If there is one image that has become the universal symbol of drunk driving, it is a person standing on the side of the road blowing into a hand-held breath measurement device. You are likely aware that in most states (Pennsylvania included) the legal blood-alcohol content limit is .08. Yet one question that many who come to see us here at the Marros Law Office have after having been arrested for driving under the influence is why do authorities rely on the breath measurement to determine the alcohol content in the blood?
The answer requires knowing exactly how it is that the alcohol you ingest gets into your bloodstream (and eventually, your lungs). The Alcohol Pharmacology Education Partnership tells us that the type of alcohol found in drinks is ethanol. Ethanol is water-soluble, which means that after you have ingested it, its molecules can permeate the lining of the organs of your digestive tract through a process known as passive diffusion. Once it has penetrated the walls of these organs, it enters the bloodstream and is carried throughout your body.
Eventually, the ethanol in your blood reaches the right atrium of the heart, where it is then pumped into your lungs via the right ventricle. In your lungs, it comes in contact with oxygen. A portion of the blood (along with ethanol molecules) is then vaporized into a gas, which is expelled from the lungs when you breathe. This process continues, with the concentration of vaporized ethanol maintaining an equilibrium with that of your blood.
The fluid nature of this process essentially makes determining your BAC through your breath akin to hitting a moving target, which may help in challenging the results of a breath test. More information on how your BAC is determined can be found throughout our site.