Physiology

DECOMPRESSION SICKNESS (DCS)

Causes of DCS

Relating to Henry’s Law, if the pressure increases (gets more) the more gas will be dissolved (go into) the liquid.  If the pressure is decreased (gets less) the gas will come out of the liquid (the human body is mostly made of liquids).  Because the body does not use nitrogen, however when under pressure (diving) our body is exposed to a higher absorption rate of nitrogen (he body has to store this nitrogen within the body) On ascent when diving the pressure on the body is reduced (gets less) and the nitrogen in the body has a higher pressure and has to come out (supersaturation – like when opening a Coca-Cola bottle after shaking it) As long as the nitrogen comes out slowly and is controlled, there is no problem.  However, if the pressure is released too fast the nitrogen will come out too fast.  This will cause BUBBLES, which cause decompression sickness.

OTHER FACTORS THAT MAY PREDISPOSE A DIVER TO DEVELOP DCS

Fat: Fat releases nitrogen slowly.  More nitrogen in solution after a dive.
Age: As we age our circulatory system becomes less efficient.
Dehydration: reduces blood in circulation, slowing nitrogen elimination.
Injuries / illness: may alter or restrict circulation.
Alcohol: before or after diving will alter circulation and causes dehydration.
Carbon Dioxide Excess: from skip breathing.
Cold Water: circulation to the extremities reduces as a diver cools, slowing nitrogen elimination from those areas.
Heavy Exercise: before, during or after a dive accelerates circulation.
Altitude / Flying: dive tables / computers are based on surfacing at sea level, thus exposure to lower pressure increases the tissue pressure gradient.

Types of DCS

TYPE I – identified as ‘pain only’ DCS
Limb pain is the most common – may be mid-limb or joints
Cutaneous DCS (skin bends) – red rashes / patches usually on shoulders and upper chest

TYPE II – identified as having life threatening or immediate injuries
Symptoms – involves brain nervous system, lungs numbness and / or tingling
Paralysis
Weakness / fatigue / nausea (getting sick)
Unconsciousness and death

FIRST AID

Treat all DCS as serious – even pain only
Give patient oxygen – preferably 100% which lowers alveolar nitrogen to accelerate elimination from tissues and raises blood Oxygen levels to assist tissues with blood flow reduced by bubble blockage.

Keep a breathing patient lying down on their left side, with head supported (recovery position) which helps keep airway clear if patient vomits.
Lying level ensures blood flow to brain.
Advise patient not to sit up or walk around, even during transport or feeling better.

Lay non-breathing patient on back for rescue breathing. Contact emergency medical care

TREATMENT FOR DCS

DCS treatment requires putting patient in a recompression chamber. Recompression reduces bubbles in body to a smaller size and forces them back into solution – often alleviates symptoms immediately. Treatment involves a long slow decompression with oxygen and drug therapy. Duration and need for drugs / oxygen makes attempting recompression in water very difficult, requiring manpower and special equipment.

The sooner recompression begins, the more likely the patient will recover without permanent injury. Patients sometimes don’t want to believe they are suffering from DCS and object to seeing a doctor. Strongly urge patients to allow medical examination by emergency medical care.

LUNG OVER-EXPANSION INJURIES

Lung over-expansion injuries are caused by:
Holding breath during ascent
Diving with a chest cold
Local blockage in the lungs due to loss of surfactant (due to smoking)
Expanding air over-expands and causes lung rupture

AIR EMBOLISM

Also called arterial gas embolism (AGE).  Air enters the bloodstream and flows into arteries Serious and immediately life threatening.  Bubbles can lodge anywhere, but the most common is to flow through the carotid arteries and cause cerebral air embolism, which can stop blood flow to parts of the brain depending on where in the arteries the embolus lodges)- there are some nice diagrams of the blood supply of the different territories of the brain which may be useful
Signs and symptoms (similar to a stroke)

• Dizziness
• Confusion
• Shock
• Paralysis (of face, arms or legs, usually one-sided)
• Personality change
• Unconsciousness and death
• Also Difficulty speaking or understanding other people
• Strange sensations like pins and needles or numbness
• Visual disturbance

PNEUMOTHORAX

Air from a rupture goes into the pleural space between the lung and chest wall causing the lung (or part of it) to collapse.  Also serious.

Signs and symptoms

• Chest pain (particularly on breathing in), increasing breathlessness (these are the cardinal signs).
• Patient may cough up blood

MEDIASTINAL EMPHYSEMA

Air from the rupture accumulates in the centre of the chest, over the heart, causing pain in the middle of the chest, this is serious because air presses on the heart and vessels, interfering with circulation (affects ability of heart to pump effectively).
Signs and symptoms

• Patient may feel faint or short of breath.

SUBCUTANEOUS EMPHYSEMA

Air from a rupture accumulates in soft tissues under the skin usually at the base of the neck.  The victim feels fullness in neck and voice may change.

Signs and symptoms

• The skin may crackle to the touch

FIRST AID

First Aid is the same as for DCS, hence the common term ‘decompression illness’ for both.  Giving Oxygen helps supply tissues deprived of blood flow because of bubbles
Treatment of air embolism requires recompression to reduce bubble size (as with DCS). Importance of swift treatment in air embolism to reduce permanent damage to area of the brain which has been underperfused with oxygen

DCS OR DCI?

Decompression Sickness – nitrogen in the body coming out too fast
Decompression Illness – a collective term for decompression sickness and lung over-expansion injuries

SILENT BUBBLES

Some nitrogen dissolves into microscopic gas pockets in the body and form tiny bubbles that are trapped.  These then diffuse harmlessly into air.  Silent bubbles are found after some dives, especially those close to table / computer limits.  These are larger bubbles than the tiny bubbles theorized to form after most dives, but are still harmless.

NITROGEN

Caused by breathing a high partial pressure of nitrogen.  Using air or enriched air, narcosis is expected to be noticeable at about 30m depth.  Helium is not narcotic even under very high pressures – this is why it is used by technical and commercial divers making very deep dives.   Ascent (going to a shallower depth) relieves narcotic symptoms and usually has no after effects.  Not directly hazardous – hazard comes from impaired judgement that may delay reactions or lead to poor decisions.

Breath Hold Diving and Apnea

During APNEA (breath-holding) the circulatory system uses oxygen stored in the lungs, muscles and blood to meet oxygen needs

BRADYCARDIA

In cool water, BRADYCARDIA (slowing of the heart) reduces circulation and is triggered by apnea (felt by cold on the face).  Though this doesn’t appear to reduce oxygen consumption in humans (it does in marine mammals).

SHALLOW WATER BLACKOUT

You can increase breath-hold time by first hyperventilating (breathing deeply and rapidly) three or four times.  This reduces circulatory carbon dioxide so it takes longer to get enough to cause breathing.  Too much hyperventilation may lead to shallow water blackout.  Occurs on ascent, near the surface.  The reduced oxygen pressure prevents the haemoglobin bonding with oxygen so tissues and brain become starved of oxygen This is because the low carbon dioxide cannot stimulate breathing.  It is the high carbon dioxide that stimulates the body to want to breath, not the lack of oxygen

CAROTID SINUS REFLEX

Carotid sinus receptors monitor pressure of arterial blood reaching the brain through the carotid arteries.  Low blood pressure triggers a higher heart rate, and high blood pressure triggers a lower heart rate Receptors interpret pressure from an excessively tight hood or wet suit constricting the neck as high blood pressure.  The heart rate slows, reducing blood flow to the brain, but pressure remains, causing yet slower heart rate.  The diver feels uncomfortable and light-headed but may lose consciousness if constriction continues unrelieved.
Avoid by not wearing excessively tight hoods, wet suit or dry suit neck seals

HYPERCAPNIA

(Hyper = excess)
Hypercapnia is TOO MUCH carbon dioxide

Causes:

• Shallow rapid breathing
• Skip breathing (holding the breath periodically)
• Overexertion
• or a combination of these.  In very rare cases air supply may be high in carbon dioxide.
• Respiratory drive impaired by head injury or drugs
• Trauma which causes respiratory muscle weakness

Signs and symptoms:

• Headache
• Accelerated breathing.
• Confusion
• Loss of consciousness
• early- flushed skin due to vasodilation, muscle- twitching, headache
• Progressing to disorientation, panic, convulsions, loss of consciousness..

Avoid by breathing deeply and normally, not skip breathing and by avoiding overexertion.

HYPOCAPNIA

(Hypo = too little)
Hypocapnia is NOT ENOUGH carbon dioxide
Too little carbon dioxide may interrupt the normal breathing cycle because carbon dioxide actually stimulates breathing.

Causes:

• Excessive hyperventilation (more than three or four breaths)
• This may be voluntary (quick breaths) or involuntary (due to stress or a fright while scuba diving) – causes light-headedness

Symptoms

• Light headedness
• Shallow water blackout>
• Visual disturbances
• Anxiety
• Pins and needles
• Muscle cramps especially in hands and feet

Visual disturbances, anxiety, pins and needles and muscle cramps especially in hands and feet

A diver ascends; the partial pressure drops and haemoglobin can no longer bond with oxygen.  The diver blacks out without warning due to hypoxia (NOT ENOUGH OXYGEN)

CARBON MONOXIDE POISONING

Caused by contaminated and poor quality air.  Smoking is another source of carbon monoxide.  Carbon monoxide bonds more readily with haemoglobin than oxygen (by 200 times) but does not release as easily. Breathing air contaminated with carbon monoxide at depth, haemoglobin carries less and less oxygen as carbon monoxide bonds with it.

When a diver surfaces, plasma no longer can carry enough dissolved oxygen.  The diver blacks out from hypoxia (NOT ENOUGH OXYGEN)

Signs and Symptoms of carbon monoxide include

• Headache
• Confusion
• Narrow vision
• Bright red lips / nails (not easily observed while underwater

Symptoms of mild cases subside after several hours of fresh air First Aid procedures: severe cases – give the diver 100% oxygen and contact emergency medical care.

OXYGEN TOXICITY (two types)

One involves the symptoms in the respiratory system, and the other involves the nervous system. Using enriched air nitrox (EANx) you can have oxygen toxicity.

CNS TOXICITY (most serious)

Central nervous system (CNS) oxygen toxicity involves nervous system reactions to oxygen exposure, and tends to be unpredictable, beyond the fact that it occurs at elevated oxygen partial pressures (greater than 1.4 bar / ATA)
Signs and Symptoms:

• Visual disturbances
• Ear ringing
• Nausea
• Twitching muscles
• Irritability
• Dizziness.

Further information
Most serious is convulsion (which cause a diver to drown)
Using normal air, a diver is risking CNS above 1.6 ATA at 66m.
On 100% oxygen a diver would reach a pp of 1.6 ATA at 6 meters.
CNS is considered life threatening in many diving situations because of sudden convulsions and unconsciousness.
Decongestants predispose you to CNS toxicity.  Vitamin ‘E’, Valium and Magnesium are said to reduce the likelihood of CNS toxicity.