Trent University Lecture 9: Sport Diving PDF

2024-11-25 Lecture 9: Sport Diving November 25th , 2024 0 Environmental Stress Review Thermal Stress Altitude stress Heat Stress Microgravity...

2024-11-25 Lecture 9: Sport Diving November 25th , 2024 0 Environmental Stress Review Thermal Stress Altitude stress Heat Stress Microgravity Cold Stress 1 1 Click to add footer 1  2024-11-25 Environmental Stress: Underwater Diving The practice of descending below the water's surface to interact with the environment. The underwater environment exposes divers to high pressures (hyperbaria) and the possibility of rapidly changing pressures and can produce severe injury or death unless the diver equalizes pressures in the body’s air-filled cavities. 2 2 Lecture Objectives Develop an appreciation of diving history: Antiquity to Present, Learn about the different types of diving: Breath-hold diving Snorkeling SCUBA Mixed-Gas Understand the health risks associated with diving and how to counteract this 3 3 Click to add footer 2  2024-11-25 Diving History: Antiquity to Present Men and women have practiced breath-hold diving for centuries as they hunted for sponges and food, salvaged artifacts, and treasures, repaired ships, observed marine life, and participated in military maneuvers. 4 4 Diving History: Antiquity to Present The 5th-century Greek historian Herodotus tells of the underwater exploits in 480 BC of the Greek patriot Scyllias and his daughter Hydna during the war against the Persians. A snorkel was first used to “escape” the enemy, but they could only remain submerged for several minutes. 5 5 Click to add footer 3  2024-11-25 Diving History: Antiquity to the Present (cont.) The first solutions to remaining submerged underwater for longer than a few minutes took place in the 1530s with the invention of diving bells supplied with surface air, with the bottom open to water, and the top portion containing air compressed by water pressure. 6 6 Diving History: Antiquity to the Present (cont.) In England and France in the 16th century, diving suits made of leather allowed descent to depths of 60 ft. Manual pumps delivered fresh air from the surface to the diver. Soon metal helmets could withstand greater water pressures, and divers could descend further. By the 1830s, perfection of the surface supplied air helmet allowed extensive underwater salvage work. 7 7 Click to add footer 4  2024-11-25 Diving History: Antiquity to the Present (cont.) In the 19th century, two main avenues of investigation—one scientific and the other technologic—accelerated underwater exploration. French physiologist Paul Bert (1833–1886) and Scottish physiologist John Scott Haldane (1860–1936) explained the physiologic effects of water pressure on body tissues, defined safe limits for compressed air diving (used a decompression chamber and animal model) Technologic improvements with compressed air pumps, carbon dioxide scrubbers, and demand-valve regulators allowed prolonged deepwater explorations 8 8 Diving Depth and Pressure Water is noncompressible so it’s pressure against diver’s body increases directly with dive depth Forces that produce hyperbaria in diving: Weight of column of water directly above diver Weight of atmosphere at water’s surface Body tissues not susceptible to increased external pressure in diving as water is part of tissues; body’s air-filled cavities change greatly with increase or decrease in diving depth 9 9 Click to add footer 5  2024-11-25 Diving Depth and Gas Volume Boyle’s Law: P1 x V1 = P2 X V2 At constant temperature, volume of a given mass of gas varies inversely with its pressure When pressure doubles, volume halves; conversely, reducing pressure by one half expands gas volume to twice its previous size Gases expand with ascent; air volume needs to escape through mouth or nose 10 10 Gas Volume and Pressure 11 11 Click to add footer 6  2024-11-25 Breath-Hold Diving Duration and depth of breath-hold dive depends on: Time until arterial Pco2 reaches breath-hold breakpoint Relationship between a diver’s TLC and RLV Most persons can breath-hold for up to 1 min, 2 min is upper limit Po2 drops to 60 mm Hg and Pco2 rises to 50 mm Hg, signaling urgency to breathe Physical activity reduces breath-hold time as oxygen consumption and carbon dioxide production increase with exercise intensity 12 12 Hyperventilation and Breath-Hold Diving Hyperventilation before breath-hold dive extends breath-hold time but has risks. Blackout, caused by critical reduction in arterial Po2. With predive hyperventilation, Pco2 decreases to 15 mm Hg, which extends dive duration until Pco2 increases to stimulate breathing. Breakpoint for breath-holding corresponds to increase in arterial Pco2 to 50 mm Hg. 13 13 Click to add footer 7  2024-11-25 Hyperventilation and Breath-Hold Diving (cont.) Other risks of hyperventilating before breath-hold dive: By reducing blood’s carbon dioxide content via hyperventilation, H+ decreases, increasing pH and alkalinity. Decrease in arterial carbon dioxide with hyperventilation can reduce cerebral blood flow to produce loss of consciousness. 14 14 Depths Limits with Breath-Hold Diving: Thoracic Squeeze Deeper dives increase likelihood of lung squeeze Diver’s TLC:RLV ratio at surface determines critical diving depth before lung squeeze Ratio averages 4:1 at surface. No danger exists if TLC remains greater than RLV as sufficient air remains in lungs and respiratory passages to equalize pressure. If TLC decreases below RLV, pulmonary air pressure becomes less than external water pressure and lung squeeze occurs. 15 15 Click to add footer 8  2024-11-25 Diving Reflex in Humans Physiologic responses to water immersion (the diving reflex) Bradycardia Decreased cardiac output Increased peripheral vasoconstriction Lactate accumulation in underperfused muscle 16 16 Heart Rate, Stroke Volume, and Cardiac Output for Elite Breath-Hold Divers 17 17 Click to add footer 9  2024-11-25 Snorkeling Snorkel allows swimmer to breathe continually with face immersed in water. Factors that limit snorkel use: Health - asthma, heart conditions, anxiety Physical fitness Weather (wind) 18 18 Factors that limit snorkel size Increased hydrostatic pressure on chest cavity as one descends beneath water Increased pulmonary dead space by enlarging the snorkel’s volume 19 19 Click to add footer 10  2024-11-25 Inspiratory Capacity and Diving Depth At 1 m depth, compressive force of water against chest cavity becomes so large that inspiratory muscles cannot overcome external pressure and expand thoracic dimensions Makes inspiration impossible without external air at sufficient pressure to counter compressive force of water 20 20 Snorkel Size and Pulmonary Dead Space Ideal snorkel averages about 38 inches in length with an inside diameter of 5/8 to 3/4 of an inch to minimize effects of added dead space and resistance to breathing Further increase in snorkel size or volume increases anatomical dead space causing encroachment on alveolar ventilation 21 21 Click to add footer 11  2024-11-25 Scuba Diving Scuba (self-contained underwater breathing apparatus) is most common apparatus to supply air under pressure. Scuba system includes a tank of compressed air and a demand regulator valve with hose and mouthpiece or full-face mask that delivers air the diver needs at a particular depth. Basic scuba designs: Open-circuit system Closed-circuit system 22 22 Open-Circuit Scuba Used by most recreational SCUBA divers Limitations of open-circuit system Because air exhaled into water contains 17% oxygen, system “wastes” about 75% of tank’s total oxygen. Limited supply of compressed air limits time underwater. 23 23 Click to add footer 12  2024-11-25 Design of an Open-Circuit Scuba Unit 24 24 Air-Time Limits 25 25 Click to add footer 13  2024-11-25 Closed-Circuit Scuba Used by military and professional divers Small cylinder feeds pure oxygen into bellows or bag from which diver breathes Breathing bag acts as pressure regulator Valves in breathing mask direct exhaled gas through carbon dioxide– absorbing canister Carbon dioxide–free gas passes back to diver Oxygen cylinder replenishes oxygen consumed allowing diver to continually rebreathe oxygen Small oxygen cylinder sustains diver for ≥3 hr 26 26 Closed-Circuit Scuba System Design 27 27 Click to add footer 14  2024-11-25 Special problems breathing gases at high pressures Henry’s Law Quantity of gas dissolved in liquid at a given temperature varies directly with: Pressure differential between gas and liquid Gas solubility in liquid 28 28 Special problems breathing gases at high pressures Underwater breathing systems must supply air, oxygen, or other gas mixtures at sufficient pressure to overcome force of water against diver’s thorax If diver inhales fully at 10 m but fails to exhale during ascent, the expanding gas eventually will rupture the lungs before diver reaches surface 29 29 Click to add footer 15  2024-11-25 Scuba Diving Hazards Air embolism Face mask squeeze Eustachian tube blockage Sinus opening blockage Mediastinal and subcutaneous emphysema Pneumothorax Alveoli rupture 30 30 Air Embolism Air volume expands in direct proportion to reduction in external pressure as diver ascends to surface. Lung burst can occur if fills lungs instead of breath-holding on ascent to surface. Air embolism from pulmonary barotrauma is second to drowning as cause of death in divers. Treatment for air embolism requires rapid decompression to reduce bubble size and force them into solution to open plugged vessels. 31 31 Click to add footer 16  2024-11-25 Face Mask Squeeze Air in facemask before a dive equals ambient air pressure at surface. As diver goes deeper, a pressure differential develops between inside and outside of mask to create a relative vacuum within mask. Periodically exhaling through nose into face mask balances pressures on both sides of the mask. Eyes to bulge or squeeze from their sockets. This leads to capillary rupture and hemorrhage in the eyes and surrounding soft tissue. 32 32 Eustachian Tube Blockage: Middle-Ear Squeeze Divers often encounter problems equalizing pressure within air space of eustachian tubes. Tubes normally remain clear so that changes in external pressure against eardrum equalize by pressure changes transmitted from lungs through eustachian tubes. In scuba diving, middle-ear pressure can equalize with external pressure by blowing gently against closed nostrils. 33 33 Click to add footer 17  2024-11-25 Aerosinusitis Inflamed, congested sinuses prevent air pressure in these cavities from equalizing during diving. Sinus air pressure that does not equalize during descent remains at atmospheric pressure while external pressure increases. This relative vacuum creates “sinus squeeze,” causing sinus membranes to bleed as blood occupies the space to equalize pressure differential. 34 34 Pneumothorax Air forced through alveoli when lung tissue ruptures migrates laterally to burst through pleural sac that covers lungs Air pocket forms in chest cavity outside lungs, between chest wall and lung Continued expansion of trapped air during ascent collapses ruptured lung To eliminate danger of air embolism and pneumothorax, divers must ascend slowly and breathe normally when using scuba gear 35 35 Click to add footer 18  2024-11-25 Composition of air The composition of air at sea level is made up of the following gases: Nitrogen: The most abundant gas, making up about 78% of the air Oxygen: The second most abundant gas, making up about 21% of the air Argon: The third most abundant gas, making up about 0.93% of the air Carbon dioxide: A trace gas, making up about 0.042% of the air 36 36 Nitrogen Narcosis Increase in inspired nitrogen pressure while breathing compressed air during diving produces a narcotic effect characterized by euphoria similar to alcohol intoxication (termed “rapture of the deep”). Dissolved nitrogen at 30 m/100 ft produces effects similar to feelings after consuming alcohol on empty stomach. “Martini’s law:” Every 15.2 m of seawater depth produces effects equal to drinking 1 dry martini due to mimicking effects of alcohol 37 intoxication. 37 Click to add footer 19  2024-11-25 Decompression sickness Occurs when dissolved nitrogen moves out of solution and forms bubbles in body tissues and fluids Results from ascending to surface too rapidly following a deep, prolonged dive Also known as “the bends” Nitrogen reaches equilibrium slowly in many tissues (particularly fatty tissues), so it leaves the body slowly 38 38 Nitrogen Elimination from Fat Tissues 39 39 Click to add footer 20  2024-11-25 Nitrogen Elimination: Zero Decompression Limits Diving at 30 m/98 ft for 30 min represents time limit before sufficient nitrogen dissolves to pose danger. Dive limit to 40 m/131 ft: 18 min. If diver exceeds depth–duration recommendations for compressed air diving, ascent to surface must progress in preestablished manner. With this approach, a recreational or commercial diver ascends at a prescribed, relatively slow rate designed not to require decompression stops. This rate of ascent enables all excess dissolved nitrogen to diffuse from tissues into blood and escape through lungs. 40 40 Zero Decompression Limits 41 41 Click to add footer 21  2024-11-25 Inadequate Decompression Consequences Bubbles within the vascular circuit initiate complications from decompression injury. With exception of bubbles in central nervous tissue that cause lesions in brain and spinal cord, primary bubbles form in venous and arterial vascular bed. Symptoms of decompression sickness appear 4 to 6 hr after diving. Degree of injury depends on bubble size and location. 42 42 Treatment of Decompression Sickness Treatment involves recompression in hyperbaric chamber, which elevates external pressure to force nitrogen gas back into solution. Gradual decompression follows to provide time for expanding gas to leave body as diver returns to surface. Immediate recompression offers best chance for success; any delay decreases prognosis for complete recovery. 43 43 Click to add footer 22  2024-11-25 Portable recompression chamber 44 44 Oxygen Poisoning Inspiring a gas with a Po2 above 2 ata greatly increases a diver’s susceptibility to oxygen poisoning, particularly at elevated metabolic rates during physical activity. Breathing high pressures of oxygen negatively affects bodily functions in three ways: Irritates respiratory passages and induces bronchopneumonia if exposure persists Constricts cerebral blood vessels at pressures above 2 ata and alters central nervous function Depresses carbon dioxide elimination 45 45 Click to add footer 23  2024-11-25 Dives to Exceptional Depths: Mixed gas Diving Three mixtures of oxygen, nitrogen, and helium used for deep and saturation diving: Nitrox (nitrogen + oxygen): Shallow recreational dives Heliox (helium + oxygen): Deep diving Trimix (helium + nitrogen + oxygen): Dives to depths that produce high- pressure nervous syndrome (HPNS) 46 46 Helium-Oxygen Mixtures Helium most common inert gas substituted for nitrogen in deep diving Breathing heliox mixtures reduce increased breathing resistance typically imposed by nitrogen Negative effects of breathing helium: High pressure neurological syndrome (nausea, cognitive or psychomotor issues Changes in voice characteristics Considerable body heat loss 47 47 Click to add footer 24  2024-11-25 Rationale for Breathing Gas Mixtures Other Than Compressed Air 48 48 Saturation Diving Breathing heliox mixture supports safe dives to depths ≥300 feet of sea water (fsw), but the time the diver must remain in water for decompression is prohibitive Dives ≤300 fsw take place with saturation diving in a deep-diving system using a trimix mixture Each inert gas in a mixture begins to concentrate in body tissues as depth and duration progress Within 24 to 30 hr, gases saturate body tissues to equal inspired gas pressure Once tissues saturate, decompression remains identical regardless of dive’s duration 49 49 Click to add footer 25  2024-11-25 Range of Percentage Oxygen Concentrations 50 50 Technical Diving Untethered dive beyond traditional compressed air range for military operations, science, salvage, and recreational pursuits Requires special equipment, expertise, and vigilant management of gas mixtures Routinely use various mixtures of trimix compressed gas to dive below 300 fsw; blending a depth-specific gas mixture allows control of hyperoxia and nitrogen narcosis potential 51 51 Click to add footer 26  2024-11-25 Closed-Circuit Mixed-Gas System for Technical Diving 52 52 Energy Cost of Underwater Swimming Drag forces impede diver’s forward movement and greatly increase energy cost of swimming underwater, Location and density of diving gear alter diver’s positioning in water and increase energy cost of swimming as much as 30% at slow speeds, Type of fin used effects kick depth and kick frequency, thus influencing drag and swimming economy 53 53 Click to add footer 27  2024-11-25 Relationship Between Oxygen Uptake and Underwater Swimming Speed 54 54 Sport-Diving Summary 1. Breath-hold diving has been practiced for centuries, while deep-sea diving had its origins in the 14th century with the invention of diving bells supplied with surface air. 2. Two factors limit snorkel size—increased hydrostatic pressure on the chest cavity during descent and increased pulmonary dead space from enlarging the snorkel’s internal volume. 3. Breath-hold dive duration depends on time until arterial Pco2 reaches the breath-holding breakpoint. 55 55 Click to add footer 28  2024-11-25 Sport-Diving Summary 2 4. Compressing the lung volume to RLV determines maximum breath- hold diving depth; lung squeeze occurs below this critical depth because internal and external pressures cannot equalize. 5. Breath-hold diving by elite divers produces intense cardiovascular changes that resemble diving mammals’ response patterns. 6. The maximum recommended diving depth for breathing compressed air is about 30 m/98 ft, beyond which high tissue oxygen and nitrogen pressures exert profound negative physiologic effects. 56 56 Sport-Diving Summary-3 7. Prolonged breathing of a gas with a Po2 above 2 ata increases a diver’s susceptibility to oxygen poisoning. 8. Closed-circuit scuba systems that use pure oxygen severely restrict dive depth and duration. 9. Nitrogen bubbles form in tissues when excess nitrogen fails to exit through the lungs if ascent progresses too rapidly causing painful decompression sickness or bends. 57 57 Click to add footer 29  2024-11-25 Sport-Diving Summary-4 10. Diving to depths below 60 fsw requires inhaling compressed mixed gases with technical precision to safely manage optimal oxygen concentrations. 11. Breathing helium and oxygen mixtures (heliox) allows dives to 2000 fsw, eliminating nitrogen narcosis risk and minimizing oxygen-poisoning risk. 58 58 Sport Diving Summary - 5 12.Rapid descent to depths from 300 to 2800 fsw from breathing heliox mixtures produces nausea, muscle tremors, and other potentially dangerous central nervous system effects. 13. Drag forces that impede a diver’s forward movement considerably increase underwater swimming’s energy cost. 59 59 Click to add footer 30  2024-11-25 Questions? 60 Click to add footer 31