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An apparatus, method and system for delivering CO2 into an inspiratory gas stream to formulate a blended respiratory gas in a manner that continuously maintains a target CO2 concentration in a volume of the inspired respiratory gas, for example, over the course of a breath or a volumetrically defina

An apparatus, method and system for delivering CO2 into an inspiratory gas stream to formulate a blended respiratory gas in a manner that continuously maintains a target CO2 concentration in a volume of the inspired respiratory gas, for example, over the course of a breath or a volumetrically definable part thereof or a series of partial or full breaths.

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1. An apparatus for adding at least one added gas (Gn) to an inspiratory gas (G0) to formulate a respiratory gas (GR) for delivery to a subject, comprising: a control system operable to maintain a targeted concentration (DAnT) of at least one component (DAn) of the at least one added gas (Gn) in a r

1. An apparatus for adding at least one added gas (Gn) to an inspiratory gas (G0) to formulate a respiratory gas (GR) for delivery to a subject, comprising: a control system operable to maintain a targeted concentration (DAnT) of at least one component (DAn) of the at least one added gas (Gn) in a respective cumulative volume of the respiratory gas (CVGR) delivered over a respective cumulative time period consisting of a cumulating series of respective time points of interest, the control system including a processor operable to:(a) obtain input of confirmed incremental volumes of at least one of the inspiratory gas (G0) and the respiratory gas (GR) flowed to the subject with respect to the respective time points of interest; and(b) obtain input of confirmed incremental volumes of at least one of the at least one added gas (Gn) and the at least one component (DAn) of the at least one added gas flowed to the subject with respect to the respective time points of interest; and(c) compute for successive respective time intervals between contiguous respective time points of interest, a respective error signal (en) representing an incremental volume of the at least one added gas (Gn) that would, if delivered with respect to the respective time interval, maintain the target concentration (DAnT) of the at least one component (DAn) of the at least one added gas in a cumulative volume of the respiratory gas (GR) including the incremental volume of the at least one added gas;the control system being operable to provide an output signal to a gas delivery device (GDn) for the respective time interval based on the respective error signal (en) computed for the respective time interval such that the target concentration (DAnT) of the at least one component (DAn) of the at least one added gas (Gn) is maintained in a respective cumulative volume of the respiratory gas (GR). 2. An apparatus according to claim 1, wherein the control system is operable to obtain input of confirmed incremental volumes of at least one of the inspiratory gas (G0) and the respiratory gas (GR) flowed to the subject with respect to the respective time points of interest, and confirmed incremental volumes of the at least one added gas (Gn) flowed to the subject with respect to the respective time points of interest; the control system being configured to compute respective cumulative volumes of delivered respiratory gas (GR) over respective cumulative time intervals comprising the respective time points of interest and respective cumulative volumes of delivered added gas (Gn) with respect to the respective cumulative time intervals and the respective error signal (en) for the successive respective time intervals between the contiguous respective time points of interest. 3. An apparatus according to claim 2, wherein the output to the gas delivery device (GDn) for each successive respective time interval is generated from a weighted sum of the respective error signal (en) computed for the respective time point of interest and the integral of the respective error signal (en) computed for the respective time point of interest. 4. An apparatus according to claim 2, wherein the gas delivery device (GDn) is controlled by a controller selected from the group consisting of a PI controller and a PID controller. 5. An apparatus according to claim 4, wherein the output signal delivered to the gas delivery device (GDn) is computed based on: a) an output of the controller; andb) an incremental volume (G0P) of inspiratory gas (G0) expected to be delivered in a time interval ΔT between the respective time point of interest and an ensuing respective time point of interest. 6. An apparatus according to claim 1, wherein the processor is operable to obtain input from a volume sensor and provide output to a proportional control valve. 7. An apparatus according to claim 1, further comprising: at least one added gas delivery conduit, wherein the gas delivery device (GDn) is operable for delivering incremental volumes of the at least one added gas (Gn) into the at least one added gas delivery conduit; anda volume sensor positioned to provide output of respective incremental volumes of the at least one added gas (Gn) delivered by the gas delivery device (GDn) into the at least one added gas delivery conduit. 8. An apparatus according to claim 1, wherein the processor, is embodied in a device selected from the group consisting of, a microcontroller and an IC chip. 9. An apparatus according to claim 1, wherein the processor is configured to obtain input of a concentration of the at least one component (DAn) of the at least one added gas (Gn) in the at least one added gas (Gn) applicable to any respective time point of, interest from a gas analyzer. 10. An apparatus according to claim 1, wherein the at least one component of the at least one added gas (DAn) is carbon dioxide. 11. A method for adding at least one added gas (Gn) to an inspiratory gas (G0) to formulate a respiratory gas (GR) for delivery to a subject, comprising: maintaining a targeted concentration (DAnT) of at least one component (DAn) of the at least one added gas (Gn)—in a respective cumulative volume (CVGR) of the respiratory gas delivered over a respective cumulative time period consisting of a cumulating series of respective time points of interest, by:(a) obtaining input of confirmed incremental volumes of at least one of the inspiratory gas (G0) and the respiratory gas (GR) flowed to the subject at the respective time points of interest;(b) obtaining input of confirmed incremental volumes of at least one of the at least one added gas (Gn) and the at least one component (DAn) of the at least one added gas flowed to the subject at the respective time points of interest; and(c) computing for successive respective time intervals between contiguous respective time points of interest, a respective error signal (en) representing an incremental volume of the at least one added gas (Gn) that would, if delivered with respect to the respective time interval, maintain the target concentration (DAnT) of the at least one component (DAn) of the at least one added gas in a cumulative volume of respiratory gas (CVGR) including the incremental volume of the at least one added gas;(d) providing, via a controller, an output signal to a gas delivery device (GDn) for the respective time interval based on the respective error signal (en) computed for the respective time interval, —such that the target concentration of the at least one component gas (DAnT) is maintained in a respective cumulative volume of the respiratory gas (GR). 12. A method according to claim 11, comprising controlling the gas delivery device (GDn) using a controller selected from the group consisting of a PI and a PID controller. 13. A method according to claim 11, wherein a processor obtains input values for each of the respective time points of interest, the input values including confirmed incremental volumes of the least one added gas (Gn) and at least one of confirmed incremental volumes of the inspiratory gas (G0) and confirmed incremental volumes of the respiratory gas (GR), the input values being sufficient to compute, for the respective cumulative time period, the respective cumulative time period including previous respective time points of interest and the last respective time point of interest: i) cumulative volumes of the at least one added gas (Gn) and at least one of cumulative volumes of the inspiratory gas (G0) and cumulative volumes of the respiratory gas (GR); andii) the respective error signal (en) with respect to a respective time interval based on the cumulative volumes computed in step i); the respective error signal (en) corresponding to a respective time interval computed by the processor using the cumulative volumes of the at least one added gas (Gn) cumulatively delivered over the respective cumulative time period and at least one of the cumulative volumes of the inspiratory gas (G0) and cumulative volumes of the respiratory gas (GR) cumulatively delivered over the respective cumulative time period. 14. A method according to claim 11, wherein the output signal delivered to the gas delivery device (GDn) is computed based on: a) an output of the controller; andb) an incremental volume of inspiratory gas (G0P) expected to be delivered in a time interval ΔT between one respective time point of interest and an ensuing respective time point of interest. 15. A method according to claim 14, wherein the signal delivered to the gas delivery device (GDn) is computed based on the sum of the output of the controller and a volume (GnP) of the at least one added gas (Gn) that must be added to the incremental volume of the inspiratory gas (G0P), so that the incremental volume of the at least one component of the at least one added gas (DAn) in the combined volume of G0P and GnP equals the target concentration (DAnT). 16. A method according to claim 15, wherein the incremental volume of the inspiratory gas (G0P) is equated with one of (i) the incremental volume of the inspiratory gas delivered in the time interval ΔT beginning at an immediately previous respective time point of interest, and ending at the respective time point of interest, and (ii) an average or weighted average of the incremental volumes of the inspiratory gas delivered in, a plurality of time intervals of interest within the respective cumulative time period. 17. A method according to claim 11, wherein the method is implemented by using a processor operatively associated with a volume controller (VCn) for controlling a gas delivery device (GDn), the processor operable to obtain input from a plurality of sensors selected from the group consisting of volume sensors and gas analyzers. 18. A method according to claim 11, wherein the at least one component of the at least one added gas (DAn) is carbon dioxide. 19. A computer readable medium encoded with computer-readable instructions that, when executed by a programmable computer, are operable for controlling a gas delivery device controlled by the computer to add at least one added gas (Gn) to an inspiratory gas (G0) to formulate a respiratory gas (GR) for delivery to a subject, characterized in that the instructions, when executed by the computer, are operable for maintaining a targeted concentration (DAnT) of at least one component of the at least one added gas (DAn) in a respective cumulative volume of the respiratory gas (CVGR) delivered over a respective cumulative time period consisting of a cumulating series of respective time points of interest, by: (a) inputting to the computer data representing confirmed incremental volumes of at least one of the inspiratory gas (G0) and the respiratory gas (GR) flowed to the subject at the respective time points of interest;(b) inputting to the computer confirmed incremental volumes of at least one of the at least one added gas (Gn) and the at least one component (DAn) of the at least one added gas flowed to the subject at the respective time points of interest; and(c) operating the computer to generate, for successive respective time intervals between contiguous respective time points of interest, a respective error signal (en) representing a incremental volume of the at least one added gas (Gn) that would, if delivered with respect to a respective time interval maintain the target concentration (DAnT) of the at least one component (DAn) of the at least one added gas in a cumulative volume of the respiratory gas including the incremental volume of the at least one added gas; and(d) providing an output signal from the computer to a gas delivery device (GDn) for the respective time interval based on the respective error signal (en) computed for the respective time interval, such that the target concentration (DAnT) of the at least one component (DAn) of the at least one added gas (Gn) is maintained in respective cumulative volume of the respiratory gas (GR). 20. A computer readable medium according to claim 19, wherein the instructions are operable, when executed by the computer, to control the gas delivery device by a controller selected from the group consisting of a PI controller and a PID controller. 21. A computer readable medium according to claim 19, wherein the instructions are operable, when executed by the computer, to obtain input values from a volume sensor for each of the respective time points of interest, the input values including confirmed incremental volumes of at least one added gas (Gn) and at least one of confirmed incremental volumes of the inspiratory gas (G0) and confirmed, incremental volumes of the respiratory gas (GR), the input values sufficient to compute, for the respective cumulative time period, the respective cumulative time period including previous respective time points of interest and the last respective time point of interest; i) cumulative volumes of the at least one added gas (Gn) and at least one of cumulative volumes of the inspiratory gas (G0) and emulative volumes of the respiratory gas (GR); andii) the respective error signal (en) with respect to a respective time interval based on the cumulative volumes computed in step i); the error signal (en) corresponding to a respective time interval computed using the cumulative volumes of the at least one added gas Gn cumulatively delivered over the respective cumulative time period and at least one of the cumulative volumes of the inspiratory gas (G0) and cumulative volumes of the respiratory gas (GR) cumulatively delivered over the respective cumulative time period. 22. A computer readable medium according to claim 19, wherein the signal delivered to the gas delivery device (GDn) is provided by a controller and computed based on: a) the respective error signal (en) output by the controller; andb) an incremental volume of inspiratory gas (G0P) expected to be delivered in a time interval ΔT between the respective time point of interest and an ensuing respective time point of interest. 23. A computer readable medium, according to claim 22, wherein the signal delivered to the gas delivery device (GDn) is computed based on the sum of the output of the controller and a volume of the at least one added gas (GnP) that must be added to the incremental volume of inspiratory gas (G0P), so that the incremental volume of the at least one component of the at least one added gas (DAn) in the combined volume of G0P and GnP equals the target concentration (DAnT). 24. A computer readable medium according to claim 23, wherein the incremental volume of inspiratory gas (G0P) is equated with one of (i) the incremental volume of inspiratory gas G0 delivered in the time interval ΔT beginning at an immediately previous respective time point of interest and ending at the respective time point of interest, and (ii) an average or weighted average of the incremental volumes of inspiratory gas (G0) delivered in a plurality of time intervals of interest within the respective cumulative time period. 25. A computer readable medium according to claim 19, wherein the computer is operatively associated with a volume controller (VCn) for controlling the gas delivery device (GDn) in accordance with input to the computer from a plurality of sensors selected from the group consisting of volume sensors and gas analyzers.