7 ms·

Mouse experiments reveal the brain-heart connections that cause fainting

124 points by birriel 3y ago

daoboy 3y ago
"researchers have discovered a neural pathway, which involves a previously undiscovered group of sensory neurons that connect the heart to the brainstem. The study, published in Nature on 1 November1, shows that activating these neurons made mice became immobile almost immediately while displaying symptoms such as rapid pupil dilation and the classic eye-roll observed during human syncope." Very cool. I did not check to see if the authors of this paper are affiialted, but reserchers contributing to data at the NeMO Archive (https://nemoarchive.org/ https://nemoarchive.org/) have recently discovered over 3000 different types of cells in the brain, most of which are in the brain stem. This has added a whole new layer of complexity to explore. Exciting times to be involved in neuroscience!
plasma_beam 3y ago
A couple years ago I took my kids to get a flu shot at a CVS. 30 seconds after my oldest had gotten his shot I felt him go limp standing against me and he collapsed against me and went to the floor. Sheer panic immediately set in and I was on the floor with him calling his name while he ever so slightly convulsed and came to wide eyed 10 seconds later. The CVS employee was the utmost professional, he calmed me down, repeated this is normal, and had me hold his head and legs as he came to. He put my son in a chair, had him sit there for a while and 20 mins later we were in the car. I felt bad when my son actually apologized to me when I told him how terrified I’d been.
- BrianB 3y ago
  I've fainted more times in my life than I'd care to admit. After a while, it's not the 'blood' you are afraid of. Instead it's the idea of fainting and causing a scene that becomes the source of anxiety. For me, anyway.
  - mfwit 3y ago
    This. So much this. Fainted for the first time, because of a nose bleed, in front of my high school physics class, literally.
  - Fire-Dragon-DoL 3y ago
    Sadly agree. I wish I could control it
    - 0x00_NULL 3y ago
      Nothing to be ashamed of. Your Vagus Nerve, the main signaling nerve for your autonomic system, can go off automatically and there’s nothing you can do to stop it. When it happens, sit down in a chair. If you can lean back and put your feet up, that’s better and the episode will resolve more quickly. These episodes will come and go quicker as you are prepared for them. My wife has had to these for years. The only treatment we’ve found helpful is transcutaneous vagus nerve stimulation (tVNS) with a tool like a Neuvana Xen - or you can go the expensive prescription route. We were actually treating her gastroparesis with this and found that modulating the signal worked for all sorts of misfirings - like when getting shots. TLDR: You can’t avoid them, but you can mitigate them by sitting in a chair, leaning back, and bringing your feet closer to your heart. If anyone is watching, it just looks like you are trying out the recline function of the chair. If your Vagus Nerve issues are bad, you can try tVNS (under the supervision of your doctor, of course).
      - derefr 3y ago
        Oddly, putting my feet closer to my heart (such as when washing my lower legs in the shower) seems to unplug my sinuses if they’re plugged. Related mechanism?
        jjulius 3y ago
        Would this be because your head is closer to your feet, or (and correct me if I'm picturing this wrong) because you're putting your head upside down?
- leethomas 3y ago
  They said it's normal to faint after receiving a flu shot? Hasn't heard of that happening to people before. What was the explanation?
  - toast0 3y ago
    Normal maybe isn't the right word, but it's an expected possibility, the FDA has a page about it [1], and that's one reason FDA recommends patients be observed for 15 minutes after a vaccination, especially for types they haven't had before. [1] https://www.cdc.gov/vaccinesafety/concerns/fainting.html https://www.cdc.gov/vaccinesafety/concerns/fainting.html
    - snvzz 3y ago
      Somewhere in EU, I (and everybody else) was told to wait 15m before leaving the area after the vaccine. This is no doubt because of the possibility of such events.
  - deleted 3y ago
    [deleted]
  - V__ 3y ago
    It's not the shot itself, it's the injection/getting stabbed. I think I fainted four or five times in my life due to injections/blood draws. I have to lay down look away and control my breathing otherwise I'm gone. It is a pain in the ass and I get light anxiety from it.
    - Fire-Dragon-DoL 3y ago
      Same. I also realized I can't get acupuncture due to this, I will just faint
      - derefr 3y ago
        I’m curious if there’s a refractory period. (I.e. if you faint and come to after the first needle goes in, then maybe you’re “past it”, and the rest won’t bother you?)
- miriam_catira 3y ago
  Yep, fainted so, so many times... Always seems to happen after getting hurt on or near a nerve for me - or after a blood draw. Was scary the first time, embarrassing and annoying every time since then. :) Had a nurse explain that the best way to prevent it is flexing / tightening the legs, to force the blood up out of them. Seems to work, at least for me.
  - BrianB 3y ago
    That works for me too. A cardiologist told me it is because it gives your body a reason to keep the blood pressure higher. He also advised drinking lots of water every day.
  - Fire-Dragon-DoL 3y ago
    Is it while standing or laying down? I don't faint if I lay down. Also if I pass a crisis without fainting, I get immunity for a good while
  - teeray 3y ago
    Fighter pilots are trained to contract their solar plexus by making a “hut” sound to do something similar when they’re passing out. I was going to try this the last time I was fainting after a blood draw, but was interrupted by the phlebotomist imploring me to breathe slow and deep—I think this just sunk me further into it.
    - lukas099 3y ago
      Valsalva maneuver against a closed glottis. As someone prone to blacking out when standing up or after a set of heavy squats, figuring this out has been very useful to me.
- imetatroll 3y ago
  I became faint, I would say, after I got my first covid shot a couple years ago. It wasn't immediately after the shot but within the 15 minute time frame post-injection when they would have you wait around to see how you feel. It was a strange sensation and there was a place where I was allowed to lie down. I don't know why it happened and it hasn't happened since with further vaccinations. I am glad they were so kind about the whole process.
  - unsupp0rted 3y ago
    I had Botox in my fingers of both hands. After the second set of fingers I became faint. The Korean clinic lady (doc? technician?) said “needle shock”. I give blood and get vaccinations easily. But yes, this Botox was rather painful so maybe “needle shock”
- m463 3y ago
  As a kid I watched the needle go in my arm as blood was drawn.... and all of a sudden tunnel vision and almost fainting. Had to be walked to the car. So I figured out watching blood come out of me causes me to feel faint, so I don't watch. I've seen blood and other person's blood, but my blood seems to be some special case. What I've figured out is - if you are bleeding, maybe your brain helps you collapse to the ground in a faint, where you will be level, have a low heart rate, and not bleed out all your blood through a wound. Could this be the evolutionary reason we faint at the sight of our own blood?
  - seniorivn 3y ago
    now it's just a trait of scared monkeys, if it wasnt for development of civilization, it could be deadly. Lucky us, first communities of monkeys learned how valuable non deadly dominance can be, which allowed smart but not very good at aggression to survive, and over the years develop additional ways of dominance, rather than just pure strength.
  - tux3 3y ago
    Maybe a convincing way to play dead, plausibly just a bug, but if the idea is not bleeding out there are already sophisticated mechanisms to regulate tension and heart rate. Dropping on the floor is not very helpful. It's never a good time to just collapse and risk crashing your head on a rock.
  - katsura 3y ago
    Interestingly, when they take my blood with a needle, I almost always faint. But if I have a nosebleed, I have no problem at all - I can look at it dripping, I can look in the mirror to clean myself, nothing happens. So, there must be some other things at play here.
    - bavell 3y ago
      Yeah, I have to look away for shots and hate having blood drawn but if I get a nasty scrape with blood gushing out - meh, no problems at all looking and poking.
- sethammons 3y ago
  Two of my kids experienced this vasovagal syncope response during injections. It is terrifying; they appear to go into a seizure, convulse, and are unresponsive for up to half a minute. Terrifying.
karmakaze 3y ago
This is interesting in that I never understood that fainting is different than what I'd experienced a number of times through my life. In my case, there's no sensory input but is rather simply low blood pressure (often combined with low blood sugar) and getting up quickly after being very inactive for a long time results in a blackout, fast but gradual fade-to-black and crouching to the ground. On the other hand, my mother who could be actively busy in the kitchen and talking to me across the room behind her, then if I'm standing close behind her as she turns around surprised to see me standing there, will fall flat on her ass. She doesn't pass out but it's definitely something along the lines of the mechanism described here.
- derefr 3y ago
  The thing you describe happening to you is known as “orthostatic hypotension.”
  - karmakaze 3y ago
    Good to know. I read that increasing salt intake can help. Searching this now, I see normally recommended daily is about 2000 mg sodium, but for those with this condition about (between 150 and 250 mmol of sodium or) 10 to 20 g of salt. Looking up the relationship of mg sodium vs mmol: To convert mmol to mg of sodium, chloride, or of sodium chloride, multiply mmol by 23, 35.5, or 58.5 (the molecular weights of sodium, chloride, and sodium chloride), respectively. So 150 and 250 mmol of sodium is 8775-14625 mg sodium or 4.4-7.3 times the normal daily recommended amount. This makes sense now that one morning I was feeling off and I did the usual things like eat something, drink water, even some coffee. The only thing that fixed it was eating a bag of chips.
- zarmin 3y ago
  This happened to me recently. I was in the kitchen and decided, for whatever reason, to stretch. There was a drawer open a few feet away. I held the stretch for long enough to induce this blackout, and it went almost exactly as you describe. The next thing I remember is a ten second fade-in to awareness: I'm sideways on the floor making gibberish noises and holding the back of my head. The drawer, now above me, was knocked off its rails. As I reflexively got up from fainting, I did not have awareness of the open drawer, and bonked the back of my head on it. It was an extremely interesting moment of observing conscious awareness that I think about all the time.
b212 3y ago
Once I tried giving myself a belly shot. Never fainted but seconds after that I’ve completely lost hearing then tunnel vision started kicking in, and I was 100% certain I’m going to die. I guess it was the needle shock, eh? The hearing loss was so peculiar though, I remember yelling like crazy and couldn’t even hear my own voice. Scary.
mikrl 3y ago
Not injection related, but I cleaned a barbell last week (pull from the floor, jump and catch it on your shoulders) and walked it over to the rack on my shoulders, and I felt like I was about to faint after I’d taken 5 steps. Vision started going dark, head got fuzzy and everything. Luckily, I recovered and racked it safely. It was my own fault I suppose, cleaning so far from the rack, but I wondered what mechanism exactly led to that moment. If I took the bar straight from the rack to my shoulders I could walk around with it no problem, but the clean motion itself probably caused those neurons to activate.
ghufran_syed 3y ago
The main thing is that if you feel like you're going to faint, get horizontal as soon as possible. Sitting on the ground is a lot better than sitting in a chair, but lying on the ground is even better and may avoid loss of consciousness - so even if your blood pressure is low for a few seconds, it's still enough to perfuse your brain if there's no hydrostatic gradient. If someone passes out in a chair, try and gently lie them down on the ground (obviously assuming it's a safe place...) - I've had a few patients who passed out in an airplane seat, and they are often out for much longer with much slower recovery than those who just crumple to the ground and end up horizontal.

124 points by birriel 3y ago

"researchers have discovered a neural pathway, which involves a previously undiscovered group of sensory neurons that connect the heart to the brainstem. The study, published in Nature on 1 November1, shows that activating these neurons made mice became immobile almost immediately while displaying symptoms such as rapid pupil dilation and the classic eye-roll observed during human syncope." Very cool. I did not check to see if the authors of this paper are affiialted, but reserchers contributing to data at the NeMO Archive (https://nemoarchive.org/ https://nemoarchive.org/) have recently discovered over 3000 different types of cells in the brain, most of which are in the brain stem. This has added a whole new layer of complexity to explore. Exciting times to be involved in neuroscience!

plasma_beam 3y ago

A couple years ago I took my kids to get a flu shot at a CVS. 30 seconds after my oldest had gotten his shot I felt him go limp standing against me and he collapsed against me and went to the floor. Sheer panic immediately set in and I was on the floor with him calling his name while he ever so slightly convulsed and came to wide eyed 10 seconds later. The CVS employee was the utmost professional, he calmed me down, repeated this is normal, and had me hold his head and legs as he came to. He put my son in a chair, had him sit there for a while and 20 mins later we were in the car. I felt bad when my son actually apologized to me when I told him how terrified I’d been.

BrianB 3y ago
I've fainted more times in my life than I'd care to admit. After a while, it's not the 'blood' you are afraid of. Instead it's the idea of fainting and causing a scene that becomes the source of anxiety. For me, anyway.
- mfwit 3y ago
  This. So much this. Fainted for the first time, because of a nose bleed, in front of my high school physics class, literally.
- Fire-Dragon-DoL 3y ago
  Sadly agree. I wish I could control it
  - 0x00_NULL 3y ago
    Nothing to be ashamed of. Your Vagus Nerve, the main signaling nerve for your autonomic system, can go off automatically and there’s nothing you can do to stop it. When it happens, sit down in a chair. If you can lean back and put your feet up, that’s better and the episode will resolve more quickly. These episodes will come and go quicker as you are prepared for them. My wife has had to these for years. The only treatment we’ve found helpful is transcutaneous vagus nerve stimulation (tVNS) with a tool like a Neuvana Xen - or you can go the expensive prescription route. We were actually treating her gastroparesis with this and found that modulating the signal worked for all sorts of misfirings - like when getting shots. TLDR: You can’t avoid them, but you can mitigate them by sitting in a chair, leaning back, and bringing your feet closer to your heart. If anyone is watching, it just looks like you are trying out the recline function of the chair. If your Vagus Nerve issues are bad, you can try tVNS (under the supervision of your doctor, of course).
    - derefr 3y ago
      Oddly, putting my feet closer to my heart (such as when washing my lower legs in the shower) seems to unplug my sinuses if they’re plugged. Related mechanism?
      - jjulius 3y ago
        Would this be because your head is closer to your feet, or (and correct me if I'm picturing this wrong) because you're putting your head upside down?
leethomas 3y ago
They said it's normal to faint after receiving a flu shot? Hasn't heard of that happening to people before. What was the explanation?
- toast0 3y ago
  Normal maybe isn't the right word, but it's an expected possibility, the FDA has a page about it [1], and that's one reason FDA recommends patients be observed for 15 minutes after a vaccination, especially for types they haven't had before. [1] https://www.cdc.gov/vaccinesafety/concerns/fainting.html https://www.cdc.gov/vaccinesafety/concerns/fainting.html
  - snvzz 3y ago
    Somewhere in EU, I (and everybody else) was told to wait 15m before leaving the area after the vaccine. This is no doubt because of the possibility of such events.
- deleted 3y ago
  [deleted]
- V__ 3y ago
  It's not the shot itself, it's the injection/getting stabbed. I think I fainted four or five times in my life due to injections/blood draws. I have to lay down look away and control my breathing otherwise I'm gone. It is a pain in the ass and I get light anxiety from it.
  - Fire-Dragon-DoL 3y ago
    Same. I also realized I can't get acupuncture due to this, I will just faint
    - derefr 3y ago
      I’m curious if there’s a refractory period. (I.e. if you faint and come to after the first needle goes in, then maybe you’re “past it”, and the rest won’t bother you?)
miriam_catira 3y ago
Yep, fainted so, so many times... Always seems to happen after getting hurt on or near a nerve for me - or after a blood draw. Was scary the first time, embarrassing and annoying every time since then. :) Had a nurse explain that the best way to prevent it is flexing / tightening the legs, to force the blood up out of them. Seems to work, at least for me.
- BrianB 3y ago
  That works for me too. A cardiologist told me it is because it gives your body a reason to keep the blood pressure higher. He also advised drinking lots of water every day.
- Fire-Dragon-DoL 3y ago
  Is it while standing or laying down? I don't faint if I lay down. Also if I pass a crisis without fainting, I get immunity for a good while
- teeray 3y ago
  Fighter pilots are trained to contract their solar plexus by making a “hut” sound to do something similar when they’re passing out. I was going to try this the last time I was fainting after a blood draw, but was interrupted by the phlebotomist imploring me to breathe slow and deep—I think this just sunk me further into it.
  - lukas099 3y ago
    Valsalva maneuver against a closed glottis. As someone prone to blacking out when standing up or after a set of heavy squats, figuring this out has been very useful to me.
imetatroll 3y ago
I became faint, I would say, after I got my first covid shot a couple years ago. It wasn't immediately after the shot but within the 15 minute time frame post-injection when they would have you wait around to see how you feel. It was a strange sensation and there was a place where I was allowed to lie down. I don't know why it happened and it hasn't happened since with further vaccinations. I am glad they were so kind about the whole process.
- unsupp0rted 3y ago
  I had Botox in my fingers of both hands. After the second set of fingers I became faint. The Korean clinic lady (doc? technician?) said “needle shock”. I give blood and get vaccinations easily. But yes, this Botox was rather painful so maybe “needle shock”
m463 3y ago
As a kid I watched the needle go in my arm as blood was drawn.... and all of a sudden tunnel vision and almost fainting. Had to be walked to the car. So I figured out watching blood come out of me causes me to feel faint, so I don't watch. I've seen blood and other person's blood, but my blood seems to be some special case. What I've figured out is - if you are bleeding, maybe your brain helps you collapse to the ground in a faint, where you will be level, have a low heart rate, and not bleed out all your blood through a wound. Could this be the evolutionary reason we faint at the sight of our own blood?
- seniorivn 3y ago
  now it's just a trait of scared monkeys, if it wasnt for development of civilization, it could be deadly. Lucky us, first communities of monkeys learned how valuable non deadly dominance can be, which allowed smart but not very good at aggression to survive, and over the years develop additional ways of dominance, rather than just pure strength.
- tux3 3y ago
  Maybe a convincing way to play dead, plausibly just a bug, but if the idea is not bleeding out there are already sophisticated mechanisms to regulate tension and heart rate. Dropping on the floor is not very helpful. It's never a good time to just collapse and risk crashing your head on a rock.
- katsura 3y ago
  Interestingly, when they take my blood with a needle, I almost always faint. But if I have a nosebleed, I have no problem at all - I can look at it dripping, I can look in the mirror to clean myself, nothing happens. So, there must be some other things at play here.
  - bavell 3y ago
    Yeah, I have to look away for shots and hate having blood drawn but if I get a nasty scrape with blood gushing out - meh, no problems at all looking and poking.
sethammons 3y ago
Two of my kids experienced this vasovagal syncope response during injections. It is terrifying; they appear to go into a seizure, convulse, and are unresponsive for up to half a minute. Terrifying.

karmakaze 3y ago

This is interesting in that I never understood that fainting is different than what I'd experienced a number of times through my life. In my case, there's no sensory input but is rather simply low blood pressure (often combined with low blood sugar) and getting up quickly after being very inactive for a long time results in a blackout, fast but gradual fade-to-black and crouching to the ground. On the other hand, my mother who could be actively busy in the kitchen and talking to me across the room behind her, then if I'm standing close behind her as she turns around surprised to see me standing there, will fall flat on her ass. She doesn't pass out but it's definitely something along the lines of the mechanism described here.

derefr 3y ago
The thing you describe happening to you is known as “orthostatic hypotension.”
- karmakaze 3y ago
  Good to know. I read that increasing salt intake can help. Searching this now, I see normally recommended daily is about 2000 mg sodium, but for those with this condition about (between 150 and 250 mmol of sodium or) 10 to 20 g of salt. Looking up the relationship of mg sodium vs mmol: To convert mmol to mg of sodium, chloride, or of sodium chloride, multiply mmol by 23, 35.5, or 58.5 (the molecular weights of sodium, chloride, and sodium chloride), respectively. So 150 and 250 mmol of sodium is 8775-14625 mg sodium or 4.4-7.3 times the normal daily recommended amount. This makes sense now that one morning I was feeling off and I did the usual things like eat something, drink water, even some coffee. The only thing that fixed it was eating a bag of chips.
zarmin 3y ago
This happened to me recently. I was in the kitchen and decided, for whatever reason, to stretch. There was a drawer open a few feet away. I held the stretch for long enough to induce this blackout, and it went almost exactly as you describe. The next thing I remember is a ten second fade-in to awareness: I'm sideways on the floor making gibberish noises and holding the back of my head. The drawer, now above me, was knocked off its rails. As I reflexively got up from fainting, I did not have awareness of the open drawer, and bonked the back of my head on it. It was an extremely interesting moment of observing conscious awareness that I think about all the time.

b212 3y ago

Once I tried giving myself a belly shot. Never fainted but seconds after that I’ve completely lost hearing then tunnel vision started kicking in, and I was 100% certain I’m going to die. I guess it was the needle shock, eh? The hearing loss was so peculiar though, I remember yelling like crazy and couldn’t even hear my own voice. Scary.

mikrl 3y ago

Not injection related, but I cleaned a barbell last week (pull from the floor, jump and catch it on your shoulders) and walked it over to the rack on my shoulders, and I felt like I was about to faint after I’d taken 5 steps. Vision started going dark, head got fuzzy and everything. Luckily, I recovered and racked it safely. It was my own fault I suppose, cleaning so far from the rack, but I wondered what mechanism exactly led to that moment. If I took the bar straight from the rack to my shoulders I could walk around with it no problem, but the clean motion itself probably caused those neurons to activate.

ghufran_syed 3y ago

The main thing is that if you feel like you're going to faint, get horizontal as soon as possible. Sitting on the ground is a lot better than sitting in a chair, but lying on the ground is even better and may avoid loss of consciousness - so even if your blood pressure is low for a few seconds, it's still enough to perfuse your brain if there's no hydrostatic gradient. If someone passes out in a chair, try and gently lie them down on the ground (obviously assuming it's a safe place...) - I've had a few patients who passed out in an airplane seat, and they are often out for much longer with much slower recovery than those who just crumple to the ground and end up horizontal.