Compensation of volumetric errors in a gas monitoring system

• US 8,696,591 B2
• Filed: 10/16/2012
• Issued: 04/15/2014
• 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 (Respironics Incorporated)
• Inventors: Orr, Joseph A., Flanagan, Craig T.
• Primary Examiner(s): Mallari, Patricia
• Assistant Examiner(s): JANG, CHRISTIAN YONGKYUN
• Application Number:
  US13/652,581
• Publication Number:
  US 20130041280A1
• Time in Patent Office: 546 Days
• Field of Search: 600529-543
• US Class Current: 600/532
• 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 method 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.

Claims

1. A method of monitoring an analyte in a gas flow comprising the acts of:

providing mainstream airway adapter having the gas flow therethrough;

producing by a gas sensing portion a signal indicative of the analyte in the gas flow;

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

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

outputting a signal indicative of the amount of analyte in a human perceivable format,

wherein the compensating act includes monitoring a tracheal dead space gas and using the monitored tracheal dead space gas to determine a difference between an analyte fraction of inspired gas and an analyte fraction of the tracheal dead space gas for determining the amount of the analyte in the gas flow.

2. The method of claim 1, wherein the first portion of gas exhaled during the expiration is a remaining gas of inspired gas, where the remaining gas has remained in a trachea and has been heated to body temperature and humidified by the trachea, and did not participate in gas exchange in lungs where oxygen has not been removed by lungs from the remaining gas.

3. The method of claim 1, wherein the analyte is oxygen, and the method further comprising the act of determining oxygen consumption (VO₂) based on the amount of analyte.

4. The method of claim 1, further comprising the act of determining a flow rate of the gas flow, and wherein determining the amount of the analyte includes the acts of:

determining oxygen concentration in the gas flow; and

determining carbon dioxide in the gas flow.

5. The method of claim 4, further comprising the act of determining oxygen consumption VO₂ as:

VO₂=V_E*Fi<sub>O2—

Ds</sub>−

*((1−

Fe_CO2−

Fe_O2)/(1−

Fi_CO2−

Fi<sub>O2—

DS</sub>))−

Fe_O2],

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

DS</sub> is a tracheal dead space oxygen concentration, Fe_CO2 is an expired carbon dioxide concentration, Fe_O2 is an expired oxygen concentration, and Fi_CO2 is an inspired carbon dioxide concentration.

6. The method of claim 1, wherein the act of determining the amount of the analyte in the gas flow based on the signal from the gas sensing portion includes the acts of:

exciting a luminescable material with an excitation energy; and

monitoring quenching of a luminescence.

7. The method of claim 1, further comprising the act of determining a flow rate of the gas flow, and wherein the act of determining the amount of the analyte includes determining an oxygen concentration in the gas flow.

8. The method of claim 7, further comprising the act of determining oxygen consumption VO₂ as;

VO₂=V_i*Fi<sub>O2—

Ds</sub>−

Ve*Fe_O2,

where Vi is an inspired volume of gas, Fi<sub>O2—

DS</sub> is a tracheal dead space oxygen concentration, V_E is an expired volume of gas, and Fe_O2 is an expired oxygen concentration.