翻译：@刘思婷

关键词：pulmonary embolism 肺栓塞、embolus 栓子、inferior vena cava 下腔静脉、superior vena cava 上腔静脉、coagulation cascade 凝血级联反应、atrial septal defect 房间隔缺损

A pulmonary embolism happens when an embolus, which is a type of blockage, suddenly gets lodged inside a pulmonary artery. Depending on which pulmonary artery or arteries are affected by the blockage, that can seriously decrease the amount of oxygenated blood that gets out to the body. 

当栓子突然卡在肺动脉内时，肺动脉栓塞发生，栓子是一种阻塞物。取决于肺动脉受到堵塞的影响，这可以严重的减少进入身体的含氧血的量。

Normally, blood makes it back to the heart from all of the tissues and organs through a network of veins that merge over and over. Superficial veins drain blood into deep veins, which rely on the skeletal muscle pump to move blood forward. The way it works is that the surrounding skeletal muscles compress the vein and propel blood forward, and the veins prevent blood from moving backwards by using one-way valves. Ultimately, all of the blood ends up in the superior or inferior vena cava and dumps into the right atrium. From there the blood goes into the right ventricle and gets pumped into pulmonary artery and eventually into the lungs. 

当栓子突然卡在肺动脉内时，肺动脉栓塞发生，栓子是一种阻塞物。浅表静脉流入深静脉，这依赖于骨骼肌泵将血液向前移动。它的工作原理是，周围的骨骼肌压迫静脉，推动血液向前流动，而静脉则通过使用单向瓣膜来防止血液反流动。最终，所有的血液都以上腔静脉和下腔静脉流入右心房。从那里，血液进入右心室并被泵入肺动脉最终进入肺部。

The pulmonary artery splits at a spot called the pulmonary saddle, which looks like a bit like a horse saddle, and then the right and left pulmonary arteries enter their respective lungs. Subsequent branches off the pulmonary artery lead to smaller and smaller arteries, then arterioles, and finally capillaries that form nets around the alveoli, which is where gas exchange occurs. When a pulmonary embolism happens, a blockage in any of the arteries leads to a decrease in blood flow to lung tissue down  stream.

肺动脉在一个叫做肺鞍的地方分裂，看起来有点像马鞍，然后右和左肺动脉进入他们各自的肺。随后的分支从肺动脉转到更小的动脉，然后是小动脉，最后是在肺泡周围形成毛细血管网，这是气体交换发生的地方。当肺栓塞发生时，任何动脉的阻塞都会导致肺组织下游的血流减少。

The majority of the time, this blockage is caused by a broken off piece of a blood clot commonly associated with deep vein thrombosis. A deep vein thrombosis most commonly develops in the lower legs, below the knee, although a blood clot can form in both superficial and deep veins and also in other parts of the body as well.In fact, in the case of pulmonary embolisms, it is thought that most pulmonary emboli originate from leg veins above the knee. 

大多数情况下，这种堵塞是由血栓破裂后的碎片引起，通常与深静脉血栓形成有关。深静脉血栓形成最常见的是下肢，膝盖以下，虽然血凝块可以浅表静脉和深静脉形成，但也在身体的其他部位形成。事实上，在肺栓塞的情况下，人们认为大多数肺栓子来自于膝盖以上的腿部静脉。

Normally, the process starts with damage to the endothelium, or inner lining of blood vessel walls, after which there’s an immediate vasoconstriction or narrowing of the blood vessel which limits the amount of blood flow. After that, some platelets adhere to the damaged vessel wall, and become activated by collagen and tissue factor, which are proteins that are normally kept separated from the blood by an intact endothelium. These platelets then recruit additional platelets to form a platelet plug. This formation of the platelet plug is called primary hemostasis.

大多数情况下，这种堵塞是由血栓破裂后的碎片引起，通常与深静脉血栓形成有关。深静脉血栓形成最常见的是下肢，膝盖以下，虽然血凝块可以浅表静脉和深静脉形成，但也在身体的其他部位形成。在此之后，一些血小板粘附在受损的血管壁上，并由胶原蛋白和组织因子激活，这些蛋白质通常是由完整的内皮细胞从血液中分离出来的。这些血小板再募集另外的血小板，形成血小板栓。这种血小板栓的形成称为原发性止血。 

After that, the coagulation cascade is activated. First off in the blood there’s a set of clotting factors, most of which are proteins synthesized by the liver, and usually these are inactive and just floating around in the blood. The coagulation cascade starts when one of these proteins gets proteolytically cleaved. This active protein then proteolytically cleaves and activates the next clotting factor, and so on. The final step is activation of the protein fibrinogen to fibrin, which deposits and polymerizes to form a mesh around the platelets. So these steps leading up to fibrin reinforcement of the platelet plug make up the process called secondary hemostasis and results in a hard clot at the site of the injury. This cascade has a huge degree of amplification and takes only a few minutes from injury to clot formation. So the activation of the cascade is carefully controlled by anticoagulation proteins that target and inactivate key clotting factors. For example, antithrombin inactivates Factors IXa, Xa, XIa, XIIa, VIIa and thrombin while protein C inactivates Factors Va and VIIIa. 

在此之后，凝血级联反应被激活。首先在血液中有一组凝血因子，大部分是由肝脏合成的蛋白质，通常这些是不活跃的，只是在血液中漂浮。当其中一种蛋白质被水解时，级联反应就开始了。这种活性蛋白被蛋白酶分解并激活下一个凝血因子，以此继续。最后一步是将蛋白质 纤维蛋白原活化成纤维蛋白，在血小板周围沉积和聚合形成网状结构。因此，这些步骤导致血小板栓子的纤维蛋白增强，形成了称为继发性止血的过程，并在损伤部位形成牢固的血栓。这种级联具有很大的放大程度，从损伤到血栓形成只需要几分钟的时间。因此，该级联的激活是由指向和灭活关键凝血因子的抗凝蛋白精心控制的。例如，抗凝血酶抑制IXa、Xa、XIa、XIIa、VIIa、凝血酶，而蛋白C则抑制Va和VIIIa。

As the clot grows in size, it limits the amount of blood able to pass by, and pressure in the vein increases. Usually the clot might start naturally breaking down, for example, enzymes like plasmin break down fibrin into fragments called D-dimers. But sometimes, the increased pressure in the vein can cause a part of the main clot to break free, becoming a thromboembolus which can travel downstream towards the heart. When that happens, a thromboemobolus - which is a blood clot on the move - can move from the spot of clot formation and get into the right atrium, and then into the right ventricle and get pumped into the lungs where it can get lodged some place - causing a pulmonary thromboembolism.

当血凝块的大小增加时，它限制了可以流过的血液的量，静脉的压力也会增加。通常，血栓可能会开始自然分解，例如，像纤溶酶这样的酶将纤维蛋白分解成d -二聚体。当这种情况发生时,血栓栓子——一个移动的血凝块——可以从血栓形成部位，进入右心房,然后进入右心室,泵入肺部,能卡在一些地方——导致肺血栓栓塞。但有时，静脉内增加的压力会导致血栓的一部分破裂，从而形成血栓栓子，流向心脏。

This is a life-threatening situation because it literally blocks blood from getting into the lungs to pick up oxygen. If there’s no blood flowing past an alveoli, then that means there are alveoli that are getting ventilated with fresh air but not getting perfused with blood. We call this a ventilation perfusion mismatch or a V/Q mismatch. The body needs oxygenated blood to function and can therefore only tolerate a bit of a V/Q mismatch, before the lungs are no longer able to meet the needs of the body. 

这是一种危及生命的情况，因为它可以阻止血液进入肺部交换氧气。如果没有血液流经肺泡，那就意味着有肺泡有新鲜空气，但没有血液灌注。我们称之为通气灌注失调或V/Q不匹配。身体需要含氧血才能发挥作用，因此只能容忍少量的V/Q失调，在肺部无法满足身体的需要之前。

The amount of V/Q mismatch ultimately depends on the number, size, and location of the pulmonary thromboembolisms, which tells us the amount of lung tissue that’s being denied blood flow. A physiologic response to all of this is hyperventilation. When that happens the body starts to rapid release carbon dioxide and that causes a respiratory alkalosis, which is a shift in the blood acid/base equilibrium resulting in an elevated blood pH.

V/Q不匹配的数量最终取决于肺部血栓栓塞的数量、大小和位置，告诉我们没有血流的肺组织的量。对这一切的生理反应是过度通气。当这种情况发生时，身体开始快速释放二氧化碳，导致呼吸性碱中毒，这是血酸/碱平衡的改变导致血ph升高。

Now, sometimes, individuals might have an atrial septal defect, which is a small opening between the right and left atrium. In these individuals, it’s possible for a blood clot to go from the right atrium to the left atrium - bypassing the lungs completely. Unfortunately, the clot goes into the left ventricle and can get pumped out to the body- often heading towards the brain and cutting off a blood vessel serving the brain, which can cause an embolic stroke. Because of this, if someone has a pulmonary embolism, it’s important check for an atrial septal defect.

有时，有些人可能有房间隔缺损，这是在右心房和左心房之间的一个小开口。在这些人中，血凝块可能从右心房到左心房——完全绕过肺部。不幸的是，血栓进入左心室，并被泵向体循环——通常是向大脑靠近，切断供应大脑的血管，这可能导致栓塞中风。因此，如果某人有肺栓塞，对于房间隔缺损是很重要的检查。

There are three main factors that lead to a deep vein thrombosis, which are referred to as Virchow’s triad.

有三种主要因素导致深静脉血栓形成，这被称为Virchow三联征。

The first factor is slowed blood flow, called stasis, in the veins. Typically, blood continuously flows smoothly through the blood vessel, but if the blood flow becomes turbulent, the linear flow is disrupted and slow or static pockets of blood are formed. Stasis can also happen during long periods of inactivity of the skeletal muscle pump like bed rest or long flights and car rides, or even during pregnancy when a growing baby compresses nearby veins. During stasis, platelets and other clotting factors contact the endothelium, and prolonged interaction leads to clotting factor adhesion, and, ultimately, activation of the clotting cascade.

第一个因素是在静脉中，血液流速减慢，叫做停滞。一般来说，血液会通过血管顺畅地流动，但如果血液流动变湍流，那么线性流动就会被破坏，缓慢或静止的血液口袋就会形成。停滞也会发生在长时间的骨骼肌不活动，比如床上休息或长时间的飞行和汽车旅行，甚至在怀孕期间，一个成长的婴儿压迫了附近的静脉。在停滞期，血小板和其他凝血因子与内皮细胞接触，延长相互作用导致凝血因子粘附，并最终激活凝血级联。

The second factor is a state of hypercoagulation, where altered amounts of clotting factors increase primary or secondary hemostasis. This can happen for genetic or acquired reasons like surgery or taking certain medications like birth control pills. During surgery, physical damage to vessels activates the clotting cascade. And birth control pills tip the balance towards clotting because they increase the levels of clotting factors and decrease the levels of some anticoagulation factors like protein C and antithrombin. 

第二个因素是一种高凝状态，在此状态下，改变了的大量凝血因子增加了原发性或继发性止血。这可能发生在遗传或后天因素，比如手术或服用某些药物如避孕药。在手术中，对血管的物理损伤会激活凝血级联。而避孕药则会导致凝血功能的失衡，因为它们会增加凝血因子的水平，降低一些抗凝因子如蛋白酶C和抗凝血酶的水平。

A third factor is damage to the endothelial cell lining of a blood vessel that exposes tissue factor and collagen. Damage can be caused by infections, chronic inflammation or toxins like those found into bacco cigarettes. Now, a small pulmonary embolism might not cause any symptoms, whereas a large one can cause sudden and severe chest pain, shortness of breath, as well as fatigue. If a large pulmonary thromboembolism happens at the pulmonary saddle, then it blocks blood from going to both lungs and this can cause sudden death. If multiple thromboembolisms happen over time, then that can lead to pulmonary hypertension,or right ventricular failure, because blocked arteries cause an increase in resistance which requires the heart to supply more pressure to move blood past the obstructed arteries. 

第三个因素是血管内皮细胞的损伤，会暴露组织因子和胶原蛋白。损伤可由感染、慢性炎症或类似于烟草的毒素引起。现在，一个小的肺栓塞可能不会引起任何症状，而大的则会引起突然的严重的胸痛，呼吸短促，以及疲劳。如果一个大的肺血栓栓塞发生在肺鞍上，那么它会阻止血液进入两个肺，这可能导致猝死。如果随着时间的推移发生多重血栓栓塞，就会导致肺动脉高压或右心室衰竭，因为阻塞的动脉会导致阻力增加，这需要心脏提供更多的压力，使血液流经阻塞的动脉。

The diagnosis of a pulmonary embolism can be done with a CT pulmonary angiogram where a dye is injected into the blood vessels to identify blockages. Also, a ventilation-perfusion scan, sometimes called a V/Q scan, can reveal areas of the lung that are ventilated but not perfused. Other helpful labs include a D-dimer blood test to detect fibrin breakdown products which are usually around when there’s a blood clot. 

肺栓塞的诊断可以通过CT肺动脉造影来完成，将染料注入血管以识别阻塞。此外，通气灌注扫描(有时称为V/Q扫描)可以显示出通气但未灌注的区域。其他有用的实验室还包括d -二聚体血液测试，用来检测纤维蛋白分解产物，通常是有血凝块时出现的。 

Generally speaking the body makes and breaks blood clots all the time, and some small clots resolve on their own, but large clots that cause symptoms typically need an intervention. Thrombolytic enzymes can be given to help break down the clot or a pulmonary thrombectomy also known as pulmonary thromboendarterectomy can be done to surgically remove the clot. Long-term treatment to prevent future thrombi from forming can include anticoagulant medications like warfarin or heparin, which inhibit the clotting cascade and prevent clot formation. Also, a filter can be surgically placed in the inferior vena cava to prevent pulmonaryembolisms. Prevention of a deep vein thrombosis is also important - compression stockings and frequent calf exercises during long periods of sitting still can help move blood through the veins to prevent stasis.

一般来说，身体会不停地产生和破坏血栓，而一些细小的血栓会自行分解，但引起症状的大血栓通常需要进行干预。血栓溶解酶可以帮助分解血栓或肺动脉血栓术，也称为肺血栓切除术可以通过外科手术切除血栓。预防未来血栓形成的长期治疗可以包括抗凝药物，如华法林或肝素，抑制凝血作用，防止血栓形成。此外，可以通过外科手术将过滤器放置在下腔静脉，以防止肺动脉栓塞。预防深静脉血栓也很重要——久坐时，压力性长袜和频繁的小腿运动仍然可以帮助血液通过静脉防止停滞。

Alright, as a quick recap … A pulmonary embolism is a blockage in the pulmonary arteries which deliver blood to the lungs to pick up oxygen. Typically, a pulmonary embolism is a thromboembolism, which happen when a blood clot formed from a deep vein thrombosis lodges itself in the pulmonary arteries. Symptoms vary by the amount of downstream lung tissue denied blood, which creates a ventilation-perfusion mismatch, so immediate treatment is important

好的，作为一个快速的回顾，肺栓塞是肺动脉的一个堵塞，肺动脉将血液输送到肺部以获取氧气。典型的肺栓塞是一种血栓栓塞，它发生在来自深静脉血栓的血栓堵在肺动脉中。症状会因下游的肺组织供血不足不一样而不同，这就造成了通气血流不匹配，所以需要马上治疗。