Faint, black out, swoon, happen out. They"re all names because that the exact same thing — a temporary loss of consciousness followed by a reasonably rapid and complete recovery. It"s frightening once it comes the end of the blue, much more so as soon as it happens again and also again. The technological term, syncope (SIN-kuh-pee), originates from a Greek native that means to cut short or interrupt. What"s being interrupted is blood flow to the brain.

You are watching: Why do you pass out if you lock your knees

Key points

Fainting occurs as soon as something interrupts blood circulation to the brain. Although typically harmless, fainting can reason injuries and sometimes signal a difficulty with the love or circulatory system.

If you faint, it"s worth talking through your doctor, especially if over there doesn"t it seems ~ to it is in an explanation for the faint.

Tensing muscle in the legs and arms can sometimes stave turn off a faint; was standing or tilt maintain can assist some people come to be less susceptible to the crossed signal that cause fainting.

Going, going, gone

It is harder for the heart to pump blood approximately the brain than down to the toes. Blood pressure helps get rid of the bottom tug the gravity and push blood to the head.

We have tendency to think the blood pressure as a fairly stable entity. The isn"t. It changes every time you stand up, sit down, bend over, eat, sneeze, go to the bathroom, acquire stressed, relax, or heft a bag of groceries. The person body is design to respond to these shifts and quickly lug blood pressure ago to its normal point. This needs an complex feedback mechanism that involves sensors in the aorta and in the carotid arteries causing the brain. This sensors stimulate a hold of nerve and hormone signal that readjust how rapid the heart beats, just how much blood the pumps with each beat, and also the contraction and also relaxation the blood vessels. However some diseases, part drugs, and also sometimes even aging interfere v these near-instantaneous corrections, bring about temporary autumn in blood flow to the brain.

Unlike many tissues, the brain doesn"t keep energy. Instead, it calls for a constant supply that sugar and oxygen. Halting blood circulation for just three to 5 seconds is sufficient to put the mind into an energy-conserving shutdown. The brain"s signals to nerves and also muscles stop, and also the human slumps come the ground. As soon as the body is horizontal, it"s less complicated for the heart to pump blood to the head, and the brain "wakes up" again.

Many things can reason sudden low flow to the brain that leader to fainting. The causes can be group loosely into two camps: troubles outside the love (noncardiac syncope), i m sorry account for the bulk of faints, and also problems in the love (cardiac syncope).

Getting come the heart of a faint

Figuring out what brought about a fainting assignment is the best way to prevent it indigenous happening in the future.

The most necessary piece of proof is her story of what happened, especially if it can be corroborated by one eyewitness or two. Your summary can indicate a vasovagal reaction (fainting as result of standing too long in the heat, getting a shot, etc.), orthostatic hypotension (fainting as soon as you was standing up), or something much more serious. A physical test is in order no matter exactly how straightforward the story.

An electrocardiogram (ECG) and also echocardiogram are vital tests for examining anyone who has fainted. The echocardiogram can spot hidden troubles in the left ventricle or other creates of structure heart disease that can cause fainting. The ECG can detect irregularities in the heart"s valuation that could be the culprit. Unfortunately, capturing erratic heartbeats in the plot is favor finding the proverbial needle in a haystack. If you have fainted a few times for no obvious reason, and the ECG to be "fine," her doctor might ask you to wear a an equipment called a Holter monitor the continuously documents the heart"s electric patterns for a 24-hour period. Longer-term monitoring deserve to be done v a wearable loop recorder or an implanted recorder. These devices constantly screen the heartbeat however store just the last numerous minutes. Once a fainting assignment hits, you press a switch to frozen the details in the recorder.

Another diagnostic test is the tilt test, in which her blood pressure and heart rate are measured while lying level on a moveable table, and then again once the table is tilted for this reason you room almost, yet not quite, stand upright.

Noncardiac causes

The most common reason because that fainting arises from crossed wires in between the mind and the part of the nervous device (the vagus nerve) the regulates blood pressure and heart rate. In response to some trigger, the blood vessels in her legs relax, making it complicated for blood to return to the heart. Blood begins pooling in the legs. To make matters worse, the love slows down just when it need to be speeding up. Blood pressure drops, and also so execute you. Root cause can range from fear, pain, or intense emotional stress and anxiety to having blood drawn or stand for too long. Less typical triggers encompass sneezing, going to the bathroom, lifting weights, a shirt collar rubbing versus the side of the neck, and also even play a brass instrument.

Some human being have faint-inducing autumn in blood pressure as soon as they get out that bed or wake up from a chair (called postural or orthostatic hypotension) or after eat (called postprandial hypotension). To recognize postural hypotension, imagine your body as a pipe of fluid. Once you lie down, the fluid distributes itself reasonably evenly indigenous head to toe. When you stand up, gravity pulls blood downward. Up to a quart of blood pools in the legs (that"s around one-fifth the full in the average adult), reduce the amount the is went back to the heart. The next few heartbeats deliver less blood 보다 usual, therefore blood push plummets. Standing after sitting has actually much the exact same effect. Dehydration can contribute to orthostatic hypotension, or sometimes even reason it. A similar thing happens after eating. Together the body directs extra blood toward the stomach and also intestines to aid digestion, less is obtainable to the heart, bring about blood push to fall.

Cardiac syncope

Fainting brought about by problem in the heart is much more worrisome 보다 noncardiac syncope. Rhythm difficulties are the most common culprit here. The heart may beat too slowly (bradycardia) due to the fact that of a defect in its electric system or the influence of medications. That can likewise beat too rapid (tachycardia) since of a valuation disorder such as atrial fibrillation or ventricular tachycardia. The last is especially dangerous, due to the fact that it can turn right into ventricular fibrillation, the most common cause of suddenly cardiac arrest.

Anything that obstructs blood circulation through the love can also lead to fainting. It might be a blocked or severely narrowed love valve, a big blood clot, or also a tumor in the heart. Various other cardiac reasons of fainting encompass a severely enlarged heart (hypertrophic cardiomyopathy), a tear in the aorta, love attack, or damages to the heart muscle.

Squeezing far a faint

*

If you feel lightheaded or feel prefer you could faint, try crossing her legs and also tensing the muscles in the reduced body, squatting and also tensing, or contracting the muscle in her arms through clasping your hands and also pulling. Each of this maneuvers can boost blood pressure. It can be enough to protect against the pass out in that is tracks, or it could just give you time to lie under or move to a safe place.

Illustrations by plunder Flewell, v permission native the Journal of the American university of Cardiology.

Fighting a faint

Most world get a couple of seconds the warning that a vasovagal pass out is ~ above its way. They turn pale, end up being dizzy or lightheaded, and may feel nauseous or an outbreak in a cold, clammy sweat. This at an early stage warning is sometimes enough time come nip a pass out in the bud. Sitting or lied down frequently works, together does the proverbial "sit down and put her head between your knees." Tensing the muscle in your hands, arms, and legs (see "Squeezing away a faint") can also help those who space composed sufficient to remember this maneuvers.

It may additionally be feasible to train your body come fight faints. Writing in the may 12, 2009, Journal the the American university of Cardiology, Drs. David G. Benditt and John T. Nguyen of the university of Minnesota medical School define an exercise called tilt training. It requires standing with your back against a wall surface while her heels are around six inches native the wall surface (see "Tilt training").

If you know you will be in a situation in i beg your pardon you might faint — say you often tend to pass the end at the vision of blood but your daughter desires you come be through her once she offers birth to your very first grandchild — right here are a couple of things to perform beforehand:

Drink a quart of juice and eat a bag of potato chips. The idea is to load up with fluid, so over there is no possibility of dehydration.

Get some special stockings that put pressure on the calf and also thigh muscles. This will help to stop pooling of blood in the legs.

Have a reclining chair in the room, best one in which the legs deserve to be increased to the level of the love if light-headedness occurs.

Tilt training

*

Some world can teach your bodies to overcome neurally mediated syncope, caused by overcome signals in between the mind and the worried system. Stand v your back lightly against a wall while your heels are about six inches (15 centimeters) from the base of the wall. Perform this for 3 to five minutes there is no moving, twice a day. Every couple of days, add a minute or so to the stand time until you can do 20- to 30-minute sessions without feeling faint. ~ that, try to do 20 minutes of wall surface standing 3 to four times a week. It"s ideal to perform this in a carpeted room, and also to have someone through you in instance you faint.

See more: How Long Can Turkey Stay Frozen Turkey Last? September 2021 September 2021

Don"t take it it lie down

Most the the time, fainting is a not authorised — despite disconcerting — event. Sometimes, though, especially in enlarge people, it can be a warning sign of a possibly dangerous heart problem. For that reason, always let your doctor know if you"ve fainted, also if you think it to be nothing to problem about. It"s better to be reassured it was "just a vasovagal spell" than to skipping something the could reason a more serious trouble down the road.