Before English chemist, William Henry, took his own life in 1836, he discovered a simple physics law to explain how gas behaves in solution. This gas law, now appropriately known as Henry's Law, together with Boyle's Law, form the basis of the pathophysiology and treatment for Decompression Illness.
US Navy Historical Video on Decompression Sickness
Most people know that SCUBA divers are at risk for developing 'the bends'. Although considerably less frequent than divers, high-altitude aviators and astronauts are also at risk for this serious medical condition. Decompression Illness (DCI) is a comprehensive term that captures all medical conditions that may occur when living organisms are exposed to hypobaric changes (going from higher to lower ambient pressure).
DCI is routinely divided into two separate conditions that differ by respective pathophysiology:
- Decompression Sickness (DCS) - occurs when a person is rapidly exposed to hypobaric changes causing inert gases (usually nitrogen) previously dissolved in the blood to come out of solution into their gaseous state as bubbles.
- Arterial Gas Embolism (AGE) - gas bubbles are introduced to the body suddenly, usually by pulmonary barotrauma (rupture of lung tissue) when lung alveoli expand to the point of failure.
Categories of Decompression Sickness
The four basic varieties based on effected organ systems, followed by the respective common eponym are:
- Cutaneous (Skin) - Creeps
- Arthopathy (Joint) - Bends
- Cardiopulmonary (Heart/Lungs) - Chokes
- Neurologic (Brain/Spinal Cord) - Staggers
Bubbles in the blood vessels act as emboli, traveling to end organs where they are thought to cause mechanical effects, ischemia, and immune-mediated inflammatory responses. The chokes and staggers are the most serious presentations and in the worst case may even be life-threatening.
Treatment
In the vast majority of DCS cases associated with aviation, symptoms will completely resolve upon descent. The mainstay of treatment for Decompression Sickness is 100% oxygen and hyperbaric therapy. More commonly, a patient with symptoms suggestive of DCS will be transported to a hyperbaric chamber for oxygen therapy under hyperbaric conditions.
Flying after diving should always be discouraged by both flight medicine and dive medicine physicians as participating in these two activities within 24 hours significantly increases one's risk for developing DCI.
REFERENCES
- Fundamentals of Aerospace Medicine (Ed. 4) by Jeffrey R. Davis (Editor), Robert Johnson (Editor), Jan Stepanek (Editor), Jennifer A. Fogarty (Editor).