Key Words: Thrombosis, Vascular Graft, Microfluidics, Wall Shear Stress / Vascular grafts are essential for the management of cardiovascular disease. However, the lifesaving potential of these devices is undermined by thrombosis arising from material and flow interactions on the blood contacting surface. To combat this issue, the use of antithrombogenic coatings has emerged as a promising strategy for modulating blood and graft interaction in vivo. Although an important determinant of graft performance, hemodynamics are frequently overlooked in the in vitro testing of coatings and their translatability remains poorly understood. We address this limitation with a microscale platform that incorporates vascular prosthesis and coatings with tuneable flow and surface conditions in vitro. As a proof of concept, we use the platform to test the thrombogenic performance of a novel class of lubricant infused (LIS) and antibody lubricant infused (anti-CD34 LIS) coated ePTFE vascular grafts in the presence of arterial wall shear stress, with and without the presence of endothelial cells. Our findings suggest lubricant infused coated ePTFE vascular grafts are thromboresistant under flow and may have potential for in vivo arterial grafting applications. It is moreover apparent that the microscale properties of the device could be advantageous for the testing and translation of novel antithrombogenic coatings or blood contacting prosthesis in general. / Thesis / Master of Applied Science (MASc)

Deep Vein Thrombosis, a potentially fatal event, occurs when a blood clot forms within the deep veins of the body. This most frequently manifests in the lower extremities. The goal of this research was to build an inexpensive device that could apply therapeutic compressive pressure to the lower leg to aid in the prevention of deep vein thrombosis using only mechanical input from the user. Several different prototypes were designed and built with varying degrees of success. Characterization of the final prototype required calibration of pressure and force measurement sensors. Additionally, a mathematical model was developed in order to predict how changes in the design of the device, as well as differing sizes and shapes of lower legs, would impact the amount of applied pressure. The predictions of this mathematical model were found to be substantially larger when compared against empirical data. However, there is evidence to indicate that the final prototype could be minimally altered to apply ample therapeutic pressure. / Bioengineering

Factor XI (FXI) is the zymogen of the coagulation protease factor XIa (FXIa) that contributes to thrombin generation through the intrinsic pathway. FXI is activated by the contact pathway protease, factor XIIa (FXIIa), in a high molecular weight kininogen-dependent manner. It is also known to be activated by thrombin in a positive feedback reaction, however, the mechanism of this activation is not yet completely understood. Therefore, our objectives were to identify the role of polyanions in the thrombin mediated FXI activation, and the role of the thrombin exosites in the activation. To study this activation, we assessed the activation of FXI by thrombin in the presence and absence of the polyanions, dextran sulfate and polyphosphate (polyP). We utilized surface plasmon resonance to determine whether FXI and thrombin bind to the polyanions, and how the exosites effect thrombin’s ability to bind using thrombin exosite 1 and 2 variants. To investigate the role of the exosites in FXI activation, we analyzed the activation of FXI by the thrombin variants. In addition, we explored how inhibiting the thrombin exosites using DNA aptamers affects thrombin’s ability to bind to polyanions and activate FXI. We found that polyanions are required as a cofactor for the activation of FXI by thrombin, and stimulate the activation in a concentration dependent fashion, suggesting a template mechanism. Our findings also show that exosite 1 and 2 are required for thrombin to bind to polyanions, however, exosite 2 plays the predominant role in FXI activation. Our aptamer data showed that either exosite can be targeted to inhibit FXI activation. These findings enrich our understanding of the mechanism of FXI activation by thrombin and provides further insight on how to attenuate the activation for potential antithrombotic therapies. / Thesis / Master of Science (MSc)

Background: Platelets provide the initial haemostatic plug at sites of vascular injury. They also participate in pathological thrombosis that leads to myocardial infarction, stroke and peripheral vascular disease. The outcome of an acute myocardial infarction depends not only on the formation and stability of an occlusive thrombus, but also on the efficacy of the endogenous thrombolytic process, which allows reperfusion of the infarct related artery and prevents recurrent ischaemic episodes. Various platelet function tests are available to measure the thrombogenic potential of an individual, but the sensitivity of these tests remain questionable as most of these tests use citrated blood and measure response to a particular agonist. Endogenous thrombolysis has been a neglected entity, and its beneficial effects on cardiovascular outcomes has not been studied in depth in the past, possibly as until recently there has been no available technique to measure spontaneous thrombolytic activity in native blood. The Global Thrombosis Test (GTT) is a new point of care tests that allows us to measure time to thrombus formation (Occlusion time: OT) using native blood, avoiding the use of agonists and making the test results more physiological. The GTT also measures the time to lyse this formed thrombi without use of any lytic agents (Lysis time: LT), allowing us to measure the patient’s endogenous thrombolytic potential. Aim: Our aim in this study was to detect patients who are at risk of future thrombotic events despite dual antiplatelet therapy, either due to prothrombotic tendency or due to impaired endogenous thrombolysis, and to determine if these two parameters were correlated. Methods: GTT was used to assess the thrombotic and thrombolytic activity in healthy volunteers, and in different patient populations. 100 healthy volunteers were tested using the GTT, and a normal range was established. 300 patients admitted to hospital with a diagnosis of acute coronary syndrome (ACS) were included in the study, and tested using the GTT after they had been stabilized on dual antiplatelet therapy (Aspirin and Clopidogrel). All these patients were followed up for a year, to determine if their baseline GTT results were a predictor of recurrent cardiac events. The primary endpoint of the study was major adverse cardiovascular events (MACE), which was a composite of cardiovascular death, nonfatal myocardial infarction, or stroke at 12 months. Results: All results were analysed using statistical package SPSS version 16.0 (SPSS Inc., Chicago, Illinois). The 100 healthy volunteers were all non-smokers, and were not taking any medications. There were 55 males and 45 females, and mean age was 38±11 years (range 22-76, IQR 11). OT was normally distributed with mean OT 377.80s, and using mean ± 2SD, we derived a normal range of 185-569s (200-550s). LT demonstrated a skewed distribution with values ranging between 457 – 2934s. Using log transformation, a normal range of 592 – 1923 (600- 2000s) was established for LT. OT and LT were both prolonged in ACS patients compared to normal volunteers (p< 0.001). No association was observed between OT and risk of major adverse cardiovascular events. LT was noted to be a significant and independent predictor of MACE in a multivariate model adjusted for cardiovascular risk factors. LT ≥ 3000 s was the optimal cutoff value for predicting 6 month MACE [hazard ratio (HR): 2.48, 95% CI: 1.2-4.8, P= 0.008] and cardiovascular death [HR: 4.04, 95% CI : 1.3-12.0, P= 0.012 ] and 12 month MACE [HR:1.9, 95% CI: 1.04- 3.5,P= 0.03] and cardiovascular death [HR: 3.9,95% CI: 1.34-11.9, P= 0.013 ]. LT ≥ 3000 s was observed in 23% of ACS patients. Conclusions: Our study suggests that endogenous thrombolytic activity based on lysis of platelet rich thrombi can be assessed by the point of care GTT assay, which can help in identification of ACS patients at high risk of future cardiac events. Prolongation of OT may be explained by the antiplatelet effects of Aspirin and Clopidogrel, as both these drugs prolong time to thrombus formation and hence increase OT. Further large studies are required to study factors which can reduce thrombogenic potential, and improve endogenous thrombolytic activity, which can be monitored using the GTT to improve cardiovascular outcomes.

A left ventricular thrombus develops in approximately 40% of patients following an anterior myocardial infarction. Embolization from these thrombi has been regarded as the most important cause of stroke following a myocardial infarction. The occurrence and characteristics of left ventricular thrombi and stroke after anterior myocardial infarction may, however, have changed after the introduction of aspirin and thrombolytics as standard therapy. The occurrence of left ventricular thrombi was examined in 99 patients with an acute anterior myocardial infarction, 74 of whom were treated with streptokinase. Thrombi were equally common in the thrombolysis group (46%, 95% confidence interval [Cl], 35-57%) as in the non-thrombolysis group (40%, 95% Cl, 21-59%). The risk of thrombus formation was related to the degree of left ventricular segmental dysfunction. Using serial echocardiographic examinations, the formation and resolution of thrombi was found to be highly dynamic. The majority of thrombi diagnosed during the hospital stay had resolved at follow-up one month later, irrespective of treatment with streptokinase or anticoagulants. The development of new thrombi was, however, observed at every follow-up examination interval. One-hundred-and-twenty-four patients suffering a stroke within 28 days of an acute myocardial infarction were identified in the northern Sweden MONICA stroke registry between 1985 and 1994. The overall event rate of ischemic myocardial infarction-related stroke was 1.07%. The risk of a stroke was highest duringt he first 5 days after the infarction. Only approximately half the strokes were preceded by an anterior myocardial infarction. In a case-control analysis, atrial fibrillation (chronic or new onset), ST elevation and a history of a previous stroke were found to be independent predictors of stroke. There was a long-term trend towards a lower incidence and event rate for myocardial infarction-related stroke. Clinical stroke characteristics were examined in 103 patients with a first-ever stroke within 28 days of a myocardial infarction and compared with stroke characteristics in 206 control subjects without a recent myocardial infarction. The sudden onset of neurological symptoms, an impairment of consciousness, a progression in neurological deficits and a stroke of the total anterior circulation infarction subclass were more common in cases than in controls. The risk of a recurrent stroke during one year of follow-up was not influenced by a recent myocardial infarction, but patients who had suffered a myocardial infarction had markedly higher mortality. To conclude, thrombolytic treatment does not reduce the occurrence of left ventricular thrombi after a myocardial infarction. The risk of thrombus formation is related to the extent of the myocardial injury. The development and resolution of thrombi is a highly dynamic process. There is a long-term trend towards a lower incidence and event rate of ischemic stroke after a myocardial infarction. Although the clinical stroke characteristics differ, they are not specific enough to differentiate between patients with and without a recent myocardial infarction. / <p>S. 1-84: sammanfattning, s. 85-136: 5 uppsatser</p> / digitalisering@umu

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 5 uppsatser.

Background: Recent studies have suggested that patients with idiopathic pulmonary fibrosis (IPF) may have a higher risk of venous thromboembolism (VTE) compared to general population even though the results were inconsistent. Objective: To investigate the risk of VTE among patients with IPF. Methods: Comprehensive literature review using MEDLINE and EMBASE database were performed to identify studies that compared the risk of VTE among patients with IPF to general population. Effect estimates from each study were combined together using random effect model, generic inverse variance method of DerSimonian and Laird. Results: Out of 510 retrieved articles, 5 studies met the inclusion criteria and were included in the meta-analysis. A significant risk of VTE in patients with IPF was observed with the pooled risk ratio of 2.11 (95% confidence interval, 1.28-3.48). The heterogeneity was moderate with I2 of 64%. Conclusion: An approximately 2-fold increased risk of VTE among patients with IPF was observed in this meta-analysis.