DWI Breath Testing: How you Breathe into the Machine may Affect the Result. by Plano DWI lawyer Troy Burleson

By Collin, Dallas and Denton County DWI Attorney Troy Burleson

If you gave a breath sample you may be familiar with the following scenario:
A police officer takes a person into the Intoxilyzer room to give a sample of his or her breath. The officer explains to the person that he or she must give two breath sample and must blow into a tube, connected to the Intoxilyzer hard enough to make the machine emit a steady, audible tone. The person then begins to blow into the machine and the officer starts cheering, like a high school pep squad,

“Keep breathing! Breathe harder! Harder! Keep going, that’s good you doing great!”


Ever wonder why the officer would seem supportive of your efforts and so enthusiastic to cheer you on? The following studies may shed some light on that question:
“How Breathing Techniques Can Influence the Results of Breath-Alcohol Analyses”, 22(4) Medical Science and the Law 275.
“Measurement of Blood Alcohol Concentration with Isothermal Breathing”, 51(1) Journal of Studies on Alcohol 6.

According to these studies, a persons breathing pattern may affect the results of a breath test in the following ways:

a) Holding your breath for 30 seconds before exhaling increased the blood-alcohol concentration (BAC) by 15.7%.

b) Hyperventilating for 20 seconds immediately before the analyses of breath, on the other hand, decreased the blood-alcohol level by 10.6%.

c) Keeping the mouth closed for five minutes and using shallow nasal breathing resulted in increasing the BAC by 7.3%, and

d) Testing after a slow, 20-second exhalation increased levels by 2%.

Moreover, Dr. Michael Hlastala, Professor of Physiology, Biophysics and Medicine at the University of Washington has gone farther and concluded:

“By far, the most overlooked error in breath testing for alcohol is the pattern of breathing….The concentration of alcohol changes considerably during the breath…The first part of the breath, after discarding the dead space, has an alcohol concentration much lower than the equivalent BAC. Whereas, the last part of the breath has an alcohol concentration that is much higher than the equivalent BAC. The last part of the breath can be over 50% above the alcohol level….Thus, a breath tester reading of 0.14% taken from the last part of the breath may indicate that the blood level is only 0.09%.”

9(6) The Champion 16 (1985).

Most police officers know this. They also know that if the machine contradicts their judgment that the person they arrested is intoxicated, they won’t look good. So when they tell the arrestee to blow into the machine’s mouthpiece, they’ll yell at the person and try to cheer them on to influence the persons breathing patter to change the way the person blows into the machine.
So, if you were wondering why you got such an ardent cheering session from the officer during your arrest for DWI, now you know the reason!!!

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