COMBINATION OF INERT GAS REBREATHING AND MULTIPLE-BREATH WASH-OUT TECHNIQUES FOR DETERMINATION OF INDICES OF VENTILATION INHOMOGENEITY

• US 20110098589A1
• Filed: 10/14/2010
• Published: 04/28/2011
• Est. Priority Date: 10/15/2009
• Status: Active Grant

• Current Assignee: IPR Holding APS
• Original Assignee: Innovision A/S (Danish Aerospace Co. A/S)
• Inventors: Nielsen, Jorgen Gronlund, Clemensen, Peter Christian
• Granted Patent: US 9,265,444 B2
• Time in Patent Office: Days
• US Class Current: 600/532
• CPC Class Codes: A61B 5/0813 Measurement of pulmonary parameters by tracers, e.g. radioactive tracers
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/093 the gases being exhaled into, or inhaled from, an expansible chamber, e.g. bellows or expansible bag

Abstract

The present invention discloses a method to determine the lung clearance index (LCI) or other indices of ventilation inhomogeneity of the lungs by combining two pulmonary gas exchange techniques; Inert gas rebreathing (IGR) is used for rapid wash-in of the inert tracer gas and for accurate determination of the functional residual capacity (FRC) by gas analysis alone. This is followed by multiple-breath wash-out (MBW) for determination of the cumulative expired volume (V_CE) required to clear the inert tracer gas from the lungs, and calculation of the LCI as the ratio between V_CE and FRC. The advantages of the method are i) significant reduction of required test time, ii) significant reduction of consumed gas mixture for wash-in of tracer gas, iii) potential for further reduction of the use of tracer gas, and iv) more accurate determination of the FRC by gas dilution alone. Furthermore the present invention relates to a corresponding system and computer-readable medium.

Claims

1. A method to determine the lung clearance index (LCI) of a test subject, said method comprising the steps of:

rebreathing of an inert tracer gas to wash-in the inert tracer gas until a constant concentration of the inert tracer gas is reached;

multiple-breath wash-out until the end-tidal tracer gas concentration has fallen below a predetermined fraction of the starting concentration;

wherein

the lung clearance index (LCI) is determined in steps of;

determining the functional residual capacity (FRC) by gas analysis alone from the inert gas rebreathing;

determining the cumulative expired volume (V_CE) required to clear the inert tracer gas concentration from the lungs below a predetermined fraction of the starting concentration;

calculation of the LCI as the ratio between V_CE and FRC.

2. A method according to claim 1 where the inert tracer gas is SF₆.

3. A method according to claim 1 where the inert tracer gas is comprised in an oxygen enriched gas mixture.

4. A method according to claim 1 where a volume of the gas mixture, corresponding to the test subject'"'"'s resting tidal volume is filled into a rebreathing bag.

5. A method according to claim 1 where the gas analysis is performed by a sensitive gas analyser e.g. based on photoacoustic spectroscopy (PAS).

14. A computer-readable medium having stored therein instructions for causing a processing unit to execute the above described method according to claim 1.

6. A system adapted to determine the lung clearance index (LCI) of the lungs of a test subject, said system comprising;

a rebreathing setup comprising at least a rebreathing bag prefilled with an inert tracer gas mixture for said test subject to rebreathe to and from during a rebreathing period;

at least one gas analyser for obtaining the fractional concentration of said inert tracer gas inhaled and exhaled by said test subject;

a flowmeter for monitoring the gas flow inhaled and exhaled by said test subject;

processing means for determining LCI of the lungs of a test subject using said obtained fractional concentration of said inert tracer gas from said rebreathing period to determine FRC and said gas flow to determine V_CE, required to clear said inert tracer gas concentration from the lungs below a predetermined fraction of the starting concentration, where LCI is determined as the ratio between V_CE and FRC.

7. A system according to claim 6 where the inert tracer gas is SF₆.

8. A system according to claim 6 where the inert tracer gas is comprised in an oxygen enriched gas mixture.

9. A system according to claim 6 where the gas analysis is performed by a sensitive gas analyser e.g. based on photoacoustic spectroscopy (PAS).

10. A system according to claim 6, comprising a CO₂ scrubber.

11. A system according to claim 6, comprising a small cylinder for containing the inert tracer gas mixture and means to dilute the inert tracer gas mixture with air or oxygen.

12. A system according to claim 6, where the processing means for determining LCI of the lungs of a test subject comprises processing means for determining FRC based on gas analysis alone and processing means for determining V_CE required to clear the inert tracer gas concentration from the lungs below 1/40th of the starting concentration.

13. A system according to claim 6, where the gas analyser for obtaining the fractional concentration of said inert tracer gas inhaled and exhaled by said test subject under the inert gas rebreathing comprises means for obtaining the partial pressure of said inert tracer gas.