To the left is WebImage, the program you'll be using to diagnose emphysema in three patients. You'll be using a stack of nine images. Move the slider bar all the way to the left so that you're looking at the first one: an illustration of the normal human respiratory system.

When healthy people inhale, they draw air first into the nasal cavity, then down the pharynx, past the epiglottis and larynx, through the trachea and into the lungs through two tubes called bronchi. Once there, the air is pulled into the bronchioles, which consist of tiny air sacs called alveoli.

Emphysema damages the alveoli and reduces the elasticity of the bronchioles. Patients who are being tested for emphysema are told to exhale as much air as they can. Doctors then measure the amount of air that remains in the lungs to diagnose emphysema.