Microvascular oxygen transport has been studied using many experimental methods. The three wavelength photometric method of Pittman and Duling (6) was the basis for this project. An optical triplicator was introduced into the microscopy assembly. The triplicator’s function was to take the image seen in the eyepiece of the microscope, triplicate it, filter it at three known wavelengths and direct each image onto the active area of a video camera. When used in-vivo, the triplicator allowed for three simultaneous intensity measurements, one at each wavelength, to be made. This measurement removed any assumptions concerning the uniformity of the blood sample which was inherent in Pittman and Duling’s design. Measurements were performed in vivo on several hamster retractor muscles. The intensity information obtained was then used to calculate oxygen saturation at regions near an arterial bifurcation. Oxygen saturation values ranged from 42.99 ± 4.20 to 96.46 ± 4.46% depending upon the location along the vessel. It was also concluded that the oxygen saturation profile across the vessel was altered near a bifurcation. The oxygen saturation profile prior to and following a bifurcation appeared to be uniform. However, in the region of a bifurcation, the asymmetry introduced nonuniformities in the profile. This paper briefly discusses the theory behind the three wavelength photometric method, the development and fabrication of the optical triplicator and the measurement techniques used to obtain oxygen saturation profiles. It will be shown that the optical triplicator has the potential to advance the study of microvascular oxygen transport beyond previously unachievable levels. / Master of Science

Heart disease remains the leading cause of death globally, and prevalence has nearly doubled over the past three decades. It is estimated that up to 90% of cardiovascular events are preventable, but early detection and treatment is crucial. In this dissertation, we report on the optimization of the ultrasound-based cardiac strain imaging technique known as Myocardial Elastography (ME), a method for the detection of the most common and most lethal forms of heart disease: Coronary Artery Disease (CAD) which affects the major coronary arteries, and Coronary Microvascular Disease (CMD) which affects smaller coronary vessels. CAD has historically been the primary focus of clinical cardiac imaging, whereas CMD has been under-diagnosed due to a lack of awareness and challenges associated with imaging at the microvascular level. Ultrasound-based cardiac strain imaging has been shown capable of detecting functional changes due to CAD and may be effective in CMD detection, although the latter has not yet been sufficiently investigated. However, the diagnostic accuracy of strain imaging is reduced by noise from transcostal imaging, known as clutter, and by the limited lateral resolution of high framerate ultrasound. These factors preclude accurate strain imaging in up to 30% of patients. Myocardial elastography is a precise high framerate strain imaging technique that analyzes radiofrequency (RF) signals to quantify myocardial deformation. We hypothesize that ME can effectively image and diagnose the functional effects of CMD and CAD, and that novel beamforming and clutter-filtering techniques can improve ME imaging and strain estimation quality, thereby increasing diagnostic accuracy. To improve disease detection, Stress ME (S-ME) was proposed as a method to compare strain measurements at rest to strain during induced cardiac stress. A novel strain difference (Δ𝜺) metric was presented and investigated in a canine model of induced acute ischemia, as well as in a human CAD patient study with validation by myocardial perfusion imaging. In the canine model, flow-limiting stenosis was induced by partial ligation in N=2 canines, and stenosis was found to significantly reduce Δ𝜺 in the affected myocardial regions. In the clinical study, radial and circumferential ME strain and radial Δ𝜺 was measured in N=49 myocardial segments from 8 patients suspected to have ischemia or infarction due to CAD. The median Δ?, radial strain, and circumferential strain magnitudes were lowest in infarcted regions and highest in regions with normal perfusion, while measurements in ischemic regions fell in between. ROC analysis of radial strain metrics revealed that Δ𝜺 had the highest AUC for detecting ischemia (AUC=0.788 p<0.01) and infarction (AUC=0.792, p<0.05), followed by radial strain during stress (ischemia AUC=0.774 p<0.05, infarct AUC=0.758 p<0.05) while the AUC was lowest when considering only the radial strain at rest (ischemia AUC=0.52 p>0.05, infarct AUC=0.58 p>0.05). The results thus indicate that S-ME may improve detection of mild CAD cases that are functionally asymptomatic at rest. Despite these promising findings, accurate strain imaging remains hindered by clutter noise and poor image quality. Two complementary techniques were thus developed to improve image quality and strain estimation in high frame rate cardiac strain imaging; a novel Sliding Window implementation of the Minimum Variance beamformer (SWMV) was proposed to enhance speckle quality, while a spatiotemporal singular value decomposition filter (SVD) was developed to increase tissue visibility and contrast by suppressing static clutter signals using automated cutoff selection. SWMV and SVD were shown to effectively improve image quality in simulation studies and phantom imaging experiments. In vivo performance evaluation consisted of applying SWMV beamforming and SVD filtering techniques to a dataset of N=70 strain images from 13 patients suspected to have CAD. CCTA imaging was used for validation of strain estimation. Tracking was improved in 92% of cases with a median improvement of 15% in displacement estimation accuracy as evaluated by an intersection-over-union (IoU) metric. The proposed techniques also improve agreement with CCTA results; ROC analysis shows improved AUC with SWMV+SVD compared to DAS when comparing healthy regions to those with any degree of stenosis (AUC 0.64 vs 0.56) as well as when comparing healthy to severely stenosed regions (AUC 0.69 vs 0.60). The observed results point to significant improvement in strain estimation reliability due to SWMV beamforming combined with SVD processing. The final aim and the overarching goal of this work is a culmination of the previous sections for a clinical evaluation of ME as a diagnostic tool for CAD and CMD. In this clinical study, the enhanced ME technique utilizing SWMV and SVD filtering was applied to a cohort of N=201 patients with suspected coronary disease. All patients underwent invasive angiography or noninvasive cardiac imaging in the form of coronary computed tomography or nuclear stress testing. In addition, demographic information and patient clinical history were collected and accounted for in a multivariate statistical analysis. A K-nearest-neighbor (KNN) classifier was trained to distinguish between healthy and stenosed myocardial regions, and achieved an AUC of 0.91, with sensitivity of 86% and a specificity of 85% after training with 10-fold cross validation. CMD was also shown to significantly reduce regional strain measurements. This retrospective study identified the clinical factors which impact strain, and assessed the potential advantages of incorporating ME imaging to the existing clinical imaging pipeline for CAD and CMD diagnosis.

Introduction : L’arrêt cardiaque réfractaire est défini par l’absence du retour à l’activité circulatoire spontané (RACS) après 30 minutes de réanimation cardiopulmonaire médicalisé. ExtraCorporeal Membrane Oxygenation (ECMO) représente une thérapie alternative urgente dans cette population. L’hémodynamique post la réanimation cardiopulmonaire extracorporel (E-CRP) est un entité complexe et le pris en charge dans les premières heures suivant l’implantation d’ECMO n’est pas bien décrit. L’objectif de cette étude est d’évaluer l’effet de deux stratégie de débit d’ECMO dans un modèle porcin d’arrêt cardiaque réfractaire sur les conséquences métaboliques, microcirculatoires et inflammatoires.Matériels et Méthodes : l’arrêt cardiaque a été induit par la ligature l’artère intraventriculaire antérieure (IVA) chez 18 cochons. E-RCP a été initié après 40 minutes de low-flow avec un débit d’ECMO bas de 30-35 ml.kg-1.min-1 ou un débit d’ECMO standard de 65-70 ml.kg-1.min-1, avec la même pression artérielle moyenne (PAM) au niveau de 65 mmHg. Les paramètres hémodynamiques et métaboliques ont été évalués avec la clairance de lactate et le débit sanguin carotidien. Les paramètres microcirculatoires ont été évalués par la microcirculation sublinguale avec l’imagerie de SDF et NIRS. Cytokines inflammatoires ont été mesurés avec un plateforme de ELISA multiplexe. Résultats : Pas de différence entre les deux groups à H basale et à l’initiation d’ECMO (H0). La clairance de lactate était plus faible dans le groupe débit bas comparé au groupe débit standard (6.67[-10.43-18.78] vs. 47.41[19.54, 70.69] %, p=0.04). Le débit carotidien était plus bas significativement (p<0.005) dans le groupe débit bas pendant les dernières quatre heures malgré le même niveau de la pression artérielle moyenne. Pour les paramètres microcirculatoires, le flux microcirculatoire sublingual évalué par SDF et le StO2 par NIRS ont été altéré transitoirement à H3 dans le groupe débit bas. Le niveau de cytokine IL-6 était plus élevé significativement dans le groupe débit bas à la fin d’expérimentation. Conclusions : Une réanimation à objectif de débit d’ECMO bas 35 ml.kg-1.min-1 versus standard 70ml.kg-1.min-1dans les six premières heures d’un ACR réfractaire n’est pas associé à une meilleure réversion des conséquences métaboliques, microcirculatoire et inflammatoire avec un objectif de PAM à 65 mmHg dans un modèle porcin / Introduction : Refractory cardiac arrest is defined by the absence of the return of spontaneous circulation (ROCS) within 30 minutes of cardiopulmonary resuscitation (CRP) under medical supervision. ExtraCorporeal membrane oxygenation (ECMO) is an emerging alternative therapy in this population. The post extracorporeal cardiopulmonary resuscitation (ECPR) hemodynamic state is a complex entity and the critical care management in the first hours following ECMO implantation is not well defined. This study was designed to assess the effect of two veno-arterial Extracorporeal Membrane Oxygenation (ECMO) blood-flow strategies in an experimental model of ECPR (extracorporeal cardio-pulmonary resuscitation) on macrocirculatory, metabolic and microcirculatory parameters in the first six hours of ECMO initiation. Material and methods : Cardiac arrest was induced in 18 pigs by surgical ligature of the left descending coronary artery. ECPR was initiated after 40 minutes of low-flow with an ECMO blood-flow of 30-35 ml.kg-1.min-1 (low-blood-flow group, LBF) or 65-70 ml.kg-1.min-1 (standard-blood-flow group, SBF), with the same mean arterial pressure target (65 mmHg). Macrocirculatory and metabolic parameters were assessed by lactate clearance and carotid blood-flow. Microcirculatory parameters were assessed by sublingual microcirculation with Sidestream Dark Field (SDF) imaging and peripheral Near-InfraRed Spectrometry (NIRS). Inflammatory cytokine levels were measured with a multiplexed ELISA-based array platform. Results : There was no between-group difference at baseline and at ECMO initiation (H0). Lactate clearance at H6 was lower in LBF compared to SBF (6.67[-10.43-18.78] vs. 47.41[19.54, 70.69] %, p=0.04). carotid blood flow was significantly lower (p<0.005) during the last four hours despite similar mean arterial pressure levels. For microcirculatory parameters, SDF and NIRS parameters were transitorily impaired at H3 in LBF. IL-6 cytokine level was significantly higher in LBF at the end of the experiment. Conclusion: In an experimental porcine model of refractory cardiac arrest treated by ECMO, a low-blood-flow strategy during the first six hours of resuscitation was associated with lower lactate clearance and lower cerebral blood-flow with no benefits on ischemia-reperfusion parameters

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xiv, 180 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xii, 195 p. : ill. Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--University of Virginia, 2008. / Includes bibliographical references. Also available in electronic form as viewed 2/16/2009.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xiv, 197 p. : ill. Vita. Includes abstract. Includes bibliographical references.

J'ai caractérisé expérimentalement la formation de clusters au cours du passage de globules rouges (GRs) sains et drépanocytaires dans microcapillaires droites. L'effet de l'agrégation a été également étudié. J'ai montré que la formation des clusters dans des conditions physiologiques est due à la combinaison des interactions hydrodynamiques et des celles causées par les macromolécules du plasma. En effet, les interactions macromoléculaires ne sont pas complètement atténuées sous contraintes de cisaillement physiologiques et au contraire ils contribuent à la stabilité des clusters. En outre, j'ai découvert la présence d’une distribution bimodale en ce qui concerne les distances entre les cellules constituant les clusters hydrodynamiques.En plus, j'ai étudié expérimentalement le comportement collectif des globules rouges drépanocytaires oxygénés et leur distribution radiale le long de microcapillaires cylindriques avec un diamètre comparable à ces des veinules et des artérioles humaines. J'ai trouvé que les GRs montrent une distribution hétérogène en fonction de leur densité: les cellules plus légères ont tendance à rester prés du centre du canal, alors que la plupart des cellules denses (et aussi plus rigides) auto-marginent sous des conditions définies. L'agrégation semble d'inhiber l'auto-margination en fonction des patients et en particuliers des facteurs d’agrégation: le dextrane, par exemple, favorise l'auto-margination dans certains patients et il la diminue dans des autres. Le plasma montre de contraster l'auto-margination des GRs dans tous les sujets, en soulignant l'importance des protéines et des molécules adhésives du plasma dans les phénomènes d'agrégation. Finalement, j'ai observé que l'auto-margination se manifeste naturellement au cours de l’écoulement de globules rouges drépanocytaires. / I experimentally characterized the clustering formation of healthy and sickle red blood cells (RBCs) flowing through straight micro-capillaries. The effect of aggregation was also investigated. I found that cluster formation under physiological conditions is most likely caused by a combination of hydrodynamic and macromolecule-induced interactions. Macromolecule-induced interactions are not fully overcome by shear stresses within the physiological range, and they contribute to cluster stability. Moreover, I found that a pronounced bimodal distribution of the cell-to-cell distances in the hydrodynamic clusters is produced.Additionally, I investigated experimentally the collective behavior of oxygenated sickle RBCs and their distribution along cylindrical micro-capillaries with diameters comparable to a human venule or arteriole. I have shown that there is a heterogeneous distribution of RBCs according to their density: low-density cells tend to stay closer to the center of the channel, while most dense cells (also more rigid) self-marginated under defined conditions. Aggregation seems to inhibit self-margination depending on the aggregative factor and patient: dextran allows self-margination in some patients and inhibits it in others. Plasma inhibits self-margination of cells in all cases, highlighting the importance of the plasma proteins and adhesive molecules in the aggregation phenomena.

Les facteurs de risque cardiovasculaires et métaboliques qui caractérisent le syndrome métabolique (SM), y compris l'hypertension, l'obésité et l'intolérance au glucose, sont accompagnés d'hyperactivité sympathique. Dans cette étude, nous avons étudié les effets d'un traitement antihypertenseur chronique utilisant des médicaments d’action centrale sur les paramètres métaboliques et microvasculaires chez les rats soumis à un régime riche en gras et en sel. Pour cela, cinquante rats Wistar ont reçu un régime normal ou riche en gras pendant 20 semaines. Le groupe HFD a reçu clonidine par voie orale, rilmenidine, LNP 599 ou véhicule. La microcirculation fonctionnelle a été évaluée par vidéomicroscopie intravitale. La microcirculation structurale a été étudiée par analyse histochimique. Nous avons conclu que la modulation de l'activité sympathique corrige la raréfaction capillaire dans le muscle squelettique et le ventricule gauche dans un modèle expérimental de SM chez le rat. / Cardiovascular and metabolic risk factors that characterize the metabolic syndrome (MS), including high blood pressure, obesity and glucose intolerance, are accompanied by sympathetic hyperactivity. In this study, we investigated the effects of a chronic oral antihypertensive treatment using centrally-acting sympatho-inhibitory drugs on the metabolic and microvascular parameters in rats under long-term high-fat diet with salt supplementation. For that, fifty male adult Wistar rats were maintained under normal or high-fat diet during 20 weeks. The HFD group received oral clonidine, rilmenidine, LNP 599 or vehicle. Functional microcirculation was evaluated by intravital videomicroscopy and the structural was studied using histochemical analysis. We concluded that the modulation of sympathetic activity reverses the capillary rarefaction in the skeletal muscle and left ventricle in an experimental model of MS in rats.

Parmi les facteurs intervienant dans la régulation et le maintien du fonctionnement d'organes, le système nerveux autonome et la microcirculation jouent un rôle prépondérant. Chez les patients critiques, comme les patients en sepsis, des altérations de la balance sympatho-vagale et de la perfusion tissulaire peuvent survenir et avoir des conséquences majeures en matière de morbidité et mortalité. La mise en oeuvre de méthodes de détection précoces de ces perturbations pourrait donc contribuer à améliorer la survie des patients à risque. En effet, le suivi des paramètres hémodynamiques, comme classiquement réalisé lors de réanimation, peut s'avérer insuffisant pour détecter des altérations de perfusion tissulaire : lors de sepsis, des altérations microcirculatoires peuvent persister en dépit de la normalisation des paramètres macrocirculatoires et sont associées à un mauvais pronostic. Eu égard à la présence de dysfunctions microcirculatoires et du système nerveux autonome chez les patients critiques, ce travail de recherche s'est proposé d'évaluer l’impact de modulateurs du système sympathique sur la balance sympatho-vagale et la microcirculation. Pour ce faire, nous avons travaillé avec des modèles animaux et des animaux admis en centre hospitalier universitaire vétérinaire. Le suivi du système nerveux autonome s'est basé sur un nouvel index de mesure du tonus parasympathique (Parasympathetic Tone Activity ou PTA). En parallèle, la microcirculation a été évaluée par vidéomicroscopie (SDF, Sidestream Dark Field imaging). L'index PTA a démontré une performance correcte pour prédire les réactions hémodynamiques chez les chiens anesthésiés. Il a aussi permis de détecter une altération de la balance sympathique chez les chevaux admis pour une chirurgie de colique ainsi qu’une altération de la microcirculation en dépit des manoeuvres de réanimation. Les études précliniques sur l’impact de la perfusion d’esmolol et de dexmédétomidine dans un modèle porcin septique ont montré que, malgré leurs effets hémodynamiques potentiels, ces agents n’ont pas eu d’effet négatif sur la microcirculation. Ainsi, les résultats de ce travail suggèrent un effet bénéfique des modulateurs du système nerveux sympathique sur la microcicultion mais nécessite d'être confirmé à plus grande échelle / Among the factors involved in the regulation and maintenance of the organs’ functioning, the autonomic nervous system and the microcirculation play a preponderant role. In critical patients, such as septic patients, alterations in the sympathovagal balance and tissue perfusion may occur and have major consequences of morbidity and mortality. The implementation of early detection methods for these disturbances could therefore contribute to improve the survival of patients at risk. Indeed, the monitoring of hemodynamic parameters, as conventionally performed during resuscitation, may be insufficient to detect tissue perfusion alterations: during sepsis, microcirculatory changes may persist despite the normalization of macrocirculatory parameters and are associated with a bad prognosis. With regard to the presence of microcirculatory dysfunctions and autonomic nervous system alterations in critical patients, this research project proposed to evaluate the impact of modulators of the sympathetic system on the sympatho-vagal balance and microcirculation. In order to achieve this, we worked on animal models and animals admitted to the faculty’s veterinary hospital center. Monitoring of the autonomic nervous system was based on a new Parasympathetic Tone Activity (PTA) index. In parallel, the microcirculation was evaluated by videomicroscopy (SDF, Sidestream Dark Field imaging). The PTA index demonstrated a good performance in predicting hemodynamic reactions in anesthetized dogs. It also detected disturbances of the sympathetic balance in horses admitted for colic surgery as well as an alteration of microcirculation despite resuscitation maneuvers. Preclinical studies on the impact of esmolol and dexmedetomidine infusion in a septic swine model showed that, despite their potential hemodynamic effects, these agents did not have a negative effect on the microcirculation. Thus, these findings suggest a beneficial effect of the modulators of the sympathetic nervous system on the microcicultion, however, these resutls should be confirmed on a larger scale