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Criminal, Family and Probate Law


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Why measure your breath to get your BAC?

On Behalf of | Apr 27, 2020 | Firm News |

The visualization that immediately comes to mind when one hears the term “drunk driving charges” is a person standing on the side of the road blowing into a breath testing device. If you have been in that position, then you likely have a number of concerns, chief of which may be how reliable are the breath test results that law enforcement authorities collect with such a device. 

This prompts the larger question of why is it that law enforcement authorities measure your breath to determine the alcohol content of your blood? Knowing this may help provide you with the knowledge needed to challenge your breath test results. 

Alcohol’s pathway to your lungs 

The Alcohol Pharmacology Education Partnership offers details on how the alcohol you ingest arrives in your lungs. The form of alcohol used in alcoholic drinks is ethanol. This a water-soluble compound, which plays a key factor in its metabolism. Because it is water-soluble, ethanol molecules can permeate membrane surfaces through a process known as “passive diffusion.” After you drink alcohol, the ethanol it contains permeates the lining of the organs of your intestinal tract and makes its way to the bloodstream, where your veins then carry it to your lungs. 

Hitting a moving target 

Upon coming in contact with the oxygen in your lungs, some ethanol molecules vaporize into a gas are then expelled when you breathe. This process continues in order to maintain an equilibrium between the gaseous alcohol content of your lungs and the liquid alcohol content of your blood. What this means is that with each breath, your blood-alcohol content lowers. 

This essentially equates the process of determining your BAC from your breath to hitting a moving target. It may be for this very reason that breath test results are often not admissible as evidence in court.