Decompression sickness, commonly known as “the bends,” is a condition affecting individuals exposed to significant pressure changes, particularly scuba divers. This medical issue arises when gases dissolved in the body form bubbles within tissues and the bloodstream during a decrease in ambient pressure. Understanding the bends involves recognizing it as a complex physiological response influenced by how quickly and extensively pressure changes, leading to various health concerns.
The Science Behind Depth and Pressure
Underwater, pressure increases with depth, approximately one atmosphere for every 10 meters (33 feet) of descent. This increased pressure causes gases divers breathe, particularly nitrogen, to dissolve into the body’s tissues and fluids in greater quantities. The amount of nitrogen absorbed depends on both the depth and the duration of the dive. This process is similar to how a carbonated drink is bottled under pressure, forcing gas into the liquid.
As a diver ascends, the surrounding pressure decreases, and dissolved nitrogen begins to come out of solution. If this pressure reduction happens too rapidly, nitrogen cannot be eliminated safely through the lungs at a sufficient rate. Instead, it forms bubbles within the blood and body tissues, much like opening a shaken soda bottle quickly causes a sudden release of fizz. These bubbles directly cause the symptoms associated with decompression sickness.
Gas laws describe this behavior. Henry’s Law states that the amount of gas dissolved in a liquid is proportional to the partial pressure of that gas above the liquid. In diving, as pressure increases, more nitrogen dissolves into the body. Boyle’s Law explains how gas volume changes with pressure, meaning that as a diver ascends, any gas bubbles in the body will expand. Therefore, the rate of pressure change and time spent at depth are factors in managing nitrogen absorption and release.
Factors Influencing Decompression Sickness Beyond Depth
While depth and dive time are significant, several other factors contribute to an individual’s susceptibility to decompression sickness. The rate of ascent is important; a slower ascent allows more time for nitrogen to off-gas safely through respiration, reducing the likelihood of bubble formation. Rapid ascents, even from shallower depths, increase the risk.
Repetitive dives within a short timeframe also elevate risk, as residual nitrogen from previous dives accumulates. Inadequate surface intervals between dives do not allow sufficient time for this excess nitrogen to dissipate. Individual physiological characteristics play a role, with factors like age, hydration levels, body fat percentage, and overall health influencing how the body absorbs and releases nitrogen.
Environmental conditions and physical exertion also influence risk. Cold water can restrict circulation, potentially slowing nitrogen elimination. High levels of exertion during a dive can increase blood flow and gas uptake, while exertion immediately after a dive might promote bubble formation. Post-dive activities, such as flying in an unpressurized aircraft too soon after a dive, can further decrease ambient pressure, mimicking a rapid ascent and increasing symptom risk.
Recognizing and Preventing Decompression Sickness
Recognizing the signs and symptoms of decompression sickness is important for timely intervention. Symptoms vary widely, ranging from mild discomfort to severe, life-altering conditions. Common mild symptoms include joint pain (often called “the bends”), skin rashes, itching, and unusual fatigue. More severe manifestations can involve neurological issues like numbness, tingling, muscle weakness, dizziness, vision disturbances, and in rare cases, paralysis or loss of consciousness.
Immediate medical attention, typically involving recompression therapy in a hyperbaric chamber, is the main treatment for decompression sickness. Prevention is important for divers. Adhering to dive tables or using dive computers helps manage nitrogen absorption by providing limits for depth and bottom time. These tools calculate safe ascent profiles and indicate when safety stops are necessary.
Controlling the ascent rate, typically not exceeding 9-10 meters (30-33 feet) per minute, is a preventative measure. Making a safety stop, usually for 3-5 minutes at a depth of 5-6 meters (15-20 feet) near the end of a dive, allows the body to off-gas additional nitrogen more gradually. Staying well-hydrated, avoiding strenuous activity immediately after diving, and observing recommended no-fly times after dives are also important steps to reduce decompression sickness risk.