Effects of increased atmospheric pressure on human body

Hydrostatic pressure

Compression and decompression of gas over liquid

the key for understanding to effects of increased pressure of ambient air on human body

decompression sickness caisson disease bends

Diving bell, hard-hat diver

Local pain

        in or near an arm joint (divers) joints of the leg (compressed-air workers) characteristically hard to describe often poorly localized deep, like something boring into the bone mild or intermittent, but it may increase inflammation and tenderness are absent not affected by motion.

Neurologic manifestations

       more common following dives with scuba than in "hard-hat" diving or caisson work currently, the proportion of neurologic problems reported among cases of decompression sickness exceeds 50%. spinal cord is especially vulnerable neurologic symptoms and signs are exceedingly variable range from mild paresthesia to major cerebral problems vestibular involvement may produce severe vertigo spinal cord lesions leading to paraplegia are a particular hazard, and delay in treatment may render the condition irreversible.

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chokes, or respiratory decompression sickness

rare in occurrence but grave in significance arises from massive bubble-embolization of the pulmonary vascular tree. some cases resolve spontaneously, but rapid progression to circulatory collapse and death is not uncommon without prompt recompression. substernal discomfort and coughing on deep inspiration or inhalation of tobacco smoke are often early manifestations of chokes. in animal studies, chokes are strongly associated with exposure to altitude soon after diving. require prompt chamber recompression.

Other manifestations

    itching, skin rash, and exceptional fatigue sometimes forerunners of much more serious problems cutaneous edema reflects obstruction of lymphatic channels by bubbles. abdominal pain may reflect bubble formation at the site

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Late effects of decompression sickness

dysbaric osteonecrosis (a form of aseptic bone necrosis). lesions adjacent to articular surfaces are most common in the shoulder and hip and can cause great damage to the joint with chronic pain and severe disability. it becomes symptomatic or is detected by x-ray months or years after the responsible insult paraplegia - delayed or inappropriate treatment of early signs of spinal cord involvement.

TREATMENT

   Recompression is imperative and should be accomplished as soon as possible it is always beneficial divers themselves, and medical facilities and rescue and police units in popular diving areas, should know the location of the nearest suitable chamber

Other treatment

  Corticosteroids (dexamethasone) may be useful in controlling CNS edema. Sedatives and narcotics may obscure symptoms and cause respiratory insufficiency.

How to avoid CD ?

  (1) restricting the uptake of gas, as by limiting the depth and duration of dives to a range that does not require decompression stops on ascent: "no decompression (no-stop) limits" (2) using an air decompression table such as that in the US Navy Diving Manual The table provides a pattern of ascent that normally allows excess inert gas to escape harmlessly.

Repetitive dives

   major source of difficulty excess of inert gas remains in the body after every dive and increases with each subsequent exposure. US Navy Diving Manual should be used.

Pitfalls

 Few decompression tables have been tested for adequacy in females or in older divers  Dives conducted at altitude and flying after diving require special procedures or precautions. Spending 24 h at the surface before going to altitude is usually recommended.

Nitrogen narcosis

Pulmonary rupture

another risk for divers

Historical view

Very first instructions to divers

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1. Men with short necks, full blooded, and florid complexions.

2. Men who are very pale, whose lips are more blue than red, who are subject to cold hands and feet, men who have what is commonly called a languid circulation.

3. Men who are hard drinkers, and have suffered repeatedly and severely from venereal disease, or who have rheumatism, or sunstroke.

Hard-hat diving

   weight of the diving helmet, weights, boots and rig is about 180 lbs in

total

obviously very heavy on the surface, although in the water the buoyancy of the suit and helmet neutralizes this weight. diver can make himself lighter or heavier, depending on what work he has to do, by operating air exhaust valve on the back of the helmet. He has control over his own buoyancy and can even inflate the suit to bring him to the surface.

Hard-hat diving

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chest weights weigh about

40lbs each and are tied down to stop the helmet rising from the diver’s shoulders.

Hard-hat diving

 Blowing up was one of the main dangers divers were taught to avoid. As the diver ascended he had to do so slowly, operating the exhaust valve on the helmet to vent air from the suit. If he did not, or he was fed too much air, the suit would inflate and he would shoot to the surface, suffering one of diving’s traumas, the bends or a burst lung, or both.

History of recompression chambers

 In 1905 Professor J S Haldane, working for the British Admiralty, devised a method of ‘Stage Decompression’ whereby divers were brought to the surface in a series of ‘stops’, allowing nitrogen to dissipate harmlessly.

 decompression accidents still occasionally occurred, and special chambers were manufactured, in which a diver could be rapidly repressurized for a very slow and controlled ‘ascent’.

Hard-hat diving

 It was soon recognized that the answer to very deep diving was to enclose the diver in a chamber strong enough to resist the immense pressure of the sea, allowing the occupant to breath under ordinary atmospheric conditions. All problems of decompression and breathing at depth would thus be eliminated.

The gases used for breathing by scuba divers

Compressed air

    nitrogen narcosis long decompression time very cheap available

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Helium and oxygen

animals breathing an 80 % helium / 20% oxygen mix could be decompressed at 1/6 the decompression time of an air breathing animal. humans subjects breathing 80% helium / 20% oxygen were found to have no apparent problems with heliox decompression schedules that were 1/4 the time required for air breathing dives. ability for humans to function "clear-headed" at depths where air breathing divers were incapacitated by nitrogen narcosis.

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Hydrogen and oxygen

Swedish Engineer, Arne Zetterstrom. hydrogen- oxygen mix is non-explosive if the percentage oxygen is less than 4% the technique was to descend to 100 feet and switch to a 4% oxygen / 96 % nitrogen mixture. After breathing this mix for sufficient time to allow oxygen concentration in lungs to drop below the "explosion threshold," the diver switched to Hydrox and continued descent hydrogen narcosis

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Multiple component mixes

it was found in 1965 that divers breathing heliox mixtures at depths below 500 feet developed nervous tremors known as High Pressure Nervous Syndrome (HPNS). small quantities of nitrogen in the heliox (termed tri-mix) helped eliminate this problem. (divers reached a depth of 2132 feet breathing tri-mix). adding helium to hydrogen-oxygen mixes (termed Hydreliox) helps to eliminate the "hydrogen effect" narcosis associated with breathing only a hydrogen-oxygen mix. Theoretical limits of hydreliox are currently placed at about 1750 feet.

Nitrox

     mixture of 68% N2 / 32% O2 Nitrox I mixture of 64% N2 / 36% O2 Nitrox II in operations shallower than 130 feet safe easily handled mix.