Freediving myth #1 The dive response

[DivingDane]

no he's quite serious i read somewhere that extended time at depth triggers the fight or flight response! so i think he is correct.

however i also remember that this response was not as strong as the euphoric feelings related to blood being forced towards the central pelvic region (also known as Bloodshift)

DD

 

[wet]

Diving & Backfloating Monkeys Unite!

 

[blueface]

It makes sense to me. I'm going to wipe away my tears and continue to stress my system.


Seriously, I'm guessing that the production of endorphins is probably to help cope with the stress. I've definately felt euphoric while diving.

 

[cebaztian]

Well...what can I say. I posted this text a few hours after the 1st of april had arrived in New Zealand. It was intended as my contribution to the aprils fool tradition.
What I wrote may be false, yet some of it may be true. I do not know.

What do we know?

When we stop breathing and imerse our face in cold water (colder than the air) there is a reaction in the body. Some call it the dive response and link it to some ancient biological traits in our autonomic nervous system, believing the response has a purpose - to save oxygen.

What has "irritated" me over the years is that it has been videly spoken of as a good thing. To wake the dive response - a good friend. Something that can be trained.

"Yeah after half an hours diving I feel the dive response kicking in". "The more I dive the earlier it comes". "Just by thinking of diving I feel my heart rate slow down", "I slow my heartrate down", "Diving is a symbiosis between man and water".

I have a very opposite experience The dive response as a dark shadow of physical anxiety, an emergency survival response in a threatened organism.

What if it is the opposite: the more we dive the less dive response reaction we have. The body gets use to the new environment and reacts less. It realises it is not going to die.

What if there is no real benefit of the so called dive response.

What if it is the blood shift (created by the pressure on the pheripheri limbs) and the high levels of CO2 that makes our extreme dives possible. Neither is part of the so called dive response.
Yes the heart rate slows down, that is cool, but so what, it is compensated with higher pump volume and higher blood pressure. What if the real saving of oxygene is the anaerobic state (yet again something that is not part of the so called dive response).

What do we really know?

Sebastian

 

[trux]

OK, so let's speak more seriously now, although it is still the 1st April:

What if it is the blood shift (created by the pressure on the pheripheri limbs) and the high levels of CO2 that makes our extreme dives possible. Neither is part of the so called dive response.
Yes the heart rate slows down, that is cool, but so what, it is compensated with higher pump volume and higher blood pressure. What if the real saving of oxygene is the anaerobic state (yet again something that is not part of the so called dive response).

I do not know what definition of diving response you refer to, Sebastian, but usually when diving response is being discussed in scientific documents, it includes many physiologic adaptation effects including not only bradycardia, but also vasoconstriction, blood-shift, metabolic changes, splenic contraction, hormonal release, etc.

Additionally, in fact the blood-shift is not purely result of the pressure change as you suggest - it is enabled by vasoconstriction, which again is part of the diving response (even in the most limited definition), and of course greatly influenced by CO2 level too. There is a well measurable blood-shift even on surface - for example this document describes a blood-shift of 0.7 l on surface:

Arborelius M Jr, Balldin UI, Lilja B, Lundgren CE.
Hemodynamic changes in man during immersion with the head above water.
Aerospace Med 43: 592–598, 1972 a écrit:

In addition to a predive increase in TLC, a redistribution of blood from the periphery to the intrathoracic blood-containing structures, a “blood shift,” allows the RV to decrease below normal. An increase in intrathoracic blood volume of 700 ml is observed during mere head-out immersion, and the effect is further pronounced by the depth-dependent compression of the lungs.

So on my mind there are no doubts we do need the diving response for successful diving. Diving response is not equal to bradycardia. Diving response includes all the other effects you described too.

 

[blueface]

You got me good!

What does RV stand for? Reserve Volume?

I can't access that link that Trux posted. Is there any other good write ups on this blood shift?

Thanks

 

[DivingDane]

RV= Residual Volume.

nice one Sebastien i almost would have believed you if it werent for you being such a dedicated Dive response enthusiest and teacher!

nicely done, how many years in a row is it now, still havent let us down yet!

DD

 

[cebaztian]

Dive reflex, dive response, the mammalian dive reflex.

I do not believe the vasoconstriction and movement of blood to torso/brain is an effect of 1000 and 1000´s of years of deep diving. It may not be there to help us swim deeper than RV. I do not think we are built for deep diving. Maybe not even built for shallow gathering of food.

I think bloodshift just HAPPENS to be a useful thing for deepdiving.
Bloodshift is mainly for survival in stressfull situations on land, I believe. Is it not so that we get bloodshift when getting cold during winter? Toes and fingers freeze.

But, both a conscious and an unconscious person can survive longer without oxygen under water than in a comparable situation on dry land.

Does that not mean that we are adapted to water/diving?
I dont know, maybe it is a "mammalian survive without oxygen reflex" (designed to help foetus survive if they are dprived of oxygen for shorter/longer periods).
Or maybe it is a "mammalian survive in cold reflex". That it is not about water, but about cold?

I still think it is a pretty good guess that the extreme bloodshift we get during deep dives is partly a mechanical thing. Pumps and hoses put under pressure. And that the vasoconstriction has more to do with cold than with water and breath hold.

So my double aprils fool joke is that I am a bit sceptic to the existance of a "dive response" and even sceptic to the claim that humans have a "mammalian dive reflex".

The response and the reflex I can not deny, but is it about water, is it about diving? It just happens to be useful for us in our stunts.

Sebastian

 

[DivingDane]

interesting Sabastien, and i partly agree.

i am also sceptical that what happens to us is something that is inherited from long ago.

and i also agree that bloodshift at depth is due to the pressure acting on "hoses and pumps" heart and arteries etc.

i still believe that Dive response is correct because all of the factors come together the way they do only in Diving. i dont think we could replicate the exact same sequence of responces with the same results under any other condition. mind you i'm happy to be prooved wrong.

Mammalien Dive reflex i believe is also a bit ambitious, thinking that it is something we have evolved over time.

but none the less it happens and we have learned to use these responses to our benefit in diving.

DD

 

[trux]

I do not believe the vasoconstriction and movement of blood to torso/brain is an effect of 1000 and 1000´s of years of deep diving. It may not be there to help us swim deeper than RV. I do not think we are built for deep diving. Maybe not even built for shallow gathering of food.

That's exact, the diving response, or the so-called "mammalian reflex" is present even at reptilians and birds (the descendants of dinosaurs), so it has likely nothing to do with the diving of our humanoid ancestors. It was simply kept by the evolution since it was useful in different situations (and as you tell, not only for diving).

I think bloodshift just HAPPENS to be a useful thing for deepdiving.

That's also correct, but that's the way evolution works - functions, features, oddities or malformations that show up to be useful, or help surviving, are kept by the natural selection. So if we are like we are today, it is because it HAPPENED, although some people claim it is by design. And the same it is with the diving response. It was kept by the evolution because it was useful, but here unlike you, I believe that water did play an important role in it too. And certainly not as much in the recent evolution of humanoids as in the period of forming of the life in the hundreds of millions years before it.

 

[cebaztian]

ha ha ha, end of discussion, lets go diving.

Aquatic Ape Theory (AAT): Sink or Swim?
The Aquatic Ape: Fact or Fiction

 

[cdavis]

No way, there are some interesting things here, April 1 or not.

I've been training my "dive reflex" for years in pool practice. Dives get longer and longer, more and more comfortable. Dives that used to be almost impossibly difficult are now very easy. Sure looks like some portions of the "dive reflex" are working better.

Here's the interesting part, I used to get some symptoms (tingling hands and arms, empty feeling legs) when I first started doing full exhale, reverse pac dives in the pool. At the same time, the urge to breathe was strong, in very short dives. The tingles certainly appeared to be the result of fairly extreme vasoconstriction. I don't get that any more, nor do I get a very fast urge to breath, even with very extreme negatives. Looks very much like a lessor "dive response", like I was getting used to extreme negatives and was getting less response as a result.

How does this fit with increasing dive times?

Connor

 

[apneaboy]

ha ha ha, end of discussion, lets go diving.

Aquatic Ape Theory (AAT): Sink or Swim?
The Aquatic Ape: Fact or Fiction

Posted via Mobile Device

 

[Fondueset]

This much is true: The body adapts.

All forms of physical practice are based on this - from Mu Thai (kicking trees till your shins get so dense you can break a baseball bat over them) to Yoga - which, incidentally - works a lot with slowing the breath. We can view the G.A.S. in a somewhat fatalistic light -wherein the body is struggling to deal with something absolutely incompatible. But this seems a kind of physiological fundamentalism. On the other hand we have the aquatic ape theory - which is like saying our ancestors had special adaptations that appear when we start kicking trees.

It goes beyond fragmented models like that.

 

[chrismar]

Yep, when cyclists train, their bodies adapt to the specific stresses that cycling puts on their bodies. They don't then turn around and claim an ancestral 'mammalian cycling response', just that training, when done right, improves performances in whatever activity you work on.

Also, ace April fools Seb

 

[Kars]

No way, there are some interesting things here, April 1 or not.

I've been training my "dive reflex" for years in pool practice. Dives get longer and longer, more and more comfortable. Dives that used to be almost impossibly difficult are now very easy. Sure looks like some portions of the "dive reflex" are working better.

Here's the interesting part, I used to get some symptoms (tingling hands and arms, empty feeling legs) when I first started doing full exhale, reverse pac dives in the pool. At the same time, the urge to breathe was strong, in very short dives. The tingles certainly appeared to be the result of fairly extreme vasoconstriction. I don't get that any more, nor do I get a very fast urge to breath, even with very extreme negatives. Looks very much like a lessor "dive response", like I was getting used to extreme negatives and was getting less response as a result.

How does this fit with increasing dive times?

Connor

My guess is:

You got used to area of discomfort, therefore are able to relax much better, have a much better energy economy in the 'lactic phase', resulting in longer dive time.

 

[cebaztian]

Looks very much like a lessor "dive response", like I was getting used to extreme negatives and was getting less response as a result. How does this fit with increasing dive times?
Connor

This is the question we have to answer.

Most people (some scientists) might stick to the idea that you have a stronger dive response.

But maybe you have just shaped your body on so many levels.

- relaxation
- technique
- blood
- spleen
- metabolic rate
- tolerance to low 02

etc

It would be interesting to know the heart rate at the end of the dives: now and when you started.

Sebastian

 

[cdavis]

Cebastion, you raised a question that I'd wondered about, it seems a paradox. Given what I am observing, my dive reflex seems to be getting weaker with more practice, but my times and comfort are getting better.

Heart rate now: When everything is working right, after about 30 minutes of practice, I start the dive in the low 50s. HR jumps into the 70s with the surface dive, then falls quickly back into the high 50s, falls slowly to the high 40s after about 2 minutes (I'm not moving). I start swimming about 2 1/2 and HR begins to rise slowly to the high 50s near 4 minutes and 50 yards. I don't feel blood shifted until after 3 1/2 minutes and not much then. C02 is pretty strong by then.

I don't know what HR was when I started training, but I'm sure it was higher all the way through. and I used to feel more blood shifted than I do now.

If I just jump in, no warm up and do a full exhale, heart rate can drop from the 60s into the high 30s after 40 seconds or so and I can feel a fairly strong blood shift beginning, although not near as much as when I began training a couple of years ago. My meter has a 10 second sampling period, so the actual minimum is probably quite a bit less than that. Successive exhale dives yield higher minimum HR

Connor

 

[Fondueset]

Yow - If I trained like that in the pool here I'd get kicked out!

 

[DivingDane]

Cdavis i know that Seb Murat, used to find that his dive responce would be reduced with more and more training as the body becomes used to the stimuli so, he would try and find more and more ways to "stress" himself to bring on th strong DR again.

maybe this is what is also happening to you.

the body is not feeling the need for such a strong DR anymore due to your training?

DD