Submitted by NimishApte t3_10a3gai in askscience
Basically, the text. The giraffe neck is around 6 feet long, so how do they generate enough pressure for air to travel six feet and also relatively fast? How do they remove air and prevent too much physiological dead space?
I would imagine the main reason for their higher blood pressure is so blood is able to reach their heads, you need roughly 23mmHg per foot in height.
yup, iirc, their skin is super tight around their legs to help get that blood to easily shoot up the neck.
Don’t fighter pilots or astronauts do the same thing with their suits to resist passing out from g forces?
Yes. They wear pneumatic over trousers which compress the legs in high g manoeuvres to keep the blood in the upper body and brain. Pilots are also trained to clench the core and hold their breath to keep pressure up.
What an incredible wealth of knowledge we all possess. I thought it was like tight stockings or something.
Fun fact: The Blue Angels don't wear G-suits because they maneuver so closely and don't want the suits to impact their controls during displays.
From their FAQ: https://www.blueangels.navy.mil/faq/
G-suits are designed with air bladders (pockets) that inflate and deflate to keep a pilot's blood from pooling in the pilots' legs while executing sharp, unpredicted combat maneuvers. Unlike combat flying, the Blue Angels demonstration pilots know the maneuvers they will fly prior to execution, so each pilot knows when one will be experiencing heavy gravitational forces. Anticipating the changes in gravitational forces allows the Blue Angels demonstration pilots to combat G-forces with muscle contractions. Additionally, G-suits would detrimentally impact flight safety.The Boeing F/A-18's control stick is mounted between the pilot's legs. The Blue Angels have a spring tensioned with 40 pounds of pressure installed on the control stick that gives the pilot a "false feel." This allows the pilot minimal room for un-commanded movement. The pilots rest their right arms on their thighs for support and stability while flying. Therefore, inflating and deflating air bladders in a G-suit would interrupt this support and stability, causing un-commanded aircraft movement.
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I use that core trick if I get lightheaded from standing up too fast and it works 100% of the time to make it stop quickly.
I've dealt with (annoying, but not dangerous) low blood pressure my whole life, and never once has a medical professional ever mentioned flexing my core as a way to combat occasional dizziness. I'm weirdly excited to try it out!
Stands up and gets dizzy so u/napincoming321zzz flexes his core
highway to the danger zone
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Yes, and they also flex their legs and core to keep blood flow to the brain.
You can do the same thing if you ever feel like you're going to pass out.
When you start getting tunnel vision, squeeze that core. It'll either resolve it, or keep you conscious long enough to find a place to sit.
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They also have a pressure regulator on their carotid artery (jugular?), which allows them to lower their head to drink.
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So, if you measured a giraffe's BP at the head (while standing tall) would it be similar to a human's? And do they suffer a major headrush when going from ground grazing to treetops?
Apparently, a giraffes BP is 280/180mmHg
Regarding the headrush, they don't
Edit:
Giraffe's have basically a vascular sponge in their brain, which dampens BP spikes when moving the head. Also, their arteries have valves as well.
Right. But where are we measuring that bp? I'd assume body as there's no need to have that much pressure at the brain.
At heart level as always. At head level it's apparently at 75mmHg while a humans at headlevel being 60mmHg
I also have a sponge in my brain. But that's another story. I dampen tictock videos and ignore all of them.
wow. I wonder if similar shaped "dinosaurs" had similar anatomy?
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23mmHg per foot is equal to 0.10133 bar/meter.
Imperial units are wonky, and mixing them with outdated half-metric converted units makes my head hurt.
That's 0.44 psi per foot, which at 6ft is 2.64 psi, which doesn't sound like a lot, but considering it's going through blood vessels, that's absolutely insane.
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Their neck arteries got many valves to help with gravity, back flow, pooling when they lower the head.
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I was told this by a Giraffe zookeeper once - also, they have the same number of neck ones as a human. Wild!
>I would imagine the main reason for their higher blood pressure is so blood is able to reach their heads, you need roughly 23mmHg per foot in height.
It's a closed loop system, so as long as it's primed you don't need much pressure to pump it from an engineering point of view, as long as you replace the blood vessels with non-compliant tubes.
Just throw a 12v centrifugal pump on there and you should be OK.
"Dead air" or dead space is the volume of air that fills the space from your mouth/nose to the small airways of your lung that exchange oxygen and carbon dioxide. An above average height man may breath about 600 ml per breath and have about 200 ml be dead space. So only 400 ml air available for exchange. If he closed his nose and put is mouth around a large straw that held 600 ml of volume, he'd have to increase his breathing depth (and frequency) compensate, and would get pretty tired.
The OP likely just learned about dead space ventilation and the giraffe is a logical follow up question.
Dinosaurs (including birds) have a circular breathing system that makes it possible to have even more extreme necks.
I learned how to circular breathe when I was in band. I once played the same note on my French horn for 5 straight minutes without stopping
Yeah. That's not the same thing. You were simply using your cheeks to store air, not genuinely continuously breathing like some birds can.
So, where does it exit. It would be so awesome to be able to do this, I could be a human fan...
The avian respiratory system is very different from the mammalian system. Bird lungs don't expand and contract like mammals' do; rather birds have several air sacs that expand and contract in an alternating fashion and push air unidirectionally through the lungs; the lungs have millions of narrow "tubes" where gas exchange occurs, whereas the alveoli in mammalian lungs are "bags" with only one opening.
Which is also why they can fly and do just fine at high altitudes where the oxygen gets thin. Amazing creatures, birds.
It can also serve as an affiliative signal when done in a certain way. You might benefit from giving it a try.
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But you don't have hollow bones to pump stale air into, except in your nose.
I was going to ask how a long neck dinosaur managed it. So, do they have two separate tubes. One for inhale and one for exhale?
What's "dead air"?
Imagine breathing through a 50-foot garden hose.
You breathe in, you might take in all the air in the hose.
You breathe out, you put that same air back into the hose.
Breathe in again, and you get the same air you breathed out but now it doesn't have much oxygen left.
By the third breath, your lungs have removed all the oxygen out of the air in the hose. The volume of air in the hose is considered "dead air" (tidal volume).
I think they're referring to what we call "dead space" in respiratory physiology, which is the part of the respiratory tract that isn't involved in oxygenation (gas exchange). Our alveoli are the only structures in our lungs that are actually exchanging gases, everything else is considered dead space (e.g. trachea, bronchus) because there is no exchange happening there. We also call those parts of the airway the conducting airway, since all they do is move air (conduction), whereas the respiratory airway refers to the alveoli since it is involved in gas exchange (respiration).
Since giraffes have very long necks and thus longer conducting airways, it would be reasonable to assume that they have much more dead space than humans do, proportionally speaking of course.
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The googles say that a male giraffe average is 2628 lbs. Given that's about 13x the size of a human I'd expect a similar lung capacity; 8x seems small.
Mass and volume scale a bit differently when it comes to biology.
For example, average blue whale weighs about 310,000lbs, easily weighing over 2,000 times as much as an average (about 154lbs) person.
Yet Blue Whale lung capacity can reach 5,000 litres, while average Joe sits around 6 litres. A whale "only" has a bit over 800 times the volume.
My intention was to say that it's a nonsensical way to explain how a giraffe copes with a long neck given the lungs really aren't that large compared to their mass.
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Can they breathe if they're mostly submerged under water, with only their head above water?
probably not. At 6' of neck length, they're looking at roughly 2.5psi worth of hydrostatic pressure to overcome. Probably another few feet from lungs being lower than neck.
It's not technically an impossible feat, but animal lungs are very generally not capable of that kind of vacuum pressure. Humans, for comparison, usually peak at around 1psi. The problem is that you're not creating that pressure with muscles -- it's from the bones in your ribcage being pre-sprung to expand; your muscles are just letting them do that. E: Right now there's another askscience thread on literally this exact topic. It's better than my sentence and a half..
They have a very hard time and they generally don’t go in water because they can’t swim. Another animal that can’t really swim is a hippo. An elephant can be in water over its head because of how their muscles and ligaments and whatnot hold their lungs. The water pressure does nothing to their lungs. Unlike with giraffes.
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>Their cavernous lungs
I love this. I need to start using "Cavernous" more. Maybe to describe the emptiness of my bank account and wallet.
Isn’t that also the reason they can’t move their head up fast because they’d pass out
>a respiration rate 1/3 as slow as a human's.
You mean 1/3 that of a human?
People forget that even exhaled air still has a lot of oxygen in it. It's not like we exhale straight CO2.
I just watched Matilda (1995) today. She gave a factoid that giraffes had beat 500 times a minute, and sounds like a hum rather than a beat.
I believe that was in reference to a mouse or a hummingbird. Generally speaking, larger animals will have much slower heart rates and smaller animals faster ones.
True, a horse for example has a resting HR in the 20s-40s and for most domestic species, the smaller they are the faster they go, and vice versa. I have never heard that a giraffe can go 500 bpm and I can’t find a zoo reference manual on a quick search but several sources claim a normal HR for a giraffe is 150-170 bpm, which is insanely fast for something that huge. A relaxed house cat is frequently less than that.
Here is one source for giraffe HR that also has some cool BP info. https://iheart.polimi.it/en/the-incredible-cardio-circulatory-system-of-giraffes-a-challenge-to-gravity/
A big heart has to have the time to fill up with blood to pump it. So, you have to have bigger arteries and higher blood pressure that can help with that, but raising the heart beat is only effective to a point were it starts to be to fast for the heart to expand. It is the reason why in humans aerobic exercise is advised to be up to 140 bpm (of course there are no absolute limits) since if you go higher the faster heart beat doesn't help circulate more blood.
So, a huge animal with a huge heart is very unlikely to have such a crazy heartbeat.That would be considered ventricular fibrillation and said huge animal would probably drop dead in a second.
It should be noted the amount of cardiovascular exertion humans are capable of would kill basically any other organism that isn't a dog.
It could probably kill a dog too if endurance in heat was a factor since we have the benefit of heat regulation through perspiration that dogs don't have.
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I am actually a CVT and am responsible for monitoring ICU patients on ECGs regularly and very familiar with basic cardiology. A high HR does not on its own equal Vfib. (I have seen SVT in large dogs well into the 300s many times, for example.) Also, giraffes are unique in many ways and cannot be compared to humans. A BP of 220/180 would also not be sustainable long term for a human but that is normal for them in order to allow a more typical pressure by the time it gets all the way up to their brain.
We are talking about 500 bpm. That's like 8 per second. In a huge heart.
I can't see how a big heart like that could pump enough blood to not faint immediately even for a human, let alone an animal several times bigger, and then, if it doesn't get pretty fast back to normal result in death.
I know the fibrillation part is an exageration, but sill, 500bpm?
Do you thing a human, let alone a bigger animal wouldn't instantly faint?
Edit: You can't compare a dog that is maybe 35-50 kg to a grown man who is 80 and then use this to talk about giraffes as you can't compare blood presure extremes to heart rate extremes.
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Don't larger mammals have a slower metabolism to avoid overheating?
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As I recall from my human physiology class, it is called tidal volume. The game is to be able to have more volume in the lungs than the trachea. And that is pretty easy to do. Giraffes do have pretty big chests. And the next area to think about is the rate of ventilation. One is able to test this for themselves. How long can nominal breaths be skipped before needing a full breath to recover? You can go for a pretty long time taking every other. So that indicates that a single breath may have more O2 than needed as well as the capacity to take CO2. And so partial mixing of the last and next breath works. It is surprisingly complex.
As far as pressure, outside and inside the giraffe are the same pressure. And so it is a matter of muscles moving gas in a manner similar to a billows. But the diaphragm does the work via a pressure differential by expanding and contracting the chest cavity causing the pluera that contains the lungs to pull the lungs open.
What is cool is if you breathe sulfur hexafluoride, it is heavier than air. And so it doesn't mix. And it is difficult if not possible to ventilate. And so drowning! Unless you hang yourself upside down.
That is the extent of my recollection of that chapter. Good Q! Hope someone more up to date can correct me.
It's not the same principle but if you're interested in this you might want to check out the breathing system on long-neck dinosaurs. For example brachiosaurus reached up to 23 meters and they were still able to breath.
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All of this is in reference to the actual size of giraffe lungs. No human comparison is made. Felt like I should clarify
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Not meaning to Hijack OP’s question. But after reading the answers regarding larger heart, larger lungs, etc. what would happen if you inverted a giraffe the way we humans sometimes do. When I get on an inversion table I get a head rush presumably from the blood to the head. Would a creature like a giraffe die from this experience?
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NimdokBennyandAM t1_j426w6o wrote
Long neck, but narrow; massive lungs, 8x the size of a human's; a strong heart that gives it blood pressure twice that of a human's; and a respiration rate 1/3 as slow as a human's.
Essentially: their throat will fill with dead air; it's too big not to. But, their lungs are huge, and they have a respiration rate 1/3 the speed of a human's, sucking as much oxygen out of their air as possible. Their cavernous lungs and ability to sip oxygen out of them, plus their hard-beating heart's ability to efficiently spread that O2 all over their bodies, mitigates the threat of dead air build-up in their throat.