Diving Physiology

Objectives

• Identify the primary components of air.• Discuss the processes of respiration and circulation.• Identify the breathing stimulus.• Describe the proper breathing pattern for a scuba diver

and explain why.• Describe three improper breathing patterns for a scuba

diver.• Identify the breathing gas you will be trained to use for

scuba and explain why.• State the cause, prevention, signs/symptoms, and first

aid for: Decompression sickness (Bends), Nitrogen Narcosis, Air Embolism, and Over-Exertion.

Components of Air

• Nitrogen– Metabolically inert – Makes up approximately 79% of the air we breathe

• Oxygen– Metabolically active– Makes up approximately 20% of the air we breathe

• Miscellaneous gases– less than 1%

Partial Pressures

• Each component gas of air exerts its own pressure.• The pressure of each individual gas is referred to as

the partial pressure of the gas.• The sum of the individual gas pressures represents the

total pressure of the gas.• The effect of the gas on the diver is determined by the

partial pressure of the gas.• Your regulator delivers the gas you breathe at ambient

pressure and volume.• At depth the mixture of the gas you breathe remains

unchanged, the partial pressure of each of the component gases in the mix increases.

The increased partial pressure of the component gases in the air you breathe at depth explains why divers must be concerned with:

– Decompression Sickness– Nitrogen Narcosis – Oxygen Toxicity

– Carbon Monoxide

Respiration/Circulation

• Air taken into lungs– 02 absorbed into blood by Hemoglobin– 02 carried to body – Used and converted to CO2

• CO2 carried to lungs where it is eliminated by respiration.

Breathing Stimulus

• Excess CO2

Breathing Patterns

• Proper Breathing Pattern

• Deeper and slower than normal.– Overcome resistance of dense air and

regulator or snorkel– Provides a calming effect

Breathing Patterns

• Hyperventilation

• Panting

• Skip Breathing

Breathing Gas

• Air – 80% N2 – 21% 02

• 02, CO2, CO and other contaminants can be toxic.

• Fill your cylinder only with air from a reputable air fill station.

• Breathe only gases you have been trained to use.

Contaminated air

• Indications– Any smell– Any taste– Any texture

• Do not dive until the problem has been identified and corrected.

Decompression Sickness

• Other Names– DCS– Bends– Taking a hit

• Niggles

– Throwing a bubble

DCS cont.

• Gas solubility: The amount of gas that dissolves in a fluid increases as the pressure of the gas in contact with the fluid increases. This process continues until equilibrium is reached. The reverse is also true; as the pressure of a gas in contact with a fluid decreases, the amount of gas dissolved in the fluid decreases to the point of equilibrium. This is known as Henry’s Law. (Just think of Henry Weinhard’s beer.)

DCS cont

• Bubble Formation: – If the pressure of a gas dissolved in a fluid is

released too quickly, bubbles form within the fluid.

• Decompression: – If the pressure on a gas dissolved in a fluid is

released gradually, excess gas can exit the liquid without bubbles forming.

DCS cont

• Application to scuba: – Scuba divers absorb N2 at increased pressure– N2 pressure within the diver increases.– If the scuba diver ascends too quickly, N2 bubbles

can form within the blood. – This can lead to Decompression Sickness (DCS or

Bends).

• Cause of Decompression Sickness– Ascending too quickly– Too deep for too Long

DCS cont

•Prevention:– Observe time and depth limits– Adhere to proper ascent rates– 30 feet per minute– Include safety stops at the end of your

dives

There is never a guarantee you will not get DCS!

DCS cont

• Skin rash• Weakness• Paralysis• Staggering• Slurred speech• Coughing • Shortness of breath• Unconscious

• Skin itch• Joint or limb pain• Unusual fatigue• Numbness/tingling• Chest/abdominal pain• Incontinence• Headache/dizziness• Nausea

DCS cont

• Onset– Typically within 20 minutes-2 hours post dive– May not show up for several hours

DCS cont

• First Aid– Treat for Shock– First aid as necessary– Provide 100% 02– Contact Emergency Medical System– Arrange transport to a recompression as

appropriate/necessary

DCS cont

• Contributing Factors– Poor physical condition– Reverse Profiles– Strenuous exercise during or post dive– Dehydration/Alcohol – Fatigue– Repetitive/multi day diving– Cold– Hot tubs post dive– Altitude

Nitrogen Narcosis

• Other Names– Narced– Rapture of the deep

Narcosis cont.

• Cause– Narcotic effect of N2 at depth

• Depth at which Narcosis occurs– Varies with the individual.

Narcosis cont.

• Symptoms/Signs– Feeling of well being or euphoria (may be

similar to alcoholic intoxication)– Idea fixation– Anxiety

Narcosis cont.

• Consequences– Impaired performance– Lack of awareness

– Depth– Time– Air – Buddy– Direction

Narcosis cont.

• Onset– Sudden or rapid– may worsen with time.

• Prevention– Dive within your limits.– Expand your limits in controlled settings – Minimize task loading.

• First Aid– Ascend to a shallower depth– End dive if necessary

Air Embolism

• Other Names

– Embolism

– Arterial Gas Embolism (AGE)

– Pulmonary overpressure

– Lung Overpressure

Embolism cont.

• Cause– Holding breath on ascent– Air in lungs expands and escapes from the

lungs into the bloodstream– Air bubble in the bloodstream blocks blood

flow to the heart or brain.

Embolism cont

• Unconsciousness (immediately or soon after surfacing)

• Paralysis or weakness

• Convulsions• Respiratory Arrest• Bloody Froth (rare)

• Personality change• Dizziness• Visual Disturbance• Chest Pain• Disorientation• Paralysis or

Weakness• Death

Embolism cont

• Onset– Typically immediately after the dive

• Prevention– Breath normally at all times– Never hold your breath especially during

ascent• This is most critical between 10 feet and the

surface

Embolism cont

• Contributing Factors– Rapid ascent– Breath-holding– Lung congestion– Asthma– Lung damage or history of lung collapse– Other air trapping conditions

• First Aid– Treat for Shock– First aid as necessary– Provide 100% 02– Contact Emergency Medical System– Arrange transport to a recompression as appropriate/necessary

Overexertion

• Causes– Poor buoyancy control– Diving overweighted– Exceeding you limits– Environmental conditions (surf, surge,

current, surf)

Overexertion cont

• Indications– Unable to keep up with buddy– Fatigue– Cold– Gasping for breathe– Muscle cramps

Overexertion cont

• Prevention– Know your limits and dive within your limits– Practice good buoyancy control– Wear the proper amount of weight– Stop and rest before you are exhausted

• First Aid– Stop and rest until recovered.– End the dive.

Dehydration

• Cause– Breathing dehumidified air from cylinder

• Symptoms– Dry mouth– Thirst

Dehydration cont.

• Prevention– Drink plenty of water

• 2 liters a day plus• 1 glass for each 20 minutes of exercise or each

dive

• First Aid– Drink plenty of water

Divers Dieresis

• Cause– Increased pressure on body while diving– Body withdrawing blood to core to preserve

core temperature

• Symptoms– You will feel the need to urinate more

frequently than normal while diving

Ear Injuries

While decompression sickness and lung overpressure are the most serious scuba maladies, ear injuries are the most common.

Descents should be performed feet first through the first 10-15 feet and slowly to allow time to equalize.

Summary

• Air is a mixed gas

• Each component of air exerts it’s own partial pressure

• Because your regulator delivers air at ambient pressure and volume the, at depth the pressure of the gas is increased.

• DCS, Narcosis, and 02 toxicity can result from increased partial pressures.

Summary cont.

• Breathe only gases you are trained to breath.

• Air embolism can result from air expansion while holding your breath on ascent.

• Breathe normally at all times.

• Ear injuries are the most common injuries in scuba.

• Descents should be feet first and slow.