[3] Below is a summary comparison of the signs and symptoms of DCI arising from its two components: Decompression Sickness and Arterial Gas Embolism.
[5] The mechanism of decompression sickness is different from that of arterial gas embolism, but they share the causative factor of depressurization.
Depressurisation causes inert gases, which were dissolved under higher pressure, to come out of physical solution and form gas bubbles within the body.
[9][10] If inert gas comes out of solution too quickly to allow outgassing in the lungs then bubbles may form in the blood or within the solid tissues of the body.
[11] The most severe types of DCS interrupt — and ultimately damage — spinal cord function, leading to paralysis, sensory dysfunction, or death.
[12][13] A similar effect, known as ebullism, may occur during explosive decompression, when water vapour forms bubbles in body fluids due to a dramatic reduction in environmental pressure.
The gas could also enter the interstitial spaces within the lungs, the neck and larynx, and the mediastinal space around the heart, causing interstititial or mediastinal emphysema, or it could enter the blood vessels of the venous pulmonary circulation via damaged alveolar capillaries, and from there reach the left side of the heart, from which they will be discharged into the systemic circulation.
[15] Sufficient pressure difference and expansion to cause this injury can occur from depths as shallow as 1.2 metres (3.9 ft).
Most doctors do not have the training and experience to reliably diagnose DCI, so it is preferable to consult a diving medicine specialist, as misdiagnosis can have inconvenient, expensive and possibly life-threatening consequences.
[17] Large areas of numbness with associated weakness or paralysis, especially if a whole limb is affected, are indicative of probable brain involvement and require urgent medical attention.
[17] Almost all arterial gas embolism is avoidable by not diving with lung conditions which increase the risk and not holding the breath during ascent.
[18] Xu et al. reported a 99.3% effectiveness rate of treating decompression illness with immediate recompression in a study of 5,278 cases across 2000-2010 in China.
In bones, dysbaric osteonecrosis leads to pathological fractures and chronic arthritis, particularly in the proximal femur, humerus, and tibia.
In the brain and spinal cord, depending on the area and severity of damage there can be neurological deficits ranging from becoming comatose, having sensorimotor weakness, incontinence, and other effects.
The pancreas, kidneys, and liver are also vulnerable, and reginal necrosis in the gastrointestinal tract can cause strictures leading to obstruction.