Zones of the lung

The zones of the lung proposed by West in 1964, divide the lung into three vertical regions, based upon the relationship between the pressure in the alveoli (PA), in the arteries (Pa), and the veins (Pv):


 * #1: alveolar > arterial > venous
 * #2: arterial > alveolar > venous
 * #3: arterial > venous > alveolar

The ventilation/perfusion ratio is higher in zone #1 (the apex of lung when a person is standing) than it is in zone #3 (the base of lung.)