Ventilation-perfusion mismatch: Difference between revisions
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# Shunt formation | # Shunt formation | ||
# Dead space formation | # Dead space formation | ||
The first three causes result in a normal V/Q and the last two result in an abnormal V/Q. | The first three causes result in a normal V/Q and the last two result in an abnormal V/Q. | ||
==== Shunts ==== | |||
Shunts are formed when the air entry is cut off from part of the lung and deoxygenated blood enters arterial circulation without getting oxygenated in the lung. Absorptive or compressive pulmonary atelectasis is the major reason for shunt formation. Pulmonary AV malformation, hepatopulmonary syndrome are the less common causes. | |||
==== Dead space ventilation ==== | |||
When blood supply to part of lung is cut off, oxygen in the ventilated atmospheric air is not able to enter the blood stream leading to lesser overall efficiency of alveolar oxygenation mechanism. Pulmonary Embolism is the m | |||
==[[Ventilation-perfusion mismatch pathophysiology|Pathophysiology]]== | ==[[Ventilation-perfusion mismatch pathophysiology|Pathophysiology]]== | ||
Revision as of 14:18, 18 August 2018
Template:Ventilation-perfusion mismatch Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Ventilation Perfusion (V/Q) mismatch is said to have occurred when there is a there is defect in alveolar gas exchange in the lung either due to poor perfusion or reduced air entry. It is a valuable tool in both understanding the normal physiology of lung and for diagnosing some of the common lung pathologies.
Ventilation of air and perfusion of blood is not distributed equally in all the 400 million alveoli of our lung. This varies based on the effects of gravity, how patent the airways are and any pathological process that affect various parts of the lung. In ideal physiologic conditions, V/Q ratio should be 1, that is 100 percent of the alveoli are recruited (full air entry), good oxygenation and 100 percent of the alveolar capillaries are perfused. However this does not happen even in healthy individuals as not all the alveoli in a healthy lung are recruited. The normal V/Q ratio is estimated to be 0.8. An easy way to interpret this value of 0.8 would be that 80 percent of the alveoli in the lung have good air ventilation and blood perfusion.
Understanding V/Q mismatch in the context of hypoxia
There are five causes of hypoxia
- Diffusion limitation
- Hypoventilation
- Low partial pressure of oxygen in inspired air
- Shunt formation
- Dead space formation
The first three causes result in a normal V/Q and the last two result in an abnormal V/Q.
Shunts
Shunts are formed when the air entry is cut off from part of the lung and deoxygenated blood enters arterial circulation without getting oxygenated in the lung. Absorptive or compressive pulmonary atelectasis is the major reason for shunt formation. Pulmonary AV malformation, hepatopulmonary syndrome are the less common causes.
Dead space ventilation
When blood supply to part of lung is cut off, oxygen in the ventilated atmospheric air is not able to enter the blood stream leading to lesser overall efficiency of alveolar oxygenation mechanism. Pulmonary Embolism is the m