Understanding the logistics of breath tests

The image of a person standing on the roadside blowing into a hand-held breath testing device has become the enduring representation of criminal charges associated with driving while intoxicated. Yet as you ponder such a scenario, one question inevitably comes to mind: why would law enforcement officers in Monroe choose to measure one’s breath to make a determination regarding their blood?

Many of those that come to see us here at the Law Offices of Huffman & Kendrick share that same question. Knowing how alcohol gets from your blood to your breath not only helps you understand how the breath tests work, but also may assist you in challenging their results when used as evidence against you.

The pathway from blood to breath

Per the Alcohol Pharmacology Education Partnership, the particular form of alcohol you ingest when drinking is ethanol. As a water-soluble compound, ethanol can permeate membrane surfaces through a process known as passive diffusion. When ethanol enters your digestive tract, it works its way through the lining of your organs and enters the bloodstream, where the veins then carry it throughout your body, eventually arriving in your lungs. Your lungs contain gaseous oxygen, which causes some of the ethanol molecules in your blood to vaporize into a gas themselves. That gas is then expelled from your body with each breath.

Maintaining equilibrium in your blood

This process continues, with the concentration of ethanol in your blood shifting to maintain equilibrium with that on your breath. Thus, with every breath, your blood-alcohol content lowers. Yet breath tests assume a static ratio of blood-to-breath when generating readings. Thus, a margin of error inherently exists with each of these tests (with some estimating that margin to be as high as 50%).

You can learn more about challenging DWI charges by continuing to explore our site.