Effects of increased atmospheric pressure on human body

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Effects of increased atmospheric pressure on
human body
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Hydrostatic pressure
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Compression and decompression of gas over liquid

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

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decompression sickness caisson diseasebends
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Diving bell, hard-hat diver
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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.

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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.

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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.

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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

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Other treatment

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

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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.

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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.

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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.

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Nitrogen narcosis
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Pulmonary rupture

• another risk for divers

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Historical view
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Very first instructions to divers

• 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.

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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.

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Hard-hat diving

• chest weights weigh about 40lbs each and are tied
  down to stop the helmet rising from the divers
  shoulders.

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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 divings traumas, the bends or a
  burst lung, or both.

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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.

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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.

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The gases used for breathing by scuba divers
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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 80helium / 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.

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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.