I'm bleeding from my hands. So why can't I hear?
May 12, 2007 7:08 AM   Subscribe

Hypotension/hypovolemia as a low-pass filter: I got cut, I went into shock, and then everything started sounding funny. I'd guess it was a 40 dB (±10) rolloff, which began near 200 Hz (±50) and left me with nothing above 1kHz. How in the world? Story, discussion of numeric estimates, off-the-cuff physiological speculations, etc...

About a week ago I had a gentlemanly disagreement with a pane of glass, which left venous blood running richly from two of my knuckles. (No winner was declared, but you should see the other guy. I totally took him.) At the first-aid station, I dropped into a typical case of shock: pallor, weakness, sweating, and thirst. I knew what it was, so I got my head between my knees and asked a bystander for water to sip. I was still feeling awful when someone got a car to drive me and my now-bandaged hands to the emergency room (where those hands would get six stitches and some iodine).

As I walked some 15 or 20 feet to the car, I experienced an unfamiliar symptom: My hearing drained out. First the high end, then the mids went very quiet. A waterfall fountain became inaudible; male voices had a very flat timbre. I could hear the bass rumble of the car engine very clearly, but not its rattling-type noises, or much road hiss/tire noise.

Note that I am pretty bad at estimating loudness, but it was a profound loss. Frequency, I'm a little better with. I understood people speaking, so I must have had some hearing up to 1000 Hz (to make out the first two vowel formants). But 700 Hz is a good estimate for the top of the road hiss that I wasn't hearing, and the loudest sounds were definitely 100-160 Hz or so.

Qualitatively, here is how much shock I was in: My vision was washed out, but not tunneled. My lips, I'm told, were colorless. I did walk 20 feet, but I'm sure I couldn't have gone 40. I had the presence of mind to keep my knees slightly bent in case I went down, and to be irritated at the people who thought that holding my elbow was really gonna help if I fainted. (Arms go limp, yo?) I did not have the presence of mind to say, 'Hold me at the shoulder, not the elbow,' or better yet, 'Wait, give me a minute here, I can't walk yet.' In the car, with a few minutes' rest and some water sipped, the normal shock symptoms receded, and the hearing loss with them.

So: What was that? Has this happened to other people? Can you propose a mechanism? (Could shock drain fluid from your cochlea, or do some fibers of the auditory nerve have a better blood supply than others, or would it more likely be the auditory cortex going under?) I welcome hypotheses, but I'm not about to go gouge myself again to test them. (Hmm, guineapigs.metafilter.com is still available.)
posted by eritain to Health & Fitness (24 answers total) 6 users marked this as a favorite
I'm not a doctor, and I'm probably talking nonsense, but my first thought was something like the following: fainting = less blood to the head = less blood to ears on side of head = less ability to process. Perhaps somehow related to how your vision goes all screwy?
posted by Solomon at 7:25 AM on May 12, 2007

I've had that happen to me before passing out. I was in a crowded restaurant, and all the background noises disappeared. Also, when my cousin turned around to talk to me, he sounded like a Charlie Brown teacher. And then, boom, I was face down in some poor little kid's dinner.
posted by Ruki at 7:28 AM on May 12, 2007

i don't think it's the shock or loss of blood, your six stitches are modest compared to a couple of my childhood lacerations. auditory hallucinations can manifest by subtraction as well as addition, perhaps the neurons usually used for transmission of 1000 hz plus sound data were temporarily commandeered to help you figure out how to cope. i have moments just walking down the street when the nature of sound itself seems to change, white noise fades in and out, i don't let it bother me.
posted by bruce at 7:32 AM on May 12, 2007

Health issues aside, this is an extremely well written question. An excellent debut post!

You've thrown around all sorts of audio engineering terms. Clearly, you're more conscious of your hearing range than others. Could your hearing loss be a common symptom that you're simply more sensitive to?
posted by aladfar at 7:46 AM on May 12, 2007

I've also had loss of sound as a precursor to (nearly) passing out on two occasions. In fact, your description of symptoms as you were walking mirror an experience I had almost exactly after a car accident. I was not injured at all, but under extreme stress. I suddenly felt light headed as an officer was questioning me, and he walked me about 20 feet to his air-conditioned cruiser. During those 20 feet I found myself fading- dim vision, loss of sound, and increasing weakness. By the time I got to the car, the cop was getting ready to call an ambulance. Even though I was very nearly unconscious, I was able to convince him that I didn't need to go to a hospital. I never fully passes out, and revived in about 3-5 minutes. Very weird.
posted by kimdog at 8:27 AM on May 12, 2007

IANAD. You probably weren't in hypovolemic shock. A person typically needs to lose more than 10% of their blood volume to present hypovolemic shock symptoms. It sounds like you had an acute stress reaction. This is a fairly common reaction to cuts, broken bones, and can look a lot like real shock. As for the hearing loss, I don't have a theory about that.
posted by tumble at 8:29 AM on May 12, 2007

Yeah, this pretty much happens every time I get blood drawn or get a flu shot. Also happened once when I cut my finger with a pocket knife. I have never actually passed out from this, just came really, really close.
posted by ArgentCorvid at 8:58 AM on May 12, 2007

Best answer: You were not in shock from blood loss. Shock from blood loss is very serious and would not have been abated by a few sips of water and sitting down. Shock from blood loss happens when the local blood flow control mechanisms in the body override the control mechanisms of the nervous system when it is trying to shunt diminshing blood flow to important organs. When the local control mechanism succeed, blood flow to the brain, heart and kidney drop rapidly and the person dies.

What was probably happening was your blood pressure was beginning to drop. Your body and nervous system responded by constricting blood vessels and releasing hormones that increased you heart rate and cardiac output in order to maintain your blood pressure. This would result in pallor weakness and sweating, but this is still just homeostasis and not shock.

Adrenalin would have been one of the hormones released in order to help maintain your blood pressure and adrenal can do some pretty funky things to hearing.

The fact that you experienced a loss of hearing in certain frequency ranges is explained by how the ear encodes sound. Nerves in the cochlea encode volume by alerting the rate at which they send signals to the brain and encode frequency by the location of the nerves that are sending the signal. So it's possible that under the heavy physiological stress of the situation information from certain frequencies that the "mind" decided were not important for survival were filtered out.
posted by 517 at 9:04 AM on May 12, 2007 [3 favorites]

Did your ears ring as your hearing worsened? The same thing happens to me at the doctor's office whenever needles or eye drops are involved, except it feels more like my hearing is being drowned out by tinnitus. Oddly, the ringing sticks around for up to an hour or so after the fainting spell is over.
posted by Drop Daedalus at 9:52 AM on May 12, 2007

I've been in shock once because of an injury, but I don't remember many of the symptoms - it was many years ago - except that my arm, which I'd broken quite badly, didn't hurt.

However, I have been in highly adrenalized (is that a word? situations and had something similar happen to my hearing. It didn't go completely, but it was definitely diminished. A very odd feeling. The post-adrenaline crash did make me feel like I was going to pass out.
posted by rtha at 10:14 AM on May 12, 2007

This is a great question, btw, and I agree that you've written it beautifully.
posted by rtha at 10:15 AM on May 12, 2007

Someone with actual medical training should correct me if I'm wrong, but from what I understand from just having studied phobias: People with most phobias react with a rush of adrenaline when confronted with what they're afraid of; they get ready to fight or flee. Blood, injections, or injury phobias are unique in that they often cause a big drop in blood pressure (which can often cause a person to faint). Ringing in the ears and difficulty hearing are typical symptoms of a big drop in blood pressure.

And I had the same thing happen to me recently at the ER, when the doctor started poking at / cleaning a deep cut on my finger.

Like I said, I learned this in relation to phobias (and I definitely have a mild blood-injection-injury phobia), but I assume most of it would still apply to non-phobic people; the first linked article mentions that blood pressure dropping in response to injury would decrease blood loss, which is probably why the body does it.
posted by occhiblu at 10:45 AM on May 12, 2007

Also, an Acute Stress Disorder requires a great many other symptoms not listed (surprise) in the Wikipedia article. "Acute Stress Reaction" looks like something not listed in the DSM... I'm not sure if it's an old name for the disorder? In any event, I don't think this was an acute anything, just regular ol' normal physical reaction to bodily harm.
posted by occhiblu at 10:56 AM on May 12, 2007

I may be completely misremembering this from my sole neuroscience class, but the ranges you mentioned (400 to 1k) were briefly mentioned in my book as the range where the ear's hair cells (theoretically) start having trouble keeping up with individual vibrations. At above 1k the hair cells have difficulty sending a 1:1 nerve signal with each peak and valley of the vibration and, instead, use clusters of hair cells that only vibrate every six or ten or however many wave peaks. It was also suggested that the brain then infers the proper sound. If you were losing blood, maybe the part of of your brain that handles this inference was not able to function properly, leaving only the pitches that get an 1:1 nerve signal.

As a disclaimer, please note that 1. I had this course several years ago, and 2. I've had trouble tracking information on this theory down on the web, so it may have been the author's pet theory/complete bullshit. If I had the text I could check for research citations but I believe I sold it off for a pittance.
posted by Benjy at 11:11 AM on May 12, 2007

Best answer: It reads like (alright-- sounds like) a classic case of vasovagal response verging on vasovagal syncope.

According to the Mayo Clinic:

Intense pain, such as due to hitting your knee on a hard corner, may cause a temporary, exaggerated vasovagal response by your autonomic nervous system. As a result, your heart rate and blood pressure drop, which reduces blood flow to your brain. This results in a feeling of warmth, lightheadedness, dimming of vision and hearing, and even fainting (vasovagal syncope).

According to the Wikipedia article, the triggers of vasovagal syncope include:

# prolonged standing or upright sitting
# stress
# any painful or unpleasant stimuli, such as

* giving blood
* watching someone else give blood
* watching someone experience pain

I've known a fair number of people, including a couple of medical students for whom it was career threatening, who developed all your symtoms merely from the sight of blood.

Blood volume does seem to be a factor. Again from the Wikipedia article:

* The cornerstone of treatment is avoidance of triggers known to cause syncope in that person. Before known triggering events, the patient may increase consumption of salt and fluids to increase blood volume. Sports drinks, such as Gatorade, may be particularly helpful.
posted by jamjam at 11:12 AM on May 12, 2007

I'm headed out the door and don't have time to check, but I think there was a really long askme about vasovagal response, quite a while ago.
posted by peep at 11:43 AM on May 12, 2007

Yeah, presyncope, not shock. The common factor is the drop in blood pressure, not caused by a drop in blood volume in this case, but instead in a quick decline in total peripheral resistance of the small blood vessels.

The funny perceptual anomalies you describe are quite common when the blood pressure gets too low to supply the brain with its full needs. If it'd gotten a little lower you would have fainted. I don't know why you'd experience a low-pass filter effect, but I've heard similar stories. Other people hear a high pitched ringing sound right before they faint, or start hearing echoes.
posted by ikkyu2 at 12:16 PM on May 12, 2007

Other people hear a high pitched ringing sound right before they faint, or start hearing echoes.

I've heard those echoes! I remember it as sounding as if I had suddenly been transported to an empty room with hard walls and a hard floor.

Now, in the context of this thread, I'm wondering if that could have been due to a breakdown of the sound location program of the brain; ordinarily we use differences in time of arrival of any given sound at the two ears to determine the direction of the origin of the sound and do not hear that as constituting two different sounds-- somewhat like the unconcious way we use differences in the retinal images of our two eyes for binocular depth perception.

If that sound location feature drops out from lack of blood flow, it seems to me a person could then experience differently timed arrivals of a sound at the two ears as an echo-- kind of like double vision.
posted by jamjam at 12:52 PM on May 12, 2007

Lots of people report this symptom prior to passing out. Very similar to the tunnel vision effect. I always assumed it had to do with decreased perfusion to the brain, the part of your auditory cortex that maps higher frequency noises losing blood pressure first.
posted by Slarty Bartfast at 1:12 PM on May 12, 2007

You'll note it wasn't just the hearing dip but the fact that you felt you couldn't walk--yes, it could be a phobia, but my bet is that your blood pressure dipped dangerously low. This gives you a feeling of light-headedness, extreme fatigue, and people sound like they are talking at you from underwater. At least that was my experience.
posted by misha at 2:53 PM on May 12, 2007

I have a high tolerance for seeing blood and my own injuries, but ten years ago I was in a motorcycle accident on the interstate that I was lucky enough to walk away from. Just bad road rash on various places. Oh, and a couple broken toes. Anyway, I thought I was pretty clear-headed, but in retrospect I was muddled for probably an hour. Was that reaction what is being described here? I had though there was a generic physiological "shock" that could be brought on by numerous things, but it sounds like from these answers that's not the case.
posted by Ethereal Bligh at 7:38 PM on May 12, 2007

Best answer: I blacked out once from hyponatremia (low salt level, caused by sweating a lot and ingesting a lot of water, essentially washing out all one's electrolytes), and right before I passed out, I had the exact same thing happen.

I won't go into the whole story, but I was talking to some people when it happened, and remember with absolute clarity that my hearing went, first from the high end, down to the low end, and then my vision went (went 'splotchy', then dim, then black), and then I lost balance, and then consciousness. I woke up lying flat on my back with a lot of people looking at me.

So anyway, I just assumed that was sort of the order that the brain shuts down in; either by 'design' (maybe it's somehow evolutionarily advantageous to lose your hearing first, before your vision, lest you get eaten by saber-toothed tigers or something) or perhaps simply because the high-frequency hearing requires the highest levels of blood O2 or is the most sensitive to shock and fails first, with vision and gross motor skills failing afterwards.

Anyway, although I wouldn't necessarily recommend doing it on purpose, having never blacked out before, it was certainly educational. Everyone should do it at least once.
posted by Kadin2048 at 10:44 PM on May 12, 2007

Response by poster: Well, it's good to know I'm not the only one who's had it happen. I didn't reckon it was actual hypovolemia—that's a lot of blood—but I couldn't pin down the term for what it was. Vasovagal response is it.

Now, the funny thing is, I have been close to fainting on a few other occasions. I have fabulously low blood pressure, so I regularly get to watch my vision go if I stand up too fast after a long, slouchy reading session on the couch. I've also been vasovagus-worthily injured a couple times. And the one time I tried to donate blood, I had some obvious mental and visual impairment, and my skin tone compared pretty favorably with a blank sheet of office paper. I've known the visual effects since I was, like, eight—for me, it's a spirally pattern of small brown squares, kind of like the head of a sunflower seed. But I've never noticed any audible effects before.

Then again, most of the serious near-faints I've been in happened before I became interested in acoustics at all, and most were before the phonetics class that taught me my way around the audible spectrum, and it's only in the last year that I've really become unhealthily interested in timbre. So maybe I had the auditory effects before, but I just wasn't hip to them.
posted by eritain at 9:38 PM on May 13, 2007

Response by poster: And no, no ringing or echoes. Just the profound dulling of every sound with warmth or sparkle. On the plus side, this made a well-used early '90s sedan sound like an ill-muffled muscle car.

Benjy, I would be very interested to chase that idea about the signalling from hair cells. I didn't sell my college physiology book, but unfortunately I'm eight time zones away from it for the time being. Help me, Google, you're my only hope.

OK. If I've understood this correctly, auditory nerve fibers have a refractory period between 500 and 750 microseconds. Depending which number you pick, that forces them out of 1:1 signalling at 1300-2000 Hz. Somewhat higher than what I heard, but maybe they quit using 1:1 at lower frequencies than they have to? Yeah, it's possible to signal at 1000 Hz, but it drinks up a lot of ATP that you could be using elsewhere. So there may be something to your theory: Starve the fancy audio post-processing unit and reserve the blood for the not-falling-down centers closer to the spine. Certainly consensus here seems to be that it was a selective impairment of the brain, and not of the ear.

I've marked some answers but will keep watching, just in case someone can come along and be authoritative. O ye who have spent countless hours installing drain valves in rat veins and MRIing them to examine the shutdown sequence in their brains ... arise, this is your time to shine. Let us have the audiophysiological paydirt.
posted by eritain at 10:06 PM on May 13, 2007

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