Ventilation/Perfusion question

This is from firecracker: "Pulmonary blood vessels constrict in response to low PO2, which decreases pulmonary blood flow to poorly ventilated alveoli and indirectly promotes blood flow to well ventilated alveoli. This hypoxic vasoconstriction is unique to the lungs, and helps maximize the efficiency of gas exchange." However, in areas of low ventilation, there is actually HIGHER PO2 in the alveoli. In areas of high ventilation, there is LOW PO2 in the alveoli. So how does this make any... Ventilation/Perfusion question
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums