Decompression allows the human body to safely adapt to changes in surrounding pressure. It involves the controlled release of dissolved gases accumulated in the body under higher pressure conditions. This physiological adjustment is essential when transitioning from a high-pressure environment to a lower-pressure one. The goal of decompression is to prevent harm from pressure changes.
The Physics of Pressure and Gas Absorption
Decompression is necessary due to fundamental scientific principles governing gas behavior under varying pressures. Henry’s Law states that the amount of gas dissolved in a liquid is directly proportional to its partial pressure. In diving, as a person descends, ambient pressure increases, leading to more inert gases, primarily nitrogen, dissolving into the body’s tissues and blood.
Boyle’s Law describes the inverse relationship between gas volume and pressure. If pressure decreases, gas volume increases. This means that if dissolved gases come out of solution too quickly during ascent, they can expand and form bubbles, similar to opening a carbonated drink. These expanding bubbles can pose a risk to the body’s tissues.
As a diver remains at depth, inert gases like nitrogen continue to be absorbed into tissues until equilibrium with the surrounding pressure is reached. Unlike oxygen, which the body metabolizes, nitrogen is largely unused and accumulates. If pressure is reduced too rapidly, these dissolved gases can form bubbles in the bloodstream and tissues, potentially causing injury.
Understanding Decompression Sickness
Decompression Sickness (DCS), often called “the bends,” occurs when dissolved inert gases form bubbles within the body’s tissues and bloodstream due to a rapid reduction in ambient pressure. This can happen if a person ascends too quickly from a high-pressure environment, such as after a dive. The symptoms and severity of DCS vary depending on where these gas bubbles form.
Common DCS manifestations include localized deep pain, often affecting joints like the shoulders, elbows, knees, and ankles. This joint pain gave DCS its colloquial name, “the bends,” as affected individuals might bend over in discomfort. Skin rashes and itching are also reported symptoms.
More severe DCS forms can impact the nervous system, leading to numbness, tingling, muscle weakness, or paralysis. Bubbles can also affect the respiratory system, causing a burning sensation in the chest, coughing, or difficulty breathing, sometimes called “the chokes.” These bubbles can obstruct blood flow, compress nerves, or cause tissue damage.
Strategies for Safe Decompression
To prevent decompression sickness, various strategies manage the release of dissolved gases from the body. A primary method involves controlling the ascent rate, where individuals ascend slowly to allow inert gases to off-gas safely through the lungs. This gradual pressure reduction helps prevent rapid bubble formation in tissues.
Decompression stops are planned pauses at specific depths during ascent, allowing additional time for inert gases to leave the body gradually. These stops are important for dives exceeding certain depth and time limits, as they allow the body to release excess gas before reaching the surface. Dive tables and modern dive computers calculate and guide safe decompression profiles based on depth, bottom time, and breathing gas mixtures.
Many recreational divers incorporate safety stops, brief pauses typically for about three minutes at 15 to 20 feet (5 to 6 meters), near the end of a dive. While not mandatory like decompression stops, safety stops provide an additional margin of conservatism by facilitating further nitrogen off-gassing, reducing the risk of DCS.
Decompression in Extreme Environments
Decompression principles extend beyond recreational diving to other environments where pressure changes occur. Commercial divers, working at greater depths and for longer durations, face complex decompression challenges. Their dive profiles require meticulous planning and extensive, mandatory decompression schedules to safely return to surface pressure.
Aviators and astronauts also encounter decompression concerns, typically involving rapid ascent to lower atmospheric pressures. Flying in unpressurized aircraft at high altitudes, or experiencing a sudden loss of cabin pressure, can lead to “altitude decompression sickness.” This happens when the body, accustomed to sea-level pressure, experiences a sudden drop in external pressure, causing dissolved gases to form bubbles.
To mitigate these risks, specialized procedures like pre-breathing pure oxygen are used before high-altitude flights or spacewalks. This helps “denitrogenate” the body, flushing out excess nitrogen and reducing bubble formation during rapid depressurization. Decompression understanding is applied in diverse fields, from underwater exploration to space travel.
Medical Response to Decompression Incidents
When decompression sickness occurs, medical intervention is necessary. The standard treatment for DCS is recompression therapy, also known as hyperbaric oxygen therapy (HBOT). This involves placing the affected individual in a specialized hyperbaric chamber, where pressure is increased significantly, often to levels equivalent to 60 feet (18 meters) of seawater or more.
Inside the chamber, the patient breathes pure oxygen. Increased pressure reduces the size of gas bubbles, forcing them back into a dissolved state in the blood and tissues. The pure oxygen assists in flushing out inert gases and improving oxygen delivery to tissues deprived due to bubble obstruction.
After initial recompression, chamber pressure is gradually reduced, allowing the body to slowly eliminate excess gases. While hyperbaric oxygen therapy is the definitive treatment, administering 100% oxygen as first-aid can be beneficial before reaching a hyperbaric facility. This helps accelerate inert gas elimination and can alleviate symptoms.