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alexpap031 t1_j42tl0u wrote

Reply to comment by h3rbi74 in How do giraffes breathe? by NimishApte

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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