In 1999 the Department of Transportation submitted a report to the GAO entitled "Highway Safety Effectiveness of State .08 Blood Alcohol Laws" in which the department detailed the expense of Driving Under the Influence (DUI) on the nation's economy.  The report was instrumental in the federal government mandating in this year's Federal Transportation Appropriations Bill that all states be made to comply with the .08 Blood Alcohol Concentration (BAC).  Under the provisions of Public Law 106-346--passed by both houses of Congress on October 6 and signed into law by the President on October 23--states will be required to enforce a national standard of .08 or risk losing highway funds over the next several years.   

An accompanying report by the House Appropriations Committee noted that safety--not concrete--should be government's primary concern with transportation issues.  Everyone is in agreement that reducing the number of DUI related accidents and fatalities is indeed a laudable goal.  However, there is also the recognition that setting a "safe" number for the BAC will always be arbitrary, since alcohol sensitivity can vary from time to time, person to person, and situation to situation.  Clear-cut empirical evidence exists in the scientific literature that no single limit can be determined from where alcohol impairment begins.  It is also recognized that there are many other contributing factors that lead to unsafe driving and many of these factors enhance or mimic the effects of alcohol.  Fatigue, prescription drug use, and metabolism problems such as diabetes or other endocrine disorders are just a few of the many variables that can influence or have a similar effect independent of and in conjunction with alcohol.

Analysis of Body Fluids --Various devices and types of BAC testing methods have been developed to help identify and remove drinking drivers from the highway.  The BAC describes the concentration of alcohol in a person's blood expressed as weight per unit of volume.  For example, at 0.10 % BAC there is a concentration of 100 mg of alcohol per 100 ml blood.  A blood test is not necessary to determine a persons BAC; however, of the available methods it is often considered the most reliable and has the advantage of being saved for future reference.  Although the BAC can also be measured by analyzing exhaled breath, urinalysis or saliva, numerous studies have shown that none of  the available methods or testing devices are 100% reliable. 

Visual Detection Guidelines --Law enforcement officers are trained to detect visual cues that may seem to indicate alcohol impairment such as driving too slow, a sudden stop or swerve, a slow or no response to a direct question.  The National Highway Traffic Safety Administration since 1975 has been sponsoring research that has led to development of standardized methods of evaluation.  Currently, the most commonly used is the Standardized Field Sobriety Test (SFST) which consists of a battery of three tests including: Horizontal Gaze Nystagmus (involuntary jerking of one's eye); Walk and Turn Test; and the One Leg Stand.  NHTSA research indicates that this method when administered properly allows proper classification of approximately 77% of suspects.  However, the test can also indicate consumption of seizure medications, phencyclidine, and a variety of inhalants, barbiturates and other depressants, disease, or a variety of physical disorders.

Since neither analysis of body fluids nor visual detection guidelines are deemed 100% accurate, nor do they allow for individual variation, in this article we will examine the acute physiological effects of alcohol and related factors that can enhance or mimic the effects of alcohol.  We will also look at some of the ways toxicologists attempt to compute or refute the BAC from available evidence, including the  alcohol content of a given beverage.     

Ethyl alcohol or ethanol, commonly known as "alcohol," is the active ingredient in most beer, wine and spirits.  Beers and wines are the direct products of the fermentation of grains and fruits.  Spirits (whiskey, rum etc.) are produced by distillation of fermented mash, a mixture of grains, water, sugar and yeast.  Regardless of which product is consumed, the primary intoxicating ingredient is alcohol.

There is also wide variation in the alcohol content of any of the three products and even more variation within the various groups.  Toxicologists should exercise caution when performing calculations to select the most appropriate estimate for alcoholic strength of any beverage.  Studies show that in any alcoholic beverage, particularly beers, there can be significant disparity between the concentration listed on the label (if any) and the actual measured alcohol concentration.  The following table provides a general overview:

The physiological effect that drinking alcohol will have on a person depends on how much alcohol builds up in the bloodstream.  The BAC is not a constant but one that rises and falls depending on the amount of alcohol consumed and how fast it is absorbed from the gastrointestinal tract, how it is distributed to the body and how quickly it is eliminated from the body.

Alcohol is absorbed along the entire length of the GI tract, but primarily in the first section of the small intestine.  Food or even the amount of mixer in a drink can slow or retard absorption into the small intestine.  A large meal or heavy snacking can slow absorption to the point that the peak is not reached for 6 hours or more and can also lower the BAC.

Almost as soon as alcohol enters the bloodstream the body starts eliminating it.  One to three percent is given off unchanged in the urine, perspiration and expired air.  The remainder of the alcohol is oxidized or burned up by various organs, but mostly by the liver.  About 75% of the oxidation of alcohol takes place in the liver.  The chemical breakdown of alcohol in the body (metabolism) is accomplished by several enzymes through a series of processes that rapidly convert the chemicals into substances usable by the body such as amino acids, carbohydrates and fats.  Weight, gender, age, time of day, drugs, health of the liver, food, menstrual cycle, disease and a multitude of other factors serve to moderate the rate at which the metabolism of alcohol occurs in the individual.  Once you allow for individual variation the rate at which alcohol is metabolized is relatively constant.   BAC charts that use the amount of alcohol consumed, weight of the individual and time factors can be helpful in that they give a snapshot average.  However, no facile computation can account for the multitude of variables that need to go into making an accurate assessment for the court.  The following  is an example of a simplistic table for charting the BAC based on 12 oz. beer at 5%, 5 oz. wine at 12% or 1½ oz. whiskey at 40% (80 proof) all equaling approximately 6 oz. alcohol:

As alcohol enters the bloodstream it travels throughout the body easily diffusing alcohol into cells through the cell membranes.   Organs with dense networks of blood vessels such as the brain, kidneys, liver and lungs rapidly attain the same alcohol level as the blood.  These organs get a higher initial concentration of alcohol than the other organs.  However, since the body is largely water eventually even distribution takes place through  the water in all of the tissues of the body and it is at this point equilibration is reached and the BAC is at its maximum.

Distribution in the body, like absorption and elimination, is a key component of the equation for computing the BAC.  Great variation exists between the water content of tissues.  For instance, adipose (fatty) tissue contains less water than muscle tissue and most women have more adipose tissue than men.  In most instances, all else being equal, a women will become intoxicated more quickly because more alcohol will remain concentrated in the fluids of a woman's body and not disperse more evenly through the more watery muscle tissue.  Women also tend to be smaller than men and weight also effects distribution; therefore, the same amount of alcohol can produce a dramatically different BAC.    

The Endocrine System (glands) also plays a role by producing and secreting hormones.   Alcohol can alter the basic functioning of glands, like the pancreas that secretes insulin to regulate the amount of sugar in the blood.  The pancreas tends to overreact in the presence of alcohol and the result can be temporary hypoglycemia (low blood sugar).  And in the case of diabetics who are already taking insulin a small amount of alcohol  could trigger a reaction mimicking a much higher level of intoxication.  Another gland that plays a key role is the pituitary which regulates how much water is retained by the kidneys.  Alcohol can inhibit the release of the antidiuretic hormone from the pituitary which leads to increased urination.   However, this phenomenon mainly takes place while the BAC is rising and generally urination falls to below normal in the later stages.  

Various guidelines have been produced  to assess the state of intoxication of an individual drinker; however, there is no observable effect that can define the moment of .08 or even come close due to individual variation and level of tolerance.  However there are certain actions on the nervous system that are somewhat predictable as the BAC rises.   In the subclinical stage there is usually no loss of coordination or any outward signs of impairment.  As the BAC rises inhibitions lower and a general euphoria or feeling of well being will follow.  In most individuals by the time the BAC reaches 0.08 there can be a slight impairment of balance, speech, vision, reaction time and hearing.    At 0.10 it is illegal to operate a vehicle in any state in the U.S. based on studies that show in most cases there can be significant impairment of motor coordination and loss of good judgment.    

Individuals can also build up a tolerance to alcohol ingestion that can make assessment by visual observation difficult if not impossible.  Studies show that in heavy drinkers changes take place in the actual physiology of the body and in their behavioral adaptation which can allow them to compensate.  An extreme example is on record in Sweden of a man actually driving with a BAC of .54 w/v, the point at which most humans would be comatose if not dead.  Although, this example is certainly not the norm; distribution, absorption and elimination are all affected in heavy drinkers and must be taken into consideration when making observations or computational assessments.

According to several recent studies fatigue can also mimic or alter the physiology of how alcohol is used by the body.  Dr. Herbert Moskowitz in his April 2000 review of the literature for the National Highway Traffic Safety Administration (NHTSA) believes more research needs to be done on the interaction of alcohol with sleep deprivation and circadian rhythms, noting "there is strong evidence produced by the studies on drowsiness that the ability to remain alert and functioning is impaired by alcohol."  Meanwhile, a 1999 study by Lamond & Dawson quantified the performance impairment associated with fatigue by systematically comparing the effects of fatigue and alcohol intoxication.  The researchers  concluded that "moderate levels of fatigue produce performance equivalent to or greater than those observed at levels of alcohol intoxication deemed unacceptable when driving, working and/or operating dangerous equipment."

Another often overlooked factor in driver impairment that can mimic or enhance the effects of alcohol is prescription and over the counter drug use, including many of the herbal preparations.  It is generally recognized that illegal drugs impair driving skills; however, common everyday drugs can impair driving skills by causing drowsiness or putting the individual in a hyperactive or highly sedated inattentive state.  The mechanism of action of each medication varies almost as much as individual reaction to the drug or combination of drugs.  This physiological variation is only magnified when combined with alcohol.   In general: 

Central Nervous System Depressants such as barbiturates, tranquilizers and other drugs that slow brain function can produce slowed reflexes, inability to divide attention, reduced inhibitions, lack of concentration, impaired vision and coordination, and slurred speech.   

Central Nervous System Stimulants such as ephedrine, amphetamines, caffeine, appetite suppressants, and various herbal preparations can also cause impairment.  Symptoms can include nervousness, irritability, inability to think or concentrate and unpredictable or bizarre behavior.  

Narcotic Analgesics including opium derivatives such as morphine and other synthetic pain relievers produce symptoms similar to many of the central nervous system depressants, but more extreme.  

The discussion above demonstrates how easily factors that mimic the effects of alcohol can lead to false or misleading conclusions.  Additionally, specific effects of alcohol consumption on an individual's cognitive and motor skills can vary dramatically after consuming  alcohol alone or in combination with prescription or over-the-counter drugs.   These differences, ranging from those arising from weight and hormone variations, fatigue, unique experiential and behavioral characteristics, and interaction with other drugs, suggest that at best we presently have very limited knowledge on the differing effects which alcohol has on an individual.  Each individual DUI case is indeed unique and the inherent variations of each case must be taken into consideration when attempting to calculate or assess blood alcohol concentration. 

SELECTED BIBLIOGRAPHY

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Lamond, N.; D. Dawson. Quantifying the Performance Impairment Associated With Fatigue. Journal of Sleep Research. 8(4): 255-262, 1999.

Logan, B. K.; G.A. Case; S. Distefano. Alcohol Content of Beer And Malt Beverages: Forensic Considerations.  J Forensic Sci 44(6): 1292-5, 1999.

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Moskowitz, Herbert; Dary Fiorintino. A Review of the Literature on the Effects of Low Doses of Alcohol on Driving Related Skills. US Department of Transportation, NHTSA, April 2000.

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