Why Breath Tests Don't Work

by Michael P. Hlastala, Ph.D.
Division of Pulmonary and Critical Care Medicine
Box 356522
University of Washington
Seattle, WA 98195-6522

How You Breath Does Make A Difference

In many states, it is illegal to drive a motor vehicle with a breath alcohol concentration of 0.08 gm/210 liters or more. Have you ever considered what is meant by "breath"? What is the breath and to what part of the breath is the statue referring? Webster's New World Dictionary has several definitions of breath, but the most relevant is "air taken into the lungs and then let out". Air becomes breath when it goes into the lungs AND is exhaled from the lungs. The only air that fulfills that criteria is the air that is exhaled from the mouth or nose. Any air within the lungs is not breath. Only that which is exhaled can be considered as breath.

Figure 6. Exhaled Breath Alcohol Profile.

The exhaled alcohol profile is shown in (Figure 6). At the beginning of exhalation, the breath has a zero or near zero BrAC. As exhalation progresses, the BrAC increases, initially quite rapidly, but eventually the rate of increase of BrAC slows down. It does not level off until the subject stops exhalation. All of this is "breath". Since the specific portion of the breath that is sought to determine alcohol concentration is not defined, we can only surmise that the average of the breath is meant. The average of the breath would include some initial breath with lower EtOH and some of the later breath with a higher concentration. The average of the breath alcohol will be a value that is near the 5 second point of exhalation (Figure 7). If a subject exhales for five seconds and then stops, the BrAC will be close to the average of the entire breath.

Figure 7. Exhaled Breath Alcohol Profile with Valid Breath Samples Identified.

Any exhalation beyond this approximate time will result in a value that will be higher than the average BrAC. Therefore the average BrAC is ALWAYS less than the breath test machine reading.

Beware of the over-eager prosecution expert who may say that the part of the breath that the state wants is the "deep-lung air". This is incorrect and must be vigorously opposed. First of all the deep-lung air is not breath (by Webster's definition). The technician will say this because he/she believes (correctly so) that any sample of breath is usually lower than a deep-lung (alveolar) sample. When we had a blood standard (illegal to drive with a BAC of 0.10 mg/dl or more, as measured by the breath), this would be a reasonable argument. However, we now have a breath standard and, therefore, the deep-lung air is not relevant.

In the State of Washington, the initial intent of the legislature was to provide a law that could make it much easier to prosecute by taking away the possibility of defense arguments concerning the variability between BrAC and BAC. In fact, the passage of the "breath per se" law has made it much more difficult for prosecution by virtue of a lack of definition of breath. In fact the average BrAC is actually much lower than any breath alcohol test machine reading. In effect, the legislature has dealt a blow to the prosecution because it is now impossible for the prosecution to prove that the average BrAC is greater than or equal to a given standard, whether it is 0.08 gm/210 L or 0.10 gm/210L.

It comes as no surprise that we are each different from one another. We have different heights, weights, chest sizes (some are ectomorphs, others are endomorphs), lung volumes, exercise capacities, respiratory muscle strength. Some of us have respiratory diseases (ie: asthma, chronic bronchitis, emphysema). Our lung volumes vary considerably from person to person. Therefore, each of differs in the relative amount of air that we can blow into the alcohol breath test machine. This variation has a profound influence on the lack of fairness in the single breath BRAC test.

In order to be able to evaluate lung disease, spirometry test have been developed as a means of assessing the lung volume and ability to exhale rapidly. Spirometry forms the basis for Pulmonary Function Tests. In order to evaluate a patient, pulmonary physicians have performed numerous measurements on normal subjects and use these values to compare normal lung
volumes with those in a particular patient. Many of these “standardized tests” have been accumulated. One or the most referenced standardized lung volume standard tables was published by Crapo et al (Crapo 1981).

All modern infrared breath testing machines require a minimum volume of exhalation before a breath sample will be taken. Once the minimum volume is exhaled (1.5 liters for the Datamaster), a breath sample is taken when the subject stops exhalating. In order to fulfill the minimum exhalation requirement of the machine, the individual with the smaller lung volume must exhale farther into the available lung volume in order to provide a sample. A 60 year old, 150 cm female must exhale 1.5 L/2.48 L = 0.604 % of the FVC before acceptance. A 20 year old, 190 cm male must exhale 1.5 L/ 6.32 L = 0.237 % of the FVC before acceptance. Thus it is more likely that a 60 year old subject will have a higher BrAC than the 20 year old male subject. The breath sample can be obtained whenever the subject stops exhaling. The minimum exhalation required may be 1.5 liters. The maximum exhalation is the exhaled lung volume of the subject. The average BrAC for the small lung volume subject is greater than the average BrAC for the large lung volume subject. On the average, the nature of the breath test machine, with the fixed minimum exhalation requirement is inherently biased against subjects with smaller lung volumes.

The alcohol breath test was founded on "old science". Progressive development of newer, more modern technologies show that it is impossible for the alcohol concentration in breath to remain unchanged during exhalation from the alveolar or "deep lung" regions to the mouth. Alcohol always exchanges between the respired air and the airway mucosa. Consequently, BrAC depends on a variety of factors including: lung volume, body temperature, breath temperature, blood hematocrit and body size, with smaller individuals having a greater BrAC.

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