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Taravana: Can free divers get bent?

Can free divers get bent?

Can free divers get bent?

The classic study by Cross in 1965 looked at Polynesian island natives of the Tuamotu Archipelago,who habitually free dive many times in quick succession, usually for food or pearls and may make 40 to 60 dives a day to 30 or 40 metres. Taravana means to ‘fall crazily’ and his report listed 35 male divers. Twelve of them suffered from vertigo and one died. The ages ranged from 19 to 62, and the greatest depth dived was about 45 m. The islanders usually dived from a canoe or an outrigger and descended using a weight of about 4 to 6 kg attached to a line and wore goggles or a face mask. Divers would hyperventilate for 3 to 10 minutes before diving with a deep inhalation, followed by deep expiration accompanied by a long drawn “whoooeee” sound. Before the dive, the diver lowered himself into the water and continued to hyperventilate at a faster rate. Just before he dived, he raised himself out of water to the waist, took a deep breath and descended feet first holding the weight. Time on the bottom ranged from 30 to 60 seconds. Ascent time was no more than 20 seconds from depths of 30 to 39m. As soon as he reached the surface, the diver hyperventilated again for 3 to 10 minutes and then dived. The maximum duration of a dive, from surface to surface, was 2 minutes and 35 seconds. The average however, was 1 minute 30 seconds for a series of timed dives. The most common symptoms of Taravana were vertigo, nausea and ‘mental anguish’. Occasionally, vertigo was the only symptom. Some of these symptoms could be due to hypoxia, hypercarbia (high CO2 in the blood) and drowning, but are highly suggestive of decompression illness, especially the neurological symptoms.

Breath hold diving causing decompression illness was then reported in 1965 by Paulev, a Medical Officer in the Royal Danish Navy, after he spent 8 minutes at 20m as an attendant in a recompression chamber and then performed a number of breath hold dives in the submarine escape training tank (SETT) to 20m. Each descent took 20-25 secs, he would then sit or walk until he felt the need to breathe, at about 2 minutes, then he ascended to the surface, which took 10 – 15 seconds. Surface intervals were short (between a few seconds and 2 minutes) and he was in the water about 5 hours. During the last 2 hours, he experienced nausea, dizziness and belching and during the last 30 minutes, he developed pain in his left hip and right knee, with the right leg and the right arm weakness. Two hours after leaving the water he had chest pain, abdominal pain, pins and needles and numbness in the right hand and blurred vision. He was treated with USN Table 3 which was partially successful although a residual weakness of the right hand persisted. Three further cases have subsequently been treated in the Norwegian SETT and each one had been compressed in the hyperbaric chamber before breath hold diving. All experienced neurological symptoms and were successfully treated, which supported the diagnosis of decompression illness from breath hold diving.

 Question 1

Can I freedive after scuba diving?

Freediving after scuba is not safe. Although there are no clear guidelines, it is generally agreed that freediving can result in decompression illness after scuba diving, as a result of the above examples.

Question 2

Is it escaped gas or evolved gas?

The clinical pictures described above are more in keeping with the slower onset and less profound neurological problems associated with evolved gas decompression illness, that are dependent on the amount of absorbed nitrogen. Rather than the sudden onset severe neurological problems associated with escaped gas arterial gas embolism.

Question 3

Can submariners get DCI?

Submarines are pressurised to around 1 atm so there is no risk of decompression illness. However, if there is a breach in the hull, any ingress of water will pressurise the remaining space and make decompression illness more likely, especially if there is then escape to the surface. I have described how submariners can get decompression illness from evolved gas after repetitive breath hold dives in SETT, however they are actually more likely to get decompression illness in SETT from escaped gas from pulmonary barotrauma if they hold their breath on ascent.

Question 4

Can cetaceans get DCI?

There have been reports in Nature journal of bubbles in the tissues of cetaceans that have been stranded, suggesting that decompression illness is a problem in these air breathing mammals. Although the truth is more difficult to ascertain, as the stranding and the bubbles could be caused by cavitation from military sonar.

Question 5

What is the difference between deep water and shallow water black out?

These 2 terms cause confusion but are caused by the same thing, except for the depth at which it happens. The urge to breath is driven by the level of CO2 in the blood. That is, until the O2 drops to a low level, when the urge to breath is driven by O2. At depth, the level of O2 and CO2 are raised due to the increased pressure and breathing can seem comfortable. But on ascent from 10m to the surface (or 30m to 10m), the levels of both halve. If the O2 levels drop beyond that required for the brain to function, then black out will occur.

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