Stanford researchers report first recording of a blue whale's heart rate (2019)
news.stanford.edu68 points by eatonphil 12 hours ago
68 points by eatonphil 12 hours ago
Note they put a Holter monitor on it
https://www.pnas.org/doi/10.1073/pnas.1914273116
to get an ECG which is one of several strategies they could use. (e.g. lately I've been interested in Heart Rate Variability which has gotten me looking at reading heart rate with cameras, radars, pressure gauges, ultrasound, etc.)
30 BPM at the surface, 4 bpm while diving.
"Analysis of the data suggests that a blue whale’s heart is already working at its limit, which may explain why blue whales have never evolved to be bigger."
Incredible to think of the volume of all the blood it's pumping around.
I don't understand how that would limit evolution. Bigger bodies can evolve together with bigger hearts, as already witnessed with the very whales being researched.
The volume of blood that needs to be pumped increases e̶x̶p̶o̶n̶e̶n̶t̶i̶a̶l̶l̶y̶ cubically with size, meaning the cells have to do more work, or there have to be more of them. The size of the heart has to match the volume of blood being pumped - if they evolved to be larger, the heart might have to be so big that it creates pathology in other areas, or has to pump so hard it damages tissue, or creates forces so great that veins or arteries collapse or burst.
It's probably not as dramatic an issue as that. It could also be sensory - past a certain size, in order to be sensitive enough to detect damage and deal with normal conditions, it would have to be irritated all the time, or numb to potential hazards.
There are all sorts of second and third order consequences limiting how various vital systems can interplay, so more than likely, it's a combination of a whole bunch of things that subtly limit the overall size to where it's at, and any further increase degrades its abilities to survive.
They're just so huge. Their brains are 4 times larger than a human's brain, but we share a whole lot of structure, from the cellular level to the macro, with two lobes, some shared sulcal features (same folding pattern) which indicates that we likely share enough connectomic structure for the ways in which our brains operate to produce similar conscious experiences. Someday, in the distant future, we should be able to use BCI to feel exactly what it's like to be a blue whale (and vice versa.)
Their brains have similar cortical structure, but even though the brains are about 7 times larger, their cortical surface area is only 2-3 times that of a human. It really puts into context how bizarrely massive our brains are for our relatively tiny size.
For contrast, titanosaur hearts would have been around 500 lbs and up to 6 feet in diameter, and their brains were about the size of a big walnut. These land animals were up to 40m long and 100 tons.
Anyway - physics of tissue and frailties of being made of meat are what keep the whales from getting much bigger.
> size of the heart
Size of one heart has restrictions that are determined by diminishing return of physics. That doesn't mean engineering a larger system is impossible or even that very difficult. Same as any other pump system. i.e. there is no reason not to have 2 or 10 hearts.
We do this to move any fluid like water or concrete up to steep terrain or maintain pressure in everything from sewage to oil or gas pipes over long enough distribution systems.
Romanticizing in popular culture not withstanding, heart is just a pump[2] and today can be replaced by (albeit for short duration) entirely by a machine or replaced in a transplant.
We are not talking about say the brain or the central nervous systems[1]. That would be like going to multi-master from single node - lot more fundamental complex rebuild and rethink of the core architecture.
[1]We are not even remotely close to fully understanding let alone attempting to replace.
[2 Amazingly well designed, very efficient, something today we probably could not (yet) build synthetically with similar reliability and durability but it is still a pump nonetheless.
But also internal space is increasing cubically—so any reason it couldn’t have mutated to have 2 hearts servicing each side of the body?
You could also claim our bodies have massive surface area, molecularly speaking. We just are factory-configured to not sense things that are too small to matter to ourselves as a whole (like small bugs and below)
> any reason it couldn’t have mutated to have 2 hearts servicing each side of the body
There are probably no hard reasons. It is most likely that the path of incremental changes leading to that solution is either unlikely, or does not convey an advantage to propagation of genes.
Klingon whales, now?
There are measurements suited to purpose, then there are "technically you could do that" measurements, and it's the former we'd want to use when measuring what sorts of power and pressure and material properties of the vascular system and cardiac tissue of a whale. Enormous amounts of blood are being pumped around, and I'd have to imagine you're in the million miles of arteries and veins and capillaries ballpark, so there's a lot of pressure holding that mass back.
That'd be a fun model to figure out for a weekend project - what sorts of forces are we talking about - how efficient is it compared to say, a hummingbird, or a human, or an earthworm heart?
But when things evolve they don't think if they will have enough heart capacity to pump the blood. They just evolve and by chance they got it right.
So why whale didn't get the chance to be bigger yet?
A binary vascular system? Do you want regenerating whales in the time vortex?
Nitpick, but the volume increases cubically (it scales with volume), not exponentially.
Thank you, I'll correct that. I was thinking inverse square law, then instead of asking an AI like a good nerd, I just winged it.
Some might say you're a purist in that regard
Side note, would positing an argument online without doing an AI fact check first be considered rawdogging your answer?
It seems fitting.
I don't understand how the square-cube law is relevant here. The volume of blood indeed scales cubically with the length, but so does the volume of the heart. Where is the quadratic part of the equation that limits the maximum size of a whale? Why would it not work to take a whale and arbitrarily scale it in photoshop?
> Where is the quadratic part of the equation that limits the maximum size of a whale?
Muscle power output increases with cross section area, ~L^2, not with volume. The heart have no separate power unit. It relies on the same muscle walls that comprise its chambers to power itself.
That just means the walls of the heart would need to grow thicker. Are they at the limit already?
Wall thickness increasing by x increases cross section/power by x^2, but also increases chamber volume/workload by x^3. So workload outruns available power. It's because of this people abusing steroids get heart failure eventually.
>chamber volume/workload by x^3. So workload outruns available power.
What do you mean by workload? Are you referring to the oxygen cost per stroke, or what?