by Kentucky Attorney Stephen J. Isaacs, Isaacs Law Office. http://www.kyduiblog.com/
While the states contend that the science behind Breath Alcohol Testing is reliable, researchers are finding flaws with the science upon which Breath Alcohol Testing is based.
Lung physiology researcher Dr. Michael P. Hlastala, Ph.D. Professor of Physiology, Biophysics and of Medicine Pulmonary and Critical Care Medicine of the University of Washington tested the consistency of measurements from breath alcohol concentration (BrAC) testing machines and compared them to measurements of blood alcohol concentration (BAC) measurements. Dr. Hlastala discovered that the results could vary by as much as plus or minus 20%.
In his research, Dr. Hlastala states that:
. . . subjects with larger lung volume may have a lower BrAC than a subject with a small lung volume because these subjects do not need to exhale as great a fraction of their vital capacity as subjects with smaller lung volume to fulfill the minimum volume exhalation required before stopping exhalation (usually ~1.5 liters). A person with smaller lung volume must breathe farther into the exhaled breath, resulting in a greater BrAC-to-BAC ratio. Michael P. Hlastala, Invited-Editorial on “The Alcohol Breath Test,” 93 Journal of Applied Psysiology 405 (2002).
According to this research, breath testing machines based on the “average” person can result in a bias favoring individuals with large lung capacities causing a low BrAC-to-BAC ratio, and against individuals with small lung capacities causing a higher BrAC-to-BAC ratio.
Stated another way, a person legally under the influence with a 0.08 blood alcohol concentration and with large lung capacity may inaccurately measure 0.064 BrAC on a breath alcohol concentration test machine. A person not considered to be under the influence with a 0.067 blood alcohol concentration and with a small lung capacity may inaccurately measure 0.08 BrAC on a breath alcohol concentration test device.
ISAACS ADDS:
“… it appears that lung size affects the value of the breath alcohol test where it may be off by as much as +- 20% (for up to a 40% maximum swing). The theory is that a person with a large lung will not need to provide a large breath sample, which means that the air deep within the lungs which the machines try to measure is not fully measured, or that persons with small lungs end up giving too much of a sample, which skews the results. “