Blood clots in the lungs can cause a number of symptoms that can appear in patients suddenly or develop slowly over time. This condition, also known as pulmonary thromboembolism or pulmonary emboli (PE), most frequently causes problems with breathing. It can also cause chest pain, irregular beating of the heart, and even sudden death in some cases. Often, blood clots found in the lungs actually originate in the veins of the legs; as a result, many affected patients also have redness and swelling in one of their legs.
One of the most common symptoms of blood clots in the lungs is difficulty breathing. Many people have shortness of breath and feel like they can't take in enough air. The feeling often causes the person to breathe more quickly, a condition also known as tachypnea.
Other symptoms can involve other parts of the body. Patients often have tachycardia, or an increased heart rate. Some people may develop a low-grade fever in response to the blood clot. Additionally, some patients can have a sharp, stabbing chest pain that is more severe when they take in a deep breath.
Occasionally, a large blood clot to the lung, called a saddle embolus, can significantly block the flow of blood. This can cause severe symptoms such as chest pain, weakness, and heart beat irregularities. The stress that this state causes can prevent the heart from pumping blood throughout the body and can be fatal.
Swelling in one leg can also be a symptom of or precursor to a blood clot in the lungs. Blood clots can develop in the veins of the legs due to a condition called deep vein thrombosis (DVT). The blood clot, or thrombus, may break off and travel to the lungs. The symptoms of a DVT can include leg redness, leg swelling, and pain, typically only in one leg at a time.
Symptoms can be less severe in patients who chronically have small clots in their lungs, as compared to people who have one large clot. Instead of experiencing the sudden onset of shortness of breath and chest pain, those with small clots can have a progressive onset of increased breathing difficulties. At first they might only feel short of breath when exercising, but with the progression of the disease, they may have trouble breathing even at rest.