Washington DUI News: Diffusion in the lung

DIFFUSION IN THE LUNG
The process of diffusion governs the exchange of gas between blood and air
in the alveolus. As blood enters the capillary in the alveolus, it is
exposed to the alveolar air. If alcohol is present in the blood, some of the
alcohol will diffuse out through the cells separating the blood from the air
and increase the alcohol concentration in the alveolar air. The amount of
the decrease of alcohol in the blood is extremely small and is governed by
the relative amount of ventilation and blood flow to the alveolus.
The exchange of alcohol across the alveolar-capillary membrane is not
limited by diffusion as has sometimes been stated in the alcohol test
literature. Blood is in the pulmonary capillary for a long enough time such
that the alcohol in the alveolar air is in equilibrium with the alcohol in
the blood after it has traversed only a small fraction of the alveolar
capillary. This equilibrium is maintained until the end of the capillary.
Under such circumstances, the distribution of alcohol is governed by the
partition ratio for alcohol in blood at the temperature in the alveolus
(normally 37° C). This is true for a very soluble gas like alcohol in a
normal alveolus with nearly the same amount of blood flow and air flow.
Gases diffuse very easily within the air of the lung. So the concentration
of alcohol is virtually identical throughout the alveolar acinus (containing
many alveoli). This addresses another common misconception in the alcohol
breath testing literature. The changing alcohol concentration during
exhalation is not because the gas near the alveolar surface is in better
equilibrium with the blood. Almost all of the gas in the lung (except that
in the dead space) is in equilibrium with the blood before exhalation. The
changing alcohol concentration during exhalation is caused by another
mechanism related to the changing of temperature of exhaled air.
For information on your Washington State DUI please contact our Snohomish
County DUI attorneys, Whatcom County DUI attorneys, King County DUI
attorneys, Whatcom Island County DUI attorneys, Island County DUI attorneys,
or Skagit County DUI attorneys at 425-493-1115 or check out our website at
http://www.washdui.com