Decompression sickness presenting as forearm swelling and peripheral neuropathy: a case report

Neurological symptoms after decompression from a dive are usually thought to be manifestations of central nervous system (CNS) decompression sickness (DCS). We present a case of DCS in which neurological symptoms are present but which the clinical findings, magnetic resonance imaging and electroneuromyographic studies suggest were caused by muscle injury and exacerbation of an existing peripheral neuropathy. This finding supports the alternative hypothesis that some neurological symptoms and signs in DCS are due to effects on peripheral nerves rather than the CNS.

Cutaneous lesions in swine after decompression: histopathology and ultrastructure

A detailed histopathologic description of skin lesions from a porcine model of decompression sickness (DCS) is presented. Pigs were dived in a dry chamber on a variety of profiles over an 11-mo period, with a 0.1-0.6 (10-60%) incidence of cutaneous lesions. The clinical appearance of the lesions evolved from irregular, sharply demarcated areas of erythema to violaceous and, eventually, darkly mottled macules. The lesions were biopsied under deep, sedative anesthesia. Histologic abnormalities were found in 91% (20/22) of the biopsies from clinically apparent cutaneous lesions. Vascular congestion was the most common finding. Focal areas of vasculitis were noted in 45% (10/22) of the lesions. Perivascular neutrophil infiltrates, edema, and occasionally, hemorrhage were also noted. Ultrastructural abnormalities were found in all of the lesions studied. Acute inflammation affecting the dermal vasculature was the most common finding. Platelets were rarely observed aggregating within vessels. The clinical and histologic features of cutaneous lesions in pigs after decompression are compared with previous accounts in humans. The model provides a useful tool for the study of cutaneous lesions in DCS and may be a means of exploring interventions in the disease.

Dysbaric osteonecrosis in divers and caisson workers. An animal model

Dysbaric osteonecrosis was induced successfully in adult sheep after 12 to 13, 24-hour exposures to compressed air (2.6-2.9 atmospheres absolute) during a 2-month period. All exposed sheep had decompression sickness and extensive bone and marrow necrosis in their long bones. Radiographic analysis of these progressive lesions showed mottled to distinct medullary opacities and endosteal thickening characteristic of dysbaric osteonecrosis. Six months after the last hyperbaric exposure, neovascularization of once ischemic fatty marrow was centripetal from the diaphyseal cortex. Proliferating endosteal new bone, fatty marrow calcification, and appositional new bone formation were widespread. Juxtaarticular osteonecrosis involved marrow fibrosis and loss of osteocytes in subchondral cortical bone. Tidemark reduplication in juxtaarticular bone and cartilage thinning suggested possible early osteoarthritis induction by recurrent episodes of transient ischemia after multiple hyperbaric exposures. Dysbaric osteonecrosis appears to involve a bone compartment syndrome of elevated intramedullary pressure initiated by decompression induced N2 bubble formation in the fatty marrow of the long bones. An animal model that can be used to investigate the pathogenesis, diagnosis, and treatment of dysbaric osteonecrosis is discussed.

Nature and incidence of bubbles in the spinal cord of decompressed goats

The nature of so-called autochthonous bubbles was investigated. Their presence in compressed/decompressed goats was compared with that in animals killed before decompression and in controls. Ten goats (group 1) were subjected to compression/decompression in air. Clinical signs of spinal decompression sickness usually occurred. Within 35 min of surfacing, the animals were given a lethal dose of thiopentone sodium, i.v.. Spinal cords were fixed by immersion in 10% formol saline. Histologically autochthonous bubbles appeared to arise from rupture of over-distended blood vessels. The incidence of grossly dilated empty vessels (GDEV) was recorded. Seven goats (group 2) were similarly compressed but killed before decompression. In five animals of group 1 there was a greater number of GDEV than in controls (group 3, seven animals) but in the other five animals the incidence was similar to the controls. The incidence of GDEV in group 2 was greater than in the controls (P < 0.05). The percentage of sections of spinal cord in which the meninges also contained GDEV was assessed. In all except two animals in group 1, the percentage was higher than in the controls, whereas in group 2 the percentage was higher than in the controls. The experiments show that autochthonous bubbles arise as an artifact and that intravascular bubbles arise in situ.

Magnetic resonance findings in scuba diving-related spinal cord decompression sickness

Scuba diving is associated with risk of severe decompression sickness (DCS type II), which results from rapid reduction of the environmental pressure sufficient to cause the formation into tissue or blood of inert gas bubbles previously loaded within tissues as a soluble phase. DCS type II constitutes a unique subset of ischemic insults to the central nervous system (CNS) with primarily involvement of the spinal cord. Ten patients with diving-related barotrauma underwent neurologic examination. Two of them presented progressive sensory and motor loss in the extremities at admission and were presumed affected by spinal cord DCS. Magnetic resonance imaging (MRI) demonstrated abnormalities in the white-matter tracts of the spinal cord in these patients, in each case corresponding to an area of the cord believed to be clinically involved. After a course of therapeutic recompressions, one patient was able to stand and walk a short distance, and MRI revealed a decreased extension of areas of spinal cord abnormalities. MRI has proved to be reliable in the detection of pathologic changes of spinal cord decompression sickness that were previously undetectable by other neuroimaging methods and also has proved to be useful in the follow-up during therapeutic hyperbaric recompressions.

Acute neurologic decompression illness in pigs: lesions of the spinal cord and brain

A detailed histopathologic description of central nervous system lesions from a porcine model of neurologic decompression illness is presented. Pigs were dived in a dry chamber to 200 feet of seawater for 24 min before the start of decompression. Of 120 pigs, 40 (33.3%) were functionally unaffected and 80 (66.6%) developed neurologic decompression illness; 16 died, 64 survived. Petechial hemorrhages were grossly visible in the spinal cord of 73% of the survivors, 63% of the fatalities, and 3% of the clinically unaffected pigs. The thoracic part of the cord was most commonly involved. Histologic cord lesions were found in 75 (63%) pigs: 83% of decompression illness survivors, 81% of the fatalities, and 23% of those clinically unaffected. Morphologically, hemorrhagic lesions were the most common (54%). Other common findings included spongiosis (48%), axonal swelling and loss (39%), and myelin degeneration (35%). White matter hemorrhages in the spinal cord were generally more numerous and extensive than those affecting the gray matter; however, gray matter hemorrhage was associated with increasing disease severity. Brain lesions were present in 23% of pigs and were most frequent in fatalities. Cerebellar and brain stem hemorrhages were the most common brain lesions; the molecular layer of the cerebellum appeared particularly susceptible. Pigs were chosen because of their cardiovascular and gas exchange similarities to humans. The clinical and histopathologic features of the pig model were compared with previous accounts in animals and humans; the model was judged analogous to severe human decompression illness. The finding of occult brain and cord lesions in clinically unaffected pigs is discussed. The model provides a useful tool for the study of dysbaric lesions of the central nervous system. Its noninvasive nature may facilitate the study of nervous system injury and repair processes.

Reversibility in blood-brain barrier, microcirculation, and histology in rat brain after decompression

To examine the changes in blood-brain barrier (BBB), cerebral microcirculation, and histology from 15 min to 72 h after decompression, 90 rats were exposed to experimental compression to 6 atm abs air for 90 min and subsequent rapid decompression. The disruption of BBB was examined by Evans blue extravasation. The cerebral microcirculation was demonstrated by perfusion with India ink. The area stained with Evans blue and the regions of defective filling with India ink, observed immediately after decompression decreased in size with time and were undetectable 3-24 h after decompression. The edematous brain tissue with enlarged perivascular space and darkly stained nerve cells also decreased to the uncompressed control level 1-24 h after decompression. These reversible dysbaric changes, however, reappeared 48-72 h after decompression. The different mechanisms, the physicochemical effects of microbubbles, and the maturation phenomenon after temporary brain ischemia induced by dysbaric microbubbles may be involved in the brain damage after decompression sickness.

Late deterioration after decompression illness affecting the spinal cord

A former amateur diver presented with a progressive paraparesis. Thirteen years previously he had developed acute spinal cord dysfunction immediately after dry hyperbaric exposure. He had completely recovered motor function in the intervening period. No alternative reason for the later decline emerged from detailed investigation.

Neurological decompression illness in swine

BACKGROUND

A porcine model of neurological decompression illness (DCI) and its treatment is described.

METHODS

Pigs (wt. 16-22 kg) underwent a simulated dive to 200 feet of seawater (fsw) (612.6 kPa) for 24 min, then decompressed at 60 fsw/min-1 (183 kPa.min-1). Pigs that developed neurological DCI were sedated with diazepam, then treated by recompression on U.S. Navy Treatment Table 6. Functional outcome was assessed by treadmill running. At necropsy 24 h postdive, carcass density was measured by underwater weighing, and tissue samples including heart, spinal cord, and brain were taken for histopathological examination.

RESULTS

Neurological DCI occurred in 73% of control animals and developed within 2-7 min in 50% of cases. Affected pigs had significantly earlier onset of skin DCI than unaffected pigs (means: 9.52 min vs. 17.9 min, p < 0.001). Only 16.4% of pigs made a full functional recovery after recompression treatment. Outcome at 24 h was not improved in 20 pigs randomized to receive adjunctive lidocaine infusion compared to 20 pigs that received saline alone. Following necropsy, 77% of cases had petechial hemorrhages grossly visible in the spinal cord. Multifocal, microscopic hemorrhages, predominantly of spinal cord white matter, were found in 86.6% of DCI cases. Neither weight, density, nor genetic predisposition were found to influence DCI risk.

CONCLUSIONS

The model is analogous to severe, early-onset, neurological DCI in humans and allows prospective evaluation of risk reduction and treatment stratagems for this form of DCI. Many applied and basic science issues relevant to diving medicine may also be studied using the model, and adaptation to study hypobaric DCI and other clinical applications of hyperbaric oxygen is feasible.

Role of extravascular gas bubbles in spinal cord injury induced by decompression sickness in the rat

We have evaluated the contribution of extravascular gas bubbles to spinal cord injury in decompression sickness. For this purpose, a model of decompression sickness was developed by subjecting rats to simulated dives using compressed air. Various diving profiles were tested and the presence of spinal cord injury was demonstrated by electrophysiologic measurements. To evaluate the space occupying lesions induced by gas bubbles in the white matter, the spinal cord was fixed by perfusion with 10% buffered formalin. Tissue blocks from cervical, thoracic, and lumbar spinal cords were embedded in paraffin. Tissue sections were double stained with luxol fast blue and hematoxylin and eosin. The space occupying lesions were quantified with a digitizer tablet. The fractional area of the lesions was 0.009% in controls and 0.026% in rats subjected to diving. We conclude that the volume of extravascular free gas present in the cord of rats with spinal decompression sickness is small and that artifacts of tissue preparation contribute to the volume estimate. As far as can be judged from the results in this animal model, the contribution of extravascular gas bubbles to spinal cord decompression injury is minor.

Protective effect of oxygen and heliox breathing during development of spinal decompression sickness

A rat model of spinal decompression sickness (DCS) allows study of spinal cord function for at least 3 h after decompression to 1 atm abs (101 kPa) after an exposure to air at 3.8 atm abs (385 kPa) for 1 h. During these 3 h, spinal evoked potentials (SEPs) elicited by peroneal nerve stimulation may be reduced or disappear, and histologic lesions in the spinal cord are observed. Three groups of animals were given either air, oxygen, or heliox (80/20) to breathe at 1 atm abs for 3 h after decompression. Both oxygen and heliox breathing impeded the development of DCS significantly as judged by the mortality of the animals and disappearance of the SEPs. The effect of heliox seemed to be superior to that of oxygen. The latency time from stimulation to the first SEP peak increased significantly during both air and oxygen breathing, whereas no significant increase was seen during heliox breathing. Histologic examination of the spinal cords of animals breathing air, oxygen, or heliox (80/20) showed focal lesions in the white and gray matter. In the white matter, degenerated myelin sheaths as well as expanded extracellular spaces compatible with bubble formation were seen. In the gray matter, perikaryal degeneration was observed. The extracellular space in the white matter was increased in all decompressed animals compared with controls (P < 0.01). Oxygen and heliox breathing caused a smaller increase in extracellular space as compared with air-breathing animals (P < 0.05) and (0.10 > P > 0.05), respectively. It is concluded that breathing of oxygen or heliox (80/20) at 1 atm abs has a preventive effect on the development of DCS when compared with air breathing; the effect of heliox seems to be superior to that of oxygen.

Spinal cord decompression sickness in sport diving

OBJECTIVE

To summarize 16 years' experience in the diagnosis and treatment of spinal cord decompression sickness in Israel.

DESIGN

The survey data were collected firsthand by physicians trained in underwater diving medicine.

SETTING

The Israeli Naval Medical Institute, Israel's national hyperbaric referral center.

PATIENTS

Sixty-eight sport divers diagnosed as having spinal cord decompression sickness.

INTERVENTIONS

Hydration and 100% oxygen breathing until the patient reached the hyperbaric chamber. All patients received recompression therapy on US Navy treatment tables using oxygen, except for six who were treated by Comex Treatment Table CX-30, which uses helium in addition to oxygen.

MAIN OUTCOME MEASURES

Neurological examination after the completion of recompression therapy.

RESULTS

Forty-one percent of the dives were performed within the decompression limits of the US Navy standard decompression tables. Risk factors were fatigue, circumstances suggesting dehydration, and extreme physical effort. The most common presenting symptoms were paresthesias, weakness of the legs, lower back pain, or abdominal pain. Full recovery was achieved in 79% of the patients. Spinal symptoms appeared immediately on surfacing in six of the eight patients who continued to have multiple neurological sequelae.

CONCLUSIONS

United States Navy air decompression tables appear not to be completely safe for sport divers. Even mild spinal symptoms identified on surfacing should be treated vigorously. High-pressure oxygen-helium therapy seems to be a promising alternative in cases of severe spinal cord decompression sickness.

Cochlear degeneration in guinea pigs after repeated hyperbaric exposures

The effects of repeated hyperbaric exposures on inner ear function and morphology in guinea pigs were investigated with auditory electrophysiological testing, histopathological and electron microscopic techniques associated with enzyme histochemical method. The results showed that repeated hyperbaric exposures, though considered "safe," did cause damage to the cochlear system. Possible causes of the pathology include direct effects of repeated compression and decompression on the ear, and the possibility of inner ear decompression sickness and barotrauma cannot be excluded.

Cerebral vasculopathy in divers

Brains from 12 amateur and 13 professional divers, all but one of whom died accidentally, were examined neuropathologically. Grossly distended, empty vessels (presumably caused by gas bubbles) were found in the brains of 15 out of 22 divers who died from diving accidents. Perivascular lacuna formation was found in cerebral and/or cerebellar white matter in three amateurs and in five professionals. In addition to lacuna formation, hyalinization of vessel walls was present in the brains of three amateurs and five professionals. Necrotic foci in grey matter occurred in seven cases and perivascular vacuolation of white matter occurred in seven cases. The vascular changes probably arose from intravascular gas bubble formation. In one professional diver, there was also unilateral necrosis of the head of the caudate nucleus.

Bubble-induced dysfunction in acute spinal cord decompression sickness

Five anesthetized dogs undertook a chamber dive, on air, to 300 feet of seawater for 15 min. After the dive, spinal cord decompression sickness was detected by recording a reduced amplitude of the somatosensory evoked potential compared with predive base-line values. After the diagnosis of decompression sickness and rapid perfusion fixation of the animal, the spinal cord was removed and examined histologically. Numerous space-occupying lesions (SOL) that disrupted the tissue architecture were found in each cord, mainly in the white matter. The size and distribution of the SOL were determined using computerized morphometry. Although SOL occupied less than 0.5% of the white matter volume, we tested a number of algorithms to assess whether the SOL may have been directly involved in the loss of spinal cord function that followed the dive. We determined that the loss of somatosensory evoked potential amplitude may be attributed to the SOL if 30-100% of the spinal cord fibers that they displaced were rendered nonconducting. A number of possible mechanisms by which SOL may interfere with spinal nerve conduction are discussed.

Arterial gas embolism as a pathophysiologic mechanism for spinal cord decompression sickness

A continuous infusion of air (1.0 ml.min-1) was delivered via a fine aortic cannula into the arterial circulation of 7 anesthetized dogs until no spinal cord function could be elicited by somatosensory evoked potentials. The animals were then rapidly perfusion-fixed and the spinal cords removed for histological examination. The appearance of the embolized cords differed substantially from eight spinal cords injured by fulminant decompression sickness (DCS). The embolized cords appeared essentially normal whereas the DCS cords featured extravascular, nonstaining, space-occupying lesions (SOLs) scattered throughout the cord, mainly in the white matter. Two spinal cords injured by DCS with a delayed onset (30 min from surfacing) appeared similar to the embolized cords. These findings are compatible with the hypothesis that two mechanisms are involved in the onset of spinal cord DCS. Fulminant disease is associated with SOLs, which are probably caused by the in situ evolution of a gas phase. Disease with a delayed onset is more likely to be caused by an ischemic mechanism, which in the acute phase is histologically indistinguishable from gas embolism.

Spinal cord degeneration associated with type II decompression sickness: case report

The medical history, clinical and neuropathological findings at necropsy are described in a 50-year-old male amateur diver who suffered from Type II decompression sickness, a spinal 'bend'. He survived as a paraplegic for 4 years. In the spinal cord upward Wallerian degeneration in the posterior columns and downward degeneration in the corticospinal tracts was explained by multiple small and medium sized infarcts affecting the centripetal blood supply to the cord. There was preservation of a rim of subpial fibres on the surface of the posterior and lateral columns. The grey matter and nearby white matter (supplied by the centrifugal arterial supply) was unaffected.

Is there a role for the autochthonous bubble in the pathogenesis of spinal cord decompression sickness?

Histological examination by light and electron microscopy of the spinal cords of four dogs rapidly perfusion-fixed after the onset of decompression sickness revealed the presence of numerous non-staining, space-occupying lesions that were absent in similarly prepared sections of control or ischemic spinal cords. We propose the hypothesis that these lesions are caused by the liberation of a gas phase. The possible significance of these lesions in the evolution of spinal cord dysfunction is discussed with reference to the principal theories of the pathogenesis of spinal cord decompression sickness.

Spinal cord degeneration in divers

Spinal cords from 8 professional and 3 amateur divers who died accidentally were examined histopathologically. Marchi-positive degeneration was found in the cords of 3 professional divers, variously affecting the posterior, lateral, and to a lesser extent the anterior columns. In 1 there was degeneration of afferent fibres within the posterior columns.

Increase in blood-brain barrier permeability by altitude decompression

Previous studies indicated that exposure to compression-decompression increases blood-brain barrier (BBB) permeability to vital dyes and antibiotics. This report concerns functional and ultrastructural BBB changes induced by altitude decompression. A 2% trypan blue solution was intravenously injected (4 ml.kg-1) into 29 experimental and 19 control rabbits. Some animals also received horseradish peroxidase. The experimental animals were subjected to 30,000 ft (4.3 psi) for 45 min. Controls were kept at ground level. The animals were sacrificed 90 min postinjection. Gross and microscopic examination and spectrophotometric dye determination revealed significantly greater tracer penetration in experimental brains (mean dye concentration 27.06 +/- 4.42 micrograms.g-1) than in controls (4.52 +/- 1.52 micrograms.g-1). No sex differences were noted. Electron microscopy suggested that the increased BBB permeability was due to transendothelial vesicular transport and, occasionally, to penetration through interendothelial junctions. These observations may have relevance to pharmacotherapy in space and at high altitudes and to the pathogenesis of altitude decompression sickness.

Consumption of platelets in decompression sickness of rabbits

Platelet behavior was studied in rabbit decompression sickness which was brought about by the exposure to 6 ATA for 40 min (bottom time) followed by rapid decompression. Platelet counts significantly decreased after the decompression. Kinetic studies with 111In-oxine-labeled platelets revealed shortened survivals of circulating platelets, and audioradiograms indicated the accumulation of radioactivity in the lungs after the decompression. Although there was no change in the mode volume of platelets after the decompression, the transient appearance of circulating smaller or fragmented platelets suggested a random overdestruction of platelets. Whole and releasable adenine nucleotide contents of platelets were decreased significantly after the decompression. There were no significant changes in cytoplasmic adenine nucleotide contents. Therefore, in decompression sickness, the circulating platelets behaved similarly to those in acquired storage pool disease. Platelet thrombi were found in the pulmonary arteries, compatible with the accumulation of 111In-oxine-labeled platelets. These findings suggest that circulating air bubbles interact with platelets, causing the platelet release reaction, and these activated platelets participate in the formation of thrombi in experimental decompression sickness.

Dysbarism. A review

This review of dysbarism outlines the development of the knowledge of the effects of pressure changes on tissues and organs, which is related to a complex of physical, physiological and pharmacological changes. It also shows that with the ever increasing pressures to which man is subject the effects can be regarded as total body rather than the traditional concept of a few target organs.

Origin and time course of gas bubbles following rapid decompression in the hamster

Because conflicting results have been obtained in studies of the hamster (Mesocricetus auratus) microcirculation following rapid decompression, we were interested in the origin of bubbles in the cheek-pouch preparation. The hamster cheek-pouch and surgically exposed femoral vessels were observed under the microscope, before and immediately following rapid decompression. The animals were placed in a hyperbaric chamber and exposed to an increased pressure of 7 ATA for 1 h. They were then decompressed at a rate of 18 m/min until reaching 1 ATA. This hyperbaric exposure produced an LD50 in 100 hamsters examined in this study. In 40% of these animals "bubbles" were seen entering the cheek-pouch artery after a delay of from 3 to 6 min following decompression. Before observing bubbles in the cheek-pouch artery, bubbles were always seen in the femoral vein. Those animals that had observable bubbles in the cheek-pouch usually demonstrated a tachypnea, followed by gasping and apnea. When bubbles were seen in the arterial circulation, few animals survived for more than 10 min following the hyperbaric exposure. Postmortem examination of these animals revealed massive gas emboli in the large venous vessels, right ventricle, and fewer bubbles in the left ventricle. Postmortem examination of surviving animals revealed that the majority of the gas was in the venous vessels and right heart. These data support the hypothesis that bubbles first form on the venous side of the circulation and, if they exceed a certain volume, move through the pulmonary circulation into the systemic arterial vessels.

A method for investigating specialised accidents with special reference to diving

This paper describes a format for the investigation of complicated accidents which result in diving deaths. It emphasises the necessity for communication between technical, medical and legal personnel to arrive at a reasoned appreciation of factors leading to an accident. Properly applied this can result in a meaningful accumulation of data, which can be periodically analysed and be used in formulating Regulations for prevention of further accidents.