Sign Up for a Free Account
  • Updated 05.26.2023
  • Released 04.21.1998
  • Expires For CME 05.26.2026

Decompression sickness: neurologic manifestations



Divers who have experienced pressures greater than 2 atmospheres absolute may develop decompression sickness if they ascend too rapidly. Decompression sickness may be mild, with only limb and joint pain ("bends," type I), or serious, with neurologic, cardiac, and pulmonary manifestations (type II). Divers with a patent foramen ovale are more likely to develop severe forms of decompression sickness than divers without a right-to-left shunt. Treatment in a pressure chamber is essential for recovery, and detailed decompression tables are used to prevent and treat decompression sickness.

Key points

• Decompression sickness usually occurs during rapid ascent from depth after diving but may also occur in rapid ascent to high altitudes from sea level.

• Systemic manifestations may involve the nervous system.

• Decompression sickness can be avoided by gradual ascent, but if decompression sickness occurs, it is treated by hyperbaric recompression.

• Hyperbaric oxygen is useful in treating decompression sickness with neurologic manifestations.

Historical note and terminology

Boyle's law. In 1660, Anglo-Irish natural philosopher Robert Boyle (1627-1691) published the first controlled experiments with "rarified air," obtained by reducing the pressure of the air (20; 21; 134).

Boyle found by 1662 that (in modern language) for a fixed mass of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional (21). For his experiments, Boyle relied on an air pump devised by English polymath Robert Hooke (1635-1703).

Dalton's law of partial pressures. In a mixture of gases, as in air, each constituent gas has a partial pressure that is the pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. This is Dalton's law, named after English chemist and physicist John Dalton (1766-1844), who determined this experimentally in 1802 (33).

At sea level, where atmospheric pressure is 760 mm Hg, the percent of the total composition and the partial pressures of the various gases are approximately as follows: 78.6%, 597 mm Hg for nitrogen; 20.9%, 159 mm Hg for oxygen; 0.04%, 3.0 mm Hg for water; and 0.004%, 0.3 mm Hg for carbon dioxide. For comparison, the percent of the total composition and partial pressures of alveolar air are as follows: nitrogen 74.9%, 569 mm Hg; oxygen 13.7%, 104 mm Hg; and water 6.2%, 40 mm Hg.

Henry’s law. Henry’s law, formulated by English chemist William Henry (1774-1836) in 1803, states that, at a constant temperature, the solubility of a gas is directly proportional to the pressure that the gas exerts on the solution (59).

When equilibrium is reached, the solution is described as "saturated," but if the pressure is then reduced, the tissues become effectively supersaturated, and the gases leave the solution and may form gas bubbles. Due to the metabolic activity of oxygen and carbon dioxide, and the comparative marked inactivity of nitrogen, it is nitrogen that is by far the most problematic. To determine the time necessary for the clearance of supersaturated nitrogen without biological damage, decompression tables have been generated based on biomathematical models (but relying on the experience and fitness of navy divers). Even following protocols established for safe decompression, problems may occur (eg, interindividual variation, flying in a commercial aircraft within 12 to 18 hours after diving, etc.), which has led to the appreciation that safety factors must be built into the estimated "safe" dive times.

The Bert and Smith "effects" of oxygen toxicity. In 1878, French zoologist, physiologist, and politician Paul Bert (1833-1886) was the first to determine the acute toxicity of high oxygen concentrations in "La Pression Barometrique” (13; 14). Bert was a student of French physiologist Claude Bernard (1813-1878).

Bert applied an apparatus of French physiologist Denis Jourdanet (1815-1892) that was intended for therapeutic use of compressed or "expanded" air. Bert experimented on himself with "superoxygenated air," that is air with an increased partial pressure of oxygen).

In 1878, Bert demonstrated convulsions in larks exposed to air at 15 to 20 atmospheres absolute, and the neurotoxic effects of oxygen at increased pressure were subsequently called the "Bert effect" (13). Then in 1899, Scottish pathologist and physiologist J(ames) Lorain Smith (1862-1931), while trying to reproduce the "Bert effect," noticed fatal pneumonia in rats after 4 days of exposure to 73% oxygen at 1 atmosphere absolute, which marked the discovery of pulmonary toxicity of oxygen at increased partial pressure--the "Smith Effect" (112; 53; 57).

Scottish pathologist and physiologist J(ames) Lorain Smith (1862-1931)

Smith discovered pulmonary toxicity of oxygen at increased partial pressure, the "Smith effect" (Smith JL. The pathological effects due to increase of oxygen tension in the air breathed. J Physiol 1899;24[1]:19-35). (Source: Pr...

Development of underwater breathing apparatus. English wool merchant John Lethbridge (1675-1759) invented the first underwater diving machine in 1715 to facilitate the salvage of shipwrecks.

English astronomer, mathematician, and physicist Edmond Halley (1656-1742), later famous for predicting the return of the comet named in his honor, developed a practical diving bell in 1717.

Halley's diving bell was constructed of wood, covered in lead, and weighted to keep in correctly oriented underwater. It was 8 feet high, 5 feet in diameter at the bottom, and 3 feet in diameter at the top. Fresh air was supplied by two lead-lined barrels with bung holes at the bottom. The barrels were alternately lowered to the sea floor where an attendant pulled the tube up toward the bell, allowing air to be forced by pressure from the barrel and into the bell. Halley and four others were able to remain on the sea floor at a depth of 9 to 10 fathoms (54 to 60 feet) for 90 minutes. An improved version of Halley's diving bell was developed by Edinburgh confectioner and amateur engineer Charles Spalding (1738-1783) in 1775, and a more sophisticated underwater breathing apparatus was developed by Kleingert in 1798.

In 1819, German-born British engineer Augustus Siebe (1788-1872) invented a diving helmet for an "open dress" form of diving to provide greater mobility to the diver.

This consisted of a metal helmet and shoulder plate attached to a water-tight jacket. The helmet was fitted to an inlet valve to which a flexible air-supply tube was attached. The tube was connected to an air pump, and the force of the pressurized air kept the water from rising in the jacket.

In 1878, pioneering English diving engineer Henry Albert Fleuss (1851-1933) was granted a patent for an apparatus that improved rebreathers, ie, a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the unused oxygen and inert gas content (42).

It consisted of a rubber mask connected to a breathing bag, with 50% to 60% oxygen supplied from a copper tank and carbon dioxide scrubbed using a rope yarn soaked in a strongly alkaline solution of caustic potash (potassium hydroxide), the system giving a working duration of about 3 hours. In 1879, Fleuss demonstrated the utility of his device by submerging himself in a water tank for an hour and then 1 week later by diving to a depth of 5.5 meters in open water. Fleuss's apparatus was first used under operational conditions in November 1880 by Alexander Lambert (c1837-1892), the lead diver of the Severn Tunnel construction project to build a railway tunnel linking South Gloucestershire in the west of England to Monmouthshire in south Wales under the estuary of the River Severn. After being trained by Fleuss, Lambert was able to close a submerged sluice door in the tunnel that had foiled hard-hat divers due to the strong water currents and the danger of their air supply hoses becoming fouled on submerged debris. The same apparatus was later used several times to rescue mine workers.

American environmental medicine and diving medicine specialist Christian James Lambertsen (1917-2011) was principally responsible for developing the rebreathers used by U.S. Navy frogmen for underwater warfare during World War II.

American environmental medicine and diving medicine specialist Christian J. Lambertsen (1917-2011)

Photo taken 1942. (Source: US Army. Public domain.)

Lambertsen designed a series of rebreathers in 1940 and in 1944, first calling his invention simply "breathing apparatus." Consequently, the U.S. Navy considers Lambertsen to be "the father of the Frogmen." Later, after the war, Lambertsen called his invention LARU (an acronym for Lambertsen Amphibious Respiratory Unit). In 1952, he again changed his invention's name to SCUBA (Self-Contained Underwater Breathing Apparatus).

Diving regulator technology was subsequently invented by French engineer Émile Gagnan (1900-1984) and French naval officer and oceanographer Jacques-Yves Cousteau (1910-1997) in 1943.

Although the Gagnan-Cousteau invention was unrelated to rebreathers and came after Lambertson's apparatus, Lambertson's "SCUBA" term is now generally applied to the Gagnan-Cousteau invention.

Use of different breathing mixtures. English-born American engineer and inventor Elihu Thomson (1853-1937) is best known for his electrical innovations and entrepreneurism (eg, in 1892 his Thomson-Houston Electric Company merged with the Edison General Electric Company to become the General Electric Company), but he was also instrumental in the development of different breathing mixtures for diving and caisson work (28).

English-born American engineer and inventor Elihu Thomson (1853-1937)

Photo c1880. (Source: Wikimedia Commons. Public domain.)

As early as 1873, Thomson published a paper on the inhalation of nitrous oxide, nitrogen, hydrogen, and other gases and gaseous mixtures (123), and in 1927, he specifically proposed the use of helium in deep diving and caisson work (124; 125).

Dysbarism. Dysbarism is a general term that encompasses disturbances in the human body resulting from a change in atmospheric pressure. Dysbarism encompasses five subentities: decompression sickness, barotrauma, gas embolism, inert gas narcosis, and oxygen toxicity.

Decompression sickness. Decompression sickness is one of several forms of dysbarism, ie, disturbances in the human body resulting from a change in atmospheric pressure. Divers, miners, tunnel workers, and caisson workers will experience decompression sickness if they progress too quickly to a lower environmental pressure. Rapid ascent to high altitudes in an aircraft with an uncompressed cabin can also produce decompression sickness. The first and least severe symptoms are characterized by limb and joint pain. In more severe cases, with ascent from greater depths, after longer bottom times, or with more rapid ascent or decompression, other nervous system, cardiac, or pulmonary symptoms may occur.

The condition was well known among caisson workers, and it was, therefore, called "caisson disease." Other terms used to describe the condition are "the bends" (limb and joint pain), "the chokes," and "hits."