Ethanol, or ethyl alcohol (grain alcohol), is one of the earliest and most widely used drugs in existence. It is a clear fluid whose low molecular weight and high solubility in water cause it to diffuse rapidly through body tissue membranes and reach equilibrium in tissues at levels proportional to water content. Blood, for example, will hold proportionately more alcohol than will muscle tissue.
The concentration of alcohol in a DUI suspect's body depends on the amount of water contained in that body. The more water 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 that exists 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 - that is, the blood-alcohol concentration will become higher. Further, where an individual has experienced trauma, as in an automobile accident, the body's percentage of water will decrease. The same can also happen due to pathological conditions, as in persons with diarrhea, heart failure, or impaired renal function.
For alcohol to produce its effect, it must reach the brain. To accomplish this, it first passes into the bloodstream after absorption through the walls of the stomach and small intestines. This is a simple biochemical process of diffusion, which will continue as long as the concentration of alcohol in the stomach and intestines is higher than that in the blood.
In contrast to ordinary foods and many drugs, alcohol is absorbed rapidly from the stomach and even more rapidly from the small intestine just beyond the stomach. In fact, the presence of alcohol is initially detectable about five minutes after consumption, and its maximum concentration within the body tissues is achieved in somewhere between 1/2 hour and 1 1/2 hours. This rate of absorption in DUI cases can be accelerated if the subject has ingested significant amounts of water or materials containing water, and it can be slowed down if he has eaten food. The type of alcoholic beverage can also be a factor: beer will cause a slower increase in blood-alcohol concentration than distilled spirits, as well as a lower peak level and faster decline. Absorption is complete when the entire gastrointestinal tract reaches equilibrium with the remainder of the body; this can take as long as 21/2 hours but commonly occurs within 30 to 90 minutes. In any event, the rate of absorption of alcohol in a DUI case - and, as a result, the effect on the nervous system - varies according to the individual.
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