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wene324 t1_j42ey49 wrote

Reply to comment by NimdokBennyandAM in How do giraffes breathe? by NimishApte

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.

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idiotcameltoilet t1_j42ibm5 wrote

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.

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h3rbi74 t1_j42ka84 wrote

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/

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alexpap031 t1_j42tl0u wrote

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.

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SuperFightingRobit t1_j43g7q1 wrote

It should be noted the amount of cardiovascular exertion humans are capable of would kill basically any other organism that isn't a dog.

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alexpap031 t1_j43hcj6 wrote

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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h3rbi74 t1_j42v004 wrote

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.

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alexpap031 t1_j42wuzd wrote

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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NimishApte OP t1_j42gi04 wrote

Don't larger mammals have a slower metabolism to avoid overheating?

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