(USMLE topics) Pulmonary arterial hypertension, PAH; Pulmonary hypertension caused by left-heart diseases; Pulmonary hypertension caused by lung disorders or hypoxemia; Pulmonary hypertension due to pulmonary artery obstruction. Classification, pathophysiology, symptoms, causes, mechanisms of pathogenesis, treatment.
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Pulmonary hypertension refers to high blood pressure in the blood vessels of the lungs.
The lungs receive oxygen-poor blood from the right side of the heart. After being reoxygenated, oxygen-rich blood returns to the left side of the heart to be pumped out to the body.
Normally, the right ventricle pumps against a low-resistance pulmonary circuit. Increased blood pressure in the lungs results in a greater resistance. The right heart must work harder to push blood through pulmonary arteries. This causes the right ventricle to thicken, enlarge and eventually fail, a condition known as right-sided heart failure.
The most common symptom of pulmonary hypertension is shortness of breath during exertion. Other signs may include dizziness, fainting, and chest pressure or pain. Swelling of legs may occur when right-sided heart failure has developed.
Pulmonary hypertension is classified into 5 groups, based on the cause and mechanism of the disease.
Group 1: Pulmonary arterial hypertension, PAH. PAH affects mostly the arterioles, the smaller arteries of the lungs. PAH can be caused by a number of factors, including genetics, certain drugs, and other health conditions. For many cases, the cause is unknown. Regardless of the underlying cause, however, the group shares similar pathological changes. These include: increased activities of vasoconstrictors, decreased activities of vasodilators, and vascular wall remodeling as a result of endothelial and smooth muscle proliferation and chronic inflammation. In addition, the increased vascular pressure injures the endothelium, activating coagulation, producing blood clots that further obstruct blood flow.
Group 2: Pulmonary hypertension caused by left-heart diseases. A number of conditions can lead to dysfunction of the left side of the heart, affecting its ability to pump effectively or to fill properly. When left-heart function is compromised, blood backs up in the lungs, where it came from, causing congestion and increased pulmonary pressure. As this happens, fluid leaks from blood vessels to lung tissue, resulting in pulmonary edema. Accumulation of fluid in the alveoli impedes the gas exchange process, causing respiratory symptoms.
Group 3: Pulmonary hypertension caused by lung disorders or low blood oxygen. When oxygen level is low, pulmonary vessels constrict in an attempt to shunt blood to better-ventilated regions of the lung. Conditions or circumstances that result in low blood oxygen are risk factors for developing pulmonary hypertension. Lung disorders, such as chronic obstructive pulmonary disease, also cause lung tissue damage, inflammation and loss of capillaries, which further contribute to disease development.
Group 4: Pulmonary hypertension due to pulmonary artery obstruction. Certain chronic disorders can repeatedly produce blood clots, typically in deep leg veins. The clots may travel to the lungs, blocking pulmonary arteries. If these clots do not resolve completely, pulmonary vessels can become narrower and stiffer. Pulmonary arteries may also be obstructed by tumors, parasites, or foreign particles.
Group 5 includes pulmonary hypertension by all other mechanisms.
Treatment should be aimed at the underlying cause whenever possible. Anticoagulants may be given to reduce the risk of blood clots. Vasodilators and supplemental oxygen can help relieve symptoms. However, vasodilators are only effective for certain types of pulmonary hypertension and should be tested for effectiveness before they can be prescribed.
7 окт 2024
