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  • Sometimes when a fish is reeled up to the surface

  • it will appear inflated,

  • with its eyes bulging out of their sockets

  • and its stomach projecting out of its mouth,

  • as if its been blown up like a balloon.

  • This type of bodily damage, caused by rapid changes in pressure,

  • is called barotrauma.

  • Under the sea, pressure increases by 14.7 pounds per square inch

  • for every 33 foot increase in depth.

  • So, take the yelloweye rockfish,

  • which can live as deep as 1800 feet,

  • where there's over 800 pounds of pressure on every square inch.

  • That's equivalent to the weight of a polar bear balancing on a quarter.

  • Now, Boyle's gas law states

  • that the volume of a gas is inversely related to pressure.

  • So, any air-filled spaces, like a rockfish's swim bladder,

  • or human lungs,

  • will compress as they descend deeper

  • and expand as they ascend.

  • After a fish bites a fisherman's hook and is quickly reeled up to the surface,

  • the air in its swim bladder begins to expand.

  • Its rapid expansion actually forces the fish's stomach out of its mouth,

  • while the increased internal pressure pushes its eyes out of their sockets,

  • a condition called exophthalmia.

  • Sometimes rockfish eyes will even have a crystallized appearance

  • from corneal emphysemas,

  • little gas bubbles that build up inside the cornea.

  • Thankfully, a scuba diver doesn't have a closed swim bladder to worry about.

  • A diver can regulate pressure in her lungs by breathing out as she ascends,

  • but must be wary of other laws of physics that are at play under the sea.

  • Henry's law states that the amount of a gas that dissolves in a liquid

  • is proportional to its partial pressure.

  • The air a diver breathes is 78% nitrogen.

  • At a higher pressure under the sea,

  • the nitrogen from the air in a scuba tank

  • diffuses into a diver's tissues in greater concentrations than it would on land.

  • If the diver ascends too quickly,

  • this built up nitrogen can come out of solution

  • and form microbubbles in her tissues, blood and joints,

  • causing decompression sickness, aka the bends.

  • This is similar to the fizz of carbon dioxide coming out of your soda.

  • Gas comes out of solution when the pressure's released.

  • But for a diver, the bubbles cause severe pain

  • and sometimes even death.

  • Divers avoid falling victim to the bends by rising slowly

  • and taking breaks along the way, called decompression stops,

  • so the gas has time to diffuse back out of their tissues

  • and to be released through their breath.

  • Just as a diver needs decompression,

  • for a fish to recover, it needs recompression,

  • which can be accomplished by putting it back in the sea.

  • But that doesn't mean that fish should just be tossed overboard.

  • An inflated body will float

  • and get scooped up by a hungry sea lion or pecked at by seagulls.

  • There's a common myth

  • that piercing its stomach with a needle will let air escape,

  • allowing the fish to swim back down on its own.

  • But that is one balloon that shouldn't be popped.

  • To return a fish properly to its habitat,

  • fisherman can use a descending device instead

  • to lower it on a fishing line and release it at the right depth.

  • As it heads home and recompression reduces gas volume,

  • its eyes can return to their sockets and heal,

  • and its stomach can move back into place.

  • This fish will live to see another day,

  • once more free to swim, eat, reproduce and replenish the population.

Sometimes when a fish is reeled up to the surface

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B2 US TED-Ed diver pressure fish gas swim

【TED-Ed】The effects of underwater pressure on the body - Neosha S Kashef

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    稲葉白兎 posted on 2015/04/14
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