BlueWater Hunting and Freediving
by Terry Maas
Copyright 1997 Terry Maas, BlueWater Freedivers

Physiology Chapter: SHALLOW-WATER BLACKOUT

Note to the reader: In the interest of freediver safety, I have elected to include the entire chapter on the subject of shallow-water blackout—probably the most serious threat to freediver safety. For a more in-depth discussion on this condition, please see our newest book Freedive! by myself and co-author David Sipperly.

Every year we lose too many divers to shallow-water blackout. Almost everyone I interviewed for this book has a story to tell about this frightening but all too common occurrence. Shallow-water blackout (SWB) is the sudden loss of consciousness caused by oxygen starvation. Unconsciousness strikes most commonly within 15 feet (five meters) of the surface, where expanding, oxygen-hungry lungs literally suck oxygen from the diver s blood.

SWB conjures up images from the movie Invasion of the Body Snatchers. Once you lose consciousness you die. The blackout occurs quickly, insidiously and without warning. Mercifully, the victims of this condition die without any idea of their impending death. Beginning breath-hold divers, because of their lack of adaptation, are not generally subject to this condition. It is the intermediate diver who is most at risk. He is in an accelerated phase of training, and his physical and mental adaptations allow him to dive deeper and longer with each new diing day sometimes too deep or too long. Advanced divers are not immune.

I blacked out once and had two near misses before the age of 22. Jerry Stugen, my early mentor, remembers me at age 16 coming up from a dive with purple lips. Unaware of my oxygen depleted state, I was rapidly preparing to dive again to remove a large fish holed up below. Jerry yanked the snorkel from my mouth and commanded me to stop diving for the day. When I was 18 years old, I passed out in a swimming pool during an underwater endurance test for my physical education class. The second I stopped swimming my coach jumped into the water and brought me to the pool deck where I regained consciousness. Aside from being frightened, the only other problem I had was painful legs lasting two days. My last near miss happened at age 22. I entered a Florida spearfishing contest with a borrowed gun. Ascending after a 70-foot dive, I shot a large jack which took off in a blur. Not wanting to lose the gun, I remember fighting the fish to within a few feet of the surface. The next thing I remember was being awakened by bumping my head against our anchored boat.

* * * *

Skip Hellen's story is typical of many shallow-water blackout incidents. Skip and I were diving at Ship Rock, one-half mile off of Catalina Island, California. We were hunting for the largest white seabass, competing in the Long Beach Neptunes annual Blue Water Meet. Ship Rock is shaped like a pyramid. Its sides consist of large boulders cascading to the sea floor 120 feet below. White seabass cruise near the boulders. Earlier in the day I shot a 50-pound white seabass. Skip, a fierce competitor, saw my fish and he was pumped! I ll never forget what happened next.

Skip dives to a boulder 50 feet below. He orients himself in the open water and waitsand waitsand waits. I am anxious to take my turn on the rock. Finally, Skip starts his ascent and I keep his image in the corner of my eye as I start down. Fifteen feet from the surface, he suddenly arches his back, his gun fires and his arms shoot out from his sides. He sinks backward as if impaled on a cross. I drop my gun and angle my dive to intercept Skip. I release his weight belt and, holding Skip around the shoulders, we ascend together.

On the surface, I hold Skip s head clear of the waves. His face is blue-black. I feel he is close to death. His jaws are clenched on his snorkel. With effort, I rip the snorkel from his mouth, and strike him on the chest. Breathe! I yell. Skip takes one ragged breath. His next breath returns him to consciousness and he exclaims, Hey! Where s my weight belt? Where s my gun?

Lucky for Skip, he recovered that day without permanent injury, and 16 years later he realized his goal, spearing a world-record 80-pound white seabass.

THE PHYSIOLOGY OF SHALLOW-WATER BLACKOUT

The human body is capable of remarkable adaptations to the underwater environment. Even untrained divers will show a dramatic slowing of the heart when immersed. This is commonly referred to as the diving reflex. Immersion of the face in cold water causes the heart to slow automatically. Chest compression can also slow the heart. Emergency-room physicians use this phenomenon to their advantage when they need to slow the heart. They might apply ice water to the patient s face and eyes, or they might have the patient take a deep breath and then tighten his abdominal and chest muscles. The result is often a dramatic slowing of the heart. Untrained divers can experience up to a 40 percent drop in heart rate. Trained divers can produce an even lower heart rate some can slow to an incredible 20 beats per minute.

Trained freedivers develop several other physiological adaptations that lead to deeper and longer dives. The spleen, acting as a blood reservoir, assists trained divers in increasing their performance. Apparently their spleen shrinks while diving, causing a release of extra blood cells.

According to William E. Hurford M.D., and coauthors writing in The Journal of Applied Physiology, the spleens of the Japanese ama divers (professional women shellfish freedivers) they studied decreased in size by 20 percent when they dove. At the same time their hemoglobin concentration increased by 10 percent (Volume 69, pages 932-936, 1990).

This adaptation, similar to one observed in marine mammals (the Weddell seal s blood cell concentration increases by up to 65 percent), could increase the diver s ability to take up oxygen at the surface. It could also increase oxygen delivery to critical tissues during the dive.

Interestingly, the spleen s contraction and the resultant release of hemoglobin is not immediate it starts taking effect after a quarter-hour of sustained diving. This spleen adaptation, as well as other physiologic changes, probably take a half-hour for full effect. This might account for the increased performance trained freedivers notice after their first half-hour of diving.

There are other known adaptations: blood vessels in the skin contract under conditions of low oxygen in order to leave more blood available for important organs, namely the heart, brain and muscles. Changes in blood chemistry allow the body to carry and use oxygen more efficiently. These changes, in effect, squeeze the last molecule of available oxygen from nonessential organs. Most importantly, the diver s mind adapts to longer periods of apnea (no breathing). He can ignore, for longer periods of time, his internal voice that begins as a whisper but soon screams BREATHE.

These adaptations, taken together, allow trained divers to dive deeper and longer, but mind control and the following techniques and factors also bring divers closer to oxygen starvation.

Hyperventilation provides yet another mechanism that the trained diver can use to bypass his need to breathe. Hyperventilation is the practice of excessive breathing with an increase in the rate of respiration or an increase in the depth of respiration, or both. This will not store extra oxygen. On the contrary,if practiced too vigorously, it will actually rob the body of oxygen. The magical benefit of hyperventilation is what it does to carbon dioxide levels in the blood. Rapid or deep breathing reduces carbon dioxide levels rapidly. It is high levels of carbon dioxide, not low levels of oxygen, that stimulate the need to breathe.

The beginning diver is very sensitive to carbon dioxide levels. These levels build even with a breath-hold of 15 seconds, causing the lungs to feel on fire. The trained diver has blown off massive amounts of carbon dioxide with hyperventilation, thus outsmarting the brain s breathing center. Normally metabolizing body tissues, producing carbon dioxide at a regular rate, do not replace enough carbon dioxide to stimulate this breathing center until the body is seriously short of oxygen. Trained divers can also short-circuit the desire to breathe by sheer willpower.

Hyperventilation causes some central nervous system changes as well. Practiced to excess, it causes decreased cerebral blood flow, dizziness and muscle cramping in the arms and legs. But moderate degrees of hyperventilation can cause a state of euphoria and well-being. This can lead to overconfidence and the dramatic consequence of a body performing too long without a breath: blackout.

Pressure changes in the freediver s descent-ascent cycle conspire to rob him of oxygen as he nears the surface by a mechanism I call the vacuum effect. Gas levels, namely oxygen and carbon dioxide, are continuously balancing themselves in the body. Gases balance between the lungs and body tissues. The body draws oxygen from the lungs as it requires. The oxygen concentration in the lungs of a descending diver increases because of the increasing water pressure. As the brain and tissues use oxygen, more oxygen is available from the lungs while he is still descending. This all works well as long as there is oxygen in the lungs and the diver remains at his descended level.

The problem is in ascent. The reexpanding lungs of the ascending diver increase in volume as the water pressure decreases, and this results in a rapid decrease of oxygen in the lungs to critical levels. The balance that forced oxygen into the body is now reversed. This vacuum effect is really a net flow of oxygen from the body to the lungs. It is most pronounced in the last 10 to 15 feet below the surface, where the greatest relative lung expansion occurs. This is where unconsciousness frequently happens. The blackout is instantaneous and without warning. It is the result of a critically low level of oxygen, which in effect, switches off the brain.

* * * *

Jack Prodonovich and Wally Potts, fathers of California spearfishing, were diving the virgin waters of the La Jolla Cove in the mid-1940s. Jack was on his paddle board removing a spear point from a grouper. Wally, stalking five large yellowtail made two dives in quick succession. He shot a large one on his third dive. Underwater, he pursued the escaping fish. Each time its tail came within his grasp, it burst ahead, tantalizingly just out of reach.

Finally grabbing the fish, he headed for the surface. Dodging a clump of kelp, he aimed for clear water above. Realizing he was not going to make it, Wally remembers dropping his fish but does not remember dropping his pole spear. The last thing I remember was seeing a cloud of little white stars before my eyes, Wally recalls. Wally was totally focused on his pursuit and capture of that fish. Jack remembers:

I couldn t find Wally he should have come up. I yelled to friends in a boat close by for help. Shortly, Wally surfaced, lifeless, arms dangling. His spear was gone. I grabbed him by the head and pulled him face down onto my surfboard. I knew he was dead for sure. In desperation, I pounded him on the back. Wally woke up mid-sentence saying, 'Gol darn, I just about had him.'

Wally never had a clue he was out. Jack accounts for Wally s good fortune because of his tendency to float. We didn t have weight belts or wetsuits in those days, Jack says (nor did they have CPR). This story illustrates two important points, one about the usefulness of positive buoyancy and the other about how a freediver s extreme focus on a goal gets him into trouble. The diver rendered unconscious by shallow-water blackout might make one convulsive spasm, but then he becomes inanimate. He either sinks or floats, depending on his buoyancy at the depth he ceases to swim. This is why divers should weight themselves for positive buoyancy at 15 feet.

Underwater exercise is a deadly problem for the freediver. Researchers have discovered that exercise also fools the breathing center, resetting it at a dangerously low level. Simply stated, heavy exercise decreases the diver s perceived need to breathe, spending valuable oxygen in the process.

The unconscious diver is now a potential drowning victim. If he floats, the vacuum effect will cease, and there might be enough residual oxygen to allow for consciousness to return. Sinking divers, while they have lost voluntary control, still have protective reflexes. The laryngospasm reflex causes the vocal cords to close, preventing water from entering the lungs. Rescuing a diver at this stage might require yanking his snorkel from his clenched jaw muscles and administering forceful mouth-to-mouth breathing pressure to overcome the spasmed vocal cords. Some recommend mouth-to-snorkel breathing as another way to get emergency oxygen into the diver. An unconscious diver may be so deprived of oxygen that his face is deep blue or black.

As oxygen starvation continues, death is so near that even the protective laryngospasm reflex relaxes and, within seconds, water enters the lungs. It is still possible to revive him at this stage. He will, however, require hospitalization and intensive treatment. When water enters the lungs, it causes a dramatic swelling of the delicate lung tissues, which leads to acute respiratory distress several hours after the incident. This is why medical evaluation is essential even if the diver appears not to have suffered any injury immediately after apparent revival.

Brothers Mike and Howard Benedict of San Diego were diving in a thick California kelp forest on a warm sunny day in the mid-1970s. Fish were everywhere. The brothers discovered a new untouched reef. They knew it was a virgin reef because of the 10-inch abalone perched prominently ontop. Soon, each had a belt stringer with 50 pounds of fish attached, hula-skirt fashion, around their waists. They separated, which is not unusual for them. Howard remembers:

I am out of breath, coming up from a dive. Curiously, I see a 10-inch abalone drifting down from the surface. My unconscious rother follows the abalone, his back is arched, his arms are straight out pointing backwards. Desperate for air myself, I still manage to reason out a plan as I swim to intercept him. I discard both of our weight belts and holding him, we both float up to the surface. I do not kick in order to conserve what little oxygen I have left.

We surface. There are no boats in sight. Mike is deep blue. He won t breathe. I cannot get his snorkel out of his clenched jaws. Finally, I free the snorkel and start mouth-to-mouth ventilation. I experience a horror you cannot believe as I force air into my dead brother s mouth. What will I tell Mom? Just then, Mike spasms. I hold him at arms length, facing me. His eyes are rolling around. When his eyes stop rolling and focus on me, he says, Did you see that abalone?! Mike drifts back in and out of consciousness several times as I swim him back to the beach.

Mike spent three days in the hospital intensive care unit while his swollen lungs responded to therapy. He remembers expending a great deal of energy pulling that abalone free from the rock. His heavy load of fish impeded his ascent. Both the exertion and load caused him to consume too much oxygen.

After six to eight minutes without oxygen, the brain suffers permanent damage. The heart often continues to beat after brain damage occurs. Cardiopulmonary resuscitation (CPR) at this point frequently revives victims to a vegetative state. CPR should always be administered to the drowning victim, no matter how long he has spent underwater because the diving reflex and a cold environment offer the brain additional protection. Victims resuscitated in the field often experience an unusual recovery. They wake up screaming and then lapse back into unconsciousness, repeating this behavior over and over again.

Hyperbaric oxygen treatments, a new technique, offer limited hope to the comatose diver. Oxygen is administered in a decompression chamber identical to the one used to rescue scuba divers from the bends. Theoretically, the oxygen, under pressure, penetrates the brain tissues and wakes up the damaged nerve cells. Some think the oxygen reactivates nerve cells forced into involuntary hibernation by the prolonged lack of oxygen. This technique is controversial not all neurologists believe it is effective and it is expensive ($400 to $800 per hour). Patients undergo 60- to 90-minute treatments from three to five times a week, sometimes for years. Many patients do not recover completely, suffering mental and physical deficits. For example, they might experience difficulty in speech and walking. Some recover to the point where they can take limited care of themselves.

PREVENTION OF SHALLOW-WATER BLACKOUT

Shallow-water blackout was a hot research topic for diving physicians in the 1960s, when they worked out the basic physiology described above. They also studied the case histories of SWB victims, identifying several factors that can contribute to this condition. These include hyperventilation, exercise, a competitive personality, a focused mind-set and youth.

The use of hyperventilation in preparation for freediving is controversial. No one disagrees that prolonged hyperventilation, after minutes of vigorou breathing accompanied by dizziness and tingling in the arms and legs, is dangerous. Some diving physicians believe that any hyperventilation is deadly because of the variation in effects among individuals and on one person, from one time to another. Other physicians, studying professional freedivers such as the ama divers of Japan, found that they routinely hyperventilated mildly and took a deep breath before descending. Their hyperventilation is very mild; they limit it by pursed lip breathing before a dive.

Probably the best approach can be found in the U.S. Navy Diving Manual (Volume 1, Air Diving), which states, Hyperventilation with air before a skindive is almost standard procedure and is reasonably safe if it is not carried too far. Hyperventilation with air should not be continued beyond three to four breaths, and the diver should start to surface as soon as he notices a definite urge to resume breathing.

Learn the deadly effects of exercise underwater and plan to deal with this situation. Freedivers learn to prolong their dives by profoundly relaxing their muscles (see the section on deep diving). Most divers make minimal use of their muscles except when they fight a fish or free an anchor. A physician writing in an Australian medical journal found, A common scenario for diving deaths in Australia is the experienced diver with weight belt on, speargun fired. Long Beach Neptune Ted Heesen chronicles the mistakes he made that could have resulted in the above scenario:

I made a shallow dive to about 25 feet, where I spotted some whites (white seabass). The largest one seemed to be about 20 pounds (my first mistake the fish was nearly twice that size). My shot was good, and I thought I should grab this dead little 20-pound fish and swim it to the surface before it got tangled in the kelp (my second mistake). Before I could reach the fish, it came to life and started to head toward the bottom as my line tangled in my reel. I could have simply let go of the gun at this point, but I surely would never have seen it again. I spent a lot of time making that gun and was not about ready to part with it.

At this point I was probably 70 to 80 feet deep, trying to untangle my line, when one of my ears hurt painfully ( I had forgotten to clear during the chase), and this woke me up to the fact that I was in trouble. The correct thing to do would have been to drop my weight belt and gun, but I was so wasted that I didn t have the brains to do that (my third mistake). Somehow I made it to the surface, still conscious but seeing stars from distant galaxies. After a few minutes of recovery, I recalled that I had shot a fish.

Ted recovered his fish, but to this day he is afraid to dive Ship s Rock on Catalina Island where this incident occurred. Ted was lucky. Too many divers have not recognized that preoccupation and excessive exercise can be lethal.

Researchers have found that the typical victim is young and highly competitive. Many SWB victims are young (teens through early thirties). I don t know if this is because they lack experience or if some ther unrecognized factor comes into play. The point is that young freedivers must be wary. Any diver who surfaces with the shakes, tunnel vision, starry vision or momentary memory loss has missed blackout by the narrowest of margins just seconds. This should be considered a near-death experience and the dive should be examined for mistakes. There is more than one story about divers, rescued once from SWB, drowning on subsequent diving trips.

Focusing on a goal is dangerous. The stories in this chapter show how the divers, preoccupied with a goal, got into trouble. Skip remembers his last thoughts before his blackout. My lungs were burning. I looked up and I saw the surface was near. I lengthened my kicking stride. I knew I was going to make it. Skip was focused on one thing getting to the surface. Wally, Mike and Ted were intent on stalking or fighting a fish. You must prepare yourself to recognize when you are focusing on a goal. An internal warning should say, I m focusing too much. It s time to leave, drop my weight belt, drop my gun.

Medical researchers feel that many pool deaths, classified as drownings, are really the result of shallow-water blackout. Most occur in male adolescents and young adults attempting competitive endurance breath-holding, frequently on a dare. Drowning victims, especially children, have been resuscitated from long periods of immersion in cold water 30 minutes or more. The same is not true for victims blacking out in warm-water swimming pools. Warm water hastens death by allowing tissues, especially brain tissues, to continue metabolizing rapidly; without oxygen, irreversible cell damage occurs in minutes.

James Warnock, the 31-year-old son of champion Ted Warnock, drowned in a warm swimming pool, chest deep. The Warnock family, hoping to prevent such deaths in other young athletes, has graciously allowed me to discuss the events surrounding their son s death. No strangers to shallow-water blackout, the Warnocks discussed this danger many times, especially after James had a near blackout years before.

Studying mariculture in Florida, James was excited to hear that the National Spearfishing Championships would be held in an area he knew well. A three-time North Atlantic Spearfishing Champion, James was eager to start training. He purchased a new stop watch and was practicing breath-hold diving in a medical-therapy pool. A concerned paraplegic patient spotted James inanimate body and summoned help. Rescuers saw James new watch fall from his hand as they pulled him from the water. Sadly, attempts at CPR were unsuccessful.

SUMMARY

This section is so important that I want to summarize ways to avoid shallow-water blackout:

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Mark Peaslee, mpeaslee@best.com
Copyright 1997 Terry Maas, BlueWater Freedivers