By way of explaining some of jdoe71's valid professional observations.
Read no further, if you're easily bored, or don't appreciate information for it's own sake.
is the passage
of alcohol into the blood.
is the temporary placement of alcohol into various body tissues.
is the removal
of alcohol from the body.
is the method of passage
of alcohol through cell membranes and is governed by concentration differences on either side of the cell wall.
The Blood Alcohol Concentration (BAC) is a measure of the difference between the rates of absorption and elimination. The change in BAC with time may be described graphically as a "blood alcohol curve," where the absorption phase is represented by a rising line and the elimination phase by a falling line.
Alcohol is absorbed from the stomach and small intestine by diffusion. Most absorption occurs from the small intestine due to its large surface area and rich blood supply. The rate of absorption varies with the emptying time of the stomach. Generally, the higher the alcohol concentration of the beverage, the faster the rate of absorption. However, above a certain concentration, the rate of absorption may decrease due to the delayed passage of alcohol from the stomach into the small intestine.
The maximum absorption rate is obtained with the consumption
of an alcoholic beverage containing approximately 20-25% (by volume or v/v) alcohol solution on an empty stomach. The absorption rate may be less when alcohol is consumed with food
or when a 40% (v/v) alcohol solution is consumed on an empty stomach. The rate may also slow down when high fluid volume/low alcohol content beverages, such as beer
, are consumed.
For normal social-type drinking, the highest BAC is usually achieved within 30 minutes after completion of consumption
, though it could take as long as 60 minutes. When large amounts of alcohol are consumed over a short time interval, or when a large quantity of food
is eaten with the alcohol, the absorption phase may not be complete for up to two (2) hours after last consumption.
In other situations, a subject may develop a plateau, where the blood alcohol level does not change for up to two hours. When this occurs the rate of absorption is equal to the rate of elimination and hence the blood alcohol concentration does not change. After two hours, the rate of elimination will exceed the rate of absorption and the blood alcohol level will begin to decrease.
Once in the blood, alcohol is carried throughout the body. The alcohol diffuses into tissues and fluids according to their water content. During the absorption phase, the BAC of arterial blood is greater than the BAC of venous blood. Arteries carry blood to a tissue, and veins remove blood from the tissue. At equilibrium, where the tissue has absorbed a proportionate quantity of alcohol, the BAC of arterial blood is equal to the BAC of venous blood.
Alcohol is eliminated from the body by excretion and metabolism. Most alcohol is metabolized, or burned, in a manner similar to food, yielding carbon dioxide and water. A small portion of alcohol is excreted, such as through the breath, leaving the body as alcohol, unchanged. It is this latter process that allows for breath alcohol testing.
Elimination occurs at a constant rate for a given individual.The median rate of decrease in BAC is considered to be 15 milligrams per cent (mg%) per hour. The range of decrease in BAC is 10-20 mg% per hour. This range represents the extreme ends of the rate encountered in a normal population. Most people eliminate at a rate of between 13 and 18 mg% per hour. Of these, the majority eliminates at the higher end. Very few people eliminate at as low a rate as 10 mg% per hour.
Hospital analyses of blood samples for ethyl alcohol content are often based upon serum or plasma as the sample matrix.
Plasma is the liquid portion of the circulating blood.
Serum is the liquid remaining after the red blood cells are removed by mechanical means, such as centrifugation.
Serum contains slightly more water than whole blood and hence will have a slightly higher alcohol level than whole blood. Scientific studies have shown that serum will contain more alcohol than whole blood by a factor of between 1.08:1 and 1.18:1, or on average, a factor of 1.12:1. As a result, a serum alcohol level of 108-118 mg% would be equivalent to an alcohol level of 100 mg% in whole blood.
Blood analysis is a direct method for the determination of a blood alcohol level and urine analysis is an indirect method. In other words, a blood sample analysis is the most accurate means to predict a blood alcohol level. To some extent a UAC can corroborate a BAC, but difficulties can arise with the use of a single
urine sample because of pooled urine in the bladder. More than one urine sample should be obtained over a known time interval.
It should be noted that individuals can be impaired by alcohol without manifesting any visible signs. Impairment is not simply the appearance of gross physical symptoms but a deterioration of judgment, attention, loss of fine co-ordination and control with a possible increase in reaction time and a diminishing of sensory perceptions. Intoxication is an advanced state of impairment in which the gross physical symptoms of the effects of alcohol are apparent. The point at which "impairment" becomes "intoxication" is unique to the subject and depends on tolerance.
Studies have shown that impairment is greater at a given blood alcohol level when the BAC is increasing than for the same BAC when the blood alcohol level is falling. This is called the Mellanby effect.