Decompression illness in goats following simulated submarine escape: 1993-2006.

The United Kingdom Ministry of Defence commissioned work to define the relationship between the internal pressure of a distressed submarine (DISSUB), the depth from which escape is made and the risk of decompression illness (DCI). The program of work used an animal model (goat) to define these risks and this paper reports the incidence and type of DCI observed. A total of 748 pressure exposures comprising saturation only, escape only or saturation followed by escape were conducted in the submarine escape simulator between 1993 and 2006. The DCI following saturation exposures was predominantly limb pain, whereas following escape exposures the DCI predominantly involved the central nervous system and was fast in onset. There was no strong relationship between the risk of DCI and the range of escape depths investigated. The risk of DCI incurred from escape following saturation was greater than that obtained by combining the risks for the independent saturation only, and escape only, exposures. The output from this program of work has led to improved advice on the safety of submarine escape.

Submarine tower escape decompression sickness risk estimation.

Actions to enhance survival in a distressed submarine (DISSUB) scenario may be guided in part by knowledge of the likely risk of decompression sickness (DCS) should the crew attempt tower escape. A mathematical model for DCS risk estimation has been calibrated against DCS outcome data from 3,738 exposures of either men or goats to raised pressure. Body mass was used to scale DCS risk. The calibration data included more than 1,000 actual or simulated submarine escape exposures and no exposures with substantial staged decompression. Cases of pulmonary barotrauma were removed from the calibration data. The calibrated model was used to estimate the likelihood of DCS occurrence following submarine escape from the United Kingdom Royal Navy tower escape system. Where internal DISSUB pressure remains at - 0.1 MPa, escape from DISSUB depths < 200 meters is estimated to have DCS risk < 6%. Saturation at raised DISSUB pressure markedly increases risk, with > 60% DCS risk predicted for a 200-meter escape from saturation at 0.21 MPa. Using the calibrated model to predict DCS for direct ascent from saturation gives similar risk estimates to other published models.

Submarine 'safe to escape' studies in man.

The Royal Navy requires reliable advice on the safe limits of escape from a distressed submarine (DISSUB). Flooding in a DISSUB may cause a rise in ambient pressure, increasing the risk of decompression sickness (DCS) and decreasing the maximum depth from which it is safe to escape. The aim of this study was to investigate the pressure/depth limits to escape following saturation at raised ambient pressure. Exposure to saturation pressures up to 1.6 bar (a) (160 kPa) (n = 38); escapes from depths down to 120 meters of sea water (msw) (n = 254) and a combination of saturation followed by escape (n = 90) was carried out in the QinetiQ Submarine Escape Simulator, Alverstoke, United Kingdom. Doppler ultrasound monitoring was used to judge the severity of decompression stress. The trials confirmed the previously untested advice, in the Guardbook, that if a DISSUB was lying at a depth of 90 msw, then it was safe to escape when the pressure in the DISSUB was 1.5 bar (a), but also indicated that this advice may be overly conservative. This study demonstrated that the upper DISSUB saturation pressure limit to safe escape from 90 msw was 1.6 bar (a), resulting in two cases of DCS.

Markers of endothelial cell activation and injury in childhood haemolytic uraemic syndrome.

Diarrhoea-associated haemolytic uraemic syndrome (D+ HUS) is usually caused by verotoxin-producing Escherichia coli. Histology shows endothelial swelling with localised thrombus. Activation of coagulation and fibrinolysis also occurs. These facts, combined with the knowledge that recovery usually follows within weeks, led us to hypothesise that verotoxin causes localised endothelial cell activation but not injury. Markers of endothelial cell activation and injury were measured serially in 30 children with acute D+ HUS, healthy children, and children receiving chronic dialysis. Interpretation of markers was complicated by the renal dysfunction characteristic of D+ HUS. Nevertheless there was no evidence for endothelial cell injury, as soluble tissue factor levels were not increased and soluble thrombomodulin levels were lower than dialysed controls (P<0.001). In the acute phase, soluble vascular cell adhesion molecule levels were raised above normal (P<0.001), but were lower than dialysed controls (P<0.001), and soluble E-selectin levels were not significantly increased compared with normal controls (P=0.2). Hence, there was no evidence for endothelial cell damage or endothelial cell activation by the time children reached hospital; but this study did not exclude the possibility that endothelial cell activation occurred prior to hospital admission.

Activation of coagulation and fibrinolysis in childhood diarrhoea-associated haemolytic uraemic syndrome.

Diarrhoea-associated haemolytic uraemic syndrome (D+ HUS) is usually caused by verotoxin producing Eschericia coli. We hypothesized that verotoxin binding to glomerular endothelial cells causes localised endothelial cell activation and thus activation of coagulation and reduction of fibrinolytic potential. We also proposed that treatment with fresh frozen plasma or dialysis would not affect these changes. Markers of activation of coagulation and fibrinolysis were measured in 30 children with acute D+ HUS serially, in healthy children and in children on dialysis. In acute D+ HUS, levels of thrombin-antithrombin III complex and prothrombin fragment 1+2 were significantly increased (p <0.001). The source of thrombin generation was unclear. Factor XIIa levels were increased in patients and controls with renal failure. Factor VIIa levels were not significantly raised in children with acute D+ HUS. D-dimers were increased, but fibrinolytic potential as measured by fibrin plate was reduced. Levels of plasminogen activator inhibitor antigen and activity and tissue plasminogen activator antigen were increased. Neither peritoneal dialysis nor administration of blood products, the most common treatments, altered parameters of coagulation or fibrinolysis.

Activation of human prothrombin by porcine aortic endothelial cells--a potential barrier to pig to human xenotransplantation.

A potential solution to the shortage of human organs for transplantation lies in the use of animal organs with the pig as the most likely donor. Perfusion of porcine organs with human blood, however, results in hyperacute rejection (xenograft reaction) which occurs within minutes to hours and is characterised by intravascular thrombosis. The pathogenesis of this xenograft reaction is attributed to xenoreactive natural antibodies (XNA) binding to epitopes on porcine endothelium activating complement with subsequent haemostatic activation. We have investigated whether there is direct activation of human coagulation by porcine endothelium in the absence of XNA and complement. Previous experiments demonstrated possible pathological activation of the common pathway, thus human prothrombin and factor X were added separately to porcine endothelium and monitored for activation. Human prothrombin was activated by porcine but not human endothelium. There was no activation of factor X. Hirudin inhibited prothrombin activation suggesting that a conformational change may occur in prothrombin on binding to porcine endothelium, such that its catalytic centre is exposed with subsequent autocatalytic cleavages. If this in vitro observation of direct prothrombin activation is translated to the in vivo situation then this phenomenon may pose a non-immunological obstacle to pig to human xenotransplantation.

Endothelial cell activation in cutaneous vasculitis.

Markers of endothelial cell activation were measured in 28 patients presenting with various forms of limited or focal type cutaneous vasculitis. Plasma levels of tissue plasminogen activator antigen (t-PA:Ag), plasminogen activator inhibitor type 1 antigen (PAI-1:Ag) and PAI-1 activity, fibrin plate, von Willebrand factor antigen (vWF:Ag), tissue factor (TF) and soluble thrombomodulin (sTM) were measured. In comparison with the control group (n = 20) there was a significant increase in t-PA:Ag, vWF:Ag and TF (P < 0.05, Mann-Whitney U-test) in the cutaneous vasculitis group. This study confirms that measurable degrees of endothelial activation occur in cutaneous vasculitis. Cutaneous vasculitis includes a diverse group of clinical conditions, which are associated with inflammatory changes in cutaneous blood vessels with local fibrin deposition. The aetiology and pathogenesis of the majority of these entities remain unknown. Causative mediators are thought to include immune complexes, anti-endothelial cell antibodies, cytotoxic lymphocytes and viruses. Histologically, immune complexes and complement are frequently detected on the vessel wall, and serologically anti-endothelial antibodies are often detected in patients with vasculitis and in systemic lupus erythematosus (SLE) which correlate with the severity of cutaneous vasculitis, arthritis and nephritis. Lymphocyte-mediated toxicity to endothelial cells has been reported in a small number of patients with giant cell arteritis and Takayasu's arteritis. The vascular endothelium plays a central part in the control of haemostasis. Under physiological conditions endothelial cells present an anticoagulant surface to blood constituents, partially due to surface expression of heparan sulphate and thrombomodulin (TM). Heparan sulphate binds antithrombin III (ATIII), thereby accelerating inactivation of intrinsic coagulation enzymes. Thrombomodulin is an endothelial cell surface glycoprotein which promotes anticoagulation by forming a complex with thrombin which then activates protein C. Activated protein C together with a cofactor, protein S, inactivates FVa and FVIIIa. von Willebrand factor (vWF) is synthesized by endothelial cells, stored in Weibel-Palade bodies and released into the circulation upon endothelial stimulation. vWF mediates the binding of platelets to the subendothelium and is the carrier molecule for FVIIIC. The endothelium controls fibrinolysis by producing t-PA and its inhibitor PAI-1. Inflammatory cytokines such as interleukin-1 (IL-1) and tumour necrosis factor (TNF) activate endothelial cells, causing a shift from an antithrombotic to prothrombotic state, including expression of tissue factor, increased synthesis of PAI-1 and decreased expression of TM. Fibrin deposition and intravascular thrombosis are seen in cutaneous vasculitis syndromes, suggesting local endothelial cell activation. The aim of this pilot study was to assess whether perturbation of the endothelium in cutaneous vasculitis could be detected in the patients' plasma samples. If so, further studies to assess any correlation in levels of these markers with disease activity might prove useful in the future.

Thrombophilic factors in ischaemic and non-ischaemic idiopathic retinal vasculitis.

Two common causes of visual loss in idiopathic retinal vasculitis (RV) are retinal ischaemia and cystoid macular oedema. This study investigated whether thrombophilic factors are more prevalent in patients with ischaemic RV than non-ischaemic RV. Twenty patients with RV (10 ischaemic, 10 non-ischaemic) were prospectively recruited before starting systemic immunosuppression. Twenty-one different haemostatic parameters were tested. Seventeen patients had at least one haemostatic abnormality. Three patients had low Protein S, one had low Protein C. Three patients had positive anticardiolipin antibody titres, 1 had poor fibrinolytic activity, 3 had raised fibrinogen levels. Ten patients had raised lipoprotein (a) levels. Fibrinogen levels were higher in the smokers (p = 0.02). Although all von Willebrand's factor levels were within the normal range, they were higher in the ischaemic group (p = 0.008), in which smoking was more prevalent. This study has shown a high prevalence of thrombophilic abnormalities in RV patients, and implicates smoking in the aetiology of ischaemic RV.

Anticoagulants from marine algae.

Anticoagulant properties were first described in extracts from marine algae over 50 years ago. Currently over 60 species, representing the three major divisions of marine algae, have been reported to have such properties. The major active components are a variety of sulphated polysaccharides, some of which characterize as proteoglycans. These sulphated polysaccharides/proteoglycans exert antithrombin properties, primarily mediated by heparin cofactor II (HCII). However antithrombin III (ATIII) mediated anticoagulant activities, as well as an element of direct antithrombin activity, have also been observed.

Structural differentiation and fluid reabsorption in the ductuli efferentes testis of the rat.

The ductuli efferentes testis of the rat form a cord which is embedded in adipose tissue. The cord is anatomically differentiated into a proximal cylindrical region, the initial zone, and an ampulla, the coni vasculosi. The initial zone contains six or seven ductuli which leave the rete testis and run in a sinuous path, roughly parallel with one another. However, the ductuli in the coni vasculosi are more sinuous than in the initial zone and they anastomose; pairs join together to form ultimately a single, common ductulus efferens. Stereological studies of paraffin sections and electron micrographs showed that the differentiation of the ductuli into two parts can be recognized at tissue and cellular levels of organization. Stereological and micropuncture studies showed that the ductuli efferentes reabsorb most of the fluid leaving the testis and it was concluded that most reabsorption occurred in the initial zone. It was estimated that the rate of fluid absorption is greater in the ductuli efferentes than in the proximal convoluted tubules of the kidney. The mechanism of fluid transport across the mucosa of the ductuli is considered in the Discussion. It is concluded that transport in vesicles and vacuoles could not account for the rate of fluid reabsorption and that the main mechanism of transport probably involves the coupling of water and active salt transport.