Compensation of Volumetric Errors in a Gas Monitoring System

• US 20080127977A1
• Filed: 11/30/2007
• Published: 06/05/2008
• Est. Priority Date: 12/04/2006
• Status: Active Grant

• Current Assignee: Philips RS North America LLC (Koninklijke Philips N.V.)
• Original Assignee: RIC INVESTMENTS LLC (Koninklijke Philips N.V.)
• Inventors: Flanagan, Craig T., Orr, Joseph A.
• Granted Patent: US 8,312,878 B2
• Time in Patent Office: Days
• US Class Current: 128/204.22
• CPC Class Codes: A61B 5/0833 Measuring rate of oxygen consumption
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/021 operated by electrical means A61M16/202 – A61M16/205 take precedence
• CPC Class Codes: A61M 16/0816 Joints or connectors
• CPC Class Codes: A61M 16/0841 for sampling
• CPC Class Codes: A61M 16/0858 Pressure sampling ports
• CPC Class Codes: A61M 16/1075 by influencing the temperature A61M16/1045 takes precedence
• CPC Class Codes: A61M 16/16 Devices to humidify the respiration air A61M16/1045 takes precedence
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2016/1025 the O2 concentration
• CPC Class Codes: A61M 2016/103 the CO2 concentration
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: A61M 2230/435 partial O2 pressure (P-O2)

Abstract

A mainstream gas monitoring system and method that includes a using a mainstream airway adapter, and a gas sensing assembly associated with the mainstream airway adapter to measure an analyte of a gas flow through the adapter. A gas sensing portion outputs a signal indicative of the analyte in a gas flow in the mainstream airway adapter. A processing portion receives the signal from the gas sensing portion and determines an amount of the analyte in the gas flow based on the signal from the gas sensing portion. The processing portion also compensates for volumetric differences between the gas flow during inspiration and the gas flow during expiration to maximize the accuracy in the measurements made using such a system and method.

Claims

1. A mainstream gas monitoring system comprising:

(a) a mainstream airway adapter; and

(b) a gas sensing assembly associated with the mainstream airway adapter and comprising;

(1) a gas sensing portion associated with the mainstream airway adapter, wherein the gas sensing portion outputs a signal indicative of an analyte in a gas flow in the mainstream airway adapter, and

(2) a processing portion adapted to receive the signal from the gas sensing portion, wherein the processing portion is programmed to determine an amount of the analyte in the gas flow based on the signal from the gas sensing portion, and wherein the processing portion is programmed to compensate for volumetric differences between the gas flow during inspiration and the gas flow during expiration.

2. The system of claim 1, wherein the processing portion compensates for the volumetric differences by monitoring a tracheal dead space gas and using the monitored tracheal dead space gas to determine the amount of the analyte in the gas flow.

3. The system of claim 1, wherein the gas sensing portion and the mainstream airway adapter are configured such that the gas sensing portion is selectively attachable to the mainstream airway adapter.

4. The system of claim 1, wherein a luminescable material is associated with the mainstream airway adapter.

5. The system of claim 1, wherein the gas sensing portion includes:

an emitter adapted to emit radiant energy; and

a detector adapted to detect energy.

6. The system of claim 1, further comprising:

a first housing containing the gas sensing portion, wherein the first housing is adapted to be coupled to the mainstream airway adapter;

a second housing containing the processing portion, wherein the second housing and the first housing are separate from one another; and

a communication link providing communication between the gas sensing portion and the processing portion.

7. The system of claim 1, wherein the gas sensing portion and the processing portion are contained in a common housing that is adapted to be coupled to the mainstream airway adapter.

8. The system of claim 1, further comprising an output device adapted to provide an output of the processing portion in a human perceivable format.

9. The system of claim 1, wherein the analyte is oxygen, and wherein the processing portion is adapted to determine oxygen consumption (VO₂).

10. The system of claim 9, further comprising a flow rate determining system, and wherein the gas sensing portion includes (a) an oxygen concentration monitoring system;

and (b) a carbon dioxide monitoring system

11. The system of claim 10, wherein the processing portion determines VO₂ as:

VO₂=V_E*[Fi<sub>O2—

DS</sub>*((1−

Fē

_CO2−

Fē

_O2)/(1−

Fi_CO2−

Fi<sub>O2—

DS</sub>))−

Fē

_O2],

where V_E is the expired volume of gas, Fi<sub>O2—

DS</sub> is the tracheal dead space oxygen concentration, Fē

_CO2 is the expired carbon dioxide concentration, Fē

_O2 is the expired oxygen concentration, and Fi_CO2 is the inspired carbon dioxide concentration.

12. The system of claim 1, further comprising a flow rate determining system, and wherein the gas sensing portion includes an oxygen concentration monitoring system.

13. The system of claim 12, wherein the processing portion determines VO₂ as:

VO₂=Vi*Fi<sub>O2—

DS</sub>−

Ve*Fē

O₂,

where V_I is the inspired volume of gas, Fi<sub>O2—

DS</sub> is the tracheal dead space oxygen concentration, V_E is the expired volume of gas, and Fē

_O2 is the expired oxygen concentration.

14. A method of monitoring system an analyte in a gas flow;

providing mainstream airway adapter having a gas flow therethrough;

producing a signal indicative of an analyte in the gas flow;

determining an amount of the analyte in the gas flow based on the signal from the gas sensing portion;

compensating for volumetric differences between the gas flow during inspiration and the gas flow during expiration; and

providing a signal indicative of the amount of analyte in a human perceivable format.

15. The method of claim 14, wherein compensating for the volumetric differences includes monitoring a tracheal dead space gas and using the monitored tracheal dead space gas to determine the amount of the analyte in the gas flow.

16. The method of claim 14, wherein the analyte is oxygen, and further comprising determining oxygen consumption (VO₂) based on the amount of analyte.

17. The method of claim 14, further comprising:

determining a flow rate of the gas flow, and wherein determining the amount of the analyte includes;

determining the oxygen concentration in the gas flow; and

determining the carbon dioxide in the gas flow.

18. The method of claim 17, further comprising determining oxygen consumption (VO₂) as:

VO₂=V_E*[Fi<sub>O2—

DS</sub>*((1−

Fē

_CO2−

Fē

_O2)/(1−

Fi_CO2−

Fi<sub>O2—

DS</sub>))−

Fē

_O2],

where V_E is the expired volume of gas, Fi<sub>O2—

DS</sub> is the tracheal dead space oxygen concentration, Fē

_CO2 is the expired carbon dioxide concentration, Fē

_O2 is the expired oxygen concentration, and Fi_CO2 is the inspired carbon dioxide concentration.

19. The method of claim 14, wherein determining the amount of the analyte in the gas flow based on the signal from the gas sensing portion includes:

exciting a luminescable material with an excitation energy; and

monitoring quenching of a luminescence.

20. The method of claim 14, further comprising determining a flow rate of the gas flow, and wherein determining the amount of the analyte includes determining the oxygen concentration in the gas flow.

21. The method of claim 20, further comprising determining oxygen consumption (VO₂) as:

VO₂=Vi*Fi<sub>O2—

DS</sub>−

Ve*Fē

_O2,

where V_I is the inspired volume of gas, Fi<sub>O2—

DS</sub> is the tracheal dead space oxygen concentration, V_E is the expired volume of gas, and Fē

_O2 is the expired oxygen concentration.