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Transcript of Diving Medicine
ED Registrar - Royal Hobart Hospital
History Of Diving
Bert - Caisson Disease
Amount of gas dissolved in a solvent is proportional to the partial pressure of the gas
So higher pressure = more dissolved gas
Total pressure = sum of all the individual gas pressures in a mixture
Ptot = ppGas A + ppGas B....
Press x Vol = Constant
Volume is proportional to 1/Pressure
Henry's Law takes time!
In the mean time...
ppGas - ppDissolved gas = Pressure Gradient
Pascal = 1 Newton / Sq.Metre
1 ATM = 101325 Pa
1 extra ATM for each 10msw
So at 30msw the pressure is...
Thats why this bubble is small...
Types of Diving
Decompression Sickness (DCS)
Arterial Gas Embolism (AGE)
Decompression Illness (DCI)
DCS and / or AGE
Pulmonary Overinflation Syndromes
Oxygen Toxicity (too much Oxygen)
Hypoxia (too little)
Boyle's Law: PV=K
Volume must decrease
Fixed containers = badness
Volume must increase
Fixed containers = badness
Herbert Nitsch - 214msw
Decompression Sickness - The Bends
Inert Gas bubbles in tissue
Any inert - He, N, H, Ne...
pp.Inert in Lungs > Gas Tension
Inert gas dissolves into tissues
Rate depends on pp.Gradient, Solubility, Perfusion
Gas tension > pp.Inert in Lungs
Inert gas leaves solution
Depends on gas solubility, tissue type
Bubbles form in tissue = Bends
Classified by location
Inner ear "Staggers"
DCS - Clinical Features
Whats so bad about bubbles?
Increased tissue pressure (reduced perfusion)
Flow flow obstruction
Venous gas emboli in lungs
Type 1 DCS
Deep dull ache
Unaffected by movement
Upper > Lower limbs
Orange Peel Skin (lymphatics)
Rash inc. Cutis marmorata
Type 2 DCS
Inner ear ("The Staggers')
Cardiopulmonary ("The Chokes")
Most common: Paraesthesia
Any neurology is possible
Disturbance of higher function
Hearing loss, tinnitus, vertigo, dizziness, nausea, vomiting
More common in heliox dives
Pathophysiology unclear - slow N washout?
Difficult to distinguish from barotrauma
Vertigo the most common complaint
Profuse intravascular bubbling
Bubbles filtered out in lungs
Retrosternal burning discomfort
Worse on deep inspiration
Severe respiratory distress, circulatory collapse, death
Arterial Gas Embolism
Pulmonary Overinflation Syndrome (POS)
Boyle's Law ("Reverse squeeze")
Large gas emboli in the pulmonary veins
Emboli expand and ambient pressure declines
Usually within 10-20 minutes from surfacing
Difficult to distinguish from Type 1 DCS...
...but it doesn't matter anyway
Too much of a good thing..
: partial pressure and time dependent
CNS oxygen toxicity "Paul Bert Effect"
Pulmonary oxygen toxicity "Lorraine Smith Effect"
Ocular oxygen toxicity (prem's don't dive)
Pulmonary Oxygen Toxicity
pO2 > 0.5ATA (ie. Air at 14msw)
12hrs at pO2 = 1 ATA
4hrs at pO2 = 2 ATA
Burning pain on inspiration
Measurable decline in lung function
CNS Oxygen Toxicity: Bad news for Divers
pO2 and time dependent
pO2 > 1.3ATA (wet) vs. pO2>2.4ATA (dry)
PADI recommended maximum: 1.4ATA
That's 55msw on air
Immersion in water
Depth (independent of pO2)
Continuous exposure (hence air-breaks)
CNS Oxygen Toxicity: Signs and Symptoms
ausea / Vomiting
witching / Tingling
onvulsions (may come first!)
Costeaus's Aqua Lung
Hypoxic symptoms begin at piO2 < 0.16ATA
Helpless at piO2 < 0.11ATA
Hypoxic diver is often unaware of the problem
Failed re-breather equipment
Switching to the wrong mix
Shallow-water blackout during breath-hold dive
High inspired CO2
Inert Gas Narcosis
Adaptation probably not possible
He2 is almost non-narcotic
Lipid solubility predicts narcotic potential
Common below 30msw on air
Alcohol, benzodiazepenes, CO2 all increase narcosis
Task fixation, euphoria, paranoia, hallucinations, LOC