Paradigm Shift for the Alcohol Breath Test

The alcohol breath test (ABT) has been used for quantification of ethyl alcohol in individuals suspected of driving under the influ- ence for more than 50 years. In this time, there has been little change in the concepts underlying this single breath test. The old model, which assumes that end-exhaled breath alcohol concentration is closely related to alveolar air alcohol concentration, is no longer acceptable. This paper reviews experimental research and mathematical modeling which has evaluated the pulmonary exchange processes for ethyl alcohol. Studies have shown that alcohol exchanges dynamically with the airway tissue both during inspiration and expiration. The airway tissue interaction makes it impossible to deliver air with alveolar alcohol concentration to the mouth. It is concluded that the ABT is dependent on physiological factors that need to be assessed for accurate testing. Over the years, breath test has become a widely used method for quantitative determination of the level of intoxication of individuals suspected of driving under the influence of alcohol. After recogni- tion of the need for quantitative assessment of intoxication, blood alcohol concentration (BAC) was considered as the single most important variable. However, concern about the invasiveness requirements of drawing a blood sample led to the development of the breath test as a noninvasive means of assessing level of intoxi- cation. The breath test is an indirect test, but has been considered to be a good estimate of the BAC because of the assumption that an end-exhaled breath sample accurately reflects the alveolar (or deep lung) air alcohol concentration which is thought to be in equi- librium with the blood in the pulmonary circulation. In spite of the considerable effort that has gone into the studies attempting to vali- date the breath test, forensic scientists and toxicologists still have only a very basic understanding of the physiological aspects of the alcohol breath test (ABT) and associated limitations. Anatomy of the Lungs The primary function of the lungs is to provide a means for exchanging respiratory gases (oxygen and carbon dioxide) between the blood and the outside environment. This organ allows inspired air to come into proximity with the blood so gases (such as oxy- gen, carbon dioxide, and ethyl alcohol) can exchange between the air and the blood. The lungs are made up of over 300 million small air sacs called alveoli. Outside air comes to the alveolus from the mouth or nose via the airways. The major airway leading to the lungs from the throat is the trachea. The trachea divides into the left and right ''main-stem bronchi'' (going to the left and right lungs) which divide further into the ''lobar bronchi.'' This division goes on about 20 times until the alveoli are reached. Actually, some alveoli begin to appear at about the 17th generation airways.