Do Breath Tests Measure Deep Lung Air?

Alcohol reaches the surface of airways by diffusing from the bronchial circulation. When a person inhales, alcohol is taken from the airway surface and the inhaled breath becomes saturated with alcohol before just as it reaches the alveoli, where “deep lung air” is found. In the alveoli alcohol in the breath is in equilibrium with alcohol in the pulmonary capillary blood. Even though ethyl alcohol may exchange with the blood in the alveoli, since there is no partial pressure difference, there is no net change. The exchange in the airways will happend even though the bronchial blood flow is only about 1% of the total cardiac output because of alcohol’s extremely high solubility.

When a person exhales, the alcohol in the air passing from the alveoli to the mouth re-deposits alcohol onto the surface of the airways. In the meantime, some alcohol has re-entered the blood stream by way of the bronchial circulation. So the airways have been partially recharged with alcohol.

But there is still a net partial pressure driving force toward the airway tissue. With an average exhalation the exhaled air loses about 20% of the alcohol that it had in the alveoli. If a person takes a full and complete inhalation and exhalation, they would lose less alcohol and the measured alcohol in the breath would be higher than it should be. If a short exhalation occurs, then the alcohol measured in the breath will be lower than expected.
Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website

Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website

You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

AddThis Social Bookmark Button

Leave a Reply

You must be logged in to post a comment.