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Alcohol and the Physiology
of the Human Body
Alcohol is a drug and must be handled with care. Knowing
its uses and abuses is just as important as reading the instructions on a
bottle of pills. It is basic preventive medicine to know how your body
handles alcohol, how much is safe to drink and, finally, how your body
gets rid of it.
When you have a drink, a small amount of alcohol enters
the bloodstream directly through the tissues of the mouth and throat. When
it reaches the stomach 30 - 40 percent of the alcohol can be absorbed in
20 minutes if the outlet valve of the stomach is closed. When the outlet
is open, however, the alcohol passes into the small intestine, where rapid
absorption takes place. The bloodstream then distributes the alcohol
uniformly throughout the body. In this manner, the alcohol reaches the
brain.
Alcohol is an anesthetic. Its effects are similar to ether or chloroform.
As a central nervous system depressant, it affects all parts of your body
controlled by the brain. Your ability to make appropriate judgments and to
exercise self-control is affected. This means that you cannot control the
effects of alcohol by an act of will.
Alcohol does not simply pass through you. Like most
things we eat or drink, it must be broken down and eliminated. Moreover,
alcohol affects the body fairly rapidly, although its impact can be
decreased according to a number of factors.
Disposing of alcohol is much more time consuming than
drinking. A process called oxidation, which breaks it down into carbon
dioxide and water, eliminates most alcohol. More than 90 percent of the
alcohol is oxidized in the liver and the remainder is discharged unchanged
through the lungs and kidneys. Only a negligible proportion is eliminated
through tears, saliva and perspiration. You cannot dance, jog, sing, ore
cry away alcohol. Frequent urination does not help. Nor is the rate of
elimination affected by a person's weight or tolerance to alcohol. It
takes as long for the experienced drinker to eliminate alcohol as it does
for the inexperienced drinker.
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Alcohol is a small molecule, which readily mixes with
water. It can be taken into the body by any of the common routes of
administration for drugs. The most practical and effective route is oral
ingestion.
As soon as alcohol comes into contact with the tissues
of the mouth and throat, absorption begins. Alcohol quickly passes through
these tissues and enters the rich blood supply of the blood vessels in
this area, by a process of simple diffusion. Unlike other complex
substances, such as fats, carbohydrates and proteins, alcohol does not
require preliminary digestion or breakdown for absorption, and no carrier
is needed for its passage into the bloodstream. Alcoholic beverages are
retained in the stomach for a period of time prior to transfer into the
small intestine.
The absorption of alcohol into the bloodstream can also
occur directly at the stomach wall, but most rapid absorption occurs
through the wall of the small intestine, a highly specialized tissue for
the uptake of nutrients into the body. It has a large surface area, one
thousand times greater than the stomach, and has thinner walls and a
greater blood supply.
Regardless of the alcohol concentration of a beverage
consumed, the concentration of alcohol in the small intestine rarely
exceeds 1 to 2% v/v. Only the mouth, the throat and the stomach come into
contact with high concentrations of alcohol, and only in the stomach is
this contact prolonged.
Anything that will retain alcohol in the stomach will
prolong absorption, while conditions that allow rapid passage of alcohol
into the small intestine will hasten the rate of absorption. Typically
about 30% of all consumed alcohol is absorbed from the stomach whereas 70%
is absorbed from the small intestine. Factors which may effect the total
rate of absorption include the type and nature of alcoholic beverages, the
concentration of the alcoholic beverage itself, the type of food and
quantity of food consumed, sex of the individual, body weight, body water
content, experience with alcohol, metabolic disposition and other
physical, biological, and physiological factors. These parameters taken
together define consumption tolerance for a given individual.
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Once alcohol has been absorbed into the bloodstream it
is circulated throughout the body diffusing into the body tissues and
fluids mixing and equilibrating with total body water. Immediately after
absorption and distribution, alcohol is distributed into the blood
throughout the body in the cardiovascular system to the various organs of
body fluids. Differences are seen between body fluids and body organs,
however, a relatively constant ration between them exists. The most
important single factor which influences the alcohol concentration in an
organ or fluid is its water content, since alcohol is soluble in water.
The alcohol that is absorbed from the stomach and small
intestine enters the portal vein that leads directly to the liver, the
major detoxifying organ of the body. The blood is then pumped through the
lungs where oxygen is taken up, carbon dioxide and other volatile
compounds such as ethyl alcohol are given off. This process takes place in
the alveolar sacs in the deep lung region. The lung contains approximately
300 million alveoli. Surrounding the alveoli is a fine network of
capillary blood vessels. In the respiratory system air moves back and
forth through the same set of tubules and there is continuous mixing of
inspired and expired air. The blood on returning from our lungs enters the
left side of the heart from which it is pumped into the arterial system
throughout the body. About 1/3 of the total blood volume pumped out of the
left heart, goes to the brain whereas the remaining 2/3 goes to the rest
of the body. The larger portion is passed through the kidneys where it is
filtered and purified.
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The elimination of alcohol from the body begins shortly
after it is present in the body and continues until it has been totally
removed. Elimination proceeds by two (2) separate means: Metabolism and
Excretion. About 90 - 98% of the total amount of alcohol consumed are
removed by metabolism. Metabolism that occurs chiefly in the liver
effectively removes alcohol from the body by changing it to other
compounds. An enzyme, alcohol dehydrogenates, brings about this reaction.
The end products of this reaction, carbon dioxide and water are non-toxic
and excreted from the body by natural means.
The combination of metabolism and excretion leads to
total amount of alcohol eliminated from the body. For a given individual,
this amount is relatively constant. The actual amount is dependent upon a
persons weight and amount of fatty tissue. For a 150 pound man, the amount
of alcohol that can be eliminated from the body in one (1) hour is
approximately 25 ml of 40% v/v liquor (about 1 ounce) or 10 ml of pure
alcohol. It is obvious therefore that the sum of the amount of alcohol
eliminated from the body since the time drinking started should provide a
fairly accurate estimate of the total amount of alcohol, a given
individual may have consumed.
The body removes alcohol at a constant rate. Once
absorption is completed, the blood alcohol concentration should decrease
until all the alcohol is removed. The rate of elimination is determined by
monitoring the decreasing blood alcohol levels with time.
If this rate of elimination were measured in all people, it would be
observed that regardless of height, weight, sex, or amount of fatty
tissue, the average rate is about the same for all people: 15 mg% per
hour. The normal range for values of this rate is 10 - 20 mg% per hour.
However, the average value of 15-mg% per hour will be used. It is possible
then to calculate with a fair degree of certainty what a person's BAC
would have been at some time previous, or what it will be, given the BAC
at a particular time. If no additional alcohol was consumed in the
interval and the BAC of the subject has been declining over the time
interval, a reasonable prediction can be made.
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When alcohol leaves the blood stream and enters the
breath it reaches a point of equilibrium in the "deep lung" or
alveolar region. The relationship between the concentration of alcohol in
the arterial blood region of the lungs and the concentration of alcohol in
the breath from the deep lung region (alveoli) at the end expiratory
breath temperature (34 C) is known as the breath-blood ratio. This ratio
has been experimentally determined by a number of research groups since
Widmarks's historic work in this field and at present the most commonly
accepted ratio is 2100:1. That is, 2100 parts of deep lung air contain the
same amount of alcohol as 1 part of blood.
Others have found the factor of 2320-2370 to 1 can be
established using re-breathed air as a means of breath alcohol
determination and have therefore proposed the adoption of 2300:1 as the
international standard. While this more closely approximates the value to
be predicted from Henry's Law, it does not take into consideration the
practical limits of the design of breath testing instruments commonly
being used for evidential and screening purposes. Thus, while the ratio of
2100:1 generally results in an under-estimation of blood alcohol
concentration from a breath alcohol analysis, this is preferred to an
over-estimation when the results of the analysis are to be used to
establish a criminal charge or other sanction.
To ensure that a proper sample of breath from the deep lung region has
been analyzed for alcohol content, a variety of techniques have been
adopted which require a controlled and uninterrupted flow of breath until
near complete expiration has occurred. It is the breath from the deep lung
region (end expiratory) that contains the highest concentration of alcohol
that is in equilibrium with the alcohol concentration of the blood.
Mixed expired breath has a lower alcohol concentration
since it is not in equilibrium with the blood. Thus, the means to sample
breath for alcohol analysis must ensure that all of the mixed expired air
is exhaled first before a sample of breath from the deep lung region is
captured for analysis.
Further, to ensure that the alcohol in the breath sample
is representative of the alcohol concentration of the blood, one must
ensure that there is no concentration of the breath sample from residual
alcohol in the mouth and throat from a recent drink. This is accomplished
by waiting fifteen (15) minutes after a last drink or rinsing the mouth
and swallowing water before conducting a breath test.
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Alcohol affects everyone. It does so, however, in
different ways, depending on your mood, physical condition, personality
and the company you keep. If you are just recovering from a cold or have
had little sleep, the effects of alcohol will be magnified. If you are
worried about your job or your love life, drinking will only compound your
feelings of anxiety and possibly lead to aggressive or hostile behavior.
Your reaction to alcohol will also vary according to the social demands
placed upon you. A few drinks with your friend will make you feel drunker
than a few drinks with the family.
You may learn to compensate for some of the more obvious
symptoms of drinking. Researchers call this behavioral tolerance and
everyone calls it "holding your liquor". While experienced
drinkers can learn the act normally when talking or walking, they cannot
control the effects of alcohol on skills demanding fine motor coordination
or precise judgment.
Some drinkers develop physical tolerance to alcohol. As
a result of prolonged regular drinking, the liver becomes more efficient
in breaking down alcohol. In addition, some cells in the brain can become
less sensitive to the effects of alcohol. As a result of both of these
factors, progressively more alcohol may be needed to produce the
mode-altering effects experienced in earlier stages of drinking.
Whatever the individual variations, there is an
established sequence of symptoms which correspond to different degrees of
intoxication. The first mental processes to be affected are those
connected with training or previous experience. One skill impaired at the
initial stages of intoxication is driving ability, particularly for
individuals who have not been driving very long.
After a few more drinks, the ability to perform familiar
and habitual tasks requiring relatively little thought, attention or skill
is impaired. At this stage, you may find you have to concentrate on
opening a bottle of wine. Simply moving around in a crowd of people at a
party may require your full attention. You may drop things and
conversations may be difficult to follow.
As the alcohol level rises in the blood, muscular
coordination is further affected and basic reflexes become progressively
depressed. There is reduced hand steadiness, difficulty in standing and
emotional outbursts. The drinker may become aggressive or hostile.
Beyond this stage, the drinker risks falling into a
stupor and eventual coma. If the coma persists for more than 10 hours, a
person usually dies of asphyxiation due to paralysis of the respiratory
center of the brain. Alcohol poisoning usually occurs at BAC's above
400-mg%.
The driving task has been described as a complex divided
attention task involving; 1) a central visual task (tracking or
maintaining the vehicle's lane position) and 2) a peripheral visual task
(scanning the environment, for objects, e.g. other traffic or potential
driving hazards). When these two activities are combined into a
time-shared or divided attention task, alcohol impairs driving performance
at BAC's as low as 50-mg%. Neither of the two activities appears to be
impaired by alcohol when performed alone. However, when combined,
performance is generally poorer on the peripheral visual task.
Alcohol impairment of performance in divided attention
tasks is most likely due to an impairment of the information processing.
It appears that alcohol has less effect on the processing of information
from a single source than on that coming from several sources. Drivers who
are under the influence of alcohol tend to concentrate on one task and
neglect others in a divided attention task.
Driving an automobile is usually taken for granted as
being a relatively easy task, not requiring much conscious effort or
critical judgment. Yet the sensory functions of the body bombard the brain
with required information which must be assimilated and processed such
that smooth, controlled operation of the automobile results. The brain
makes decisions and regulates motor activity based upon training and
previous experiences. Thus, the many complete maneuvers that one makes
while driving occurs "automatically" and one does not have to be
consciously aware of it.
Because alcohol acts to depress the reticular activating
system, several things occur. The altering mechanism is depressed such
that a person does not become aware of potentially hazardous or dangerous
situations that the sensory functions detect. The sensory functions
themselves are deteriorated and may not be supplying complete or correct
information to the brain. A person's motor of functions are impaired; yet,
because of alcohol's depressant effect that person will feel less
inhibited and more self confident about his driving skills. As a result a
person, after having consumed alcohol, is more likely to speed into
high-risk situations which would normally be avoided or treated
cautiously.
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Following oral consumption, alcohol is absorbed from the
gastro-intestinal tract and distributed throughout the body by the
circulatory system. Alcohol diffuses freely and is found in relative
concentrations according to the water content of the various tissues. By
processes of metabolism and simple excretion, including its passage into
the breath, alcohol is removed from the body.
The relative concentration of alcohol in the various
tissues, including blood, urine, lachrymal fluid and saliva, can be
predicted and correlated on the basis of their respective water contents.
Alcohol passes unchanged from the blood stream into the breath and,
therefore, the alcohol concentration of the blood may be calculated from a
breath alcohol determination.
The process of respiration takes place at the juncture of the blood and
the breath within the alveolar sacs, deep in the lungs. Blood coming from
the right side of the heart is pumped through the pulmonary arteries that
circulate through the alveolar region and carries with it carbon dioxide
and other volatile gases that are produced in the body as a result of
metabolism. These gases pass freely through the walls of the blood vessels
in the alveoli. At the same time, oxygen from the breath diffuses through
the alveolar walls to the blood stream. This process is concentration
dependent, the gases diffuse from an area of higher concentration to an
area of lower concentration. The pulmonary veins then carry the
oxygen-enriched blood from the lungs back to the left side of the heart
where it is distributed throughout the body.
To conduct a proper breath analysis for alcohol content, it is necessary
to sample breath from the deep lung region. A variety of techniques have
been employed for this purpose but, generally, try to mimic the
respiratory profile.
A variety of techniques have been employed to ensure the
collection of a proper sample of breath, some of which rely upon operator
judgment and training, while other techniques are completely automatic in
their nature. One of the techniques is to provide a continuous and
uninterrupted flow of breath above a minimum threshold pressure and for a
minimum duration of time to a breath alcohol detector. This protocol
ensures the sampling of deep lung air for the alcohol concentration
necessary to the accuracy of the breath-testing instrument. |
