DRU SIN

Diving Physiology

BasicTerminolo

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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.Spira, Alan. "Diving and Marine Medicine Review Part I: Diving Physics and Physiology." Journal of Travel Medicine 6.1 (1999): 32-44.

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)

Air Pressure

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.

Spira, Alan. "Diving and Marine Medicine Review Part I: Diving Physics and Physiology." Journal of Travel Medicine 6.1 (1999): 32-44.

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 LawAt 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 LawThe 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.eduesources.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 ToxicityPulmonary

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.

Lindholm, P., and C. E. Lundgren. "The Physiology and Pathophysiology of Human Breath-hold Diving." Journal of Applied Physiology 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. Lindholm, P., and C. E. Lundgren. "The Physiology and Pathophysiology of Human Breath-hold Diving." Journal of Applied Physiology 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 .

Loske, Achim M. "Fundamentals of SCUBA-Diving Physics." International Journal of Sports Science 3.2 (2013): 37-45. Google Scholar.

Dive Table

Loske, Achim M. "Fundamentals of SCUBA-Diving Physics." International Journal of Sports Science 3.2 (2013): 37-45. Google Scholar.

Decompression Sickness 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)

Decompression Sickness

Limb Bends

Central Nervous System (CNS) DCS

Cerebral Decompression Sickness

Pulmonary DCS

Skin Bends

Inner-Ear Decompression Sickness

Decompression SicknessLimb 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

Decompression SicknessCentral 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

Decompression SicknessPulmonary 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

Decompression SicknessInner-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

Decompression SicknessWhile 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 stopsUse longer surface intervalsPlan the dive, dive the plan and have a

backup planMaintain 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

Loske, Achim M. "Fundamentals of SCUBA-Diving Physics." International Journal of Sports Science 3.2 (2013): 37-45. Google Scholar.

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.