The brain under pressure

Last week we read about what happens to our brain when we hold our breath and free dive. What about those of us who want less physically demanding diving? Do we experience similar physiological effects while SCUBA diving?

SCUBA diver

By Soljaguar (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)%5D, via Wikimedia Commons

Effectively, yes. Except SCUBA diving also introduces effects on the body from breathing air under pressure for an extended time period. For a recreational diver, nitrogen is our worst enemy. While we’re enjoying the eels, nitrogen is silently dissolving itself in our blood stream. Unlike oxygen, our body does not metabolize nitrogen, so it builds up in our tissue like carbon dioxide in a soft drink. If we stay down too long and ascend too quickly, the dissolved nitrogen will turn into bubbles like when you crack open that bottle of soft drink.

These are not the sort of entertaining bubbles you enjoyed as a kid – bubbles in tissue and blood are dangerous as they disrupt cells, causing a wide variety of symptoms known as decompression sickness. The smaller bubbles are less disruptive, most likely only causing limb and joint pain. The nickname of ‘the bends’ comes from the bent and twisted posture of suffers trying to relieve the pain in their limbs.

However if we were unlucky enough to get larger or a greater number of bubbles, we’d most likely start experiencing neurological symptoms. These can include headaches, stroke, paralysis, seizures, vestibular problems, inappropriate behaviour, and visual disturbances. The most common neurological complications of decompression sickness are those of numbness and paralysis of the legs, caused by a lesion around the 6th to 8th thoracic segment in the spinal cord. This is believed to be due to the increased susceptibility of this region to ischemia. However bubbles can also damage the nervous system by causing axon degeneration or even demyelination. Certain neurological conditions may be made worse, such as cerebral palsy, ADHD, and epilepsy.

Once you’ve had decompression sickness, you seem to be at an increased risk of getting it again, although the exact reason for this is unknown. There is unfortunately little scientific consensus as to the long-term effects of decompression sickness, mostly due to the difficulty of finding an adequate control group for reliable research. One suggested effect of repeated decompression sickness is osteonecrosis, or bone death, resulting from bubbles trapped in blood vessels that supply bone. Disruption of blood vessels may also cause an increased risk of associated neurological incidents such as stroke. Thankfully, people may recover from neurological damage through repeated treatments with oxygen in a high-pressure chamber.

Although unfortunately, you can have too much of a good thing. Prolonged breathing of too much oxygen at increased partial pressures has it’s own problems, namely oxygen toxicity. Central nervous system oxygen toxicity can cause disorientation, dizziness and nausea followed by seizures, resulting from oxidative damage to cell membranes. This is really only a risk for more advanced technical divers, who use various gas mixtures with enriched oxygen or who dive to depths greater than 60m with normal air.

This definitely isn’t meant to scare people off SCUBA diving! Recreational divers following the basics of their training will be well within safe limits. But be aware of the effects the increased pressure is having on your body.

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