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 tissue injury caused by changing pressure human body has limited ability to distend and compress 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 pressure is not allowed to equalize with air from outside the space Gas Toxicity gases like CO, O2, CO2, N2 and He can be dangerous under certain circumstances CO: dangerous for all life forms 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 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 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 CNS symptoms include nausea contraction of the field of vision Convulsions lack of sphincter control Unconsciousness death can also cause arrhythmias mechanism that causes it is unknown 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 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 2 Uncomfortable breathing Headache Mental deterioration Violent respiratory distress Unconsciousness Convulsions Nitrogen Narcosis 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 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 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 Decompression Sickness (the Bends) 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 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 Hyperbaric exercise 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 expensive equipment and facility technically exacting open water measurements are complex b/c of restraints of aqueous environment Factors adding difficulty to exercising underwater increased air density cold decreased efficiency CO2 retention 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 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 O2 consumption increases with submax work with increasing depth increased energy cost of breathing maintaining body temp. movement in higher hydrostatic pressures Experienced divers can achieve ~91% of their landmeasured max O2 but work efficiency is reduced 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 Strength: decreases with muscle temperature below 25°C Commercial Diving Methods 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 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