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Mammalian Diving Reflex just a Romanticism?

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havn't they missed the piont a little?

"Decreased heart rate from the dive reflex does not reduce metabolism or the oxygen demands of the body's vital organs"

yes, the brain and the heart still uses as much oxygene as normal but with the redused bloodflow to arms and legs, the "non-vital" organs, the TOTAL oxygeneconsumption goes down.....hasnt everybody here experienced the build-up of lactic acid long before that same lactic build-up would occur if we where breathing while exercising...?..

just a thought...

The sentence that gets me is:

"Field studies (where you're allowed to step on the thermisters) indicate that the dive reflex does not extend breathholding time."

Then why is it that we do experience significantly longer breath holds after the dive reflex kicks in? Doesn't it seem like this doctor either doesn't have much experience with freedivers or that she has a different definition of what is the dive reflex?

Maybe the divers that were studied had no spleens! ;)

Johan - ya that is the first thing that occured to myself as well. Either she does not understand the effect of reduced blood flow to the limbs or we don't fully understand what she is getting at! But I found that making the following statement:

"...dive reflex does not reduce the need for oxygen underwater as it does in marine mammals."

is a pretty strong suggestion, so is there something we are missing?

Anyhow I have emailed her the following:


Hello Dr. Jolie Bookspan,

I recently read your online artice with the title "Six Famous Myths of SCUBA Diving". The first myth you state that "...the dive reflex does not reduce the need for oxygen underwater as it does in marine mammals." I find this statement rather ambiguos in meaning and was hoping you could clarify your understanding/meaning.

Basically my understanding is that the diving reflex causes vasoconstriction and bradycardia. Vasoconstriction to the limbs would seem to imply less oxygen supply to the limbs and therefore less oxygen consumption by the limbs specifically fed by the vasoconstricted blood routes. The bradycardia would imply less frequency of pressure upon the blood throughout the veins, which would also suggest less oxygen absorbtion through the vascular walls. Both of these seem to suggest an overall reduction in the amount of oxygen consumed by the body for a given period of time. All of this with the benefit to the body of retaining a consistent supply of oxygen to the vital organs (heart/brain).

Therefore, your statement as follows:
"Decreased heart rate from the dive reflex does not reduce metabolism or the oxygen demands of the body's vital organs."

is totally in agreeance to my understanding, but I do not understand how that relates to the overall oxygen demands of the body, which is supposed to be the key of reduced oxygen requirements, based on diving reflex?

Could you please clarify how your statements relate to my understanding and where they may differ? It appears that you are suggesting an understanding of something beyond these ideas.

Much appreciated,

Tyler Zetterstrom
As I said before, I would be very careful of judging experiments on breath-hold diving as they have very often been performed on unsuitable subjects and/or without suitable controls. The former problem is not so common anymore.

One philosophical point about these experiments on 'unsuitable' subjects, is the question of who the results are aimed at - freedivers, or 'normal' human beings? In most cases it is the latter and therefore the experimental design is appropriate and the results correct. The classic example is a lot of the early research on breathold time and facial immersion - where no differnce was found between apneas out of water and those in - the results of which are now put down to the lack of training in the subjects - i.e. they got more freaked by having their faces submerged. Which makes the results quite appropriate for non-divers.

Tyler - my 20m-ish dives are both with assistance and under power - basically it takes a lot longer for my heart rate to drop if I have had any exertion leading up to the 'static' part of the dive. I'm sure this is much in common with your own experiences.
Here is the reply I received consider the article mentioned above:

"In humans, the vasoconstriction reduces heat loss. Just having less flow to an area doesn't have to reduce oxygenation - hemoglobin releases more O2 to keep levels the same."
I think the article is missing the other ways to keep the metabolism in low or no oxygen situation. Like the phosphagen ways and anaerobic glycolisis.
Without blood flow, there is no oxygen-from haemoglobin, but from myoglobin.
Independent from its origin, we experiment some physiological changer during apnea, and all contribute to keep the blood flow in systems that depend only in Oxygen carried by the haemoglobin. The skeletal muscles (not cardiac) can "support" more time without blood flow, so their irrigation is not vital for us.
The reflex is there but why?

With some grievance I must admit that I believe that its mostly romanticism.

The responses we get from holding our breath, holding our breath in water and holding our breath at depth (three different reactions)– I would say are mostly a chock reaction to what is happening at that very instance not because of some trait in our biology that is half aquatic (as Paul Kotik described with what would happen to a mechanic model in a similar situation).

It takes great many years to adept to environment – and once we might have been those seaside monkies – but all those (most?) traits I believe have worked its way out of our systems. It would have been “Darwinian stupidness” to keep them – better to adapt fully to land where we have spent hundreds of thousands of years.

Our mammalian diving reflex might not be a memory from a distant past in our biology – it might just be signs of two things:

1) Our bodys adaptation to live 9 months in water during pregnancy.
2) Our bodys just trying to survive (in fear of death).

The diving reflex I believe is more a CHOCK REACTION (in a body that believes it might be die-ing very soon).
I am a bit confused about this thread.

If I read about the dive reflex in the physiology book of Corriol (2002) or Lundgren (1987), it seems the basic dive reflex is strongest triggered by low temperature in facial immersion, and not directly by depth. Most profound effects are bradycardia (slowing of the heart) , a lower cardiac output (less blood transported by the heart), and peripheral vasoconstriction. This all in a flat lying position with the face immerged.

But in this thread several other things are taken into the tale like; spleen contractions, lower metabolism, higher blood pressure and CO2 tolerance. Unless I am very bad informed, these are quite different subjects. Perhaps they belong to the diving response, but in that case, diving response isn’t the same as diving reflex. Or is it?
Hi Rik,
Understand your confusion.
I don't think we can call this a "shock response", many marine mammals have it, and they aren't close to death, they dive for food, as many humans in the world and as our ancestral relatives did it. In fact, in that shock states our body develops tachycardia (faster hear rate).
The main reason to dive, was to get food from the ocean.
The diving response is composed by: Bradycardia, Lower Cardiac Output, peripheral vasonconstriction, spleen contraction. The high pressure and arrythmias are more prominent in human beings, and shows and imperfect, yet, adaptation.
Diving response or diving reflex, for me just a semantic problem, is how our body adapts to aquatic enviroment, or maybe a memory from his initial aquatic life.
Just my opinions
My oximeter (Christmas gift to myself) came in and I have been playing. Tylerz, your right my heart rate does drop substantially as the hold progresses and continues to drop until I quit.

One big surprise is that my heart rate and O2% was about the same on the first hold as later progressive holds over the same periods (1, 2, 3, & 4 minutes). The only explanation I can think of for this is that earlier holds build up C02 tolerance more for me than bradycardia and vasoconstriction. Anyone else experienced this?

If this theory is correct than I could do a much longer hold for my first, if I could just handle the pain!
Hey Don,

Glad you got to see yourself as a lab rat!

Anyhow I did not understand fully what you were meaning with your finds of heart rate and O2 being the same. Were you meaning that the curves were the same but for different periods of time? What were you expecting to see? Maybe if you can give an example comparison of what you saw between your 1st and 2nd breath-holds?


Sure Tyler,
I mean for all my holds (5 total), at 1:00 my heart rate was 66 – 81 with 100% O2, 2:00 57 – 62 bpm with 100% O2, 3:00 48-52 bpm with 91 –93% O2. My last hold had 42 bpm and 84% O2 at 4:00, and 58 bpm and 80% 02 at 4:30.

So what I am trying to say is my heart rate at 3:00 minutes wasn’t lower on my 5th hold than it was on my 1st, and my 02% wasn’t higher either.

The later holds were easier, but the question is why? The warm up holds did not, from the numbers, appear to be putting me into the dive reflex. Maybe all they did was increase my CO2 tolerance for the later holds?
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Originally posted by donmoore
The later holds were easier, but the question is why? The warm up holds did not, from the numbers, appear to be putting me into the dive reflex. Maybe all they did was increase my CO2 tolerance for the later holds?

If I am not misstaken, the relative ease of de later dives is connected to the increase of the CO2 tolerance. If only I could remember where I have read that.

Yep, that's right Rik - increased CO2 tolerance from the release of HCO3- ions, which end up buffering the acidity from extra CO2.

I have been using my oximeter for years, and I have created several 'benchmark' tests which can predict various things:

1. Sit or lay down comfortably, until you are totally rested. Take one deep breath, hold for 5-10 seconds, exhale, inhale, hold for 5-10 seconds, exhale inhale, then pack (if you normally pack). Hold the breath for 3'30" only. Record the time of the first contraction (if any), record SaO2 @ 3'30", then once you start breathing, watch as the SaO2 continues to drop, then record SaO2 [min]. I call this the 3'30" test. It is quite accurate in predicting your general state from one day to the next. Remember you must have warm fingers, with hot blood flowing into your fingers, otherwise the oximeter is both inaccurate, and alse very delayed (i.e. displayed reading is 30 seconds behind the truth). SaO2[min] of >= 90% is generally a 'good' day for me, although I have recorded days with SaO2[min] of 93% for the 3'30" test. SaO2[min] will show up anywhere from 5 to 30 seconds after you finish the breath-hold, depending on how warm your fingers are. The best time for this test is right after you get up in the morning. It will predict if you are fighting illness or otherwise 'impaired', long before you would ever know it.

2. Using any method to breathe up or warm up, hold your breath and check your SaO2 @ 5'00". In my experience, I need 82% or more at 5'00" to hit 7'00". Kirk told me that Martin Stepanek is around 90% @ 5'00". The highest I ever had @ 5'00" was 92% during a yogic style breath-hold using the contraction blocking technique. When I did my pb of 7'35" I was at 87% @ 5'00". My guess is that you need 90%+ @ 5'00" to hit 8'00".

Eric Fattah
BC, Canada
You keep popping up with these wonderful little tidbits (maybe not so little. :) Can you describe the "contraction blocking technique? Thanks.

Eric and all,
That’s really interesting. I’m really having fun with this oximeter. I have been closing comparing my results to Sebastian’s on his site http://www.webvideo.nu/freediving/features/breathhold.html . My holds are not nearly as long as his for three reasons. First I’m not as good with a PR of only 6:00, 2nd I’m not doing nearly the proper preparation and warmup he did, and second I’m not in the nice relaxed state of lying down.

Instead I’m at a desk and watching the watch, the heart rate, and the O2 readings and writing it all down. I purchased the inexpensive Nonin Onyx (all in one) unit, which from reading the info is suppose to have the latest technology and is very accurate, but there is no recording feature – so it just me and my pencil until I can get someone to do it for me.

And interesting comparison to Sebastian’s results is my O2 drops faster than his at first to a maximum of 5% less at 4:00 min, but my heart rate is lower through out and at 3:00 min it reaches a max lower of 42%. At 4:30 my O2 is only 2% lower than his, but my heart rate is still 31% lower. I’m hoping this trend continues to where my O2 doesn’t fall as fast and is eventually higher than his at later times, because my metabolism is less and using less O2.

If this theory is true it will be consistent with my experiences. When I have a good hold I will go through a hard struggle phase with some pretty good contractions, but then things get better and I feel like I am in a zone. If I’m in a pool with a spotter they get pretty concern that I have reached my limit much earlier than my true limit is. It also is consistent with the loss of heat and blood to my extremities I experience.

Eric what is your heart rate at 4:30 or 5:00? How does it affect your O2 use? Anyone else?

PS Rik and Ben thanks for the info on CO2 tolerance. The really cool thing about an oximeter is it helps you determine what your limiting factors are. If you are stopping your holds at 70 –80% O2 than the limiting factor is not low O2, but instead CO2 tolerance and mental control. I would love to have the ability of Eric Fattah and Sebastian to take it to the limit!
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Don't you have a camcorder, PC camera, digital camera w/video? If so, have them record your oximeter info for you! ;) As far as diving reflex, I find sitting makes my statics much worse (even though others, ahem... Eric... don't) and focusing on the info produced from the oximeter probably keeps your brain feeding aggressively. Sometimes I even use picture imagery in my mind to attempt to convince the body it is diving and in the water. I have not found noticeable results with this. However, through a similar technique where I do not relate to water or diving, I seem to be able to assist/influence vasoconstriction. I would love to test is this is accurate.

I was not previously sure why successive holds became easier, but figured the body would be continually adapting during the first apnea to be able to withstand the conditions as best it could, this adaptation persisting for some time after our static finishes. Ben Gowland, or anybody else, do you have any good references to the nature of the release of HCO3- and its triggers?


I have found another article of interest, by Peter Lindholm, along the lines of the original ideas of this thread, that begins with the following statement, "We sought to determine whether apnea-induced cardiovascular responses resulted in a biologically significant temporary O(2) conservation during exercise."


A quote from this link:

"We conclude that bradycardia and hypertension during apnea are associated with a significant temporary O(2) conservation and that respiratory arrest, rather than the associated hypoxia, is essential for these responses."

This also seems to favor (or support) the idea of apnea being the strongest cause of oxygen-conserving responses (bradycardia and vasoconstriction), as opposed to water/diving.


you should be able to find reference to this release of carbonate ions in human physiology text books.

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