Do you know what MDR is?

[tylerz]

Recently I have noticed a barrage of references to people thrilled that they are experiencing MDR and accounting all their progresses to this fact. Most seem to be fairly new to freediving and have picked up the subject from various sources, including here and freediving clinics. So, years after the first bout on the subject("Mammalian Diving Reflex just a Romanticism?" - http://forums.deeperblue.net/showthread.php?t=40688&highlight=mdr ), let's see where we are and what state things are in. After all this appears to be one of the first things people are promoted to know about... so what knowledge is there?

First, here is a recent article that emphasize how the public can receive this topic. In response to David Blaine's stunt, with Performance Freediving as the trainers and safety, somebody wrote:
http://abcnews.go.com/Health/story?id=1913767&page=1
"May 2, 2006 — When humans enter water they can automatically hold their breath longer than they can on land.
That's because the body immediately goes into "oxygen saving mode" by slowing the heart rate and shunting blood to the body's core.
Known as the mammalian diving reflex, this trick of human physiology (and of whales, dolphins and seals) will benefit magician David Blaine, who is living underwater in an 8-foot acrylic sphere in front of New York's Lincoln Center all this week."

This is obviously a grossly inaccurate suggestion but it is reflected in many teachings and discussions on the topic to various degrees.

First, I think we should clarify what constitutes an experience of MDR and what does not.
Second, I think we need to address, with regards to the experiences people have, what are other likely explanations for what occurs within them.
Thirdly, I think we need a reassessment of what assists the MDR to kick in.

Waiting for me to answer those questions? Uh unh... I will kick it off, you guys drive the exploration. I am just planting the seed and will try to support that exploration as it occurs, with the information and experiences I have.

My seed:
I was freediving regularly for three years, throughout all seasons, reaching depths of 55m, and yet I still was never experiencing MDR. However, I was having peaceful long dives, I had managed statics of over 8min, and I was diving in all manner of temperatures and environments. Why would I claim that even when I generally feel similar experiences as many of the new voices that believe they were under the spell of MDR?

 

[feign]

Ok Tyler I will take some of your bait.

The mammalian diving reflex is a real phenomenon. Scientifically sound..done deal. I think everyone agrees with this. The diversity of human experiences, personal attributes, conditions and situations will greatly affect how this reflex is provoked, to what degree or if even at all. How do we measure if someone is experiencing the diving reflex? I guess the objective way is to plug them into monitors and measure a physiological response. Here are some thoughts I have that lead me to believe that we are close to the diving reflex. We may not be aware that it is there or to what degree, just as we aren't aware of every beat of our heart, or the digestion process of our bowels.

We see the diving reflex very early in our mortal existence. In fact, as a child being born our bodies used the diving reflex to survive the hypoxic episodes of each uterine contraction as we were expelled from our mother's womb. This bradycardia and peripheral vasoconstriction that occurs in the fetus during this time is called in the medical field the "diving reflex".

The diving reflex is provoked by increased stimulation of the parasympathetic nervous system (this is the side that does everything opposite of the fight or flight sympathetic system). In particular the vagus nerve, is our friend that slows the heart.

The diving reflex is so handy at slowing electrical conduction of the heart that it can be used to halt some dangerous arrhythmias, specifically SVT - a type of tachycardia. When some one presents to an Emergency room with SVT, "vagal maneuver's" are attempted to elicit the diving reflex and return the heart rate to a normal rhythm. If this is not successful then further measures are employed.

Vagal maneuver's are done to try and stimulate the vagus nerve or generally speaking increase the parasympathetic nervous system stimulation.
What are the vagal maneuver's? Typically, the major ones in adults are
Valsalva (sound familiar ) and carotid body massage.

Valsalva - by straining against a closed glottis during a held breath there is an abrupt increase in intrathoracic and intra-abdominal pressure....long story short....increases vagal tone....decreases heart rate. Increase in intrathoracic and intraabdominal pressure (subsequent intra-arterial pressure changes is an important part of the process) from diving pressure depths will also reinforce the process. This is essentially what happens in the birthing child mentioned previously with the forceful uterine contractions increasing pressure on the child.

In little kids with certain arrhythmias, since it is hard to tell them to "bear down" and perform valsalva, ice packs or cold water cloth can be placed on the face in an attempt to elicit the diving reflex. This is where we Canadian divers might have some advantage:t ....probably voided by the 15 lbs of lead and 7mm suits to get down :head.

As far as what other experiences people are having that aren't the diving reflex? I don't really know, other than good relaxation, which would probably be a biofeedback type of turning down one's own sympathetic nervous system?

lee

 

[naiad]

I don't know whether this is MDR or not, but I always go pale after holding my breath in the pool...
[ame="http://forums.deeperblue.net/showthread.php?t=64374"]Blood shift during static?[/ame]

 

[ncunuclear718]

My heart rate 60 per min.

I got "Vagal maneuver's" but my heart rate still 60.
How long should I do Vagal maneuver's for slow down heart rate,1min or 10min

 

[naiad]

My heart rate doesn't always decrease when I hold my breath, in fact some of my best times have been done with a high heart rate. I certainly can't hold my breath longer underwater than I can on land.

 

[ncunuclear718]

My heart rate doesn't always decrease when I hold my breath, in fact some of my best times have been done with a high heart rate. I certainly can't hold my breath longer underwater than I can on land.

High heart rate!! Are you have hyperventilation?
If you do that you can got your new PB but that is dangerous for diving right?

 

[naiad]

It happens even if I don't hyperventilate. I haven't discovered anything that slows my heart rate down. It sometimes slows down a bit at the end of a long static, but usually it stays slightly higher than normal for most of a static. This is not a big problem, and I am happy with my static times.

I have only noticed my heart rate for dry statics, I haven't measured it properly in the pool.

 

[ncunuclear718]

It happens even if I don't hyperventilate. I haven't discovered anything that slows my heart rate down. It sometimes slows down a bit at the end of a long static, but usually it stays slightly higher than normal for most of a static. This is not a big problem, and I am happy with my static times.

I have only noticed my heart rate for dry statics, I haven't measured it properly in the pool.

Thanks! for your reply.

 

[lungfish]

Part of initiating the reflex is correctly cueing your body.... submerging facial muscles for 5-8min is the first step.... I breath up through a snorkel, on my face, unless it is a performance dive. The next thing is to do some submersions with negative pressure to further stimulate the body towards the MDR. Finally, using the reflex along with tolerance training makes an incredible difference in swimming performance.

As a lifelong competitive swimmer who trained at a fairly high level, I can tell you that there is definitely a transitional state that moves me from a generally uncomfortable state in the water to a supremely comfortable one.... whatever you want to call it. It never occured as a surface swimmer, only when diving or sounding over a long period of time. It is a natural sensation and those of us with the body awareness to do so can sense it. Maybe it isn't as "romantic" as some make it out to be, yet it is terrifically dramatic when it is experienced by neophytes. The idea that it is an altered state of physical and mental being leaves a lot of room for imagination.

 

[cdavis]

OK Tyler, I'll bite that seed, it looks tasty. Good time to clarify everybody's thinking.
I always thought MDR was pretty straightforward, mammalian physiology, some of the opinions in the original thread not withstanding. All divers experiance MDR (as I define it) whether they know it or not. You say you are not, but what's your definition of MDR? I went back and read some of the threads you referenced. Seems like some divers might be misidentifying some things as MDR(at least by my definition), but maybe. . . . I tend to separate the physiological MDR response from the emotional, relaxation aspects but maybe that's not right. Is it possible that a strong physical MDR extends into the relaxation/emotional realm? or that either can reinforce the other?

Responses?

Connor

 

[tylerz]

Hey, great information so far. I have been too busy to respond the last little bit, and now that I have thought about it, I feel it would be much more valuable to attempt to organize the many various gold nuggets of information that have arisen on this topic in and out of the forums. So, shortly I should have a document which is a collection of the thoughts and facts surrounding MDR. Stay tuned.

Meanwhile, what questions are out there regarding MDR that you feel have not been answered or addressed very clearly? What other information pertinent to the issue have you come across? What studies do you know of, have information on, or links to?

Cheers,
Tyler

 

[fcallagy]

surely the biggest measuerment you can do yourself is the extremities getting cold as the blood shifts to the core I,ve got my heart rate pretty low but have a fairly poor static in pool due to not training with anyone or will this coldness take over anyway as you are no longer moving in the pool. I thought in a nother post eric fattah kept his heart rate fairly high and obvoiusly still had great static times but I could be wrong.

 

[Fondueset]

I really don't push the envelope or train seriously like most of you on this thread. But, as I"ve mentioned elsewhere - I've noticed a few things - particularly regarding cold water diving. I've been diving all winter in a 5 mil suit - around here the water is as cold as fresh water can get without become solid. I've stayed in well over an hour during the coldest times and often have a pretty good chill from the wind blowing across my back and wicking out the heat. If I want to get warm - I dive. I can be on the edge of shivering uncontrollably - dive - and be quite comfortable during and for a few minutes after the dive. This also occurs without a wetsuit in somewhat warmer water. Without a suit it is somewhat more intentional - that is I intentionally relax along the surfaces of my body - and pay attention to the 'boundary layer' of comfort that seems to surround my body. With a wetsuit there is no 'shock' - so there is less need for this kind of effort.

 

[naiad]

surely the biggest measuerment you can do yourself is the extremities getting cold as the blood shifts to the core

I have noticed this even during dry statics in a warm environment. I don't know if it is MDR...

 

[jome]

Yeah, I don't know. A few things are obvious, and I've witnessed them many times in my self, and others. I'll take the non-scientific approach (as there are people here with much stronger background in the scientific), and just go with the gut feeling and personal account

-Submersion in water slows the heart. The colder and deeper, the stronger the effect. Combined with apnea, it is very strong
-Same effect to lesser degree with dry apnea
-The emptier the lungs, the stronger the effect (both dry and wet)

Heck, I'll throw in a graph from my heart rate monitor. This was a dive done without any preparation (as you can see from the HR of 130, I had just swam to the buoy), with FRC to about 10 meters in 4c water. If you look at the time scale, the drop is imminent. From 130 to around 40 in 10 or so seconds!


I think this, among other things, is partly simply a mechanical result of lower pressure in the lungs -> higher blood volume -> less pumping

Packing is really counter productive in terms of all this, it more or less eliminates the effect.

When I "experience" MDR, it is almost always with FRC or "not completely full" lungs.

But, all that said, these facts remain:
-My best perfomances are done packing to the point of uncomfortable and relatively high heart rate (in the 70-80s vs 40-50s without packing)
-I still perform better in apnea on dry land
-Exception being deep diving, for which there is no way (?) to compare to dry apnea results, but there definately is a "jump" in performance (for example a 2 minute dynamic in the pool is torture, but 2-3 minutes in cw goes by like you don't even notice).

Personally, I believe the 2 biggest factors in "MDR" to be the breath hold and pressure. In fact I usually call it "apnea reflex". I don't think there much debate weather or not it exists...Facial immersion etc may have some effect, but at least for me it is negliable. Sure I feel nicer doing statics face in water, it may even show in the HRM, but the objective truth is, the times are not getting any longer. Maybe there are strong personal differences? But anyway, for me it seems that in pool conditions, it doesn't really "happen" with just floating face down. But with empty lung dives to 4m I sure can invoke some pretty cool HRM graphs

For me, personally, MDR is a series of "tricks" I do to get "into the zone". Which means this strange, slowed down, state which feels almost like being a little drunk. During that state I can do long dives and be very comfortable. Never really feeling the need to come up. But, I've noticed, it doesn't seem to affect (at least very dramatically) the absolute performace. I can crank out just as long or deep dives without it and feeling like crap...It's just that the former method is much more fun!

 

[Morg]

Wow interesting graphs there jome.

Next time I am going to do some statics I will try and find a heart rate monitor and get some readings as well.

 

[naiad]

But, all that said, these facts remain:
-My best perfomances are done packing to the point of uncomfortable and relatively high heart rate (in the 70-80s vs 40-50s without packing)
-I still perform better in apnea on dry land
-Exception being deep diving, for which there is no way (?) to compare to dry apnea results, but there definately is a "jump" in performance (for example a 2 minute dynamic in the pool is torture, but 2-3 minutes in cw goes by like you don't even notice).

My best performances are done with full lungs and often a high heart rate. I perform better in apnea on dry land. I hope I will be better at deep diving than I am at dynamic.

 

[tylerz]

Most of my response here is targeting everybody and in response to many opinions I have come across. I am just working from some key statements Connor has presented.

I always thought MDR was pretty straightforward, mammalian physiology... <snip>... All divers experiance MDR (as I define it) whether they know it or not. You say you are not, but what's your definition of MDR?

Connor, good point that throws us right into the heart of the issue. MDR is frequently presented as an aquatic adaptation passed on from our ancestors (aquatic ape? other sea mammal?). Often, it is taught that we need to reengage or awaken the reflex in ourselves. This is suggestive of a reflex, as clarified by Ben Gowland in the original thread:

The term reflex should be reserved for an event which triggers a neurological or endocrinological response. If the 'reflex' is not 'controlled' by the body, and is a mere reaction/effect of pressure, then we decided that reaction was a better term.

Connor, what are you meaning by “straightforward” physiology? Are you referring to mechanical physiology as opposed to the involvement of the nervous system?

If one looks at the issue from the stand point of mechanical physiology, then we should be referring to the “diving reaction”. Further it seems largely presumptuous to refer to it as a mammalian DIVING reflex. Instead, in reference to Feign's post above, it could have been called the “birthing reaction”, or separated into “high-pressure reaction” and “hypoxic reaction”. At the time of first using diving reflex, I wonder if “facial-immersion reflex” was considered under the term diving reflex.

So, here we are with a term that in a minor way has had its use in the medical field, but it appears has not had enough attention or focus to really distinguish that there are multiple concepts and physiological systems at work, all being thrown under “diving reflex”. Not only does that cause a great ambiguity, but considering that the medical community goes to great lengths to separate and distinguish between the physiological systems, their workings, and interrelations, the “diving reflex” does not appear to reflect a mature concept. This suggests it has not been relevant or important enough to be repackaged and refined. To summarize some of the responses and reflexes suggested as covered by the MDR:

bradycardia reflex to apnea
bradycardia reflex to facial immersion
bradycardia in response to cold
vasoconstriction response to apnea
vasoconstriction reflex to apnea
vasoconstriction reflex to facial immersion
vasoconstriction in response to increased external pressures
vasoconstriction in response to cold
lowered cardiac output in response to core blood volume increases.
​

To summarize a few situations where at least one of these end results occurs:

life threatening bodily wounds
hypothermic conditions
meditation
yoga
​

If a person claims they are experiencing the MDR, it seems to suggest they are experiencing everything associated with MDR. It seems, MDR should not be referred to in the singular if a person is only experiencing a single physiological response that has come to be associated with the MDR. If MDR, as it's name implies, refers to a “reflex”, and only those responses which satisfy the term reflex, then a person claiming they have triggered the MDR, would be referring to triggering something in their nervous or endocrine systems. In this situation, referring to the MDR as a whole may make sense. However, if we are talking about mechanical responses/reactions, then referring in the singular to MDR suggests that all the responses are logically tied to each other, and unless impeded, will all take place upon diving, correct? Also, concluding MDR is taking place due to witnessing a subset of the responses occurring, whether diving or not, logically suggests that these responses are naturally originating from the need to deal with diving conditions. However, as we know, these responses occur in many conditions which have nothing to do with diving, therefore even though it is possible that diving conditions were the main push for such responses, it seems presumptuous to conclude it was so.

Packaging the MDR as all the things that we freedivers have come to associate with it, seems like looking at a human laughing, crying, bouncing about, heart-rate increasing, jaw muscles flexing, etc., from being tickled, and suggesting they are all responses originating and integrally owned by the “tickle reflex”. Of course these responses do occur in response to being tickled, but they occur in response to many things. Would it not be presumptuous to claim that these responses individually originated due to being tickled or some essentially equivalent situation? Does it seem realistic to suggest muscle growth in the jaw, an instance of crying, an increase in momentary heart rate, etc, all developed in the human body to deal with being tickled, or are a sign of an active “tickle reflex”? I wonder if this relation to MDR doesn't strike you as being a fair logical comparison?

So, I am inclined that MDR should more appropriately be used as a container to label what responses we “can” undergo as a response to diving conditions. That is what we do “know”. Science and the medical community attempt as much as possible to reflect what we tend to call knowledge. What we don't know is that the responses automatically occur when anybody dives, that the responses originate as an adaptation to water submersion specifically, or that the responses were not an adaptation to more prevalent conditions of mammals out of the water. Since we don't know that, I don't think the science or medical community would, or should, back a definition that suggests otherwise.

I went back and read some of the threads you referenced. Seems like some divers might be misidentifying some things as MDR(at least by my definition), but maybe. . . .

So, let's see some definitions that people think are appropriate for MDR?

To give mine, I need to specify that there should be at least two separate concepts we refer to:
MDR – a collection of reflexes in mammals that are known to sometimes occur in response to water submersion.
Diving Responses – a collection of physiological responses in mammals that sometimes occur due to water submersion.

Now, those are my choices of definition, but what not everybody may see is the degree of implication within each of those statements. There are implications of how to use the terms and what is covered by the terms. Statements, such as, "I felt my heart-rate drop significantly when diving the other day, therefore the MDR kicked in strongly," would not be a statement that could logically follow or take credence from my suggested definitions.

I tend to separate the physiological MDR response from the emotional, relaxation aspects but maybe that's not right. Is it possible that a strong physical MDR extends into the relaxation/emotional realm? or that either can reinforce the other?

Depending upon the definition, emotional may very well be part or not of MDR. It is all about definition and that is why I think there is so much confusion around the topic. It has not strictly been defined or where those definitions exist, too much imprecise extrapolation has occurred.

I am hoping that with enough participation here and promotion of clarifications that arise, our community can drive a set of definitions that are precise and accurate, which maybe will push the relevant fields to also eventually develop upon that need. As more freediving research occurs, it will happen anyhow. It would be nice if when that occurs, freedivers are not looked upon as having it all misconstrued and actively promoting weak reasoning and romanticism, for our own interests. The public currently receives its understandings mostly from the freediving community, therefore I believe we should be striving to be on top of things with a level of professionalism whether it benefits how we see ourselves or not.

Thoughts?

 

[cdavis]

Tyler, you think more deeply about this stuff than I do, part of why its fun to think about your posts.

To me MDR includes reflex and (as I understand your term) reaction, response. Its all the physiological changes that go on in the body that kick in when we start diving, get wet, hold our breath, etc. For me that would include dumping red blood cells into the bloodstream from the spleen, something most people might categorize differently. Thirty minutes into a diving session and my dives are approaching their best, I might say, " My reflex has kicked in all the way."
Not sure I understand your question about "straightforward physiology." Mechanical, I think. I readily see your point about fuzzy MDR definitions. I'm as guilty as anyone. It would be very useful to develop a set of well thought out definitions for all or part of the various diving related responses. Food for lots more threads in "Freedive Training" and better ways to better focus our training.

I agree with your points about the "aquatic ape" theory. Fun theory with some interesting supporting data, but I'm a bit sceptical. Maybe it is sufficient to explain MDR, but it certainly isn't necessary.

I am fascinated with the idea that MDR can include emotional reactions. Seems logical, given a proper definition, just never thought about it. Spearo background. How about expound on the ties between emotional and physiological responces the may or may not be associated with MDR type reactions. Anybody else??

Connor

 

[Ben Gowland]

Nice one Tyler - I barely remembered the original thread!

I still remember the issues surrounding Reflex versus Response/Reaction. Ironically, even within the scientific literature the two have been interchanged as if they are the same. I'd prefer to call it a Response as it captures all of the potential changes in the body. Although I believe there are some true reflexes there that have highly variable strengths between individuals and within individuals (depending on conditions).

But in the end so what - it is about maximising the response (reflex or not) so that we have great dives!