When the internal pressure of the body drops too low, a condition known as decompression sickness (DCS) can set in. DCS occurs when gases that were previously dissolved in the blood or other body tissues become undissolved. Divers who come up to the surface of the water too quickly are susceptible to this illness, as are pilots flying at high altitudes in planes without pressurized cabins. The term “the bends” is commonly used by divers to describe the joint pain that is a sign of decompression sickness.
Decompression sickness is always caused by a drop in barometric pressure. Because pressure is generated by the weight of the column of air above the body pressing down on the body, barometric pressure is significantly lower at high altitude compared to the surface of the Earth. Extremely high pressures exerted on divers at depth are also caused by the weight of a water column bearing down on the body. The fast drop in pressure that divers experience when they rise up from the high pressure of deep water to the now low pressure of sea level is what causes decompression sickness (DCS), which occurs at normal barometric pressure (at sea level). A dive in a deep alpine lake, where the atmospheric pressure at the lake’s surface is lower than that at sea level, is more likely to result in decompression sickness (DCS) than a dive in water at sea level.
When DCS occurs, the blood’s dissolved gases, primarily nitrogen, rapidly escape their dissolved state, causing bubbles to develop in the blood and other tissues. This happens because a lower gas pressure above the liquid reduces the amount of gas that may remain dissolved in the liquid. The proper distribution of gases in the blood is maintained by the pressure exerted by the atmosphere. Less gas is left dissolved when the pressure is lowered. When you open a can of soda, you observe this phenomenon firsthand. When the bottle’s seal is broken, the gas pressure exerted over the liquid is reduced. Because of this, bubbles form as the gas (carbon dioxide) escapes from solution in the liquid.
Joint discomfort is the most common symptom of DCS, followed by headache and visual abnormalities (10-15 percent of cases). Extreme DCS can be fatal if left untreated. Pure oxygen is used as an emergency treatment. Afterwards, the patient is taken to a hyperbaric chamber. A hyperbaric chamber is an enclosed space that is pressured to a level higher than that of the atmosphere. Repressurizing the body with this treatment is effective for DCS because it allows for a more progressive pressure reduction. Increased blood oxygen levels result from the hyperbaric chamber’s method of administering oxygen at high pressure. The result is that some of the nitrogen in the blood gets swapped out for oxygen, which is more manageable in its gaseous form.