Ever experience a SWB?

[Pratesi]

Sorry about loosing your brother. It is important to practice safe and proper technique in all you do. Thanks for the refresher Bindlestitch. You have to respect what you do and constantly remind yourself about the negative things that can happen-its not good to be overly confident,thats when mistakes happen.

 

[codecruncher]

Wow Bindlestitch! That about sums it up. i will add just a couple:
* Make sure you're correctly weighted.
* Never force an equalisation and abort the dive if equalisation ever fails.
* Never freedive after a dive on SCUBA.
* Remove snorkel for duration of dive!
* Use appropriate lines and/or rigging.
* Rapid "turn arounds" should be avoided, this has been implicated in some "deep water blackouts".
* Refrain from looking down on descent and up on ascent.
* Stay hydrated!!

Why remove your snorkel? On ascent I usually give a small puff in it for the clearing action it gives. What I am missing?

 

[John C. Ratliff]

On one of the other threads (about breathholding for 15 minutes) I posted a file of the study by E.R. Cross of the breathholding diver's disease, taravana. I have been researching this for many years, and again looked in my computer files for this writeup I made in the mid-1970s. I have experienced shallow water blackout in a pool, as was described above. But my situation turned out differently.

I was in an underwater swimming contest with my buddy, Tom Lengyl, and Tom had just completed 4 lengths of a 20 yard pool (Salem, Oregon YWCA pool, where we were holding our swim team practice). I was determined to beat Tom, and so I hyperventilated for about 5 minutes, until my arms tingled and I saw spots.

I then dove in and started swimming my lengths underwater, using a modified breast stroke. I swam the first two lengths easily, and quite comfortably. I started "feeling it" at the end of my third length, where I made my turn. As I swam the fourth length, it was getting urgent that I breath, but I surpressed it. I told myself tat I would swim to the end of the pool, turn, take one stroke underwater, then surface and swim to the side of the pool. This is exactly what I did, but I don't remember anything after the turn. The next thing I knew, I was holding on to the side of the pool, with my head swimming (dizzy).

I told my coach (Tom's mother, and a former Olympic Silver Medalist in breast stroke, 1956), and she immediately ended forever any underwater swimming contests as a team event.

When I become a scuba instructor, I wrote the following handout, and illustrated it with graphs. I have updated the graphs into one graph via computer (it looks better than the yellow, mimiographed copy of the original). It is the only graphic representation of pO2 and pCO2 levels that I have seen, although one in this thread is close, as is the definitions found here:

http://en.wikipedia.org/wiki/Shallow_water_blackout

Here is what I wrote in the 1970s:

Taravana. or Shallow Water Blackout
by John C. Ratliff, NAUI #2710
Originally written in ~1978, put into Microsoft Word on March 14, 1997

Taravana is the South Sea Islander’s name for a disease which can effect all breath hold divers. It is a deadly disease, and is also known as an expert’s disease, for it most often effects those who have a great deal of experience. However, it can effect anyone, diver or underwater swimmer, who stays underwater too long. It usually effect those who try various techniques to extend their breath hold diving time, who dive repeatedly or who compete or try to set underwater distance records.

Divers who suffer taravana usually follow similar predive preparations. They hyperventilate (inhale deeply and exhale completely at a fairly fast rate) for a prolonged period, usually until they get dizzy, en the mistaken idea that they would increase the amount of oxygen in their lungs or blood. They would then either dive right in or wait a little to come back to normal and then dive in for the underwater swim. Once in the water, victims often commented that they felt great, as if they could “swim forever.” Towards the end of the dive these symptoms were felt: slight urge to breath, blind spots in the vision, seeing “shooting stars” and luminous sparklings, dizziness, nausea, vertigo, and partial or complete paralysis.
Those who suffer those symptoms, including South Sea Island pearl divers, unanimously agree that once the symptoms were felt it was too late to do anything about them. With astounding suddenness the victims then blacked out. Some continued swimming after memory loss and some, until they collapsed and died. Many of those who recovered needed mouth-to-mouth artificial respiration.

After effects included being dizzy, “shaky,” having a slight headache, exhaustion, sluggishness in responding to commands, periods of non-breathing, roving eyes, a bloody froth in the mouth, partial paralysis (sometimes permanent) and mental retardation. When the victims must be pulled out of the water they are flaccid (limp), non-breathing and very cyanotic (a condition in which the skin, lips and nails turn blue). Those who lived through the ordeal apparently didn’t cough or inhale water. Those who didn’t survive were found with a bloody froth in the mouth and lungs filled with water, apparently due to a relaxation of the throat muscles after blackout. Death is due to hypoxia, or a lack of oxygen.

But how does a person get himself into such a jam? Here the explanation gets a bit technical. When a diver hyperventilates, two things happen.

First, the percentage of carbon dioxide (CO2) in the blood is lowered, but the percentage of oxygen remains approximately the same since arterial blood is normally 95% oxygenated. Secondly, hyperventilation causes a decrease in blood flow to the brain which results in cerebral anemia for a period of time before the dive begins. This is why a person gets dizzy and sees stars after prolonged hyperventilation.

However, it is the increase in the percentage of CO2 in the blood which is critical, for this is what triggers the breathing reflex in the brain. A lack of oxygen doesn’t trigger this response. But increased CO2 makes the diver feel that he must breath. Hyperventilation, by lowering the CO2 Level in the blood, postpones this signal (see Graph I). It becomes dangerous when the signal is postponed to a point where the oxygen level in the blood becomes insufficient for the maintenance of consciousness.

This can happen in two ways. One is on a shallow dive, when the diver experiences the urge to breath and, with the lowered percentage of CO2 from hyperventilation, stays underwater until he blacks out (represented in Graph I).

The other way happens on deeper dives, those deeper than 33 feet (10 meters). This is taravana, the feared disease of the South Seas. The diver hyperventilates, as before, then dives deep. As (s)he dives the pressure increases, and the partial pressure of oxygen also increases. The diver pushes himself to stay somewhat longer than he normally would, and is finally forced to the surface. As he does, the pressure decreases and the partial pressure of oxygen also decreases in the lungs. But the partial pressure of oxygen in the blood remains high, since it is almost a closed system. However at the lungs, oxygen, because of the higher partial pressure in the blood, passes back into the lungs and is lost for metabolic purposes. Couple this to another phenomena, than the body has a higher tolerance to higher percentages of CO2 when exercising which allows the diver to stay down even longer before the urge to breath is felt, and the result is catastrophic: acute hypoxia and unconsciousness. Brain damage is imminent if the diver isn’t resuscitated immediately because the brain is already depleted of oxygen. This condition is depicted in Graph II.

How can shallow water blackout, or taravana, be prevented? The most important point is NOT TO HYPERVENTILATE. Ventilate the lungs with a couple of deep breaths, but not more than three. When breath hold diving, it takes about 15 minutes for the body to adjust to the water. Establish a cycle to diving, where the divers dive until they feel the urge to breath, surface and stay on the surface recovering until they feel comfortable (at least two or three minutes) then dive again. With practice, the diving times will lengthen. The deeper the dives, the longer the recovery time needed by the diver; the same advice goes for submergence time--the longer the breath holding time, the greater the need for longer surface recovery. Deep, long dives (undefined--individual’s vary) may take 15 minutes for recovery. During the time the divers are recovering, they can monitor their buddy.

Wearing a functional life vest is highly advised when breath hold diving. If a diver questions whether (s)he can regain the surface, (s)he can inflate the vest or take off the weight belt and hold it. In doing so, the diver will regain the surface if blackout occurs. Spare cartridges can be kept on a float or boat.

If any symptoms of taravana are felt, discontinue diving for the day. And, always dive with a buddy who’s capable of rescuing you (and vice versa) and who watches you while you dive.

Finally, it is my hope that you’ll abide by those warnings. I’ve experienced both blackout and vertigo on two occasions, and it’s not pleasant. I’ve also lost a good friend to this disease. So please, take preventive measures and breath hold diving can be an inexpensive, safe and interesting sport.

John C. Ratliff
NAUI #2710

SeaRat

 

[John C. Ratliff]

Why remove your snorkel? On ascent I usually give a small puff in it for the clearing action it gives. What I am missing?

You may not have that puff to give, and need all the air you have to reach the surface. Then breathing directly from air eliminates the "dead air" in the snorkel for better immediate oxygenation. Also, you can breath faster when the head breaks the surface and easier without the snorkel. Finally, recent studies in PubMed show that a forced exhalation in seals as they ascent, even with the decrease in buoyancy, apparently is practiced routinely, and the researchers felt it may be protective from shallow water blackout. This exhalation is protective, they surmise, because by eliminating the "sink" of lower-oxygenated air in the lungs one can prevent the reverse flow of oxygen out of the blood stream and into the lungs. This is speculative, but the seals do it most every dive (See the 15 mintue dive thread at this site for further details, and the species of seal.)

SeaRat

PS--Here's the article I told you about:

Ascent exhalations of Antarctic fur seals: a behavioural adaptation for breath-hold diving?

Hooker SK, Miller PJ, Johnson MP, Cox OP, Boyd IL.

Sea Mammal Research Unit, University of St Andrews, Fife KY16 8LB, UK. s.hooker@st-andrews.ac.uk

Novel observations collected from video, acoustic and conductivity sensors showed that Antarctic fur seals consistently exhale during the last 50-85% of ascent from all dives (10-160 m, n > 8000 dives from 50 seals). The depth of initial bubble emission was best predicted by maximum dive depth, suggesting an underlying physical mechanism. Bubble sound intensity recorded from one seal followed predictions of a simple model based on venting expanding lung air with decreasing pressure. Comparison of air release between dives, together with lack of variation in intensity of thrusting movement during initial descent regardless of ultimate dive depth, suggested that inhaled diving lung volume was constant for all dives. The thrusting intensity in the final phase of ascent was greater for dives in which ascent exhalation began at a greater depth, suggesting an energetic cost to this behaviour, probably as a result of loss of buoyancy from reduced lung volume. These results suggest that fur seals descend with full lung air stores, and thus face the physiological consequences of pressure at depth. We suggest that these regular and predictable ascent exhalations could function to reduce the potential for a precipitous drop in blood oxygen that would result in shallow-water blackout.

PMID: 15734689 [PubMed - indexed for MEDLINE]

 

[dumpsterDiver]

two reasons to remove the snorkel on descent:

If you pass out, retaining the snorkel underwater requires that the mouth is open and it is supposed to provide a more open conduit for flooding of the lungs, if you have your mouth shut I guess the feeling is that it may remain closed for some time even when unconscious and give more time for a rescue and delay the onset of drowning.

The other reason is that when you ascend, you want to breath the best clean air during the initial recovery. If you exhale through the snorkel all the "old" air will be inhaled from the snorkel on your first inhalation (i.e., dead air space). This may sound petty and inconsequential until you realize that black outs commonly occur after the diver has reached the surface. The shallow water black out danger period extends for a good 20 seconds AFTER the surface is reached. I have personally witnessed a diver come to the surface, take a breath and then just quitely and gently begin to sink. It was deceptively peaceful, no struggle, no convulsions. Sometimes freedivers that take a breath or two and then pass out, are able to self-rescue (i.e., wake up or regain conciousness while submerged).

Also (a third reason) when hunting. the bubbles gurgling slowly out of the snorkel on descent may make too much noise. If the snorkel is spit out on descent, it immediately floods and will not make additional unwanted noise.

The other posts contain good advice. I would add one more I didn't see mentioned:

Watch your buddy for a good twenty (20) seconds after he reaches the surface to ensure that he doesn't immediately pass out after taking one or two breaths at the surface. (Remember that just because you take a few quick breaths at the surface doesn't mean that your brain has received that oxygen. When you surface, your brain is still metabolizing a very limited store of oxygen and it takes a finite time for the fresh supply of oxygen to diffuse through the aveloli in the lungs and get picked up by the red blood cells, move through the capillary beds, travel through the larger blood vessels and heart, diffuse out of a second set of caplillaries feeding the brain and then for the oxygen molecules to finally make it to the brain cells).

If you are doing shallow snorkeling for fun and your dives are shallow and very easy, say maybe 15 or 25 seconds and you include long surface rest periods, removal of the snorkel is probably not worth the hastle. I leave the snorkel in for 20 or 25 ft fun dives that are very short. For anything more strenuous, it is a little safer to remove the snorkel upon descent and then to take a breath or two without it on ascent.

 

[Chad Carney]

Code Cruncher picked up on this nearly year old thread, but it was a good one.

A lot of good information guys.

Another reason to not use a snorkel is that it is much easier to relax jaw and facial muscles if you remove it just prior to diving.

Here's a statistic from Kirk Krack (Performance Freediving International)
In blackout cases, 90% reach the surface and take 1 -4 breaths, often while signaling "OK". He recommends watching a buddy for 30 seconds minimum after surfacing.

Another thing that often causes blackout at the surface, is the sudden drop in blood pressure upon exhalation. A better way to recovery breathe is a partial exhalation, (1/2 volume, then inhale). It's called hook breathing. Make three of these hook breaths, then start clensing breaths, (full exhalations and inhalations.)

A surface blackout victim sinks like a rock after exhaling, and can be gone in seconds.

When I have more time I'll put up my own experience with a static BO.

Chad

I just started a thread here on SB with a link to a PDF by Terry Maas, about a freediving safety vest.
http://www.scubaboard.com/showthread.php?p=1579971#post1579971