Scuba diving and Decompression Sickness

Decompression sickness or the bends is a name given to a variety of symptoms suffered by a person exposed to a decrease in pressure around the body. When inert gases, such as nitrogen, are forced to come out of physical solution as the pressure reduces gas bubbles are formed within the body resulting in signs and symptoms of decompression sickness. Lung Over-expansion injury's also involve gas entering the body. The mechanism for bubble formation differs from DCS but the ultimate problem is the same: bubbles blocking blood flow and causing other forms of tissue damage. An air embolism, caused by other processes, can have many of the same symptoms of DCS. DCS and air embolism are grouped together under the term DCI or Decompression Illness.

Henry's Law and how gases work in our bodies

According to Henry's Law, when the pressure of a gas over a liquid is decreased, the amount of gas dissolved in that liquid will also decrease. When your subjected to pressure by diving nitrogen and other physiologically inert gases dissolve into your tissues as a direct consequence of Henry's Law. Henry's Law states that the quantity of gas dissolved is proportional to the partial pressure of the gas. Henry's law also states that the human body will dissolve inert gas in proportion to the surrounding pressure.

"At the surface before a dive your body is saturated with nitrogen, meaning the tissues of your body are holding as much nitrogen in solution as possible at surface pressure. When you descend and the pressure increases, your body is no longer saturated because at the higher pressure, more nitrogen from your breathing gas goes in to solution. In your body, gases enter solution via your respiratory and circulatory systems. As you descend, nitrogen partial pressure in alveolar air increases, dissolves into alveolar blood and is carried throughout the body by circulation. Arterial nitrogen diffuses into the tissues since it has a higher pressure. The higher the pressure difference between the nitrogen in the alveolar air and the nitrogen in solutio in the blood, the faster nitrogen dissolves in the blood."

The human body absorbs nitrogen at different rates in different tissues. The amount of nitrogen absorbed into your tissues directly relates to the dive's depth and duration. The deeper you ascend, the greater the pressure gradient between the nitrogen pressure in your lungs and the nitrogen pressure in your tissues. The higher gradient, the more rapidly nitrogen diffuses from your lungs into your blood stream and tissues. Also, the longer you remain uder pressure, the more time your body has to absorb nitrogen.

In conclusion, always make the recommended safety stop that is required for your dive and outlined on your RDP. A 3 minute safety stop is not mandatory after all dives but it is a good idea to get the happen of stopping at 15ft for 3 minutes after every dive you complete.


Signs and symptoms of DCS an DCI

Decompression sickness tends to be delayed after a dive and may take as long as 36 hours to manifest. DCS can worsen over the first few hours after onset. Based on these facts, a physician would know that a symptom appearing 48 hours after a dive, or one that appears shortly after a dive but quickly improves without any first aid or treatment, ls likely not DCS.

Physiologists have traditionally designated DCS as either Type 1 (non-serious, pain only) or Type II (serious, involving central nervous system) based on the symptoms present in a patient.

Type I DCS (pain only)

Cutaneous Decompression Sickness (skin bends); red rash in patches, usually on the shoulder and upper chest.


Type II DCS (relate to the nervous system)

Neurological DCS (effects on the nerve system); peripheral tingling and numbness, unconsciousness, respiratory affrest and paralysis.

Pulmonary DSC (manifest in lung capillaries)

Cerebral DSC (bubbles passing through pulmonary capillaries)