Monthly Archives: March 2005
In my previous post, I discussed the problem of mouth alcohol – that is, falsely high breathalyzer readings caused by alcohol samples coming from the mouth rather than from the lungs. And the response from some of our more sophisticated readers (law enforcement and/or lawyers?) has been predictable: What about mouth alcohol detectors? Some breath machines have what is called a slope detector, commonly referred to as a “mouth alcohol detector”. This is an electronic circuit designed to detect the presence of mouth alcohol as the breath is being captured by the machine. It does this by detecting any pronounced negative slope in the alcohol intake curve, since alcohol content from the mouth or throat will decline more rapidly than alcohol from the lungs. In theory, the presence of mouth alcohol will cause the test to abort. Unfortunately, these “detectors” are simply unreliable, due primarily to a design flaw. Rather than try to explain the technical defects, I will let Dr. Michael Hlastala, Professor of Physiology, Biophysics and Medicine at the University of Washington School of Medicine, explain:
The slope detector is problematic for all breath instruments and has been misrepresented by the manufacturers. When a subject with alcohol in the blood, with no extra alcohol in the breath, exhales, the breath alcohol continues to increase during exhalation. It does not reach a “plateau” until the end of airflow. It continues to rise, giving a positive slope. If you swish a little alcohol in the mouth (and have no alcohol in the blood), wait awhile and exhale, the breath alcohol will rise until a peak is reached about 1/3 of the way into the exhalation, and then decline gradually. It is the declining breath alcohol (negative slope) that triggers the slope detector to register the breath as having mouth alcohol. If the subject has alcohol in the blood as well as the mouth, then the normal rising breath alcohol curve will add to the declining mouth alcohol curve to produce what is often a level curve. Thus, the slope detector is unable to detect the presence of mouth alcohol when some is present in the mouth, yet breath alcohol concentration will be higher than it should be. The slope detector cannot detect false mouth alcohol under this circumstance.
To make matters worse, the slope/mouth alcohol detectors are never calibrated by the police, as this has to be done at the factory. The only thing police technicians do is simply rinse their mouth with alcohol and then breath into the machine: if the detector is triggered, it is assumed to be working. But as Professor Hlastala has observed:
Whenever the slope detector is checked, it is done with alcohol in the mouth, but not in the blood. Therefore, the slope detector serves no purpose and mouth alcohol frequently affects the breath alcohol reading.
Bottom line: Despite the claims of manufacturers anxious to sell their machines, these detectors are unreliable and mouth alcohol remains a serious problem in breath alcohol analysis.
One of the most common causes of falsely high breathalyzer readings is the existence of mouth alcohol.
The breathalyzer’s internal computer is making a major assumption when it captures a breath sample and then analyzes it for blood alcohol concentration (BAC): It assumes that the alcohol in the breath sample came from alveolar air — that is, air exhaled from deep within the lungs. Since we are trying to measure how much alcohol is in the blood, rather than in the breath, the computer applies a formula to translate the results. This formula is based upon the average ratio of alcohol in the breath to alcohol in the blood. This so-called partition ratio is 1 to 2100 — that is, in the average person there will be 2100 units of alcohol in the blood for every unit measured by the breathalyzer in the breath. Put simply, the machine’s computer multiplies the amount of alcohol detected in the suspect’s breath sample by 2100 and reports that as the blood alcohol level.
But what if the alcohol in the sample is not from the lungs?
Too bad: the machine doesn’t know any better. If there is even a miniscule amount of alcohol in the DUI suspect’s mouth or throat, it will be tremendously magnified by the breathalyzer and it will report a much higher BAC than the true one.
Alcohol can be found in the mouth for a number of reasons. The most obvious is that the individual has recently consumed some alcohol; it usually takes 15-20 minutes for the alcohol to dissipate through the rinsing action of saliva. Or he/she may have recently used mouthwash or breath freshener (most contain fairly high levels of alcohol) — possibly to disguise the smell of alcohol when being pulled over by police. See my earlier post, Breath Fresheners and Breathalyzers.
The most common source of mouth alcohol is from eructation (burping or belching). This causes the liquids and/or gases from the stomach — including alcohol if it is there — to rise up into the soft tissue of the esophegus and mouth, where it will stay until it has dissipated. For this reason, police officers are required to keep a DUI suspect under observation for at least 15 minutes prior to administering a breath (in reality, however, many if not most officers are unwilling to stand around watching a suspect for a quarter of an hour).
Acid reflux can greatly exacerbate this problem. As was discussed in a previous post, GERD, Acid Reflux and False Breathlayzer Results, the stomach is normally separated from the throat by a valve. When this valve becomes herniated, there is nothing to stop the liquid contents in the stomach from rising and permeating the esophegus and mouth. The contents — including any alcohol — is then later breathed into the breathalyzer. Since it has not yet been absorbed through the stomach wall and into the blood and eventually into the lungs, this alcohol should not be read as breath from the lungs and multiplied by 2100. Of course, the breathalyzer doesn’t know this. See the article by Kechagias, et al., “Reliability of Breath-Alcohol Analysis in Individuals with Gastroesophogeal Reflux Disease”, 44(4) Journal of Forensic Sciences 814 (1999).
The mouth alcohol problem can also be created in other ways. Dentures, for example, will trap alcohol for much longer than 15-20 minutes. Periodental disease can also create pockets in the gums which will contain the alcohol for longer periods. And so on…. As the American Medical Association’s Committee on Medical Problems concluded in its Manual for Chemical Tests for Intoxication (1959):
True reactions with alcohol in expired breath from sources other than the alveolar air (eructation, regurgitation, vomiting) will, of course, vitiate the breath alcohol results.
Ok, this story isn’t exactly about drunk driving, but it sure reflects the increasingly arrogant attitude of prosecutors we encounter in DUI cases here in Southern California:
LOS ANGELES (March 24) AP – Jurors who acquitted actor Robert Blake of murder – and were later called “incredibly stupid'’ by District Attorney Steve Cooley – want an apology.
“I’m just disgusted,'’ Blake jury foreman Thomas Nicholson said Thursday. “It appears to me he has no faith in the jury selection. After all, it was his people who helped choose us.'’
Loyola University law professor Laurie Levenson called Cooley’s comment a
major lapse in judgment – and “much more of an embarrassment for him than the jurors'’….. On Thursday night, Cooley stood by his comments.
But this is the real mind-blower:
“Bottom line it was the wrong verdict,'’ he said. “Sometimes jurors should be held accountable for their mistakes.'’
I hate to think what Cooley has in mind for making jurors “accountable”, but I’m pretty sure ”mistakes” means aquittals…..
The previous two posts on the physiological sources of inaccuracy in breath alcohol analysis have apparently caused considerable interest…and a number of queries. Let me be clear: Simpson is far from alone in his conclusions. Those involved in forensic alcohol analysis will generally recognize that the most recognized authorities in the field include Dubowski, Jones, Simpson and Hlastala. In the posts I quoted supporting conclusions from Dubowski and Hlastala; Jones has expressed somewhat similar views. To quote further from Professor Dubowski on physiological sources of error (as opposed to operator error or defects in the design or function of the machine itself — of which there are many):
First, not all blood and breath alcohol curves follow the Widmark pattern, nor is the elimination phase linear. Second, alcohol absorption is not always complete within 60 to 90 minutes as often claimed. Third, the peak alcohol concentration cannot be validly predicted or established in an individual instance without frequent and timely measurement of alcohol concentrations. Fourth, it is not possible to establish whether an individual is in the absorption or elimination phase, or to establish the mean overall rate of alcohol elimination from the blood or breath, from the results of two consecutive blood or breath alcohol measurements, however timed. Fifth, significantly large short-term fluctuations occur in some subjects and result in marked positive and negative departures from the alcohol concentration trend line. Sixth, short-term marked oscillation of the blood or breath alcohol concentration can occur at various points on the curve, resulting in repeated excursions of the alcohol concentration above and below a given concetration within a few minutes or for hours. Finally, no forensically valid forward or extrapolation of blood or breath alcohol concentrations is ordinarily possible in a given subject and occasion solely on the basis of time and individual analysis results.
Dubowski, "Absorption, Distribution and Elimination of Alcohol", 10 Journal of Studies on Alcohol, Suppl. 98 (1985). And those are just some of the physiological problems when trying to measure blood alcohol. We also have to consider: possible errors by the cop in operating the machine; malfunctions in the machine; design defects (there are many: see, for example, "Breathalyzers — and Why They Don’t Work" and "Why Breathalyzers Don’t Measure Alcohol"); maintenance and repair issues; calibration errors; and so on…. But, as they say in DUI law enforcement, "close enough for government work".
I’ve received considerable response to yesterday’s post, "Breathalyzer Inaccuracy: Testing During the Absorptive State", including questions concerning the accuracy of breath machines after the absorptive state. Even in the post-absorptive state — that is, when the body has reached a state of equilibrium, or uniform distribution of alcohol — there are numerous sources of error attributable entirely to physiological factors. Simpson’s research has found that breath tests are inherently unreliable, indicating uncertainty levels of 15 to 27 percent. In an article written shortly before the one cited yesterday, he noted:
Over 90% of this uncertainty is due to biological variables of the subject, and at least 23% of subjects will have their actual blood alcohol concentration overestimated. Manufacturers’ specifications for the accuracy and precision of these instruments are inconsistent with the experimental values reported in the literature and I recommend that an appropriate amount of uncertainty be reflected in the results from these breath analyzers, especially when they are used for law-enforcement purposes.
Simpson, "Accuracy and Precision of Breath Alcohol Measurements for Subjects in the Absorptive State", 33(2) Clinical Chemistry 261 (1987). Another noted expert, Professor Michael Hlastala, Professor of Physiology, Biophysics and Medicine at the University of Washington’s Medical School, concludes:
Breath testing, as currently used, is a very inaccurate method for measuring BAC. Even if the breath testing instrument is working perfectly, physiological variables prevent any reasonable accuracy…
Hlastala, "Physiological Errors Associated with Alcohol Breath Testing", 9(6) The Champion 19 (1985).