Does the Breath Test Really Measure Deep Lung Air?

     One of the assumptions upon which breath alcohol testing has rested since the 1950’s is the belief that the instruments measure “deep lung” or alveolar air.  This outdated assumption has been eroded as research over the past two decades has yielded a greater understanding of the exchange of highly soluble gases by the lungs.  No longer can it be assumed that alveolar air is in equilibrium with blood alcohol simply because the breath test reading reaches a plateau. 

     The findings of Dr. Michael Hlastala of the University of Washington confirm that during inspiration the relatively cool and dry air being inhaled becomes warmer and absorbs liquid in the airways.  This air also absorbs soluble gas dissolved in the airway tissue.  During exhalation the air is cooled and dehumified.   The alcohol present in a breath sample comes entirely from the lining of the airways.  This mucus and tissue, not the blood in the lower part of the lungs, is the source of “breath alcohol concentrations.”

     Further research has shown that breath alcohol concentration continues to rise as a person exhales until he or she cannot exhale any longer, which causes the flattening or plateau of the breath alcohol concentration.   It has also been confirmed that the average directly measured partition coefficient for alcohol in blood at 98.6 degrees Fahrenheit is 1756:1, not  2100:1 as asssumed by the Intoxilyzer 5000.   Also of significance is the discovery that an increase in exhaled volume beyond the minimum required by a breath testing instrument results in an increased breath alcohol reading and a decreased blood to breath partition ratio.  For those with smaller lung capacity, these findings also have negative consequences because a greater portion of their vital capacity (maximum volume of air that can be inhaled and exhaled) is necessary in order to generate a printed result.  On the other hand, those with larger lungs will benefit from an unfair advantage. 

Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website

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