Spectroscopic breath analysis

Abstract

Methods and apparatus for the analysis of exhaled breath by spectroscopy are disclosed. An optical cavity containing the exhaled breath, typically comprising a pair of opposing high reflectivity mirror, is used to implement a cavity enhanced absorption technique. Pairs of 12 CO 2 and 13 CO 2 absorption lines suitable for use in spectroscopic breath analysis are also disclosed.

1 - 22 . (canceled)  
   
   
       23 . A method of using cavity enhanced absorption spectroscopy to quantify one or more isotopically-labelled carbon compounds in a sample, the method comprising the steps of: 
 passing at least a portion of said sample into an optical cavity;    illuminating said sample in said optical cavity with radiation emitted by an optical source, wherein the optical cavity is arranged to allow radiation emitted from the optical source to be repeatedly reflected and retrace its path to excite a plurality of cavity modes; and    measuring a wavelength-dependent reduction in the intensity of radiation in said optical cavity caused by variations in cavity ringdown time caused by absorption of said radiation in said optical cavity by said one or more isotopically-labelled carbon compounds, thereby to quantify said one or more isotopically-labelled carbon compounds.    
   
   
       24 . A method according to claim  1  wherein said one or more isotopically-labelled carbon compounds are compounds of carbon  13 .  
   
   
       25 . A method according to claim  1  wherein said one or more isotopically-labelled carbon compounds comprise bacterial metabolites.  
   
   
       26 . A method according to claim  3  wherein said one or more isotopically-labelled carbon compounds comprise bacterial metabolites of urea.  
   
   
       27 . A method according to claim  1  wherein said one or more isotopically-labelled carbon compounds comprise enzyme metabolites.  
   
   
       28 . A method according to claim  1  wherein said one or more isotopically-labelled carbon compounds comprise compounds indicative of fat digestion.  
   
   
       29 . A method according to claim  1  wherein said one or more isotopically-labelled carbon compounds comprise carbon dioxide.  
   
   
       30 . A method according to claim  1  wherein said one or more isotopically-labelled carbon compounds comprise volatile organic compounds.  
   
   
       31 . A method according to claim  1  wherein said one or more isotopically-labelled carbon compounds comprise at least one of the group comprising: methane, alkanes, pentanes, methylpentane, formaldehyde.  
   
   
       32 . A method according to claim  1  wherein said sample is breath.  
   
   
       33 . A method of using cavity enhanced absorption spectroscopy to quantify one or more nitrogen compounds in a sample, the method comprising the steps of: 
 passing at least a portion of said sample into an optical cavity;    illuminating said sample in said optical cavity with radiation emitted by an optical source, wherein the optical cavity is arranged to allow radiation emitted from the optical source to be repeatedly reflected and retrace its path to excite a plurality of cavity modes; and    measuring a wavelength-dependent reduction in the intensity of radiation in said optical cavity caused by variations in cavity ringdown time caused by absorption of said radiation in said optical cavity by said one or more nitrogen compounds, thereby to quantify said one or more nitrogen compounds.    
   
   
       34 . A method according to claim  11  wherein said sample is breath.  
   
   
       35 . A method according to claim  11  wherein said one or more nitrogen compounds comprise at least one of nitric oxide and ammonia.  
   
   
       36 . A method of using cavity enhanced absorption spectroscopy to quantify isotopically-labelled water in a sample, the method comprising the steps of: 
 passing at least a portion of said sample into an optical cavity;    illuminating said sample in said optical cavity with radiation emitted by an optical source, wherein the optical cavity is arranged to allow radiation emitted from the optical source to be repeatedly reflected and retrace its path to excite a plurality of cavity modes; and    measuring a wavelength-dependent reduction in the intensity of radiation in said optical cavity caused by variations in cavity ringdown time caused by absorption of said radiation in said optical cavity by said isotopically-labelled water, thereby to quantify said isotopically-labelled water.    
   
   
       37 . A method according to claim  14  wherein said sample is breath.  
   
   
       38 . A method of using cavity enhanced absorption spectroscopy to detect the presence of bacteria in a sample, the method comprising the steps of: 
 contacting said sample with a metabolizable compound;    collecting gas produced by said sample;    passing at least a portion of said gas into an optical cavity;    illuminating said gas in said optical cavity with radiation emitted by an optical source, wherein the optical cavity is arranged to allow radiation emitted from the optical source to be repeatedly reflected and retrace its path to excite a plurality of cavity modes; and    measuring a wavelength-dependent reduction in the intensity of radiation in said optical cavity caused by variations in cavity ringdown time caused by absorption of said radiation in said optical cavity by metabolites of said compound, thereby to detect the presence of said bacteria.    
   
   
       39 . A method according to claim  16  wherein said metabolizable compound is an isotopically-labelled carbon compound  
   
   
       40 . A method according to claim  16  wherein said metabolizable compound is an isotopically-labelled compound of carbon  13 .  
   
   
       41 . A method according to claim  16  wherein said metabolizable compound is isotopically-labelled urea.  
   
   
       42 . A method according to claim  16  wherein said metabolites of said compound comprise bacterial metabolites of urea.  
   
   
       43 . A method according to claim  16  wherein said gas is collected from breath.  
   
   
       44 . A method of using cavity enhanced absorption spectroscopy to detect the presence in a sample of at least one compound indicative of one of: explosives, nerve gas, natural gas deposits, and oil deposits, the method comprising the steps of: 
 passing at least a portion of said sample into an optical cavity;    illuminating said gas in said optical cavity with radiation emitted by an optical source, wherein the optical cavity is arranged to allow radiation emitted from the optical source to be repeatedly reflected and retrace its path to excite a plurality of cavity modes; and    measuring a wavelength-dependent reduction in the intensity of radiation in said optical cavity caused by variations in cavity ringdown time caused by absorption of said radiation in said optical cavity by said at least one compound, thereby to perform said detection.