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Forensic Toxicology

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  1. Forensic Toxicology Chapter 6 (PART 1) Concept Checklist Numbers 1-10

  2. What is the primary duty of a forensic toxicologist? • Forensic toxicologists detect and identify drugs and poisons in body fluids, tissues, and organs.

  3. Ethyl alcohol • Legal, over-the-counter substance for individuals 21 years of age or older • Is the most heavily abused drug in Western Countries • 17,500 fatalities (traffic deaths) in U.S. are alcohol related. • 2 million injuries each year from alcohol-related traffic accidents require hospital treatment.

  4. The Metabolism of Alcohol • Metabolism: the transformation of a chemical in the body to other chemicals to facilitate its elimination from the body • Metabolism consists of three basic steps: absorption, distribution, and elimination.

  5. Absorption • Passage of alcohol across the wall of the stomach and small intestine into the bloodstream

  6. When the absorption period is completed, the alcohol becomes distributed uniformly throughout the watery portions of the body-that is, throughout about 2/3 of the body volume. Fat, bones and hair are low in water content and therefore contain little alcohol. After absorption is completed, a maximum alcohol level is reached in the blood, and the postabsorption period begins. Then alcohol concentration slowly decreases until a zero level is again reached. Distribution

  7. List at least three significant factors that determine the rate at which alcohol is absorbed into the bloodstream • Factors that determine the rate at which alcohol is absorbed into the bloodstream include • The total time taken to consume the drink. • The alcohol content of the beverage. • The amount of beverage consumed. • The quantity and type of food in the stomach at the time of drinking.

  8. Elimination • As the alcohol is circulated by the bloodstream, the body begins to eliminate it. • Alcohol is eliminated through two mechanisms Oxidation Excretion

  9. Oxidation The combination of oxygen with ethyl alcohol to produce carbon dioxide and water. Oxidation takes place in the liver. Ethyl alcohol in liver -> acetaldehyde -> acetic acid Acetic acid -> carbon dioxide and water Elimination – Oxidation Phase

  10. Elimination - Excretion • Excretion- elimination of alcohol from the body in an unchanged state; alcohol is normally excreted in breath and urine.

  11. Nearly all of the alcohol consumed is eventually oxidized to carbon dioxide and water. The remaining alcohol is excreted unchanged in the breath, urine and perspiration. The fact that the amount of alcohol exhaled in the breath is in direct proportion to the concentration of alcohol in the blood has led to the development of instruments that quickly, easily, and reliably measure breath for alcohol consumption. Name and describe the process by which most alcohol is eliminated from the body. How is the remaining alcohol eliminated and how is this useful in testing for alcohol?

  12. What are the requirements of a suitable test for alcohol intoxication? • Tests for alcohol intoxication must be rapid and specific, they must be designed to test hundreds of thousands of motorists annually without causing them undue physical harm or unreasonable inconvenience; and they must provide a reliable diagnosis that can be supported and defended within the framework of the legal system.

  13. Fate of alcohol in the body • Absorption into the bloodstream • Distribution throughout the body’s water • Elimination by oxidation and excretion. • The elimination or “burn off” rate of alcohol varies in different individuals; 0.015 percent w/v (weight per volume) per hour.

  14. Blood-Alcohol Concentration BAC • Logically, the most obvious measure of intoxication would be the amount of liquor a person has consumed. • Unfortunately, most arrests are made after the fact, when such information is not available to legal authorities; furthermore, even if these data could be collected variables affect the rate at which alcohol is absorbed by the body.

  15. Blood-Alcohol Concentration

  16. Alcohol in the Circulatory System • The extent to which an individual my be under the influence of alcohol is usually determined by measuring the quantity of alcohol present in the blood system. • This is accomplished two ways (1) by analyzing the blood for its alcohol content. (2) by measuring the alcohol content in the breath.

  17. Human Circulatory System • Arteries – blood vessels that carry blood away from the heart • Veins – blood vessels that carry blood toward the heart • Capillary – a tiny blood vessel that receives blood from arteries and carries it to veins, and across whose walls exchange of materials between blood and the tissues take place.

  18. Absorption of Alcohol • Alcohol is ingested and moves down esophagus to the stomach. • 20% of alcohol is absorbed through the stomach walls into the portal vein • 80% of alcohol is absorbed through the walls of the small intestine. • Once in the blood, alcohol is transported to the liver where it is oxidized.

  19. As blood (still carrying alcohol) leaves the liver It moves up to the heart Blood enters the right atrium of the heart Blood then enters the right ventricle of the heart Blood then must be pumped to the lungs where it becomes aerated. In the lungs, the respiratory system bridges with the circulatory system so that oxygen can enter the blood and carbon dioxide can leave it. Carbon dioxide and alcohol can leave the blood and enter the alveoli. During breathing the carbon dioxide and alcohol are expelled through the nose and mouth. Alcohol in the Circulatory System

  20. Why is a blood test for alcohol taken shortly after drinking more advantageous for the suspect than taken thirty minutes or more after drinking? • The administration of a blood test for alcohol requires drawing blood from a vein, but alcohol in the veins diffuses very rapidly into body tissues during early stages of absorption compared to blood in the arteries. • This, blood drawn from a vein can show a misleadingly low blood-alcohol concentration immediately after drinking • Once absorption is complete, alcohol becomes equally distributed throughout the blood system so blood taken from a vein a short time after drinking shows a more accurate BAC.

  21. The first successful breath-test device was the Breathalyzer. It measured the concentration of alcohol in aveolar breath. The Breahalyzer used chemical reactions to detect the presence of alcohol. Modern testing devices use infrared radiation. What was the first successful breath- test device and what did it measure to determine blood-alcohol concentration? What is the main difference between this device and the breath-test devices currently in use?

  22. Describe how a fuel cell detector measures blood alcohol • In a fuel cell detector, alcohol in a suspect’s breath combines with oxygen in the air to produce acetic acid. • This process generates an electrical current that is proportional to the quantity of alcohol present in the breath.

  23. The key to accuracy of a breath tester is to ensure that the device captures the alcohol in the aveolar (deep-lung) breath of the subject. This is typically accomplished by programming the unit to accept a minumum amount of breath (typically 1.5 liters) from the subject. The subject must blow for a minimum time with a minimum breath flow rate. What is the key to the accuracy of a breath-tester? Describe two steps the operator takes to ensure that this key requirement is met.

  24. A divided-attention task tests a subject’s ability to comprehend and execute two or more simple instructions at one time. The walk and turn test requires the suspect to walk in a straight line, touching heel to toe for nine steps then turn around on the line and repeat the process. The one-leg stand requires the suspect to stand on one foot while holding the other foot several inches off the ground for thirty seconds and simultaneously counting out loud. What is a divided-attention task? Name and describe two divided-attention tasks often administered during field sobriety tests.

  25. Horizontal-gaze nystagmus is an involuntary jerking of the eye as it moves to the side. The subject is asked to follow an object with his or her eye as far to the side as the eye can go. The higher a person’s blood-alcohol concentration, the less the eye has to move toward the side before jerking and nystagmus begins. What is horizontal –gaze nystagmus and how does the test for it reveal blood alcohol levels?