Washington DUI News: The physiology of the lungs

Okay, time for some science. The following is information on how the lungs
work and ultimately, how they work in conjunction with the breath testing
machinery in DUI cases.
PHYSIOLOGY OF THE LUNGS
The lungs are located within the chest. The organ allows inspired air to
come into close proximity with the blood so gases (such as oxygen and carbon
dioxide) can exchange between the air and the blood. The lung is made up of
over 300 million small air sacs called alveoli. Outside air comes to the
alveoli from the mouth or nose via the airways. The major airway leading to
the lungs from the throat is the trachea. The trachea divides into the left
and right "mainstem bronchi" (going to the left and right lungs) which
divide further into the "lobar bronchi." This division goes on about 23
times until the alveoli are reached. Actually, some alveoli begin to appear
at about the seventeenth generation airways. Surrounding each alveolus are
small blood vessels. The thinness (less than 0.001 millimeter) of the
membrane separating blood from the air in the lungs allows oxygen and carbon
dioxide to exchange readily between the blood and air. Because of the large
number of very small alveoli, there is a very large surface area (70 square
meters) for this gas exchange process. The alveolar region is where alcohol
comes from the blood into the air in the lungs. But in order for an alcohol
test to occur, the breath must first pass from the alveoli along the
branching network of airways to the mouth. During this journey through the
airways, a great deal happens to the air that changes the alcohol
concentration.
The lung does not actively participate in the breathing process. The muscles
that cause breathing are located outside the lung in the chest wall
(intercostal muscles) and the abdomen (diaphragm). There are small muscles
in the lung around the blood vessels and airways which assist in controlling
the way in which blood flow and air flow are distributed to different
alveolar groups (acini). To initiate inspiration, the external intercostal
muscles are contracted. This pulls the ribs upward and outward increasing
the chest size. In addition, the diaphragm pulls downward, also increasing
the chest size. The change in chest size causes a decrease in pressure
around the lung which causes the lung to expand and air to move into the
lung. To initiate exhalation, the diaphragm and external intercostal muscles
are relaxed. The previously stretched lung and chest wall then relax and
shrink down increasing the pressure of the air in the alveoli causing air to
flow out of the lung. If a rapid exhalation or an exhalation against a
resistance, such as that caused by an alcohol breath testing instrument, is
required, then the internal intercostal muscles can also be used to pull the
ribs down, assisting with the exhalation.
The number of molecules that leave the blood and enter the alveolar air is
dependent on the blood alcohol concentration and the partition ratio (PR).
In order to calculate the BAC from an alveolar sample, the alveolar alcohol
concentration and the partition ratio each must be known precisely. However,
it is impossible to sample air directly from the alveoli because of the
small size of the airways. Therefore, all alcohol breath testing devices
attempt to take a sample from the end of the breath for analysis under the
assumption that the concentration of alcohol in the end-exhaled breath is
the same as the concentration of alcohol in the air within the alveoli. In
other words, it is assumed that nothing happens to the alveolar air sample
as it is passing through the airways to the breath tester. However, changes
do occur to the breath as it is exhaled which serve to alter the breath
alcohol concentration.
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