APPARATUS FOR MEASURING A LEVEL OF A SPECIFIC GAS IN EXHALED BREATH

• US 20120271188A1
• Filed: 10/29/2010
• Published: 10/25/2012
• Est. Priority Date: 11/03/2009
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Van Kesteren, Hans Willem
• Granted Patent: US 9,671,389 B2
• Time in Patent Office: Days
• US Class Current: 600/532
• CPC Class Codes: A61B 5/0095 by applying light and detecting acoustic waves, i.e. photoacoustic measurements
• CPC Class Codes: A61B 5/082 Evaluation by breath analysis, e.g. determination of the chemical composition of exhaled breath A61B5/083, A61B5/091 take precedence
• CPC Class Codes: G01H 5/00 Measuring propagation velocity of ultrasonic, sonic or infrasonic waves , e.g. of pressure waves
• CPC Class Codes: G01N 2021/1704 in gases
• CPC Class Codes: G01N 21/1702 with opto-acoustic detection, e.g. for gases or analysing solids
• CPC Class Codes: G01N 2291/0215 Mixtures of three or more gases, e.g. air
• CPC Class Codes: G01N 2291/02809 Concentration of a compound, e.g. measured by a surface mass change
• CPC Class Codes: G01N 29/024 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/2425 optoacoustic fluid cells therefor
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01N 33/497 of gaseous biological material, e.g. breath

Abstract

There is provided an apparatus for measuring levels of a specified gas in exhaled breath, the apparatus comprising a photoacoustic sensor for providing a measurement representative of the level of the specified gas in the exhaled air, wherein the photoacoustic sensor comprises a light source that is modulated at a first frequency; a sound speed measurement module for measuring the sound speed of the exhaled breath, wherein the sound speed measurement module operates either at a second frequency that is substantially different to the first frequency or in a pulsed mode; wherein the first frequency of the modulated light source is adjusted during exhalation in accordance with the measured speed of sound of the exhaled breath.

Claims

1. An apparatus (2) for measuring levels of a specified gas in exhaled breath, the apparatus (2) comprising:

a photoacoustic sensor (10) for providing a measurement representative of the level of the specified gas in the exhaled air, wherein the photoacoustic sensor (10) comprises a light source (20) that is modulated at a first frequency;

a sound speed measurement module (6) for measuring the sound speed of the exhaled breath, wherein the sound speed measurement module (6) operates either at a second frequency that is substantially different to the first frequency or in a pulsed mode;

wherein the first frequency of the modulated light source (20) is adjusted during exhalation in accordance with the measured speed of sound of the exhaled breath.

2. An apparatus (2) as claimed in claim 1, wherein the photoacoustic sensor (10) comprises a resonator chamber (18) that is operated in a plane wave mode, and wherein the first frequency of the modulated light source (20) is adjusted in accordance with the measured speed of sound of the exhaled breath and the acoustic mode of the resonator chamber (18).

3. An apparatus (2) as claimed in claim 1, wherein the sound speed measurement module (6) comprises a pair of transducers (12, 14), each transducer (12, 14) being arranged to transmit an ultrasonic pulse through the exhaled breath to the other transducer (12, 14).

4. An apparatus (2) as claimed in claim 1, wherein the sound speed measurement module (6) comprises a photoacoustic unit comprising two light sources which are anti-phase modulated.

5. An apparatus (2) as claimed in claim 4, wherein the sound speed measurement module (6) operates at a second frequency that is approximately half of the first frequency.

6. An apparatus (2) as claimed in claim 1, wherein the sound speed measurement module (6) comprises:

a pair of transducers (12, 14)arranged on opposite sides of a passage (16) through which the exhaled breath passes, each transducer (12, 14) being arranged to transmit an ultrasonic pulse through the exhaled breath to the other transducer (12, 14) and to provide a signal indicative of the transit time of the ultrasonic pulse;

wherein the pair of transducers (12, 14) are arranged such that each transducer (12, 14) transmits their respective ultrasonic pulses along an axis that is at a non-zero angle with respect to a plane that is perpendicular to the direction in which the exhaled breath flows; and

a processor (24) for determining the sound speed in the exhaled breath from the sum of the transit times, and the exhalation flow from the difference of the transit times of the ultrasonic pulses through the exhaled breath;

wherein the apparatus (2) is configured to provide a measurement of the specified gas and the exhalation flow.

7. An apparatus (2) as claimed in claim 1, wherein sound speed measurement module (6) comprises:

a pair of transducers (12, 14) arranged on opposite sides of a passage through which the exhaled breath passes, each transducer (12, 14) being arranged to transmit an ultrasonic pulse through the exhaled breath to the other transducer (12, 14) and to provide a signal indicative of the transit time of the ultrasonic pulse;

a temperature sensor (21) for determining the temperature of the gas close to the transducers (12, 14); and

a processor (24) for determining the sound speed in the exhaled breath from the transit time of the ultrasonic pulse, and a molar mass from the transit time and temperature; and

wherein the apparatus (2) is configured to provide a measurement of the specified gas and the molar mass.

8. An apparatus (2) as claimed in claim 1, wherein the specified gas is nitric oxide.

9. An apparatus (2) as claimed in claim 8, wherein the apparatus (2) further comprises a converter (8) for converting nitric oxide in the exhaled breath to nitrogen dioxide to provide a measurement sample, and wherein the photoacoustic sensor (10) measures the levels of nitrogen dioxide in the measurement sample, the measured levels of nitrogen dioxide corresponding to the levels of nitric oxide in the exhaled breath.

10. An apparatus (2) as claimed in claim 8, wherein the apparatus (2) further comprises a processing unit (24) for determining one or more parameters describing the nitric oxide production in the airways based on the exhaled nitric oxide and flow patterns during one or more exhalations.

11. An apparatus (2) as claimed in claim 8, wherein the apparatus (2) further comprises a processing unit (24) for determining one or more parameters describing the nitric oxide production in the airways based on the exhaled nitric oxide, flow and molar mass patterns during one or more exhalations.

12. A method of measuring levels of a specified gas in exhaled breath, the method comprising:

measuring the speed of sound of the exhaled breath (107);

adjusting a modulation frequency of a light source in a photoacoustic sensor during exhalation in accordance with the speed of sound of the exhaled breath (115); and

using the photoacoustic sensor to provide a measurement representative of the level of the specified gas in the exhaled breath (117);

wherein the speed of sound is measured either at a frequency that is substantially different to the modulation frequency or in a pulsed mode.

13. A method as claimed in claim 12, wherein the photoacoustic sensor provides a measurement representative of the level of the specified gas in the exhaled breath by:

passing the laser beam through a measurement sample of the exhaled breath that is contained in a resonance chamber of the photoacoustic sensor, the laser beam having a wavelength in the absorption range of the specified gas (115); and

measuring the sound generated from the laser beam passing through the measurement sample of the exhaled breath to provide the measurement representative of the specified gas in the exhaled breath (117).

14. A method as claimed in claim 12, wherein the specified gas is nitric oxide and wherein the method further comprises the step of:

passing a sample of the exhaled breath through a nitric oxide to nitrogen dioxide converter to generate a measurement sample (111);

wherein the photoacoustic sensor measures the level of nitrogen dioxide in the measurement sample to provide the measurement representative of the level of nitric oxide in the exhaled breath.