The common perception of a drunk driver is one standing on the side of a road in Naperville blowing into a hand-held breath measurement device to determine the blood-alcohol content. Yet the comparison of the two elements being measured in this scenario (one's breath and their BAC) might prompt many to ask why law enforcement would measure a person's breath to determine the concentration of alcohol in their blood. Understanding how alcohol ends up in one's breath may help those facing DUI charges to challenge the results of breath test measurements being used against them.
According to The Alcohol Pharmacology Education Partnership, the alcohol used in beverages is ethanol. This is a water-soluble compound, meaning that once ingested, it can pass through the membranes of the organs of the digestive system through a process known as passive diffusion. Thus, much of the ethanol in any drink consumed will eventually end up in the bloodstream. When ethanol gets in the blood, it is eventually carried to the heart by the veins, where it is then pumped into the lungs via the right ventricle. In the lungs, the ethanol comes in contact with oxygen, which will cause some of it to vaporize into a gas. That gas is then expelled from the body when one breathes.
The concentration of alcohol in the blood is constantly adjusting as more and more ethanol vaporizes to maintain a state of equilibrium. This fluid nature of BAC can provide the evidence needed to challenge breathalyzer measurements. With every breath, one's BAC concentration is lowered, making it's true measurement a moving target. This no doubt contributes that to 50 percent margin of error that the National Motorists Association reports being inherent with breathalyzer readings.