What is the consequence of a portion of the lung having a V/Q ratio of 0?

When a section of the lung has a ventilation/perfusion (V/Q) ratio of 0, this indicates that there is ventilation failure in that region while perfusion (blood flow) is still occurring. In practical terms, this means that the area is receiving blood but not air, which leads to conditions similar to a right-to-left shunt.

In a right-to-left shunt, deoxygenated blood bypasses the alveoli where gas exchange occurs, directly entering the systemic circulation. This results in mixed venous blood returning to the body without being adequately oxygenated, leading to hypoxemia or a low level of oxygen in the blood.

Thus, when a region of the lung exhibits a V/Q ratio of 0, the blood flowing through that region doesn't pick up oxygen, manifesting as an absolute shunt. This condition can contribute significantly to overall hypoxemia, as oxygenated blood is diluted with unoxygenated blood from the shunted area. The recognition of this pathological V/Q relationship is crucial for understanding various respiratory conditions and management strategies.