Airways and congestionWithin the lungs are small airways (bronchi and bronchioles). The first illustration below shows a cutaway of a clear airway, allowing for the free passage of air (represented by the arrow), to the alveoli (round structures forming bunches in illustration), for oxygen to enter the blood stream and carbon dioxide to be removed from the blood.
Asthma patients suffer from constriction in the small airways, due to smooth muscle contraction (circular bands on bronchiole) as shown in the second illustration. The lumen (air passageway) becomes constricted as well, due to edema (swelling) of the mucous membranes lining the small airways because of the inflammation. Increased mucus excretion during an asthma attack will add to the airway clogging. During severe attacks, as seen in the cutaway, the small airways can become completely obstructed because of these changes.
Illustrations by Nick Lang