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This contrasts with the classical explanation of HPV which presumes that hypoxia is sensed at the pulmonary artery smooth muscle cell itself. Specialized epithelial cells (neuroepithelial bodies) that release serotonin have been suggested to contribute to hypoxic pulmonary venoconstriction. [8]
In individuals with chronic obstructive pulmonary disease who receive supplemental oxygen, carbon dioxide accumulation may occur through two main mechanisms: [6] Ventilation/perfusion matching: under-ventilated lung usually has a low oxygen content which leads to localized vasoconstriction limiting blood flow to that lung tissue.
To be classified as pulmonary heart disease, the cause must originate in the pulmonary circulation system; RVH due to a systemic defect is not classified as pulmonary heart disease. Two causes are vascular changes as a result of tissue damage (e.g. disease, hypoxic injury), and chronic hypoxic pulmonary vasoconstriction. If left untreated, then ...
By contrast, in the lungs, the response to hypoxia is vasoconstriction. This is known as hypoxic pulmonary vasoconstriction, or "HPV", and has the effect of redirecting blood away from poorly ventilated regions, which helps match perfusion to ventilation, giving a more even oxygenation of blood from different parts of the lungs. [81]
Dead space reduces the amount of fresh breathing gas which reaches the alveoli during each breath. This reduces the oxygen available for gas exchange, and the amount of carbon dioxide that can be removed. The buildup of carbon dioxide is usually the more noticeable effect unless the breathing gas is hypoxic as occurs at high altitude.
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Histidine residues in hemoglobin can accept protons and act as buffers.Deoxygenated hemoglobin is a better proton acceptor than the oxygenated form. [1]In red blood cells, the enzyme carbonic anhydrase catalyzes the conversion of dissolved carbon dioxide to carbonic acid, which rapidly dissociates to bicarbonate and a free proton:
Pulmonary interstitial pressure (Pi) rises as lung volume decreases due to reduced radial tethering of the lung parenchyma. Pi is highest at the base of the lung due to the weight of the above lung tissue. Pi can also rise due to an increased volume of 'leaked' fluid from the pulmonary vasculature (pulmonary edema). An increase in Pi causes ...