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.