These triggers set off a reflex in our nervous system that causes our hearts to paradoxically slow down instead of speed up and our blood vessels to dilate instead of constrict. Blood pressure and brain blood flow plummet, causing us to faint.
Excessive heat plays a role, too, as it makes it more difficult for the body to maintain blood pressure. With the weather warming across the country, now is a good time to know the signs and symptoms that lead to fainting. As a physiologist, I can offer some pointers.
Blood Pressure Regulation
Physiologists, neurologists, and cardiologists have long studied how people regulate blood pressure and maintain consciousness while standing. When we stand up, there is an immediate decline in blood pressure, and the body must respond to this decline. The normal response includes constricted blood vessels, increased heart rate, and the release of various hormones into the bloodstream.
Together these responses help to maintain blood pressure. By protecting blood pressure, our oxygen-thirsty brain ensures that it will continue to be adequately nourished. Usually the response is flawless, and we can stand without any trouble.
But various triggers can mess up this finely tuned response, and the summer heat makes it more challenging to regulate blood pressure.
Ultimately, if blood pressure is not maintained, brain blood flow will decline. The fancy term for this is cerebral hypoperfusion, the defining characteristic of fainting, whatever the cause or trigger.
The symptoms that precede fainting, also called syncope, vary, but may include sweating, nausea, paleness, and abdominal discomfort.
Who Is Vulnerable?
Soldiers standing guard for long periods in the heat without moving can have excessive pooling of blood in their legs, which can trigger a faint. But simply shifting weight from one leg to another will contract the leg muscles and propel blood toward the heart and head. This will usually prevent a severe decline in blood pressure.
Astronauts returning to Earth after a sojourn in space are especially sensitive to gravity. When they first return to Earth, many astronauts cannot stand for more then a few minutes without experiencing syncope. Fortunately, this is resolved once they become reaccustomed to Earth’s gravity over the following days.
Sometimes extreme emotion elicits a faint–think Aunt Pittypat swooning in “Gone with the Wind.”
Other triggers include experiencing pain, seeing blood, or watching a medical procedure. Also, anything that depletes the body of fluid can increase the risk of fainting. This includes dehydration, diarrhea or diuretics (water pills).
Some Health Conditions Can Pose a Risk
Life-threatening issues involving the heart are also a cause of fainting.
Abnormal heart rhythms that are too slow or too fast can cause a faint. These abnormal rhythms dramatically decrease the blood pumped out by the heart, which causes blood pressure and brain blood flow to decrease.
Structural heart problems (cardiomyopathies) are sometimes the cause of these abnormal heart rhythms. Other times, inherited disorders related to faulty ion channels in the heart cells (channelopathies) are a cause. Fortunately, these are rare.
For reasons not completely understood, women faint more than men. And the economic burden of syncope is high: Direct hospitalization costs in the United States can total $3 billion per year.
Preventing a Faint
Can you prevent a faint? Sometimes. Here are some tips: Stay well-hydrated, avoid extreme temperatures (including long hot showers), and avoid fasting for too long.
When standing, be sure to shift your weight from one leg to another, and if you begin to feel woozy, cross your legs and clench the muscles in your buttocks and legs. This really can help to prevent a faint. Also, avoid drinking alcohol, hyperventilating, or suddenly changing your posture.
If you faint, be sure to consult a health care provider. Determining the cause of fainting is not always easy.
If fainting occurs more than once, your health care provider may recommend increasing salt and water intake, and may prescribe medication to help manage symptoms. Exercise training is also often recommended. While fainting is often benign, especially in younger patients, it is important to get checked out.