effects of exposure to high pressure (hyperbaria) dangers stem from changes in gas volumes within...
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Effects of exposure to high Effects of exposure to high pressure (hyperbaria)pressure (hyperbaria)
dangers stem from changes in dangers stem from changes in gas volumes within enclosed gas volumes within enclosed spaces and increased solubility of spaces and increased solubility of gasesgasesPressure increases 1 Pressure increases 1 atmosphere (760 mm Hg) for atmosphere (760 mm Hg) for every 10 m (33ft)every 10 m (33ft)
BarotraumaBarotrauma
tissue injury caused by changing pressuretissue injury caused by changing pressure human body has limited ability to distend human body has limited ability to distend
and compressand compress trauma comes from exceeding those limitstrauma comes from exceeding those limits
Boyle’s Law applies here: vol. of a gas Boyle’s Law applies here: vol. of a gas decreases or increases as a diver goes up decreases or increases as a diver goes up or downor down
pressure is not allowed to equalize with air pressure is not allowed to equalize with air from outside the spacefrom outside the space
Gas ToxicityGas Toxicity
gases like CO, Ogases like CO, O22, CO, CO22, N, N22 and He can be and He can be
dangerous under certain circumstancesdangerous under certain circumstances
CO: dangerous for all life formsCO: dangerous for all life forms compressed air may have been compressed air may have been
contaminated by exhaust fumescontaminated by exhaust fumes danger due to high affinity for danger due to high affinity for
hemoglobin: 240 more times the affinity hemoglobin: 240 more times the affinity than Othan O22
problem is compounded if diver is a problem is compounded if diver is a smoker or exposed to air pollutionsmoker or exposed to air pollution
OO22 Toxicity Toxicity
OO22 at high pressure is toxic to all life forms at high pressure is toxic to all life forms
-- depends on its concentration and length -- depends on its concentration and length of exposureof exposure
physical exercise speeds up development physical exercise speeds up development of toxicityof toxicity
principle sites of Oprinciple sites of O22 toxicity are lungs and toxicity are lungs and
CNSCNS
Pulmonary symptoms include Pulmonary symptoms include
substernal distress with soreness in substernal distress with soreness in chestchest
airway resistance on inspirationairway resistance on inspiration histological changes in alveolihistological changes in alveoli pulmonary edemapulmonary edema flushing of the faceflushing of the face cough that starts out dry and gets wetcough that starts out dry and gets wet
CNS symptoms include nauseaCNS symptoms include nausea
contraction of the field of visioncontraction of the field of vision ConvulsionsConvulsions lack of sphincter controllack of sphincter control UnconsciousnessUnconsciousness deathdeath can also cause arrhythmiascan also cause arrhythmias
mechanism that causes it is unknownmechanism that causes it is unknown
hyperbaric Ohyperbaric O22 may interfere with CO may interfere with CO22 transport transport at high pressure, more Oat high pressure, more O22 is dissolved into the is dissolved into the
bloodblood hemoglobin doesn’t desaturate thus isn’t hemoglobin doesn’t desaturate thus isn’t
available for Oavailable for O22 transport transport increased COincreased CO22 vasodilates cerebral blood vessels vasodilates cerebral blood vessels
causing acidosis and increased POcausing acidosis and increased PO22 in the brain in the brain cell function may also be disrupted as well as cell function may also be disrupted as well as
neural transmission in CNSneural transmission in CNS
COCO22 Toxicity Toxicity
most common in closed-circuit scuba most common in closed-circuit scuba systems and hose-supplied helmetssystems and hose-supplied helmets
inadequate respiratory exchange leads to inadequate respiratory exchange leads to hypercapnia with heavy exercise at high hypercapnia with heavy exercise at high pressures pressures
happens if diver tries to suppress their Ve happens if diver tries to suppress their Ve in order to conserve air, COin order to conserve air, CO22 builds up builds up
Symptoms of COSymptoms of CO22 Toxicity Toxicity
Uncomfortable breathingUncomfortable breathing HeadacheHeadache Mental deteriorationMental deterioration Violent respiratory distressViolent respiratory distress UnconsciousnessUnconsciousness ConvulsionsConvulsions
Nitrogen NarcosisNitrogen Narcosis
some gases exert a narcotic or anesthetic some gases exert a narcotic or anesthetic effect at high pressureeffect at high pressure
effects depends on the partial pressure of effects depends on the partial pressure of the gas and its solubility in the body’s the gas and its solubility in the body’s tissue and fluidstissue and fluids
nitrogen can cause condition: nitrogen nitrogen can cause condition: nitrogen narcrosis ~30 m (100ft) narcrosis ~30 m (100ft)
Progression of symptomsProgression of symptoms
EuphoriaEuphoria Impaired performanceImpaired performance WeaknessWeakness DrowsinessDrowsiness UnconsciousnessUnconsciousness
caused by interference in the transfer caused by interference in the transfer of signals across the neural synapsesof signals across the neural synapses
this is why the use of compressed air this is why the use of compressed air is limited to ~ 50 m (165 ft)is limited to ~ 50 m (165 ft)
replace nitrogen with helium replace nitrogen with helium below 150 m (500ft) can cause below 150 m (500ft) can cause
neuromuscular disorder called high-neuromuscular disorder called high-pressure nervous syndrome (HPVS): pressure nervous syndrome (HPVS): tremors, vertigo and nauseatremors, vertigo and nausea
slowing compression rate during dive and slowing compression rate during dive and adding nitrogen to Oadding nitrogen to O22 mixture can help mixture can help prevent thisprevent this
nitrogen narcosis is a limiting factor during nitrogen narcosis is a limiting factor during deep divesdeep dives
almost impossible to avoid in commercial almost impossible to avoid in commercial divesdives
slows down information processing in the slows down information processing in the brain, but does not distort perceptionbrain, but does not distort perception
slowing down activity level can helpslowing down activity level can help
Decompression Sickness (the Decompression Sickness (the Bends)Bends)
caused by a nitrogen bubble formation in caused by a nitrogen bubble formation in the tissue due to too rapid of an ascentthe tissue due to too rapid of an ascent
symptoms include itchy skin, fatigue, pain symptoms include itchy skin, fatigue, pain in the muscles, joints, and bones, in the muscles, joints, and bones, perspiring, nauseaperspiring, nausea
more serious ones include respiratory distress, more serious ones include respiratory distress, ataxia (loss of muscle coordination), vascular ataxia (loss of muscle coordination), vascular obstruction, paralysis, unconsciousness, and obstruction, paralysis, unconsciousness, and deathdeath
called “the chokes” when it affects the lungs called “the chokes” when it affects the lungs and “the staggers” when it affects the CNSand “the staggers” when it affects the CNS
symptoms appear about 1 hour after surfacing symptoms appear about 1 hour after surfacing but can occur either immediately or up to 12 but can occur either immediately or up to 12 hours posthours post
if decompression is too rapid, Nif decompression is too rapid, N22 returns to returns to gaseous state and bubbles form in blood and gaseous state and bubbles form in blood and tissuestissues
decompression tables help divers figure decompression tables help divers figure absorption levelsabsorption levels decompression time increases with depth decompression time increases with depth
and length of divesand length of dives must also consider body fat, age, physical must also consider body fat, age, physical
condition, gas mixtures, alt of divecondition, gas mixtures, alt of dive
Hyperbaric exerciseHyperbaric exercise
Studies are conducted in hyperbaric Studies are conducted in hyperbaric chamber or underwaterchamber or underwater
Chamber provides opportunity to isolate Chamber provides opportunity to isolate variables like partial pressures, variables like partial pressures, temperature, and gas mixturestemperature, and gas mixtures
can simulate ocean dives too, to help can simulate ocean dives too, to help understand differences understand differences
Biological measurements Biological measurements difficult in hyperbaric difficult in hyperbaric
environmentenvironment expensive equipment and facilityexpensive equipment and facility technically exactingtechnically exacting open water measurements are complex open water measurements are complex
b/c of restraints of aqueous environmentb/c of restraints of aqueous environment
Factors adding difficulty to Factors adding difficulty to exercising underwaterexercising underwater
increased air densityincreased air density coldcold decreased efficiencydecreased efficiency COCO22 retention retention inert gas narcosisinert gas narcosis
Ve may be limiting factor b/c Ve may be limiting factor b/c maximal voluntary Ve maximal voluntary Ve decreases with depthdecreases with depth
results in progressively smaller difference results in progressively smaller difference between exercise Ve and max capacitybetween exercise Ve and max capacity
higher densities of air increase flow higher densities of air increase flow resistance in scuba equipment and resistance in scuba equipment and airways, causes hyperventilation airways, causes hyperventilation which leads to retention of COwhich leads to retention of CO22, ,
increased work to breatheincreased work to breathe ability to increase expiratory flow rate ability to increase expiratory flow rate
is limitedis limited after reaching max flow rate, further after reaching max flow rate, further
effort results in partial airway collapseeffort results in partial airway collapse
OO22 consumption increases with consumption increases with
submax work with increasing submax work with increasing depthdepth
increased energy cost of breathingincreased energy cost of breathing maintaining body temp.maintaining body temp. movement in higher hydrostatic movement in higher hydrostatic
pressurespressures
Experienced divers can Experienced divers can achieve ~91% of their land-achieve ~91% of their land-measured max Omeasured max O22 but work but work
efficiency is reducedefficiency is reduced max capacity is dictated by tolerance to max capacity is dictated by tolerance to
high levels of COhigh levels of CO22 and % of max O and % of max O22
consumption attained before reaching consumption attained before reaching critical PCOcritical PCO22
Swimming angle and drag Swimming angle and drag produced by scuba equipment produced by scuba equipment greatly affects energy cost of greatly affects energy cost of underwater work and underwater work and individual differences in individual differences in swimming efficiencyswimming efficiency
Diving bradycardiaDiving bradycardia HR decreases as water temp. decreases HR decreases as water temp. decreases
and pressure increasesand pressure increases divers should not use land-measured divers should not use land-measured
relationship between HR and Orelationship between HR and O22
consumption, dangerousconsumption, dangerous HR can be used to estimate energy cost in HR can be used to estimate energy cost in
diving only when HR/VOdiving only when HR/VO22 relationship is relationship is
know for a certain diver at a certain depthknow for a certain diver at a certain depth
Strength: decreases with Strength: decreases with muscle temperature below 25°Cmuscle temperature below 25°C
Commercial Diving MethodsCommercial Diving Methods
Scuba is most widely known, but not used Scuba is most widely known, but not used muchmuch
Surface demand diving commonly used at Surface demand diving commonly used at depth ~50m (164 ft)depth ~50m (164 ft)
Diver connected to reinforced hoses, air Diver connected to reinforced hoses, air supplied form surfacesupplied form surface
Atmospheric diving (submarine with robot Atmospheric diving (submarine with robot arms)arms)
Saturation diving: exposure to Saturation diving: exposure to hyperbariahyperbaria uses He-Ouses He-O22 gas mixtures gas mixtures most commonly used method below 50 metersmost commonly used method below 50 meters divers become totally saturated with inert gases divers become totally saturated with inert gases
after 24-36 hoursafter 24-36 hours after that, further exposure doesn’t require after that, further exposure doesn’t require
additional decompression timeadditional decompression time divers live in decompression chamber when not divers live in decompression chamber when not
workingworking