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Diving decompression fails to activate complement
Abstract
The present study evaluated complement activation during decompression after air dives in a hyperbaric chamber. Intravascular bubbles were quantified by Doppler ultrasound scoring. Eighteen subjects completed 92 dives, of which 74 produced bubbles. Complement activation was assessed by plasma C3a des Arg and red-cell-bound C3d before and after each dive. These parameters of in vivo complement activation failed to show significant activation. In vitro complement activation susceptibility tests on pre-dive sera were performed to explore their association with in vivo complement activation and intravascular bubbles. Such tests failed to identify a distinct complement-sensitive group and did not correlate with in vivo complement activation during the dives and/or intravascular bubble appearance. Two subjects developed decompression sickness but were not different from the rest of the group regarding in vitro complement sensitivity or complement activation during dives.
... However, in vivo testing failed to demonstrate this phenomenon, and subjects who developed DCS showed no difference in complement activation during dives compared to healthy subjects. 36 Finally, a history of cigarette smoking may predispose an individual to DCS. A retrospective analysis of the Divers Alert Network (DAN) database found that heavy smokers (>15 pack-year history) were 1.88 times more likely to have DCS than divers who had never smoked and 1.56 times more likely than light smokers (0-15 pack-year history). ...
... However, several studies have reported that the complement proteins of human divers 3 R-00260-2004.R2 FINAL ACCEPTED VERSION remained within normal ranges when they were on a regular diving schedule with repetitive pressure exposure (12,26). These data weaken the consumption theory. ...
Diving acclimatization refers to a reduced susceptibility to acute decompression sickness (DCS) in individuals undergoing repeated compression-decompression cycles. We demonstrated in a previous study that the mechanism responsible for this acclimatization is similar to that of stress preconditioning. In this study, we investigated the protective effect of prior DCS preconditioning on the severity of neurological DCS in subsequent exposure to high pressure in rabbits. We exposed the rabbits (n = 10) to a pressure cycle of 6 absolute atmospheres (ATA) for 90 min, which induced signs of neurological DCS in 60% of the animals. Twenty-four hours after the pressure cycle, rabbits with DCS expressed more heat-shock protein 70 (HSP70) in the lungs, liver, and heart than rabbits without signs of disease or those in the control group (n = 6). In another group of rabbits (n = 24), 50% of animals presented signs of neurological DCS after exposure to high pressure, with a neurological score of 46.5 (SD 19.5). A course of hyperbaric oxygen therapy alleviated the signs of neurological DCS and ensured the animals' survival for 24 h. Experiencing another pressure cycle of 6 ATA for 90 min, 50% of 12 rabbits with prior DCS preconditioning developed signs of DCS, with a neurological score of 16.3 (SD 28.3), significantly lower than that before hyperbaric oxygen therapy (P = 0.002). In summary, our results show that the occurrence of DCS in rabbits after rapid decompression is associated with increased expression of a stress protein, indicating that the stress response is induced by DCS. This phenomenon was defined as "DCS preconditioning." DCS preconditioning attenuated the severity of neurological DCS caused by subsequent exposure to high pressure. These results suggest that bubble formation in tissues activates the stress response and stress preconditioning attenuates tissue injury on subsequent DCS stress, which may be the mechanism responsible for diving acclimatization.
Synonyms of decompression illness (DCI) are dysbaric illness (DI), decompression sickness (DCS), decompression accident or caisson disease. As DCS and AGE quite often occur together, these are commonly summarised as DCI or DI which is used as the preferred term for decompression-related accidents. DCS alone is rather subject to inert gas bubbles related to decompression effects as aetiology by itself. Neurological symptoms of DCS might be quite similar to AGE caused by pulmonary barotrauma. However, spinal symptoms are only found in DCS. DCI is a spectrum, which may have no symptoms at all, minor unspecific symptoms like fatigue up to fatal complications.
Deep sea diving might cause a tremendous physical or psychological stress to the divers. The present study aims to evaluate the stress response to a simulated wet dive in Navy divers. Nineteen Navy divers took part in this study when they were undergoing annual deep dive training. Ten divers were exposed to 190 feet of sea water (fsw) breathing compressed air on day 1 and to 250 fsw breathing helium-oxygen (Heliox) gas mixture on day 3. Another 9 divers were exposed to 220 fsw on day 1 and 285 fsw on day 3 breathing Heliox gas mixture. The bottom time ranged from 5 to 8 min, and then the standard U.S. Navy air and Heliox decompression tables were followed for surfacing. Predive levels of serum heat shock protein 72 (sHsp72) were 9.95 +/- 0.56 ng/ml, which were significantly higher than those in the control group (8.01 +/- 0.77 ng/ml). After simulating Heliox dive, the sHsp72 increased to 10.43 +/- 0.56 ng/ml, but this was not statistically significant. Our results demonstrated that the serum level of Hsp72 is higher in the Navy divers who underwent regular intensive exercise. However, it remains unknown whether this increase of stress protein is associated with the diving stress or exercise preconditioning in the Navy divers.
Diving acclimatization refers to a reduced susceptibility to acute decompression sickness (DCS) in individuals undergoing repeated compression-decompression cycles. We postulated that mechanisms responsible for the acclimatization are similar to that of a stress preconditioning. In this study, we investigated the protective effect of prior heat shock treatment on air embolism-induced lung injury and on the incidence of DCS in rats. We exposed rats (n = 31) to a pressure cycle that induced signs of severe DCS in 48% of the rats, greater wet-to-dry ratio (W/D) of lung weight compared with the control group (5.48 +/- 0.69 vs. 4.70 +/- 0.17), and higher protein concentration in bronchoalveolar lavage (BAL) fluid (362 +/- 184 vs. 209 +/- 78 mg/l) compared with the control group. Rats with DCS expressed more heat shock protein 70 (HSP70) in the lungs than those without signs of disease. Prior heat shock (n = 12) increased the expression of HSP70 in the lung and attenuated the elevation of W/D of lung weight (5.03 +/- 0.17) after the identical decompression protocol. Prior heat shock reduced the incidence of severe DCS by 23%, but this failed to reach statistical significant (chi(2) = 1.94, P = 0.163). Venous air infusion (1.0 ml/40 min) caused profound hypoxemia (54.5 +/- 3.8 vs. 83.8 +/- 3.2 Torr at baseline; n = 6), greater W/D of lung weight (5.98 +/- 0.45), and high protein concentration in BAL fluid (595 +/- 129 mg/l). Prior heat shock (n = 6) did not alter the level of hypoxemia caused by air embolism, but it accelerated the recovery to normoxemia after air infusion was stopped. Prior heat shock also attenuated the elevation of W/D of lung weight (5.19 +/- 0.40) and the increase in BAL protein (371 +/- 69 mg/l) in air embolism group. Our results showed that the occurrence of DCS after rapid decompression is associated with increased expression of a stress protein (HSP70) and that prior heat shock exposure attenuates the air bubble-induced lung injury. These results suggest that bubble formation in tissues activates a stress response and that stress preconditioning attenuates lung injury on subsequent stress, which may be the mechanism responsible for diving acclimatization.
Immune reactivity, stress responses, and inflammatory reactions may all contribute to pathogenic mechanisms associated with decompression sickness (DCS). Currently, there are no biomarkers for DCS. This research examined if DCS is associated with increased levels of biomarkers associated with vascular function, early/non-specific stress responses, and hypothalamic-pituitary-adrenal (HPA) axis stress responses.
Rats undergoing a test dive to 175 ft of seawater (fsw) (6.2 ATA) for 60 min with a rapid decompression were observed for DCS (ambulatory deficit). Animals exercised on a rotating cage (approximately 3 m x min(-1)) throughout the dive and subsequent 30-min observation period. All animals were euthanized and blood and tissue samples (brain, liver, lung) were collected for analysis of CRP and ET-1 by ELISA and stress markers by PCR.
HO-1 and HSP-70 increased in the brain, and HO-1, Egr-1, and iNOS increased in the lungs of animals with DCS. There was no difference in any stress marker in the liver, or in serum levels of CRP or ET-1.
The results demonstrate that < 30 min after surfacing, there are genomic changes in animals with DCS compared with animals not showing signs of DCS. Identification of specific markers of DCS may permit use of such biomarkers as predictors of DCS susceptibility and/or occurrence.
Previously, complement activation has been associated with decompression sickness (DCS). However data, both in humans and in animals, are controversial. Hypothesis: Complement activation and depletion occurs after exposure to the hyperbaric environment and is associated with increasing risk of DCS.
We obtained serological samples from 102 dives (120-300 feet of seawater) with a constant partial pressure of O2 set at 1.3 ATA in thirty-five U.S. Navy diver volunteers. Blood was obtained within one hour of diving and within one hour of surfacing. Plasma was extracted and analyzed for complement depletion. The risk of DCS was estimated using a validated model of DCS risk.
Pre-post dive concentrations of C3a were significantly related to estimated risk of DCS (Figure 1), but the variation in predicted DCS explained by C3a was small (correlation co-efficient (r2 = 0.19, p < 0.0001).
There was a reduction in total Ca3 levels in divers after exposure to dives with a high estimated risk of DCS. This decomplementation appeared to increase as the estimated risk of DCS increased.
The adult respiratory distress syndrome is characterized by arterial hypoxemia as a result of increased alveolar capillary permeability to serum proteins in the setting of normal capillary hydrostatic pressures. Because bacterial sepsis is prominent among the various diverse conditions associated with altered alveolar capillary permeability, we studied the effect of bacteremia with attendant complement activation on the sequestration of microorganisms and the leakage of albumin in the lungs of guinea pigs. Pneumococci were injected intravenously into guinea pigs and their localization was studied. Unlike normal guinea pigs, complement-depleted guinea pigs did not localize injected bacteria to the lungs. Preopsonization of organisms did not correct this defect in pulmonary localization of bacteria in complement-depleted animals, suggesting that a fluid-phase component of complement activation was required. Genetically C5-deficient mice showed no pulmonary localization of bacteria. C5-sufficient mice demonstrated the usual pulmonary localization, thus further suggesting that the activation of C5 might be important in this localization. The infusion of activated C5 increased alveolar capillary permeability to serum proteins as assayed by the amount of radioactive albumin sequestered in the lung. Neutropenic animals did not develop altered capillary permeability after challenge with activated C5. Thus, complement activation through C5, in the presence of neutrophils, induces alterations in pulmonary alveolar capillary permeability and causes localization of bacteria to the pulmonary parenchyma. Complement activation in other disease states could potentially result in similar clinical manifestations.
Quantitation of complement activation by polyacrilonitrile (PAN) dialyzer membrane is complicated by the high adsorptive capacity of the membrane for fluid phase anaphylotoxins. Assays for these anaphylotoxins, therefore, underestimate the degree of complement activation produced by this membrane. Alternative methods of measuring in vitro complement activation by the PAN and Cuprophan membranes were explored by incubating normal human erythrocytes with the membranes in the presence of serum. This led to deposition of C3d on these "innocent bystander" red cells, and provided an independent parameter for measuring complement activation. The PAN membrane caused significantly more C3d deposition on red cells, and thus more complement activation than Cuprophan. The possible significance of complement activation by PAN membrane, in consideration of its property of binding the resultant anaphylotoxins, is discussed.
Complement activation may be responsible for some of the symptoms of decompression sickness. In the present study, complement activation was studied by exposing human sera with or without red blood cells to nitrogen bubbles. Nitrogen bubbles activated human complement as measured by generation of the fluid-phase, complement-split product C5a des Arg. In addition, we found that complement activation continued after exposure to bubbles was stopped. This continued complement activation may explain the failure of recompression treatment in some patients. Complement activation induced by nitrogen bubbles in human sera was enhanced when red cells were present. Red cells may be able to provide a stable membrane surface on which complement activation by bubbles can occur more efficiently. Complement activation by nitrogen bubbles in serum also led to the binding of activated C3 to red cells. Quantitation of bystander red-cell-bound C3d may allow the assessment of complement activation occurring by nitrogen bubbles in individuals undergoing decompression.
Complement activity has been linked to decompression sickness (DCS), but the effects of intravascular bubbles on complement activation are poorly understood. We have investigated intravascular complement activation by measuring red blood cell (RBC)-bound C3d after repetitive air diving in man. Subjects were exposed to a single, 20 min, 170 fsw (feet of sea water) dive, or to 2 such dives with a 6-h surface interval. Doppler monitoring for venous gas emboli was performed postdive. Predive blood samples were studied to determine sensitivity of complement to activation by air bubbles. Other predive and postdive venous samples were evaluated for intravascular complement activation. No cases of DCS occurred in 39 dives. Baseline complement sensitivity appeared normally distributed, thus "sensitive" and "insensitive" subjects were not clearly distinguishable. RBC-bound C3d did not increase after 1 dive but did increase after the repetitive dive (P less than 0.05). Furthermore, maximum bubble grade was independent of complement activation.
A perfluorocarbon blood substitute, Fluosol, is undergoing clinical trials as an adjunct to chemotherapy. The adverse effects associated with its administration have been postulated to result from complement activation. When gel electrophoresis and Western blotting of Fluosol are used after its incubation with serum, activated C3 and factors Bb and H are bound to the Fluosol particles in a time-dependent fashion, which suggests that complement activation with Fluosol, as does that with zymosan, occurs on the surface of the particles. Paradoxically, it is found, both by the measurement of Fluosol-bound C3d and by fluid-phase C5a, that lower concentrations of Fluosol cause greater amounts of complement activation, which suggests a complex interaction of activators and inhibitors that changes as the available surface area is decreased. Studies performed with bystander red cell-bound C3d demonstrated in vivo complement activation occurring in six patients receiving Fluosol as an adjunct to chemotherapy for colon cancer. In two patients, there was a marked increase in red cell-bound C3d after Fluosol infusion; these two patients also developed adverse reactions during Fluosol infusion. These studies suggest that the Fluosol surface plays a major role in the initiation and regulation of complement activation that is seen during Fluosol infusion.
Biomaterials activate the complement system which is important since C3a promotes platelet aggregation and release, and C5a activates neutrophils that may augment coagulation. Tiny air nuclei (microbubbles) are found in the surface roughness of biomaterials on exposure to a liquid, therefore two interfaces exist: (a) a blood/biomaterial, and (b) a blood/air interface. Experiments were carried out that documented that air bubbles activate complement and augment in vitro platelet aggregation in human plasma. The air nuclei were removed from the surface of silicone rubber by a technique termed denucleation to determine if complement activation and platelet aggregation could be reduced. We observed a significant reduction in C3a and C5a in the plasma samples incubated with denucleated silicone rubber as compared to the control samples (p less than 0.001, ANOVA). The plasma incubated with the denucleated silicone caused reduced platelet aggregation as compared to the plasma incubated with the control silicone when added to a platelet suspension (p less than 0.001, ANOVA). Surface chemical analysis by x-ray photo-electron spectroscopy (XPS) showed no change in the silicone rubber surface after the denucleation procedure.
Noncardiogenic pulmonary edema is a recognized but uncommon manifestation of type 2 decompression sickness. It typically occurs within 6 hours of a dive. Because the adult respiratory distress syndrome in this setting is believed to be due to microbubbles in the pulmonary vasculature, recompression in a hyperbaric chamber has been recommended as a form of therapy. A patient developed noncardiogenic pulmonary edema following a seawater dive to 75 feet. There was complete radiologic and clinical resolution within 5 hours of hyperbaric therapy.
Decompression sickness sometimes occurs in routine hypobaric chamber runs. Susceptibility to decompression sickness has been correlated with increases in C3a and C5a metabolites of complement activation by air bubbles. If personnel susceptible to decompression sickness show changes in C3a and C5a after decompression, then measurement of these metabolites may be useful in assisting diagnosis. C3a and C5a metabolites of complement activation were measured in 11 male and 2 female volunteers 1 h before (A), 1 h after (B), and 24 h after (C) exposure in routine hypobaric chamber runs to 25,000 ft equivalent altitude. The results were compared with 4 controls (3 males and 1 female). A one-way analysis of variance showed no significant difference between the experimental and control groups overall (p = 0.308; p > 0.05; N = 17). T-tests at each of the results further suggest non-significant differences between the experimental and control groups (p = 0.473; p = 0.341; p = 1.051; p > 0.05; N = 17) at results A, B, and C, respectively. The C5a assay was less than 10 micrograms.L-1 in all individuals, and the particular kit used was not sensitive below 10 micrograms.L-1. As none of the participants developed decompression sickness, it would be useful to determine levels of C3a and C5a in individuals who subsequently develop decompression sickness. One member of the experimental group who had undergone many chamber runs had much higher pre- and post-chamber run levels of C3a. This raises the question of the effect of repeated exposure in low pressure chambers on complement activation, and requires further study.
In this study, the levels of activated complement fragments C3a and C5a were measured on 11 U.S. Navy divers as they performed a 28-day saturation dive to a pressure equivalent of 1,000 feet of seawater (fsw, 31.3 atm abs). Two subjects developed symptoms consistent with the high pressure nervous syndrome (HPNS) and three were treated for type I DCS (joint pain only). These events allowed us to test two hypotheses: a) alterations in C3a or C5a levels during compression are related to the occurrence of HPNS and b) increases in complement fragments are an indicator of decompression stress associated with type I DCS. There was no correlation between changes in C3a and C5a levels during compression and the diagnosis of HPNS. Our results suggest that an increase in C3a and C5a levels during saturation diving correlates with decompression stress and the clinical diagnosis of type I DCS.
A role for the activated complement system in the pathogenesis of decompression sickness has recently been suggested. In this study we aimed at evaluating the response of the complement system to decompression in 24 human volunteers. A significant reduction was observed in the levels of iC3, which is a conformationally changed form of the third complement component (C3), and C3A after decompression (P < 0.001). The levels of total C3 did not change during the experiment. A relatively mild decompression has thus led to a distinct change in the complement activation profile in human volunteers.