FAMILY MEDICINE® COLUMN
By John C. Wolf, D.O.
Associate Professor of Family Medicine®
Ohio University College of Osteopathic Medicine

BLOOD CLOTS IN THE LUNGS USUALLY START IN LEGS

Question: I became so short of breath a few weeks ago that I went to the hospital. The doctor in the emergency department determined that I had a pulmonary embolism as the cause of my shortness of breath and admitted me to the hospital. I'm home now and feel fine, but I still don't understand exactly what a pulmonary embolism is. I know it is something to do with a blood clot in the lungs, but how did it get there and how did it make me so short of breath?

Answer: We doctors have a complicated vocabulary that isn't always the best for clearly explaining health problems to non-physicians. Any place you see the term "pulmonary," as in "pulmonary embolism," you can accurately substitute "lung." The term "embolism" is used as medical shorthand to save writing out the following definition taken from my American Heritage Dictionary: "An embolism is a mass, such as an air bubble, a detached blood clot, or a foreign body, that travels through the bloodstream and lodges so as to obstruct or occlude a blood vessel."

Next, I want to remind you of the workings of normal lungs. As I'm sure you know, the lungs are the organs where the body picks up oxygen from the air and releases waste carbon dioxide. This exchange of gasses occurs in the tiny "air sacks" of the lungs, called alveoli. The alveoli are surrounded by capillaries the smallest of blood vessels. The capillaries bring oxygen-poor but carbon dioxide-rich blood to the alveoli and carry away oxygen-rich blood to the heart's left side chambers from which it is pumped to all other organs of the body.

In your condition, pulmonary embolism (PE), a small blood clot becomes mixed with the normal blood that is being pumped by the heart. After leaving the heart, the clot ultimately encounters a lung capillary or larger branch of a pulmonary artery that is smaller in diameter than it is. The clot, therefore, effectively plugs up that part of the circulation to the lung. These small blood clots, or emboli, typically break off from clots within the veins deep in the upper legs. Because the clot is small, it can pass from the legs back to the heart without difficulty.

Blocking part of the blood supply to the lung doesn't initially keep the alveoli in the region of the lung from filling then emptying with air. However, it does prevent them from exchanging carbon dioxide for oxygen because the oxygen-poor blood can't reach them.

When a PE affects a relatively small area of the lung, it causes a sense of being short of breath, just as you described. It is also common to have a fast heart rate and a sense of anxiety or dread with a PE. When there are a number small clots or a few larger ones, a greater percentage of the lung's circulation is damaged. This causes chest pain, fever, coughing up blood, fainting, and can even bring on sudden death in the most severe cases. Fortunately, these severe pulmonary emboli are uncommon.

Pulmonary embolism is a potential complication of blood clots in the leg veins a condition called thrombophlebitis. Thrombophlebitis is more common in people who have had hip or knee surgery or cancer treatments. Also at greater risk are pregnant women and those who use birth control pills, as well as people who have congestive heart failure or other conditions that cause physical inactivity and debility. The risk of having subsequent attacks of PE are directly linked to these risk factors. I'm sure that your doctor has talked with you about your risks and the things you should do to minimize them.

Family Medicine® is a weekly column. To submit questions, write to John C. Wolf, D.O., Ohio University College of Osteopathic Medicine, Grosvenor Hall, Athens, Ohio 45701.