How Does a Breath Measurement Determine Your BAC?

On behalf of The Berger Firm July 6, 2018

Whenever the issue of drunk driving comes up in Covington, you likely immediately envision a person blowing into a breathalyzer device on the side of the road. That device is checking that person’s blood-alcohol content. This might immediately cause you to question why law enforcement officials with test your breath to determine your BAC?

The answer lies in understanding two concepts: passive diffusion and equilibrium. According to The Alcohol Pharmacology Education Partnership, the form of alcohol that enters your body when you consume alcoholic drinks is actually ethanol. It is water-soluble, which not only allows it to dissolve easily in liquid, but also allows it to permeate through porous linings. That is exactly what happens as it passes through your stomach and small intestine. It eventually enters into your bloodstream, which then carries it throughout your body. Eventually, it finds its way to your heart, where it is then pumped into your lungs via the right ventricle.

Your lungs, of course, contain oxygen. As liquid ethanol enters the lungs and comes in contact with the oxygen, a small portion of it vaporizes into a gaseous state. That gas is then expelled through your lungs as you breathe. The remaining ethanol continues its through the bloodstream, reacting with the other water-soluble compounds in the blood to achieve an equilibrium. With each breath, more ethanol is breathed out, and the concentration of ethanol in your blood continues to lower until it has been completely absorbed and metabolized or expelled through your breath.

It is for this reason why many question the accuracy of breathalyzer tests. Your BAC is constantly changing with each breath as your body works to achieve an equilibrium relative to its ethanol concentration. This contributes to a wide margin for error (as much as 50 percent, according to some experts).