Elective Presentation Final 2

Basic
Terminolo
gy
Decompression
Recompression
Hyperbaric
Compression

Types of Diving
 Surface Free Diving
 Bell Diving
 Surface Support Diving
 Scuba Diving
 Saturation Diving
Spira, Alan. "Diving and Marine Medicine Review Part I: Diving Physics and Physiology." Journal of Travel Medicine 6.1 (1999): 32-44.

Fundamental Laws of Diving
 Archimedes' principle:
The weight of the diver and his equipment,
and the weight of the volume of displaced
water determine whether the diver will
float or sink.
 Snell's law:
The diver sees objects closer and larger
than they are, because the refraction
indexes of water and air are different.
 Boyle's law:
As pressure changes, the volume of gases
in the diver's body and soft equipment
varies.
 Gay-Lussac's (Charles) law:
If the temperature changes, the pressure
inside the diving tank varies.
 Dalton's law:
The concentration of each component of
the air breathed by the diver can be
determined by its partial pressure.
 Henry's law:
Gas absorption by the tissues of the human
body is proportional to the partial pressure
of the gas.
Loske, Achim M. "Fundamentals of SCUBA-Diving Physics." International Journal of Sports Science 3.2 (2013): 37-45. Google Scholar.

Buoyancy
(Archimedes Principle)
 Objects either float in water or sink,
while others neither float nor sink.
This is due to the buoyancy of an
object.
 Positively buoyant objects float.
 Negatively buoyant objects sink.
 Neutrally buoyant objects
neither sink or float.
 Archimedes principle.
 Diving – maintain neutral
buoyancy.

Pressure
 Atmospheric pressure
 Sea level – 1 atmosphere of pressure (ATA)
 1 ATA = 1 Bar = 760 mmHg = 101.3 KPa = 14.7 psi = 760 Torr
Gauge pressure –
Difference between atmospheric
pressure and the pressure being
measured
(atmospheric pressure = 0)

Hydrostatic Pressure
Force of a column of water acting upon a submerged object.
Additional atmosphere of pressure for every 10 meters a diver descends
in sea water.
Depth
0 m
10 m
20 m
30 m
40 m
Pressure
1 ATA
2 ATA
3 ATA
4 ATA
5 ATA
Absolute pressure = atmospheric pressure + hydrostatic pressure
(diving and flying, altitude diving).

Boyles law
(Volume and Pressure Changes) at Depth
Sea level 1 ATA 1 or 100% 20 l
10 M 2 ATA 1/2 or 50% 10 l
20 M 3 ATA 1/3 or 33 % 6.7 l
30 M 4 ATA 1/4 or 25 % 5 l
40 M 5 ATA 1/5 or 20% 4 l
90 M 10 ATA 1/10 or 10% 2 l
Depth Pressure Relative Volume Volume
NB: Change in volume with pressure is the greatest nearer the surface

Effects of Pressure on the Human Body
For all practical purposes, water is
incompressible.
Pressure on the surface of water is
transferred equally in all directions
through the liquid.
The human body can therefore
endure tremendous pressures
exerted on it under water.
Bodies air spaces are susceptible to
pressure-related injuries during
diving.

Boyle’s Law and the Diver
P1 x V1 = P2 x V2
While descending (P) air must enter the body air cavities to equalize the pressure
with the surrounding pressure to prevent distortion and damage to the tissues
(sinuses and middle ear).
While ascending the air in the body spaces will expand and must therefore be
released to equalize the pressure (e.g. lungs).
If a scuba diver has 3l of air in his
lungs at 10 m (breathing freely)
and holds his breath while
ascending, the volume of his
lungs will double (6l) – injury,
ruptured alveoli may occur.
This law is also used in the treatment
of decompression sickness.

Barotrauma
Barotrauma is tissue damage caused by
the expansion or contraction of enclosed
air-spaces due to the pressure changes.
Occur during both descent and ascent:
During descent due to an inability to
equalize pressure within the body cavity
(middle ear or sinuses) as the
surrounding pressure increases.
During ascent due to an expansion of the
gases in body cavities due to a decrease
in the surrounding pressure.
www.scuba-tutor.com
Lindholm, P., and C. E. Lundgren. "The Physiology and Pathophysiology of Human Breath-hold Diving." Journal of Applied Physiology
106.1 (2008): 284-92.

Temperature Changes - Charles Law
At a constant pressure (P) the volume (V) of a mass of gas is proportional to the
absolute temperature (T). i.e. the volume of a gas varies with temperature.
T x P = V
Therefore V1 / T1 = V2 / T2
Heat produced when you compress gasses.
Tanks are filled in water to keep them cool (10l tank
filled to 200 bars).
Full tanks left in the sun can explode.
Full air cylinder (200 bar) containing warm air may
read only 175 Bar in cold water.

Pressure Related Problems
(Direct)
Descent (Squeezes)
 Ears
 Sinuses
 Mask
 Teeth
 Stomach/Intestines
 Suit
Ascent (expansion)
 Air embolism
 Pneumothorax
 Mediastinal Emphysema
 Subcutaneous Emphysema
Ferretti, Guido. "Extreme Human Breath-hold Diving." Eur J Appl Physiol European Journal of Applied Physiology 84.4 (2001): 254-71.

Pressure Related Problems
(Indirect)
 Decompression sickness
 Nitrogen partial pressures
 Solubility
 Nitrogen narcosis
 Oxygen toxicity
Ferretti, Guido. "Extreme Human Breath-hold Diving." Eur J Appl Physiol European Journal of Applied Physiology 84.4 (2001): 254-71.

Characteristics of Gases
 Oxygen (O2)
 21% of atmosphere
 Important for life
 Toxic for humans (conc > 30%)
 Supports Combustion
 Carbon dioxide (CO2)
 1.5% of atmosphere
 Product of metabolism & combustion
 Determines our rate of ventilation
 Shallow water blackout - drowning
 Carbon monoxide (CO)
 Product of incomplete combustion
 Produced by compressors
 High affinity for Hb & cytochrome A3 system
 Toxic
 Nitrogen (N2)
 Inert gas
 79% of atmosphere
 Breathing nitrogen during diving can cause
problems:-
 Nitrogen narcosis
 The bends
 Decompression tables
 Helium (He)
 Inert gas, lighter than nitrogen
 Used as a substitute for nitrogen during deep dives
 Prevent N2 narcosis
 Helium / Oxygen mixtures are easier to breath
 High thermal conductivity (rapid body heat loss
when breath heliox)
 Donald-duck like speech – sound travels faster in a
heliox mixture
 Use associated with high-pressure neurological
syndrome

Partial Pressure of Gasses - Dalton’s Law
The total pressure exerted by a mixture of non-reactive gasses is the sum of the
partial pressures that would be exerted by each gas alone as if it alone occupied the
total volume.
Ptotal = Poxygen + Pcarbon dioxide + Pnitrogen
This law explains:
 Oxygen toxicity
 Nitrogen narcosis
 Dangers of contaminating gasses
(e.g. CO)
 Use of gas mixtures (reduce the
amount of inert gases) to reduce
decompression sickness during very
deep dives
web.carteret.edu
esources.yesican-science.ca

Oxygen Toxicity
 The partial pressure of O2 and the duration of exposure can
damage tissue (dose-time relationship).
 Two types of toxicity:
 Pulmonary Oxygen Toxicity (Whole Body Oxygen Toxicity)
 Occurs at > 0.5 ATA (is a problem at sea level)
 Long exposure (Hours) – 12 hours 100% O2 at sea level
 Central Nervous System Toxicity
 Occurs at > 2 ATA (CNS toxicity not a problem at sea level)
 Shorter exposure

Oxygen Toxicity
Pulmonary
 Whole-Body oxygen toxicity is a
slow developing condition
resulting from exposure to above
normal PO2, generally at levels
below those causing CNS toxicity
but above a PO2 of 0.5 atm
 Whole-Body oxygen toxicity is of
little concern to divers doing no-
stop dives, even when breathing
oxygen-enriched mixtures
(nitrox), but it may be seen during
intensive diving operations or
long oxygen treatments in a
hyperbaric chamber
CNS
 The end result may be an
epileptic-like convulsion not
damaging in itself, but could
result in drowning
 Susceptibility is highly variable
from person to person and even
from day to day in a given
individual

Nitrogen Narcosis
Neurological impairment.
Caused by dissolved nitrogen in the blood under pressure.
Progressive signs and symptoms:
 Impairment of reasoning, judgment, memory and
concentration.
 Sense of well-being and levity.
 Anxiety.
 Loss of coordination and physical dexterity.
 Hallucination, terror and vertigo.
 Unconsciousness and death.
106.1 (2008): 284-92.

Nitrogen Narcosis
• Develops with an increase in the partial pressure of nitrogen (30 m or less).
• Limiting factor of compressed air dives (39 m for recreational diving).
• A euphoric anesthetic / narcotic effect of inert gasses.
• Mechanism poorly understood.
Number of theories:
• Fat solubility: N2 dissolves in brain cell lipids causing membrane swelling and
disruption of cell function.
• Molecular mass: Narcotic effect of inert gasses increases with increase in MW.
• Clathrate formation: Water molecules form an ordered structure around most
inert gases which can inhibit synaptic transmission.
106.1 (2008): 284-92.

Decompression Sickness
(The Bends)
 At sea level (1 ATA) the human body contains approximately 1l of N2 in
solution. At 30 m (4 ATA) four times the amount of N2 would dissolve in
all body tissues once equilibrium is reached.
 As the partial pressure of nitrogen drops (during ascent) the nitrogen gas
moves out of solution (supersaturated).
 During a rapid pressure drop bubbles can form in tissues – causing
decompression sickness (Joint Pain - Bends).
 The volumes of these bubbles increase as the pressure continues to drop
(Boyles law).
 Dive Tables – used to prevent decompression sickness .

Dive Table

 Type I includes skin itching or marbling; brief, mild pain called
“niggles,” which resolve typically within ten minutes; joint pain;
lymphatic swelling, and sometimes included extreme fatigue
 Type II DCS is considered to be respiratory symptoms,
hypovolemic shock, cardiopulmonary problems, and central or
peripheral nervous system involvement
 Type III includes arterial gas embolism and is also called
decompression illness (DCI)

 Limb Bends
 Central Nervous System
(CNS) DCS
 Cerebral Decompression
Sickness
 Pulmonary DCS
 Skin Bends
 Inner-Ear Decompression
Sickness

 Limb Bends – Dull, throbbing, deep pain in the joint or
tissue; usually in the elbow, shoulder, hip, or knee
 Pain onset is usually gradual and slowly intensifies
 In severe cases limb strength can be affected
 In divers, upper limbs are affected about three times as
often as lower limbs

 Central Nervous System (CNS) DCS – May cause
muscular weakness, numbness, “pins and needles,”
paralysis, loss of sensation, loss of sphincter control,
and, in extreme cases, death
 Cerebral Decompression Sickness – May produce
almost any symptom: headache, visual disturbance,
dizziness, tunnel vision, tinnitus, partial deafness,
confusion, disorientation, emotional or psychotic
symptoms, paralysis, and unconsciousness

 Pulmonary DCS – aka the Chokes accounts for about
2% of DCS cases
 Symptoms include: pain under the breastbone on
inhalation, coughing that can become paroxysmal, and
severe respiratory distress that can result in death
 Skin Bends – Come in two forms: harmless simple
itchy skin after hyperbaric chamber exposure, or rashy
marbling on the torso that may warn of serious DCS

 Inner-Ear Decompression Sickness – aka Vestibular
DCS or Ear Bends
 Signs and symptoms include vertigo, tinnitus, nausea,
or vomiting
 Ear Bends occur more often after deep dives containing
helium in the breathing mixture; particularly after
switching to air in the later stages of decompression
 Shallow water and/or air divers are not immune

 While an individual can do everything
correctly and still suffer from DCS, prevention
can be enhanced if:
 Ascend slowly (30 ft/min [9 m/min])
 Make safety stops
 Use longer surface intervals
 Plan the dive, dive the plan and have a backup plan
 Maintain good physical fitness, nutrition, and
hydration

1. Pre-dive hyperventilation.
2. Develop hypocapnia (blow off CO2, low blood
CO2 levels) without increasing O2 levels.
3. “Abnormal” pre-dive state.
4. Free dive.
5. O2 levels drop.
6. Blood CO2 levels are not high enough to trigger
breathing reflex.
7. Cerebal hypoxia.
8. Loss of consciousness.
9. Drowning.
Shallow Water Blackout
http://en.wikipedia.org

shallowwaterblackoutprevention.org

Deep Water Blackout
 Loss of consciousness due to
cerebral hypoxia.
 Occurs on ascending after a breath
holding (free) dive from a deep
dive (>10M).
 Blackout near the surface.
 1˚ cause drop in PO2 in the lungs
during ascent.
1. Consciousness depends on a minimum PO2 (not
absolute amount of O2 in the body) in the brain.
2. Depressurisation on ascent.
3. PO2 drops as the dive ascents.
4. Probably coupled with hypocapnia due to pre-dive
hyperventilation (no urge to breath).
5. Loss of consciousness.
6. Drowning.
www.forensicmed.co.uk

Hearing and Sight
 Sound travels 4.5 times faster in water than air.
 Reduced ability to locate the direction of the sound.
 Water absorbs light, 20% of light reaches 10 m and 12% 85 m.
 Most reds and oranges absorbed, blue light penetrates the
deepest.
 Distortion of colours at varying depths
 Underwater the refractive power of the air-cornea interface is
lost, eye cannot focus.
 Refraction also occurs at the mask surface, causing objects to
appear closer (75% of their actual distance and larger by
30%).
 Masks also reduce visual fields.

Elective Presentation Final 2

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