Optimal Decompression of Divers Procedures for Constraining Predicted Bubble Growth

The human body is not adapted for living underwater, but mankind’s abilities to invent, create, and use technical equipment allows underwater breathing. The activity of diving started as free diving, where the diver’s lung capacity was the limiting factor. In the 18th century the invention of the diving suit made it possible to supply divers with air from the surface. Although economically profi table, this invention was disastrous for divers, who sometimes suffered from extreme pain, permanent paralysis, and occasionally death. These symptoms were initially named caisson disease [1] but are now classifi ed as decompression sickness (DCS). Diving (see Figure 1) involves breathing either pressurized air or a gas mixture consisting of oxygen plus one or more inert gas, typically nitrogen or helium. Oxygen is transported in blood 99% bound to hemoglobin and is metabolized in cellular processes. However, the pressurized inert gas reaches equilibrium with its environment by rapid diffusion across the alveoli membrane in the lungs to the arterial side of the circulatory system. This gas is transported in the bloodstream to body tissues, where it accumulates over time [2]. During ascent to the surface, the inert gas may come out of solution and form gas bubbles, which cause DCS. This process is similar to what occurs when the cork is popped from a bottle of champagne, where bubbles instantly form when the pressure drops. To prevent bubble growth, decompression procedures are performed to allow divers to ascend safely from depth. By making controlled stops during the ascent to the surface, time is allowed for the blood circulation to wash out the excess inert gas through the lungs, thus preventing a pressure drop sufficient to cause significant bubble growth. These procedures are calculated by a decompression algorithm, which is implemented either as a precalculated table, dive-planning software, or a real-time dive-computer algorithm. A decompression procedure is used by the diver if the combination of bottom depth and time exceeds a no-decompression-limit (NDL). The first decompression model, created in 1908 [3], uses multiple, parallel tissue compartments with different time constants, where first-order linear equations describe inert-gas partial pressures. A drop in ambient pressure results in supersaturation, which is defined as the ratio between the compartment-gas partial pressure and the ambient pressure. The decompression procedures are calculated by setting a threshold for acceptable supersaturation at each instant of time. This approach yields a simple, analytical solution for how long the diver must remain at each decompression stage. Despite more than 100 years of decompression research, this model remains the foundation of most current algorithms and tables. Advances in electronics and computer technology over the last few decades have given birth to dive computers. A diver carries these small electronic devices during the dive and continually measures depth and time spent under water. The decompression algorithms used to calculate