The neurons of the central nervous system demonstrate the effects of systemic hypoxia before most other tissues in the body. The CNS has a high requirement for oxygen and carriers of energy. In fact, one fifth of blood flow is involved in supplying the brain with oxygen even though the mass of the brain constitutes about one twentieth of total body mass. This high requirement for oxygen also results in greater sensitivity to oxygen deprivation. The bulk of oxygen is used in the process of mitochondrial oxidation. The mitochondrion are engaged in the production of energy through adenosine triphosphate. The energy produced by the mitochondrion are necessary for the survival of cells.
Decompression (DCS, the Bends)
DCS can occur when the body undergoes depressurization such as that which occurs when divers surface too quickly. This process causes gases that are dissolved into the blood stream come out of the solution and form bubbles inside the body. These bubbles can form anywhere in the body and therefore can produce a variety of symptoms and may result in death.

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The ascent and resulting pressure change brings inert gasses out of solution. This process occurs normally in the lungs but this process occurs by the process of gas exchange. When “outgassing” occurs too quickly to be accommodated by the lungs, the excess gas is released into bubbles. The amount of damage done depends upon where these bubbles form and how many bubbles form. If bubbles form under the skin or in the joints, the symptoms are milder and can involve muscle spasms and pain. However, larger numbers of bubbles forming in the lungs may cause damage to the lungs themselves. When the condition becomes severe, it can interrupt the function of the spinal cord and, in the most severe conditions, damage the spinal cord.
These bubbles may enter the arteries creating an embolism. In some cases, a condition called “ebullism” In this case, water vapor forms bubbles in the body fluids.

Musculoskeletal symptoms can include a localized deep pain mostly in the large joints of varying levels of severity. Some may develop itching around the head , neck, arms and chest. There may be the mottled or marbled skin in those areas and even swelling with pitting edema. Neurological symptoms include an altering of sensation, paresthesis or hyperthesia. Some individuals may become confused, display dramatic changes in mood or behavior, develop seizures, or may become unconscious.

If the spinal cord is involved, the individual may become paralyzed or weakened. There may be girdling around the abdomen or chest. Individuals may also experience a headache, shortness of breath, fatigue and general malaise. There can be dizziness, loss of balance, or hearing loss.

Treatment involves administration of 100% oxygen early on followed by hyperbaric oxygen therapy. In most mild cases, many of the symptoms will disappear. An older but still effective treatment involves recompression in a recompression chamber. Oxygen and recomplression has been the treatment of choice since the mid-1900’s. Since dehydration can sometimes be a precipitant for the development of the condition, administration of fluids is also recommended. Individuals should place in the supine position as part of first aid.

When 100% oxygen is administered immediately and followed up by recompression in a hyperbaric chamber, most individuals will not experience long term effects. DCS is a relatively rare condition. Of those who experience “the Bends’ only about 16% had permanent neurological damage.

    References
  • Berezovskii, V.A. and Yaroshenko, V.T. (2002). Systemic and Cellular Responsiveness of the CNS to Hypoxia, Neurophysiology, 34(5), p 386-390.
  • Pulley, Stephen A (2007). Decompression Sickness. Medscape