What is ventilation-perfusion coupling? How is this accomplished?
Gas exchange requires not only good ventilation of the alveolus, but also good perfusion of its capillaries. Ventilation–perfusion coupling is the ability to match ventilation and perfusion to each other.
Poor ventilation causes local constriction of the pulmonary arteries, reducing blood flow to that area and redirecting this blood to better-ventilated alveoli. Good ventilation, by contrast, dilates the arteries and increases perfusion so that most blood is directed to regions of the lung where it can pick up the most oxygen