The study of possible long-term effects of diving is limited by certain constraints including definitions (subject, diving exposure, etc.) and other variables. The range and intensity of diving activity in terms of time, frequency, depth, gas mixtures, etc. is large and the same individual may be exposed to a wide variety of conditions over a working lifetime. Divers themselves are highly self selected and the nature of their work makes epidemiological follow-up for scientific purposes difficult. Nevertheless bone necrosis has been successfully investigated in a group of professional divers and the study of even small numbers of divers with neurological defects associated with diving is likely to produce important information. The Decompression Sickness Central Registry in the University of Newcastle upon Tyne is in a unique position to contribute to the long-term study of professional divers but there are difficult problems arising from current economic pressures and the need to maintain good records over a sufficiently long period of time.
Concern about possible long-term effects of professional diving has grown over the last few years and intensified as deep diving techniques have developed. Early diving legislation in the United Kingdom1 required medical examination and a chest radiograph but unfortunately there was no mechanism for evaluating the results of these examinations so that no published useful information has emerged from them. With the beginning of the rapid development of commercial diving associated with the discovery and exploitation of gas and oil in the 1960s the main concern was with accidental deaths and the acute risks of diving, particularly in North Sea conditions. In 1975 The British Medical Association's Scottish Council published a widely read report2 which attempted to define the hazards of diving and drew attention to the then high mortality in North Sea divers. The adverse conditions which prevailed at that time have as a result largely been controlled. Nevertheless it was seen that modern commercial deep diving had evolved a long way from the type of diving which had been useful and fairly static over the long period since August Siebe perfected the diving helmet in 1837. The possibility of unknown long-term effects as a direct result of new diving techniques, especially saturation diving on mixed gas, began to be considered. In 1978, for example, the Mines Safety and Health Commission of the Commission of the European Communities held a Workshop in Luxembourg on ‘Long-term Health Hazards of Diving’ which included papers on the central nervous system3, bone, the internal ear, chromosomes, carbon dioxide toxicity and metabolic changes.
Some of the concerns of 1978 are still unresolved and a cause of worry but others have receded in importance since then. But in few or perhaps none of these hazards is it possible to be satisfied that adequate solutions have been arrived at.
In evaluating factors which might in the long term be likely to cause permanent damage and in attempting to assess what if any changes might result from them, certain difficulties present themselves which limit the acquisition of good data on which to base conclusions. For example, tissues such as bone and nerve react in a relatively limited number of ways to a wide variety of harmful agents, so that unless highly specific changes can be identified and linked with particular diving exposures epidemiological techniques must be used. This means comparing groups of divers with similar work experience, with control groups on non-divers matched for age, sex, obesity and so on. The nature of diving activity makes it difficu