No description available.

No description available.

No description available.

Este trabalho apresenta a implementação de um sistema de velocimetria de imagens de partícula (VIP) para estudo do escoamento do sangue em um dispositivo de assistência ventricular para uso pediátrico (DAVP). O sistema VIP implementado é constituído por uma fonte de iluminação composta por um par de lasers de Nd:YAG (pulso de aproximadamente 18mJ de energia e duração de 5ns), um sistema óptico contendo duas lentes convergentes, uma câmera CCD e uma câmara para visualização. O DAVP estudado foi construído em acrílico transparente e é constituído de uma câmara de sangue e uma câmara pneumática, divididas por uma membrana flexível. A câmara sanguínea possui dois orifícios dotados de válvulas de tecido biológico para a entrada e saída de sangue. A câmara pneumática é conectada a um gerador de pulsos de pressão positiva. O fluido foi semeado com esferas de poliestireno (10 \"mu\" de diâmetro). Foram determinadas as distribuições de velocidades instantâneas nas freqüências de batimento de 80, 100 e 120 bpm em três campos (65 mm x 65mm) da câmara paralelos à membrana e um campo situado no canal de entrada do DAVP, usando correlação cruzada com base na transformada rápida de Fourier. Um gerador de pulsos foi utilizado para sincronizar a detecção das imagens pelo sistema VIP com as fases de interesse no ciclo de bombeamento. Na freqüência de batimentos de 80 bpm as velocidades máximas foram de 1,94 m/s no canal de entrada durante o período de enchimento e 1,66 m/s nas regiões próximas à membrana durante o período de ejeção. Em 100 bpm, as velocidades máximas foram de 1,68 m/s no canal de entrada e 1,15 m/s nas regiões próximas a membrana. As distribuições de velocidades instantâneas mostram a ocorrência de pequenos vórtices, principalmente durante a fase de enchimento. Estes vórtices apresentam grande variabilidade ciclo-a-ciclo produzindo turbulências no fluxo e tensões de Reynolds elevadas. No ciclo a 80 bpm, ) parte da energia cinética turbulenta é dissipada devido à desaceleração do fluxo na câmara sanguínea antes do inicio da fase de ejeção. Isto ocorre para as freqüências de 100 e 120 bpm. A máxima tensão de Reynolds foi observada no canal de entrada do DAVP no valor de 222 N/m2 durante o enchimento, persistindo por 25 ms. No plano da membrana a maior tensão encontrada foi igual a 250 N/m2 durante o enchimento, persistindo por 25 ms. O campo de velocidades media contém vórtices permanentes durante a fase de enchimento que influenciam significativamente o fluxo na câmara e cujo numero aumenta com a freqüência de batimentos, provocando aumento de turbulências. Estes resultados indicam que existe maior possibilidade de ocorrer o processo de hemólise durante o enchimento do que durante a ejeção. Vetores com baixas velocidades foram observados na região compreendida entre os canais de entrada e saída do fluxo na câmara sanguínea no período de ejeção, sugerindo a possibilidade de ocorrer à formação de trombos nesta. / --

Abstract Cessation of the blood circulation for some time during surgery of the aortic arch and repair of congenital heart defects is normally required to allow a bloodless operation field. Hypothermia is the most important mechanism for end-organ protection, particularly the brain, during such operations. Cardiopulmonary bypass is used for core cooling before total hypothermic circulatory arrest (HCA) or selective cerebral perfusion (SCP) are initiated. During hypothermic cardiopulmonary bypass, pH can be managed according to either pH- or alpha-stat principles. In the present work, the optimal pH management strategy for operations requiring HCA or SCP was explored. An experimental porcine model was used. Firstly, outcome was evaluated in a HCA model using either the α- or pH-stat perfusion strategy (I). Secondly, we sought to determine which acid-base management is more effective in attenuating ischemic brain injury during combined HCA and embolization conditions (II). In the third study, the impact of propofol anesthesia and α-stat perfusion strategy on outcome was explored (III). Finally, the acute effects of perfusion strategies in a SCP porcine were compared (IV). Hemodynamics, temperature, EEG (I-III), brain microdialysis, intracranial pressure (I-III), brain tissue oxygen partial pressure (I-III), and intravital microscopy (IV) were monitored intraoperatively. In the chronic studies, survival, postoperative neurologic recovery and brain histopathologic examination were evaluated (I-III). pH-stat strategy was associated with superior outcome compared to the α-stat strategy during a 75-minute period of deep HCA (I). In addition, despite the pH-stat strategy-related cerebral vasodilatation, this method provided better neuroprotection in a setting of cerebral particle embolization prior to a 25-minute period of deep HCA (II). Propofol anesthesia combined with α-stat perfusion strategy was observed to deteriorate the brain injury during HCA evaluated by key brain microdialysis parameters (III). Finally, when employing moderately hypothermic SCP, the differences between pH- and α-stat strategies in cerebral metabolism and microcirculation were minimal. These findings are clinically relevant since α-stat perfusion strategy is still the most commonly used acid-base perfusion strategy during hypothermic cardiopulmonary bypass in adults, and propofol one of the most used anesthetics in clinical practice. It is also noteworthy that the pH-stat strategy is not currently used in adults because of the perceived increased risk of atherosclerotic embolization. However, the advantage of pH-stat strategy over α-stat strategy could not be observed when employing SCP.

Abstract In the repair of complex congenital heart defects or in surgery of the aortic arch, normal circulation may be temporarily halted to ensure a clean, bloodless operation field. The brain is the organ most vulnerable to ischemic injury during this no-flow period, and the mortality and morbidity of these procedures today consists mostly of neurological complications. Hypothermia decreases the need for oxygen and other metabolites, and cooling the patient with an extracorporeal heart-lung machine can provide enough time to perform the necessary surgical procedures during a circulatory standstill. This procedure is referred to as hypothermic circulatory arrest (HCA). Sometimes the cerebral circulation can be maintained even if the rest of the body undergoes circulatory arrest, and this strategy, involving separate catheterization of brain-destined vessels, is referred to as selective cerebral perfusion (SCP). In this work, four separate brain protection strategies were evaluated. Two studies were performed on a surviving porcine model (I, II) to evaluate neurological recovery as well as cerebral metabolism and histopathology, and two were acute in design (III, IV), employing the modern technology of intravital microscopy to examine cerebral microcirculation. The first study (I) showed that the administration of hypertonic saline dextran (HSD) led to a decrease in intracranial pressure, improved brain metabolism, better neurological recovery and less histopathological injury of the brain tissue in association with HCA. In the second study (II) a novel pharmacological molecule, levosimendan, reduced the intracranial pressure during the operation, but no improvement in terms of cerebral metabolism, neurological recovery or histopathological brain injury was observed after HCA. In the third study (III), real-time intravital microscopy showed that in association with HCA, a leukocyte depleting filter (LDF) attached to the cardiopulmonary bypass circuit reduces the number of activated leukocytes in cerebral microcirculation. In the fourth study (IV), cerebral metabolism and microcirculation were similar during SCP independent of the acid-base management strategy. The results of this work suggest that HSD could be assessed in human trials, that levosimendan needs further studies to optimize its potential, that the LDF functions as designed and that the differences between the α- and the pH-stat acid-base management strategies with SCP did not differ in moderate hypothermia.

INTRODUCTION Apixaban has revolutionized anticoagulation in patients with atrial fibrillation in preventing strokes. Anticoagulant-induced nephropathy with warfarin is well known, but nephropathy with apixaban is a rare entity, and here we present a case of Apixaban-induced nephropathy. Case Description A 71-year-old patient with a medical history of persistent atrial fibrillation on apixaban, Ischemic cardiomyopathy, and chronic kidney disease stage (CKD) IIIa presented to the hospital with complaints of dyspnea and hemoptysis and tea-colored urine of three-day duration. On admission, the patient had acute kidney injury (AKI) on CKD, Methicillin sensitive Staphylococcus aureus (MSSA) bacteremia, and elevated international normalized ratio (INR) and apixaban were held. The hemoptysis worsened and prompted bronchoscopy revealing diffuse alveolar hemorrhage. The urinalysis showed gross hematuria with high red blood cell (RBC) count and 1+ proteinuria presumed secondary to MSSA associated glomerulonephritis. Evaluation for coagulopathy with serum mixing studies and autoimmune workup has been unremarkable. The patient's coagulopathy was considered secondary to decreased clearance of apixaban with AKI on CKD. However, the patient's kidney function continued to worsen, needing continuous renal replacement therapy and a kidney biopsy for a definitive diagnosis for his decline in kidney function. Kidney biopsy revealed IgA dominant infection associated glomerulitis with one out of hundred glomeruli with the crescent formation and signs of anticoagulant induced nephropathy with several intratubular RBC casts out of proportion to the degree of glomerular injury causing acute tubular damage. The patient's INR improved on dialysis. However, he continued to be oliguric before being terminally extubated. DISCUSSION With the increasing incidence of atrial fibrillation and the use of oral anticoagulants, it is vital to have anticoagulant induced as a differential in patients presenting with supra therapeutic INR and AKI. Apixaban-induced nephropathy is a subset of anticoagulant-induced nephropathy and an uncommon cause of the acute decline in kidney function needing dialysis. Prompt recognition and treatment will prevent further deterioration in kidney function and possible improvement.

In this paper, old as well as new technological findings to decrease premature infant mortality are reviewed. This paper discusses fetal development throughout pregnancy from conception to full-term status as well as fetal lung development specifically from conception until full-term status. Several ideas to rapidly develop and mature fetal lungs are discussed such as mothers ingesting artificial surfactant supplements, either independently or coupled with antenatal corticosteroids, as well as intra-amniotic instillation prior to 28 weeks gestational. Drawbacks regarding these two are mentioned as well such as the fetus’s lungs not being mature enough to use the artificial surfactant leading into the idea of researching ways to rapidly develop fetal lungs, either week-by-week or stage-by-stage. Lastly, if the baby is born pre-maturely and is severely underdeveloped, research is currently being done on an artificial womb that the baby can be placed in to simulate a uterus where the fetus can develop on a normal timeline as he or she would in the mother’s womb.

Functional hyperemia and arteriolar vasodilation are impaired with chronic ischemia. We sought to examine the impact of chronic ischemia on collateral artery function. For this we used two hindlimb ischemia models to dissect the impact of different repair processes on collateral function. Ligation of the femoral artery increases shear stress in the muscular branch and results in outward remodeling and arteriogenesis. In contrast, resection of the femoral artery proximal to the muscular branch induces blood flow divergence and neutral remodeling along with expectedly greater hypoxia and inflammation. On day 14 after each surgery the diameter of the muscular branch was measured using sidestream dark field (SDF) imaging before and after gracilis muscle stimulation. A slight, but not statistically significant, impairment in functional vasodilation was observed in ligated mice (69±10% average diameter increase compared to 74±7% average diameter increase). Resected mice exhibited slightly (not statistically significant) enhanced collateral artery functional vasodilation (104±16% average diameter increase) but were also refractory to the restoration of resting vascular tone following the cessation of stimulation. Outward remodeling did not significantly impair vascular function, whereas neutral remodeling and tissue hypoxia induced impaired vascular tone.

<p> This thesis describes the analytical study of the stability of the structural system under circulatory loading and/or parametric excitation. The model is a double pendulum, composed of two rigid weightless bars of equal length and two concentrated masses at the ends of each bar, on an oscillating base. The vertical oscillation of the base produces parametric excitation to the system. A circulatory force is applied at the free end. At the joints the restoring moments are produced by spring and damping. The damping coefficients are taken as positive, and the gravitational effects are included. </p> <p> The combined effect of the circulatory loading and parametric excitation on stability of the system is investigated. The problem is so formulated that the stability of the system is represented by coupled Mathieu equations. The effect of damping on the boundary of stability is also determined. </p> / Thesis / Master of Engineering (ME)