Too Much of a Good Thing by Lee Goldman

Author:Lee Goldman
Language: eng
Format: epub
Tags: Science / Life Sciences / Evolution, Science / Life Sciences / Biology, Health & Fitness / Diseases / General
Publisher: Little, Brown and Company
Published: 2015-12-07T16:00:00+00:00

Too Much Clotting

Just as too few clotting proteins or platelets can lead to excessive bleeding, too many clotting proteins or platelets can lead to excessive clotting. These clotting tendencies, often inherited but also commonly found in pregnant women and in some people with cancer, especially predispose us to clots in our veins.

Blood flows more slowly in our veins than in our arteries, and any vein has the potential to clot and cause problems. For example, blockage of the veins that drain the kidney raises pressure in its capillaries, and the resulting damage can cause severe kidney dysfunction. Clots in key veins draining blood back from the brain to the heart can cause severe headaches, strokelike symptoms, and seizures.

But by far the most common site for vein clots is in our legs. The reason is pretty simple—in our leg veins, blood has to flow uphill, against gravity, back to the heart whenever we’re standing or sitting, and it also needs to deal with kinks in the veins when we’re sitting. For example, about 3 percent of us will develop detectable blood clots in our legs after an eight-hour plane trip, and the risk goes up if the flight is even longer. Muscle activity in our legs serves as a bit of a pump, even though the resulting pumping action is only about 5 percent as strong as the forward pumping by the heart muscle. Fortunately, that 5 percent is enough to keep blood flowing smoothly if our leg muscles remain minimally active—for instance, when we flex our calf muscles or get up and walk around even briefly.

When clots form in superficial leg veins that we can see, we call them varicose veins. Fortunately, varicose veins usually cause nothing more than cosmetic embarrassment and mild discomfort. By comparison, clots in the larger, deep veins, developing either on their own or by extension from a superficial vein, can get a lot bigger and can cause substantial discomfort and even swelling of the leg. But what’s especially dangerous is if a piece of one of those larger clots, especially a deep clot that began or has extended into the thigh, breaks off and travels through increasingly larger veins back to the right side of the heart. Typically the clot will pass easily through the right atrium and right ventricle into the pulmonary artery. However, as the branches of the pulmonary artery become progressively smaller, the clot will lodge and obstruct blood flow to the lung. This serious and sometimes even fatal complication is called a pulmonary embolism.

Although clots in our veins can be dangerous, clots in our arteries, which take blood from the heart to all our organs—much more rapidly and under much higher pressure—are even worse. In our arteries, even an otherwise perfectly normal clotting system can get activated despite perfectly normal flow—not because of a true laceration of a blood vessel but rather because of damage to the single layer of cells in its protective inner lining. And by far the most important underlying explanation for such damage is atherosclerosis.

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