DECOMPRESSION SICKNESS

Decompression Sickness or DCS for short, is also commonly called 'the bends', is probably the bane of divers. The symptoms can range from rashes and molting skin in mild cases  to disability and death in severe cases. 

CAUSES

DCS arises from the build up of biologically inert gases, namely nitrogen, in bodily tissues as the diver is descends. The amount of gas dissolved in tissue is dependent on the Dalton's and Henry's Laws and the solubility of the gases in the tissue. 

Nitrogen is also more soluble in lipids. than in water. Hence tissues containing a lot of lipids will take up a greater amount of nitrogen leading to an increase risk of DCS.

As a diver goes deeper, the partial pressure of nitrogen increases and will cause more nitrogen to dissolve in the body than on the surface. At 20m the rate of dissolving is 3 times faster hence a diver will become saturated with nitrogen faster than he would on the surface. Tissues rich in blood flow e.g. the brain, heart and kidneys get saturated faster then tissue with less blood flow like cartilage in joints and fat stores.

The reverse process call outgassing occurs as the diver ascends to the surface. Ambient pressure is reduced as well as partial pressure of nitrogen in the lungs. Dissolved nitrogen in the body will then be diffused from the tissues to the blood and back to the atmosphere by respiration. However, if the diver ascends to quickly, the ambient and partial pressure will drop suddenly and gas bubbles will form. Imagine a fizzy drink bubbling when suddenly opened. These bubbles will increase in volume as expected from Boyle's Law as the diver continues to ascend. The bubbles of gas can clump together and attract platelets and blood proteins forming a large foreign body or embolus in the blood. The embolus can get stuck in blood vessels and restrict blood flow to the tissues, causing the tissues to become hypoxic and may be permanently damaged.

If bubbles occur in tissues, the expanding volume of the bubble as the diver ascend can damage surrounding tissue structure by the exerting excess pressure and restricting blood flow by pressing on nearby blood vessels.

SYMPTOMS

There are two classifications of DCS. The less serious Type 1 and more serious Type 2.

Type 1 DCS includes Epidermal DCS and Muscular-skeletal DCS.                                                                

Epidermal DCS are manifested usually as rashes, itching and mottled patches on the skin. Caused by bubblethe epidermal tissue.                                                                                                                       

Muscular-skeletal DCS is the most common form of DCS. It involves bubbles forming usually in large joints like the shoulders and knees. Resulting aches can last for several hours in minor cases. In more serious cases, pain increases in severity over 12 - 24 hours. Usually keeping the joint flexed and immobile eases the pain, giving rise to the term "the bends". The condition normally clears in a week if left alone but it is still recommended to seek recompression treatment.

Type 2 DCS includes Central nervous system DCS, Heart and Lung DCS and Bone Necrosis.          

Nervous system DCS occur when bubbles occur in the brain or spinal cord. Patients will experience numbness and tingling sensations in mild forms. Severity increases to weakness or paralysis of limbs, particularly the legs, difficulty with vision and balance, confusion, convulsions and unconsciousness. Judgment can be impaired and is potentially very dangerous because the diver cannot make sound decisions on his physical conditions hence increasing risks of worsening his condition or drowning.

Heart and lung DCS symptoms are shortness of breath, tightness around the chest and coughs. The condition is also called 'chokes' or gas embolism. Small bubbles circulating in the blood return through the right side of the heart to the lungs, where they are trapped in the lung capillaries which are then passed slowly to the alveoli.

Normally, this isn't a problem unless the diver has a hole in his heart, Patent Foraman Ovale (PFO). Here the bubbles pass to the left side of the heart can get pumped directly to the rest of the body where they may get lodged in other organs like the brain. Bubbles may also form a froth in the lungs and the right side of the heart, blocking the circulation to the lungs, causing low blood pressure and shock. 

Bone necrosis is a believed to be a delayed effect of DCS. Bubbles of nitrogen or swelling of fat cells in the bone marrow cut the supply of blood to the affected area of bone and that area dies. No symptoms are felt unless it is at the joints where arthritis occurs. It is also known as chronic DCS.

DCS can also happen in the gut but it is very uncommon. It can cause pain in the abdomen, vomiting, diarrhoea or bleeding. 

Treatment

Decompression treatment prevents further gas bubbles from forming in the body, remove those that are already formed and to relieve the secondary symptoms that occurs as a result of bubble formation. Treatment is immediate recompression and gradual recompression to simulate a slow ascend where the gases can slowly diffuse out. This is done at medical centers with the help of a recompression camber.