Along with this, the oxygen is consumed in cellular metabolism, which in turn produces carbon dioxide (CO2) which is transported intravenously (by hemoglobin and low dissolved form) to the lungs.

During a dive the partial pressure of nitrogen is significantly increased, creating an imbalance between the partial pressure and tissue tension.  Following the laws of dissolution and diffusion of gases, tissues were in phase and begin to absorb, sub-saturated, to balance N2 again.  But this saturation occurs in gradient and different rates depending on the tissue.

The blood and nervous tissues become saturated quickly, while bones and tendons are the latest.  The reverse process occurs on the rise; in ascending to the surface a diver’s tissues are super-saturated of N2 and will tend to release at rates equivalent to de-saturation.

If the surrounding pressure is lower than the voltage of N2 in a tissue, the dissolved gas (i.e. in liquid form) may not be evacuated from the tissue by diffusion.  What happens then is that the N2 turns back to its gaseous phase into the tissue.  This means that bubbles form in tissues that normally should have no gas phase.

In a normal ascent some micro bubbles forming N2 and CO2 are progressively eliminated via the lungs.  But if the rise is too fast or decompression is disregarded, the number and size of micro bubbles may be more important. This macro will then tend to form bubbles and a very specific form of barotrauma from scuba diving.

This type of barotrauma is known by the name of decompression sickness.  It is virtually impossible to bring it on in apnea diving because times are no longer than a few minutes and are interspersed with pauses at the surface.

The decompression sickness, then, is induced by tissue super-saturation above a critical level.  The presence of bubbles in the tissue can cause blood clots (thrombosis), stroke and even tissue necrosis. The effects may be immediate or progressive

The bearing is usually in the dive boat, just before returning. But it may be also “drift”.  It is customary, particularly in France, to avoid diving with bearings in the context of recreational diving. However, during deep diving (wrecks, caves, or record attempts), deep stops and times are required. They are then made with gases (trimix, nitrox and pure oxygen) whose proportions have been calculated beforehand to be the most effective for a range of depths.

Bearings with pure oxygen

Bearings with pure oxygen (100%) have several advantages and disadvantages:

Advantages:  Significantly reduce the risk of decompression illness. The composition from 21% (air) to 100% O2.

Reduce the decompression time by about 1/3.

Reduce the surface interval time before making a dive in succession.

Decrease of fatigue after a dive.

Disadvantages:

Possibility of hyperoxic crisis (also called “Paul Bert effect”), so increasing the partial pressure of oxygen (PpO> 1.6 * b) or 6 meters.

Have an extra bottle. 3 techniques are used:

Method of narghile (bottle on the boat connected to a long hose).

Bottle bearing (under the boat).

Method “Pony” or “bottle Relay” (keep the bottle diving with you).

The price: It varies between center’s inflations but it is generally more expensive than air. They require diving equipment suitable for this gas which is an extremely powerful oxidant with a risk of explosion.

Specific training (e.g. Nitrox diver confirmed).

In contrast, in the context of professional diving (including diver), because of the working depth, the divers change “saturation”. That then means they can stay several days at a great depth. In this case, the range is very long (up to 36 hours) and is recompression. Note:

The bearings are usually made at depths of 3, 6 and 9 meters corresponding to 10, 20 and 30 feet in the Anglo-Saxon measurement system. There since the early 2000s and recent research in the field has been controversial regarding depth levels. They are no longer made at a fixed depth and are unchanging in an area (between 6 and 3 yards for the final level). This limit of 1.6 bars of partial pressure of O2 (PpO2) is fixed by the decree of August 28th 2000 on recreational diving mixtures.

Certain body regions may suffer temporary paralysis and sometimes permanent injuries occur and even death.  This decompression sickness is also known as “disease of the divers” or “bad stress”.

The first time this process was observed in 1839, it soon became known among divers and workers who had to remain for prolonged periods in compressed air chambers. The symptoms appeared when they returned to normal atmospheric conditions. The only therapeutic measure that was known was to restore the victim to a high pressure chamber and decompression was started slowly and gradually. No one knew the cause of symptoms.

During the Second World War, the development of the aviation planes allowed a depth of over 9,000m to be reached in 6 minutes.  At that altitude, atmospheric pressure is less than one third of atmospheric pressure at sea level. A sudden depressurization often led to the emergence of a syndrome of decompression in the pilot.

Studies of illness

For this reason they began to examine in depth the mechanism of the disease: a sudden drop in air pressure causes a decrease in the solubility of gases in solution, and therefore dissolved gases return to gas in the bloodstream forming air bubbles.

These air bubbles released into the bloodstream can block some of the terminal vessels (arterioles), interrupting the blood supply to the nerve endings, thus triggering the symptoms that occur as a result of ischemic frames (strokes) in different areas: brain; bone; kidney etc.

Oxygen and carbon dioxide becomes a soluble state within the blood, but the nitrogen remains gaseous and is therefore primarily responsible.  You can prevent the onset of the disease by giving the pilot only pure oxygen to breathe during flight, but also before it. Thus nitrogen is removed from circulation.

For this sickness in divers, they should breathe a gas mixture containing one or more inert gases (e.g. nitrogen, helium and hydrogen), and must remain at a certain time and depth so that there is a considerable saturation inert gas in tissues. Under these conditions it is essential during the static stops for the diver to remove the excess of inert gas that accumulates in the tissues.

If you omit these stops there will be an excess of inert gas that may reach the critical point of super saturation at which the gas changes of state and forms bubbles.  Bubbles that may be intravascular and/or extra vascular are responsible for the pattern of symptoms of decompression sickness.

Rouquayrol and Denayrouse were able to run their “diving apparatus” with the minimum safety requirements. The plunger device Rouquayrol was approved by the Imperial French Navy in 1864 and won the gold medal at the Paris Exposition of 1867, but it could still not solve the problem of sufficient autonomy (half an hour at 10 meters deep at most) due mainly to the limit of compressed air that could be contained in the reserves. PORTATILES of the time (30 to 40 bars of pressure, no more). The problem was solved in 1943 with the invention of modern scuba gear.
1943: Control of autonomy
Pressure, pressure gauge, depth gauge and direct system

During the German occupation of the Second World War, France was experiencing a shortage of gasoline constantly requisitioned by the Germans. Emile Gagnan (Engineer at Air Liquide) gave the company a regulator Piel Rouquayrol to operate gasifiers and file a patent regulator.

Henri Melchior, his boss, then thought that this regulator may be of service to his son, Jacques-Yves Cousteau, who had, since 1937 sought to develop an efficient aqualung and automatic flow (or flow “on demand”) because of the time it was to be used by hand (”pressure regulator” Le Prieur). Melchior then made presentations to the two men who met in Paris in December 1942.

Cousteau adjusted a reserve of compressed air and made the Marne the first sub-test of its water regulator: when the diver is horizontal the regulator is working correctly, but when he is standing he gets continuous flow and when it is upside down it hangs. Cousteau and Gagnan then brought the same solution as Rouquayrol, Denayrouze and Commeinhes had brought before them, they returned at the end of the membrane valve, which balanced the air pressure room and closed the flow during expiration. It worked.

Cousteau then left for Bandol in the Var, having commanded Gagnan to send three new prototypes, received on June 28^th 1943. These three prototypes are intended by Frederic Dumas and Philippe Cousteau Tailliez to achieve the first sea trial in the Mediterranean. The test took place successfully at the end of June in the range of Barry town of Bandol, in the same year Cousteau and Gagnan patented their “diving Cousteau Gagnan”.

At the end of the war a few copies of “Cousteau-Gagnan” were built as prototypes, but Cousteau and Gagnan patented the “CG-45″ in 1945 (”C” Cousteau, “G” for Gagnan and “45″ for 1945), which is also marketed under the name “Aqua-Lung” (English term invented by Cousteau for marketing and means “water lungs”).

The CG-45 will be manufactured in series from 1946 and sold around the world until the arrival of Mistral (1955) and other increasingly sophisticated models (Royal Mistral, Spiro 8, Crystal).

The development of scuba gear is linked to several technological breakthroughs: the invention of efficient compressors and storage cylinders for compressed air is relatively small (based on physical laws of gas pressure of Boyle and Mariotte (1660) and the development of palm by Commander Louis corlieu in 1934)

Scuba Stabilizer dorsal
1) 1st stage regulator
2) cylinder valve
3) shoulder straps
4) Bladder stabilizer
5) valve pressure of the bladder drain and pull lower
6) 2nd floor of the regulator (with “octopus”)
7) Console (gauge, depth gauge & compass)
Connect the hose-inflator coat dry
9) Support plate (model Lacasse)
10) Connect the hose and button control inflator stabilizer
11) tip of the hose of stabilizing inflation and purge button above stabilizer
12) Strap-on cutale
13) abdominal

one or more bottles, we talk about diving block, the block contains a mixture of gases (air, nitrox, trimix, hydreliox) under pressure between 170 and 300 bar) whose capacity at atmospheric pressure can be 2,3,6, 9, 12, 15, 18 or 20 liters of mixture. These blocks are made of steel, sometimes reinforced with carbon, or aluminum;
a regulator, which allows breathing the gas mixture at ambient pressure;

a stab connected to the bottle via the direct system allowing it to vary its buoyancy depending on the depth and needs.
pressure gauges to monitor the pressure of the gas mixture in the block and know the amount of remaining gas;
instruments of relief, the most common being the dive computer, but some still use a diver’s watch and a decompression table;
a parachute landing;
a weight belt (if necessary).

Some divers use a re-breather in which exhaled air is treated to be breathable again without danger: the CO2 is absorbed and exhaled air is enriched with oxygen. Air circulates well closed or semi-closed (semi-closed Rebreather, SCR). The first solution does not bubble on the surface. In the near future, it should be possible to see the arrival of diving suits using respiratory fluid instead of gas mixtures.
Instructions for use

Bottle diving, equipped with a pressure regulator, pressure gauge and direct system
The scuba permits: to charge air automatically according to the needs of the diver and not continuously; to provide proper air pressure corresponding to the depth of water, which allows the diver to inspire without effort; easy to get rid of carbon dioxide content excess in exhaled air.

The buoyancy compensator (often shortened to “stab” or “waistcoat” simply, but also called Buoyancy Control Jacket in English, also abbreviated as “BC”) can change the buoyancy and balance in the water following the Archimedes’ principle. The stab may be inflated by mouth or automatically with the direct system, which is connected to the bottle.

Autonomy diving and exploration ranges from 2 hours to 30 minutes on a very large number of parameters: The main one is the depth (2 hours at 10 meters and 30 minutes to 60 meters, regardless of decompression). Because of the cold environment the body of the plunger tended to consume more oxygen. The lower the temperatures go, even unconsciously, uses more air from its reserves.

There is no age limit for scuba diving. A doctor specializing in sports or even scuba diving is very often has the sole responsibility of granting or not granting the diver medical certificate without which it will have no right to plunge into the natural environment. Regarding the movement in the water, the diver gets moving quicker and more flexibly with a good knowledge of his own hydrodynamics. His palms allow him to swim in 3 dimensions.
Using leisure

Two recreational divers discovered the seabed Maria la Gorda, Cuba. Since marketing by Cousteau and Gagnan their invention has meant (in 1946: the first model marketed regulator, the CG45), millions of scuba divers have plunged and continued to dive just for fun, in the seas around the world, photographing living marine or aquatic animals. But the visible breath may scare more timid animals.
Using professional
The scuba was very useful in many areas related to the water world: underwater archaeology; marine biology; maintenance and repair of buoys or anti-shark nets near the ports and coasts; looking for objects or corpses in the river and marine divisions of the military; gendarmerie; police or firefighters and oceanographic exploration. In the field of tourism, and according to each legal structure, many dive centers are allowed to form a private company to offer, against payment, services to recreational divers.

It is necessary to note that the first company in the field, using the Cousteau aqualung-Gagnan was created by Andre Galerne in 1952. It brought together young members of the clan of Eclaiteurs Claude Sommer of France aboard a barge concrete bridge located at Bercy. Here, is now the Ministry of Finance. Called first SGTMF for general society of maritime and rivers, it became in 1955 the famous SOGETRAM.