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/showthr...&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 ....probably voided by the 15 lbs of lead and 7mm suits to get down .

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...
http://forums.deeperblue.net/showthread.php?t=64374

[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]

Originally Posted by 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.

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]

Originally Posted by 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.

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]

Originally Posted by fcallagy

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!