Ventilation-perfusion mismatch pathophysiology: Difference between revisions
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==Overview== | ==Overview== | ||
Any discrepancy between pulmonary blood flow and [[ventilation]] is called V/Q mismatch. Ideally [[Ventilation (physiology)|ventilation]] and [[perfusion]] should be equal with a V/Q ratio of 1, but the normal lung varies due to a higher perfusion at the [[Base of lung|base of the lung]] than the [[Apex of lung|apex of the lung]]. This causes a higher V/Q ratio at the apex compared to the base. The average V/Q ratio in a normal lung is about 0.8, with about 4 liters of oxygen and 5 liters of blood entering the lung per minute. Diseased lung can cause a V/Q mismatch due to decreased blood flow or oxygenation. This results in [[hypoxemia]], and there are many causes of it. | Any discrepancy between pulmonary blood flow and [[ventilation]] is called V/Q mismatch. Ideally [[Ventilation (physiology)|ventilation]] and [[perfusion]] should be equal with a V/Q ratio of 1, but the normal lung varies due to a higher perfusion at the [[Base of lung|base of the lung]] than the [[Apex of lung|apex of the lung]]. This causes a higher V/Q ratio at the apex compared to the base.<ref>{{Cite journal | ||
| author = [[Malay Sarkar]], [[N. Niranjan]] & [[P. K. Banyal]] | |||
| title = Mechanisms of hypoxemia | |||
| journal = [[Lung India : official organ of Indian Chest Society]] | |||
| volume = 34 | |||
| issue = 1 | |||
| pages = 47–60 | |||
| year = 2017 | |||
| month = January-February | |||
| doi = 10.4103/0970-2113.197116 | |||
| pmid = 28144061 | |||
}}</ref> | |||
The average V/Q ratio in a normal lung is about 0.8, with about 4 liters of oxygen and 5 liters of blood entering the lung per minute. Diseased lung can cause a V/Q mismatch due to decreased blood flow or oxygenation. This results in [[hypoxemia]], and there are many causes of it. | |||
==Pathogenesis== | ==Pathogenesis== | ||
Revision as of 21:45, 25 November 2018
Template:Ventilation-perfusion mismatch
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aida Javanbakht, M.D.
Overview
Any discrepancy between pulmonary blood flow and ventilation is called V/Q mismatch. Ideally ventilation and perfusion should be equal with a V/Q ratio of 1, but the normal lung varies due to a higher perfusion at the base of the lung than the apex of the lung. This causes a higher V/Q ratio at the apex compared to the base.[1]
The average V/Q ratio in a normal lung is about 0.8, with about 4 liters of oxygen and 5 liters of blood entering the lung per minute. Diseased lung can cause a V/Q mismatch due to decreased blood flow or oxygenation. This results in hypoxemia, and there are many causes of it.
Pathogenesis
V/Q mismatch is one of the most common reasons of hypoxemia in patients with lung diseases like obstructive lung diseases, pulmonary vascular diseases, and interstitial diseases . An increased V/Q mismatch is caused by a decrease in blood flow to the lung, for example a pulmonary embolism. A decreased V/Q mismatch is caused by a decrease in ventilation or an airway obstruction, for example Asthma. A V/Q mismatch due to a perfusion defect will improve with 100% oxygen therapy.
In normal condition when there is a low ventilation, the body tries to keep this ratio in a normal range by restricting the perfusion in that specific area of the lung. This unique mechanism is called hypoxic pulmonary vasoconstriction. If this process continues for a long time it can cause pulmonary hypertension .
Associated Conditions
Some conditions that cause decrease in V/Q are:
Some conditions that cause increase in V/Q are:
Genetics
The association between V/Q mismatch and genetic depends on the etiology of the mismatch. For example ORMDL3 and GSDML genes play a role in causing asthma .
Gross Pathology
The gross pathology depends on the exact reason for the V/Q mismatch.
Microscopic Pathology
The microscopic pathology depends on the exact reason for the V/Q mismatch. For example in asthma there are extracellular Charcot-Leyden crystals and increased mucosal goblet cells.
- ↑ Malay Sarkar, N. Niranjan & P. K. Banyal (2017). "Mechanisms of hypoxemia". Lung India : official organ of Indian Chest Society. 34 (1): 47–60. doi:10.4103/0970-2113.197116. PMID 28144061. Unknown parameter
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