basically in zone 1, the Pressure in the alveoli is greater than the vessel pressure, for this reason, blood only flows through that region in a pulsatile fashion, at the end of expiration.
In zone 3, the blood pressures are greater than the alveolar pressure. therefore blood is constantly flowing here.
This leads to the realization that in zone 3, Q is greater than V. And that in Zone 1, V is greater than Q. Essentially, V/Q ratio goes down as you move down the lung. (even though both V and Q independently increase as you go down the lung.....Q is increasing at a great magnitude.)
Zone 2 is in between.
As an aside, all this changes during exercise. More air and more blood in the apices. more air and more blood everywhere.
