Pass on the smelling salts

September 26, 2007 11:14 PM

Why do people faint? What are the physical/psychological causes of fainting? and also, can you faint on purpose? How?
posted by barrakuda to health (21 comments total)

Low blood pressure is one physiological cause of fainting. Anxiety and/or stressful situations can be psychological triggers, and hyperventilating can make you faint.
posted by parkerama at 11:38 PM on September 26, 2007

I doubt anyone can do it on purpose. But someone could fake it.
posted by Steven C. Den Beste at 11:54 PM on September 26, 2007

I have 'positional hypotension' and I pass out when standing up too quickly, especially if I'm dehydrated or hungry or it's right after sex (I can't really explain that one beyond there being too much blood the lower extremities and not enough in my head :)... My blackouts range from loss of vision and ringing in the ears to full on WHAP! oh shit, I'm face down on the floor blackouts. Apparently, it's nothing to worry about, says the doc.

If I concentrate on the act of standing up, I won't black out-- I only lose it if I'm not paying attention. I've tried and never been able to jump up quickly and cause myself to pass out, because I'm aware that a faint might be coming!
posted by jstef at 12:05 AM on September 27, 2007

The medical term of fainting is "syncope." The WP article on 'vasovagal sycope' (one of the more common causes for fainting) is pretty good. From that page, explaining the Bezold-Jarisch Reflex:

Prolonged upright posture results in some degree of pooling of blood in the lower extremities that can lead to diminished intracardiac volume. This phenomenon is accentuated if the individual is dehydrated. The resultant arterial hypotension is sensed in the carotid body baroreceptors, and afferent fibers from these receptors trigger autonomic signals that increase cardiac rate and contractility. However, pressure receptors in the wall and trabeculae of the underfilled left ventricle may then sense stimuli, indicating high-pressure C-fiber afferent nerves from these receptors. They may respond by sending signals that trigger paradoxical bradycardia and decreased contractility, resulting in additional and relatively sudden arterial hypotension.

Here's my translation of that (though I'm not an M.D.): if you're standing or sitting in one place for too long, particularly if you're dehydrated, blood can pool in your legs and lower abdomen. This is bad because then it's not available to do its job, namely carry oxygen around. Your body notices the lack of blood via pressure receptors (think of the oil pressure gauge in a car), and initially tries to compensate by making your heart beat faster. But when that doesn't cause the problem to resolve itself, your body slows the heart down very suddenly, actually dropping your blood pressure even further -- sending a message to the brain in a very direct way. The result is that your brain does a sort of panic-stop: it sends out a signal to relax everything, everywhere. The result is a loss of consciousness (due to low BP) and you hit the floor.

I've heard it said that syncope is thought to be a survival mechanism; a way for your reptilian brain to override whatever stupidity your higher brain is doing and get you horizontal, quickly -- because arranged horizontally, it's a lot easier for your heart to move blood around from your legs to your brain.

And yes, it's possible for some people to make themselves faint, if you really try hard. Ironically, the way most kids try to do it (by holding their breath) doesn't work. The easiest way to make yourself pass out is to hyperventilate for a while, then take a big breath and hold it. In some people, this can cause a blackout, although I'm not sure the mechanism is exactly the same as the vasovagal syncope described above. (There are occasionally reports of drowning or near-drowning due to this, usually with people trying to stay underwater the longest; you hyperventilate, then take a deep breath, hold it, and dive underwater where the pressure of the water on your chest adds to it somehow ... where you promptly pass out. Ouch.)*

I'm not 100% sure of why the hyperventilation thing causes syncope (and to clarify, it won't do it all the time, or to everyone). I have a dim recollection of it having to do with blowing off your blood CO2 (your breathing drive is linked to your CO2 level, not your O2 level) so that your heart and lungs basically decide to take a break, causing your BP to drop very quickly, causing the syncope response from the brain.

* This is called "diver's syncope" or "shallow-water blackout syndrome." Incidentally, the second link confirms my thoughts about it being related to CO2 blowoff during the hyperventilation phase.
posted by Kadin2048 at 12:19 AM on September 27, 2007 [1 favorite]

I have postural hypotension too, though not as severely as jstef. I've heard variations of the hyperventilate, then get a bearhug (or stand up quickly) to make yourself pass out. I did make myself pass out with the standing up move. Luckily I didn't injure myself, since it's a pretty dumbass thing to do. I saw someone do the pressure on the chest variant to a friend back in college. It only lasts a few seconds, as opposed to being knocked out cold.
posted by O9scar at 12:21 AM on September 27, 2007

We used to use the hyperventilation trick back in high school. Knocked each other right out, every time.

(That's all I've got. Anecdotal info on the second part of your question.)
posted by routergirl at 12:25 AM on September 27, 2007

I fainted once. I was in a bar/restaurant and had eaten dinner along with two Spanish coffees. While chatting with Mr. Adams, I suddenly felt unnaturally hot, like it was stifling in the room. I excused myself to go to the ladies' to splash some cold water on my face. As I arose, the room took a somewhat orange-y hue. Next thing I knew, I was looking at the ceiling and folks were gathered around me. At the ER later, all they could surmise was that I'd been dehydrated. About six months later, I was dx'd with Antiphospholid Antibody Syndrome, a condition that causes blood clots, and my rheumatologist believes that that's what caused me to faint.

When I was a kid, the rumor was that if you held your breath and did somersaults, you could make yourself faint. I never tried it, thought.
posted by Oriole Adams at 12:41 AM on September 27, 2007

can you faint on purpose?

Yikes, yes. When I was in elementary school, we used to play the "fainting game"... We'd breath in and out very deeply (essentially forcing ourselves to hyperventilate), and then hold our breath until we passed out... We always had a friend, or friends, with us, who would make sure we were revived... It was very weird, and we thought it was "cool," but I certainly wouldn't recommend it to anyone.
posted by amyms at 12:51 AM on September 27, 2007

The main physical reason for fainting is lack of oxygen going to the brain. As previously mentioned, you can either lower the amount of oxygen in the blood by hyperventilating, or reduce the amount of oxygen getting to the brain. Low blood pressure can cause fainting, or "dizzy spells" - my aunt used to have this problem.

One of the reasons you fall down when you faint is to make it easier for blood to flow back to the brain. It's not fighting against gravity.

When I was at school, we used to make ourselves faint al the time. The technique was this - crouch down, and hyperventilate. Then stand up, and right away have someone squeeze your neck. They would put their wrists together and form a "v" shape with their hands. The point of the "v" would go over the adam's apple, the fingers would curl round the neck, and they would squeeze.

Worked like a charm every time. I do not recommend that you do this.
posted by Solomon at 2:10 AM on September 27, 2007

See, this is why kids need drugs.

We used to do this (make each other pass out) when we were too young to just go buy pot or play "hey mister." I swear that after that, simply getting up too fast had a totally different feeling to it.
posted by GooseOnTheLoose at 2:28 AM on September 27, 2007

Variation on making yourself faint: you hyperventilate, let out all your breath, and then you lean against the wall and someone pushes hard against your chest. I let myself get talked into this once and the person who was supposed to catch me, did not. As mentioned, it only lasts a few seconds.

I used to get the fainty feeling when standing up a couple of times a year -- mostly it was tunnel vision, and a couple of times I fell down. Then a few years ago I stopped smoking and started eating meat again and since then it hasn't happened. It's probably due to quitting smoking, I always felt like nicotine fucked with my circulation.
posted by creasy boy at 3:36 AM on September 27, 2007

i remember being in choir as a kid and the choir director impressing upon us not to lock our knees, because we would pass out. apparently this is not uncommon. i guess the posture impedes proper circulation after a while?
posted by thinkingwoman at 4:22 AM on September 27, 2007

I can make myself faint, whenever I want to, of course I never *want* to, and it always happens at bad times.
Of course, I have neurocardiogenic syncope...or positional orthostatic tachycardia, they really can't seem to decide. My last tilt table test took me 9 minutes to go down.

It's pretty interesting, my BP goes from about 110/60 or so to about 50/35, then right before I go down it shoots to about 190/140, and then I hit the floor. Pulse goes from ~55 or 60 to about 25 or 30, then back up to about 140.

Pretty certain I have neurocardiogenic syncope, which is basically that the bloodvessels in my legs dilate instead of contract when I change position rapidly, so the blood pools in my legs, and that causes the sudden drop. By the time my body realizes it, it jumps it up and BOOM I'm out.
posted by TomMelee at 4:24 AM on September 27, 2007

I have the stand up fast when hungry/dehydrated dizzy faint thing. It's a complete mindfuck. I sort of like it. I feel like for 30 to 45 seconds my sense of reality is fractured.
posted by corpse at 4:50 AM on September 27, 2007

Every so often when I am on the first day of my period I faint. Not fun, especially at work. It can happen when I am standing but more often when I am sitting (usually with my head between my kness because I can feel it coming on and I always try to avoid it.)
posted by saucysault at 5:54 AM on September 27, 2007

You can faint on purpose, as amyms said. The fainting game was popular when I was in grade school. A while ago I was wondering if it was possible to administer a blood choke such as a sleeper hold to yourself. I didn't follow through but my field of vision narrowed and I was starting to see sparkles. Obviously you can't apply a reverse naked choke to yourself but if you think about the mechanics that occur you can figure out how to do it.
posted by substrate at 6:53 AM on September 27, 2007

I, too, have neurocardiogenic syncope (or had it--I haven't hit the floor in a while, thankfully), though I should point out that it can present very differently in different people. My particular brand of fainting seemed similar to the survival instinct of fainting goats (even though they don't really faint)--induced by sudden pain or stress (a sharp hit to the funny bone, dehydration, panic, etc.), which would somehow trigger a sudden drop in my blood pressure. Apparently, this is more common in women, especially those who've had large growth spurts during teenage years.

A caution to those inducing fainting: eventually, my fainting spells began to include convulsions (no, it wasn't epilepsy, definitely just n.c. syncope).
posted by eralclare at 8:25 AM on September 27, 2007

On a long and uneventful bus trip in track season my friend choked out another kid with a sleeper hold, which did cause him to lose consciousness. My friend immediately let go of him. I believe that kind of fainting is due to a loss of blood pressure in the brain.

My girlfriend has vasovagal syncope, and during long (3+ hour) volleyball practices, she would become dehydrated and pass out. It is apparently when blood circulates through your legs and not your head, where it's needed.
posted by trim17 at 9:43 AM on September 27, 2007

I've had vasovagal syncope since high school (10 years ago) and every now and then i'll faint. curiosly, this has happened 4 times at gigs, and for a long time i thought it was just due to overheating, combined with the intense emotional content of the music. It has happened twice at Dirty 3 gigs, and they produce some amazing hypnotic, evocative instrumental music.

turns out i've just got circulation problems. I found out about vasovagal syncope through watching Scrubs.

The symptoms i get are pretty cool though, and i usually have at least 5 minutes warning to get out of wherever i am, get some air and get on the floor, so ican usually avoid actually fainting.
posted by robotot at 3:42 PM on September 27, 2007

As for fainting on purpose: google "fainting game" or "choking game" for a ton of articles about kids deliberately making each other faint. Some of the articles are scare-tacticky, some are more science-based -- either way, depriving your brain of oxygen isn't something to mess with.
posted by LobsterMitten at 3:44 PM on September 27, 2007

I had a bunch of friends who did this back in high school and video taped it. One time they decided to let one of them fall down (figuring they'd just slump). He went off the side of the door jam, crashed through a glass table with his ass and his head bounced off the floor with a concussion.

It's on my youtube.
posted by Brainy at 10:42 PM on September 27, 2007