Underwater Swim Training- Shallow Water Blackout

[John C. Ratliff]

DD,

I looked over your short video and got these two photos off it. The first was your buddy diver as he was when he first surfaced and you first got to him. The second was shortly after he took his first breath. In the first, you can see that he is not completely conscious. The second, after just a few breaths, he has recovered.

You asked about permanent brain damage, and assert that it doesn't happen. Well, it could. As you stated, if resuscitation is started very quickly, there will probably be no residual brain damage. I can attest to the fact that one can black out without brain damage, or I would not have graduated college and earned a MSPH degree after my high school SWB incident. However, and this is where some of us are coming from, there is a very short span, in minutes and/or seconds (depending upon the situation), between success and failure to revive a person with SWB.

I will say more on this subject in a few minutes, after I digest a report I got from the Rubicon Foundation titled Physiology of Breath-Hold Diving. You can download this 1987 report too--it makes for interesting reading.

SeaRat

 

[John C. Ratliff]

DD,

You stated,

..Also, as for the definition of shallow water black out. It has a very specific meaning in the freedive community. Application of this term to swimmers in a pool is not consistent with the common usage. That was my original point.

If the pool safety Nazi's want to hijack the term for their own use...and dilute the meaning of the word.. well not much we can do to stop them i guess...

I would like to point out that the use of the term "Nazi" and modifying it with "safety" is an oxymoron. It also shows a weak argument, as the concern about SWB was first associated with underwater swimming in pools in published studies:

Hyperventilation before an endurance underwater swim can cause underwater syncope and subsequent drowning. Underwater swimmers hyperventilate to increase arterial oxygen content in an attempt to delay the time when the desire to breathe becomes overwhelming. However, the increase in arterial oxygen content is negligible, while the reduced carbon dioxide results in reduced cerebral blood flow, reduced oxygen dissociation from hemoglobin and lack of stimulus for breathing. Fifteen deep breaths may set the stage for an underwater blackout."
Underwater Blackout--A Mechanism of Drowning, Dumitru and Hamilton, GP, April 1964
http://www.safetylit.org/citations/index.php?fuseaction=citations.viewdetails&citationIds[]=citjournalarticle_13813_11

In 1973 I was on a search mission with the 304th Aerospace Rescue and Recovery Squadron (Reserve) in the Columbia Gorge, looking for a light airplane. We searched broken trees (wind damage, it turned out), then the pilot decided to head to the north side of the Columbia River. As we were mid-way across the river, the helicopter's engine (an old, HH-34 recip engine helicopter we got from the Navy), quit. We were headed down, and the pilot notified us in the crew compartment to prepare for an autorotation and landing or ditching in the water. I heard the message on the headphone, sat down and buckled up. The other PJ did not sit down; he was in the doorway, looking out. I got up and poked him, saying that he needed to sit down and buckle up. He was new, and I out-ranked him, but he continued to ignore me. So I physically picked him up, shoved him into the seat, and forced him to get his seat belt on, then I sat down and belted in again too. I was very happy to see the shoreline go under our chopper, and we settled into a cattle field on the north side of the river for a perfect autorotation landing. The pilot came out and said, "Look at these hands, look at these hands!" His hands were shaking almost uncontrollably from the adrenaline. The other PJ, when I asked him why he didn't buckle up, he said he was watching another logging company helicopter with a full load of logs, and it was climbing really fast...he couldn't understand why it was climbing so fast with that load. It wasn't climbing; we were falling out of the sky!

I felt somewhat the same way with you a few posts back, when you continue to ignore the science behind the two mechanisms for shallow water blackout (which Wiki now splits into Shallow Water Blackout and Deep Water Blackout). I feel like putting my Staff Sergeant stripes back on, and yelling at you to "Shut up, sit down and listen!" Respecting your elders in the diving community wouldn't hurt either. So here goes again:

--All blackouts are potentially life-threatening.
--Without immediate in-water help, SWB can and has killed divers and swimmers.
--Hyperventilation will induce a low blood CO2, hypocapnea, which will postpone the "must-breath" signal to the brain.
--Even if not hyperventilating, a deep diver can blackout near the surface due to the decreased pressure resulting in a loss of oxygen to the brain when that oxygen goes back into the lungs (reverse osmosis).
--All blackouts are potentially preventable. This has to do with technique, and knowing limitations of breath-hold diving.

In the 1987 paper I linked above, there are two descriptions of blackout, "Breath-hold Blackout" and "Ascent Blackout." These are detailed below:

BREATH-HOLD BLACKOUT.

BH blackout (BB) is most commonly recognized in mishaps that occur in swimming pools and other relatively shallow water. Often, the swimmer or diver made no attempt at all to reach the surface. The same sequence can presumably occur at any depth, but few cases other than those observed from the surface would be recognized and attributed to BB. Al Craig (2) deserves gratitude for describing BB and bringing it to the attention of physicians and the aquatic public.

I like Hermann Rahn's way of depicting the physiological basis of BB. Fig 1 was borrowed from him. It is based on an
02-C02 diagram. The "C02 reservoir" on the right includes a small column representing the lung. The blood-and-tissue reservoir is much larger; but it can be depleted by hyperventilation, and the input from CO2 production during a BH may not bring it back even to a normal level. As the lower arrow on the graph suggests, subsequent gas exchange may carry the P02 well into the hypoxic zone before the combined effect of falling P02 and PC02 would produce significant air hunger...

...ASCENT BLACKOUT.

Ascent blackout CAB) is an insidious hazard. A diver who starts ascent in good condition and at a seemingly appropriate time may lose consciousness and drown before he can resume breathing. The basic difference between AB and typical BB is a factor that I call IIborrowed II Increased pressure at depth permits a diver to consume more oxygen from his alveolar gas than would be available at pressure. The mortgage comes due when he ascends. As ambient pressure drops, the P02 of-expanding alveolar gas drops in proportion, and the final alveolar and arterial P02 consciousness. If the alveolar P02 falls below the mixed venous oxygen tension in the process, the lung will extract oxygen from the blood. In their recent computer modeling of breath-hold dives, Olszowka and Rahn (5) have refined our understanding of this process especially for deeper dives, but I will use a more common sort of example...

Thinking this dialog through, I think that there is a difference between the freediving community and the scientific community on a lot of this discussion of SWB. I also think that some of what the freediving community thinks is based as much upon mythology as on science. Let's think about that, and see whether we can come to some sort of agreement. I have some other references, but this is already way too long.

SeaRat

 

[dumpsterDiver]

Well, as for the pictures of my buddy after the ascent... He claims he was fully conscious and aware and he performed the "back laying" maneuver as a means of insurance or self rescue. This little technique is NOT recognized or promoted by the freedive community. When people BO or come close to it, their awareness is reduced (or eliminated) and their memory of the incident is similarly affected. So neither of us really knows if he was on the verge of a BO. Often (but not always) a LMC (Loss of motor control) occurs before a BO. He may have been exhibiting a little of that on the second ascent. I don't know.

Also, the video was just a record of some dives we did during a tournament. There was a considerable rest period between the two dives, in fact, due to the currents, we had to get on the boat, rest, drive up current and then drift into the lost gun/fish before he could make a subsequent dive to attempt a recovery of the entangled fish and gun from the bottom..

You make the following comments:

--All blackouts are potentially life-threatening.
--Without immediate in-water help, SWB can and has killed divers and swimmers.
--Hyperventilation will induce a low blood CO2, hypocapnea, which will postpone the "must-breath" signal to the brain.
--Even if not hyperventilating, a deep diver can blackout near the surface due to the decreased pressure resulting in a loss of oxygen to the brain when that oxygen goes back into the lungs (reverse osmosis).
--All blackouts are potentially preventable. This has to do with technique, and knowing limitations of breath-hold diving.


I am in agreement with you on most of the above, but the word osmosis should be replaced with diffusion if you want to be more correct (osmosis is generally defined as the diffusion of water, FYI).

Also the issue about BO being preventable. In theory this is true. Don't hold your breath underwater - will generally prevent BO. Of course you can BO BEFORE a dive as well from excess hyperventialtion, but that is straying off topic to some degree.

However, from a safety and practical matter, your assertion that technique will prevent BO is something I disagree with completely. This is a crux of the matter. As I have repeated now several times, any kind of moderately aggressive breathhold activities underwater generates a distinct potential for a BO. It is irresponsible and impractical to tell people that if they use a certain technique - then they will be safe. The reality of the matter is that the potential for a BO can never be eliminated and therefore it is imperative that a buddy be actively supervising the diver. This is the message that the freedive training community is trying to hammer home. It is a tough sell to some segments of the freedive spearfishing community.

The only other material point of contention (raised in this thread) is the previous (false) assertion that a BO will invariably result in death or brain damage.

I am completely out of my league with respect to discussion of what the freediving community knows versus the scientific community, but there is absolutely no disagreement that the freediving community has a long history of completely refuting and disproving the prevailing "scientific" knowledge generated by scientists.

These guys go out and smash records and then the scientists have to back track and try to explain how the hell they did that. This has been occurring for a long time now.. if you do a little research on Bob Croft (a name you probably recognize - from the old coot era) you will see that his record setting dives were thought to be impossible (i.e., deadly) before he disproved the scientific community. Now dives like his are commonplace within the competitive freedive community.

In essence, the scientists thought his thoracic cavity would collapse from the depths he dove to, but it is my understanding that leakage of blood plasma and possibly other phenomenon are taking place - which science was previously unaware of.

 

[The Chairman]

For me it's simple: It was a blackout that happened in shallow water. Like DCS, there can be more than one mechanism that gives the same result. I had this happen to me in a pool. I was getting over being sick and was attempting my monthly 100yd UW swim. I was pushing myself and didn't feel that I could make it, and then it all got super easy. I felt I was going to be able to touch the wall and go back. Next thing I can remember is fighting with the life guard. It took me a few moments to realize I had completely blacked out three feet from the wall. I haven't attempted that UW swim since.

If you want to do this, don't do it alone. Inform the lifeguard what you're going to attempt. Try not to punch them out when you regain consciousness.

 

[dumpsterDiver]

Most pool and lifeguards will NOT allow people to do such things Pete. There is a big push from the "pool safety" people to ban all breathhold activities.

 

[John C. Ratliff]

DD,

Good catch on "diffusion" verses "osmosis."

Also the issue about BO being preventable. In theory this is true. Don't hold your breath underwater - will generally prevent BO. Of course you can BO BEFORE a dive as well from excess hyperventialtion, but that is straying off topic to some degree.

However, from a safety and practical matter, your assertion that technique will prevent BO is something I disagree with completely. This is a crux of the matter. As I have repeated now several times, any kind of moderately aggressive breathhold activities underwater generates a distinct potential for a BO. It is irresponsible and impractical to tell people that if they use a certain technique - then they will be safe. The reality of the matter is that the potential for a BO can never be eliminated and therefore it is imperative that a buddy be actively supervising the diver. This is the message that the freedive training community is trying to hammer home. It is a tough sell to some segments of the freedive spearfishing community.

If you substitute "decompression sickness" in there for BO, you can see the problem I have with this statement. In general, I agree about the need for actively supervising the breath-hold diver by the buddy. But there are measures of technique that can help prevent SWB.

Note also that we are talking about two different populations; I am talking to advanced divers who may be reading this discussion, and you are talking about competitive freediving spear fishermen (note, not too many women do this, although there are some), and sanctioned breath-hold competitions. For the community I'm addressing, the recommendations of shallowwaterblackout.org can help prevent deaths.

For your community, there will be incidents, and the recommendations you provide help, but cannot completely prevent, SWB. Below is Table 2 of a paper from J. R. FITZ-CLARKE titled Adverse events in competitive breath-hold diving. Note that even under extremely good supervision, they had 3 incidents of "ascent syncope." They also had a total of 25 "Adverse Events." These people are on the "knife edge" of physiology. (We used to use the concept of "knife edge" to describe divers who approach the edge of the no-decompression limits, as that is where this term is coming from.) With SWB, being on that knife edge between a good breath-hold dive and blackout is measured is a few seconds, and perceptions of feeling that might well betray the diver.

I also get the impression that you do not read much of the studies that I post. Please look over this one as there are some very interesting findings, and it is fairly recent (2006). Note, there are links imbedded in this text to these sites.

SeaRat

 

[dumpsterDiver]

Yes there are many things a diver can do to lessen the probability of a
LMC or BO. The discussion is not directed toward competitive or expert divers. they know everything I have said. As mentioned, it is common knowledge. Are you under the false impression that supervision is going to reduce the frequency of BO or LMC?

The message needs to be delivered to new divers who are just starting out in freediving.. dive with a buddy and be prepared to handle a BO and or LMC.

 

[TONY CHANEY]

I also believe that we are sometimes talking about different causes of SWBO.
There are the basic 3:
Hypercapnia: An increase in CO2.

Hypoxia: a decrease in the oxygen available, to include the decrease of O2pp from one depth to another and/or breathing a mixture with lower FiO2 (hypoxic mix).

Anoxia: Very little to none oxygen provided to the brain or other organs.

With the first I can get you back usually rather fast. The second one kinda fast but might leave some brain damage. The third deprives the brain and other organs of oxygen and almost always leads to brain damage, organ damage and death. I might be able to get you back from an anoxia hit but not usually and, as for me, I have never seen a total recover where there was no damage.

Much like NetDoc, I was the one to set the goal by being the only one to swim underwater for three - four pools lengths (home pool). This past summer was the last time...it is just not worth the chance.

There has been some good feedback pertaining to this thread and I am always looking for more knowledge. Let's all dive as safe as we can and have fun.

 

[John C. Ratliff]

Yes there are many things a diver can do to lessen the probability of a
LMC or BO. The discussion is not directed toward competitive or expert divers. they know everything I have said. As mentioned, it is common knowledge. Are you under the false impression that supervision is going to reduce the frequency of BO or LMC?

The message needs to be delivered to new divers who are just starting out in freediving.. dive with a buddy and be prepared to handle a BO and or LMC.

To your question, it isn't supervision, but technique and avoidance of the "knife edge" that will reduce the frequency of BO and the other complications of breath-hold diving (hemoptysis, pulmonary edema, laryngospasm, and loss of motor control).

As an example, I used to make noon-time finswims of about half a mile in the North Umpqua River near Roseburg, Oregon. I would breath-hold dive in the river and chase fish for the fun of it. I did this solo, and never even came close to any of the adverse events of breath-hold diving. I did not hyperventilate, did not go deep (greatest depth of the river there was about twenty feet), and came up before the urge to breathe. Note, I don't advocate solo breath-hold diving, and haven't done this in many years, but did this during the 1980s when I was Finswimming Director for the Underwater Society of America.

I also trained the research divers for a special project in the same river involving surveys for dying salmon below a low-head hydroelectric project (Winchester Dam). We did numerous snorkeling surveys, with underwater breath-hold diving, without incident.

Now, what training do you propose to be a good buddy for a breath-hold diver who's pushing the limits? My thoughts are a certification in CPR, an understanding of the physiology of breath-hold diving, a platform from which to provide emergency aid (paddle board, minimum, but better a boat), immediate availability of oxygen, and a waterproof radio or phone (for calling for assistance) with emergency numbers programmed into it. Actually, one person as a buddy probably is not enough, as there is a need to both provide hands-on aid immediately, and to summon aid immediately. Talking about summoning aid immediately, I used to carry a small card in my wallet:


This ensured that I would have the local phone numbers available, and twenty cents to use a pay phone if necessary (note: that was a while ago ). That card would go under my windshield wiper when diving in Yaquina Bay, Oregon, for instance. What would you (any of you) recommend?

SeaRat

 

[TONY CHANEY]

I rather like your card but I have on my wrist plate my next of kin, blood type, allergies (if any), past medical history, home phone and date of birth and any meds used. I figure that it might same time in the ER.