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Blood alcohol concentration measuring from respiratory air

  • US 5,971,937 A
  • Filed: 06/25/1996
  • Issued: 10/26/1999
  • Est. Priority Date: 06/26/1995
  • Status: Expired due to Fees
First Claim
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1. A method for obtaining a reliable blood alcohol concentration value from respiratory gases of a subject undergoing examination, the subject respiring gases in a respiratory cycle having an exhalation phase with exhalation stages, a respiratory cycle exhalation phase suitable for providing a reliable blood alcohol concentration value having a plateau stage, the plateau stage having a beginning and a concluding portion, respiratory gases of the subject exhaled in the plateau stage comprising alveolar gas of the subject, said method comprising the steps of:

  • sampling the respiratory gases of the subject during the exhalation phase to obtain a plurality of CO2 concentration measurements, the sampling occurring at successive points in time in an exhalation phase and including points occurring in the plateau stage of a suitable exhalation phase;

    sampling the respiratory gases of the subject during the exhalation phase at at least one point in time having a predetermined temporal relationship to the concluding portion of the plateau stage to obtain at least one alcohol concentration measurement;

    comparing a CO2 concentration measurement obtained from the respiratory gases to a predetermined CO2 concentration threshold value to determine whether the CO2 concentration measurement is greater or less than the predetermined CO2 concentration value;

    detecting from the measurements of CO2 concentration obtained from the sampling at successive points in time, the existence of a plateau stage in the exhalation phase being sampled;

    if the existence of a plateau stage is detected and if the CO2 concentration measurement exceeds the predetermined threshold value, producing, as reliable, a blood alcohol concentration value output using the at least one alcohol concentration value measurement; and

    if at least one of the conditions comprising the existence of a plateau stage and the CO2 concentration measurement exceeding the predetermined threshold value is not present, providing an output differing from that produced when the conditions are present.

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