The veins of the human body are divided into two systems, superficial veins and deep veins. The “veins” that we usually 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 both the deep and superficial venous systems is to return the venous blood to the heart after it has been utilized by the tissues. Figuratively speaking, the two are like the body’s sewers, which return the “sewage” to the designated place – the heart. The role of the deep venous system is much greater than that of the superficial venous system. Deep vein thrombosis is the abnormal clotting of blood in the deep veins within the lumen of the deep veins, blocking the vessel. Of all the veins, the deep veins of the legs are the most prone to thrombosis because the veins of the legs are the furthest away from the heart and because the upright position of human beings also results in the venous blood of the legs having to overcome gravity in order to return to the heart. The three main culprits of thrombosis in blood vessels are: high blood coagulation, slow blood flow, and damage to the lining of blood vessels. Blood is not a completely uniform density of liquid, there are many red blood cells, white blood cells, platelets, etc., constantly transporting all kinds of cells from the heart to the periphery, and transporting cells from the periphery back to the heart. In some special cases, the number of cells that need to be transported increases, resulting in a higher concentration of blood, and if the blood flow slows down, the red blood cells, white blood cells, etc. in the blood have a tendency to be deposited in the walls of the blood vessels. Just as the Yangtze River mixed with a lot of sediment to the estuary flat place, the water flow a slow sediment deposition, the formation of the Yangtze River delta this umbrella-type alluvial plains. If there is damage to the inner wall of the blood vessel at this time, it will activate the platelets in the blood to release a variety of substances to start the coagulation system. While repairing the damage, tiny emboli are formed in the blood vessels, which are likely to grow larger and larger, forming life-threatening blood clots. So just what are the signs of a DVT and what are the risks to the patient? After the formation of thrombus, the blood can not return effectively, just like a sewer blockage, sewage can not be discharged, resulting in blockage of the distant blood stagnation, limb swelling; not through the pain, swollen limbs tend to have varying degrees of pain, walking on the ground is more pronounced. Once the thrombus is dislodged, it travels along the blood circulation pathway: inferior vena cava – right atrium – right ventricle, and eventually enters the pulmonary artery, causing pulmonary embolism. The embolism may only cause ischemia in a small part of the lungs, but it is actually like igniting a bomb in an ammunition depot, with explosions coming one after the other in a chain reaction leading to ischemia in a large part of the lungs and loss of blood-gas exchange, often killing the patient. The most typical case is that many patients with a history of being bedridden for a long time, unable to move their limbs or only able to move them slightly, start to get out of bed and increase their activities, then stand up and suddenly cry out “ah”, and then fall down, with tightness in the chest, shortness of breath, accelerated heartbeat, and finally stopping their heartbeat and inhalation. Many conditions can lead to DVT. Risk factors include advanced age, mid- to late-stage pregnancy, malignancy, obesity, varicose veins, paralysis, a history of severe trauma, major surgery on the lower extremities (especially the hip), prolonged bed rest, or heart failure. Without preventive measures, the chance of these patients suffering from calf deep vein thrombosis can be as high as 40%~80%, and the chance of fatal pulmonary embolism is 1%~5%. The prevalence of thrombosis is very high even in normal people who travel long distances by airplane. As mentioned above, high blood coagulation, slow blood flow, and endothelial damage are the three main culprits of thrombosis. During a long flight, the lack of oxygen in the cabin, the repeated circulation of air, and forgetting to drink water when fatigued …… all of these factors make the blood in a high coagulation state. Many passengers on the plane, they are accustomed to sitting in the seat or simply sleep, the lack of movement makes the blood flow slow down, the interaction of all factors, the blood is very easy to form blood clots. The airline in order to arrange the most seats, the distance between the front and back of the economy class seat is very narrow, objectively restricting the movement of passengers, so that passengers traveling in the economy class are most prone to deep vein thrombosis, historically known as this thrombosis disease occurred in long-distance flights for the economy class syndrome. But this in no way means that passengers in first class can rest easy, if you do not pay attention to prevention, also prone to thrombosis. A survey found that: for ordinary passengers, flight time in 3 to 4 hours or more may occur pulmonary embolism; flight time, the longer the passengers occur deep vein thrombosis and pulmonary embolism risk is higher. Pregnant women, oral contraceptives, high blood viscosity and other travelers whose blood is in a state of high coagulation, more likely to be favored by the disease.