Ventilation–perfusion coupling

The respiratory system and major airways participating in ventilation include the nostril, nasal cavity, mouth, pharynx, larynx, trachea, bronchus, and lungs.

The alveolar capillary specifically participates in perfusion to get in contact with the alveoli for the gas exchange and oxygen delivery to the body tissues.

[4] The diaphragm and intercostal thoracic muscles alter the lung's pressure gradient, which generates ventilation driving force.

[2] The primary function of ventilation is the replacement of the stale gases in the lungs with oxygen-rich air through the removal of carbon dioxide for oxygenation of the blood.

Once oxygen enters the bloodstream, it dissolves in plasma by binding to hemoglobin (Hb) of red blood cells and transported to body tissues.

Ventilation rate (V) is the total gas volume that enters and leaves the alveoli in a given amount of time, commonly measured per minute.

[9] Perfusion rate (Q) is the total blood volume that enters the alveolar capillaries per unit time (1 minute) during the gas exchange.

Furthermore, adequate achievement of ventilation and perfusion matching is essential as it ensures the continuous supply of oxygen and withdrawal of waste products from the body.

[3] Towards the base of the lungs, the fluid volume in the pleural cavity increases due to gravity, resulting in greater intrapleural pressure.

Towards the apex of the lungs, the hydrostatic pressure is reduced due to gravity, which lowers the blood flow, thus decreasing perfusion.

[11] Alveolar dead space and insufficient perfusion result in a V/Q ratio above 0.8 with decreased fresh oxygen in the alveoli.

It likely results in hypoxemia (low oxygen level), and the common symptoms of ventilation-perfusion mismatch include dizziness, headache, and fatigue.

[medical citation needed] Low V/Q ratio may have been caused by pneumonia, pulmonary edema, asthma, or the blockage of the bronchus.

Smoking (long-term exposure to chemical irritants) can cause COPD, increasing the risk of lung cancer and heart disease.

[14] Asthma is a common inflammatory disease causing the airway to swell and disturb breathing and ventilation(low V/A ratio).

The cause is unrevealed, but allergens such as pollen, mold, respiratory infections, and air pollutants(cigarette smoke) are potential stimulators.

Restricted blood flow in the pulmonary circulation results in alveoli ventilated but not perfused, thus, increasing the V/Q ratio and decreasing gas exchange.

Common symptoms are shortness of breath, chest pain, anxiety, irregular heartbeat, heart racing, headache, memory loss, and confusion in the brain.

[16] ARDS, pneumonia, chronic bronchitis, pulmonary edema, and airway obstruction are lung diseases that also commonly cause a ventilation-perfusion mismatch.

Long exposure to cigarette smoke induces airway inflammation and enlargement, which eventually restricts airflow and associates a high risk of V/Q mismatch.

[20] Corticosteroids, antibiotics, pulmonary rehabilitation therapy, anticoagulants, and surgery can also serve as a medical treatment for ventilation-perfusion mismatch-related symptoms and diseases.