Capnometer

Abstract

We describe a capnometer for detecting a concentration of a component in a gas, wherein said gas is inhaled and/or exhaled by a patient, said capnometer comprising: an air flow region through which said gas passes to and/or from said patient's lung; a mid-IR semiconductor emitter configured to provide IR light at a wavelength in the range 3-5 μm;a mid-IR semiconductor detector to detect said IR light; a reflector to reflect said IR light emitted by said emitter; wherein said emitter, said detector and said reflector are arranged such that said IR light emitted by said emitter passes through said air flow region via said reflector to said detector.

1 . A capnometer for detecting a concentration of a component in a gas, wherein said gas is inhaled and/or exhaled by a patient, said capnometer comprising:
 an air flow region through which said gas passes to and/or from said patient's lung;   a mid-IR semiconductor emitter configured to provide IR light at a wavelength in the range 3-5 μm;   a mid-IR semiconductor detector to detect said IR light;   a reflector to reflect said IR light emitted by said emitter;   wherein said emitter, said detector and said reflector are arranged such that said IR light emitted by said emitter passes through said air flow region via said reflector to said detector.   
     
     
         2 . A capnometer as claimed in  claim 1 , wherein said detection of said concentration of said component in said gas comprises detecting a temporal variation of said concentration. 
     
     
         3 . A capnometer as claimed in  claim 1 , wherein said emitter is located at a first location on a first side of said air flow region, wherein said detector is located at a second location on a second side of said air flow region, and wherein said second side is opposite said first side from said air flow region. 
     
     
         4 . A capnometer as claimed in  claim 3 , wherein said reflector is located at a third location on a third side of said air flow region, wherein said third side is adjacent said first and second sides, respectively. 
     
     
         5 . A capnometer as claimed in  claim 4 , wherein said reflector is further located at a fourth location on a fourth side of said air flow region, wherein said fourth side is opposite said third side from said air flow region. 
     
     
         6 . A capnometer as claimed in  claim 1 , wherein said emitter is located at a first location on a first side of said air flow region, wherein said detector is located at a second location on a second side of said air flow region, wherein said first side is adjacent said second side, wherein said reflector is located at a third location on a third side of said air flow region, and wherein said third side is opposite said first side or opposite said second side. 
     
     
         7 . A capnometer as claimed in  claim 1 , wherein said emitter is located at a first location on a first side of said air flow region, wherein said detector is located at a second location on said first side of said air flow region, wherein said reflector is located at a third location on a second side of said air flow region, and wherein said second side is opposite said first side. 
     
     
         8 . A capnometer as claimed in  claim 1 , further comprising a breath tube, wherein said breath tube defines a channel between said emitter/detector and said reflector for said air flow region. 
     
     
         9 . A capnometer as claimed in  claim 8 , wherein said breath tube is removable from said capnometer. 
     
     
         10 . A capnometer as claimed in  claim 8 , wherein said emitter, said detector and said reflector are mounted in said breath tube. 
     
     
         11 . A capnometer as claimed in  claim 10 , further comprising an optical layer between said emitter and said reflector and/or between said detector and said reflector for improving a collection efficiency of said IR light emitted by said emitter onto said detector. 
     
     
         12 . A capnometer as claimed in  claim 11 , wherein said optical layer comprises silicon. 
     
     
         13 . A capnometer as claimed in  claim 8 , wherein said emitter and said detector are located external to said breath tube, and wherein said breath tube comprises a mid-IR transmissive portion, said mid-IR transmissive portion being aligned with said emitter and said detector to allow mid-IR light to pass therethrough into and out of said breath tube. 
     
     
         14 . A capnometer as claimed in  claim 13 , wherein said mid-IR transmissive portion comprises a separate window. 
     
     
         15 . A capnometer as claimed in  claim 14 , further comprising a seal arranged between said breath tube and said separate window. 
     
     
         16 . A capnometer as claimed in  claim 13 , wherein said mid-IR transmissive portion comprises an anti-reflection coating and/or an anti-fog coating. 
     
     
         17 . A capnometer as claimed in  claim 13 , further comprising a first heater for heating said mid-IR transmissive portion. 
     
     
         18 . A capnometer as claimed in  claim 13 , further comprising an optical layer between said emitter and said reflector and/or between said detector and said reflector for improving a collection efficiency of said IR light emitted by said emitter onto said detector. 
     
     
         19 . A capnometer as claimed in  claim 18 , wherein said optical layer comprises an anti-reflection coating and/or an anti-fog coating. 
     
     
         20 . A capnometer as claimed in  claim 18 , further comprising a second heater for heating said optical layer. 
     
     
         21 . A capnometer as claimed in  claim 18 , wherein said optical layer and said mid-IR transmissive portion are integral. 
     
     
         22 . A capnometer as claimed in  claim 18 , wherein said optical layer comprises silicon. 
     
     
         23 . A capnometer as claimed in  claim 13 , wherein said reflector is mounted in the breath tube. 
     
     
         24 . A capnometer as claimed in  claim 23 , wherein said reflector comprises a coating on an inner surface of said breath tube. 
     
     
         25 . A capnometer as claimed in  claim 13 , wherein said breath tube comprises one or more alignment features for enabling said arrangement of said reflector with said emitter and said detector. 
     
     
         26 . A capnometer as claimed in  claim 25 , wherein said one or more alignment features comprise alignment pins. 
     
     
         27 . A capnometer as claimed in  claim 13 , wherein said reflector is located external to said breath tube, and wherein said breath tube comprises a second mid-IR transmissive portion, said second mid-IR transmissive portion being aligned with said reflector to allow mid-IR light to pass therethrough into and out of said breath tube. 
     
     
         28 . A capnometer as claimed in  claim 1 , wherein said emitter is configured to provide said IR light at two or more different wavelengths in the range 3-5 μm, and wherein said detector is configured to detect said two or more different wavelengths for said signal processor. 
     
     
         29 . A capnometer as claimed in  claim 1 , further comprising a reflector mounting for supporting said reflector. 
     
     
         30 . A capnometer as claimed in  claim 1 , further comprising a memory to store said level data output. 
     
     
         31 . A capnometer as claimed in  claim 1 , wherein said component is CO 2 . 
     
     
         32 . A capnometer as claimed in  claim 1 , wherein said emitter comprises a III-V mid-IR semiconductor emitter. 
     
     
         33 . A capnometer as claimed in  claim 1 , wherein said detector comprises a III-V mid-IR semiconductor detector. 
     
     
         34 . A capnometer as claimed in  claim 1 , wherein said reflector comprises a reflective metal film coated with an organic layer. 
     
     
         35 . A capnometer as claimed in  claim 1 , wherein said air flow region has a cross-sectional area which is reduced where said IR light passes through said air flow region. 
     
     
         36 . A capnometer as claimed in  claim 1  in combination with a medical device, said capnometer further comprising blocking means to inhibit air surrounding said capnometer from flowing into said medical device. 
     
     
         37 . A capnometer as claimed in  claim 1 , wherein said emitter comprises a plurality of emitters, and wherein each of said plurality of emitters emits light centred at a different, respective wavelength. 
     
     
         38 . A capnometer as claimed in  claim 1 , wherein said detector comprises a plurality of detectors, and wherein each of said plurality of detectors detects light at a different, respective range of wavelengths. 
     
     
         39 . A method of determining when a measurement of a CO 2  level in a gas exhaled by a patient in an inspiration/expiration cycle through a capnometer is void, the method comprising:
 measuring a CO 2  level in said gas during said inspiration using said capnometer; and   determining that said measurement of said CO 2  level in said gas during said expiration is void when said measured CO 2  level in said gas during said inspiration is outside a first range of CO 2  levels.   
     
     
         40 . A method as claimed in  claim 39 , further comprising determining a corrected CO 2  level in said gas during said expiration when said measurement has been determined to be void. 
     
     
         41 . A method as claimed in  claim 40 , wherein said correction is applied to one or both of a signal from an emitter of said capnometer and a signal from a detector of said capnometer. 
     
     
         42 . A method of determining when a measurement of a CO 2  level in a gas inhaled and/or exhaled by a patient in an inspiration/expiration cycle through a capnometer is void, the method comprising:
 providing said capnometer with a plurality of emitters, wherein each of said plurality of emitters emits light at a different, respective wavelength,   wherein each of said different, respective wavelengths is within a detecting wavelength range of a detector of said capnometer;   pulsing said plurality of emitters during a said inspiration and/or during a said expiration such that said light of each of said plurality of emitters is detected by said detector at a different, respective point in time;   determining that the measurement is void when a scattering of said light emitted by said plurality of emitters correlates between at least two said emitters of said plurality of emitters.   
     
     
         43 . A method as claimed in  claim 42 , wherein one of said plurality of emitters emits light substantially centred at 4.26 μm. 
     
     
         44 . A method as claimed in  claim 43 , further comprising correcting a signal from said emitter which emits light substantially centred at 4.26 μm when said measurement is void. 
     
     
         45 . A method as claimed in  claim 42 , further comprising correcting a signal from said detector when said measurement is void. 
     
     
         46 . A method of calibrating a capnometer, the method comprising:
 providing a capnometer, in particular a capnometer as claimed in  claim 1 , providing a breath tube comprising a gas with a known CO 2  level;   inserting said breath tube into said capnometer;   measuring said CO 2  level of said gas in said breath tube using said capnometer;   correlating said measured CO 2  level to said known CO 2  level; and   storing said correlation in a memory of said capnometer.   
     
     
         47 . A method of calibrating a capnometer, the method comprising:
 providing a capnometer, in particular a capnometer as claimed in  claim 1 , measuring, using said capnometer, a known CO 2  level of air surrounding said capnometer;   correlating said measured CO 2  level to said known CO 2  level; and   storing said correlation in a memory of said capnometer.   
     
     
         48 . A method of calibrating a capnometer, the method comprising:
 providing a capnometer, in particular a capnometer as claimed in  claim 1 ;   measuring, using said capnometer, a CO 2  level of air surrounding said capnometer at two points in time before and after an exhaling-inhaling cycle of a user of said capnometer, to provide a first and second CO 2  background level input; and   calibrating said capnometer based on a difference between said first and second CO 2  background level inputs.   
     
     
         49 . A method as claimed in  claim 48 , wherein said CO 2  level of air surrounding said capnometer is measured before and after a plurality of said exhaling-inhaling cycles. 
     
     
         50 . A method as claimed in  claim 48 , wherein air exhaled by said user exits said capnometer through a first part of the capnometer which is different to a second part of the capnometer through which air inhaled by said user enters said capnometer. 
     
     
         51 . A capnometer, in particular the capnometer of  claim 1 , comprising a diversion device for blocking one of a first and a second air-flow path in the capnometer at a time,
 wherein said first air-flow path connects an inhaling/exhaling portion of the capnometer at which a user of the capnometer inhales/exhales air and an intake portion of said capnometer through which air enters said capnometer, and   wherein said second air-flow path connects said inhaling/exhaling portion and an exit portion of said capnometer at which air exits said capnometer.   
     
     
         52 . A capnometer as claimed in  claim 51 , wherein said diversion device comprises a diverting valve which is controlled by said inhalation/exhalation of said air by said user. 
     
     
         53 . An inhaler comprising a capnometer according to  claim 1 , wherein said capnometer is configured to monitor a CO 2 level in air inhaled through or exhaled through said inhaler. 
     
     
         54 . A system comprising:
 a capnometer according to  claim 1 , the capnometer configured to output gas concentration data from a gas inhaled/exhaled from a patient; and   a data processor configured to receive said gas concentration data, and configured to perform the method according to  claim 39 .   
     
     
         55 . (canceled)