Background and Purpose: The endothelium is a single-cell layer positioned at the blood-vascular wall interface, where in response to blood-borne signals and hemodynamic forces, endothelial cells act as central regulators of vascular homeostatic processes including vascular tone, growth and remodeling, inflammation and adhesion, and blood fluidity and coagulation. Agonist- or flow-stimulated endothelium-dependent vasorelaxation becomes impaired in states of cardiovascular disease (CVD) risk and has been identified as a possible biomarker of overall endothelial dysfunction leading to vascular dysregulation and disease pathogenesis. Accordingly, it is important to elucidate the mechanisms accounting for this endothelial vasomotor dysfunction. Upon stimulation, endothelial cells can synthesize and release a variety of endothelium-derived relaxing factors (EDRFs), the most prominent of which is nitric oxide (NO) derived from NO synthase (NOS). In addition, under certain CVD risk conditions including hypertension and aging, stimulated endothelial cells can become a prominent source of endothelium-derived contracting factors (EDCFs) produced in a cyclooxygenase (COX)-dependent manner. Consequently, endothelial dysfunction may be caused by under-active EDRF signaling and/or competitive over-active EDCF signaling. Much attention has been given to elucidating the mechanisms of under-active EDRF signaling and its role in causing endothelial dysfunction, wherein excess reactive oxygen species (ROS) accumulation and oxidative stress under CVD risk conditions have been recognized as major factors in reducing NO bioavailability thus causing under-active EDRF signaling and endothelial dysfunction. Less attention however, has been given to elucidating the mechanisms of over-active COX-mediated EDCF signaling and its role in causing endothelial dysfunction. Moreover, while COX-mediated EDCF signaling activity has been investigated in some segments of the vasculature, most notably the aorta, it has not been well-investigated in the common carotid artery (CCA), a highly accessible cerebral blood flow conduit particularly advantageous in exploring the roles of the endothelium in vascular pathogenesis. It was the global purpose of this thesis to gain a better understanding of the cellular-molecular mechanisms accounting for endothelial dysfunction in the CCA of animal models known to exhibit COX-mediated EDCF signaling activity, in particular essential (spontaneous) hypertension and aging. Experimental Objective and Approach: This thesis comprises three studies. Study I and Study II investigated the CCA of young-adult (16-24wk old) normotensive Wistar Kyoto (WKY) and Spontaneously Hypertensive (SHR) rats. Study III investigated the CCA of Adult (25-36wks old) and Aging (60-75wks old) Sprague Dawley (SD) rats treated in vivo (or not; CON) with L-buthionine sulfoximine (BSO) to chronically deplete the cellular anti-oxidant glutathione (GSH) and increase ROS accumulation and oxidative stress. The global objective and approach across these studies was to systematically examine the relative contributions of NOS and COX signaling pathways in mediating the acetylcholine (ACh)-stimulated endothelium-dependent relaxation (EDRF) and contractile (EDCF) activities of isometrically-mounted CCA in tissue baths in vitro, with a particular focus on elucidating the mechanisms of COX-mediated EDCF signaling activity. An added objective was to examine the in vivo hemodynamic characteristics of the CCA in each animal model investigated, serving both to identify the pressure-flow environment that the CCA is exposed to in vivo and to provide assessment of potential hypertension, aging, and oxidative stress effects on large artery hemodynamics. Key Findings: Study I hemodynamic analysis confirmed a hypertensive state in young adult SHR while also exposing a reduction in mean CCA blood flow in SHR compared to WKY accompanied by a multi-faceted pressure-flow interaction across the cardiac cycle relating to flow and pressure augmentation. Study III hemodynamic analysis found that neither aging nor chronic BSO-induced GSH depletion affected CCA blood pressure or blood flow parameters in SD rats. Study I and II demonstrated that a COX-mediated EDCF response impaired ACh-stimulated endothelium-dependent vasorelaxation in pre-contracted CCA from young adult SHR, while EDRF signaling activity, predominantly mediated by NO, remained well-preserved compared to WKY. Examining ACh-stimulated contractile function specifically from a quiescent (non pre-contracted) state revealed that EDCF activity did exist in WKY CCA but could be completely suppressed by NO-mediated EDRF signaling activity, whereas the similarly robust NO-meditated EDRF signaling activity in SHR CCA could not fully suppress its >2-fold augmented EDCF activity vs. WKY CCA. Further pharmaco-dissection of ACh-stimulated contractile function in the SHR-WKY CCA model revealed that the EDCF signaling activity was completely dependent on the COX-1 (but not COX-2) isoform of COX and was almost exclusively mediated by the thromboxane-prostanoid (TP) sub-type of the prostaglandin (PG) G-protein coupled receptor family and by Rho-associated kinase (ROCK), a down-stream effector of the molecular switch RhoA. Furthermore, it was found that while exogenous ROS-stimulated CCA contractile function was similarly >2-fold augmented in SHR vs. WKY and dependent on COX-1 and TP receptor and ROCK effectors, ACh-stimulated CCA EDCF signaling activity was only minimally affected by in-bath ROS manipulating compounds. Additional biochemical and molecular analysis revealed that ACh stimulation was associated with PG over-production from an over-expressed COX-1 in SHR CCA, and with CCA plasma membrane localization and activation of RhoA. Study III demonstrated that a COX-mediated EDCF response impaired ACh-stimulated endothelium-dependent vasorelaxation in pre-contracted CCA from Aging SD rats, while EDRF signaling activity, predominantly mediated by NO, remained well-preserved compared to Adult SD rats. Specific examination of ACh-stimulated contractile function revealed that EDCF activity did exist in Adult CCA but could be completely suppressed by NO-mediated EDRF signaling activity, whereas the similarly robust NO-meditated EDRF signaling activity in Aging CCA could not fully suppress its >3-fold augmented EDCF activity vs. Adult CCA. Further pharmaco-dissection of ACh-stimulated contractile function in the Adult-Aging SD rat CCA model revealed that EDCF signaling activity was completely dependent on COX-1, but while exogenous ROS was able to elicit a COX-dependent CCA contractile response, in-bath ROS manipulating compounds were found to be without effect on ACh-stimulated CCA EDCF signaling activity. Furthermore, biochemical analysis revealed that aging was not associated with a change in tissue (liver and vascular) GSH content or ROS accumulation. Chronic in vivo BSO treatment was effective in depleting tissue GSH content and increasing ROS accumulation, to a similar extent, in both Adult and Aging SD rats. However, regardless of age, neither ACh-stimulated NO-mediated EDRF signaling activity nor COX-mediated EDCF signaling activity were affected by these BSO-induced perturbations. Conclusions and Perspective: In the CCA of animals at the early pathological stages of either essential hypertension (young adult SHR) or normotensive aging (Aging SD rats), endothelial vasomotor dysfunction can be caused solely by over-active EDCF signaling, apparently disconnected from changes in NO bioavailability or oxidative stress. While NO and ROS may act, respectively, as negative and positive modulators of the established COX-PG-TP receptor-RhoA-ROCK cell-signaling axis mediating endothelium-dependent contractile activity, these factors do not appear to be essential to the mechanism(s) underlying the development of over-active EDCF signaling. Further elucidation of the cellular-molecular causes of over-active EDCF signaling, and its patho-biological consequences, in the SHR-WKY and Adult-Aging SD rat CCA models of EDCF activity established and hemodynamically characterized in this thesis, may help to identify new or more effective targets to be used in prevention or treatment strategies to combat the pathogenesis of CVD.

Background and Purpose: The endothelium is a single-cell layer positioned at the blood-vascular wall interface, where in response to blood-borne signals and hemodynamic forces, endothelial cells act as central regulators of vascular homeostatic processes including vascular tone, growth and remodeling, inflammation and adhesion, and blood fluidity and coagulation. Agonist- or flow-stimulated endothelium-dependent vasorelaxation becomes impaired in states of cardiovascular disease (CVD) risk and has been identified as a possible biomarker of overall endothelial dysfunction leading to vascular dysregulation and disease pathogenesis. Accordingly, it is important to elucidate the mechanisms accounting for this endothelial vasomotor dysfunction. Upon stimulation, endothelial cells can synthesize and release a variety of endothelium-derived relaxing factors (EDRFs), the most prominent of which is nitric oxide (NO) derived from NO synthase (NOS). In addition, under certain CVD risk conditions including hypertension and aging, stimulated endothelial cells can become a prominent source of endothelium-derived contracting factors (EDCFs) produced in a cyclooxygenase (COX)-dependent manner. Consequently, endothelial dysfunction may be caused by under-active EDRF signaling and/or competitive over-active EDCF signaling. Much attention has been given to elucidating the mechanisms of under-active EDRF signaling and its role in causing endothelial dysfunction, wherein excess reactive oxygen species (ROS) accumulation and oxidative stress under CVD risk conditions have been recognized as major factors in reducing NO bioavailability thus causing under-active EDRF signaling and endothelial dysfunction. Less attention however, has been given to elucidating the mechanisms of over-active COX-mediated EDCF signaling and its role in causing endothelial dysfunction. Moreover, while COX-mediated EDCF signaling activity has been investigated in some segments of the vasculature, most notably the aorta, it has not been well-investigated in the common carotid artery (CCA), a highly accessible cerebral blood flow conduit particularly advantageous in exploring the roles of the endothelium in vascular pathogenesis. It was the global purpose of this thesis to gain a better understanding of the cellular-molecular mechanisms accounting for endothelial dysfunction in the CCA of animal models known to exhibit COX-mediated EDCF signaling activity, in particular essential (spontaneous) hypertension and aging. Experimental Objective and Approach: This thesis comprises three studies. Study I and Study II investigated the CCA of young-adult (16-24wk old) normotensive Wistar Kyoto (WKY) and Spontaneously Hypertensive (SHR) rats. Study III investigated the CCA of Adult (25-36wks old) and Aging (60-75wks old) Sprague Dawley (SD) rats treated in vivo (or not; CON) with L-buthionine sulfoximine (BSO) to chronically deplete the cellular anti-oxidant glutathione (GSH) and increase ROS accumulation and oxidative stress. The global objective and approach across these studies was to systematically examine the relative contributions of NOS and COX signaling pathways in mediating the acetylcholine (ACh)-stimulated endothelium-dependent relaxation (EDRF) and contractile (EDCF) activities of isometrically-mounted CCA in tissue baths in vitro, with a particular focus on elucidating the mechanisms of COX-mediated EDCF signaling activity. An added objective was to examine the in vivo hemodynamic characteristics of the CCA in each animal model investigated, serving both to identify the pressure-flow environment that the CCA is exposed to in vivo and to provide assessment of potential hypertension, aging, and oxidative stress effects on large artery hemodynamics. Key Findings: Study I hemodynamic analysis confirmed a hypertensive state in young adult SHR while also exposing a reduction in mean CCA blood flow in SHR compared to WKY accompanied by a multi-faceted pressure-flow interaction across the cardiac cycle relating to flow and pressure augmentation. Study III hemodynamic analysis found that neither aging nor chronic BSO-induced GSH depletion affected CCA blood pressure or blood flow parameters in SD rats. Study I and II demonstrated that a COX-mediated EDCF response impaired ACh-stimulated endothelium-dependent vasorelaxation in pre-contracted CCA from young adult SHR, while EDRF signaling activity, predominantly mediated by NO, remained well-preserved compared to WKY. Examining ACh-stimulated contractile function specifically from a quiescent (non pre-contracted) state revealed that EDCF activity did exist in WKY CCA but could be completely suppressed by NO-mediated EDRF signaling activity, whereas the similarly robust NO-meditated EDRF signaling activity in SHR CCA could not fully suppress its >2-fold augmented EDCF activity vs. WKY CCA. Further pharmaco-dissection of ACh-stimulated contractile function in the SHR-WKY CCA model revealed that the EDCF signaling activity was completely dependent on the COX-1 (but not COX-2) isoform of COX and was almost exclusively mediated by the thromboxane-prostanoid (TP) sub-type of the prostaglandin (PG) G-protein coupled receptor family and by Rho-associated kinase (ROCK), a down-stream effector of the molecular switch RhoA. Furthermore, it was found that while exogenous ROS-stimulated CCA contractile function was similarly >2-fold augmented in SHR vs. WKY and dependent on COX-1 and TP receptor and ROCK effectors, ACh-stimulated CCA EDCF signaling activity was only minimally affected by in-bath ROS manipulating compounds. Additional biochemical and molecular analysis revealed that ACh stimulation was associated with PG over-production from an over-expressed COX-1 in SHR CCA, and with CCA plasma membrane localization and activation of RhoA. Study III demonstrated that a COX-mediated EDCF response impaired ACh-stimulated endothelium-dependent vasorelaxation in pre-contracted CCA from Aging SD rats, while EDRF signaling activity, predominantly mediated by NO, remained well-preserved compared to Adult SD rats. Specific examination of ACh-stimulated contractile function revealed that EDCF activity did exist in Adult CCA but could be completely suppressed by NO-mediated EDRF signaling activity, whereas the similarly robust NO-meditated EDRF signaling activity in Aging CCA could not fully suppress its >3-fold augmented EDCF activity vs. Adult CCA. Further pharmaco-dissection of ACh-stimulated contractile function in the Adult-Aging SD rat CCA model revealed that EDCF signaling activity was completely dependent on COX-1, but while exogenous ROS was able to elicit a COX-dependent CCA contractile response, in-bath ROS manipulating compounds were found to be without effect on ACh-stimulated CCA EDCF signaling activity. Furthermore, biochemical analysis revealed that aging was not associated with a change in tissue (liver and vascular) GSH content or ROS accumulation. Chronic in vivo BSO treatment was effective in depleting tissue GSH content and increasing ROS accumulation, to a similar extent, in both Adult and Aging SD rats. However, regardless of age, neither ACh-stimulated NO-mediated EDRF signaling activity nor COX-mediated EDCF signaling activity were affected by these BSO-induced perturbations. Conclusions and Perspective: In the CCA of animals at the early pathological stages of either essential hypertension (young adult SHR) or normotensive aging (Aging SD rats), endothelial vasomotor dysfunction can be caused solely by over-active EDCF signaling, apparently disconnected from changes in NO bioavailability or oxidative stress. While NO and ROS may act, respectively, as negative and positive modulators of the established COX-PG-TP receptor-RhoA-ROCK cell-signaling axis mediating endothelium-dependent contractile activity, these factors do not appear to be essential to the mechanism(s) underlying the development of over-active EDCF signaling. Further elucidation of the cellular-molecular causes of over-active EDCF signaling, and its patho-biological consequences, in the SHR-WKY and Adult-Aging SD rat CCA models of EDCF activity established and hemodynamically characterized in this thesis, may help to identify new or more effective targets to be used in prevention or treatment strategies to combat the pathogenesis of CVD.

This thesis deals with determination of representative constitutive model for describing atherosclerotic carotid artery behavior. The first part of the thesis provides brief summary of medical knowledge needed as well as detailed describtion of current experimental methods for determination of mechanical properties of atherosclerotic arteries. The main part is focused on mechanical testing of atheroslecotic carotid arteries. The description of sample preparation, testing device and the experiment itself is involved. Statistical analysis of measured data is done, focusing on comparison of factors potentially influencing mechanical behavior. In conclusion, the FEA analysis on simplified geometry of carotid artery with atheroma is performed. Emphasis is placed on the impact of material model obtained from experiments on equivalent stress in fibrous cap.

This doctoral thesis deals with the analysis of ultrasound (US) video sequences. It specifically focuses on long-term tracking of the common carotid artery (CCA) in transversal section and measurement of its geometric parameters in a sequence of US images. The design and implementation of a system for automatic tracking of the artery is described in this thesis. The proposed system utilizes Viola-Jones detector and Hough transform to localize the artery in the image. Interest points are detected in the area of the artery wall. These points are then tracked using optical flow. The proposed system comprises a number of innovative methods which allow to perform accurate long-term measurement of parameters of CCA and store the results. A novel mathematical model describing the movement of CCA in transversal section during a cardiac cycle is defined afterwards taking the influence of breathing into consideration. A number of artificial sequences of US images based on this model have been created. These sequences were consequently used to evaluate the accuracy of the proposed system in terms of measuring the parameters of CCA. The sequences are unique because of their length which makes them suitable for evaluation of tracking accuracy even in long video sequences.

Σκοπός είναι να ερευνηθεί αν οι μετρήσεις του Πάχος του Ενδοθηλίου των Κοινών Καρωτίδων (ΠΕΚΚΑ) σε ασθενείς με Αγγειακό Εγκεφαλικό Επεισόδιο (ΑΕΕ) σχετίζονται με την άμεση ή μακροπρόθεση έκβαση του ΑΕΕ, με την μελλοντική εμφάνιση νοητικής έκπτωσης ή κατάθλιψης και με την υποτροπή του ΑΕΕ. ΜΕΘΟΔΟΙ: 284 ασθενείς με πρώτο ισχαιμικό ΑΕΕ που υποβλήθηκαν σε υπερηχογραφική μέτρηση του ΠΕΚΚΑ στην οξεία φάση, παρακολουθήθηκαν για ένα χρόνο. Η άμεση έκβαση εκτιμήθηκε κατά την έξοδο, ενώ η μακροπρόθεσμη έκβαση, η νοητική και συναισθηματική κατάσταση εκτιμήθηκαν μετά από 12 μήνες. Επίσης καταγράφηκαν οι υποτροπές στη διάρκεια του πρώτου χρόνου. ΑΠΟΤΕΛΕΣΜΑΤΑ: το ΠΕΚΚΑ δε συσχετιζόταν με την άμεση ή μακροπρόθεσμη έκβαση του ΑΕΕ ούτε με την ύπαρξη κατάθλιψης ένα χρόνο αργότερα. Αντίθετα, αυξημένες τιμές ΠΕΚΚΑ σχετίζονταν σημαντικά και ανεξάρτητα τόσο με την ύπαρξη νοητικής έκπτωσης 12 μήνες αργότερα όσο και με τoν κίνδυνο υποτροπής του ΑΕΕ κατά τη διάρκεια του πρώτου χρόνου. ΣΥΜΠΕΡΑΣΜΑ: οι μετρήσεις του ΠΕΚΚΑ αμέσως μετά από ισχαιμικό ΑΕΕ μπορεί να χρησιμεύουν στην αναγνώριση ασθενών με αυξημένο κίνδυνο για μελλοντική νοητική έκπτωση ή υποτροπή του ΑΕΕ. / Thesis objective is to investigate whether the measurements of Common Carotid Artery Intima Media Thickness (CCA-imt) in patients with acute stroke are associated with the stroke outcome, either short term or long term, with the future development of post stroke cognitive impairment and post stroke depression and with stroke recurrences within the first year after the stroke. METHODS: 284 consequent patients with first ever ischaemic stroke that underwent carotid ultrasonographic measurement of CCA-imt in the acute phase, were followed-up for one year. The short-term outcome was assessed at discharge. The long-term outcome and the presence of cognitive impairment and depressive symptoms were assessed 12 months later. The number of recurrences within the first year was also recorded. RESULTS: CCA-imt values were not associated with the short- or long-term stroke outcome or the presence of depression one year after the ictus. On the contrary, increased CCA-imt values were significantly and independently associated with cognitive impairment and with the risk of recurrence during the first year. CONCLUSION: measurements of CCA-imt right in the acute phase after an ischaemic stroke can help with the identification of patients in higher risk for future cognitive impairment and stroke recurrence.