual capacity of the subject's lung, anatomic dead space of the subject's lung, metabolic production of gas X in the respective breath [i], metabolic consumption of gas X in the respective breath [i], and tidal volume of the respective breath [i]. 
     
     
         93 . The method of claim  13 , the method further comprising tuning the estimated value functional residual capacity over a series of tuning breaths. 
     
     
         94 . 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 
 
     
     
         95 . 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 P ET X[i] for computing F I X at the start of a sequence; 
 selecting a target end tidal partial pressure of gas X (P ET X[i] T ) for at least one tuning breath [i+x} wherein P ET X[i+x] T  differs from P ET X[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. 
 
     
     
         96 . The method of claim  13 , the method further comprising tuning the estimated value of the metabolic production or consumption of gas X over a series of tuning breaths. 
     
     
         97 . The method of claim  17 , wherein tuning the estimated value of the metabolic production or consumption of gas X comprises targeting a sequence of end tidal partial pressure of gas X, the targeting comprising:
 comparing a targeted end tidal partial pressure of gas X (P ET X [i+x] T ) for the at least one tuning breath [i+x] with a corresponding measured end tidal partial pressure of gas X for the corresponding breath [i+x] to quantify any discrepancy; and   adjusting the estimated value of the total metabolic production or consumption of gas X in proportion to any discrepancy to reduce the discrepancy in any subsequent prospective computation of F I X.   
     
     
         98 . The method of claim  17 , wherein tuning the estimated value of the metabolic production or consumption of gas X comprises targeting a sequence of end tidal partial pressure of gas at least once by:
 obtaining input of a measured baseline steady state value for P ET X [i] T  for computing F I X at the start of a sequence;   targeting a selected target end tidal partial pressure of gas X (P ET X [i+x] T ) for each of a series of tuning breaths [i+1 . . . i+n], wherein P ET X [i]  T  differs from the baseline steady state value for P ET X[i];   comparing the targeted end tidal partial pressure of gas X (P ET X[i+x] T  for at least one tuning breath [i+x] in which the targeted end tidal gas concentration of gas X has been achieved without drift in a plurality of prior breaths [1+x−1, 1+x−2 . . . ] with a corresponding measured end tidal partial pressure of gas X for a corresponding breath [i+x] to quantify any discrepancy and adjusting the estimated value of the metabolic production or consumption of gas X in proportion to the discrepancy to reduce the discrepancy to reduce the discrepancy in a subsequent prospective computation of F / X including in any subsequent corresponding tuning breath [i+x] forming part of an iteration of the sequence.   
     
     
         99 . The method of claim  13 , wherein the gas X is selected from a group consisting of carbon dioxide and oxygen.