why do people faint when giving blood
Getting dizzy and fainting at the sight of someone else's blood doesn't seem to be the most, uh,
evolutionarily appropriate response. How's that going to help you when you're trying to take down a buffalo? And despite it being relatively common--3 to 4 percent of people suffer from blood phobia or a related disorder--the symptoms of it are totally different from most phobias: phobics' blood pressure and heart rate will rise then drop when they see blood, as opposed to the just-heart-racing caused by most fears. So what gives? John Sanford at Stanford Medicine has. Here's what that fainting/nausea/dizziness response is: This is a vasovagal response. The vagus nerve, a component of the parasympathetic nervous system, meanders from the brain stem through the neck, chest and abdomen. It helps to control involuntary "rest and digest" functions, such as lowering heart rate and promoting the secretion of gastric juices. But when it overreacts в in response to hunger, dehydration, standing up quickly, standing too long, intense laughter, sudden fright, severe coughing, pain, vomiting and, of course blood, among other triggers в it causes a vasovagal response, which does not generally occur with other phobias.
Turns out, there are a few theories on why we might respond like this, from it being a way of "playing dead" in dangerous situations to low blood pressure keeping you from bleeding out after you've been cut. (There appears to be some kind of hereditary relationship with the phobia, so there's at least some reason to put stock in that theory. ) As Sanford found out, there are specialists dedicated to ridding people of their phobias. By clenching their muscles while being systematically exposed to stimuli, phobics can learn to handle the symptoms. Doctors have phobics tense up, and slowly expose them to more and more realistic versions of blood--first a dot, then a red dot, then a photo of blood, etc. --until the phobics are looking directly at blood without fainting.
The exposure technique is used for treatment of other fears like, say, arachnophobia, but the tensing specifically counter-acts the drop in blood pressure caused by blood phobia and similar disorders. It's proven to be a surprisingly quick and effective treatment for the phobia. Good news if you're looking to donate blood (or hunt buffalo without passing out). During a full blood donation, a person gives 450 ml of blood. That is about 10 percent of an adults blood volume. Giving this amount is safe and doesnt typically cause any ill effects. Infrequently (e. g. 1 percent of donations at our Blood Centre) the donor may experience side reactions during or after the donation: weakness, dizziness, cold sweat, fainting and other symptoms). Risks of adverse reactions can be increased by: emotional stress (anxiety about the procedure, seeing blood or other donors giving blood) Fainting or a feeling of faintness or dizziness can be caused by a drop in blood pressure.
Always make sure you are healthy, rested and have eaten before you give blood. Remember: to drink plenty of fluids before and after giving blood, including on the day after making a donation; to prefer lean and iron-rich food (red meat, liver, dark greens and colourful vegetables etc); if your blood pressure tends to be low, eat saltier food increase your salt intake before and after the donation, as this will help raise your blood pressure; to consume plenty of fluids after giving blood as well; the Blood Centre offers complimentary tea, coffee and juice. And nibble on snacks sweet cookies and salty biscuits; to rest after giving blood, before you go on with your everyday activities, and let your body get used to the lower blood volume; its advisable to avoid strenuous physical exertion on the day of the donation and the following day (working out, saunas, swimming) on the day you give blood and the day after.
Fainting while giving blood is usually caused by psychological factors, however. To prevent this: the Blood Centre worker is by your side throughout the procedure and ready to help you if needed. Tensing your muscles also keeps blood pressure from dropping: squeeze a rubber ball, periodically contract your gluteal and leg muscles. After giving blood, you may feel faint if you stand up abruptly or if you have been standing for a long time. If you feel that you are getting weak, then to avoid fainting: do exercises using your muscles: cross your legs, tense your muscles all over your body or your gluteal muscles this will keep blood pressure from dropping; if possible. lie down and elevate your legs; consume salt (salty biscuits at the Blood Centre, salty meal after leaving the centre); consume fluids. We hope that your donation is a pleasant experience and free of adverse effects.
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