Decompression sickness (DCS), commonly known as “the bends,” is a serious injury resulting from a rapid reduction in ambient pressure, typically occurring during diving. This condition results when inert gases, primarily nitrogen, dissolved in the body’s tissues under high pressure, come out of solution too quickly. These gases form bubbles within the body, which can obstruct blood flow, damage tissues, and lead to a wide range of symptoms. Understanding the physical forces that precipitate bubble formation is crucial for prevention.
The Underlying Physics of Decompression Sickness
The mechanism leading to decompression sickness is rooted in gas physics, specifically the principle known as Henry’s Law. This law states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. In diving, descent increases ambient pressure, which raises the partial pressure of nitrogen in the breathing gas.
This increased pressure causes inert nitrogen to dissolve into the blood and tissues, a process called “on-gassing.” The longer and deeper the dive, the greater the amount of nitrogen absorbed and stored in the body’s tissues. Problems begin during ascent, when the ambient pressure drops rapidly.
As pressure decreases, nitrogen must exit the tissues and be eliminated through the lungs, a process called “off-gassing.” If the ascent is too fast, the dissolved nitrogen cannot escape quickly enough, causing the tissues to become supersaturated. This supersaturation leads to the formation of gas bubbles within the blood and tissues, causing the physical injury associated with DCS.
The Minimum Depth Threshold for Decompression Sickness
The question of how deep you can get the bends has no fixed number, as risk is a function of both depth and time. For recreational divers breathing air, the risk of DCS increases exponentially with depth and duration. DCS can technically occur after any exposure to increased pressure, even relatively shallow dives.
This occurs if the ascent is rapid or the dive time is excessive. While a diver can stay for a very long time at depths like 15 feet without risk, the “no-decompression limit” time decreases sharply as depth increases. For example, a person spends significantly less time at 60 feet before needing mandatory decompression stops than at 40 feet.
The effective pressure change also depends on the diver’s final altitude. Traveling to a higher elevation, such as flying or driving up a mountain, immediately after a dive further reduces ambient pressure, increasing the risk of bubble formation. Divers are advised to wait a specified period before flying, as reduced cabin pressure can be equivalent to ascending thousands of feet. Post-dive altitude exposure can initiate or worsen a case of DCS, even if the dive profile was safe.
Factors That Increase Decompression Sickness Risk Beyond Depth
While depth and time are the main drivers of decompression risk, several physiological and environmental factors modify susceptibility. Exertion during the deepest phase of a dive is significant because it increases blood flow, accelerating the absorption of inert gas into the tissues. Mild exercise during a decompression stop aids gas elimination, but heavy exertion immediately after surfacing should be avoided.
Body temperature also plays a role. A warm body absorbs gas more readily at depth, and a warmer state during ascent promotes faster off-gassing. Becoming cold during ascent or decompression stops slows circulation, hindering nitrogen removal and increasing bubble risk. Dehydration may also increase DCS risk by affecting blood volume and circulation.
Certain pre-existing medical conditions, such as a Patent Foramen Ovale (PFO), a small opening between the upper chambers of the heart, can substantially raise the risk. A PFO allows venous blood containing small gas bubbles to bypass the lungs’ filtering system and pass directly into the arterial circulation. This enables bubbles to travel to sensitive organs like the brain and spinal cord, increasing the likelihood of neurological DCS.
Recognizing Symptoms and Immediate Response
Decompression sickness manifests in a spectrum of severity, categorized by the affected body system. Type I DCS is less severe, involving musculoskeletal and skin symptoms. The classic symptom is deep, “boring” pain, often localized in the joints, which gives the condition its name, “the bends.”
Type I involvement also includes itching, skin mottling (cutis marmorata), or a rash. Type II DCS is more serious, indicating involvement of the nervous system, respiratory system, or inner ear. Symptoms can include numbness, tingling, muscle weakness, paralysis, difficulty with urination, or loss of balance.
Onset typically occurs within one hour of surfacing in about 50% of cases, and within six hours in 90% of cases. Immediate response to suspected DCS involves administering high-flow oxygen via a non-rebreather mask. The individual should be kept lying down, hydrated, and transported immediately to a facility providing hyperbaric oxygen therapy. This treatment involves recompressing the person in a chamber, which shrinks the bubbles and allows the gas to safely dissolve back into the tissues for gradual elimination.