Airway Pathology

This chapter examines the anatomy of the human lung and the pathology of both asthma and chronic obstructive pulmonary disease (COPD). The normal human bronchogram shows that the length of pathways from the trachea to the terminal airways differs depending on the pathway followed and it can take as few as 8 or as many as 24 divisions of airway branching to reach the gas-exchanging surface. The small bronchi and bronchioles 2 mm in diameter are spread out from the fourth to the fourteenth generation of airway branching. The pathology of asthma is dominated by widespread plugging of the segmental, subsegmental, and smaller conducting airways that leads to hyperinflation but not destruction of the parenchyma. These airway plugs are a manifestation of the fluid and cellular exudative phase of an inflammatory process based in the airway tissue. The chronic bronchitis of COPD is defined by excess cough with sputum production and is associated with an inflammatory process located in the mucosa, gland ducts, and glands of intermediate-sized bronchi between 2 and 4 mm internal diameter. The airway obstruction in COPD is the result of a similar inflammatory response in the smaller bronchi and bronchioles under 2 mm internal diameter, where the repair process associated with chronic inflammation thickens the airway wall and narrows the lumen to cause fixed airway obstruction.