The Science of Diving: Things your instructor never told you

ABSTRACT: Decompression illnesses (DCI), or as they are called more scientifically: dysbaric disorders, represent a complex spectrum of pathophysiological conditions with a wide variety of signs and symptoms related to dissolved gas and its subsequent phase change.1,2 Any significant organic or functional dysfunction in individuals who have recently been exposed to a reduction in environmental pressure (i.e. decompression) must be considered as possibly being caused by DCI until proven otherwise. However, apart from the more obvious acute manifestations of a single, sudden decompression, individuals who have experienced repetitive exposures (e.g. commercial or professional divers and active recreational divers) may also develop sub-acute or chronic manifestations, even if subtle and almost symptomless.3 It is generally accepted that there exist sub-clinical forms of decompression sickness (DCS), with little or no reported symptoms, and that these may cause changes in the bones, the central nervous system and the lungs. When studying the physiology of decompression, the presence of symptoms (or not) may not be the most sensitive or reliable marker. In recent years, analysing “decompression stress” has taken more and more importance in the research of understanding decompression. Current research into DCS is focused on biological markers that can be detected in the blood. Investigators are exploring the potential association between decompression stress and the presence of membrane microparticles (vesicles shed from a variety of cell types) in the blood.4–6 Microparticle levels increase in association with many physiological disease states as well as with the shearing stress caused by bubbles in the blood. The working hypothesis is that certain microparticles (possibly induced by inert gas bubbles) may initiate, be a marker of or contribute to the inflammatory response that leads to DCS. This investigation goes beyond the pure bubble model. While bubbles in the blood certainly play a key role in the development of DCS, their presence or absence does not reliably predict DCS symptom onset. Investigating this process at the molecular level may teach us a great deal more about DCS, providing insights that we hope will improve the effectiveness of both prevention and treatment. Modern approaches to evaluating decompression stress have considered a wide range of other markers and influencing factors: physiological changes during and after the dive (reduction of flow mediated dilatation, dehydration, changes in blood pressure), physiological factors of personal susceptibility (age, sex, VO2max), environmental factors (temperature, altitude), as well as bubble counts. All this shows how much today’s approach to decompression is far removed from “traditional” concepts of saturation and desaturation. In 2009, a European Commission project was initiated, providing the opportunity for education and tutoring of a number of young, inexperienced researchers in the field of decompression research. Baptised the “PHYPODE” project (Physiology of Decompression) these ESR (Early Stage Researchers) and ER (Experienced Researchers) had the opportunity to gain formal training and experience in various leading research institutions all over Europe. Nearing the end stages of the project, the 14 researchers who have been working for three years in PHYPODE have summarized current concepts and ideas, as well as some results of their cutting-edge research projects into a book, this book “The Science of Diving”. It is not only written in such a way that it should allow divers to learn more about the modern approaches to understanding decompression and its problems, but also, contribute to expanding the diving decompression knowledge of physiologists, medical personnel and basically anyone with an interest in “the heart of the matter”. Almost every young scientist participating in the PHYPODE project had the responsibility of writing a chapter. This was by no means a simple job, considering the different linguistic origins of this group of young researchers, many of whom had their own doctoral theses or research programmes to complete in parallel. Authors include renowned and established scientists and diving medicine specialists from the tutoring PHYPODE partner centres. The Internet contains already a huge amount of information available on the Internet on such a topic. Why then, is this book necessary? Let us illustrate our motivation by means of a story from Japan, where, quite recently, one major cosmetics company received a customer complaint because he received an empty soapbox. The company launched a huge investigation into the matter and discovered that the defect arose in the packaging department. They decided to develop a robust and reliable system ensuring zero defects in the process of product packaging and the company invested heavily in the design and implementation of a solution. A few weeks later, a similar problem occurred in a small soap-manufacturing company in India. This time the approach was very different: the manufacturer bought a big industrial fan and placed it facing the soapbox chain. Any boxes that were empty simply blew off the chain and the rest moved ahead to the storage house! Our aim was to keep the concepts as clear as possible but maintain the scientific integrity of the subject. References are limited and proposed as further reading. Having as authors many of those conceiving some of the new approaches provided the opportunity of being the “fan that blows empty boxes”. Have fun reading! Prof. Costantino BALESTRA, PhD Dr. Peter GERMONPRE, MD Editors Miroslav Rozloznik, PhD Peter Buzzacott, PhD. Dennis Madden, MSc. Co-EditorsThe editors and authors of this book are a cadre of scientists and physicians with broad experience and knowledge of diving physiology and decompression theory. As is often the case, it requires a group effort to succeed in advancing practical knowledge. The colloquialism “the whole is greater than the sum of its parts” is often true and the PHYPODE Research Group epitomizes this concept. By logically grouping the various elements of diving science and medicine with provocative "food for thought" sections the text offers valuable lessons to those interested in the current state of diving. Despite nearly 170 years of research, the fundamental nature of decompression stress remains elusive. As is well outlined in this book, great advances have been made to the practical elements allowing for safe diving. Nonetheless, there are glaring voids of knowledge related to the nature of bubble nucleation, its consequences and methods to ameliorate risk. The synergy exhibited in this text not only provides a foundation for what is known, it offers a glimpse of where research is taking us. --- Professor Stephen R. Thom, Dept. of Emergency Medicine, University of Maryland School of Medicine