Diving Reflex (and freediving and sperm whales)

[Shadowdweller]

James Nestor is a journalist who wrote a book about freediving. He makes a number of interesting albeit somewhat dubious claims here regarding physiology and biology: https://www.youtube.com/watch?v=R_ck0Nzdo_U

Some of what he says is scientifically grounded...but other stuff seems exaggerated. (For example at one point throws off a statement about sperm whales eating 60-foot long squid...which is larger for Architeuthis than has been verified, but is a fairly minor nitpick). Thoughts, anyone? How much of a kook is this guy...if at all? There is extensive scientific literature regarding the diving reflex in humans and other mammals, for example. But I'm having a little trouble finding/verifying consensus.

 

[William Parcher]

I can't watch YouTube on this slow service. Could you post the claims?

 

[Dancing David]

Spleen size: https://www.npr.org/sections/goatsa...e-secret-to-deep-diving-may-lie-in-the-spleen

 

[Shadowdweller]

I can't watch YouTube on this slow service. Could you post the claims?

Yeah, sorry. Some of the claims Nestor makes are:

Freediving:

* Infants lose swim reflex when they learn how to walk
* Human heart rate lowers 25% on immersion in water
* Past 35 feet human body becomes negatively buoyant
* Air in lungs shrinks by half every thirty-three feet diver goes down
* Heart rates of freedivers recorded as low as 14 bpm - one recorded as low as 7 bpm. While still conscious. For reference: The human heart averages 60-100 bpm while at rest.
* Modern freedivers diving to 800 feet (on single breath of air - w/o scuba gear; these are upper-tier trained athletes).
* World record breath hold (while freediving) - 12+ minutes

Marine Biology:
* Marine animals don't swim away from freedivers; but do swim away from divers with scuba gear
* Only way to study some marine animals - such as sperm whales - is by freediving
* Humans or some humans can echolocate (think this one has been verified)
* Sperm whale echolocation clicks can vibrate human body to death

Some of these claims have a very clear scientific basis. I'm just not sure whether they all do - and whether to the extent and in the context Nestor claims; the latter of which I'm sorry if I haven't communicated.

 

[MikeG]

.....The human heart rate averages 60-100 bpm while at rest.

No. Anyone who is up around 100 bpm is seriously unwell. 60 to 70 is the generally accepted average. Decent endurance athletes can have a resting pulse in the 40s (30s occasionally).

 

[Shadowdweller]

No. Anyone who is up around 100 bpm is seriously unwell. 60 to 70 is the generally accepted average. Decent endurance athletes can have a resting pulse in the 40s (30s occasionally).

Maybe. 60-100 are the numbers they teach us in nursing school...

 

[BowlOfRed]

* Infants lose swim reflex when they learn how to walk

Never heard of this. I have no knowledge one way or the other, but I could easily see that both happen near the same point in time developmentally. I would however be surprised to learn that the process of learning to walk actually affects the swim reflex, rather than it just being coincidental.

* Past 35 feet human body becomes negatively buoyant

There is such a point, but to name a single depth seems silly. It's heavily dependent on how much air is in your lungs. It's possible (for some people) to be negatively buoyant at the surface by reducing the air in the lungs. Some divers need weights to be neutrally buoyant at that depth.

* Air in lungs shrinks by half every thirty-three feet diver goes down

Definitely a simplification. At that depth, pressure is approximately double that above the surface. But the body isn't a thin-walled balloon. Some limited pressure is borne by the body, so the volume won't decrease by exactly half.

The bigger problem is that each 33feet increases the pressure by 1 atmosphere. So the volume doesn't halve each time. It would be 1/2, then 1/3, then 1/4, etc.

 

[Andy_Ross]

* Marine animals don't swim away from freedivers; but do swim away from divers with scuba gear
* Only way to study some marine animals - such as sperm whales - is by freediving

The noise of the regulator exhaust might be part of this.
Divers using Closed Loop Rebreathers don't have the problem.

 

[Delvo]

No. Anyone who is up around 100 bpm is seriously unwell. 60 to 70 is the generally accepted average. Decent endurance athletes can have a resting pulse in the 40s (30s occasionally).

Maybe. 60-100 are the numbers they teach us in nursing school...

I take a few dozen pulses a day (to screen potential donors of blood plasma). Our acceptable range is 50-100, or 40-100 in some cases if we know they're athletic. Of course, nobody told me the reasoning for the upper limit because all I need to know is what the limit is to do my part, but it's possible that the limit is not exactly based on ideal health and might include other considerations like that 80-100 might be unhealthy but still not pose any greater risk in donating, or that the donors' pulses usually go down while waiting to donate and donating...

Just from talking to the ones that are over the line (to tell them they can't donate today) or even close to it (because they might go over it next time if nothing is done to bring it down), it seems that most of those who are around 90 or more turn out to be people who took caffeine or tobacco within about the last hour or so, or exercised practically immediately before coming in (including just rushing to get there)... but not all. There are a handful with pulses in the 80s and 90s for no apparent reason and with no sign of anything (else) wrong or out of the ordinary. Sometimes they're already aware of it and have asked their doctors and been told "you have a high pulse and that's just the way it is". It appears to be their normal state.

 

[lomiller]

Not going to address everything. Overall he seems to be stretching some facts to create a narrative.

Humans do have a dive response and my understanding is that it’s a notably strong one for a land based mammal. It’s not comparable to that possessed by aquatic animals.

Infants can’t swim, they just wave their limbs around and some people interpret this as swimming. Most instinctively hold their breath and IIRC there are some structures that aid them in doing so that are lost later on but if these exist it seems likely that they are related to living inside a womb.

Having a point where you are negatively buoyant seems inevitable as the air inside your lungs is compressed.

Some people can do a rudimentary from of echolocation, but it’s not like it requires some exotic organ humans don’t possess. Most mammals could do the same. I’m more intrigued by the number of mammals can detect magnetic fields (Dogs, cows deer) and wonder if we don’t have some capacity for that as well.

 

[bobdroege7]

I am negatively buoyant when I exhale and thus can do fun pool tricks, like doing pushups on the bottom of the pool.

I took a swim class in college and there was a guy who was a wide receiver on the football team and he could not float at all.

 

[MikeG]

.......... there was a guy who was a wide receiver on the football team and he could not float at all.

I'm pretty much the same.

 

[Ziggurat]

I took a swim class in college and there was a guy who was a wide receiver on the football team and he could not float at all.

"Lifting isn't just a hobby, it's a journey. And that journey often begins with feelings of inadequacy, and ends with feelings of inadequacy, but now you can't wear jeans and you sink in pools."

 

[casebro]

..... I’m more intrigued by the number of mammals can detect magnetic fields (Dogs, cows deer) and wonder if we don’t have some capacity for that as well.

Isn't there an iron compound involved? If humans have it, we would know from the usual autopsies, or at least some done specifically.

But the ability to find your way back, or to give/follow directions, varies immensely.

 

[lomiller]

Isn't there an iron compound involved? If humans have it, we would know from the usual autopsies, or at least some done specifically.

But the ability to find your way back, or to give/follow directions, varies immensely.

I don’t think an autopsy would necessarily show anything. In spite of the large number humans have taken apart over the years the tendency for Cow and Deer to line themselves up with magnetic fields was only identified from Google Earth imagery in 2008 while the paper suggesting dogs align themselves with magnetic fields when they poop only came out in 2015.

 

[Shadowdweller]

Infants can’t swim, they just wave their limbs around and some people interpret this as swimming. Most instinctively hold their breath and IIRC there are some structures that aid them in doing so that are lost later on but if these exist it seems likely that they are related to living inside a womb.

Indeed. Nestor doesn't actually make the claim IIRC that infants can actually swim (i.e. move themselves), though he kind of implies that the reflex might be linked to some sort of aquatic past. I'm more apt to believe in some sort of survival mechanism...the breath-holding part of the swim reflex, for example, is fairly important. Question in my mind is...why does it disappear?

Some people can do a rudimentary from of echolocation, but it’s not like it requires some exotic organ humans don’t possess. Most mammals could do the same. I’m more intrigued by the number of mammals can detect magnetic fields (Dogs, cows deer) and wonder if we don’t have some capacity for that as well.

I'm personally much more impressed by the echolocation - for example, the clip of the blind man apparently riding a bike. Given that our nerves, sensory neurons, and muscle cells all work by voltage-gated ion flow, it's not that much of a stretch to imagine that magnetic fields (of at least certain field strengths) might be discernible in some circumstances.

 

[casebro]

I don’t think an autopsy would necessarily show anything. In spite of the large number humans have taken apart over the years the tendency for Cow and Deer to line themselves up with magnetic fields was only identified from Google Earth imagery in 2008 while the paper suggesting dogs align themselves with magnetic fields when they poop only came out in 2015.

I was thinking in comparison to homing pigeons.

 

[lomiller]

I'm personally much more impressed by the echolocation - for example, the clip of the blind man apparently riding a bike.

Our brains have more than enough general processing power for simple echolocation. The fact that this ability can be evolved and specialized to do what dolphins and bats do is remarkable but the simple version doesn't seem all that impressive to me.

Given that our nerves, sensory neurons, and muscle cells all work by voltage-gated ion flow, it's not that much of a stretch to imagine that magnetic fields (of at least certain field strengths) might be discernible in some circumstances.

Our nerves operate via electrochemical signals not electromagnetic. There are no large conductors involved in which a magnetic field could be induced. This doesn't rule out magnetic fields interacting with sensory neurons or nerves but the effect would be really small. Microscopic bits of magnetic material would seem to be a more likely source for this sensory ability. IOW Unlike echolocation that can leverage existing brain+hearing magnetic field detection would seem to require an actual specialize sensory cells.

 

[Shadowdweller]

Our nerves operate via electrochemical signals not electromagnetic. There are no large conductors involved in which a magnetic field could be induced. This doesn't rule out magnetic fields interacting with sensory neurons or nerves but the effect would be really small. Microscopic bits of magnetic material would seem to be a more likely source for this sensory ability. IOW Unlike echolocation that can leverage existing brain+hearing magnetic field detection would seem to require an actual specialize sensory cells.

Magnetic fields are produced whenever there is movement of charged particles. Neurons produce distinct and measurable magnetic fields when firing en masse. There are neuroimaging tests that revolve around this concept. Example: http://ilabs.washington.edu/what-magnetoencephalography-meg. Furthermore, despite the frequent presence of magnets in a host of quack medical and pseudoscientific practices, there has been very extensive and real research into the effects and potential therapeutic uses of magnetic fields on human physiology. Token examples:
https://www.sciencedirect.com/science/article/pii/S1388245704000033
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0013883

The effects, of course, are neither simple, consistent, nor well understood. Naturally, there is a world of difference (/continuum of potential sensory acuity) between being able to sense the presence or absence of magnetic fields in some circumstances versus being able to pinpoint location or navigate long migrations based on the earth's magnetic field, as some birds have demonstrated. Just as there is a difference between hearing an echo and being able to produce a three-dimensional mental representation of nearby objects including texture, velocity, and potentially substances based on echoes.

 

[lomiller]

Magnetic fields are produced whenever there is movement of charged particles. Neurons produce distinct and measurable magnetic fields when firing en masse. There are neuroimaging tests that revolve around this concept. Example: http://ilabs.washington.edu/what-magnetoencephalography-meg. Furthermore, despite the frequent presence of magnets in a host of quack medical and pseudoscientific practices, there has been very extensive and real research into the effects and potential therapeutic uses of magnetic fields on human physiology. Token examples:
https://www.sciencedirect.com/science/article/pii/S1388245704000033
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0013883

The effects, of course, are neither simple, consistent, nor well understood. Naturally, there is a world of difference (/continuum of potential sensory acuity) between being able to sense the presence or absence of magnetic fields in some circumstances versus being able to pinpoint location or navigate long migrations based on the earth's magnetic field, as some birds have demonstrated. Just as there is a difference between hearing an echo and being able to produce a three-dimensional mental representation of nearby objects including texture, velocity, and potentially substances based on echoes.

Again, though, you don’t have charge moving down a conductor. That isn’t how nerves and neurons work. Yes there is some physical movement of charged ions within a nerve cell and any movement of charge will create a tiny magnetic field but this is negligible. Your own link says it takes 100 000 simultaneous neurons firing to generate a measurable magnetic field.

This relationship is not symmetrical. Just because you can get a tiny magnetic field from an ion moving within a nerve cell when it fires, it does not mean that same nerve cell will fire in response to even a large magnetic field. This just not seem to be a viable mechanism for animals detecting magnetic fields, and research into exactly how animals detect magnetic fields is focusing on specific proteins that have the capability to function as a magnetic compass.
http://rsif.royalsocietypublishing.org/content/15/140/20180058