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This article explains this facinating and high risk sport.
Introduction
Apnea is the term used to describe breath holding. There are four main types of apnea diving:
- Constant weight apnea -
On only one breath of air, freedivers attempt to reach their maximum depth. They must be weighted perfectly so that they are able to sink but are not too have to fin back up. Freedivers cannot use the line to which the tag is attached to assist them.
- No-limits apnea -
The freediver descends with the aid of a ballast-filled sled that runs down a line. At the required depth, the diver stops and inflates a lifting bag that assists in the ascent.
Currently medical experts are predicting that death will follow if freedivers push the limits any further. This is perhaps the most controversial form of freediving, and is not recognized by any official sporting bodies.
- Dynamic apnea -
Involves swimming horizontally as far as the freediver can on one breath of air. Monofins are a popular means of propulsion, as opposed to normal fins.
- Static apnea -
Takes place in a swimming pool, with freedivers lying in a position in which it is impossible to breathe, and remaining in this position until they need to breath. Towards the end of their attempt, they must indicate to a spotter that they are OK by responding to physical signals.
Physiological changes
 The following is a brief description of the physical changes that actually occurred to Francisco Pipin Ferreras during his World Record Breaking breathold dive... this amazing man went down to 127.5 metres in 95 seconds on one breath of air (Key Largo, Florida, 1994). His training for this dive took 22 years and he had logged 550 free dives...
- Surface: To prepare for this dive, he hyperventilates until he carries 8.2 litres of air... then slips down into the blue.
- The first 30m -
For the first 30 metres his rate of descent is 3 metres per second. During this time his heart beat slows down to 45 beats per minute ( on average, a normal persons heart rate is around 80 to 100) and he does not get the urge to breath at all.
- At 60m -
He slows his rate of descent to 2 metres per second and maintains this speed to reach 100m depth. During World War II submarines would actually crumple if they went deeper than 85 metres!! (the pressure of the water above him is 9 atmospheres).
- 100m and deeper -
This is where his difficulties start... he finds it difficult to compensate his middle ear. The 8.2 litres of air which he sucked in on the surface has compressed to less than a quarter of a litre, and the body knows it must prevent the lungs from collapsing...so it stops pumping blood to all extremities and redirects the blood supply to the lungs...filling them with blood plasma, knowing that liquid is not compressible!
This phenomenon is known as a Blood Shift and occurs in all marine mammals that descend to this depth. The small amount of air he has left in his body has lodged in his nasal passages, forced there from equalizing his ears.
- 105m -
Now he cannot equalise anymore as the air is almost totally compressed. But he has one trick left... he removes his noseplug and lets water flood his nasal passages, forcing the compressed air from his sinuses to his internal ears and thereby forcing equalization.
- 116m -
By now his heart rate has slowed to 14 beats per minute. His body knows to conserve as much energy as possible and is only pumping blood to his brain now... it knows that he must remain thinking to survive... he has a series of questions which he asks himself to test how alert he still is... He descends still further and at 124m he can feel both his body and his spirit weakening.
- 127.5m WORLD RECORD -
He has reached his goal! He inflates a bag with a bottle of compressed air and begins to rise back to the surface. At 80m the blood plasma starts to leave his lungs, and his blood starts to flow back into his arms and legs...
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