Scientific Evidence in California Criminal Cases – Alcohol Intoxication
I.Physiological Aspects of Alcohol Ingestion Associated with Intoxication
6.1 A. Purpose of Chapter
As the laws regarding driving under the influence (DUI) have become stricter and the penalties harsher, individuals accused of driving while intoxicated are seeking legal assistance more frequently. The purpose of this chapter is to introduce the practitioner to the evidence regularly introduced in a DUI case, the scientific underpinnings, and the areas for examination when preparing the case for trial.
Many persons reading this will have had personal experience with alcohol. At some level, we understand that we ingest alcohol and some time later we feel the effects of the alcohol. There are many factors that determine how quickly we feel the effects of alcohol, how intoxicated we become, and how long we feel the effects of alcohol. The purpose of this chapter is not to completely discuss each of the aspects that may affect the medicolegal aspects of alcohol, but to introduce some of the major factors affecting the absorption, elimination, and measurement of alcohol.
6.2 B. Physiological aspects of Alcohol Ingestion
Alcohol is commonly ingested orally and passes from the mouth through the esophagus, into the stomach, and then into the small intestine via the pyloric sphincter. A majority of the alcohol consumed is absorbed into the blood as it passes through the small intestine; however, some absorb into the blood is then distributed to the rest of the body simultaneously. Tortora, Principles of Human Anatomy, chap 12 (10th ed 2005)
Because alcohol is completely soluble (miscible) in water, it is eventually distributed uniformly in body water and in all the soft tissues of the body. Urine, being mainly water, will contain a given ratio relative to the blood which makes the urine a potential fluid for determining blood alcohol level. Likewise, due to the water solubility and the volatility of alcohol, the breath contains a given ratio of the alcohol relative to the blood alcohol level as well. See Saferstein, Criminalistics; An Introduction to Forensic Science, chap 9 (10th ed 2011)
However, during the absorptive phase, there are significant differences between alcohol concentration in arterial blood, venous blood, breath, and urine, with arterial blood having the highest concentration of alcohol. It is believed that during the absorptive phase, breath alcohol concentration is closer to the concentration of alcohol in arterial blood than it is to the concentration of venous blood. The question of whether breath alcohol concentration more accurately reflects the concentration of alcohol in the brain where the depressant effects are manifest is still unresolved see Saferstein, Criminalistics, chap 9. See also Simpson, Accuracy and Precision of Breath Alcohol Measurement for subjects in the Absorptive State, 33 Clinical Chemistry 753, 755 (June 1987); for the online version of this article, go to http://www.clinchem.org/cgi/reprint/33/6/753.
Fatty tissue have lower water concentrations than other tissues such as muscle. Thus, a lean person who consumes a given amount of alcohol potentially attains a lower blood alcohol concentration (BAC) than a person of the same weight with a higher body fat content. Because women normally have more subcutaneous fat and less total body water than men do, a woman who consumes the same amount of alcohol as a man of the same weight potentially attains a higher BAC, although some studies suggested that women tend to have faster elimination rates. Mumenthaler,Taylor O’Hara & Yesavage, Gender Differences in Moderate Drinking Effects, 23 Alcohol Res & Health 55, 57 (Winter 1999); for the online version of this article, go to https://webapps.ou.edu/alcohol/docs/09GenderDiffinModDrinking55-64.pdf. See also NIAAA, Women and Alcohol (Feb 2011) available online at http://pubs.niaaa.nih.gov/publications.womensfact.womensfact.htm
The Morales Law Firm would like to thank Scientific Evidence in California Criminal Cases for sharing this information with us.