A Scientific Interpretation Of the Breath Alcohol Concentration Test Result — Part II: Theory

By Wayne Morris, MS

Morris-Kopec Forensics, Inc.
A breath alcohol concentration is the determined by a breath alcohol testing procedure using a breath alcohol testing device. What has just been stated means that an analytical test is being used. Analytical testing is governed by the area of Analytical Chemistry and, as such, several conditions must be met for the testing to have scientific reliability. These conditions are universal to all chemical testing that give a quantitative result. As such, it is important to first understand the implications raised by the fact that we are dealing with a scientific method.

A scientific method, under the protocols of Analytical Chemistry, must be based upon scientific theories. The theories involved in infrared spectroscopic measurements have been shown to meet scientific protocols and can be used to measure the absorption of alcohol vapor in a sample.

However, the application of such testing to the breath alcohol concentrations of human subjects must also pass the threshold of scientific protocols and theory. Part I discussed the protocols in terms of the variation of a subject’s blood-breath ratio. Part II will discuss the scientific basis for the blood-breath ratio.

The blood-breath ratio is the scientific basis for breath alcohol concentration testing. The theory is based upon the understanding of lung respiration which was known in the early 1900’s and 1950’s. The blood contains alcohol which entered the blood as the stomach contents passed through the ileum, the start of the small intestines.

The blood carried the alcohol to the liver where metabolism took place and to the various water containing sera and tissues in the body where the alcohol was distributed to these moieties. As the blood passed through the capillaries in the lung, gas exchange took place during which oxygen entered the blood from the alveoli and carbon dioxide and other volatile and semi-volatile components passed into the alveoli sacs.

Simple diffusion was the mechanism by which the alveolar alcohol content migrated into the upper lung portions. This meant that the longer a person blew into the breath testing device, the closer one approached the alveolar alcohol content and the closer one approached the alveolar blood-breath ratio assumed to be 2100:1 in the United States.

As the shorter breaths would be further from this blood-breath ratio, the lower values observed in the scattering patterns of the simultaneous blood-breath studies was explained and bolstered this concept. The higher values were explained by variations in body temperature, in blood solids, lung size, experimental errors and other means.

The fact that a false low breath alcohol concentration was to the benefit of the subject was recognized as a good thing. If a person had a low first test, it was expected that a longer second sampling would produce a higher reading and, if above the 0.02 difference allowed, a third test of a similar duration would be in agreement with the igher value obtained. With some exceptions, these expectations were met and again bolstered belief in the blood-breath ratio.

In 2000, a new paradigm to lung respiration and the exhalation of volatile and semi-volatile gases was presented by Dr. Hlastala. In this model, the blood-alveolar exchange takes place with some simple diffusion occurring. The incoming air during inhalation cools down the mucosal lining in the bronchi. The following exhaled breath will pass over the cooled mucosal lining with the volatile and semi-volatile components being absorbed and adsorbed onto the mucosal lining.

Continued exhalation will heat the mucosal lining until the absorbed and adsorbed components escape into the warmer xhaled breath. In the case of ethanol, the exhaled breath sample will consist of ethanol desorbed from the mucosal lining during the continued exhalation and some bronchial ethanol that was not absorbed by the mucosal lining. The amount of alcohol easured in breath alcohol testing will be somewhat related to the amount of alcohol consumed in that the more alcohol ingested, the higher the absorbed and adsorbed alcohol in the mucosal lining.

However, there will be no simple relationship — no blood-breath ratio – observed. What would be expected is a scattering of points for the simultaneous blood and breath alcohol concentrations, both higher and lower than the line of equality. This is exactly what has been observed in all of the past studies.

Furthermore, there is no reliable relationship between the observed exhaled breath alcohol concentration and the blood alcohol concentration at the time of sampling. It is this lack of relationship between the blood alcohol content and exhaled breath alcohol arising from desorption of ethanol from the mucosal lining that contradicts the long held assumption of a blood-breath ratio. This also explains the reason why the simultaneous blood and breath alcohol concentrations do not show an average in the blood-breath ratio within a smaller experimental error.

Impairment is due to the brain tissue alcohol concentration. As the sampling of brain tissue of a living person is frowned upon, blood alcohol concentration, which is related to brain tissue alcohol content by a brain tissue-blood alcohol ratio, was used to relate impairment to the amount of alcohol consumed. For various reasons, blood sampling was replaced by breath alcohol testing based upon the assumed blood-breath ratio.

Without the existence of a blood-breath ratio, there is no relationship between the observed breath alcohol content to either the blood alcohol content or to the brain tissue alcohol content and thus no direct relationship between the observed breath alcohol content and impairment. As such, without the blood-breath ratio, there is no scientific basis to relate the results of breath alcohol testing to impairment.

WAYNE MORRIS holds a B.S. degree in Chemistry from the University of Miami and an M.S. in Physical Chemistry from Texas A & M University. His thesis work was in the area of infrared spectroscopy. He has qualified to testify as an expert on many issues of DUI breath/blood alcohol testing. He has ten years experience with the Florida Department of Law Enforcement in the areas of drug and chemical analysis and has taught Florida Bar CLE approved courses regarding the scientific basis of DUI testing.

He has also written a course book for these courses, “ A Florida Primer: Blood and Breath Alcohol—Scientific and Legal Issues.” Currently, he is President of Morris-Kopec Forensics, Inc. and a Forensic Scientist specializing in blood and breath alcohol theory and testing, in urine drug testing and in the analysis of controlled substances.

He may be contacted at Morris-Kopec Forensics, Inc., 4200 St. John’s Parkway, Sanford, Florida 32771, by telephone at 407-341-0452, by fax at 407-831-5515 or by e-mail at wmorris400@aol.com.