Vital issues in computing decompression schedules from fundamentals. II. Diffusion versus blood perfusion in controlling blood: tissue exchange.
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Diving with self-contained underwater breathing apparatus (scuba) has become a popular recreational sports activity throughout the world. A high prevalence of cardiovascular disorders among the population makes it therefore likely that subjects suffering from cardiovascular problems may want to start scuba diving. Although scuba diving is not a competitive sport requiring athletic health conditions, a certain medical fitness is recommended because of the physical peculiarities of the underwater environment. Immersion alone will increase cardiac preload by central blood pooling with a rise in both cardiac output and blood pressure, counteracted by increased diuresis. Exposure to cold and increased oxygen partial pressure during scuba diving will additionally increase afterload by vasoconstrictive effects and may exert bradyarryhthmias in combination with breath-holds. Volumes of gas-filled body cavities will be affected by changing pressure (Figure 1), and inert gas components of the breathing gas mixture such as nitrogen in case of air breathing will dissolve in body tissues and venous blood with increasing alveolar inert gas pressure. During decompression a free gas phase may form in supersaturated tissues, resulting in the generation of inert gas microbubbles that are eliminated by the venous return to the lungs under normal circumstances. Certain cardiovascular conditions may have an impact on these physiological changes and pose the subject at risk of suffering adverse events from scuba diving. Arterial hypertension may be aggravated by underwater exercise and immersion. Symptomatic coronary artery disease and symptomatic heart rhythm disorders preclude diving. The occurrence of ventricular extrasystoles according to Lown classes I and II, and the presence of atrial fibrillation are considered relative contraindications in the absence of an aggravation following exercise. Asymptomatic subjects with Wolff-Parkinson-White syndrome may be allowed to dive, but in case of paroxysmal supraventricular tachycardia they must refrain from diving. Pacemakers will fail with increasing pressure, but some manufacturers have proven their products safe for pressure equivalents of up to 30 m of seawater, so that patients may dive uneventfully when staying within the 0-20 m depth range. Significant aortic or mitral valve stenosis will preclude diving, whereas regurgitation only will not be a problem. Right-to-left shunts have increasingly gained attention in diving medicine, since they may allow venous gas microbubbles to spill over to the arterial side of the circulation enabling the possibility of arterial gas embolism. Significant shunts thus preclude diving. The highly prevalent patent foramen ovale is considered a relative contraindication only when following certain recommendations for safe diving (Table 2). Metabolic disorders are of concern, since adiposity is associated with both, higher bubble grades in Doppler ultrasound detection after scuba dives when compared to normal subjects, and an increased epidemiologic risk of suffering from decompression illness. In conclusion, cardiovascular aspects are important in the assessment of fitness to dive, and certain cardiovascular conditions preclude scuba diving. Any history of cardiac disease or abnormalities detected during the routine medical examination should prompt to further evaluation and specialist referral.
There has been a steady increase in the number of recreational scuba divers in the last years, with a growing number of diving associated diseases involving ENT medicine. Disorders of the ears, sinuses and pharynx are those most common in divers. In particular, external otitis and barotrauma of the middle ear are commonly treated by every ENT specialist. They usually do not lead to any permanent complaints. Incidents involving the cochleovestibular system are less common, but can result in deafness, vertigo and tinnitus, and therefore have to be treated appropriately. To treat diving medical disorders, the physician has to have some basic understanding of the physical laws that lead to diving incidents. This article will inform the reader of the forces that are encountered by divers, and then give details of the treatment of acute ENT diseases which result from diving incidents.
Decompression illness (DCI) is becoming more prevalent as more people engage in activities involving extreme pressure environments such as recreational scuba-diving. Rapid diagnosis and treatment offer these patients the best chance of survival with minimal sequelae. It is thus important that critical care physicians are able to evaluate and diagnose the signs and symptoms of DCI. The cornerstones of current treatment include the administration of hyperbaric oxygen and adjunctive therapies such as hydration and medications. However, managing patients in a hyperbaric environment does present additional challenges with respect to the particular demands of critical care medicine in an altered pressure environment. This article reviews the underlying pathophysiology, clinical presentation and therapeutic options available to treat DCI, from the intensivist's perspective.
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We report a case of decompression illness in which the patient developed paraparesis during scuba diving after rapid ascent. MRI of the spine revealed a focal intramedullary lesion consistent with the symptoms. The pathophysiological and radiological aspects of spinal decompression illness are discussed.
This was a controlled cross-sectional study to investigate the prevalence of dysbaric osteonecrosis (DON) in military divers. MRI examinations of the large joints and adjacent bones were performed in a cross-sectional group of 32 highly experienced military divers and 28 non-divers matched for age and anthropometric data. Additional plain radiographs and follow-up controls were performed in all persons with signs certain or suspicious of DON. In two subject groups (one of divers and one of non-divers), lesions characteristic of DON were detected. From this controlled study, it may be concluded that MRI is a highly sensitive method to detect signs of osteonecrosis. It could be shown that the prevalence of bone lesions characteristic of osteonecrosis in highly experienced military divers is not higher than in non-diving subjects of comparable age. The outcome of this comparably small study group fits to the results of previous extensive studies performed with radiographs. The detected low incidence of DON in this collective may be due to the fact that military divers follow stricter selection criteria, decompression schemes and medical surveillance than commercial divers.
The pathophysiology, differential diagnosis, and currently available management of barotrauma affecting the ears and sinuses after scuba diving are reviewed, along with medical standards for resuming scuba diving after barotrauma has resolved.
Doppler ultrasound signals are widely used to grade the quantity of circulating venous bubbles in divers. Current techniques rely on trained observers, making the grading process both time-consuming and subjective. The automated detection of bubbles, however, is confounded by the presence of other signals, primarily those arising from blood motion. Empirical Mode Decomposition was used here to calculate the intrinsic mode functions (IMFs) of a number of Doppler ultrasound signals from recreational divers, post-decompression. The IMFs provide a basis set for signal decomposition, each IMF corresponding to a different timescale in the signal. Each signal was found to comprise approximately 20 IMFs: the precise number being dependent upon the nature of the signal. A method is presented to detect bubbles using the IMF; features are first identified in the individual heart cycles, these having been previously determined using a robust peak detection method, by examining deviations from the ensemble averaged IMF. Bubbles are then identified as features appearing in more than one IMF, with significant energy in the original signal. This method has been applied to a subset of the available database and appears to perform with good sensitivity even when the signal has variable signal strength.
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