Method and apparatus for determining indirectly the concentration of a specific substance in the blood

Abstract

Method and apparatus for determining in a person's exhalation air the concentration of a specific substance in the blood by measuring the concentration of the substance and the concentration of water vapor in the exhalation air and utilizing a known relationship between these concentrations. When the method is applied, the exhalation air is exhaled freely in a defined air volume having a predetermined composition, and the concentrations are measured in this air volume. The apparatus for working the method comprises a device which defines a space for receiving the exhalation air, which has two mutually opposite openings through which the space communicates with the surrounding air, and means for selective quantitative detection of the substance in the air in the defined space.

1 - 19 . (canceled)  
     
     
         20 . Method for determining indirectly in a person's exhalation air the concentration of a specific substance in the blood by measuring the concentration of said substance and the concentration of water vapor in the exhalation air, and utilizing a known relationship between these concentrations the exhalation air being exhaled as undiluted alveolar gas at one end of a defined flow passage and said concentrations being determined by measuring the undiluted alveolar gas in the flow passage, wherein the exact evaporation temperature of the alveolar gas is determined, and the concentration of said substance in the blood is determined according to said relationship with consideration of deviation of the predetermined evaporation temperature from a normal value.  
     
     
         21 . A method according to  claim 20 , wherein the normal value is the normal body temperature of 37° C.  
     
     
         22 . A method according to  claim 20 , wherein a reference gas of a predetermined composition before measuring the undiluted alveolar gas is passed through the flow passage, and said concentrations are determined by measuring the alveolar gas for calibration of the measurement equipment used for the measurement.  
     
     
         23 . A method according to  claim 22 , wherein the reference gas is passed through the flow passage after measuring the undiluted alveolar gas, and the measurement of the reference gas is repeated for control of the calibration.