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Why is breath used to measure BAC?

| Mar 17, 2020 | Drunk Driving Defense |

Mention the term “drunk driving charges” to anyone in Rochester, and they will likely immediately think of a person standing on the side of the road blowing into a hand-held breath testing device. If this is an all-too-familiar scenario to you, then you may be wondering how exactly you might challenge the results of a breath test being used against you.

Indeed, this may prompt you to contemplate even further why law enforcement officials would use a measurement of your breath to determine if you are intoxicated. After all, it is the alcohol content of your blood that indicates whether or not you may be impaired. How is it, then, that your breath is used to measure your blood?

Alcohol leaving your body on your breath

According to the Alcohol Pharmacology Education Partnership, the alcohol ingested while drinking is ethanol. As a water-soluble compound, ethanol is able to pass through the membrane barrier lining the organs of your digestive system through a process known as passive diffusion. Once that happens, ethanol molecules then enter the bloodstream and are transported throughout your body, eventually making their way to your heart, and then your lungs.

In your lungs, the ethanol in your blood comes in contact with gaseous oxygen, which causes a small portion of it to itself vaporize into a gas. That gas is then expelled from your body as you breathe.

Achieving equilibrium

This process continues, with ethanol vaporizing (and its content in your blood lowering to maintain equilibrium). Breath testing devices assume a blood-to-breath concentration ratio when generating readings. Yet as your BAC is technically lowering with each breath, this may provide the grounds for challenging the results of a breath test (since that blood-to-breath ratio does not remain constant).

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