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