Kinetics Of Clot Formation Research Articles

Multiple Levels of Degradation Diminish Hemostatic Potential of Thawed Plasma

Severe bleeding after injury requires transfusion of blood products, including fresh frozen plasma (FFP). Many centers are keeping thawed plasma (TP) ready for massively transfused patients. According to the American Association of Blood Banks Standards, TP is approved for transfusion up to 5 days after thawing, when stored at 1°C to 6°C. However, there are no clinical data analyzing the effects of the approved 5-day storage on plasma. We hypothesize that the hemostatic potential (HP) of freshly thawed (FFP-0) was superior to plasma stored for 5 days (FFP-5). FFP from 30 single donors were thawed at 37°C and kept at 1°C to 6°C for 5 days. HP was evaluated at day 0 and 5 by measuring kinetics of thrombin generation (TG), kinetics of clot formation by thromboelastography, clotting factors and inhibitors, and cell-derived microparticles (MPs) by flow cytometry. When comparing FFP-5 to FFP-0, FFP-5 exhibited only 40% of the potential of FFP-0 for TG (6.2 nM/min vs. 14.3 nM/min, p<0.0001), a slower clotting response via thromboelastography (reaction time: 4.3 minutes vs. 3.2 minutes, p<0.0001) and a longer delay in reaching maximum thrombus generation (5.7 minutes vs. 4.6 minutes, p<0.01). Diminished HP was accompanied by a significant decline in multiple coagulation proteins, including FV, VII, VIII, von Willebrand factor, and free Protein S, by up to 30%, and a decrease of 50% in MP counts. The HP and clot forming ability of TP significantly declined with storage. Hence, freshly TP may have a greater ability to restore hemostasis and correct coagulopathy compared with FFP-5. The clinical consequences for transfused patients deserve further exploration.

Thromboelastography/-metry and external quality control

Thromboelastography/thromboelastometry (TEG/ROTEM) is widely used in near-patient setting, especially in perioperative and intensive care medicine for the management of acute bleeding. Until now a comprehensive quality management especially an external quality control of TEG/ROTEM results is not established. Here we report about our results of a pilot survey performed in 2008 and 2009 integrated in the External Quality Assessment Schemes (EQAS) performed by INSTAND. According to this first EQAS data ROTEM results can be controlled in external quality schemes using lyophilized plasma samples. The clot firmness (A20) and clot formation kinetics characterized by the alpha-angle showed very good reproducibility both between the participants and between different surveys. Variations for CT and CFT were considerably higher especially in the plasma sample with reduced fibrinogen level. Regular participation in an external quality assurance will help to confirm this beneficial technology in emergency settings.

Effects of Angiotensin-Converting Enzyme Inhibition on Thromboelastogaphy for Infants and Children Presenting for Elective Cardiac Surgery.

Introduction: Thromboelastography (TEG) is a point-of-care whole blood coagulation test used commonly with cardiac and liver operations, surgeries for which intraoperative and postoperative bleeding and coagulopathies occur and transfusion is likely. Angiotensinconverting enzyme inhibitors (ACEI) have been found to decrease plasminogen activator inhibitor I (PAI-1), increase tissue plasminogen activator (tPA), decrease tissue factor (TF) production by monocytes, and decrease platelet aggregation.Methods: With IRB approval, kaolin-activated heparinase TEG data were collected on 634 infants and children under 18 yr presenting for elective cardiac surgery between January 2004 and December 2007 for retrospective review utilizing the Haemoscope Thromboelastograph® Coagulation Analyzer (Haemoscope Corp., Niles, IL). Six TEG parameters are analyzed: R (reaction time to reach clot initiation), K (time to reach 20 mm amplitude after R), alpha (clot kinetics), MA (maximum amplitude), LY30 (amount of lysis 30 min after MA), and CI (coagulation index). Infants and children are analyzed based on preoperative therapy with an ACEI.Results: In those receiving ACEI, the time to initial fibrin formation is faster (R, p=0.0007), although subsequent clot formation is slower (K, p=0.0201; alpha, p=0.0092) than without ACEI drugs. Moreover, there is markedly less fibrinolysis (LY30, p=0.0019) in those receiving an ACEI. Clot strength and overall clot dynamics (MA and CI, p=NS) were similar in both groups (Table 1). Subjects with baseline oxygen saturation of 88% differ in that they do not have a significant change in K or alpha but do have a higher CI.Table 1.Ranges for Kaolin-activated Heparinase Thromboelastography ParametersGroupR (min)K (min)alpha (degrees)MALY30%CIControl7.27±2.201.83±0.6865.0±8.464.2±6.42.28±2.87−0.68±2.81ACEI6.54±1.881.99±0.8162.7±10.263.3±5.81.12±2.05−0.39±2.87p value0.00070.02010.0092NS0.0019NSDiscussion: A number of investigators have found antithrombotic effects of ACEI drugs in adults but children have not been studied. The TEG provides an ex vivo means of assessing whole blood clotting dynamics. This preliminary analysis of infants and children reveals a delay in the time required to initiate clot via the intrinsic coagulation cascade as activated by kaolin (R) and slowed clot formation (K and alpha). Final clot strength shows no difference and LY30 shows less fibrinolysis. A shift in plasma hemostasis towards fibrinolysis would potentially delay R, prolong K, decrease alpha, and increase LY30. Paradoxically, we see a decrease in R and LY30. Reduced platelet aggregation is consistent with slowed kinetics of clot formation (K and alpha) but would be expected to cause a reduction in MA that is not seen. Further analysis of this data will separate the subjects into age groups as TEG parameters vary with age in infants and children. Also, since there is evidence that enalapril may not have the antiplatelet effects of captopril and may increase tPA in women but not men, further analysis of gender and type of ACEI given will be completed.

Thromboelastometry as an adjunctive test in thrombophilia screening for adverse pregnancy outcome

ING FOR ADVERSE PREGNANCY OUTCOME LEONIE FLACH, JORIS LENGLET, HERMAN VAN GEIJN, ANTOINETTE BOLTE, VU University Medical Center, Obstetrics & Gynecology, Amsterdam, Netherlands OBJECTIVE: Thrombophilia has been associated with adverse pregnancy outcome. Thromboelastometry is an easy, rapid and reproducible test that offers the opportunity to investigate all phases of coagulation and fibrinolysis in whole blood. The purpose of this study was to determine if an additional group of women with coagulopathy could be found with the use of thromboelastometry, that are not yet identified with routine thrombophilia screening and that are at risk of adverse pregnancy outcome. STUDY DESIGN: Included were women that had been referred for routine thrombophilia screening because of their complicated obstetric histories. The routine thrombophilia screening includes testing for protein S, protein C, antitrombin III, APC resistance, factor V Leiden, prothrombin mutation, antiphospholipid antibodies and methionine loading testing. Thromboelastometry was performed with ROTEM Gamma (Pentapharm GMBH, Munchen, Deutschland). Studied are the kinetics of clot formation, clotting time, clot formation time and the maximum clot firmness. RESULTS: 46 non-pregnant women with a history of previous severe preeclampsia, HELLP syndrome, IUGR, placental abruption, fetal loss and recurrent miscarriage were included. In 16 women thrombophilia was diagnosed by routine testing, in this group 5 women also had abnormal thromboelastometry. In 30 women no trombophilia was found, in this group 10 women had an abnormal tromboelastometry. Thromboelastometry identified only 31% of women with an abnormal thrombophilia screening. However, in 33% of the women with normal thrombophilia screening an abnormal thromboelastometry was found. CONCLUSION: Thromboelastrometry does detect a group of women with abnormal coagulation that are not detected by routine thrombophilia screening. Additional studies are warranted to determine if thromboelastometry identifies a subset of women with a prothrombotic tendency that are at an increased risk of recurrent adverse pregnancy outcome.

New methods showing in vitro changes of platelets

Introduction In vitro methods for assessing stored platelets are time consuming and variably correlate with in vivo survival. We used the ADVIA 120 and the Thromboelastogram (TEG) to assess changes during storage to determine a correlation of the results with those of other commonly used measures. Methods Platelet concentrates were tested at 1 and 5 days of storage. In vitro test included platelet count, aggregation response, the hypotonic shock response (HSR), The Kunicki morphology score (KMS) and platelet activation using CD62. The ADVIA ® was used to measure the platelet density and the granule content. The TEG measured the kinetics of clot formation. Results The platelet count and HRS did not change during storage. Aggregation decreased 50% by day 5. The KMS dropped from 307 at day 2–170. The MPC fell below 200 g/l. There was slight platelet activation; the rate of clot formation decreased. Conclusions Standard measures of in vitro platelet function indicated alterations during storage. A MPC of less than 200 corresponded to a Kunicki morphology score of less than 200. The TEG results correlated will with the KMS. These measurements may prove useful in predicting platelet survival and recovery.

The effect of glycaemic control on fibrin network structure of type 2 diabetic subjects

Diabetic subjects have been shown to have altered fibrin network structures. One possible cause may be fibrinogen glycation resulting in altered structure/function properties. We investigated the effect of glucose control on fibrinogen glycation and fibrin network structure in type 2 diabetes. Blood samples were taken from twenty uncontrolled diabetic subjects at baseline to determine the levels of fibrinogen glycation and fibrin network structures. The subjects were then treated with insulin until blood glucose control was achieved before end blood samples were taken. Twenty age- and BMI-matched non-diabetic subjects were included as a reference group. The diabetic subjects had significantly higher mean fibrinogen glycation at baseline than the non-diabetic subjects (7.84 vs. 3.89 mol glucose / mol fibrinogen; p < 0.001). This was significantly reduced during the intervention (7.84 to 5.24 mol glucose / mol fibrinogen; p < 0.0002) in the diabetic group. Both groups had high mean fibrinogen concentrations (4.25 and 4.02 g/l, diabetic and non-diabetic subjects respectively). There was no difference in fibrinogen concentration, porosity, compaction and kinetics of clot formation between the diabetic subjects and non-diabetic subjects at baseline, nor were there any changes during the intervention despite the reduced fibrinogen glycation. Fibrin network characteristics correlated well with fibrinogen but not with any markers of glycaemic control. Improved glycaemic control resulted in decreased fibrinogen glycation but not fibrinogen concentration. It seems as though porosity, compaction and kinetics of clot formation are more related to fibrinogen concentration than fibrinogen glycation in this model.

The influence of fibrin polymerization and platelet-mediated contractile forces on citrated whole blood thromboelastography profile

Thromboelastography analysis providing a global assessment of coagulation is gaining new interest in clinical practice. MinimalTF triggered whole blood thromboelastography provides a valuable tool for studying the kinetics of clot formation (expressed by the parameters R, K and alpha-angle) and the physical characteristics of the clot, such as its firmness and the elastic modulus shear (expressed by the parameters maximal amplitude MA and G). We studied the influence of fibrin polymerization and platelet functional status on each parameter of thromboelastographic trace obtained by minimalTF activation inWB by employing increasing concentrations of a fibrin polymerization inhibitors (the tetrapeptide Gly-Pro-Arg-Pro-OH.AcOH; Pefabloc-FG) and an inhibitor of actin polymerization (Cytochalasin D). Pefabloc-FG at concentrations higher than 5 mg/ml prolonged the R and K times and decreased the alpha-angle in a concentration-dependent manner but it did not modify MA and G parameters. At the concentration of 5 mg/ml, Pefabloc-FG completely inhibited clot formation. Cytochalasin D had no effect on R time but decreased the alpha-angle, MA and G parameters by reaching a plateau at the concentration of 5 microM. The effect of cytochalasin D was more pronounced on MA and G than on the alpha-angle. A combination of both Pefabloc-FG (0.5 mg/ml) and cytochalasin D (50 microM) significantly decreased alpha-angle compared to control as well as their single effect. However, G value was dramatically reduced in the presence of cytochalasin D exposure, without any additional effect when both inhibitors were combined. This study confirms the importance of fibrin polymerisation on the kinetics of thrombus formation and demonstrates the close association between the quality of the thrombus and the functional status of platelets. Normal platelet contractile forces are of major importance for the maximum amplitude of TEG which is related to the strength and elastic modulus of the thrombus.

Peroxynitrite Decreases Rabbit Tissue Factor Activity In Vitro

Tissue factor (TF) is a primary initiator of physiological coagulation in vivo. Peroxynitrite (OONO(-)), a molecule formed from nitric oxide (NO) and superoxide (O(2). (-)), decreases human TF activity in vitro. Coagulopathy has been associated with hepatoenteric ischemia-reperfusion known to involve formation of OONO(-). Further, circulating TF activity decreases in rabbits after hepatoenteric ischemia-reperfusion. We hypothesized that exposure of rabbit TF to OONO(-) would result in a decrease in activity. OONO(-) generation was performed with 3-morpholinosydnonimine (SIN-1), a molecule that produces both nitric oxide and superoxide. Rabbit brain TF was incubated at 37 degrees C for 90 min with 1) 0 mM SIN-1, 2) 5 mM SIN-1, 3) 5 mM SIN-1 and 2000 U/mL recombinant human superoxide dismutase (hSOD1), or 4) 2000 U/mL hSOD1 (n = 8 per condition). TF activity was assessed by addition of TF samples to human plasma and measuring clot formation kinetics with a thrombelastograph(R). TF exposure to SIN-1 resulted in a 48% decrease in activity that was significantly different from the other three conditions (P < 0.001). There were no significant differences between the other conditions. We conclude that rabbit TF is inhibited by OONO(-), and further investigation to determine the role of OONO(-) in coagulopathies associated with hepatoenteric ischemia-reperfusion is warranted. Tissue factor (TF) initiates physiological coagulation in vivo. Hepatoenteric ischemia-reperfusion injury is associated with peroxynitrite (OONO(-)) formation, coagulopathy and decreased TF activity in rabbits. We determined that OONO(-) decreased rabbit TF activity in vitro via thrombelastography(R).

The role of platelets and recombinant factor VIIa on thrombin generation, platelet activation and clot formation.

In the present study we assessed the effect of platelet counts and rFVIIa on thrombin generation, platelet activation and clot formation after tissue factor pathway activation in human plasma aiming to investigate the mechanism by which rFVIIa induces haemostasis in patients with severe thrombocytopenia. Plasma samples with platelet counts from 5 x 10(9)/l to 150 x 10(9)/l were spiked with rFVIIa (1 micro g/ml) or buffer. Clotting was initiated in the presence of diluted thromboplastin. Thrombin generation was assessed using the Thrombogram-Thrombinoscope trade mark assay. The kinetics of platelet activation was assessed using flow cytometry to measure the expression the P-selectin on platelet membrane of washed platelets suspended in defibrinated homologous PPP. Thromboelastography was used to evaluate the effect of platelets and rFVIIa on the kinetics of clot formation and clot's firmness. In the presence of low platelet counts the endogenous thrombin potential (ETP) and the maximum concentration of generated thrombin (Cmax) were reduced by 60%-70%. The lag-time of thrombin generation and the time required to reach the Cmax (Tmax) were prolonged, the velocity of platelet activation was decreased and thrombus formation was delayed. Recombinant FVIIa accelerated thrombin generation and platelet activation but it did not significantly modify ETP or Cmax. Recombinant FVIIa enhanced platelet activation in a TF and thrombin dependent manner since its effect on the studied parameters was abolished when TF was omitted or when hirudin was added into the experimental system respectively. Recombinant FVIIa normalized the velocity of clot formation but it did not modify clot firmness, which depended mainly on platelets' count. In conclusion, in experimental conditions simulating severe thrombocytopenia rFVIIa in the presence of low amounts of TF, accelerates thrombin generation, without increasing the maximum amount of generated thrombin, thus leading in enhanced platelet activation and rapid clot formation.

Monitoring coagulation and the clinical effects of recombinant factor VIIa

Accurately monitoring hemostasis in patients with coagulation disorders is vital in order to allow physicians to optimize anticoagulant therapy and deliver effective patient management. Traditional assays, based on the measurement of the time to first evidence of clot formation, fail to describe the kinetics of clot production that ultimately define the quality of the final clot. This review describes the technologies that have been developed to accurately describe and monitor the kinetics of clot formation. Using clinical examples, the utility of these technologies is assessed and conclusions drawn about the most useful diagnostic measures for monitoring hemostasis.

RETRACTED: Effects of a new modified, balanced hydroxyethyl starch preparation (Hextend®) on measures of coagulation

Hydroxyethyl starch (HES) may affect blood coagulation. We studied the effects of a modified, balanced, high-molecular weight [mean molecular weight (MW) 550 kDa], high-substituted [degree of substitution (DS) 0.7] HES preparation (Hextend) on coagulation in patients undergoing major abdominal surgery. Patients were allocated randomly to receive Hextend) (n=21), lactated Ringer's solution (RL, n=21) or 6% HES with a low MW (130 kDa) and a low DS (0.4) (n=21). The infusion was started after induction of anaesthesia and continued until the second postoperative day to maintain central venous pressure between 8 and 12 mm Hg. Activated thrombelastography (TEG) was used to assess coagulation. Different activators were used (extrinsic and intrinsic activation of TEG) and aprotinin was added to assess hyperfibrinolytic activity (ApTEG). We measured onset of coagulation [coagulation time (CT=reaction time, r)], the kinetics of clot formation [clot formation time (CFT=coagulation time, k)] and maximum clot firmness (MCF=maximal amplitude, MA). Measurements were performed after induction of anaesthesia, at the end of surgery, 5 h after surgery and on the mornings of the first and second days after surgery. Significantly more HES 130/0.4 [2590 (SD 260) ml] than Hextend) [1970 (310) ml] was given. Blood loss was greatest in the Hextend) group and did not differ between RL- and HES 130/0.4-treated patients. Baseline TEG data were similar and within the normal range. CT and CFT were greater in the Hextend) group immediately after surgery, 5 h after surgery and on the first day than in the two other groups. ApTEG MCF also changed significantly in the Hextend) patients, indicating more pronounced fibrinolysis. Volume replacement using RL caused moderate hypercoagulability, shown by a decrease in CT. A modified, balanced high-molecular weight HES with a high degree of substitution (Hextend) adversely affected measures of coagulation in patients undergoing major abdominal surgery, whereas a preparation with a low MW and low DS affected these measures of haemostasis less. Large amounts of RL decreased the coagulation time.

Influence of a new hydroxyethylstarch preparation (HES 130/0.4) on coagulation in cardiac surgical patients

Objective: To compare volume therapy with HES 130/0.4, a new hydroxyethylstarch (HES) solution with a gelatin-based fluid replacement strategy. Design: Prospective, randomized, safety study. Setting: Urban, university-affiliated hospital (single institution). Participants: Forty-two patients undergoing elective cardiac surgery. Interventions: Patients were prospectively randomized into 2 groups: In group 1 (n = 21), gelatin was given perioperatively for volume support until the 1st postoperative day to keep the central venous pressure (CVP) between 10 and 14 mmHg; in group 2 (n = 21) HES 130/0.4 was administered using the same protocol as in group 1. Measurements and Main Results: Standard coagulation variables and modified thromboelastography (TEG®) were used. Using different activators for extrinsic and intrinsic activation and heparin inactivation by heparinase, the onset of coagulation (coagulation time), kinetics of clot formation (clot formation time), and maximum clot firmness were measured. Measurements were performed after induction of anesthesia (T0), at the end of surgery (T1), 4 hours after surgery (T2), and on the morning of the 1st postoperative day (T3). A total of 3310 ± 810 mL of gelatin and 3070 ± 570 mL of HES 130/0.4 were used in the 2 groups during the study period. The 2 groups did not differ with regard to postoperative bleeding or in use of packed red blood cells or fresh frozen plasma. Standard coagulation variables were similar between the 2 groups. All TEG® variables were within the normal range at baseline. Coagulation time and clot formation time data were significantly elevated after surgery and in the intensive care unit, without showing specific differences between the 2 volume replacement groups. Intrinsic TEG® and heparinase TEG® clot formation times remained significantly higher until the end of the study period. No differences were seen between HES-treated and gelatin-treated patients. Conclusions: Volume replacement with the new HES preparation was as safe as gelatin-based volume replacement with regard to coagulation in cardiac surgical patients. HES 130/0.4 is an alternative plasma substitute to treat volume deficits. Copyright © 2001 by W.B. Saunders Company

Assessment of rVIIa as a universal haemostatic agent in a model of haemodilution

Haemostatic failure, secondary to large volume fluid replacement, is a major component to the mortality and morbidity associated with blunt trauma. Progressive bleeding in multiply injured patients is due to both dilution effects and specific inhibitory effects on platelet function of the colloids used. Recombinant factor VIIa (rVIIa) is seen increasingly as a possible universal haemostatic agent that could act to reverse or prevent haemostatic failure associated with dilution and the direct effects of the colloids within the 'Golden' hour of haemorrhagic shock. We have conducted a pilot preclincal study to evaluate the potential role of rVIIa as a universal haemostatic agent in a model of large volume fluid replacement using thrombelastography (TEG). TEG is a method of global haemostasis assessment, providing information on the rate of clot formation, clot strength and durability. Whole blood samples from normal donors were tested undiluted (100%) or diluted (50% and 80%) with standard colloid replacement solutions (Haemacel, Albumin, Gelofusine, Hydroxyethyl starch) and N/Saline. Global haemostasis was assessed in the TEG, ± 90 μg/kg rVIIa added. In undiluted blood (100%) there were no statistically significant changes in any TEG parameter when rVIIa was added. At dilutions of > 50% addition of rVIIa significantly improved the kinetics of clot formation and rate of platelet reactivity, P < 0.05, although time to the start of coagulation and final clot strength were not significantly different. The beneficial effects of addition of rVIIa did not differ between different fluid replacement solutions. Addition of rVIIa therefore appears to improve markers of global haemostasis in this model of large volume fluid replacement. Further work is required to assess its potential value as a universal haemostatic agent in the setting of blunt trauma and large volume fluid replacement.

Platelets and Endothelial Cells Act in Concert to Delay Thrombolysis – Evidence from an In Vitro Model of the Human Occlusive Thrombus

The molecular and cellular mechanisms that over a period of hours render a human thrombus progressively resistant to fibrinolysis have been probed with a novel in vitro model. The kinetics of clot formation and fibrinolysis were monitored by laser light scattering with platelet-rich model thrombi contained in cylindrical flow chambers. In selected experiments, human umbilical vein endothelial cells were also cultured to confluence on the inner walls of these "glass blood vessels". Following an "aging" period (0.5, 2 or 4 h), each thrombus was gently perfused with a bolus of plasminogen/recombinant tissue plasminogen activator to induce fibrinolysis. Platelets delayed lysis of 2 h-aged thrombi by approximately 70% and (non-stimulated) endothelial cells by approximately 30%, compared to cell-free control clots. However, even greater lytic delays (approximately 260%) resulted when both vascular cells were present in the same 2 h-aged thrombus. In contrast, rapid lysis was consistently achieved with R298E,R299E t-PA, a genetically engineered plasminogen activator that is insensitive to inhibition by plasminogen activator inhibitor type 1. These observations suggest platelets and endothelial cells act in concert to enrich the fibrin scaffold of an aging human thrombus in plasminogen activator inhibitor. We propose that the presence of both platelets and endothelial cells may contribute to progressive thrombolytic resistance.

Fibrin formation: effect of calcium ions

Using laser fluctuation spectroscopy, a technique that measures particle size change in solution, the kinetics of fibrin clot formation from fibrinogen can be studied. With this technique the effect of calcium on the three distinguishable phases of clot formation, (1) proteolysis of fibrinogen, (2) fibrinogen-fibrin monomer complex formation, and (3) fibrin monomer polymerization, were investigated. Only a small change in the length of the induction period that results from the fibrinogen-fibrin monomer interactions was observed. However, there was a marked increase in the rate of fibrin monomer polymerization in the presence of calcium ions. These data show that calcium decreases the time required for fibrin formation from fibrinogen by markedly accelerating the phase of fibrin monomer polymerization.

Fibrin Formation: Effect of Calcium Ions

Abstract Using laser fluctuation spectroscopy, a technique that measures particle size change in solution, the kinetics of fibrin clot formation from fibrinogen can be studied. With this technique the effect of calcium on the three distinguishable phases of clot formation, (1) proteolysis of fibrinogen, (2) fibrinogen-fibrin monomer complex formation, and (3) fibrin monomer polymerization, were investigated. Only a small change in the length of the induction period that results from the fibrinogen-fibrin monomer interactions was observed. However, there was a marked increase in the rate of fibrin monomer polymerization in the presence of calcium ions. These data show that calcium decreases the time required for fibrin formation from fibrinogen by markedly accelerating the phase of fibrin monomer polymerization.

Human fibrinogen and asialo-fibrinogen: A comparison of coagulation parameters

The effect of desialylation of fibrinogen on its conversion to fibrin has been investigated with particular reference to the kinetics of clot formation and structure. Also examined was the role of sialic acid in fibrinogen (factor I) poor in factor XIII (fibrinstabilizing factor) and factor I containing F XIII. The removal of more than 90% of the sialic acid of fibrinogen does not alter the thrombin clotting time, the clot solubility in monochloroacetic acid, the extent of cross-linking in the fibrin polymer, or the firmness and elasticity of the evolved clot. The data indicate that the sialic acid residues of fibrinogen do not contribute significantly to its conversion to fibrin by thrombin.

Studies on Fibrin Formation and Effects of Dextran

SummaryIn this study highly reproducible turbidimetric techniques are used to investigate clotting of human platelet-poor plasma and purified human fibrinogen solutions by thrombin. Three phases are clearly distinguishable turbidimetrically during clotting. All the three phases are altered by dextran. This effect of dextran is not mediated by any action on the enzymatic activity of thrombin. Further, it is independent of the molecular weight of dextran, but is found related to the final dextran, thrombin and fibrinogen concentrations. Evidence is presented to show that dextran accelerates the polymerisation of fibrin monomer. However, it seems clear that dextran has an additional action quite apart from this effect. These actions of dextran are discussed in relation to kinetics of clot formation.

Comparison of the kinetics of clot formation, fibrinogen, fibrinolysis, and hematocrit in pregnant women and adults

Pregnant women in labor and adult controls were studied for differences in the kinetics of clot formation, using the thromboelastograph, a sensitive optical instrument which allows for a continuous recording of all phases of coagulation and gives information regarding the mechanical properties of the clot. Pregnant women were found to be significantly more hypercoagulable than adult controls. This hypercoagulability was further demonstrated by higher fibrinogen levels and less over-all fibrinolytic activity (longer fibrinolysis times) as compared to adult controls. Pregnant women in premature labor had higher fibrinogen levels and less fibrinolytic activity (longer fibrinolysis times) than those at term. The significances of these findings are discussed.

Fibrinolytic activity, thrombin inhibitor and kinetics of clot formation in premature infants with respiratory distress syndrome.

Fibrinolytic activity, thrombin inhibitor and kinetics of clot formation in premature infants with respiratory distress syndrome.