Effects of exposure to high pressure (hyperbaria) dangers stem from changes in gas volumes within enclosed spaces and increased solubility of gases 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) Pressure increases 1 atmosphere (760 mm Hg) for every 10 m (33ft)

Barotrauma tissue injury caused by changing pressure tissue injury caused by changing pressure human body has limited ability to distend and compress human body has limited ability to distend and compress trauma comes from exceeding those limits trauma comes from exceeding those limits

Boyle’s Law applies here: vol. of a gas decreases or increases as a diver goes up or down 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 pressure is not allowed to equalize with air from outside the space

Gas Toxicity gases like CO, O 2, CO 2, N 2 and He can be dangerous under certain circumstances gases like CO, O 2, CO 2, N 2 and He can be dangerous under certain circumstances

CO: dangerous for all life forms compressed air may have been contaminated by exhaust fumes compressed air may have been contaminated by exhaust fumes danger due to high affinity for hemoglobin: 240 more times the affinity than O 2 danger due to high affinity for hemoglobin: 240 more times the affinity than O 2 problem is compounded if diver is a smoker or exposed to air pollution problem is compounded if diver is a smoker or exposed to air pollution

O 2 Toxicity O 2 at high pressure is toxic to all life forms -- depends on its concentration and length of exposure O 2 at high pressure is toxic to all life forms -- depends on its concentration and length of exposure physical exercise speeds up development of toxicity physical exercise speeds up development of toxicity principle sites of O 2 toxicity are lungs and CNS principle sites of O 2 toxicity are lungs and CNS

Pulmonary symptoms include Pulmonary symptoms include substernal distress with soreness in chest substernal distress with soreness in chest airway resistance on inspiration airway resistance on inspiration histological changes in alveoli histological changes in alveoli pulmonary edema pulmonary edema flushing of the face flushing of the face cough that starts out dry and gets wet cough that starts out dry and gets wet

CNS symptoms include nausea CNS symptoms include nausea contraction of the field of vision contraction of the field of vision Convulsions Convulsions lack of sphincter control lack of sphincter control Unconsciousness Unconsciousness death death can also cause arrhythmias can also cause arrhythmias mechanism that causes it is unknown mechanism that causes it is unknown

hyperbaric O 2 may interfere with CO 2 transport hyperbaric O 2 may interfere with CO 2 transport at high pressure, more O 2 is dissolved into the blood at high pressure, more O 2 is dissolved into the blood hemoglobin doesn’t desaturate thus isn’t available for O 2 transport hemoglobin doesn’t desaturate thus isn’t available for O 2 transport increased CO 2 vasodilates cerebral blood vessels causing acidosis and increased PO 2 in the brain increased CO 2 vasodilates cerebral blood vessels causing acidosis and increased PO 2 in the brain cell function may also be disrupted as well as neural transmission in CNS cell function may also be disrupted as well as neural transmission in CNS

CO 2 Toxicity most common in closed-circuit scuba systems and hose-supplied helmets most common in closed-circuit scuba systems and hose-supplied helmets inadequate respiratory exchange leads to hypercapnia with heavy exercise at high pressures 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, CO 2 builds up happens if diver tries to suppress their Ve in order to conserve air, CO 2 builds up

Symptoms of CO 2 Toxicity Uncomfortable breathing Uncomfortable breathing Headache Headache Mental deterioration Mental deterioration Violent respiratory distress Violent respiratory distress Unconsciousness Unconsciousness Convulsions Convulsions

Nitrogen Narcosis some gases exert a narcotic or anesthetic effect at high pressure 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 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) nitrogen can cause condition: nitrogen narcrosis ~30 m (100ft)

Progression of symptoms Euphoria Euphoria Impaired performance Impaired performance Weakness Weakness Drowsiness Drowsiness Unconsciousness Unconsciousness

caused by interference in the transfer of signals across the neural synapses 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) this is why the use of compressed air is limited to ~ 50 m (165 ft) replace nitrogen with helium replace nitrogen with helium below 150 m (500ft) can cause neuromuscular disorder called high- pressure nervous syndrome (HPVS): tremors, vertigo and nausea below 150 m (500ft) can cause neuromuscular disorder called high- pressure nervous syndrome (HPVS): tremors, vertigo and nausea

slowing compression rate during dive and adding nitrogen to O 2 mixture can help prevent this slowing compression rate during dive and adding nitrogen to O 2 mixture can help prevent this nitrogen narcosis is a limiting factor during deep dives nitrogen narcosis is a limiting factor during deep dives almost impossible to avoid in commercial dives almost impossible to avoid in commercial dives slows down information processing in the brain, but does not distort perception slows down information processing in the brain, but does not distort perception slowing down activity level can help slowing down activity level can help

Decompression Sickness (the Bends) caused by a nitrogen bubble formation in the tissue due to too rapid of an ascent 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 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 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 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 symptoms appear about 1 hour after surfacing but can occur either immediately or up to 12 hours post

if decompression is too rapid, N 2 returns to gaseous state and bubbles form in blood and tissues if decompression is too rapid, N 2 returns to gaseous state and bubbles form in blood and tissues decompression tables help divers figure absorption levels decompression tables help divers figure absorption levels decompression time increases with depth and length of dives decompression time increases with depth and length of dives must also consider body fat, age, physical condition, gas mixtures, alt of dive must also consider body fat, age, physical condition, gas mixtures, alt of dive

Hyperbaric exercise Studies are conducted in hyperbaric chamber or underwater Studies are conducted in hyperbaric chamber or underwater Chamber provides opportunity to isolate variables like partial pressures, temperature, and gas mixtures Chamber provides opportunity to isolate variables like partial pressures, temperature, and gas mixtures can simulate ocean dives too, to help understand differences can simulate ocean dives too, to help understand differences

Biological measurements difficult in hyperbaric environment expensive equipment and facility expensive equipment and facility technically exacting technically exacting open water measurements are complex b/c of restraints of aqueous environment open water measurements are complex b/c of restraints of aqueous environment

Factors adding difficulty to exercising underwater increased air density increased air density cold cold decreased efficiency decreased efficiency CO 2 retention CO 2 retention inert gas narcosis inert gas narcosis

Ve may be limiting factor b/c maximal voluntary Ve decreases with depth results in progressively smaller difference between exercise Ve and max capacity 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 CO 2, increased work to breathe higher densities of air increase flow resistance in scuba equipment and airways, causes hyperventilation which leads to retention of CO 2, increased work to breathe ability to increase expiratory flow rate is limited ability to increase expiratory flow rate is limited after reaching max flow rate, further effort results in partial airway collapse after reaching max flow rate, further effort results in partial airway collapse

O 2 consumption increases with submax work with increasing depth increased energy cost of breathing increased energy cost of breathing maintaining body temp. maintaining body temp. movement in higher hydrostatic pressures movement in higher hydrostatic pressures

Experienced divers can achieve ~91% of their land- measured max O 2 but work efficiency is reduced max capacity is dictated by tolerance to high levels of CO 2 and % of max O 2 consumption attained before reaching critical PCO 2 max capacity is dictated by tolerance to high levels of CO 2 and % of max O 2 consumption attained before reaching critical PCO 2

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 HR decreases as water temp. decreases and pressure increases divers should not use land-measured relationship between HR and O 2 consumption, dangerous divers should not use land-measured relationship between HR and O 2 consumption, dangerous HR can be used to estimate energy cost in diving only when HR/VO 2 relationship is know for a certain diver at a certain depth HR can be used to estimate energy cost in diving only when HR/VO 2 relationship is know for a certain diver at a certain depth

Strength: decreases with muscle temperature below 25°C

Commercial Diving Methods Scuba is most widely known, but not used much Scuba is most widely known, but not used much Surface demand diving commonly used at depth ~50m (164 ft) Surface demand diving commonly used at depth ~50m (164 ft) Diver connected to reinforced hoses, air supplied form surface Diver connected to reinforced hoses, air supplied form surface Atmospheric diving (submarine with robot arms) Atmospheric diving (submarine with robot arms)

Saturation diving: exposure to hyperbaria uses He-O 2 gas mixtures uses He-O 2 gas mixtures most commonly used method below 50 meters most commonly used method below 50 meters divers become totally saturated with inert gases after hours divers become totally saturated with inert gases after hours after that, further exposure doesn’t require additional decompression time after that, further exposure doesn’t require additional decompression time divers live in decompression chamber when not working divers live in decompression chamber when not working