Breath end-tidal gas monitor

Abstract

An improved apparatus and method for capturing and analyzing the end-tidal portion of an exhalation. The CO2 level of air drawn into the system (10) is monitored to distinguish inhalation and exhalation of breath. Upon detection of a decrease in the CO2 level in the air drawn into the system (10), indicating a transition between exhalation and inhalation a pair of flow selector valves (26, 28) are operated to capture the end-tidal volume of air drawn into the system (10) immediately prior to the detection of the decrease in the CO2 level. Incoming air is diverted around the captured volume of air, and the CO2 levels are continually monitored to ensure that the captured volume of air corresponds to the end-tidal portion of an exhalation. Once the captured volume of air is positively identified as the end-tidal portion of an exhalation, the captured volume is routed through a gas analyzer (44) for analysis of one or more predetermined gas levels.

1 . A breath gas analyzer having a pump configured to draw a flow of air through a capnograph adapted to identify a transition point between an exhalation and an inhalation, and to subsequently direct said flow of air through at least one gas analyzer, comprising:
 a first flow selector valve disposed downstream from said capnograph, said first flow selector valve configured to selectively divert said flow of air through a sample volume to said pump and to divert a bypass flow of air past said sample volume to said pump;   a second flow selector valve disposed downstream from said first flow selector valve, said second flow selector valve configured to isolate said sample volume from said first flow selector valve;   a third flow selector valve disposed downstream from said second flow selector valve, said third flow selector valve configured to receive said bypass flow of air from said first flow selector valve and to isolate said sample volume from said pump;   a fourth flow selector valve disposed downstream from said pump, said fourth flow selector valve configured to selectively exhaust said flow of air and to route said flow of air into said isolated sample volume; and   wherein said second flow selector valve is further configured to selectively exhaust said sample volume through the at least one gas analyzer.   
     
     
         2 . The breath gas analyzer of  claim 1  wherein said second flow selector valve and said third flow selector valve are responsive to signals from said capnograph to isolate said sample volume from said first flow selector valve and from said pump. 
     
     
         3 . The breath gas analyzer of  claim 1  wherein said fourth flow selector valve is responsive to signals from said capnograph to route said flow of air into said isolated sample volume. 
     
     
         4 . The breath gas analyzer of  claim 3  wherein said fourth flow selector valve is responsive to signals from said capnograph to route said flow of air through a one-way valve into said isolated sample volume. 
     
     
         5 . The breath gas analyzer of  claim 1  wherein said second flow selector valve is responsive to signals from said capnograph to exhaust said sample volume through the at least one gas analyzer. 
     
     
         6 . The breath gas analyzer of  claim 1  wherein the at least one gas analyzer includes a CO gas analyzer. 
     
     
         7 . The breath gas analyzer of  claim 1  wherein the at least one gas analyzer includes an O 2  gas analyzer. 
     
     
         8 . The breath gas analyzer of  claim 1  further including a microprocessor configured to receive signals from said capnograph and to control operation of each of said flow selector valves. 
     
     
         9 . A method for capturing and analyzing the end-tidal portion of an exhalation, including the steps of:
 drawing a flow of air from the breath of a patient;   monitoring the CO 2  level of said flow of air;   identifying a point of transition between an increasing CO 2  level and a decreasing CO 2  in said flow of air, said point of transition representative of a change from exhalation to inhalation in the breath of said patient;   upon identification of said transition point, isolating a sample volume of said flow of air drawn prior to said transition point;   diverting a continued flow of air past said sample volume;   monitoring the CO 2  level of said continued flow of air to confirm said change from exhalation to inhalation in the breath of said patient;   measuring, upon confirmation of said change from exhalation to inhalation in the breath of said patient, at least one gas level in said isolated sample volume.   
     
     
         10 . The method of  claim 9  for capturing and analyzing the end-tidal portion of an exhalation wherein the step of measuring includes measuring the CO level in said isolated sample volume. 
     
     
         11 . The method of  claim 9  for capturing and analyzing the end-tidal portion of an exhalation wherein the step of measuring includes measuring the O 2  level in said isolated sample volume. 
     
     
         12 . The method of  claim 9  for capturing and analyzing the end-tidal portion of an exhalation further including the step of exhausting said measured sample volume. 
     
     
         13 . The method of  claim 9  for capturing and analyzing the end-tidal portion of an exhalation further including the step of diverting said continued flow of air into said isolated sample volume prior to said measuring step, said diverted continued flow of air displacing said isolated sample volume air through at least one gas measurement component. 
     
     
         14 . A breath gas analyzer system including:
 an air inlet configured to receive aspirated air from the respiratory system of a subject;   a capnograph coupled to said air inlet, said capnograph adapted to identify a transition point between an exhalation and an inhalation of air in the respiratory system;   a sample volume coupled to said capnograph, said sample volume configured to selectively isolate a sample of aspirated air; and   at least one gas analyzer configured to receive a sample of aspirated air from said sample volume; and   wherein said at least one gas analyzer is further configured to measure at least one gas concentration in said sample of aspirated air.   
     
     
         15 . The breath gas analyzer system of  claim 14  further including a pump, said pump configured to draw said aspirated air through said air inlet, said capnograph, and into said sample volume; and
 wherein said pump is further configured to expel said sample of aspirated air from said sample volume, and through said at least one gas analyzer. 
 
     
     
         16 . The breath gas analyzer system of  claim 14  further including a plurality of flow selector valves, said plurality of flow selector valves configured to selectively control a flow of air between said air intake, said capnograph, said sample volume, and said at least one gas analyzer. 
     
     
         17 . The breath gas analyzer system of  claim 14  further including at least one exhaust port configured to discharge air; and
 an airflow bypass pathway configured to selectively route an airflow from said capnograph to said exhaust port, bypassing said sample volume. 
 
     
     
         18 . A method for capturing and analyzing the end-tidal portion of an exhalation, including the steps of:
 drawing a flow of air from the respiratory system of patient;   identifying a point of transition representative of a change from exhalation to inhalation in the breath of said patient;   upon identification of said transition point, isolating a sample volume of said flow of air drawn prior to said transition point;   confirming said change from exhalation to inhalation in the breath of said patient;   measuring, upon confirmation of said change from exhalation to inhalation in the breath of said patient, at least one gas level in said isolated sample volume.   
     
     
         19 . The method of  claim 18  for capturing and analyzing the end-tidal portion of an exhalation wherein the step of identifying a point of transition includes monitoring changes in a concentration of gas in of said flow of air to identify a point of transition. 
     
     
         20 . The method of  claim 19  for capturing and analyzing the end-tidal portion of an exhalation wherein the step of identifying a point of transition includes monitoring changes in a concentration of CO 2  in of said flow of air, said point of transition corresponding to a transition from an increasing CO 2  level to a decreasing CO 2  level in said flow of air. 
     
     
         21 . The method of  claim 18  for capturing and analyzing the end-tidal portion of an exhalation wherein said step of measuring includes measuring a CO concentration in said isolated sample volume. 
     
     
         22 .- 30 . (canceled)