Opinion ID: 1989907
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Heading: Scientific and Physiological Framework

Text: Much of the scientific evidence in the record before the Court is undisputed. In fact, the basic physiological mechanisms on which all breath testing devices rely are not themselves controversial. We set these scientific propositions forth here, however, to provide the basis for our analysis of the scientific matters that are in dispute.
Alcohol is ordinarily ingested orally and enters the stomach where it is absorbed through the stomach's walls and intestines and is thereafter carried by the blood through the liver to the heart. The heart pumps the blood and, along with it, the alcohol, through the body, including carrying it to the brain and the lungs. Alcohol exerts its effects on an individual when the blood containing the alcohol reaches the brain. Absorption begins immediately once a person starts drinking. The rate of absorption varies greatly from one person to the next and can even vary in the same person at different times. It depends on a wide variety of factors including general health, recent food consumption, physical makeup, amount of alcohol consumed, weight, and gender. Elimination of alcohol also starts as soon as a person begins to drink. Alcohol is eliminated through excretion and metabolization, which occur when alcohol passes through the liver and is broken down by enzymes and dehydrogenates. When a person's body is absorbing alcohol faster than he or she is eliminating it, the concentration of alcohol in the blood will continue to rise. This period of time is ordinarily referred to as the absorptive phase. The concentration will reach its peak, and it will achieve a plateau, at the time when elimination and absorption are occurring at about the same rate. When the person stops ingesting alcohol, or slows down ingestion to the point where the body is eliminating alcohol more quickly than absorbing it, the body enters what has generally been referred to as the post-absorptive phase. During this period of time, the concentration of alcohol in the blood decreases.
The reported concentration of alcohol in any particular person varies depending upon the source of the test sample. An understanding of the relationship of these potential test sample sources to BAC is important to our analysis. Alcohol passes into the lungs, through the walls of the air sacs, called alveoli. As it does so, it mixes with the air that the person has inhaled. When the person exhales, alcohol passes out of the body as part of the breath. An individual's breathing pattern can influence the amount of alcohol that appears in any particular breath. In addition, the amount of alcohol in the breath sample represented by a single act of exhalation will vary from the beginning to the end. This is because the breath actually comes from different parts of the body, from the mouth to the deepest part of the lungs. Except for the possible interference that would occur if the test subject had ingested alcohol so recently that residual mouth alcohol were captured, the first part of the breath comes from the mouth and throat where there is little contact with the alcohol passing through the alveoli. However, as the person continues to exhale, the expelled air comes from deeper in the respiratory system, where it contains alcohol that more closely represents the amount passing through the lungs from the circulating blood.
Our statute establishes the violation in terms of blood, and not breath alcohol concentration. Although testing an individual's blood would presumably provide more direct evidence of that person's BAC, there are obvious practical and logistical problems associated with attempting to collect blood samples from suspected drunk drivers routinely. As a result, although because of our statute New Jersey is considered to be a blood state, we have long permitted BAC to be established through breath testing, in which breath samples are tested and converted to determine blood alcohol levels. Breath testing therefore uses an indirect measure of BAC by calculating the alcohol concentration in the breath (breath alcohol concentration, or BrAC) and extrapolating to derive the BAC using a blood/breath ratio. Breath testing has become the preferred method for field testing because it can be performed easily, is highly automated, does not require scientific skill, and produces an immediate result.