Decompression sickness, often called “the bends,” is a medical condition that occurs when the body moves too quickly from a high-pressure environment to a lower-pressure one. While widely associated with scuba diving, it can also impact aviators, astronauts, and people working in compressed-air settings like caissons. The condition results from a rapid decrease in the pressure surrounding the body, which triggers a specific set of physiological events.
The Physiological Cause of Decompression Sickness
The mechanism behind decompression sickness is governed by a principle in physics known as Henry’s Law. This law states that the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas over the liquid. For a scuba diver, the air they breathe is compressed, and as they descend, the surrounding water pressure increases. This increased pressure causes more inert gases, primarily nitrogen, to dissolve into the body’s fluids and tissues, particularly in those with high fat content like nerves.
A useful analogy is a carbonated beverage bottle. When the bottle is sealed, the contents are under high pressure, and the carbon dioxide gas remains dissolved in the liquid. When the cap is removed, the pressure is suddenly released, causing the dissolved gas to come out of solution and form bubbles. A similar process occurs in the human body during a rapid ascent from a dive. If the pressure decreases too quickly, the dissolved nitrogen cannot be gradually eliminated through the lungs.
The nitrogen then transitions from a dissolved state back into a gaseous one, forming bubbles directly within the blood and tissues. These bubbles are the direct cause of the injuries associated with decompression sickness. They can obstruct blood flow in small vessels, distort tissues, and trigger inflammatory responses. This process is a physical consequence of gases reacting to a swift reduction in ambient pressure.
Recognizing Signs and Symptoms
The signs of decompression sickness can manifest in numerous ways, depending on where the gas bubbles form in the body. Symptoms typically appear within minutes to several hours after a rapid pressure change, though in some cases, their onset can be delayed. The most common presentation involves deep, aching pain in the joints, such as the elbows, shoulders, and knees. This symptom is what originally earned the condition the name “the bends,” as individuals would bend over in discomfort.
Beyond joint pain, symptoms can affect the skin, appearing as an unusual itch, a rash, or a distinctive purplish, marbled pattern known as cutis marmorata. This skin mottling is caused by bubbles interfering with blood flow in the small vessels of the skin. These presentations are generally considered milder forms of the condition.
More serious issues arise when bubbles affect the central nervous system. Neurological symptoms can be severe and may include:
- Dizziness or vertigo
- Numbness or tingling sensations
- Muscle weakness or paralysis
- Difficulty with coordination
- Problems with cognitive function
Other symptoms can include profound fatigue or shortness of breath. Medical professionals often distinguish between Type I DCS, which includes pain and skin symptoms, and Type II DCS, which involves these more severe neurological or respiratory symptoms.
Medical Treatment for Decompression Sickness
When decompression sickness is suspected, immediate medical intervention is needed to prevent long-term damage. The definitive treatment is recompression in a hyperbaric chamber. This therapy involves placing the person in a sealed, high-pressure chamber. The increased pressure shrinks the nitrogen bubbles that have formed, allowing the gas to dissolve back into the bloodstream.
Once the bubbles are redissolved, the pressure inside the chamber is slowly reduced, simulating a very slow ascent. This controlled depressurization allows the dissolved nitrogen to be safely transported by the blood to the lungs, where it can be exhaled. Patients in the chamber also breathe 100% oxygen at specific intervals, which helps wash out the excess nitrogen and promotes oxygen delivery to tissues that may have been deprived of it.
While awaiting transport to a medical facility with a hyperbaric chamber, certain first aid measures can be taken. Administering 100% oxygen is a primary step, as it helps facilitate the elimination of nitrogen. It is also recommended that the individual lie down and remain still. Providing non-alcoholic, caffeine-free fluids can help with hydration, which supports circulation.
Prevention and Key Risk Factors
Preventing decompression sickness centers on controlling the rate of pressure change. For divers, this means following established dive tables or using a dive computer to manage depth and time. These tools provide guidelines for a controlled ascent rate and incorporate safety stops at specific depths. These stops allow time for the gradual off-gassing of absorbed nitrogen, preventing it from forming bubbles.
Certain activities after a dive can also increase risk. It is advised to avoid flying or traveling to high altitudes for a period after diving, as the lower atmospheric pressure can be enough to trigger bubble formation from residual nitrogen. The recommended waiting time varies depending on the frequency and depth of the dives performed.
Personal health and physiological factors can also influence an individual’s susceptibility. Several factors may increase risk:
- Dehydration, which can impair efficient gas exchange.
- Obesity, as nitrogen is readily stored in fat tissue.
- Fatigue or previous physical injuries.
- Age, as circulatory efficiency can decrease over time.
Maintaining good hydration is an important preventative measure.