Transcript Effects of exposure to high pressure (hyperbaria)

Effects of exposure to high
pressure (hyperbaria)
dangers
stem from changes in
gas volumes within enclosed
spaces and increased solubility of
gases
Pressure increases 1
atmosphere (760 mm Hg) for
every 10 m (33ft)
Barotrauma
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tissue injury caused by changing pressure
human body has limited ability to distend
and compress
trauma comes from exceeding those limits
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Boyle’s Law applies here: vol. of a gas
decreases or increases as a diver goes up
or down
pressure is not allowed to equalize with air
from outside the space
Gas Toxicity
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gases like CO, O2, CO2, N2 and He can be
dangerous under certain circumstances
CO: dangerous for all life forms
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compressed air may have been
contaminated by exhaust fumes
danger due to high affinity for
hemoglobin: 240 more times the affinity
than O2
problem is compounded if diver is a
smoker or exposed to air pollution
O2 Toxicity
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O2 at high pressure is toxic to all life forms
-- depends on its concentration and length
of exposure
physical exercise speeds up development
of toxicity
principle sites of O2 toxicity are lungs and
CNS
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Pulmonary symptoms include
substernal distress with soreness in
chest
 airway resistance on inspiration
 histological changes in alveoli
 pulmonary edema
 flushing of the face
 cough that starts out dry and gets wet
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 CNS
symptoms include nausea
contraction of the field of vision
 Convulsions
 lack of sphincter control
 Unconsciousness
 death
 can also cause arrhythmias
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mechanism that causes it is unknown
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hyperbaric O2 may interfere with CO2
transport
at high pressure, more O2 is dissolved into
the blood
hemoglobin doesn’t desaturate thus isn’t
available for O2 transport
increased CO2 vasodilates cerebral blood
vessels causing acidosis and increased
PO2 in the brain
cell function may also be disrupted as well
as neural transmission in CNS
CO2 Toxicity
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most common in closed-circuit scuba
systems and hose-supplied helmets
inadequate respiratory exchange leads to
hypercapnia with heavy exercise at high
pressures
happens if diver tries to suppress their Ve
in order to conserve air, CO2 builds up
Symptoms of CO Toxicity
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Uncomfortable breathing
Headache
Mental deterioration
Violent respiratory distress
Unconsciousness
Convulsions
Nitrogen Narcosis
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some gases exert a narcotic or anesthetic
effect at high pressure
effects depends on the partial pressure of
the gas and its solubility in the body’s
tissue and fluids
nitrogen can cause condition: nitrogen
narcrosis ~30 m (100ft)
Progression of symptoms
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Euphoria
Impaired performance
Weakness
Drowsiness
Unconsciousness
caused by interference in the transfer
of signals across the neural synapses
 this is why the use of compressed air
is limited to ~ 50 m (165 ft)
 replace nitrogen with helium
 below 150 m (500ft) can cause
neuromuscular disorder called highpressure nervous syndrome (HPVS):
tremors, vertigo and nausea
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slowing compression rate during dive
and adding nitrogen to O2 mixture can
help prevent this
 nitrogen narcosis is a limiting factor
during deep dives
 almost impossible to avoid in
commercial dives
 slows down information processing in
the brain, but does not distort
perception
 slowing down activity level can help
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Decompression Sickness (the
Bends)
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caused by a nitrogen bubble formation in
the tissue due to too rapid of an ascent
symptoms include itchy skin, fatigue, pain
in the muscles, joints, and bones,
perspiring, nausea
more serious ones include respiratory
distress, ataxia (loss of muscle
coordination), vascular obstruction,
paralysis, unconsciousness, and
death
 called “the chokes” when it affects the
lungs and “the staggers” when it
affects the CNS
 symptoms appear about 1 hour after
surfacing but can occur either
immediately or up to 12 hours post
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if decompression is too rapid, N2
returns to gaseous state and bubbles
form in blood and tissues
 decompression tables help divers
figure absorption levels
 decompression time increases with
depth and length of dives
 must also consider body fat, age,
physical condition, gas mixtures, alt
of dive
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Hyperbaric exercise
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Studies are conducted in hyperbaric
chamber or underwater
Chamber provides opportunity to isolate
variables like partial pressures,
temperature, and gas mixtures
can simulate ocean dives too, to help
understand differences
Biological measurements
difficult in hyperbaric
environment
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expensive equipment and facility
technically exacting
open water measurements are complex
b/c of restraints of aqueous environment
Factors adding difficulty to
exercising underwater
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increased air density
cold
decreased efficiency
CO2 retention
inert gas narcosis
Ve may be limiting factor b/c
maximal voluntary Ve
decreases with depth
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results in progressively smaller difference
between exercise Ve and max capacity
higher densities of air increase flow
resistance in scuba equipment and
airways, causes hyperventilation
which leads to retention of CO2,
increased work to breathe
 ability to increase expiratory flow
rate is limited
 after reaching max flow rate, further
effort results in partial airway
collapse
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O2 consumption increases with
submax work with increasing
depth
increased energy cost of breathing
 maintaining body temp.
 movement in higher hydrostatic
pressures
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Experienced divers can
achieve ~91% of their landmeasured max O2 but work
efficiency is reduced
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max capacity is dictated by tolerance to
high levels of CO2 and % of max O2
consumption attained before reaching
critical PCO2
Swimming angle and drag
produced by scuba equipment
greatly affects energy cost of
underwater work and
individual differences in
swimming efficiency
Diving bradycardia
HR decreases as water temp.
decreases and pressure increases
 divers should not use land-measured
relationship between HR and O2
consumption, dangerous
 HR can be used to estimate energy
cost in diving only when HR/VO2
relationship is know for a certain diver
at a certain depth
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Strength: decreases with
muscle temperature below 25°C
Commercial Diving Methods
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Scuba is most widely known, but not used
much
Surface demand diving commonly used at
depth ~50m (164 ft)
Diver connected to reinforced hoses, air
supplied form surface
Atmospheric diving (submarine with robot
arms)
Saturation diving: exposure to
hyperbaria
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uses He-O2 gas mixtures
most commonly used method below 50
meters
divers become totally saturated with inert
gases after 24-36 hours
after that, further exposure doesn’t require
additional decompression time
divers live in decompression chamber
when not working