Apnea.nl - Decompression Sickness and Breath-hold diving: Is it an issue?

By Rik Rösken

If you should name a typical diving disorder that has been illusive for both science as the typical freediving classroom, then it is probably Decompression Sickness, also known as Caisson Disease or "The Bends".In this article, we will go into one of the most debated subject within the medical breath-hold diving community: Decompression Sickness.

What is Decompression Sickness (DCS)

When diving deep, gas is forced into our body during diving. Normally, when the ammount of gas solved in our body is small and there have been sufficient time to release the gas during ascent, no symptoms or problems occur.

But when we dive for a too long period times too deep, the solved gas can form tiny bubbels of gas. Dependant of the location where these bubbels form, they can create symptoms that divers call decompression sickness. The bubbels that cause these symptoms exists of nitrogen, therefore that we also speak from nitrogen stress, when speaking about DCS and riskfactors.

The disease have been known to exist in divers on compressed air, and workers on compressed air for a long time. Breath-hold divers where considered immune for decompression sickness because their short dive time, and relative shallow depths.

Decompression Sickness in Breath-hold Divers

This vieuw changed in 1965, when a French scientist discovered breath-hold divers on the Tuamoto Archipelago, who suffered from bends like symptoms after diving. These divers dove four to six hours to depths of 30 to 50 meters. The disease was called locally "Taravana", which means "to fall crazily". More then once, people died after diving due this disease.

Also the Japanese divers, often considered to dive more safely, have been known to suffer from this disease. Just as their pacific counterparts did they often suffer from neurological decompression sickness, as research turned out. Evidence was not only found in clinical symptoms, but also MRI research was able to bring brain lesions to light.

New cases where reported during the eighties and nineties when breath-hold diving with the use of a underwater scooter became a new endevour. Early cases where dismissed as being caused by decompression sickness, and often the neurological symptoms are confused with ascent black-out and loss of motor controll. Even after several reports has made it into the dive medical journals, there are still ill-informed physicans who are not well informed about breath-hold diving and its DCS risk.

Mechanics of DCS in breath-hold divers

Just like the exact mechanics of DCS in SCUBA divers is not well understood, very little is understood from DCS in breath-hold divers. One thing that have been proved however, is that with every dive, independent of its depth or time, a nitrogen build-up occurs in the divers body. When a diver dives repeated deep enough and remains only at the surface for a brief time, the load could be sufficient to cause DCS. The fast ascent certainly could play a role in the creation of bubbels and severe symptoms.

Comparing DCS in breath-hold and SCUBA divers

DCS in SCUBA divers has been described in two types, where the first type often describes skin and joint symptoms, and the second type more neurological symptoms as paralisis and coordination problems. DCS in breath-hold diving is often described as being "Taravana" altough its classic symptoms do have many similarities with DCS type two.

Why Taravana doesn't follow the same pattern as with compressed gas divers is not completely understood. It could be imagined that silent bubbels could play a role here. Bubbels created during breath-hold diving can get stuck in the lungs. A second breath-hold dive, could shrink the size of these bubbels sufficiently that they can bypass the lungs and cause problems in the brains or other neural tissue. Strangly however is that when DCS is occurs after Breath-hold diving after SCUBA diving, DCS type I is observed.

The breath-hold diver and DCS

Breath-hold divers can get DCS when they perform many repetitive dives with short surface intervals, like some spearfishers perform and they perform a small number of deep dives with relative short surface intervals, like training competitive divers perform.

There haven't been any literature or evidence based knowledge on how deep and how many repetitive dives are needed before DCS can occur with breath-hold diving.

Discussions at medical German symposia suggested that all dives below 40 meter do impose a risk on the diver on DCS and that at least ten minutes, and preferable more, is needed between every dive. Further it have been suggested that the use of oxygen between these deep dives could facilitate in pursing the body of nitrogen. Advise on this by qualfied medical personal is strong encouraged. Published articles and unpublished research seems to point out that dives below 40 meters cause measurable nitrogen stress on the divers body.

However without further research, these suggestions have a limited value and should not be considered as absolute safetyrules. This should also account for the theoretical tables that exist for breath-hold diving.

Advised could be that spearfishers should limited their dives, especially if these dives are performed in deep water. Breath-hold divers who train for competitions should plan their dives. Try to limit the dives below 40 meters and plan additional surface time for deep dives. Keep in mind that buddy dives between two deep dives influence the addition and removal of nitrogen. Be aware that due the diving pattern with open unplanned depth training can cause decompression sickness when the depth increases.

Not only diveplanning is important with these deep breath-hold dives. Also the knowledge and experience of the supporting team is essential. Be sure that the assisting divers and supporters are aware of the diveplan and know what the difference is between decompression sickness and ascent black-out. Further keep in mind that oxygen is not only the first treatment for loss of consciousness due ascent black-out, but is also the first choice to start decompression treatment.

However oxygen at site with a suspect decompression sickness incident never replaces examination and treatment at a hyperbaric medical facility. Be aware of the procedures how to activate medical assistance during with a diving emergency!

Conclusion

Overall, DCS is a risk that divers, especially competitive divers and spearfishers, should be able to understand and identify from other diving diseases. Especially with the limited knowledge available, it is something that should always be considered when planning a dive. Needeless to say, breath-hold diving should never be performed after diving on compressed gas.

DCS and Breath-hold diving:

Is it an issue?