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Breath Test Basics

Alcohol and the Human Body
When an alcoholic beverage is consumed it passes down the esophagus through the stomach and into the small intestine. Although a small amount of alcohol is absorbed into the bloodstream through the mucous membrane, that vast majority of alcohol enters the bloodstream through the walls of the small intestine. Alcohol is water-soluble and the bloodstream rapidly transports the ethanol throughout the body where it is absorbed into the body tissues in proportion to their water content.

Alcohol is greatly diluted by the body fluids. For example, a 1-ounce shot of 80-proof whiskey, which contains 0.4 fluid ounces of ethanol will be diluted in a 150-pound human, producing somewhere in the neighborhood of an 0.02% blood alcohol concentration. With a user that is smaller with say one half of the water weight in his or her body than the individual in the prior example, that same 0.4 fluid ounce of ethanol would likely produce an alcohol concentration at or near 0.04%.

How Alcohol is Eliminated from the Body
Metabolism is the body's process of converting ingested substances to other compounds. Metabolism involves a number of processes, one of which is referred to as oxidation. Through oxidation in the liver, alcohol is detoxified and removed from the blood, preventing the alcohol from accumulating and destroying cells and organs. A minute amount of alcohol escapes metabolism and is excreted unchanged in the breath, in the sweat and in urine. Until all the alcohol consumed has been metabolized, it is distributed throughout the body, affecting the brain and other tissues.

The liver can metabolize only a certain amount of alcohol per hour, regardless of the amount that has been consumed. The rate of alcohol metabolism depends, in part, on the amount of metabolizing enzymes in the liver, which varies among individuals and. In general, after the consumption of one standard drink, the amount of alcohol in the drinker's blood peaks within 30 to 45 minutes. (A standard drink is defined as 12 ounces of beer, 6 ounces of wine, or 1.5 ounces of 80-proof distilled spirits, all of which contain the same amount of alcohol.) Some individuals take up to an hour or 11/2 hours to reach peak alcohol absorption. Alcohol is metabolized more slowly than it is absorbed. Generally, alcohol metabolism is divided into three plashes: 1) absorption 2) peak 3) burn off, or elimination.

A Few Factors Influencing Alcohol Absorption and Metabolism
Food. A number of factors influence the absorption process, including the presence of food and the type of food in the gastrointestinal tract when alcohol is consumed. The rate at which alcohol is absorbed depends on how quickly the stomach empties its contents into the intestine. Food in the stomach acts like a ‘sponge’ soaking up alcohol then slowly releasing it for absorption. This results in a lower peak or blood alcohol level for a given number of drinks. Also, the higher the dietary fat content, the more time this emptying will require and the longer the process of absorption will take. One study found that subjects who drank alcohol after a meal that included fat, protein, and carbohydrates absorbed the alcohol about three times more slowly than when they consumed alcohol on an empty stomach.

Gender. Women absorb and metabolize alcohol differently from men. They have higher Blood Alcohol Concentration's (BAC) after consuming the same amount of alcohol as men and are more susceptible to alcoholic liver disease, heart muscle damage, and brain damage. The difference in BAC's between women and men has been attributed to women's smaller amount of body water, likened to dropping the same amount of alcohol into a smaller pail of water. Women have less body water (52% for the average woman v. 61% for the average man). This means that a man's body will automatically dilute the alcohol more than a woman's body, even if the two people weigh the same amount.

An additional factor contributing to the difference in BAC's may be that women have lower activity of the alcohol-metabolizing enzyme ADH in the stomach, causing a larger proportion of the ingested alcohol to reach the blood. Women also have less dehydrogenase, a liver enzyme that breaks down alcohol, than men. So a woman's body will break down alcohol more slowly than a man's. Hormonal factors Premenstrual hormonal changes cause intoxication to set in faster during the days right before a woman gets her period. Birth control pills or other medication with estrogen will slow down the rate at which alcohol is eliminated from the body.

Ancestry. Some people of Asian and Native American descent have more difficulty metabolizing alcohol. They may experience facial flushing, nausea, headache, dizziness and rapid heartbeat. It appears that one of the liver enzymes that are needed to process alcohol is not active in these individuals. It is estimated that up to 50% of Asians and Native Americans are susceptible to these reactions to alcohol. Approximately 45 to 53 % of the Chinese, Japanese and Vietnamese population are deficient in the ALD2H.

Age. Generally, as the body ages, the lean body mass decreases. This change in body composition results in a smaller volume of distribution and consequently, a higher peak alcohol concentration compared to younger subjects.

Stomach Diseases. Any physical changes to the stomach and intestines have the potential for affecting the absorption kinetics of alcohol.

Cigarette Smoking. Any substance that slows gastric emptying slows down absorption of alcohol that is consumed near a meal. Cigarette smoking close in time to a meal has been found to slow gastric empting and increase the time to reach maximum absorption.

If the amount of ethanol consumed is not great, the oxidization of the alcohol can keep up with the rate that the ethanol is entering the bloodstream and the alcohol concentration will not increase, (The ethanol disposal rate in a 150-pound human is about 0.5 ounce of ethanol per hour, which corresponds to 12 ounces of beer, 6 ounces of wine, or 1.5 ounce of hard liquor.) However, if the alcohol intake is greater than the rate at which the user is able to metabolize it, the blood and breath alcohol concentration of that individual will increase over the drinking period.

How Alcohol Gets from the Blood into the Breath
Ethanol is volatile and as a result, an amount of alcohol, in proportion to the concentration in the blood, transfers from the blood into the alveolar air sacs in the lungs. This occurs in much the same way that carbon dioxide leaves the alveolar blood and enters the lungs for exhalation from the body. As a result, it is possible to analyze an alveolar breath sample, determine the breath alcohol concentration (BrAC) and predict (using an assumed ratio) the blood alcohol concentration at that same point in time.

History and Early Studies of Breath Testing
The study of human breath originated in the classic studies of French chemist Antoine Lavoisier conducted between 1774 and 1785. Aside from defining respiration as the uptake of O2 and the output of CO2, Lavoisier’s invention, the “gasometer,” was the first instrument to make accurate measurements of the respiration gases. In 1874, British physician Francis Anstie, trapped the human breath and applied colorimetric analysis to study the fate of alcohol in the body. Building on this knowledge, actual analytical analysis of expired breath for blood alcohol concentration was first proposed in the 1920’s.

Early versions of quantitative breath testing machines included the Drunkometer® (1938), Breathalyzer® (1954), and Alkotest® tube (1954). These early methods employed wet chemistry; generally, oxidation with potassium permanganate, potassium dichromate, or iodine pentoxide. Gas chromatography was employed in the early 1970’s, and, in 1974, infrared (IR) technology took the lead in popularity.

Henry's Law
The amount of ethanol that partitions between the blood and the lungs generally follows the basic rules of Henry’s Law. Henry’s Law states that the amount of gas which dissolves in a liquid is dependent on the partial pressure of the gas in contact with the liquid and the solubility coefficient of the gas in that particular liquid. However, the application of Henry’s Law to breath alcohol testing is not without flaw. When alveolar air is exhaled, there is a re-equilibration between the air and the mucous membranes of the upper respiratory tract, and a corresponding drop in temperature of the breath. Thus, the assumption that breath and body temperature is fixed is erroneous. In addition, there can be subject variability, depending on the circumstances, of the blood to breath partition ratio. To overcome these problems, the legislature in California mandated that all individuals will be presumed to have the same partition ratio even though 20% variances are not unusual!

The theory of operation of the reference sample device is based upon Henry's Law. In a closed system, the amount of ethanol in the airspace above a liquid (lavender dots) is proportional to the amount of ethanol in the liquid (blue dots). Henry's law applies to closed systems at a given temperature and pressure. The Intoxilyzer 5000 does a good job at accurately predicting the amount of ethanol in the reference sample.

However, when the Intoxilyzer 5000 is used to predict the amount of ethanol in human breath the situation changes dramatically. If you assume the liquid in the closed system illustrated here is human blood, and the airspace illustrated is the air in the lungs, even a lay person can quickly recognize potential problems.

First, the human lung is not a closed system. Pressure in the lungs is constantly changing as we inhale and exhale. As the pressure changes so does the amount of ethanol in the airspace above the blood in our lungs. Furthermore, the temperature of the system is critical. If the solution temperature is low, the results will be low. If the solution temperature is high, the results will be high.

The problem with the Intoxilyzer 5000?
It assumes a constant pressure and it assumes a predicted temperature within the system. If the pressure is changing then Henry's Law can only be used to approximate the concentration of ethanol in human breath. Moreover, the Intoxilyzer does not measure the temperature of the suspect's breath sample. Without knowing the precise temperature the Intoxilyzer can only make assumptions that might not bear out in a particular case. If the temperature of the person's breath is different than what the machine assumes it is, then the results obtained will be erroneous.

Introduction to Breath Testing Technology
There are a variety of breath alcohol testing instruments available to law enforcement. Many of the evidential devices are listed in the Federal Register Conforming Products List of Evidential Breath Measurement Devices.

Types of Breath Alcohol Testing Machines

Differences Between IR and EC Technology
There are significant differences between IR (infrared) and EC (electrochemical) and SC (semiconductor) technology.

A benefit of the IR method is the ability of the machine to successively monitor the incoming breath concentration, since the analysis of the breath by IR does not destroy the breath sample with each measurement. As the subject blows into the machine and reaches the deeper lung air, which theoretically contains the highest alcohol concentration, the machine accepts the breath and assumes it is a reliable sample.

On the other hand, fuel cells (EC) cannot monitor the incoming breath to ascertain that alveolar air is being tested. This is because the EC analysis is a chemical reaction, and can only take a “snapshot” of the breath at only one time per test.

IR Machine Limitations
In a true spectrophotometer, the IR spectrum of the entire wavelength region is compared against the spectrum of a known compound. In breath testing technology, however, only the absorption at a particular (or several) wavelength is measured. Thus, breath testing machines do not identify ethanol, they merely identify the absorption of a particular bond or functional group. Since there are many organic molecules that contain similar bonds or functional groups, breath machines can never be totally specific or actually identify the entire molecule of ethanol.

Using a limited number of wavelengths rather than the entire spectrum can lead to false positives for some interfering substances. Dual wavelength infrared detection and infrared coupled with a fuel cell assist in identifying a limited number of possible interfering substances. For example, the Intoximeter® 3000 (3.4 um infra-red plus Taguchi cell) and the BAC DataMaster® (dual wavelength infra-red) both will identify acetone as an interfering substance. However, other substances will not be identified, and will subsequently falsely elevate a true BAC reading.

“Tyndall Effect” in IR Machines
When ethanol molecules are in the breath chamber, not only can other substances absorb the light as well, but particles in the breath chamber can scatter the light and keep some light from reaching the detector. Any substance that decreases the amount of light that reaches the detector increases the apparent BrAC reading.

Scientist John Tyndall (1820-1893) discovered that scattering of light occurs when the particles that are causing the scattering are larger than the wavelength of the radiation that is scattered. Reflection of the light from the surfaces of the particles, and in some instances reflection from the interior walls of the particles causes these particles to be seen. For example, the Tyndall effect is responsible for being able to see the narrow path of a car headlight shining through fog, or the narrow path of the laser or light in a dusty room.

The “AirBag” issue: Loose dirt in the breath chamber and fine particles blown in during sampling will scatter light as well. This issue becomes especially relevant when the driver has been subjected to a deployed airbag. Fine particles of talc and cornstarch can get blown into the machine and lead to an erroneous reading.

Please feel free to contact our office at 800.978.0186 or for answers to any questions you may have about DUI breath testing.