Von Guericke developed the first effective air pump in 1650. This permitted pressurization of gas for respiration at elevated ambient pressure. Shortly afterward, in 1670, Robert Boyle exposed experimental animals to the effects of increased and decreased pressures. His reports of these experiments included the first description of the presumed pathological vector of DCS, a bubble, in this case moving to and fro in the aqueous humour of the eye of a viper. The snake was ‘tortured furiously’ by the formation of bubbles in the ‘blood, juices and soft parts of the body’.
There was a long hiatus before related effects were recognized in humans. In the 1840s Colonel Pasley noted rheumatism and excessive fatigue in divers employed on the wreck of the Royal George. The divers were presumably suffering from DCS, not surprising because their bottom times exceeded the accepted limits by a factor of three.
A French mining engineer, Jean Triger, described cases of DCS in humans in 1841. He designed and constructed what came to be known as a ‘caisson’; a pressurized vertical shaft sunk into sites that would otherwise be flooded such as pylon sites in bridge construction or mine shafts extending below the water table. The air pressure excluded water from the shaft, and men could work at the bottom, albeit under whatever pressure was required to maintain a dry environment. Triger himself suffered knee pain on several occasions after pressure exposure in caissons, and as their use expanded there were fatalities and episodes of paralysis. There were almost certainly manifestations of DCS. Two physicians, Pol and Watelle, in 1854, published a report indicating the nature of the disease, together with case histories to demonstrate the relationship between decompression and onset of symptoms.
Hoppe-Seyler repeated the almost 200-year-old Boyle experiments, and in 1857 he described the obstruction of pulmonary vessels by bubbles and the inability of the heart to function adequately under those conditions. He suggested that some of the cases of sudden death in compressed air workers were the result of this intravascular liberation of gas. He also recommended recompression to remedy this.
Le Roy de Mericourt, in 1869, and Gal, in 1872, described an occupational illness of sponge divers that was attributed to the breathing of compressed air and equated this with the caisson workers’ disease. Although some informed physicians were postulating a role for bubbles, a host of other imaginative theories were proposed during the nineteenth century to explain the aetiology of this disorder.
In 1872, Freidburg reviewed the development of compressed air work and collected descriptions of symptoms of workers given insufficient decompression after exposure to high pressure. He compared the clinical course of severe and fatal cases of DCS with that of the venous air embolism occasionally seen in obstetrics and surgery. He believed that rapid decompression would be responsible for a rapid release of the gas that had been taken up by the tissues under increased pressure. He suggested that the blood was filled with gas bubbles that interfered with circulation in the heart and lungs.
Smith described ‘caisson disease’ or ‘compressed air illness’ in 1873 as a disease dependent on increased atmospheric pressure, but always developing after reduction of the pressure. It was characterized, he noted, by moderate or severe pain in one or more of the extremities and sometimes in the trunk as well. There may or may not be epigastric pain and vomiting. In some cases, there may be elements of paralysis that, when they appear, are most frequently confined to the lower half of the body. Cerebral symptoms, such as headache, vertigo, convulsions and loss of consciousness, may be present.
Paul Bert, in 1878, demonstrated in a most conclusive manner that DCS is primarily the result of inert gas (nitrogen in the case of compressed air divers and caisson workers) dissolved in blood and tissues during pressure exposure and then released into the gas phase during or following decompression. He used various oxygen concentrations to hasten decompression, demonstrated the value of oxygen inhalation once experimental animals developed DCS and proposed the concept of oxygen recompression therapy.
Andrew Smith, a surgeon from the Manhattan Eye and Ear Hospital in New York, noted in the 1870s the origin of the term ‘bends’. Because pain in the hips and lower extremities was generally aggravated by an erect position, the victims often assumed a stooping posture. Sufferers among the workers on the Brooklyn Bridge caissons in New York were the objects of good-natured ridicule by their comrades, who likened their angular postures to a fashionable stoop in walking, termed the ‘Grecian bend’, which was practiced by sophisticated metropolitan women at the time. He was aware of the value of recompression, but this was unacceptable to some of his patients. Instead he used hot poultices, ice packs, hot baths, ergot, atropine, whiskey and ginger – or morphine if the others failed. He constructed the first specialized treatment chamber.
Moir, in the early 1890s, working on the Hudson River caisson tunnel in New York, reduced the DCS death rate from 25 per cent of the work force per annum to less than 2 per cent by the use of more careful decompression from caisson exposures and by recompression therapy for symptomatic cases. However, problems were not eliminated, and in projects requiring exposure to relatively high pressures to construct tunnels under New York’s East River in the early 1900s there remained a significant problem with mortality and morbidity, as reported by Keays in 1909.
Not surprisingly, during the early part of the twentieth century there was considerable controversy regarding the speed and manner in which divers and caisson workers should be decompressed. An English physiologist, John Scott Haldane, proposed equations to describe tissue inert gas kinetics and proposed that limiting inert gas supersaturation (see later) during decompression was the key to preventing DCS. His decompression tables, first published in 1908, resulted in a remarkable reduction in the incidence of DCS in both diving and caisson work, and variants of Haldane’s methodology are still in use for planning decompression today. These issues are discussed in Chapter 12.