Shallow- and Deep-Water Blackouts

[feitr]

Matt if you want to see your hemoglobin saturation drop then start doing exhale statics. You basically start up like a normal static but on the last breath hold you exhale completely - your CO2 levels will build at the same rate but you will get hypoxic much quicker.

1 min is not very long at all (not being offensive, just letting you know that almost anybody can basically do twice that right off) - do a routine along the lines of normal breathing followed by 2 mins of slow deep breathing to calm/relaxe yourself then a few deep breaths then hold. Then repeat. First you may get a minute, second you should get more, by third or fourth you should hit 2mins+.

And yea depends on a few factors but it may take 3 minutes before O2 saturation even begins to lower (so basically it feels like you are dying but your cells are still getting completely oxygenated.

Presumably a pulse oximeter won't work at depth because the ratio of oxygen to hemoglobin molecules doesn't change. I do have to say I don't completely understand the relationship between ppO2 while free diving and hemoglobin saturation (somebody want to take a crack?)

 

[Sleepdr]

No, to my knowledge, there isn't -- and where I dive, it would be pretty darned hard to make one, because your fingers and toes are so cold, it would be hard to get any kind of reading, even if you could waterproof the probe!

Not only that, but the software for most commonly-available pulse oximetry has an apparent lag between sensing, processing, and display. The Nonin fingertip unit I have at home looks to take 5 seconds at its fastest. Some of the Nellcor & Phillips monitors I've seen can take up to 15 seconds. That time lag is stress-inducing even as a trained airway person watching someone's saturations fall off a cliff (especially young kids). Free diving, that could be catastrophic. The monitor could conceivably just start indicating desaturation, half a minute after your brain had already checked out after a ride down the steep part of the O2-hemoglobin curve.

That's about as useful as a freeway exit sign placed 100 yards after the actual exit.

 

[John C. Ratliff]

I wrote this piece quite some time ago, and present it on this thread (Shallow Water Blackout) and as a blog as I wrote it.

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

PS: Instead of two graphs, I present only one as I feel it states what I wanted to convey. This topic was originally written about by E.R. Cross, in a paper he published in the 1950s. I have a copy of that original paper. The original paper described the symptoms as attributable to anoxia:

The most likely cause of taravana is lack of oxygen in the blood and tissues of the body. The simple phenomena of anoxia. The effect of this condition on the central nervous system and the brain could account for the many and varied symptoms the disease takes. it would also explain the difference in the duration of the symptoms which vary from several hours to permanent damage. And it might also explain the effect of the only “cure” the native divers have for the disease.

However, later work showed that most likely these free divers experienced decompression sickness. This does not take away the concepts of preventing shallow water blackout.

In recent years, I have found that I can establish a rhythm of breath-hold diving which does not require hyperventilation to attain longer times underwater. This involves simply taking a at the most two to three deep breaths, submerging until the urge to breath come, then surfacing. I take a minimum of two minutes between dives, then submerge again. After keeping this up for about 15 minutes, I find my times extending naturally until I'm pretty comfortable swimming underwater for 1 minute, 30 seconds. I don't try to extend beyond that, but have reached 3 minutes. By doing this rhythm free diving, I can allow my body to adapt; it may have to do with the mammalian diving reflex too, but I'm not sure of that. But I find this adaptation does occur. Combining this technique with buddy diving, where the buddy watches from the surface, and free diving can be pretty easy and safe.

Limitations have to do with free diving in the Pacific Northwest, where visibility is limited. This presents special problems to divers who spearfish, as it may not be possible for the buddy to see the diver at all times. I do feel that the buddy system is more important for free diving than for scuba diving, as Shallow Water Blackout can happen very quickly, and without warning.

My two experiences with Shallow Water Blackout occurred many, many years ago. The first occurred in our 20 yard long YMCA pool in Salem, Oregon when we were in swim team practice, probably about 1962. My friend on the team, Tommy Lengyl, swam four lengths of that pool underwater. We were having a contest, so I decided I would swim further than Tommy. I hyperventilated until I saw stars (about a minute), and dove in. I swam a modified underwater breaststroke, and felt very good for the first two lengths. On the third I felt a bit of an urge, but was still comfortable. On the fourth length I was feeling the urge, but suppressed it. I told myself I would swim to the wall, make my turn, take one stroke underwater, surface and swim to the pool's side. That is exactly what I did too. The problem is that I don't remember anything after the turn. I'm convinced that if I had not pre-programmed my brain to take one stroke, then surface, I would not be here today. The second time was free diving in Puget Sound as a teenager, where I dove deep, stayed too long, and almost blacked out surfacing. I did take my weights off and hand-held them. When I got to the surface, I was seeing stars, but did not black out (I retained my weights, which is how I know).

PS2: I went looking for confirmation of the numbers I put on this graph years ago. I had lost the papers I used (4 jobs and 16 years ago). I found in the Wikipedia references on Shallow Water Blackout the following reference, The Breath-Hold Diving Workshop 2006. This makes a very good read on Shallow Water Blackout.