LAW OF GASEOUS DIFFUSION: a gas always moves from an area of high pressure to an area of lower pressure until the pressure is equal.

TIDAL VOLUME = volume of gas you inhale and exhale in a normal breath.

VITAL CAPACITY = maximum volume that you can inhale after total expiration.

RESIDUAL VOLUME = the air left in your lungs after you exhale completely.

Dead Air Space increases = snorkel and regulator
Tidal volume in the water = reduced 15-20%
Shallow breathing = CO2 level increases, breathing rate increases.

How to avoid problems? by deep normal breathing.

DEAD AIR SPACE = Portion of your tidal volume that plays not direct part in gas exchange.

During apnea, the body uses oxygen stored in the lungs, muscles and blood.

Accumulating CO₂ creates the urge to breathe.

BRADYCARDIA: Slower heart rate than normal due to immersion.

Slowing of the heart caused by constriction of the carotid arteries.

Symptoms: discomfort and lightheadedness, eventually leads to unconsciousness.

How to avoid it: Not wearing a tight wetsuit, hood or drysuit neck-seal.

Causes: overexertion, dead air space, rapid shallow breathing, skip breathing.

Symptoms: headache, confusion, feeling of air starvation.

How to avoid it: breathe deeply and reduce activity at the first symptoms of overexertion.

Causes: hyperventilation.

Symptoms: dizziness, light-headedness, fainting.

How to avoid it: don’t hyperventilate before a breath-hold dive.

Carbon Monoxide (CO) is hazardous because it bonds with hemoglobin, more readily that O₂, thereby interfering with oxygen transport.

Symptoms:  headache, confusion, narrowed vision and with more exposure unconsciousness.

How to avoid it: Fill your tanks only from reputable fill stations!

CENTRAL NERVOUS SYSTEM (CNS)

Cause: Exposure to PO2 greater than 1.4 ata

Symptoms [VENTID] : visual disturbances (tunnel vision, blurring) ear disturbances (ringring, music), nausea, twitching (especially in the face), irritability, dizziness (vertigo)

Hyperoxic seizure = convulsion. Underwater there is the risk of drowning

How to avoid it: Don’t exceed and PO2 of 1.4 bar/ata

PULMONARY TOXICITY

Cause: Lengthy exposure to elevated PO2 greater than 0.5 bar/ata

Symptoms: mild throat irritation, cough, lung irritation, burning in the chest, decrease of the vital capacity and reduction of the lungs’ ability to exhale gas.

How to avoid it: follow the oxygen exposure limits on the DSAT Oxygen Exposure Table

The body appears to recover (10-36h) when return to normoxic (normal oxygen 0.21 bar/ata) conditions.

Causes: toxicity of inert as under high pressure (Nitrogen)

Symptoms: euphoria, bad judgment, slow motor skills.

Contributing Factors: individual susceptibility; drugs and alcohol; poor conditions (limited visibility, cool water) stress, etc.

Avoid by:

• Limit depth to <30m
• Training and Experience
• Add Helium to breathing gas

BAROTRAUMA= pressure injury. Results when a body air space is not equalised with the ambient pressure.

SQUEEZE = Ambient pressure is more than body air space (descending).

REVERSE BLOCK (REVERSE SQUEEZE) = Expanding air from body air space cannot escape during ascent.

How to Avoid: If pain is felt in ears, sinuses or teeth during ascent, descend slightly, stop, wait, then ascend slowly.

Lung Overexpansion injury is a type of Reserve Squeeze cause by holding breath on ascent.

EAR = Middle Ear Squeeze; Eardrum Rupture; Reverse block; Round Window Rupture

LUNGS = Lung Thoracic Squeeze; Overexpansion Injuries: Air Embolism (AGE), Pneumothorax, Mediastinal Emphysema, Subcutaneous Emphysema

SINUSES

MASK

Causes: failure to equalize or inability to equalize due to congestion (with a cold).

Process: Eardrum flexes inward from pressure. Hydrostatic pressure forces blood and fluid into middle ear until equilibrium is restored.

Symptoms: sharp pain, reduced hearing

How to avoid it: by equalizing, and stopping descent if unable to equalize.

Causes: failure to equalize, but pressure increases faster than fluids can fill the middle ear. Eardrum tears due to pressure.

Symptoms: momentary sharp pain, then relief. Risk of infection and permanent damage.

How to avoid it: equalizing, and stopping descent if unable.

VERTIGO = cold water in the vestibular canals.

Cause: diving with a cold or using decongestants

Process: A blockage, such as mucus in the eustachian tube, stops excess pressure escaping a body air space during an ascent.

How to avoid it: Do not dive with a cold!

If you feel pressure building in ears, sinuses or even teeth fillings, stop or slow ascent and wait for trapped air to dissipate.

Cause: delayed equalization accompanied by forceful Valsalva equalization (exhaling against pinched nostrils).

Symptoms: balance problems, can cause permanent deafness

How to avoid it: Equalize early, often and gently.

Causes: breath-hold dive to a depth where the lung volume is reduced below the residual volume can cause a lung squeeze.

Symptoms: fluid accumulate in the lungs

Causes: expanding air over-expands in the lungs causing lung rupture.

Types (in order of severity): Air Embolism (AGE), Pneumothorax, Mediastinal Emphysema, Subcutaneous Emphysema.

First Aids:

• Administer Oxygen: accelerates N2 elimination raises O2 levels maximizing the effectiveness of the blood
• Unconscious Breathing Patient: Lie level the left side, head supported
• Non breathing Patient: ABCABs

Cause: air enters the bloodstream.

Bubbles can lodge anywhere, but most common is to via the carotid arteries cause cerebral air embolism.

Treatment: prompt re-compression.

Cause: air accumulates between lung and chest wall, causing lung collapse

Symptoms: chest pain, cough up blood

Treatment: may require surgical removal of air.

Cause: air accumulates in center of chest over heart

Symptoms: feel faint and/or short of breath

Treatment: will dissipate on its own.

Cause: air accumulates in soft tissues at base of neck.

Symptoms: feels fullness in neck and voice may change. The skin may crackle to the touch.

Treatment: will dissipate on its own.

Sinuses = spaces in the head connected to the nose. The sinuses filter and moisturize the air before it reaches lungs.

Cause: diving with a cold

Symptoms: sinuses fill with blood and fluid during dive – sharp pain against eyes. Diver surfaces with blood in mask.

How to avoid it: do not dive with a cold!

Causes: very rapid descends. When a diver neglects to equalize the mask air space by exhaling through the nose.

Symptoms: swelling damages capillaries, bruising the skin around the eyes and the cheeks, red eyes. Looks dramatic but clears without complication

How to avoid it: equalise the dead air space of the mask

Gases dissolve into liquids proportionately to the pressure exerted.

While diving, nitrogen goes into solution in body tissues. Different tissues absorb and release nitrogen at different rates. Recreational dives are too short to reach saturation.

Upon ascent, higher nitrogen pressure in tissues results in nitrogen dissolving out of the body. If pressure gradient is within limits, elimination is harmless.

Some excess nitrogen collects in microscopic pockets in the blood vessels forming tiny bubbles. Tiny bubbles come together to form larger, but still harmless silent bubbles.

Silent bubbles are detectable by Doppler ultrasound flow meters.

DECOMPRESSION SICKNESS (DCS) = Refers specifically to conditions caused by nitrogen coming out of solution in the body.

Symptoms depend on amount and location of bubble formation.

DECOMPRESSION ILLNESS (DCI) = Refers to both decompression sickness and lung over-expansion injuries.

Same Emergency Procedure for all DCI

PREDISPOSING FACTORS:
Excess CO₂, Dehydration, Injuries/illness, Alcohol, Cold water, Heavy exercise, Altitude / flying, Body Fat, Age

DCS FIRST AIDS
Administer Oxygen: accelerates N2 elimination raises O2 levels maximizing the effectiveness of the blood

Unconscious Breathing Patient: Lie level the left side, head supported

Non breathing Patient: ABCABs,

DCS TREATMENT

• re-compression
• slow decompression
• oxygen administration

CUTANEOUS DCS = skin bends
Not immediate life threatening. Res rashes, patches on the skin.

LIMB AND JOIN PAIN = pain only
Not immediate life threatening. tingling, numbness.

NEUROLOGICAL DCS
Symptoms: numbness, touch, paralysis, fail of life support functions, unconsciousness, death.

PULMONARY DCS “The Chokes”
Symptoms: circulatory system failure, breathing pain, air-starved, shock, unconsciousness, death.

CEREBRAL DCS
Symptoms: [=AGE] blurred vision, headache, confusion, unconsciousness, death

TYPE III: theoretical interaction of DCS and AGE
FATIGUE: most common DCS symptom
INNER EAR DCS: symptoms are similar to ear barotrauma

HEAT EXHAUSTION

The body works at maximum capacity to cool down.

Symptoms: weak rapid breathing; weak rapid pulse; cool clammy skin; profuse perspiration; nausea.

First Aid: remove the diver’s exposure suit, put the diver in a cool environment, have the diver rest and drink non alcoholic fluids.

Heat Stroke

The body’s ability to maintain correct temperature breaks-down

Symptoms: strong rapid pulse; no perspiration; hot flushed skin; convulsions.

Firs Aids: remove the diver’s exposure suit, put the diver in a cool environment, contact emergency medical care.

Mild Hypothermia

Symptoms: Reduced blood flow to extremities (vasoconstriction), Shivering, numbness, blueness, loss of coordination.

Firs Aid: remove anything wet, wrap in insulating clothes and blankets, drink warm non alcoholic fluids.

Extremely Advanced Hypothermia

Failure of the body temperature maintaining system

Symptoms: no shivering, drowsiness, lack of coordination, unconsciousness, coma, death.

Firs Aid: remove anything wet, wrap in insulating clothes and blankets , contact emergency medical care, ABCABS.