23 June 2006

Decompression sickness

Decompression sickness, better known as the Bends, is the presence and entrapment of expanding nitrogen bubbles in the body's bloodstream and tissues.

Decompression sickness, better known as the Bends, is the presence and entrapment of expanding nitrogen bubbles in the body's bloodstream and tissues, caused by a rapid ascent from deep waters (increased pressure) to the surface (normal atmospheric pressure).

When divers resurface, they need to do so slowly, with regular intervals, to allow nitrogen to seep out of the blood and lungs at a controlled and safe rate. This is done according to specifically drafted diving tables. If this is not done, the pressurised nitrogen will begin to form bubbles, similar to that of a can of soda fizzing up when it is opened.

Once caught up in the body, these nitrogen bubbles may be removed from the blood or the lungs. This can cause major damage to tissue, nerves and organs as they slowly expand and become lodged in parts of the body.

The problem does not really occur when descending into deep waters, as the body is quite easily adapted to depths. However, the problem occurs when the body resurfaces.

The most common symptoms of decompression sickness are the following:
  • joint pain
  • itchiness
  • dizziness
  • nausea
  • numbness
  • shortness of breath
  • skin rashes and swelling

Can be fatal
In rare cases, decompression sickness can be fatal, especially if it begins to affect brain function. Nitrogen bubbles have a dangerous effect on the white matter of the spine, and various theories attempt to explain this phenomenon. White matter forms part of the central nervous system, which sends messages to the brain. Nitrogen bubbles may lodge in brain or cord capillaries, preventing regular blood flow or within the tissues themselves. In such cases, the symptoms may be severe and the following may occur:

  • a sudden tingling, or feeling of constriction, around the chest or abdomen upon surfacing
  • numbness
  • weakness
  • loss of bowel and bladder control
  • pain in the neck and chest
  • loss of consciousness
  • paralysis
  • brain damage
  • mottled or marbled skin accompanied by swelling may accompany these neurological problems

Why 'The Bends'?
Patients with bubble disease often have joint pain that is relieved by bending the joint or hunching over – hence the term 'The Bends'.

The condition is treated using a hyperbaric chamber (decompression chamber). The diver will enter this chamber for several hours (depending on the severity), according to a table or recompression followed by a slow controlled decompression with gas mixtures enriched with oxygen. The nitrogen bubbles formation is arrested by filling the chamber with compressed air, and then slowly the pressure will weaken until surface pressure is reached. This process allows the nitrogen to seep out slowly as if the diver were decompressing under water.

More about pressure
The human body is designed to withstand an average 6.7kg per 6,5 square centimetres, the pressure at sea level. If the same area of water and air were compared, water weighs far more than that of the air. Therefore, water pressures on your body are far higher than the equivalent to that of air pressure.

Forty metres is the usual recommended maximum depth that recreational divers should dive to. The pressure at this level is the equivalent to five atmospheres (approximately 90 tons of pressure).

At deep depths, divers need to breathe compressed air. Below 30 metres, nitrogen in the compressed air becomes toxic, causing an anaesthetising effect on divers, leading them to laugh and/or hallucinate. This is known as nitrogen narcosis.

(Health24, June 2006)

Source: Jos Beer, Safety and Training Manager, Cape Diving (Pty) Limited

Source: Dr Jonathan Rosenthal, Hyperbaric Physician, Diving Medical Examiner

Source: Last Breath, Cautionary Tales from the Limits of Human Endurance, Peter Stark, Chapter 9, Bubbling from the Bottom Up, The Bends

Reviewed by Dr Jonathan Rosenthal, Hyperbaric Physician, Diving Medical Examiner

Read more:
Hyperbaric Oxygen Therapy


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