Alternative Hypotheses and Future Directions

One newer avenue of research in relation to DCS pathophysiology that is very active but not concluded as this book goes to press relates to the role of so-called intravascular ‘microparticles’. Microparticles are small fragments of membrane material that are shed from the surface of some formed elements of blood and also endothelium. Their presence in the circulation appears to activate or amplify inflammatory processes and coagulation, and as a result they appear capable of initiating or at least exacerbating vascular injury. Microparticles are increased in a variety of disease states including sepsis, myocardial infarction and vasculitis.

Microparticle numbers also appear to be increased by decompression stress, that is, in the presence of tissue supersaturation with inert gas. This raises the possibility that some of the pathophysiological events in DCS that are currently attributed to circulating bubbles may in fact be caused or exacerbated by microparticles. However, many questions remain unanswered. For example, is microparticle generation in decompression stress secondary to bubble formation, or is there some other unknown consequence of inert gas supersaturation that is responsible? How can the invariably wide distribution of harmful microparticles be reconciled against the selective vulnerability of certain organs such as the spinal cord and inner ear in DCS? Similarly, why does the brain seem relatively resistant to harm when in fact its luxurious perfusion would render it at highest risk of exposure to microparticles?

The answers to such questions are unlikely to be simple. The more effort that goes into researching the microparticle phenomenon, the more complex it seems to become. For example, it seems clear that microparticles are not homogeneous; they have different origins, some appear to have mixed origins and they seem to have variable inflammatory potential. Some larger microparticles even appear to have characteristics of gas micronuclei and may contain a core of gas.

This is an exciting line of research that is in its infancy but that has the potential to modify our pathophysiological paradigm for DCS significantly. Alternatively, it may transpire that microparticles are little more than an interesting epiphenomenon. It is a subject for those interested in the detail of this matter to watch closely.