[Influence of breath volume on alcohol analysis]

In order to obtain reliable results in breath-alcohol analysis it is necessary to consider alveolar air. In former examinations of the question, which part of expired air contains almost pure alveolar air, a separation between the influence of temperature and volume had not been made. Only after a temperature correction has been performed the influence of volume can clearly be seen in drinking experiments. Measurements undertaken with the ALCOMAT clearly show the influence of varied breathing techniques on the results of breath-alcohol determinations. The demand of a minimum volume in the breath test is not sufficient by itself. In order to get a correct result the expiration volume should be more than 70% of the subject's vital capacity. In case of an expired volume remarkably below 50% of the vital capacity the measured values can be more than 10% below the expected values. Such big deviations can only be the result of a deliberate inspiration and expiration technique of the subject.