We have now talked about a clot that forms in the veins of the leg. The Pulmonary Embolism Occurs – The Blood Clot Travels From the Leg Veins to the Lung Where It Is Trapped So as you can imagine, the perfect candidate for developing a clot would be a person that is in bed after a leg injury, unable to do much activity, with a disease such as cancer leading to thicker blood, also taking medicine that leads to a higher likelihood of clot forming. We just talked about the triad that consists of blood more likely to clot, slow flow, and injury to the vein. Pulmonary embolism usually starts with a DVT. You should now have a good understanding of what causes clots to form in the veins known as DVT’s. For this reason, if there has been damage to the vessels through surgery, or if someone has fallen or been hit on the leg, a clot would be more likely to form. When the cells are injured they are more likely to do that. The cells will release chemicals that attract cells that can form clot in an attempt to stop the bleeding.

A good example is if there is injury to the vessel that causes bleeding. These cells can secrete chemicals and send signals if they want certain things to happen. These cells can sense everything from patterns of blood flow to the composition of the blood. The arteries and veins of the body are not just lifeless tubes for blood to flow through they are made of cells that are smart and always active known as the endothelium. These patients are at risk of developing blood clots in their veins and are therefore at risk of pulmonary embolism. Good examples are really long plane flights, or patients that have had surgery and are unable to be active for a while. If you sit still for a long time, blood flow is much slower and of course clots are more likely to form. Every time you stand up or walk, you pump blood through the veins.

For this reason clot is much less likely to form in the high pressure arteries and much more likely to form in the low pressure veins. The clotting factors in the blood need time to work and if the blood is flowing fast they don’t really have time. If you were to take the same blood and pour it down a steep hill it wouldn’t clot because it’s moving fast. If you were to take some blood and pour it into a cup and wait a minute, the blood would form a clot because it’s not flowing. These pills are therefore well-recognized risk factors for clot formation and pulmonary embolism. A good example of this is birth control pills. Certain medicines, diseases or genetic abnormalities, can influence the clotting factors and make the blood more likely to be thick. Of course if the blood is super thick then clots will be more likely to form. Simply put, these can make the blood super thick or super thin. These chemicals known as clotting factors influence the whole process of clot formation. Don’t worry, its not that complicated, I’ll explain below.įirst in the triad was hypercoagulability, this basically means that for some reason the blood is more likely to form clots because of the changes in the chemicals within it. These three things are known as Virchow’s triad.

Firstly is something called hypercoagulability, second is flow pattern and third is injury to the vessel. So why do clots occur? Three things are thought to be critical in clot formation. With an arterial bleed some serious pressure would need to be applied. In fact with a venous bleed you could easily stem the flow of blood with gentle pressure over the skin. If you were to cut one of your veins then blood would certainly pour out, but since the pressure is low it would be nowhere near as fast or forceful as an arterial bleed. Flow in the veins is much slower with a much lower pressure. Once the blood has reached the target organ, it must return to the heart, and it does this through the veins. For that reason if you were to cut your artery, blood would spurt out fast and furiously because of the high pressures in arteries. The blood is pumped with force and the flow in these arteries is fast. Let’s take a little time to explain this in a simple manner so we can understand pulmonary embolism better.Įvery time the heart beats it pumps blood to the body through arteries.

Really where it all starts is that clots form in the veins of the leg known as a DVT, short for deep venous thrombosis. How Does Pulmonary Embolism Start? – It All Starts With A DVT, a Clot That Forms In the Veins of the Leg These specimens are clot that have been surgically removed from the lung arteries in a patient with massive pulmonary embolism.

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