Decompression sickness, commonly known as the bends, represents one of the most serious risks associated with scuba diving and compressed air work. This condition occurs when dissolved gases, primarily nitrogen, form dangerous bubbles in the tissues and bloodstream. Understanding the specific causes and mechanisms is essential for every diver to mitigate risk and ensure safe practices underwater.
Understanding Gas Laws and Physiology
The fundamental cause of decompression sickness lies in the physical laws governing gases under pressure. As a diver descends, the surrounding water pressure increases, forcing more inert gas molecules into the body's tissues. The deeper and longer the dive, the greater the amount of gas absorbed. When a diver ascends, the pressure decreases, and the gas must be released. If the ascent is too rapid, the gas cannot safely diffuse out through the lungs fast enough, leading to supersaturation and bubble formation.
Primary Causes: Rapid Ascent and Pressure Changes
The most direct cause of decompression sickness is an ascent that exceeds the recommended rate. Divers are trained to ascend slowly, often no faster than 30 feet per minute, to allow the body sufficient time to off-gas. Ignoring depth limits, running out of air at depth, or failing to perform a mandatory safety stop are common scenarios that dramatically increase the risk. These actions force a sudden reduction in ambient pressure, triggering bubble nucleation.
Exceeding no-decompression limits (NDLs) without performing decompression stops.
Rapid ascents due to panic, running out of air, or buddy separation.
Skipping safety or decompression stops required by the dive profile.
Contributing Risk Factors
While rapid ascent is the immediate trigger, several internal and external factors can increase a diver's susceptibility. These elements do not cause the sickness on their own but lower the threshold at which problems occur, making careful planning and personal awareness critical.
Physical Condition and Dive Profile
A diver’s physical state plays a significant role. Dehydration is a major contributing factor because it reduces blood volume, making it harder for the blood to carry dissolved gas safely through the body. Strenuous exercise during the dive can also increase circulation speed, potentially transporting bubbles to critical areas faster. Furthermore, repetitive dives without sufficient surface interval, known as flying or repetitive diving, accumulate nitrogen load in the body, increasing the burden on the second dive.
Medical and Physiological Variability
Not every diver will experience the same risk profile even under identical conditions. Pre-existing medical conditions can significantly alter how the body handles gas saturation. Patent foramen ovale (PFO), a small hole in the heart that fails to close after birth, is a notable condition that allows venous blood to bypass the lungs. This means gas bubbles can directly enter the arterial system, potentially causing stroke-like symptoms.
