The veins in the human body are divided into two systems: superficial and deep veins, the “veins” that we can see are the superficial veins, while the deep veins are described as “deep” because they are located deeper, usually between the muscles, and cannot be seen by the naked eye. The role of the deep and superficial venous systems is to return the venous blood to the heart after it has been used by the tissues, figuratively speaking, they are like the sewers of the body, sending the “sewage” back to its designated place – the heart. The deep venous system plays a much greater role than the superficial venous system. Deep vein thrombosis is the abnormal clotting of blood in the deep vein lumen, blocking the vessel. Of all the veins, the veins of the legs are the farthest from the heart, and the uprightness of humans also causes the venous blood of the legs to overcome gravity in order to return to the heart, so the deep veins of the human legs are the most prone to thrombosis. First, the three main culprits of intravascular thrombosis are: blood hypercoagulation, slow blood flow, and vascular intima damage. Blood is not a completely uniform liquid, there are many red blood cells, white blood cells, platelets and so on, which constantly transport all kinds of cells from the heart to the periphery, and then transport the peripheral cells back to the heart. And in some special cases the cells that need to be transported increase, resulting in a higher concentration of blood, and if the blood flow is slow, the blood has a tendency to deposit red blood cells, white blood cells, etc. in the walls of the blood vessels. Just as the Yangtze River, which is laden with a lot of sediment, reaches a flat place at the mouth of the sea, when the water flow slows down and the sediment is deposited, an umbrella-shaped alluvial plain like the Yangtze Delta is formed. If there is damage to the inner wall of the blood vessels at this time, it will activate the platelets in the blood to release a variety of substances and activate the clotting system. While repairing the damage, tiny emboli are also formed in the blood vessels, which are likely to accumulate larger and larger, forming life-threatening blood clots. Second, what exactly is the manifestation of deep vein thrombosis, and what is the danger to the patient? After the thrombosis, the blood can’t flow back effectively, just like a blocked sewer, the sewage can’t be discharged, resulting in blood stagnation and swelling of the limb far away from the blockage; if it doesn’t pass, it hurts, and the swollen limb often has different degrees of pain, which is more obvious when walking on the ground. Once the thrombus is dislodged, it will follow the blood circulation pathway: inferior vena cava – right atrium – right ventricle, and finally enter the pulmonary artery, causing pulmonary artery embolism. The embolism may cause ischemia in only a small part of the lung, but in fact, like igniting a bomb in an ammunition depot, the explosion follows one after another, and a series of chain reactions lead to ischemia in a large area of the lung, losing the function of blood gas exchange, often killing the patient. The most typical case is that many patients who have a history of being bedridden for a long time and can’t or can only move their limbs slightly, just start to get out of bed and increase their activities, then stand up and suddenly shout “ah”, then fall down, chest tightness, shortness of breath, accelerated heartbeat, and finally heartbeat and respiratory arrest. Deep vein thrombosis can be caused by many diseases. Risk factors include advanced age, mid to late pregnancy, malignancy, obesity, varicose veins, paralysis, history of severe trauma, major surgery on the lower extremities (especially the hip joint), prolonged bed rest or heart failure. Without preventive measures, the chance of these patients suffering from deep vein thrombosis in the lower leg can be as high as 40% to 80%, and the chance of fatal pulmonary artery embolism is 1% to 5%. Even in normal people who fly long distances by airplane, there is a very high prevalence of thrombosis. As mentioned above, blood hypercoagulation, slow blood flow and intimal damage are the three main culprits of thrombosis. During long flights, lack of oxygen in the cabin, repeated circulation of air, and forgetting to drink water when fatigued …… all these factors make the blood in a hypercoagulable state. Many passengers on the plane, they are used to sitting in the seat or simply sleep, the lack of exercise makes the blood flow slows down, all factors interact, blood is very easy to form blood clots. In order to arrange the most seats, the distance between the front and back of the economy class seats is very small, which objectively limits the movement of passengers, making passengers in economy class most likely to get deep vein thrombosis, which is historically known as this thrombosis disease in long-distance flights as economy class syndrome. But this in no way means that passengers in first class can rest easy, if not pay attention to prevention, also easy to get blood clots. A survey found that for ordinary passengers, pulmonary embolism may occur after 3 to 4 hours of flight time; the longer the flight time, the higher the risk of deep vein thrombosis and pulmonary embolism. And pregnant women, oral contraceptive pill users, high blood viscosity and other passengers whose blood itself is in a state of high coagulation, are more likely to be favored by the disease. Third, finally, how to prevent and treat deep vein thrombosis? First of all, we should strengthen the awareness, especially the high-risk group of the disease, and raise the vigilance at all times; secondly, we should drink more water to reduce the viscosity of the blood; in addition, we should pay attention to not keep a posture for a long time, and stand up regularly for activities; also, we should avoid smoking and drinking, which are bad habits that can make the blood in a hypercoagulable state. In addition, for those who often make long-distance travel (please note that it is not limited to air travel) friends, there are some additional recommendations: 1, travel clothing and shoes and socks to be loose, which helps blood circulation. 2, the seat is not stuffed with luggage, so that the legs have plenty of space to move. 3, sleep to maintain a comfortable state, do not cross your legs, do not tighten the body, because this will form a squeeze on the blood system. 4. Travelers who are in a hypercoagulable state themselves should consult their doctors before traveling to see if they are fit to travel or what special precautions should be taken, such as wearing long elastic stockings and taking oral anticoagulants. If you find or suspect that you have deep vein thrombosis, you should consult a doctor in time to have the diagnosis confirmed and standardized treatment by a professional. It is not difficult to diagnose deep vein thrombosis by ultrasound, CT, MRI and some related tests of lower limb blood vessels. Treatment methods can be divided into two categories: medication and surgical thrombosis. Drug treatment includes anticoagulants (heparin, coumarin derivatives, etc.), thrombolytic drugs (streptokinase, urokinase) and blood volume expanding drugs (dextran), etc. In turn, the surgical methods can be divided into traditional incisional embolization and endovascular treatment. Among them, endovascular treatment is gaining more and more attention due to its less invasive, high safety and short recovery period. Through the peripheral vein route, a metal stent with a filter is placed into the inferior vena cava using a specially designed delivery device, which can prevent the dislodged thrombus in the deep veins of the lower limbs from entering the inferior vena cava and prevent the occurrence of pulmonary embolism. It provides the most reliable guarantee for the patient’s life safety. Among them, intermittent balloon compression and graded compression elastic stockings have both preventive and therapeutic effects. The former requires a fixed power supply and compresses the legs with regular inflation and deflation sequence of the airbags wrapped around the legs to promote the return of blood to the heart; the latter has a pressure that does not make sense in different parts, gradually decreasing from the soles of the feet to the thighs, which can play a role in driving back the blood when the wearer’s legs are active. Because of its health effects even many people who are not at risk also like to wear.