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Why measure your breath to get your blood alcohol concentration?

The implications of you refusing to submit to a breath test in Fort Myers have been detailed on this blog in the past. While refusing a chemical breath test is a violation of the state's implied consent law, refusing a preliminary alcohol screening (like a Breathlyzer test) is not. Yet despite the setting or the circumstances, you might wonder why your breath is even measured when your level of impairment is determined by the alcohol concentration in your blood. How does your breath offer a measurement of the content of your blood? 

The Alcohol Pharmacology Education Partnership explains how. Ethanol is the chemical form of alcohol found in beer, wine and liquor. It is used in such drinks because it is water soluble. This is the pathway ethanol travels upon entering your body: 

  • After being ingested, it passes through the membranes of your stomach and small intestine into the bloodstream via passive diffusion.
  • Once in the blood, capillaries carry it to the veins, which then carry it to the heart, which then pumps the venous blood (which is oxygenated) to the lungs.
  • In the lungs, some of the ethanol vaporizes into a gas via exhalation, while the rest returns to the heart and is sent in the blood to the rest of the body via the arteries running from the left ventricle.
  • Ethanol gas built up in the lungs (more specifically, the alveolar sac) escapes when you exhale. 
  • As ethanol gas escapes, more is vaporized from the bloodstream to achieve an equilibrium. 

While this describes the relationship between the alcohol concentrations in your breath and your blood, it also shows what a dynamic process this is. One could then reasonably argue that the constant shifts towards equilibrium occuring with your every breath may make Breathalyzer measurements unreliable. 

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