diving medicine diving medicine diving medicine, also called undersea and hyperbaric medicine (uhb), is the diagnosis, treatment and prevention of conditions caused by humans entering the undersea environment. it includes the effects on the body of pressure on gases, the diagnosis and treatment of conditions caused by marine hazards and how relationships of a diver's fitness to dive affect a diver's safety. diving medical practitioners are also expected to be competent in the examination of divers and potential divers to determine fitness to dive. a recompression chamber is used to treat some diving disorders. diving medicine physicianoccupationnamesphysicianoccupation typespecialtyactivity sectorsmedicinedescriptioneducation required doctor of medicine (m.d.) doctor of osteopathic medicine (d.o.) bachelor of medicine, bachelor of surgery (m.b.b.s./mbchb) fields ofemploymenthospitals, clinics hyperbaric medicine is a corollary field associated with diving, since recompression in a hyperbaric chamber is used as a treatment for two of the most significant diving-related illnesses, decompression sickness and arterial gas embolism. diving medicine deals with medical research on issues of diving, the prevention of diving disorders, treatment of diving accidents and diving fitness. the field includes the effect of breathing gases and their contaminants under high pressure on the human body and the relationship between the state of physical and psychological health of the diver and safety. in diving accidents it is common for multiple disorders to occur together and interact with each other, both causatively and as complications. diving medicine is a branch of occupational medicine and sports medicine, and at first aid level, an important part of diver education. range and scope of diving medicine further information: diving disorders, list of signs and symptoms of diving disorders, and list of diving hazards and precautions the scope of diving medicine must necessarily include conditions that are specifically connected with the activity of diving, and not found in other contexts, but this categorization excludes almost everything, leaving only deep water blackout, isobaric counterdiffusion and high pressure nervous syndrome. a more useful grouping is conditions that are associated with exposure to variations of ambient pressure. these conditions are largely shared by aviation and space medicine. further conditions associated with diving and other aquatic and outdoor activities are commonly included in books which are aimed at the diver, rather than the specialist medical practitioner, as they are useful background to diver first aid training. the scope of knowledge necessary for a practitioner of diving medicine includes the medical conditions associated with diving and their treatment, physics and physiology relating to the underwater and pressurised environment, the standard operating procedures and equipment used by divers which can influence the development and management of these conditions, and the specialised equipment used for treatment. scope of knowledge for diving medicine the echm-edtc educational and training standards for diving and hyperbaric medicine (2011) specify the following scope of knowledge for diving medicine: physiology and pathology of diving and hyperbaric exposure. human physiology of underwater diving hyperbaric physics diving related physiology hyperbaric pathophysiology of immersion pathophysiology of decompression a brief introduction to acute dysbaric disorders chronic dysbaric disorders hyperbaric oxygen therapy basis – physiology and pathology oxygen toxicity pressure and inert gas effects nitrogen narcosis high pressure neurological syndrome medication under pressure non-dysbaric diving pathologies diving technology and safety basic safety planning compressed air work diving procedures wet bells and stages scuba diving on air and mixed gas surface supplied diving standard diving (copper helmet) rebreather diving (semi-closed and closed circuit) other diving procedures characteristics of various divers diving equipment as used to c.50m and chambers diving tables and computers regulations and standards for diving saturation diving saturation mode physiology of deep exposure compression at depth in a living chamber bell excursions fitness to dive fitness to dive criteria and contraindications for divers, compressed air workers and hbot chamber personnel fitness to dive assessment fitness to dive standards (professional and recreational) diving accidents diving incidents and accidents emergency medical support with no chamber on site barotrauma: ent; dental; cutaneous, conjunctival, etc. physical injuries decompression illness pathophysiological basis and mechanisms of dci differential diagnosis of decompression illness management of decompression incidents at the surface immediate management, recompression tables and strategies rehabilitation of disabled divers diving accident investigation clinical hbo recompression chambers scope of knowledge for hyperbaric medicine the echm-edtc educational and training standards for diving and hyperbaric medicine (2011) specify the following scope of knowledge for hyperbaric medicine additional to that for diving medicine: physiology and pathology of diving and hyperbaric exposure. hbo-basics – effects of hyperbaric oxygen – physiology and pathology clinical hbo chamber technique (multiplace, monoplace, transport chambers, wet recompression) mandatory indications hbo recommended indications hbo experimental and anecdotal indications hbo data collection / statistics / evaluation hbo general basic treatment (nursing) hbo diagnostic, monitoring and therapeutic devices in chambers risk assessment, incidents monitoring and safety plan in hbo chambers hbo safety regulations diagnostics main article: list of signs and symptoms of diving disorders the signs and symptoms of diving disorders may present during a dive, on surfacing, or up to several hours after a dive. divers have to breathe a gas which is at the same pressure as their surroundings, which can be much greater than on the surface. the ambient pressure underwater increases by 1 standard atmosphere (100 kpa) for every 10 metres (33 ft) of depth. the principal conditions are: decompression illness (which covers decompression sickness and arterial gas embolism); nitrogen narcosis; high pressure nervous syndrome; oxygen toxicity; and pulmonary barotrauma (burst lung). although some of these may occur in other settings, they are of particular concern during diving activities. the disorders are caused by breathing gas at the high pressures encountered at depth, and divers will often breathe a gas mixture different from air to mitigate these effects. nitrox, which contains more oxygen and less nitrogen is commonly used as a breathing gas to reduce the risk of decompression sickness at recreational depths (up to about 40 metres (130 ft)). helium may be added to reduce the amount of nitrogen and oxygen in the gas mixture when diving deeper, to reduce the effects of narcosis and to avoid the risk of oxygen toxicity. this is complicated at depths beyond about 150 metres (500 ft), because a helium–oxygen mixture (heliox) then causes high pressure nervous syndrome. more exotic mixtures such as hydreliox, a hydrogen–helium–oxygen mixture, are used at extreme depths to counteract this. decompression sickness main article: decompression sickness decompression sickness (dcs) occurs when gas, which has been breathed under high pressure and dissolved into the body tissues, forms bubbles as the pressure is reduced on ascent from a dive. the results may range from pain in the joints where the bubbles form to blockage of an artery leading to damage to the nervous system, paralysis or death. while bubbles can form anywhere in the body, dcs is most frequently observed in the shoulders, elbows, knees, and ankles. joint pain occurs in about 90% of dcs cases reported to the u.s. navy, with neurological symptoms and skin manifestations each present in 10% to 15% of cases. pulmonary dcs is very rare in divers. pulmonary barotrauma and arterial gas embolism if the breathing gas in a diver's lungs cannot freely escape during an ascent, the lungs may be expanded beyond their compliance, and the lung tissues may rupture, causing pulmonary barotrauma (pbt). the gas may then enter the arterial circulation producing arterial gas embolism (age), with effects similar to severe decompression sickness. gas bubbles within the arterial circulation can block the supply of blood to any part of the body, including the brain, and can therefore manifest a vast variety of symptoms. nitrogen narcosis main article: nitrogen narcosis nitrogen narcosis is caused by the pressure of dissolved gas in the body and produces temporary impairment to the nervous system. this results in alteration to thought processes and a decrease in the diver's ability to make judgements or calculations. it can also decrease motor skills, and worsen performance in tasks requiring manual dexterity. as depth increases, so does the pressure and hence the severity of the narcosis. the effects may vary widely from individual to individual, and from day to day for the same diver. because of the perception-altering effects of narcosis, a diver may not be aware of the symptoms, but studies have shown that impairment occurs nevertheless. the narcotic effects dissipate without lasting effect as the pressure decreases during ascent. high-pressure nervous syndrome helium is the least narcotic of all gases, and divers may use breathing mixtures containing a proportion of helium for dives exceeding about 40 metres (130 ft) deep. in the 1960s it was expected that helium narcosis would begin to become apparent at depths of 300 metres (1,000 ft). however, it was found that different symptoms, such as tremors, occurred at shallower depths around 150 metres (500 ft). this became known as high-pressure nervous syndrome, and its effects are found to result from both the absolute depth and the speed of descent. although the effects vary from person to person, they are stable and reproducible for the individual. oxygen toxicity main article: oxygen toxicity although oxygen is essential to life, in concentrations significantly greater than normal it becomes toxic, overcoming the body's natural defences (antioxidants), and causing cell death in any part of the body. the lungs and brain are particularly affected by high partial pressures of oxygen, such as are encountered in diving. the body can tolerate partial pressures of oxygen around 0.5 bars (50 kpa; 7.3 psi) indefinitely, and up to 1.4 bars (140 kpa; 20 psi) for many hours, but higher partial pressures rapidly increase the chance of the most dangerous effect of oxygen toxicity, a convulsion resembling an epileptic seizure. susceptibility to oxygen toxicity varies dramatically from person to person, and to a smaller extent from day to day for the same diver. prior to convulsion, several symptoms may be present – most distinctly that of an aura. treatments treatment of diving disorders depends on the specific disorder or combination of disorders, but two treatments are commonly associated with first aid and definitive treatment where diving is involved. these are first aid oxygen administration at high concentration, which is seldom contraindicated, and generally recommended as a default option in diving accidents where there is any significant probability of hypoxia, and hyperbaric oxygen therapy, which is the definitive treatment for most conditions of decompression illness. oxygen therapy main article: oxygen therapy the administration of oxygen as a medical intervention is common in diving medicine, both for first aid and for longer term treatment. normobaric oxygen administration at the highest available concentration is frequently used as first aid for any diving injury that may involve inert gas bubble formation in the tissues. there is epidemiological support for its use from a statistical study of cases recorded in a long term database. recompression and hyperbaric oxygen therapy main article: hyperbaric medicine recompression treatment in a hyperbaric chamber was initially used as a life-saving tool to treat decompression sickness in caisson workers and divers who stayed too long at depth and developed decompression sickness. in the 21st century, it is a highly specialized treatment modality found to be effective for treating many conditions where the administration of oxygen under pressure is beneficial. hyperbaric oxygen treatment is generally preferred when effective, as it is usually a more efficient and lower risk method of reducing symptoms of decompression illness, but in some cases recompression to pressures where oxygen toxicity is unacceptable may be required to eliminate the bubbles in the tissues in severe cases of decompression illness. medical examination for fitness to dive fitness to dive, (or medical fitness to dive), is the medical and physical suitability of a person to function safely in the underwater environment using underwater diving equipment and procedures. depending on the circumstances it may be established by a signed statement by the diver that he or she does not suffer from any of the listed disqualifying conditions and is able to manage the ordinary physical requirements of diving, to a detailed medical examination by a physician registered as a medical examiner of divers following a procedural checklist, and a legal document of fitness to dive issued by the medical examiner. the most important medical examination is the one before starting diving, as the diver can be screened to prevent exposure when a dangerous