Blood-Alcohol Physiology

In organs with a rich blood supply, such as the kidneys, brain, and liver, the tissues quickly attain alcohol equilibrium with the arterial blood. Voluntary muscle tissue, however, has a much smaller blood flow per unit of weight and, as a result, requires longer to reach alcohol equilibrium after ingestion. Since the muscles comprise about 40 percent of body weight, this delay in alcohol absorption by the muscles results in high concentrations of alcohol in arterial blood and in the brain during active absorption of alcohol. The result is the common phenomenon that an individual may appear greatly affected only a few minutes after taking two or three drinks, and then rapidly sober up within 15 to 30 minutes, in apparent contradiction to normal expectations. This, of course, can raise serious doubts about the relevance of blood-alcohol tests in DUI cases.

Many factors in blood alcohol physiology can affect the rate of absorption and distribution of alcohol into the system and, ultimately, into the brain. The most common is that different individuals have different rates, which can vary within a given individual. But, external factors can also cause variation. The effects of cold weather or extreme stress, for example, can cause less blood to be delivered to the muscles and more to the brain. With more blood being delivered to the brain, more alcohol is also delivered, and an elevated BAC is the result. [Ritchie, The Aliphatic Alcohols, in Goodman and Gilman’s The Pharmacological Basis of Therapeutics (7th ed., 1985)]. Thus, it would appear that the stress in DUI cases caused by interrogation, field sobriety tests, and handcuffing could cause higher blood-alcohol levels when the individual is later tested at the police station.

The concentration of alcohol in a DUI suspect’s body depends upon the amount of water contained in that body. The more water is present in the body, the more diluted the alcohol will become as it is absorbed into the system. And the simple fact is that individuals vary according to the percentage of water in their bodies.

In a study entitled Pharmacokinetics of Ethanol in Plasma and Whole Blood: Estimation of Total Body Water by the Dilution Principle, (Jones, Hahn, and Stalberg, 42 European Journal of Clinical Pharmacology 445 (1992)), researchers confirmed that the body-water content varies from person to person. The content in men, interestingly, decreases with age, with a result that the blood-alcohol concentration will increase. Further, where an individual has experienced trauma, as in an automobile accident, the body’s percentage of water will decrease. The same can happen as a result of pathological conditions, such as in persons with diarrhea, heart failure, or impaired renal function.

Yet another factor affecting absorption rates among individuals is the sex of that individual. It has been known for some time that women are generally more susceptible to the effects of alcohol than men. This has generally been explained by pointing out that women are smaller and have relatively more fat and less water than men. But recent research seems to indicate that a more important reason may be that women have significantly lower amounts of an enzyme which provides a protective barrier in the stomach by breaking alcohol down before it circulates into the body.

In an article appearing in the Los Angeles Times (January 11, 1990, page A27), scientists at the University School of Medicine in Trieste, Italy, and the Veterans Affairs Medical Center, Bronx, New York, found that the stomach lining contains an enzyme called gastric alcohol dehydrogenase which breaks down alcohol. To determine the effects of the enzyme, they administered alcohol both orally and intravenously (by-passing the stomach) to a group of fourteen nonalcoholic men, six alcoholic men, seventeen nonalcoholic women, and six alcoholic women.

There were two interesting results. First, in both the nonalcoholic and alcoholic groups, women had higher blood-alcohol concentrations than men after ingesting an equivalent dose of ethanol; by contrast, there were no differences when the ethanol was taken intravenously. With weight differences taken into account, the researchers found that women became legally intoxicated after consuming 20% to 30% less alcohol than men; absent allowance for weight, an average-size woman reaches a given blood-alcohol level after consuming about 50% less alcohol than a man.

Second, the alcoholic men and women had significantly higher BAC levels after oral ingestion than the nonalcoholic men and women; the levels reached by alcoholic women indicated a nearly total absence of the protective enzyme in their stomachs.

The scientists concluded that legislatures may need to consider sex differences when defining safe levels of drinking for criminal DUI purposes. Although they did not address the issue, the findings concerning alcoholics would also seem to pose some interesting legal and factual issues.

Absorption and actual concentration are only two aspects of blood-alcohol analysis in DUI cases. Elimination, or the rate of disappearance of alcohol from the body, is of equal importance. The body reduces the amount of alcohol by oxidation in the liver. The rate of this alcohol elimination is, once again, a matter that varies from one person’s physiology to another’s, but it appears probably to be independent of concentration. The rate of disappearance is generally about .015 percent per hour, that is, the body will “burn off” about .015 percent alcohol in the blood in an hour. If a DUI suspect has a reading of .08 percent, for example, they should have a reading an hour later (assuming, of course, no further consumption of alcohol) of about .065 percent. Put another way, an individual will eliminate approximately 1/2 to 2/3 of an ounce of 100-proof whiskey in an hour. This rate of disappearance can vary from .010 percent to .020 percent per hour, although dissipation of as high as .06 percent has been scientifically observed. Again, the wide variation in individual rates of elimination gives the lie to attempts to test all drunk driving suspects on the theory of uniform burn-off rates.

How does all this translate into the DUI situation? An average person of 150 to 170 pounds probably must consume, on an empty stomach, approximately 8 to 10 ounces of 100-proof whiskey (8 to 10 beets or 4 to 5 highballs) to reach a blood-alcohol level of .15 percent; this is equal to 15 parts of alcohol per 10,000 parts of blood in the subject’s system by weight, or about 2 parts of alcohol by volume for every 1,000 parts of blood. But, again, the ever-present aspect of individuality can confound scientific premises. Because of altered physiology or biochemical reactions, a heavy drinker may have to drink 12 ounces of 100-proof whiskey before that same level of .15 percent is reached. More importantly, a level of .15 percent can have wildly different effects on the nervous systems of different individuals and their ability to operate motor vehicles safely.

The knowledgeable DUI attorney may encounter an attempt by the prosecution expert witness to estimate the amount of alcohol in the defendant’s body at a given point in time. The method most commonly used by criminalists in a California DUI case is to apply the following formula:

(Body weight) x (blood-alcohol level) x (0.26 for men or 0.23 for women) = number of ounces of 100-proof alcohol (or 1/10th the number of ounces of 10-proof beer)

This formula is subject to the well-known computer caveat of “garbage in, garbage out” – the resulting figure is no more valid than the data fed into the formula. And all three of the variables in the formula depend upon assumptions: (1) the DUI suspect’s weight usually comes from an estimate or from an old driver’s license; (2) the blood-alcohol level obtained by the police may be inaccurate; and (3) the 0.26/0.23 figures are only physiological averages. Prosecution experts in California DUI cases are fond of dealing with the mythical “average person” rather than with individuals, as exemplified by their use of average alveolar air-to-blood ratios.

Finally, in yet another study, researchers discovered that a blood-alcohol concentration (BAC ) of .10% caused no impairment in the reaction time of tested subjects. [Baylor, Layne et al., Effects of Ethanol on Human Fractionated Response Times, 23 Drug and Alcohol Dependency 31 (1989)].