Diving Technology Innovations Quiz

Lecture 9: Sport Diving

• Environmental Stress Review:

  • Thermal Stress
    • Heat Stress
    • Cold Stress
  • Altitude stress
  • Microgravity

• Environmental Stress: Underwater Diving:

  • The practice of descending below the water's surface to interact with the environment
  • Exposes divers to high pressures (hyperbaria) and rapidly changing pressures
  • Can produce severe injury or death if pressures in the body's air-filled cavities aren't equalized

Lecture Objectives

• Develop an appreciation of diving history from Antiquity to the Present
• Learn about different types of diving
  • Breath-hold diving
  • Snorkeling
  • SCUBA
  • Mixed-Gas
• Understand health risks associated with diving and how to counter them

Diving History: Antiquity to Present

• Men and women have practiced breath-hold diving for centuries to hunt, salvage artifacts, participate in military maneuvers etc.
• The 5th-century Greek historian Herodotus tells of underwater exploits in 480 BC.
• Early solutions to remain submerged for longer than a few minutes included diving bells supplied with surface air, with the bottom open to water, and a top portion containing air compressed by water pressure.

Diving History: Antiquity to the Present (cont.)

• In England and France, 16th-century diving suits made of leather allowed descent to 60 ft
• Manual pumps delivered fresh air from the surface
• Metal helmets, perfection of surface supply air, and allowed extensive underwater salvage work

Diving History: Antiquity to the Present (cont.)

• In the 19th century, scientific and technological advances in underwater exploration included explanations of physiological effects of water pressure on body tissues
• Physiologists Paul Bert and John Scott Haldane defined safe limits for compressed air diving and using decompression chambers
• Technologic improvements included compressed air pumps, carbon dioxide scrubbers, and demand-valve regulators, allowing prolonged deep water explorations

Diving Depth and Pressure

• Water is non-compressible, so its pressure against a diver's body increases directly with depth
• Forces that produce hyperbaria in diving include the weight of the column of water directly above the diver, and the weight of the atmosphere at the water's surface
• Body tissues are not susceptible to external pressure changes in diving as water is part of the tissues; however, air-filled cavities in the body are affected significantly with changes in diving depth

Diving Depth and Gas Volume

• Boyle's Law: P₁ x V₁ = P₂ x V₂
  • At constant temperature, the 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

Breath-Hold Diving

• Duration and depth of breath-hold dive depends on time until arterial Pco2 reaches breath-hold breakpoint, relationship between diver's TLC and RLV, and the physical activity level
• Most people can breath-hold for up to 1 minute; a 2-minute limit is an upper limit
• Physical activity reduces breath-hold time as oxygen consumption and carbon dioxide production increase with exercise intensity

Hyperventilation and Breath-Hold Diving

• Hyperventilation before breath-hold diving extends breath-hold time, but has risks like blackout
• With predive hyperventilation, PCO2 decreases to 15 mm Hg, extending dive duration
• Break point for breath-holding corresponds to increase in arterial PCO2 to 50 mm Hg

Hyperventilation and Breath-Hold Diving (cont.)

• Other risks of hyperventilating before breath-hold diving include reduction in blood's carbon dioxide content decreasing blood pH and increasing alkalinity.
• Decrease in arterial carbon dioxide with hyperventilation can reduce cerebral blood flow, potentially leading to loss of consciousness

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 respiratiory passaged to equalize pressure
• If TLC decreases below RLV, pulmonary air pressure becomes less than external water pressure and lung squeeze occurs

Diving Reflex in Humans

• Physiological responses to water immersion (the diving reflex) include: Bradycardia, Decreased cardiac output, Increased peripheral vasoconstriction, Lactate accumulation in underperfused muscles

Snorkeling

• Snorkel allows swimmers to breathe continuously with face immersed in water
• Factors that limit snorkel use include health concerns (asthma, heart conditions, anxiety), physical fitness, and weather conditions (wind)
• Increased hydrostatic pressure on chest cavity as one descends beneath water
• Increased pulmonary dead space by enlarging the snorkel's volume

Inspiratory Capacity and Diving Depth

• At 1 m depth, compressive force of water significantly impedes inspiratory muscles from expanding thoracic dimensions
• Inspiration becomes impossible without external air at sufficient pressure to counter compressive force of water

Snorkel Size and Pulmonary Dead Space

• Ideal snorkel averages 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

Scuba Diving

• Scuba (self-contained underwater breathing apparatus) is the most common apparatus to supply air under pressure.
• Scuba system includes a tank of compressed air and a demand regulator valve
• Basic scuba designs include open-circuited and closed-circuited systems

Open-Circuit Scuba

• Used by most recreational SCUBA divers
• Limitations include that exhaled air into water contains 17% oxygen, wasting about 75% of the tank's total oxygen
• Limited supply of compressed air limits time underwater

Design of an Open-Circuit Scuba Unit

• Diagram details the components and flow paths

Air-Time Limits

• Graph illustrating air time remaining in relation to depth and time

Closed-Circuit Scuba

• Used by military and professional divers
• Small cylinder feeds pure oxygen into bellows or bag
• Breathing bag acts as a 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 allowing continuous breathing

Closed-Circuit Scuba System Design

• Diagram outlining the components and flow path

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, and gas solubility in liquid
• Underwater breathing systems must supply air, oxygen, or other gas mixtures at sufficient pressure to overcome water's force
• Expanding gases from inhaling fully and failing to exhale during ascent can rupture lungs

Scuba Diving Hazards

• Air embolism, face mask squeeze, Eustachian tube blockage, mediastinal and subcutaneous emphysema, pneumothorax, and alveoli rupture (caused by rapid ascent)

Face Mask Squeeze

• Air pressure inside the face mask doesn't equalize as diver descends

Eustachian Tube Blockage: Middle-Ear Squeeze

• Tubes normally clear equalizing pressure between external pressure and lungs
• Divers can equalize by blowing gently against closed nostrils

Aerosinusitis

• Inflamed, congested sinuses prevent air pressure from equalizing during diving

Pneumothorax

• Air forced through alveoli when lung tissue ruptures, migrating laterally
• Air pocket forms between chest wall and lung

Composition of air

• Nitrogen = 78%
• Oxygen = 21%
• Argon = 0.93%
• Carbon dioxide = 0.042%

Nitrogen Narcosis

• Increase in inspired nitrogen pressure produces a narcotic effect similar to alcohol intoxication
• Dissolved nitrogen at 30 m = similar to feelings after alcohol consumption
• 15.2 meters of seawater depth = effects of drinking a dry martini

Decompression Sickness

• Occurs when dissolved nitrogen moves out of solution, forming bubbles
• Results from ascending too rapidly
• Also known as "the bends"
• Nitrogen reaches equilibrium slowly, so it leaves the body slowly

Decompression Limits

• Diving depth and duration parameters limiting decompression time

Inadequate Decompression Consequences

• Bubbles within the vascular circuit initiate complications
• Symptoms of decompression sickness appear 4–6 hours after diving
• Degree of injury depends on bubble size and location

Treatment of Decompression Sickness

• Treatment involves recompression in a hyperbaric chamber, elevating external pressure
• Gradual decompression follows to allow expanding gases to leave body
• Immediate recompression offers best chance for success
• Any delay decreases prognosis for complete recovery

Portable recompression chamber

• Diagram details the components and flow paths

Oxygen Poisoning

• Inspiring a gas with a P(O2) above 2 ata increases a diver's susceptibility
• Breathing high pressures of oxygen negatively affects bodily functions
• Irritates respiratory passages, constricts cerebral blood vessels, and alters central nervous function
• Depresses carbon dioxide elimination

Dives to Exceptional Depths: Mixed gas Diving

• Three mixtures of oxygen, nitrogen, and helium for deep and saturation diving
  • Nitrox (nitrogen + oxygen): Shallow recreational dives
  • Heliox (helium + oxygen): Deep diving
  • Trimix (helium + nitrogen + oxygen): Dives to depths with High-pressure nervous syndrome (HPNS)

Helium-Oxygen Mixtures

• Helium substitutes nitrogen in deep diving
• Breathing heliox mixtures reduces breathing resistance
• Negative effects of breathing helium include high pressure neurological syndrome, nausea, cognitive problems, psychomotor issues, changes in voice characteristics, and considerable body heat loss

Rationale for Breathing Gas Mixtures Other Than Compressed Air

• Breathing heliox mixture supports safe deep dives
• Dives using a trimix mixture, each inert gas in mixture begins to concentrate in body tissues as depth and duration progress

Saturation Diving

• Breathing heliox mixture supports safe dives to depths ≥300 feet
• Dives using a trimix mixture, take place with saturation diving
• Each inert gas in mixture begins to concentrate in body tissues
• Within 24–30 hours, gases saturate body tissues, decompression remains identical regardless of dive's duration

Range of Percentage Oxygen Concentrations

• Graph illustrating oxygen concentration in relation to depth

Technical Diving

• Untethered diving beyond traditional compressed air range
• Requires special equipment, expertise, and vigilant management of gas mixtures
• Routinely uses variable mixtures of trimix compressed gas to dive below 300 fsw

Closed-Circuit Mixed-Gas System for Technical Diving

• Diagram outlining the components and flow path for closed circuit systems

Energy Cost of Underwater Swimming

• Drag forces impede diver's forward movement and greatly increase energy cost
• Diver's positioning in water and diving gear significantly increases energy cost
• Type of fin used effects kick depth and kick frequency which influences drag and swimming economy

Relationship Between Oxygen Uptake and Underwater Swimming Speed

• Graph illustrates oxygen uptake in relation to underwater swimming speed

Sport-Diving Summary

• Breath-hold diving has a long tradition
• Factors that limit snorkel size include hydrostatic pressure and pulmonary dead space
• Breath-hold dive duration depends on time until arterial Pco2 reaches the breath-holding breakpoint

Sport-Diving Summary 2

• Compressing the lung volume to RLV determines maximum breath-hold diving depth.
• Breath-hold diving by elite divers produces intense cardiovascular changes
• Maximum recommended diving depths for breathing compressed air is ~30m (98ft), beyond which negative effects from high pressure of oxygen and nitrogen occur

Sport-Diving Summary 3

• Prolonged breathing of a gas increases a diver's susceptibility to oxygen poisoning
• Closed-circuit scuba systems limit depth and dive duration
• Nitrogen bubbles form in tissues when excess nitrogen fails to exit the lungs due to rapid ascent causing painful decompression sickness or the bends

Sport-Diving Summary 4

• Diving to depths below 60 fsw requires inhaling compressed mixed gases
• Breathing helium and oxygen mixtures (heliox) allows dives to 2000 fsw and minimizes risks

Sport Diving Summary 5

• Rapid descent to depths of 300 to 2800 fsw from breathing heliox mixtures produces adverse effects
• Drag forces that impede diving movement considerably increase energy cost underwater

Questions?