In West Zone 2, perfusion is primarily determined by which pressure?

In West Zone 2 of the lung, perfusion is primarily influenced by the arterial-alveolar pressure gradient. This is because, in this zone, the blood flow is intermediately affected by the pressures in the pulmonary arteries and the alveolar spaces. As the arterial pressure exceeds the pressure in the alveoli, perfusion is facilitated, leading to effective blood flow.

The arterial-alveolar pressure gradient plays a crucial role in determining how well blood can flow through the pulmonary capillaries. This gradient must be positive for perfusion to occur; if the alveolar pressure were to exceed arterial pressure, perfusion would be minimal or nonexistent.

Mean arterial pressure, while important in overall circulatory perfusion, does not specifically capture the unique conditions present in West Zone 2 where the relationship between the arterial pressure and the alveolar pressure is pivotal. Similarly, venous pressure and capillary pressure are not the primary determinants in this specific context, as they do not account for the dynamics of both arterial blood flow and alveolar air pressure that uniquely define perfusion characteristics in this zone.