Accurate measurement of blood alcohol concentration with isothermal rebreathing.

The importance of interaction of exhaled air with the airway surface was evaluated by comparing the effects of different breathing maneuvers and inhaled air temperature on the relationship between breath alcohol concentration (BRAC) and blood alcohol concentration (BAC). Breath alcohol was measured with an infrared absorption unit. Blood and simulator liquid alcohol concentrations were measured by gas chromatography. Breath samples were measured after both low and high exhaled volumes and after rebreathing. Breathing maneuvers were performed after either hyperventilation, breathhold or normal breathing. Inspired air temperature was varied between 0 degree C and 40 degrees C. The rebreathing method for sampling alveolar alcohol samples was evaluated with a new isothermal rebreather that was designed to provide a substantial amount of heat to the rebreathed air in order to heat the airway surfaces. Using a single breath test, the indicated BAC values vary from 14% above the actual BAC to as low as 55% below the actual BAC. Hyperventilation caused a significant decrease in BRAC and breathhold caused a significant increase in BRAC. When isothermal rebreathing is applied to such tests, the breath test results were always within +/- 10% of the true BAC, even with an altered breathing pattern. Isothermal rebreathing provided an accurate sample of alveolar air that was not affected by altered breathing pattern or air temperature.