Opinion ID: 2635209
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Heading: The Science of Alcohol Testing

Text: Alcohol affects the central nervous system. When ingested, it is absorbed into the blood and carried through the carotid arteries to the brain. ( State v. Downie (1990) 117 N.J. 450 [569 A.2d 242, 245] ( Downie ); State v. Brayman (1988) 110 Wn.2d 183 [751 P.2d 294, 297] ( Brayman ).) After passing through the brain, alcohol travels through venous blood to the liver and heart, and from there, to the lungs, where it diffuses into alveolar air space and is exhaled in the breath. ( Downie, 569 A.2d at pp. 245-246.) As a practical matter, it is impossible to measure the amount of alcohol in a person's carotid arteries or brain. ( Id. at p. 246; Taylor & Tayac, supra, Forensic Chemist: Blood-Alcohol, § 12.2, p. 712.) However, most experts agree that measurements of alcohol in venous blood or breath give a good indication of the amount of alcohol in the brain during the postabsorptive phase. [5] ( Downie, at p. 246.) When a subject blows into a breath-testing machine, the device measures the amount of alcohol vapor expelled into alveolar spaces deep in the lungs. From this measurement of breath alcohol, a blood-alcohol percentage can be computed using a mathematical constant. The conversion from breath alcohol to blood alcohol is based on the chemistry principle of Henry's law, which holds that there is a constant ratio between the concentration of alcohol in the blood and the concentration of alcohol in the alveolar air of the lungs. (Taylor & Tayac, supra, Forensic Chemist: Blood-Alcohol, § 12.19, p. 770.) Breath-testing machines in California use a conversion factor of 2,100 to 1, meaning the amount of alcohol in 2,100 milliliters of alveolar breath is equivalent to the amount of alcohol in 1 milliliter of blood. (Cal. Code Regs., tit. 17, § 1220.4, subd. (f); see People v. McDonald (1988) 206 Cal.App.3d 877, 880 [254 Cal.Rptr. 384].) This ratio is used, apparently without exception, in breath-testing devices throughout the United States. (See Brayman, supra, 751 P.2d at p. 297; State v. McManus (1989) 152 Wis.2d 113 [447 N.W.2d 654, 656].) Nevertheless, courts here and across the country have long recognized that actual partition ratios vary, both among members of the population and within a single individual. In Bransford, supra, 8 Cal.4th at page 889, we noted that an individual's ratio of breath-alcohol to blood-alcohol concentration can be influenced by many variables, including body temperature, atmospheric pressure, medical conditions, sex, and the precision of the measuring device. [Citations.] (See also Brayman, supra, 751 P.2d at p. 297 [mentioning, in addition to these factors, hematocrit level and elapsed time between drinking and breath-alcohol measurement].) Experts have also described a wide range of variability in partition ratios throughout the general population. In People v. McDonald, supra, 206 Cal.App.3d at page 880, for example, the people's expert testified a person's ratio could be as high as 2,700 to 1 or as low as 1,550 to 1, and in Downie, supra, 569 A.2d at page 247, the court noted that partition ratios measured in a group of experimental subjects ranged from a low of 1,706 to 1 to a high of 3,063 to 1. Despite this recognized variability, most scientists agree that the 2,100-to-1 ratio roughly approximates or even underestimates the ratio of most people. In the late 1980's, the New Jersey Supreme Court considered evidence presented by ten experts at a hearing addressing partition ratios and the reliability of breath test results. ( Downie, supra, 569 A.2d at pp. 243-244.) These experts generally agreed that breath-testing machines using the 2,100-to-1 partition ratio will usually underestimate the amount of alcohol in the blood for several reasons. ( Id. at p. 247.) First, most people's partition ratios may be closer to 2300:1 than to 2100:1. Second, the breathalyzer results are truncated, or the third decimal position is dropped when read. If a person reads 0.099 on the breathalyzer, the results will be shortened to read 0.09, thereby underestimating the breath alcohol. Third, a suspect may not provide enough deep breath to register all of the alcohol present in the alveolar air. Fourth, the breathalyzer's scale is set 0.003 below the start line and this gives suspects an added benefit. ( Ibid. ) Several experts opined that the standard partition ratio is set artificially low, and the true mean ratio in the population is closer to 2,300 to 1. ( Id. at p. 247.) Dr. Robert Borkenstein, inventor of the breathalyzer machine, stated that breathalyzer researchers and members of the National Safety Council adopted the 2100:1 partition ratio instead of the more accurate 2300:1 ratio because they wanted to err on the low side and have almost no errors on the high side. ( Id. at p. 247.) [6]