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. | 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. | ||
==Pathogenesis== | ==Pathogenesis== | ||
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==Associated Conditions== | ==Associated Conditions== | ||
Some conditions that cause decrease in V/Q are: | Some conditions that cause decrease in V/Q are: | ||
* [[Chronic Bronchitis]] | * [[Chronic Bronchitis]] | ||
* [[Asthma]] | |||
* [[Foreign body aspiration]] | |||
* [[Asthma]] | |||
* [[Foreign body aspiration]] | |||
* [[Hepatopulmonary syndrome]] | * [[Hepatopulmonary syndrome]] | ||
* [[ARDS]] | * [[ARDS]] | ||
* | * [[Bronchiectasis]] | ||
* [[Interstitial Lung disease]] | |||
* [[Cystic Fibrosis]] | |||
* [[Pulmonary Hypertension]] | |||
Some conditions that cause increase in V/Q are: | Some conditions that cause increase in V/Q are: | ||
* [[Pulmonary embolism]] | * [[Pulmonary embolism]] | ||
* [[Emphysema]] | |||
* [[Emphysema]] | |||
==Genetics== | ==Genetics== | ||
Revision as of 22:33, 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. 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:
- Chronic Bronchitis
- Asthma
- Foreign body aspiration
- Hepatopulmonary syndrome
- ARDS
- Bronchiectasis
- Interstitial Lung disease
- Cystic Fibrosis
- Pulmonary Hypertension
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.