Apnea and DCS
(document for the Bizzy Blue Hole
by Sebastian Naslund. Incorporated comments from: Kastrinakis , Gautier, Rosken, Graves, Fattah
Updated may 11th
Decompression sickness. DCS = Nitrogen bubbles get trapped in our blood due to pressure at depth. Long stay, repetative dives or quick ascents increases the risk. It has mostly been an issue for No-limit (and VWT divers) but as competetive freediving develops it is becoming an issue for all elite freedivers.
Just as squeeze, this can be far more common than we know. Signs and symptoms can be hidden behind other signs of exhaustion after a dive. Its not a question of getting DCS or not getting it, it can be a sliding scale. More or less of it.
At Bizzy Blue Hole 2009 we offered the opportunity to dive two competition dives in one day. For the beginner and intermediate diver this is an advantage. It is not uncommon to fail a dive due to inexperience which results in early turns, and silly (unecessary) rule violations is not uncommon either.
Also the intermediate competition freediver might benefit from a second chance in the same day: for instance if mouthfill is lost or early turns from any other reason. People who want to try a second discipline where they are "weaker" may benefit from this extra chance.
In this way F.BIZ wants to develop the concept of freediving competitions. Most of us travel far for few dives, and some can only stay short time at a comp. In short:
many options=effectiveness. You can give your AP for
the second comp session after the first try.
Doing two deep freedives in one day raises major DCS issues. There are no hard facts on decompression and freediving. If there were we would still see differences inbetween individuals and difference from day to day in the individual diver. It also depends on you dive profile, and what you do inbetween dives.
GENERAL RULE (if advice and precautions has been followed):
No more than 120 meter depth in one day (example: 70+50)
No more than 5 minute total dive on the competition dives.
EDIT: We did allow a known diver with extensive experience of multiple deep dives to do 132 meters in two dives with 4 hours inbetween.
ADVICE for the deeper freedivers:
- Hydrate well before (12hrs before) and inbetween dives.
- Rest well inbetween dives (no snorkelling or safety diving)
- Follow your intuition, if you feel stressed, tired - skip the second dive.
- No diving below 50 meter the day before the comp. Better stay out of water.
- No diving the day after the comp.
- No flying within 24 hours after extensive freediving.
- Avoid extremly long hangs as warm-up.
- keep your ascents as slow as possible.
- Never finish your day with a deep dive. A 30 sec hang at about 15 meters could be a beneficial "recompression" releasing nitrogen.
- Be DAN insured (includes freediving but not any personal records or record attempts),
or check your home/travel insurance attitude towards diving.
- Go for your deepest dive first. Switch to a shallower discipline on the second dive
(contradictory advice exists)
We have choosen this year not to offer oxygen at depth after deep dives (not even for those with scuba licence). We do not have the personell to properly supervise that proceedure, we also think it might create an injustice inbetween those who have and do not have scuba licence, we are also worried that directly going under again might hide a lot of symptoms that the medical and safety personell need to see if they occur, like DCS symptoms, squeeze symptoms and other unknown injuries.
We will offer 10 min O2 at surface for specially
deep dives (70+).
(Note: Any >10m dive directly after this may be lethal!)
We do not want to offer O2 to support general recovery of an athlete that has done an elite performance - the ability to recover is part of the performance/skill.
We will be able to offer 5+ hours of rest inbetween deep dives in special cases.
4 hours in most cases.
NOTES ON DCS
- DCS can kill you or make you crippled for life. Permanent neurological damage.
- A single 50 meter dive can accumulate nitrogen that is still there in the blood after surfacing.
- The divetime could be just as important as the depth. That is: a hang at 30 could cause nitrogen bubbles in the blood.
- The nitrogen bubbles can manifest in larger joints, brain, spinal cord, skin and lungs.
Fast apnea descents and ascents are believed to skip the first stages of DCS injuries, and produce the neurological symptoms more directly (DCS 2). Breathing oxygen (specially at depth) are very beneficial to preempt such symptoms.
But using oxygen treatment without special cause is
not a good idea since oxygen in high concentrations
in itself is not healthy for the body.
AIDA´S advice: rest double your dive time (on dives down to 30 meter). Up to 60 meter dives rest 1/5 of the depth (in minutes). Example 40 meters = 8 minutes rest. Do not repeat 60+ dives.
SIGNS: Signs are things you can observe as a first aid provider. Some of the signs can be observed, while the victim isn't aware of them.
Skin rash, swelling of the skin, accompanied by tiny scar-like skin depressions
Paralysis (numbness maybe some 30 min after diving)
Personality change, confusion (memory loss)
Unequal pupil size
Coughing of shortness of breath
Collapse or unconsciousness
Symptoms: Symptoms are complaints that the victim of an accident can tell you.
You as a first aid provider should ask for them.
Skin itch, usually around the ears, face, neck, arms, and upper torso
Joint or limb pain
Numbness, tingeling (in joints up to 5 hours after dive)
Abnormal sensations, burning, stinging and tingling (paresthesia)
Chenst or abdominal pain
Deafness or ringing in the ears
Bladder or bowel incontinence
Headache, dizziness or nausea
Spots in visual field, tunnel vision, double vision, blurry vision
We will in this competition focus on detecting
squeeze symptoms with direct observation and
oxymeter, since this might lead to increased risk of
trouble in a possible second dive during the day (or
next day). We will do this oxy test directly after a
dive in certain cases and if need be a "pox" test
under slight exercise later.
We will evaluate every freediver individually.
Can Freediving Cause DCS?
by Fred Bove, M.D., Ph.D.
A reader recently asked me if freedivers ever developed decompression sickness. This has been studied in several countries but the best information comes from the natives of the Tuamotu Archipelago in Polynesia, where freedivers in the past made 40 to 60 dives a day to depths of 100 to 140 feet to gather pearls. Their descents were assisted by a lead weight and they ascended by pulling themselves up a rope tethered to a collection basket. An assistant then raised the basket to retrieve the shells gathered on the bottom. Descent times were 30 to 50 seconds, total dive time, about 100 seconds and the surface interval between dives was four to six minutes. Many of the divers developed a severe illness called Taravana, the symptoms of which are similar to those of decompression sickness-paralysis, visual changes, hearing loss and dizziness. Some divers died. Many who survived had permanent brain and spinal cord injuries. Although Taravana is most likely decompression sickness, some symptoms do not fit the picture of decompression sickness and other causes, such as hypoxia, have been proposed.
The mechanism whereby freedivers can develop decompression sickness (DCS) was studied by Dr. P. Paulev in Denmark. He studied the freedivers who accompanied trainees as they performed the free ascents required to qualify for naval submarine duty. Dr. Paulev described his findings in a Danish naval medical officer. He states, 'The author has intimate knowledge of the event, because the medical officer happens to be himself.' He performed about 60 dives to 100 feet with a two minute bottom time and surface intervals of one to two minutes. After about five hours of freediving, he noticed pain, paralysis of the legs, nausea, visual changes and weakness of the right arm. He was treated in an hyperbaric chamber and, following a full treatment table, all abnormalities disappeared.
Dr. Paulev calculated the nitrogen in his tissues after the repetitive breath-hold dives. He determined the short surface intervals did not allow tissue nitrogen to be eliminated and thus it was equivalent to that resulting from a continuous dive. Further studies by Dr. E. Lanphier indicated that the ratio of dive time to surface time and the rate of ascent were important factors in the development of decompression sickness from freediving. He calculated that a ratio of surface interval to dive time of one gave a depth exposure equivalent to about 50 percent of the actual depth of the dive. Thus a dive to 100 feet with a 90 foot second dive and a 90 second surface interval would be equivalent to a continuous dive to about 50 feet. If ascent rate was rapid, the equivalent depth would be about 65 percent of actual depth (65 feet). These calculations explain why many repetitive freedives in the 100 to 140 foot range will eventually cause decompression sickness. Those who freedive for three to five hours will greatly exceed the no decompression times for their equivalent depths and are very prone to developing severe neurologic DCS.
The Taravana syndrome and the experience of freedivers in submarine escape training provide adequate data that this is a real phenomenon. For the average freediver Taravana is not a problem, but if you want to dive for pearls making 130 foot dives every two minutes for five hours, you will get DCS. By increasing the ratio of surface time to dive time to two (e.g. 90 second dive, 180 second surface interval), equivalent depth would be about 30 feet when freediving to 100 feet and no risk of decompression sickness would occur.
The information on Taravana was published in 1965 in a book entitled Breathhold Diving and the Ama of Japan, edited by H. Rahn and T. Yokoyama. It is publication number 1341 of the National Research Council, Washington, D.C.Another situation that has not been studied involves freediving after scuba diving. There are several stories of divers getting DCS this way. A surface interval spent freediving is not really a surface interval and the calculation of decompression will not be correct. The best advice is to avoid freediving during surface intervals. If you want to snorkel, stay on the surface.
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