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> > dci is a biochemical not mechanical problem... > It's both. The following is from my book, due out sometime, from the section on decompression sickness: MECHANICAL EFFECTS OF DCS How do decompression bubbles hurt you? In general terms the primary effects of bubbles are mechanical. Bubbles compress blood and lymph vessels from the outside and obstruct from within. Vessels and adjacent tissue structures get squashed, even torn from bubbles forming near them. Decrease in blood supply from all this interference is called ischemia (pronounced ih-skeeU-me-uh). Pain and loss of function follows ischemia. If you examine the word TischemiaU closely you can find the Greek word ThaimaU meaning blood. Other well known words from this root are hemorrhage, hemophilia, hemoglobin, even hemorrhoid. In serious cases of decompression injury, bubbles injure the spinal cord in several ways. Bubbles physically disrupt the nerve cells called neurons. Royal Navy Surgeon Commander Francis calculated how many neurons might be involved and concluded it was not enough to account for loss of function. Another possibility is that because of a fairly tight membrane surrounding the spinal cord, expanding gas bubbles inside the membrane compress the spinal cord promoting ischemia. However there may not be enough gas to raise cord pressure sufficiently to account for global ischemia. Bubbles also compress nerves. Nerves, particularly central nervous system nerves, don't like being pushed around. A small compression quickly impairs function. This nerve compression may be behind symptoms of decompression illness that occur soon after the dive. Loss of function from nerve compression occurs much faster than loss of function from problems with blood flow. Another way bubbles affect the spinal cord is to tear blood vessels. Small blood vessels in the cord don't have much supporting connective tissue as does the rest of the body. These small vessels easily tear and bleed, a serious problem in the central nervous system. One intriguing problem with bleeding is that blood contains iron, a potent promoter of certain types of toxic oxygen reactions. In the body iron is usually found in a form that is tightly bound with a protein, as in hemoglobin. When it becomes available in unbound form it turns on harmful oxygen reactions. See Section 3 on oxygen toxicity in this chapter for the basics of oxygen injury. It is possible that this type of hemorrhagic injury is part of the delayed problems that go along with spinal cord hits. BIOCHEMICAL EFFECTS OF DCS Secondary effects of bubbles include a complicated series of biochemical changes. Bubbles are more than small mechanical presences. They interact with your bodyUs ready defences against foreign invaders. White blood cells called leucocytes and blood clotting cells called platelets come together and adhere to bubbles. Electrochemical forces congregate little globs of free fats into blockages called fat emboli. Several biochemical pathways like coagulation and an enzymatic break down process called fibrinolysis also get busy on bubble invaders. Reactions may distribute throughout your system to take place far from the original site of bubbles. All add to existing problems of obstructed blood flow, edema, and possibly toxic oxygen free radicals, discussed later in the section on oxygen toxicity. there's much more ... get the book :-)
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