Introduction to pulmonary hypertension

Disease name: Introduction to pulmonary hypertension: Pulmonary hypertension refers to the average pulmonary artery pressure >3.33 kPa (25 mmHg) or >4 kPa (30 mmHg) during exercise. Causes: (1) Causes of the disease 1. Increased pulmonary blood flow (1) Congenital cardiovascular abnormalities of left-to-right shunt: atrial septal defect, ventricular septal defect, patent ductus arteriosus, permanent arterial trunk. (2) acquired intracardiac shunt: aortic aneurysm rupture or aortic Valsalva aneurysm broke into the right ventricle or right atrium, ventricular septal perforation (defect) after myocardial infarction. 2. Increased vascular resistance around the lungs (1) Reduction of pulmonary vascular bed: pulmonary embolism caused by various causes. (2) pulmonary artery wall lesions: 1 pulmonary arteritis: Raynaud's syndrome, scleroderma, localized intradermal calcium deposition, Raynaud's phenomenon, finger (toe) scleroderma and capillary dilatation syndrome (CREST syndrome), class Rheumatoid arthritis, systemic lupus erythematosus, polyneuritis, dermatomyositis, granulomatous arteritis, eosinophilia, arteritis. 2 primary pulmonary hypertension: plexus pulmonary vascular disease, microthrombus formation, pulmonary vein occlusion disease. 3 pulmonary artery congenital stenosis. (3) pulmonary fibrosis or interstitial granuloma: diffuse pulmonary interstitial fibrosis, radiation pulmonary fibrosis, miliary tuberculosis, pneumoconiosis, lung cancer, cystic fibrosis, idiopathic hemosiderosis, etc. . (4) pulmonary vasospasm caused by hypoxemia: 1 chronic obstructive pulmonary disease: chronic bronchitis, emphysema, bronchial asthma. 2 respiratory dyskinesia: pleural disease, thoracic deformity, multiple polio, muscle atrophy, obesity. 3 plateau lack of oxygen. (5) Changes in blood viscosity: increased plasma viscosity, polycythemia, increased red blood cell accumulation, and increased red blood cell hardness. 3. Increased pulmonary venous pressure (1) pulmonary vein occlusion: mediastinal tumor or granulomatous disease, mediastinal disorder, congenital pulmonary vein stenosis. (2) Heart disease: left ventricular dysfunction, mitral stenosis or insufficiency, mitral annulus calcification, left atrial myxoma, three-female heart. (B) pathogenesis 1. Pathogenesis The pulmonary circulation includes the right ventricle, pulmonary artery, capillaries and pulmonary veins, the main function of which is gas exchange. Hemodynamics have the following four characteristics: 1 low pressure: pulmonary artery pressure is 19/16mmHg at normal resting, average pressure is (12±2) mmHg, systolic blood pressure is less than 25mmHg, 1/6 of aorta, lung The vascular perfusion pressure is also low, the pressure difference between the pulmonary artery and the left heart chamber is only 6mmHg, which is l/7～1/10 of the normal aortic pressure; 2 the resistance is small: due to short pulmonary vessels, thin wall, large degree of expansion, blood flow The resistance is small. Normal human pulmonary vascular resistance is 1/5 ~ l/10 of systemic resistance; 3 fast flow rate: the lung receives all the blood from the heart, but the process is much shorter than the systemic circulation, so the flow rate is fast; 4 capacity is large: pulmonary vascular bed It is large in size and can hold 900mL of blood, accounting for 9% of the whole blood. Pulmonary arterial pressure = pulmonary vascular resistance × pulmonary blood flow + left atrial pressure Therefore, pulmonary hypertension is determined by pulmonary vascular resistance, pulmonary blood flow and left atrial pressure. The pulmonary artery consists of three types of caliber and structural vessels, namely elastic arteries with an outer diameter of >1000 μm, muscle arteries between 100 and 1,000 μm and small arteries with an outer diameter of <100 pμm. Muscular arteries and small arteries affect pulmonary artery pressure. Important part. The formation mechanism of pulmonary arterial pressure is very complicated and can be divided into the following cases: (1) High-dynamic pulmonary hypertension (increased pulmonary blood flow): Due to the low resistance, low pressure and high volume of pulmonary circulation, pulmonary blood vessels can adapt to pulmonary blood volume. The increase does not cause significant fluctuations in pulmonary arterial pressure, but there is also a limit. When the cardiac output is increased by 2 to 3 times, the average pulmonary artery pressure is only increased by 20% to 50%. When the blood pressure is increased by 4 to 5 times, the pulmonary artery pressure can be increased. 1 times. If the long-term continuous increase in blood flow causes the blood vessels to dilate, it can cause changes in the structure of the pulmonary artery and become irreversible. Pulmonary hypertension caused by increased pulmonary blood flow is more common in congenital heart disease with left-to-right shunt or large arteriovenous fistula (Eisenmenger syndrome). At rest, the pulmonary circulation pressure is mostly normal, and the cardiac output increases significantly during exercise. If the vasospasm or vascular bed is reduced, and the compensatory expansion of the vascular volume is limited, the pulmonary artery pressure rises sharply. (2) high-resistance pulmonary hypertension (increased vascular resistance around the lung): 1 reduction of pulmonary vascular bed: pulmonary vascular reserve capacity, large expansion, when the vascular bed is reduced by more than 70%, significant pulmonary hypertension will occur. A. Extravascular compression: various diffuse pulmonary interstitial lesions such as pulmonary fibrosis, pulmonary granuloma and pulmonary infiltration, caused by bronchial tension changes, increased alveolar pressure, scar tissue contraction, lung tissue swelling or Tumor compression, etc., narrow and occlude small blood vessels in the lungs. B. Causes of blood vessels itself: severe emphysema, alveolar septum rupture, many alveoli fuse into large bubbles, the capillaries are stretched and slender, or by the vascular wall itself inflammation or invasive lesions, small arterial intimal hyperplasia and middle layer hypertrophy. C. Endovascular embolization: occlusion of pulmonary arterioles after arteritis, as well as pulmonary artery trunk and small vessel embolization or thrombosis. 2 pulmonary vasoconstriction: pulmonary vasoconstriction is the most important cause of increased pulmonary hypertension. Hypoxemia is a strong stimulating factor that causes pulmonary capillary contraction, which causes an increase in vascular resistance, leading to pulmonary hypertension. Pulmonary hypertension is closely related to pulmonary oxygen saturation (SaO2) in patients with chronic obstructive pulmonary disease (COPD). When SaO2<80%, 2/3 patients have elevated pulmonary arterial pressure, and SaO2<75% has 95.4. % of patients have elevated pulmonary arterial pressure. High altitude pulmonary hypertension is also caused by hypoxia. The oxygen content in the air is related to the altitude. At an altitude of 3400m, the partial pressure of oxygen in the air is 100mmHg, and the altitude of the air is 5000m. The partial pressure of oxygen in the air is 80mmHg. Acute pulmonary edema can occur in the early high altitude due to acute hypoxia, causing an increase in irreversible pulmonary hypertension. Pulmonary vasoconstriction caused by hypoxia may be related to the following factors: A. Autonomic nervous mechanism: pulmonary vasculature is governed by adrenergic sympathetic and cholinergic parasympathetic nerves, and adrenergic alpha and beta receptors are present around the pulmonary arterioles. The partial pressure of oxygen is lowered, the partial pressure of carbon dioxide is increased, and when the concentration of hydrogen ions is increased, the impulse is transmitted to the sympathetic nerve center of the hypothalamus by stimulating the aorta and carotid sinus, and the pulmonary artery is contracted by reflex. In the case of acidosis, the blood vessel The response to hypoxia contraction is significantly increased. B. Humoral factors: In the absence of oxygen, the proliferation of mast cells in the lungs increases, the ability to produce histamine is enhanced, degranulation occurs, and histamine and serotonin are released, which directly affects the cell membrane, causing the loss of intracellular potassium ions. Increased calcium levels lead to increased muscle excitability. Prostaglandins are elevated in the lungs during hypoxia. Prostaglandin F2a (PGF2a) and thromboxane (TXA2) are potent pulmonary vasoconstrictors, which directly affect the excitation and contraction of calcium ions on smooth muscle and can cause platelets. Agglutination promotes thrombosis and increases vascular resistance. In the absence of oxygen, the activity of angiotensin I converting enzyme in the lung is increased, which causes angiotensin II to increase, causing pulmonary vasoconstriction. Increased systemic circulation pressure is also an important cause of increased pulmonary artery pressure. C. Cellular factors: ATP production is reduced in hypoxia, cell membrane ATPase activity is decreased, potassium and sodium are lost in pulmonary artery smooth muscle, negative membrane potential is decreased, and muscle excitability is improved. . At the same time, in the hypoxic acid poisoning, the free calcium ions in the blood increase, which promotes the entry of calcium ions into the smooth muscle cells, and initiates the contraction device, which can cause the blood vessels to contract, and the resistance increases, leading to pulmonary hypertension. 3 pulmonary vascular elasticity is reduced: long-term hypoxia causes persistent pulmonary contraction or bronchial inflammation to affect pulmonary arterioles, which can cause organic vascular damage, especially small arteries with an inner diameter of 300 μm or less, causing smooth muscle edema, degeneration, necrosis, and elasticity. Plate rupture and endothelial cell and elastic tissue hyperplasia, fibrosis, and even luminal occlusion, resulting in thickening and stiffness of the vessel wall. The mesenteric muscle layer of the pulmonary arterioles with a diameter of less than 80 μm can reduce the compliance of the wall and increase the vascular resistance. 4 increased blood viscosity: visible in primary polycythemia or long-term hypoxia caused by secondary polycythemia to increase blood viscosity. When the hematocrit is >50%, the pulmonary vascular resistance is increased. (3) pulmonary venous hypertension (post-capillary pulmonary hypertension): due to the characteristics of pulmonary circulation, the pressure difference between pulmonary arteries and veins is very small, only 2 ~ 10mmHg, so some diseases cause pulmonary hypertension to increase when pulmonary venous pressure is increased. Common in mitral valve disease, three-atrial heart, left atrial myxoma, can also occur in long-term left ventricular dysfunction, left ventricular responsiveness and so on. When the pulmonary venous pressure is elevated, the pulmonary arterioles are reactively contracted or occur in the basal fibrosis of the lungs, which causes the pulmonary vascular bed to be squeezed, which is also the cause of pulmonary hypertension. A slight increase in left atrial pressure has little effect on pulmonary artery pressure, and a one-fold increase will affect pulmonary artery pressure. 2. Pathological changes Pulmonary arterial hypertension caused by any cause can cause anatomical and structural changes of pulmonary arterioles and muscular small arteries, thickening of the wall and stenosis of the lumen, and partial local atrophy as long as there is sufficient severity and time. Tumor expansion, in terms of pathological morphology, is mainly divided into four categories: (1) plexus pulmonary artery disease: this type is most common in left-to-right shunt congenital heart disease, also seen in pulmonary arterial blood derived from the aorta Branch lung isolation and typical primary pulmonary hypertension, occasionally seen in cirrhotic portal hypertension, portal vein thrombosis and schistosomiasis, AIDS. Histology is characterized by muscular hypertrophy of the pulmonary artery, intimal hyperplasia, formation of conjunctival fibrosis, constriction of the lumen, arterialization of the arteries, vasodilator lesions, cellulose-like necrosis and formation of plexiform lesions. The blood vessels of this site are limitedly dilated. The wall of the tube is composed of only a thin elastic membrane to form a dilated blood vessel, which is prone to thrombosis. The thrombotic endothelial cells enter the thrombus to form a cavernous hemangioma. (2) embolic and thrombotic pulmonary vascular disease: the muscle layer of the pulmonary artery is often not obvious, there are new and old thrombosis, thrombosis after the formation of eccentric plaque-like intimal fibrosis, and then the formation of fiber spacing. (3) pulmonary venous hypertension pulmonary vascular disease: any disease that can block venous blood flow can cause similar pulmonary vascular disease, such as mitral valve disease, left atrial myxoma, left heart failure and mediastinal fibrosis, etc. Involved pulmonary arteries, muscle arteries, arterioles, lymphatic vessels, lung tissue are also involved, muscle type of pulmonary artery hypertrophy, arterialization of the arteries, severe intimal fibrosis, thickened arterialization of the pulmonary veins and intimal fibrosis. (4) Hypoxic pulmonary hypertension pulmonary vascular disease: pulmonary vascular disease is mainly limited to smaller blood vessels, the arterioles are mechanized, the intima has longitudinal smooth muscle cell bundles or layers, similar lesions can also be seen in venules, larger muscles. The type of pulmonary artery may be normal or slightly moderately thick. Read more...