Hypobaric hypoxia induced renal damage is mediated by altering redox pathway

Systemic hypobaric hypoxia is reported to cause renal damage; nevertheless the exact pathophysiological mechanisms are not completely understood. Therefore, the present study aims to explore renal pathophysiology by using proteomics approach under hypobaric hypoxia. Six to eight week old male Sprague Dawley rats were exposed to hypobaric hypoxia equivalent to altitude of 7628 metres (pO₂-282mmhg) at 28°C and 55% humidity in decompression chamber for different time intervals; 1, 3, and7 days. Various physiological, proteomic and bioinformatic studies were carried out to examine the effect of chronic hypobaric hypoxia on kidney. Our data demonstrated mild to moderate degenerative tubular changes, altered renal function, injury biomarkers and systolic blood pressure with increase in duration of hypobaric hypoxia exposure. Renal proteomic analysis showed 38 differential expressed spots, out of which 25 spots were down regulated and 13 were up regulated in 7 dayhypobarichypoxic exposure group of rats as compared to normoxia control. Identified proteins were involved in specific molecular changes pertinent to endogenous redox pathways, cellular integrity and energy metabolism. The study provides an empirical evidence of renal homeostasis under hypobaric hypoxia by investigating both physiological and proteomics changes. The identification of explicit key proteins provides a valuable clue about redox signalling mediated renal damage under hypobaric hypoxia.

Acute and Chronic Gas Bubble Lesions in Cetaceans Stranded in the United Kingdom

The first evidence suggestive of in vivo gas bubble formation in cetacea, including eight animals stranded in the UK, has recently been reported. This article presents the pathologic findings from these eight UK-stranded cetaceans and two additional UK-stranded cetacean cases in detail. Hepatic gas-filled cavitary lesions (0.2-6.0 cm diameter) involving approximately 5–90% of the liver volume were found in four (two juvenile, two adult) Risso's dolphins ( Grampus griseus), three (two adult, one juvenile) common dolphins ( Delphinus delphis), an adult Blainville's beaked whale ( Mesoplodon densirostris), and an adult harbour porpoise ( Phocoena phocoena). Histopathologic examination of the seven dolphin cases with gross liver cavities revealed variable degrees of pericavitary fibrosis, microscopic, intrahepatic, spherical, nonstaining cavities (typically 50–750 μm in diameter) consistent with gas emboli within distended portal vessels and sinusoids and associated with hepatic tissue compression, hemorrhages, fibrin/organizing thrombi, and foci of acute hepatocellular necrosis. Two common dolphins also had multiple and bilateral gross renal cavities (2.0–9.0 mm diameter) that, microscopically, were consistent with acute ( n = 2) and chronic ( n = 1) arterial gas emboli-induced renal infarcts. Microscopic, bubblelike cavities were also found in mesenteric lymph node ( n = 4), adrenal ( n = 2), spleen ( n = 2), pulmonary associated lymph node ( n = 1), posterior cervical lymph node ( n = 1), and thyroid ( n = 1). No bacterial organisms were isolated from five of six cavitated livers and one of one cavitated kidneys. The etiology and pathogenesis of these lesions are not known, although a decompression-related mechanism involving embolism of intestinal gas or de novo gas bubble (emboli) development derived from tissues supersaturated with nitrogen is suspected.

“Gas and Fat Embolic Syndrome” Involving a Mass Stranding of Beaked Whales (Family Ziphiidae) Exposed to Anthropogenic Sonar Signals

A study of the lesions of beaked whales (BWs) in a recent mass stranding in the Canary Islands following naval exercises provides a possible explanation of the relationship between anthropogenic, acoustic (sonar) activities and the stranding and death of marine mammals. Fourteen BWs were stranded in the Canary Islands close to the site of an international naval exercise (Neo-Tapon 2002) held on 24 September 2002. Strandings began about 4 hours after the onset of midfrequency sonar activity. Eight Cuvier's BWs (Ziphius cavirostris), one Blainville's BW (Mesoplodon densirostris), and one Gervais' BW (Mesoplodon europaeus) were examined postmortem and studied histopathologically. No inflammatory or neoplastic processes were noted, and no pathogens were identified. Macroscopically, whales had severe, diffuse congestion and hemorrhage, especially around the acoustic jaw fat, ears, brain, and kidneys. Gas bubble-associated lesions and fat embolism were observed in the vessels and parenchyma of vital organs. In vivo bubble formation associated with sonar exposure that may have been exacerbated by modified diving behavior caused nitrogen supersaturation above a threshold value normally tolerated by the tissues (as occurs in decompression sickness). Alternatively, the effect that sonar has on tissues that have been supersaturated with nitrogen gas could be such that it lowers the threshold for the expansion of in vivo bubble precursors (gas nuclei). Exclusively or in combination, these mechanisms may enhance and maintain bubble growth or initiate embolism. Severely injured whales died or became stranded and died due to cardiovascular collapse during beaching. The present study demonstrates a new pathologic entity in cetaceans. The syndrome is apparently induced by exposure to mid-frequency sonar signals and particularly affects deep, long-duration, repetitive-diving species like BWs.

Enriched Air Nitrox Breathing Reduces Venous Gas Bubbles after Simulated SCUBA Diving: A Double-Blind Cross-Over Randomized Trial

Objective

To test the hypothesis whether enriched air nitrox (EAN) breathing during simulated diving reduces decompression stress when compared to compressed air breathing as assessed by intravascular bubble formation after decompression.

Methods

Human volunteers underwent a first simulated dive breathing compressed air to include subjects prone to post-decompression venous gas bubbling. Twelve subjects prone to bubbling underwent a double-blind, randomized, cross-over trial including one simulated dive breathing compressed air, and one dive breathing EAN (36% O₂) in a hyperbaric chamber, with identical diving profiles (28 msw for 55 minutes). Intravascular bubble formation was assessed after decompression using pulmonary artery pulsed Doppler.

Results

Twelve subjects showing high bubble production were included for the cross-over trial, and all completed the experimental protocol. In the randomized protocol, EAN significantly reduced the bubble score at all time points (cumulative bubble scores: 1 [0–3.5] vs. 8 [4.5–10]; P < 0.001). Three decompression incidents, all presenting as cutaneous itching, occurred in the air versus zero in the EAN group (P = 0.217). Weak correlations were observed between bubble scores and age or body mass index, respectively.

Conclusion

EAN breathing markedly reduces venous gas bubble emboli after decompression in volunteers selected for susceptibility for intravascular bubble formation. When using similar diving profiles and avoiding oxygen toxicity limits, EAN increases safety of diving as compared to compressed air breathing.

Trial Registration

ISRCTN 31681480

[Role of tumor necrosis factor-alpha in spinal cord injury of rabbits with decompression sickness]

OBJECTIVE

To observe the pathological changes in rabbits with spinal cord injury induced by decompression sickness (DCS), and to investigate the role of tumor necrosis factor-alpha (TNF-α) in spinal cord injury induced by DCS.

METHODS

Rabbits were randomly divided into normal control group, DCS group, and safe decompression group. The rabbit model of DCS was established. Light microscopy, real-time PCR, and immunohistochemical method were used to observe the pathomorphological changes in the thoracolumbar spinal cord and the mRNA and protein expression of TNF-α, respectively. The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) was used to observe the apoptosis in the spinal cord.

RESULTS

In the DCS group, cavities formed in the white matter of spinal cord and gliosis occurred around necrotic areas. Moreover, the mRNA and protein expression of TNF-α was significantly higher in the DCS group than in the normal control group and the safe decompression group (P<0.01). The results of TUNEL showed that the number of positive apoptotic cells was significantly larger in the DCS group than in the normal control group and the safe decompression group (P<0.05).

CONCLUSION

Apoptosis plays an important role in spinal cord injury induced by DCS. In the early stage of DCS, the massive release of TNF-α initiates apoptosis and contributes to the pathological changes in spinal cord injury induced by DCS.

Hyperbaric oxygen treatment reduced the lung injury of type II decompression sickness

OBJECTIVE

To detect the ultrastructural changes in rabbits with type II decompression sickness (DCS), and study the therapeutic effects of hyperbaric oxygen (HBO).

METHODS

Twenty-seven male New Zealand rabbits were randomly divided equally into the DCS group, HBO treatment group and control group. Experimental models of each group were prepared. Lung apex tissues were harvested to prepare paraffin- and EPON812-embedded tissues.

RESULTS

In the DCS group, macroscopic and histological examination revealed severe and rapid damage to lung tissue. Ultrastructural examination revealed exudation of red blood cells in the alveolar space. Type I alveolar epithelial cells exhibited retracted cell processes and swollen mitochondria, and type II cells showed highly swollen mitochondria and decrease in cytoplasmic lamellar bodies. Dilatation and congestion of capillary vessels were accompanied by swelling of endothelial cells and incomplete basement membrane. In the HBO treatment group, the findings were somewhat similar to those in the DCS group, but the extent of damage was lesser. Only a small amount of tiny bubbles could be seen in the blood vessels. Type I alveolar epithelia cells and endothelial cells of the capillaries illustrated slight shortening of cells, swollen cytoplasm and decreased cell processes. Type II alveolar epithelial cells showed slight swelling of the mitochondria, decreased vacuolar degeneration of lamellar bodies, and increase in the number of free ribosomes.

CONCLUSIONS

Our microscopic and ultrastructural findings confirm that the lung is an important organ affected by DCS. We also confirmed that HBO can alleviate DCS-induced pulmonary damage.

Expression changes of TNF-α, IL-1β and IL-6 in the rat lung of decompression sickness induced by fast buoyancy ascent escape

Fast buoyancy ascent escape is the general submarine escape manner adopted by the majority of naval forces all over the world. However, if hyperbaric exposure time exceeds the time limit, fast buoyancy ascent escape has a high risk to result in decompression sickness (DCS). Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-6 have been all implicated in the process of inflammation associated with acute lung injury (ALI). Our work demonstrated that DCS caused by simulated fast buoyancy ascent escape could induce ALβ in the rat model. The purpose of the present work was to study the expression changes of TNF-α, IL-1β and IL-6 in the rat lung affected by DCS caused by simulated fast buoyancy ascent escape. The lung tissue mRNA levels of TNF-α, Il-1β and Il-6 were significantly increased at 0.5 hour after DCS caused by simulated fast buoyancy ascent escape. The lung contents of TNF-α, IL-1β and IL-6 were at an expression peak at 0.5 hour, although showing no statistical difference when compared with the normal control group. In conclusion, the rat lung expression variations of TNF-α, IL-1β and IL-6 are the most obvious at 0.5 hour within 24 hours after the lung injury by DCS caused by simulated fast buoyancy ascent escape.

MRI of the central nervous system in rats following heliox saturation decompression

AIMS

The main objectives of the present study was to establish an animal model of decompression sickness (DCS) after heliox saturation diving, and to use this model to evaluate possible morphological changes in the CNS induced by DCS using structural MRI.

METHODS

Two groups of rats were pressurized with heliox to 5 bar (pO2 = 50 kPa). The saturation time was three hours; decompression rate was 1 bar/10 seconds or 1 bar/20 seconds. A 7.0 Tesla small animal MRI scanner was used for detection of possible morphological changes in the brain and spinal cord, two hours and one week after the dive, compared to one week prior to the dive.

RESULTS

Neurological symptoms of DCS were observed in seven out of 10 animals. MRI of the brain and spinal cord did not reveal any morphological CNS injuries.

CONCLUSION

This diving procedure was successful in causing DCS in a large proportion of the animals. However, despite massive neurological signs of DCS, no visible CNS injuries were observed in the MRI scans.

Expression changes of inflammatory factors in the rat lung of decompression sickness induced by fast buoyancy ascent escape

Fast buoyancy ascent escape is one of the major naval submarine escape maneuvers. Decompression sickness (DCS) is the major bottleneck to increase the depth of fast buoyancy ascent escape. Rapid decompression induces the release of inflammatory mediators and results in tissue inflammation cascades and a protective anti-inflammatory response. In our previous study, we found that DCS caused by simulated fast buoyancy ascent escape could induce acute lung injury (ALI) and the expression changes of the proinflammatory cytokines: tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β and IL-6 in rat lung tissue. In order to study the expression change characteristics of TNF-α, IL-1β, IL-6, IL-10 and IL-13 in the rat lung of DCS caused by simulated fast buoyancy ascent escape, we detected the rat lung mRNA and protein levels of TNF-α, IL-1β, IL-6, IL-10 and IL-13 at 0.5 hour after DCS caused by simulated fast buoyancy ascent escape (fast escape group), compared with the normal control group (control group) and diving DCS (decompression group). We observed that DCS caused by simulated fast buoyancy ascent escape could increase the mRNA levels of TNF-α, IL-1β, IL-6, IL-10, and the protein levels of TNF-α, IL-10 in rat lung tissue. At the same time, we found that the protein level of IL-13 was also downregulated in rat lung tissue. TNF-α, IL-10 and IL-13 may be involved in the process of the rat lung injury of DCS caused by simulated fast buoyancy ascent escape. In conclusion, the expression changes of inflammatory factors in the rat lung of DCS caused by simulated fast buoyancy ascent escape were probably different from that in the rat lung of diving DCS, which indicated that the pathological mechanism of DCS caused by simulated fast buoyancy ascent escape might be different from that of diving DCS.

Decompression sickness ('the bends') in sea turtles

Decompression sickness (DCS), as clinically diagnosed by reversal of symptoms with recompression, has never been reported in aquatic breath-hold diving vertebrates despite the occurrence of tissue gas tensions sufficient for bubble formation and injury in terrestrial animals. Similarly to diving mammals, sea turtles manage gas exchange and decompression through anatomical, physiological, and behavioral adaptations. In the former group, DCS-like lesions have been observed on necropsies following behavioral disturbance such as high-powered acoustic sources (e.g. active sonar) and in bycaught animals. In sea turtles, in spite of abundant literature on diving physiology and bycatch interference, this is the first report of DCS-like symptoms and lesions. We diagnosed a clinico-pathological condition consistent with DCS in 29 gas-embolized loggerhead sea turtles Caretta caretta from a sample of 67. Fifty-nine were recovered alive and 8 had recently died following bycatch in trawls and gillnets of local fisheries from the east coast of Spain. Gas embolization and distribution in vital organs were evaluated through conventional radiography, computed tomography, and ultrasound. Additionally, positive response following repressurization was clinically observed in 2 live affected turtles. Gas embolism was also observed postmortem in carcasses and tissues as described in cetaceans and human divers. Compositional gas analysis of intravascular bubbles was consistent with DCS. Definitive diagnosis of DCS in sea turtles opens a new era for research in sea turtle diving physiology, conservation, and bycatch impact mitigation, as well as for comparative studies in other air-breathing marine vertebrates and human divers.

Diving fatality investigations: recent changes

Modifications to the investigation procedures in diving fatalities have been incorporated into the data acquisition by diving accident investigators. The most germane proposal for investigators assessing diving fatalities is to delay the drawing of conclusions until all relevant diving information is known. This includes: the accumulation and integration of the pathological data; the access to dive computer information; re-enactments of diving incidents; post-mortem CT scans and the interpretation of intravascular and tissue gas detected. These are all discussed, with reference to the established literature and recent publications.

Simulated dive in rats lead to acute changes in cerebral blood flow on MRI, but no cerebral injuries to grey or white matter

In this study, the effect of a simulated dive on rat brain was investigated using several magnetic resonance imaging (MRI)-methods and immunohistochemistry. Rats were randomly assigned to a dive- or a control group. The dive group was exposed to a simulated air dive to 600 kPa for 45 min. Pulmonary artery was monitored for vascular gas bubbles by ultrasound. MRI was performed 1 h after decompression and at one and 2 weeks after the dive with a different combination of MRI sequences at each time point. Two weeks after decompression, rats were sacrificed and brains were prepared for histology. Dived rats had a different time-curve for the dynamic contrast-enhanced MRI signal than controls with higher relative signal intensity, a tendency towards longer time to peak and a larger area under the curve for the whole brain on the acute MRI scan. On MRI, 1 and 2 weeks after dive, T2-maps showed no signal abnormalities or morphological changes. However, region of interest based measurements of T2 showed higher T2 in the brain stem among decompressed animals than controls after one and 2 weeks. Microscopical examination including immunohistochemistry did not reveal apparent structural or cellular injuries in any part of the rat brains. These observations indicate that severe decompression does not seem to cause any structural or cellular injury to the brain tissue of the rat, but may cause circulatory changes in the brain perfusion in the acute phase.

Diving under a microscope--a new simple and versatile in vitro diving device for fluorescence and confocal microscopy allowing the controls of hydrostatic pressure, gas pressures, and kinetics of gas saturation

How underwater diving effects the function of the arterial wall and the activities of endothelial cells is the focus of recent studies on decompression sickness. Here we describe an in vitro diving system constructed to achieve real-time monitoring of cell activity during simulated dives under fluorescent microscopy and confocal microscopy. A 1-mL chamber with sapphire windows on both sides and located on the stage of an inverted microscope was built to allow in vitro diving simulation of isolated cells or arteries in which activities during diving are monitored in real-time via fluorescent microscopy and confocal microscopy. Speed of compression and decompression can range from 20 to 2000 kPa/min, allowing systemic pressure to range up to 6500 kPa. Diving temperature is controlled at 37°C. During air dive simulation oxygen partial pressure is optically monitored. Perfusion speed can range from 0.05 to 10 mL/min. The system can support physiological viability of in vitro samples for real-time monitoring of cellular activity during diving. It allows regulations of pressure, speeds of compression and decompression, temperature, gas saturation, and perfusion speed. It will be a valuable tool for hyperbaric research.

Diffusion tensor MRI of spinal decompression sickness

In order to develop more sensitive imaging tools for clinical use and basic research of spinal decompression sickness (DCS), we used diffusion tensor MRI (DTI) validated by histology to assess DCS-related tissue injury in sheep spinal cords. DTI is based on the measurement of water diffusion indices, including fractional anisotropy (FA) and mean diffusion (MD) to detect tissue microstructural abnormalities. In this study, we measured FA and MD in white and gray matter spinal cord regions in samples taken from sheep following hyperbaric exposure to 60-132 fsw and 0-180 minutes of oxygen pre-breathing treatment before rapid decompression. The main finding of the study was that decompression from >60 fsw resulted in reduced FA that was associated with cell death and disrupted tissue microstructure in spinal cord white matter tracts. Additionally, animals exposed to prolonged oxygen pre-breathing prior to decompression demonstrated reduced MD in spinal cord gray matter regions regardless of dive depth. To our knowledge, this is the first study to demonstrate the utility of DTI for the investigation of DCS-related injury and to define DTI biomarkers of spinal DCS.

A forensic diving medicine examination of a highly publicised scuba diving fatality

A high-profile diving death occurred in 2003 at the site of the wreck of the SS Yongala off the Queensland coast. The victim's buddy, her husband, was accused of her murder and found guilty of manslaughter in an Australian court. A detailed analysis of all the evidence concerning this fatality suggests alternative medical reasons for her death. The value of decompression computers in determining the diving details and of CT scans in clarifying autopsy findings is demonstrated. The victim was medically, physically and psychologically unfit to undertake the fatal dive. She was inexperienced and inadequately supervised. She was over-weighted and exposed for the first time to difficult currents. The analysis of the dive demonstrates how important it is to consider the interaction of all factors and to not make deductions from individual items of information. It also highlights the importance of early liaison between expert divers, technicians, diving clinicians and pathologists, if inappropriate conclusions are to be avoided.

Protective effects of fluoxetine on decompression sickness in mice

Massive bubble formation after diving can lead to decompression sickness (DCS) that can result in central nervous system disorders or even death. Bubbles alter the vascular endothelium and activate blood cells and inflammatory pathways, leading to a systemic pathophysiological process that promotes ischemic damage. Fluoxetine, a well-known antidepressant, is recognized as having anti-inflammatory properties at the systemic level, as well as in the setting of cerebral ischemia. We report a beneficial clinical effect associated with fluoxetine in experimental DCS. 91 mice were subjected to a simulated dive at 90 msw for 45 min before rapid decompression. The experimental group received 50 mg/kg of fluoxetine 18 hours before hyperbaric exposure (n = 46) while controls were not treated (n = 45). Clinical assessment took place over a period of 30 min after surfacing. At the end, blood samples were collected for blood cells counts and cytokine IL-6 detection. There were significantly fewer manifestations of DCS in the fluoxetine group than in the controls (43.5% versus 75.5%, respectively; p = 0.004). Survivors showed a better and significant neurological recovery with fluoxetine. Platelets and red cells were significantly decreased after decompression in controls but not in the treated mice. Fluoxetine reduced circulating IL-6, a relevant marker of systemic inflammation in DCS. We concluded that fluoxetine decreased the incidence of DCS and improved motor recovery, by limiting inflammation processes.

Evidence of injury caused by gas bubbles in a live marine mammal: barotrauma in a California sea lion Zalophus californianus

A yearling male California sea lion Zalophus californianus with hypermetric ataxia and bilateral negative menace reflexes was brought to The Marine Mammal Center, Sausalito, California, U.S.A., in late 2009 for medical assessment and treatment. The clinical signs were due to multiple gas bubbles within the cerebellum. These lesions were intraparenchymal, multifocal to coalescing, spherical to ovoid, and varied from 0.5 to 2.4 cm diameter. The gas composed 21.3% of the total cerebellum volume. Three rib fractures were also noted during diagnostic evaluation and were presumed to be associated with the gas bubbles in the brain. The progression of clinical signs and lesion appearance were monitored with magnetic resonance imaging, cognitive function testing and computed tomography. Gas filled voids in the cerebellum were filled with fluid on follow up images. Clinical signs resolved and the sea lion was released with a satellite tag attached. Post release the animal travelled approximately 75 km north and 80 km south of the release site and the tag recorded dives of over 150 m depth. The animal re-stranded 25 d following release and died of a subacute bronchopneumonia and pleuritis. This is the first instance of clinical injury due to gas bubble formation described in a living pinniped and the first sea lion with quantifiable cerebellar damage to take part in spatial learning and memory testing.

[A theoretical estimation of the safety of dives culminating in an uninterrupted lifting]

It has been shown using the previously developed model of decompression sickness, which determines the cumulative probability of the development of the symptoms of this illness by the exponential equation whose index is the integral function of cumulative risk of damage to all body tissues by bubbles, Fcum(t) = SigmaFn(t), that underwater dives are practically safe if the function Fcum(t) during its growth will not exceed some small value Fcum-max = SigmaFn-max. Using the hypothetical values of parameters of tissues and functions Fn(t), the curves depth-duration for practically safe non-stop dives on respiration with air and with mixtures of oxygen with helium, neon, and argon have been calculated. The distributions of Fn-max values relative to the half-times of washout of the inert gas from tissues have been obtained, which show that the tissues that experience the largest risks of bubble lesions are different for dives of different duration. A comparison of the curves shows that the short-term dives with air are less dangerous and the long-term dives are more dangerous than the dives with helium-oxygen mixture. It has been shown that the least risk of bubble lesions of tissues arises on dives with neon-oxygen mixture and the greatest risk, on dives with argon-oxygen mixture.

Decompression Sickness: MRI of the Spinal Cord

Decompression sickness (DCS) typically causes changes in the white matter of the spinal cord on MR imaging. We present a case of DCS in a scuba diver with dorsal white matter lesions typical of venous infarction. In addition, some central gray matter involvement was noted. Characteristic features of venous spinal cord infarction can be recognized on MR imaging in DCS but may be more extensive in severe cases.

[Retinal examination with ophthalmic endoscopy in forensic autopsy]

Autopsy by forensic pathologist is a main mean currently to determine the cause of sudden unexpected death. Retinal examination is important but seldom performed during a forensic autopsy for various reasons. The value of retina examination has not been recognized. With invention of ophthalmic endoscopy and its subsequent application in postmortem retina examination, it has proved to be useful adjunct to determine the cause of death and to estimate the postmortem interval.

Cerebro-spinal decompression sickness: report of two cases

STUDY DESIGN

Two case reports.

OBJECTIVE

To describe two unusual cases of deep diving followed by cerebro-spinal decompression sickness (DCS).

SETTING

Midlands Centre for Spinal Injuries, England.

METHODS

Observation of the outcome of two different cases of cerebro-spinal DCS, who have received two different modalities of treatment.

RESULTS

The first patient's symptoms developed after he surfaced, he was treated according to the US Navy treatment table 6. He also received steroids for almost 3 weeks. His MRI of the brain and spinal cord, which was performed within 24 h of injury did not show any abnormality, while a repeat MRI 3 weeks later revealed abnormal signals in the brain and spinal cord. The second patient's symptoms started before he surfaced, he was treated with Comex 30 treatment table for 14 days and received no steroids, his MRI was performed 3 days after the injury showed high signals in the brain and spinal cord.

CONCLUSION

Both divers developed cerebro-spinal dysfunction. They had encephalopathy (manifested by loss of consciousness), which indicates bilateral cerebral dysfunction. DCS can occur even when dives are conducted according to the procedures described by the US Navy. The use of high-dose steroids has not been formally tested in DCS; their use is controversial.

Evaluation of a porcine model to study in vivo platelet activation

INTRODUCTION

In order to investigate if decompression sickness involves platelet activation an animal model was evaluated.

MATERIALS AND METHODS

Twenty-four thiopentone-midazolam-fentanyl-anaesthetized pigs in four groups received 5-min infusions of adenosine diphosphate (25 mg/kg) or platelet activating factor (0.4 microg/kg). Groups 1 and 2 (adenosine diphosphate, n=6 and platelet activating factor, n=6) were studied for 30 min and then sacrificed. Groups 3 and 4 (adenosine diphosphate, n=6 and platelet activating factor, n=6) were sacrificed immediately afterwards to study short-term changes. Haemodynamics, platelet counts and post mortem lung platelet aggregates were registered. Groups 1 and 2 also had indium platelet labelling, lung scintigraphy and platelet accumulation index calculations performed.

RESULTS

Adenosine diphosphate induced immediate and more profound transient shocks. Platelet and leukocyte count decreases and occurrences of post mortem lung platelet aggregates were significantly more profound in the 5-min adenosine diphosphate group (Group 3) than in the platelet activating factor group (Group 4). With platelet labelling there were positive platelet accumulation index trends in the 30-min adenosine diphosphate group (Group 1). Adenosine diphosphate also produced platelet aggregation in platelet-rich porcine plasma. Only adenosine diphosphate (an intermediate platelet agonist) showed signs of platelet activation when considering all platelet parameters. The model should be further evaluated with different bolus doses of adenosine diphosphate, but may be used to evaluate if gas bubbles introduced into the circulation (as with decompression sickness), or possibly if clinical drugs, might produce platelet activation in vivo.

Fatal scuba diving incident with massive gas embolism in cerebral and spinal arteries

CT and MRI have the potential to become useful adjuncts to forensic autopsy in the near future. The examination of fatal injuries facilitates a profound experience in the clinical-radiological examination of these cases; the more severe findings in corpses with autopsy verification can help one to understand the tiny signs seen in clinical cases of surviving victims. We present the case of a 44-year-old male diver who died from severe decompression sickness after rapid ascent from approximately 120 m. Post-mortem CT and MRI studies of the brain and spinal cord revealed extensive gas inclusions in cerebral arteries, spinal arteries and cerebrospinal fluid (CSF) spaces, while the intracranial venous sinuses remained unaffected. These findings were confirmed at autopsy. Appropriate imaging techniques can help forensic pathologists to aim their autopsies at findings that might otherwise remain undetected.

Cumulative sperm whale bone damage and the bends

Diving mosasaurs, plesiosaurs, and humans develop dysbaric osteonecrosis from end-artery nitrogen embolism ("the bends") in certain bones. Sixteen sperm whales from calves to large adults showed a size-related development of osteonecrosis in chevron and rib bone articulations, deltoid crests, and nasal bones. Occurrence in animals from the Pacific and Atlantic oceans over 111 years made a pathophysiological diagnosis of dysbarism most likely. Decompression avoidance therefore may constrain diving behavior. This suggests why some deep-diving mammals show periodic shallow-depth activity and why gas emboli are found in animals driven to surface precipitously by acoustic stressors such as mid-frequency sonar systems.

Consensus factors used by experts in the diagnosis of decompression illness

INTRODUCTION

The diagnosis of decompression illness (DCI) is entirely based on clinical findings and DCI experts are rare. Of all the chambers reporting to Diver's Alert Network (DAN), 86% see less than 10 cases per year. Simulated diving injury cases (vignettes) were used to identify diagnostic factors important to 11 international experts attending the 2003 Undersea and Hyperbaric Medical Society symposium on DCI diagnosis.

METHODS

There were 200 vignettes evaluated for the probability of DCS and/or arterial gas embolism (AGE). Vignettes were constructed from 141 factors that modeled information from DAN's emergency call system. Factor probability mirrored DAN's 2001 Report on Decompression Illness and Diving Fatalities. Factors included: diver characteristics, exposure characteristics, signs, symptoms, treatment, and response. Multiple linear regression with stepwise elimination identified and ordered the significant factors in terms of their importance to the experts. Results were confirmed with logistic regression.

RESULTS

For DCS, the top five factors in order of importance were: 1) a neurological symptom as the primary presenting symptom; 2) onset time of symptoms; 3) joint pain as a presenting symptom; 4) any relief after recompression treatment; and 5) the maximum depth of the last dive. For AGE, the top five factors were: 1) onset time of symptoms; 2) altered consciousness; 3) any neurological symptoms as a presenting symptom; 4) motor weakness; and 5) seizure as the primary presenting symptom. Age, gender, or physical characteristics were not statistically important.

CONCLUSIONS

The vignette concept may be useful in the development of consensus standards for DCI diagnosis.

Magnetic Resonance Imaging and Neuropathology Findings in the Goat Nervous System following Hyperbaric Exposures

Divers may be at risk of long-term CNS damage from non-symptomatic hyperbaric exposure. We investigated the effect of severe, controlled hyperbaric exposure on a group of healthy goats with similar histories. Thirty goats were exposed to various dive profiles over a period of 5 years, with 17 experiencing decompression sickness (DCS). Brains were scanned using magnetic resonance (MR) imaging techniques. The animals were then culled and grossly examined, with the brain and spinal cord sent for neuropathological examination. No significant correlation was found between age, years diving, DCS or exposure to pressure with MR-detectable lesions in the brain, or with neuropathological lesions in the brain or spinal cord. However, spinal scarring was noted in 3 animals that had suffered from spinal DCS.

[Idiopathic medullary decompression sickness: myth or reality?]

Severe decompression sickness occurs unfrequently, with, generally an identifying cause (error in decompression protocols, promoting factors.). We report a case of severe spinal cord damage; onset after a common dive, neither deep nor long, without any promoting factor, absence of responsiveness to recompression, three hours post-dive, importance of MRI signal abnormalities, make us to point out the confounding variability of onset and evolution of such illness.

Risk of decompression illness among 230 divers in relation to the presence and size of patent foramen ovale

BACKGROUND

The risk of developing decompression illness (DCI) in divers with a patent foramen ovale (PFO) has not been directly determined so far; neither has it been assessed in relation to the PFO's size.

METHODS

In 230 scuba divers (age 39+/-8 years), contrast trans-oesophageal echocardiography (TEE) was performed for the detection and size grading (0-3) of PFO. Prior to TEE, the study individuals answered a detailed questionnaire about their health status and about their diving habits and accidents. For inclusion into the study, > or =200 dives and strict adherence to decompression tables were required.

RESULTS

Sixty-three divers (27%) had a PFO. Overall, the absolute risk of suffering a DCI event was 2.5 per 10(4) dives. There were 18 divers (29%) with, and 10 divers (6%) without, PFO who had experienced > or =1 major DCI events P=0.016. In the group with PFO, the incidence per 10(4) dives of a major DCI, a DCI lasting longer than 24 h and of being treated in a decompression chamber amounted to 5.1 (median 0, interquartile range [IQR] 0-10.0), 1.9 (median 0, IQR 0-4.0) and 3.6 (median 0, IQR 0-9.8), respectively and was 4.8-12.9-fold higher than in the group without PFO (P<0.001). The risk of suffering a major DCI, of a DCI lasting longer than 24 h and of being treated by recompression increased with rising PFO size.

CONCLUSION

The presence of a PFO is related to a low absolute risk of suffering five major DCI events per 10(4) dives, the odds of which is five times as high as in divers without PFO. The risk of suffering a major DCI parallels PFO size.

Whales, sonar and decompression sickness

We do not yet know why whales occasionally strand after sonar has been deployed nearby, but such information is important for both naval undersea activities and the protection of marine mammals. Jepson et al. suggest that a peculiar gas-forming disease afflicting some stranded cetaceans could be a type of decompression sickness (DCS) resulting from exposure to mid-range sonar. However, neither decompression theory nor observation support the existence of a naturally occurring DCS in whales that is characterized by encapsulated, gas-filled cavities in the liver. Although gas-bubble formation may be aggravated by acoustic energy, more rigorous investigation is needed before sonar can be firmly linked to bubble formation in whales.

Detection of leukocyte activation in pigs with neurologic decompression sickness

BACKGROUND

In a porcine model of neurological decompression sickness (DCS), perivascular leukocyte activation was a consistent finding in biopsies of associated cutaneous DCS. This prompted examination of other organs for similar changes; multifocal leukocyte activation was found in the lungs (pneumonitis) and liver (hepatitis).

HYPOTHESIS

DCS in pigs induces leukocyte aggregation and activation in the liver and lungs.

METHODS

Male Yorkshire swine, trained to run on a modified treadmill, were compressed to 200 ft of seawater (fsw) in a dry, air-filled compression chamber. Decompression varied according to the profile under study.

RESULTS

In 106 pigs, evidence for association of leukocyte aggregation and activation with the clinical diagnosis of neurologic DCS was sought. The incidence of pneumonitis (20/68, 29% with DCS; 4/38, 10% without DCS) and hepatitis (23/68, 33% with DCS; 4/38, 10% without DCS) were strongly correlated with the incidence of neurologic DCS via Pearson Chi-squared analysis (p = 0.026 pneumonitis and p = 0.008 hepatitis). Additionally, Kruskal-Wallis rank analysis for numbers of organs involved and incidence of neurologic DCS showed a strong correlation between the increasing occurrence of neurologic DCS and the involvement of both the liver and lungs (p = 0.004).

CONCLUSIONS

The results imply that, at least in pigs, DCS induces leukocyte aggregation and activation in the liver and lungs. These organs are not normally considered targets of DCS. Leukocyte aggregation in these organs may be related to their roles as highly perfused organs. Leukocyte aggregation may be a marker for DCS, providing further evidence for wider, systemic effects of DCS.

Cigarette smoking and decompression illness severity: a retrospective study in recreational divers

BACKGROUND

Severe decompression illness (DCI) could be more likely in cigarette smokers because of airway obstruction or vascular disease. The present study evaluated the severity of DCI as a function of cigarette smoking in recreational divers.

METHODS

We examined all DCI reports recorded in the Divers Alert Network (DAN) database from 1989 through 1997. Smoking history was quantified as heavy (>15 pack-years), light (0 to 15 pack-years), and never smoked. DCI symptoms were classified as severe (alteration in consciousness, balance or bladder/bowel control, motor weakness, visual symptoms, convulsions), moderate (other neurological symptoms), or mild (pain, skin, or nonspecific symptoms). The proportional odds model and generalized logits were used for the adjusted analysis when accounting for other covariates.

RESULTS

There were 4,350 patients included in the analysis. After adjustment for confounding variables, heavy smokers were more likely to have severe vs. mild symptoms than nonsmokers (OR = 1.88) (95% CI 1.36, 2.60) or light smokers (OR = 1.56) (95% CI 1.09, 2.23). Heavy smokers and light smokers were more likely to have severe vs. moderate symptoms than nonsmokers (OR = 1.36) (95% CI 1.06, 1.74) and (1.22) (1.02, 1.46), respectively. Although these data do not reveal whether smoking predisposes to DCI, the results are consistent with a tendency, when DCI occurs, for cigarette smoking to trigger more severe symptoms.

CONCLUSIONS

The data suggest that when DCI occurs in recreational divers, smoking is a risk factor for increased severity of symptoms.

[Acute myelopathy in a diver caused by decompression sickness. A case description and a survey of the literature]

INTRODUCTION

Decompression sickness (DS) is caused when bubbles of an inert gas usually nitrogen, since oxygen is metabolised in the tissues are released into the bloodstream and tissues during fast ascents once the atmospheric pressure is lowered near the surface. Neurological complications are its most serious form of expression and include vertigo, headache, stroke and acute myelopathy, among others. DS that affects the spinal cord is infrequent.

CASE REPORT

A male, 42 years old, who presented progressive tetraparesis 15 minutes after returning to the surface following several immersions up to 40 metres deep in the same day. Neurological exploration revealed tetraparesis that was predominantly distal and in the lower limbs, a posterior cord syndrome, urinary incontinence and neurogenic pain. Total column magnetic resonance imaging showed areas of diffused hypersignal in the T2 sequence in the thoracic and cervical (C2 to C6) regions, predominating in the posterior cords. The echocardiogram, transcranial Doppler and spirometric studies ruled out an arterial gas embolism following pulmonary barotrauma.

CONCLUSIONS

Spinal DS can give rise to a serious myelopathy, which affects the pyramidal pathway, posterior cords and sphincteral control, and which generally appears after sudden ascents from the deep dives.

[Central nervous system involvement in patients with decompression illness]

Dysbarism or decompression illness (DCI), a general term applied to all pathological changes secondary to altered environmental pressure, has two forms decompression sickness (DCS) and arterial gas embolism (AGE) after pulmonary barotrauma. Cerebral and spinal disorders have been symptomatically categorized as AGE and DCS, respectively. Magnetic resonance images (MRIs) of divers with DCI showed multiple cerebral infarction in the terminal and border zones of the brain arteries. In addition, there were no differences between MRI findings for compressed air and breath-hold divers. Although the pathogenesis of the brain is not well understood, we propose that arterialized bubbles passing through the lungs and heart involved the brain. From the mechanisms of bubble formation, however, this disorder has been classified as DCS. We propose that there is a difference between clinical and mechanical diagnoses in the criteria of brain DCI. In contrast to brain injury, the spinal cord is involved only in compressed air divers, and is caused by disturbed venous circulation due to bubbles in the epidural space. The best approach to prevent diving accidents is to make known the problems for professional and amateur divers.

Multiple sclerosis presenting as neurological decompression sickness in a U.S. navy diver

A case of clinically definite multiple sclerosis presenting as neurological decompression sickness is presented. A 23-yr-old U.S. Navy diver experienced onset of hypesthesia of the left upper trunk approximately 19 h after making two SCUBA dives. She did not seek medical attention until 3 wk later, at which time she was diagnosed with possible neurological decompression sickness. She was treated with hyperbaric oxygen, but demonstrated no improvement. Further evaluation led to the diagnosis of multiple sclerosis. This case underscores the potential similarity in neurological presentation between multiple sclerosis and decompression sickness. The differential diagnosis of neurological decompression sickness, particularly in atypical cases, should include multiple sclerosis. The appropriateness of medically clearing multiple sclerosis patients for diving is discussed.

Change of occurance of type 1 and type 2 decompression sickness of divers treated at the Croatian Naval Medical Institute in the period from 1967 to 2000

A significant change of occurrence (p=0.0343) of type 1 and type 2 decompression sickness (DCS) of divers in Croatia was observed in the period from 1991 to 2002 (type 1: n=26, 37.68% and type 2: n=43, 62.32%) compared with the period from 1967 to 1990 (type 1: n=93, 52.84% and type 2: n=83, 47.16%). The change was attributed to the extensive usage of diving computers and artificial gas mixtures which enable extended bottom times and deeper dives, thus putting divers at an increased decompression risk. The importance of the results of this report is in the fact that permanent neurological deficit occurs only after type 2 DCS. Injured divers with permanent loss after type 2 DCS are not fit for diving and require a long term medical care, thus becoming a significant public health problem.

MR imaging of subclinical cerebral decompression sickness. A case report

Diving accidents related to barotrauma constitute a unique subset of ischemic insults to the central nervous system. Victims may demonstrate components of arterial gas embolism, which has a propensity for cerebral involvement, and/or decompression sickness, with primarily spinal cord involvement. Decompression sickness-related radiology literature is very limited. We present our MR findings including FLAIR images in a decompression sickness patient with atypical presentation and review the related literature. We believe MR can be useful in follow-up studies and in early diagnosis of decompression sickness when symptoms do not fit the classic picture or loss of consciousness in surfacing.

Vascular leukocyte sequestration in decompression sickness and prophylactic hyperbaric oxygen therapy in rats

BACKGROUND

Evidence for a causal relationship between decompression sickness (DCS) and leukocyte sequestration was assessed in a rat model based on the effects of interventions which impede cell-to-cell adherence, including hyperbaric oxygen therapy (HBO2).

HYPOTHESIS

We hypothesized that leukocyte adhesion to vessels may play a role in DCS.

METHODS

Rats were subjected to decompression stress and their ability to ambulate on a rotating drum was assessed to quantify functional neurological deficits. Leukocyte adherence in the brain was measured by a myeloperoxidase (MPO) radioimmunoassay. Interventions included infusion of antibodies to render rats neutropenic or to inhibit leukocyte beta2 integrin adhesion molecules. Tissue gas bubbles were imaged and quantified using a transmission ultrasound camera.

RESULTS

Decompressed rats manifested a deficit in their ability to ambulate and a five-fold elevation in concentration of MPO in brain. Neutropenic rats, and those infused with antibody fragments to inhibit leukocyte beta2 integrins, did not exhibit brain MPO elevations, nor a deficit in ambulatory function. HBO2 was used in a prophylactic manner to address its ability to inhibit leukocyte beta2 integrin-mediated adherence without reducing the presence of decompression-induced bubbles. Prophylactic HBO2 prevented cerebral leukocyte sequestration and the performance deficit.

CONCLUSIONS

The results implicate beta2 integrin-mediated leukocyte adhesion in neurological deterioration after decompression stress, and offer new insight into the therapeutic action of HBO2. Immunomodulatory approaches, including prophylactic HBO2, may improve the safety of decompression procedures in undersea and space exploration.

Early and late morphological effects of experimental HPNS animal model of psychosis?

The high pressure neurological syndrome (HPNS), a neurological condition during elevated pressure especially in deep diving, has been simulated with experimental animals. Rats were subjected to 61 bars with slow pressure increase and one or two hours constant high pressure; subsequently the pressure was released to sea level within 20 seconds--leading to immediate oxygen depletion and death of animals--or with slow decompression rates allowing survival. In all animals, brains and partly other organs were investigated morphologically. In animals sacrificed immediately, subtle changes in different brain regions were found: symmetrical occurrence of dark neurons in the hippocampus formation, cortex and brain stem, reduced expression of tyrosin hydroxylase in the substantia nigra and enhanced expression of Bax protein in some of these regions. The dark neurons were only observed after aldehyde fixation, otherwise the brains were unaltered despite ultrarapid decrease of highly elevated pressure. In animals that were allowed to survive for different time periods, some of these subtle changes were equally noted by light and electron microscopy. Furthermore, the ventricles were enlarged, the astrocytic reaction in the hippocampus increased and some signs of the destruction of the adrenal gland were visible. We conclude, that HPNS leads to minimal changes within the nervous system. The behaviour of animals during pressure was slightly altered, the weights after the experiments reduced, but no lasting sequelae were noted. Since both in human and experimental deep diving conditions signs of psychosis were reported, this HPNS model must be considered as a tentative animal model of human psychosis.

Neurologic outcome of controlled compressed-air diving

The authors compared the neurologic, neuropsychological, and neuroradiologic status of military compressed-air divers without a history of neurologic decompression illness and controls. No gross differences in the neuropsychometric test results or abnormal neurologic findings were found. There was no correlation between test results, diving experience, and number and size of cerebral MRI lesions. Prevalence of cerebral lesions was not increased in divers. These results suggest that there are no long-term CNS sequelae in military divers if diving is performed under controlled conditions.

Neurological accidents caused by repetitive breath-hold dives: two case reports

We report two Japanese male professional breath-hold divers (33 and 39 years of age) who experienced neurological disorders during repetitive dives to over 20 m of seawater. One patient had right homonymous hemianopsia, and the other presented with right hemiparesis with facial involvement and sensory deficit. In addition, they each had a history of neurological problems following such dives. Magnetic resonance images of their brains disclosed multiple T2-weighted hyperintensities corresponding to their neurological symptoms. Their brain lesions suggest a multiple cerebral infarction caused by occlusion of the cerebral arteries. We conclude that the repetitive deep breath-hold dives induced the brain involvement.

Natural history of severe decompression sickness after rapid ascent from air saturation in a porcine model

We developed a swine model to describe the untreated natural history of severe decompression sickness (DCS) after direct ascent from saturation conditions. In a recompression chamber, neutered male Yorkshire swine were pressurized to a predetermined depth from 50-150 feet of seawater [fsw; 2.52-5.55 atmospheres absolute (ATA)]. After 22 h, they returned to the surface (1 ATA) at 30 fsw/min (0.91 ATA/min) without decompression stops and were observed. Depth was the primary predictor of DCS incidence (R = 0.52, P < 0.0001) and death (R = 0.54, P < 0.0001). Severe DCS, defined as neurological or cardiopulmonary impairment, occurred in 78 of 128 animals, and 42 of 51 animals with cardiopulmonary DCS died within 1 h after surfacing. Within 24 h, 29 of 30 survivors with neurological DCS completely resolved their deficits without intervention. Pretrial Monte Carlo analysis decreased subject requirement without sacrificing power. This model provides a useful platform for investigating the pathophysiology of severe DCS and testing therapeutic interventions. The results raise important questions about present models of human responses to similar decompressive insults.

Computed chest tomography in an animal model for decompression sickness: radiologic, physiologic, and pathologic findings

This study was conducted to investigate the early pulmonary effects of acute decompression in an animal model for human decompression sickness by CT and light microscopy. Ten test pigs were exposed to severe decompression stress in a chamber dive. Three pigs were kept at ambient pressure to serve as controls. Decompression stress was monitored by measurement of pulmonary artery pressure and arterial and venous Doppler recording of bubbles of inert gas. Chest CT was performed pre- and postdive and in addition the inflated lungs were examined after resection. Each lung was investigated by light microscopy. Hemodynamic data and bubble recordings reflected severe decompression stress in the ten test pigs. Computed tomography revealed large quantities of ectopic gas, predominantly intravascular, in three of ten pigs. These findings corresponded to maximum bubble counts in the Doppler study. The remaining test pigs showed lower bubble grades and no ectopic gas by CT. Sporadic interstitial edema was demonstrated in all animals--both test and control pigs--by CT of resected lungs and on histologic examination. A severe compression-decompression schedule can liberate large volumes of inert gas which are detectable by CT. Despite this severe decompression stress, which led to venous microembolism, CT and light microscopy did not demonstrate changes in lung structure related to the experimental dive. Increased extravascular lung water found in all animals may be due to infusion therapy.

[Structural changes in the parenchymatous organs in animals in venous gas embolism of varying intensity and acute decompression disease]

Structural changes in tissues of liver, kidneys and lungs were studied in guinea pigs in post-decompressive gas venous embolism of high and low intensity. In moderate gas venous embolism cells of the organs studied display cytoplasm vacuolization due to the rupture of inner mitochondrial membrane and appearance of single rounded spheroidal structure with homogeneous contents situated near the cell nuclei that were thought to reflect formation of gas bubble within the cell. Possible pathogenetic mechanisms of formation of chronic decompressive disorders in asymptomatic gas formation are discussed.

Probable decompression sickness in a trainee with atopic dermatitis

Hypobaric chamber training has a potential risk of inducing decompression sickness (DCS). A case of a patient with an atopic dermatitis who complained of paresthesia and numbness in his left arm and shoulder during the altitude exposure is presented here. His symptoms were severe enough for the attending medical officer to diagnose Type II DCS, but it turned out to be a probable case of simple skin bends requiring no treatment. The author can find no better explanation for this discrepancy than the contribution of dermatitis. The possibility of atopic dermatitis confounding the correct diagnosis of the severity of DCS is proposed.