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Harvard Commentaries
35320
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School


Healthy Heart Healthy Heart
 

When The Lights Go Out


July 09, 2013

By Thomas H. Lee M.D.

Harvard Medical School


He has always been squeamish, but it’s never been more than part of his charm. He has fainted when having his blood drawn, and gotten very woozy upon seeing the victim of an auto accident.

But now his wife is ill and will need a series of medical procedures. She would like him there with her when possible, but no one wants him to pass out during potentially chaotic moments. What should he do? Stay out of the room? Or go in and risk a fainting spell? And is there anything he can do to reduce the risk?

This dilemma may be unusual, but fainting spells are not. For a small percentage of people, these episodes, called "syncope," can be the warning sign of increased risk of sudden death. For the vast majority of people, however, fainting spells do not have any ominous long-term significance — but can be inconvenient, to say the least.

Most episodes of loss of consciousness are due to a brief fall in blood pressure. During these “low flow” spells, the brain is not getting enough oxygen and sugar to do its work. Without the minute-to-minute supply of these crucial fuels, the brain shuts down. The fainting person slumps to the ground, and the blood pressure is then usually high enough to allow normal brain functions to resume, allowing the person to regain consciousness. This mechanism explains why hardly anyone faints while lying down.

Why does blood pressure fall? There are three main reasons. First, the heart may not be pumping enough blood. In some cases, the heart is going too slow, perhaps because a defect in its electrical system or because of medications. In other cases, the heart may be going too fast, and working inefficiently. Examples might be the sudden onset of atrial fibrillation or another sustained heart-rhythm abnormality.

The second reason that blood pressure may fall is that not enough blood is returning to the heart for it to pump out a normal “cardiac output.” This can happen if people have lost blood due to, for example, dehydration or a bleeding ulcer, or if they have a blood clot blocking normal blood flow, such as a pulmonary embolism (clot in the vessels supplying the lungs). The most common cause of insufficient blood is much more benign — simple pooling of blood in a person’s legs. To get back to the heart, the blood in your legs must be “pumped” by the squeezing action of the muscles surrounding your veins. If you are standing for a long time, the blood can pool there – which is why so many people faint while standing in line.

The third major reason for falls in blood pressure is over-relaxation of the arteries of your body. Ordinarily, when you stand up, the muscles in the walls of your arteries should tense up, making those vessels constrict and increasing your blood pressure, allowing blood to reach your brain. But if medications or emotional factors make your blood vessels dilate, the pressure falls, and the lights go out.

Most people with fainting spells have “vasovagal” syncope, which involves all three of these processes. In the setting of emotional stress, or perhaps simply standing too long in one place, they get the “wrong” combination of processes in their body. Their arteries and veins dilate, so that not enough blood returns to their hearts, and the arteries are too relaxed to keep pressure up. To make matters worse, their heart rate slows when it ought to speed up. Blood pressure falls, and down they go.

Typically, people know when these spells are occurring. They have 10 seconds of warning, during which they feel light-headed, and they can often prevent the actual faint by sitting or lying down. Tensing the muscles in your hands, arms, and legs is also extremely helpful for people who are composed enough to remember this maneuver.

Even if you are pretty sure you have this benign form of fainting, it is a very good idea to discuss any fainting spells with your physician, because there are some more serious problems that can cause fainting, including some heart-rhythm abnormalities and seizures. But most people end up with reassurance from physicians that their fainting is just a vasovagal spell.

Now, back to our light-headed husband. What can he do? Assuming that he really does want to be in the room when his wife undergoes these procedures, here's my advice to him:

  1. Drink a quart of juice and eat a bag of potato chips. The idea is to load up with fluid, so there is no chance of dehydration.
  2. Get some special stockings that put pressure on the calf and thigh muscles. This will help to prevent pooling of blood in the legs.
  3. Have a reclining chair in the room, preferably one in which the legs can be raised to the level of the heart if light-headedness occurs.

Regardless of precautions, he should be prepared for the possibility that, despite these measures, he may faint during the procedure. He should warn the physician and the nurse in the room so they are ready, and remind himself that his physical presence is probably the most important thing to his wife — even if he stays in the recliner!

Thomas H. Lee, M.D. is the chief executive officer for Partners Community HealthCare Inc. He is a professor of medicine at Harvard Medical School. He is an internist and cardiologist at Brigham and Women's Hospital. Dr. Lee is the chairman of the Cardiovascular Measurement Assessment Panel of the National Committee for Quality Assurance.

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