Breath Alcohol Concentration (BrAC) is a clinical metric that quantifies the amount of ethanol vapor present in a measured volume of exhaled breath, serving as a non-invasive proxy for the concentration of ethanol in the systemic blood. This measurement relies on the principle of equilibrium partitioning of alcohol between the blood and the alveolar air in the lungs, providing a rapid and clinically relevant index of intoxication. BrAC is directly related to the systemic metabolic load and its subsequent impact on neuroendocrine function.
Origin
The term is derived from forensic science and clinical toxicology, establishing a reliable, standardized method for estimating Blood Alcohol Concentration (BAC). The physiological basis for this measurement was established by determining the partition ratio of alcohol between blood and breath, typically standardized to a ratio of 2,100:1. This allows for the indirect, real-time assessment of systemic alcohol levels without requiring phlebotomy.
Mechanism
The underlying mechanism is the passive diffusion of ethanol from the pulmonary capillary blood into the alveolar air space of the lungs, following Henry’s Law of gas solubility. As the systemic blood circulates through the lungs, volatile ethanol molecules transfer across the thin alveolar membrane until equilibrium is reached between the blood and the air. Exhaling this deep-lung air captures the ethanol vapor, which is then quantified by an electrochemical sensor or infrared spectroscopy to determine the concentration.
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