Motivated by the physiological phenomena of collapse and flow limitation for a serial pulmonary artery stenosis, we investigated the three-dimensional influence of spatial configuration on the wall motion and hemodynamic. Our numerical study focused on the effect of two geometrical parameters: the relative distance and the angular orientation between the two stenoses. The collapse of a compliant arterial stenosis may cause flow choking, which would limit the flow reserve to major vital vascular beds such as the lungs, potentially leading to a lethal ventilation-perfusion mismatch. Flow through a stenotic vessel is known to produce flow separation downstream of the throat. The eccentricity of a stenosis leads to asymmetric flow where the high velocity jets impinge on the sidewall, thereby inducing significant dissipation. The additional viscous dissipation causes a higher pressure drop for a flow through a stenotic vessel, than in a straight compliant vessel. It is likely that some particular morphology would have a higher vulnerability to the fluid induced instability of buckling (divergence), under physiological pulsatile flow. It was found that fluid pressure distribution have substantial implication for the downstream wall motion, under conditions of strong coupling between nonlinear vessel geometries, and their corresponding asymmetric flow. The three-dimensional fluid structure interaction problem is solved numerically by a finite element method based on the Arbitrary Lagrangian Eulerian formulation, a natural approach to deal with the moving interface between the flow and vessel. The findings of this investigation reveal that the closeness between stenoses is a substantial indication of wall collapse at the downstream end. Moreover, the results suggest a close link between the initial angular orientation of the distal stenosis (i.e. the constriction direction) and the subsequent wall motion at the downstream end. For cases showing evidence of preferential direction of wall motion, it was found that the constricted side underwent greater cumulative displacement than the straight side, suggestive of significant wall collapse.

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1969. / Bibliography: leaves [131]-135. / ix, 135 l graphs, tables

Bibliography: leaves 249-279. / xv, 279 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--The University of Adelaide, Dept. of Applied Mathematics, 1999

Atrial fibrillation is the most common sustained arrhythmia; however, its mechanism is not well understood. Several conditions such as valvular disease, heart failure, and hypertension predispose to atrial fibrillation. Identifying the electrophysiological substrate in these clinical conditions would yield insight into the mechanism of atrial fibrillation and aid in developing strategies to prevent or cure it. Rheumatic mitral stenosis is associated with high prevalence of atrial fibrillation. While atrial stretch itself may be adequate to explain the occurrence of atrial fibrillation in this population, it is not known if the disease process would remodel the atria so as to increase its propensity. Chapters 2 and 3 present the results of the studies evaluating the substrate for atrial fibrillation in both the left and right atria in rheumatic mitral stenosis. These studies have demonstrated extensive conduction abnormalities both regional and site specific associated with low voltage area and scar. Despite the prolonged atrial refractoriness, the propensity for atrial fibrillation was increased; lending support to the theory that structural remodelling associated with conduction abnormalities plays a greater role in the substrate predisposing to atrial fibrillation. Chapters 4 and 5 present the results of the studies evaluating the immediate effects of chronic atrial stretch reversal on the atrial electrical remodelling. These studies demonstrated that immediately after percutaneous mitral commissurotomy there was decrease in P wave duration, improvement in site specific conduction delay and conduction velocity associated with increase in the voltage. However, there was no change in atrial refractoriness. Chapter 6 studies the substrate long-term after reduction of stretch. There was further increase in conduction velocity and voltage associated with decrease in atrial refractoriness and conduction delay across the crista terminalis. These observations suggest that strategies aimed at reducing atrial stretch in different disease conditions would potentially decrease the burden or prevent atrial fibrillation. There is mounting evidence of the effect of stretch on the atria; however, the effect of stretch on the triggers of atrial fibrillation has not been evaluated before. Chapter 7 and 8 present the results of the study examining the effect of acute and chronic stretch on human pulmonary veins. Simultaneous pacing of the right ventricle and pulmonary vein induced acute stretch. The effect of chronic stretch was evaluated in patients with mitral stenosis. The atrial refractoriness was abbreviated in acute stretch while it was prolonged in the chronic form. Nevertheless, both resulted in marked pulmonary vein conduction abnormalities that were pronounced with chronic stretch and extra-stimuli. Additionally, structural remodelling was seen with chronic stretch. These abnormalities implicate stretch in the milieu for re-entry and pulmonary vein arrhythmogenesis in conditions predisposed to atrial fibrillation. In summary, this thesis has evaluated the effects of stretch on the substrate and triggers of atrial fibrillation. It provides evidence for the importance of structural changes and the associated abnormalities in conduction in predisposing to atrial fibrillation. These observations may be important in the development of tools to treat, cure and prevent atrial fibrillation. / Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2008

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 5 uppsatser.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 132-143).

OBJECTIVE: This study aims to corroborate recent research demonstrating that patients with low body mass indexes tend to have worse postoperative survival outcomes compared to normal BMI patients. It also intends to compare survival outcomes and postoperative complications in transcatheter and surgical aortic valve replacement patients to determine which procedure, TAVR or SAVR respectively, is better for this challenging low BMI patient population. METHODS: This is a retrospective, single-center study comparing patient data collected from 2000-2013 at New York Presbyterian Hospital/Columbia University Medical Center. Patients were dividing into three groups on the basis of BMI and aortic valve procedure: low BMI SAVR (BMI < 22 kg/m2; n = 148; 20.36%), normal BMI SAVR (22-25 kg/m2; n = 458; 63.00%), and low BMI TAVR (< 22 kg/m2; n = 121; 16.64%). There is a total of 606 SAVR patients and 121 TAVR patients. To corroborate recent research that low BMI patients tend to fare worse than normal BMI patients, an unadjusted comparison were used to compare baseline demographics and postoperative outcomes of 148 low BMI patients who underwent SAVR with 458 normal BMI patients who underwent isolated SAVR. These cohorts were then compared via a Kaplan-Meier survival analysis and the log-rank test for 30 days, 6 months, 1 year and 3 years survival outcomes. The 148 low BMI SAVR patients were then compared to 121 low BMI patients who underwent TAVR on baseline demographics and preoperative risk factors. The two cohorts were compared using the Kaplan-Meier analysis and postoperative complications were compared utilizing a multivariable logistic regression after adjustment for age, gender, BMI and STS Scores. RESULTS: The unadjusted analysis of the low BMI and normal BMI SAVR cohorts displayed similar patient demographics and preoperative risk factors. The normal BMI group demonstrated higher EF (55% vs. 51.5%; p = 0.002) and incidence of HLD (47.68% vs. 37.76%; p = 0.038). Conversely, the low BMI cohort had more females (61.49% vs.42.79%; p < 0.001) and individuals with a history of Afib (27.78% vs.16.96%; p = 0.004). As shown in the Kaplan Meier curve, the normal BMI SAVR patients exhibited superior 6 months, 1 year and 3 years survival rates and low BMI was shown to be a significant independent predictor of mortality (HR 2.56; 95% CI: 1.47 – 4.47; p = 0.0009 at 1 year). The two groups had similar postoperative outcomes, however, the low BMI cohort had longer overall hospital stays (8 vs. 6.5 days; p = 0.0003). The low BMI SAVR and TAVR patient cohorts varied significantly on most patient demographics and preoperative risk factors. The low BMI TAVR patients tend to be older (95.04% vs. 55.41% of patients > 75 years old) and had higher STS Scores (10.41 vs. 3.88; p < 0.0001). They also demonstrated significant increases in all the preoperative risk factors excluding DM and prior CVA. The SAVR patients had significantly longer overall hospital stays (8 vs. 6 days; p < 0.0001), more re-exploration for bleeding (5.41% vs. 0.85%; p = 0.0411) and more patients discharged to home (68.24% vs. 50.85%; p = 0.0039) while the TAVR patients demonstrated higher rates of GI bleed (3.39% vs. 0.00%; p = 0.0240) and new PPM (10.17% vs. 0.68%; p = 0.0004). The low BMI SAVR cohort demonstrated better survival rates at 1 year and 3 years and low BMI TAVR was determined to be a significant independent predictor of mortality (HR 0.51; 95% CI: 0.30 – 0.88; p = 0.0146 at 1 year). After controlling for specific covariates in the multivariate logistic regression analysis, the low BMI SAVR had 1.73 times longer ICU stays, 1.90 times longer hospital stays and the odds of being discharged home was 17% less than the TAVR group (p = 0.0005, <0.0001, 0.5665). CONCLUSION: Although the rates of postoperative complications are fairly similar, patients with low BMIs demonstrated worse survival outcomes when compared to the normal BMI SAVR patients. With the current analysis, low BMI TAVR patients had a significantly worse preoperative profile compared to the corresponding SAVR cohort which explains the worse survival and postoperative outcomes. Despite this, the multivariable analysis showed that the low BMI SAVR patients had longer ICU and hospital stays as well as fewer discharges to home. As this is an ongoing study, steps should be made to balance the preoperative profile such that the low BMI SAVR and TAVR groups are comparable prior to survival and postoperative assessment. However, at the current status, TAVR has proven itself to be the preferred treatment for low BMI patients. / 2018-07-13T00:00:00Z

Objetivos: Determinar a acurácia do estridor em predizer a ocorrência de estenose subglótica (ESG) por intubação em pacientes pediátricos quando comparado ao seu diagnóstico por endoscopia de via aérea. Delineamento: Coorte Prospectiva. Métodos: Foram elegíveis todas as crianças de 28 dias a quatro anos de idade internadas na Unidade de Terapia Intensiva Pediátrica do Hospital de Clínicas de Porto Alegre que necessitaram de intubação endotraqueal por mais de 24 horas. Foram excluídas as com história de intubação, doença laríngea prévia, presença de traqueostomia atual ou no passado, presença de malformações craniofaciais e aquelas consideradas portadoras de doença terminal. Foram acompanhadas diariamente e, após a extubação, submetidas à fibronasolaringoscopia (FNL). Novo exame era realizado em sete a dez dias naquelas com alterações moderadas a graves no primeiro. Se essas persistissem ou surgissem sintomas, independentemente da FNL inicial, realizava-se laringoscopia sob anestesia geral. Após a extubação, verificou-se diariamente a ocorrência de estridor, classificado como presente ou ausente. Resultados: Foram acompanhados, de novembro de 2005 a agosto de 2012, 194 pacientes. A incidência de estridor pós-extubação foi de 43,81%. O estridor apresentou uma sensibilidade de 77,78% (IC 95%: 51,9 – 92,6) e especificidade de 59,66% (IC 95%: 52,0 – 66,9) em detectar ESG nessa amostra, o valor preditivo positivo (VPP) foi de 16,47% (IC 95%: 9,6 – 26,4) e o valor preditivo negativo (VPN) foi de 96,33% (IC 95%: 90,3 – 98,8). O estridor quando presente por mais de 72 horas ou quando esse surgiu após as primeiras 72 horas da extubação apresentou uma sensibilidade de 66,67% (IC 95%: 41,2 – 85,6) e especificidade de 88,5% (IC 95%: 83,1 – 93,1). O VPP foi de 38,8% (IC 95%: 22,4 – 57,7) e o VPN foi de 96,23 (IC 95%: 91,6 – 98,5). A área da curva ROC foi 0,78 (IC 95%: 0,65 – 0,91). Conclusões: A ausência de estridor mostrou-se adequada para afastar o diagnóstico de ESG por intubação em pacientes pediátricos após o período neonatal. Melhor especificidade foi encontrada quando o estridor ocorreu por mais de 72 horas após a extubação ou quando teve o início depois desse período. A partir desse estudo, parece adequado indicar endoscopia de via aérea, para a confirmação de ESG, apenas naqueles pacientes que apresentarem estridor após 72 horas da extubação. / Objective: To determine the accuracy of stridor in predicting the occurrence of postintubation subglottic stenosis (SGS) in pediatric patients when compared with endoscopy airway diagnosis. Design: Prospective cohort. Methods: Children aged 28 days to four years admitted to the Pediatric Intensive Care Unit of Hospital de Clinicas de Porto Alegre who required endotracheal intubation for more than 24 hours were eligible for study. Patients with previous intubation, history of laryngeal disease, current or past tracheostomy, presence of craniofacial malformations and those considered terminal by the staff were excluded from the study. Children were monitored daily and underwent flexible fiberoptic laryngoscopy (FFL) after extubation. Those who presented moderate to severe abnormalities in this first examination underwent another FFL between 7 and 10 days later. If these lesions persisted or symptoms developed, regardless of the findings in initial examination, laryngoscopy under general anesthesia was warranted. Occurrence of stridor was verified daily after extubation and classified as either present or absent. Results: We followed 194 children between November 2005 and August 2012. The incidence of post-extubation stridor was 43.81 per cent. Stridor had a sensitivity of 77.78% (CI 95%: 51.9 – 92.6) and specificity of 59.66% (CI 95%: 52.0 – 66.9) to detect SGS in this sample. The positive predictive value (PPV) was 16.47% (CI 95%: 9.6 – 26.4) and the negative predictive value was 96.33% (CI 95%: 90.3 – 98.8). Stridor, when present more than 72 hours or when started after these first 72 hours after extubation, showed a sensitivity of 66.67% (CI 95%: 41.2 – 85.6), specificity of 88.5% (CI 95%: 83.1 – 93.1), PPV of 38.8% (CI 95%: 22.4 – 57.7) and NPV of 96.23% (CI 95%: 91,6 – 98,5). ROC curve area was 0,78 (CI 95%: 0.65 – 0.91). Conclusions: Absence of stridor proved to be adequate to rule out the diagnosis of post-intubation SGS in pediatric patients. Improved specificity was found when stridor occurred for more than 72 hours after extubation or when started after that. From this study, it seems appropriate to indicate airway endoscopy under general anesthesia for the confirmation of SGS only in those patients who present stridor after 72 hours following extubation.

Objetivos: Determinar a acurácia do estridor em predizer a ocorrência de estenose subglótica (ESG) por intubação em pacientes pediátricos quando comparado ao seu diagnóstico por endoscopia de via aérea. Delineamento: Coorte Prospectiva. Métodos: Foram elegíveis todas as crianças de 28 dias a quatro anos de idade internadas na Unidade de Terapia Intensiva Pediátrica do Hospital de Clínicas de Porto Alegre que necessitaram de intubação endotraqueal por mais de 24 horas. Foram excluídas as com história de intubação, doença laríngea prévia, presença de traqueostomia atual ou no passado, presença de malformações craniofaciais e aquelas consideradas portadoras de doença terminal. Foram acompanhadas diariamente e, após a extubação, submetidas à fibronasolaringoscopia (FNL). Novo exame era realizado em sete a dez dias naquelas com alterações moderadas a graves no primeiro. Se essas persistissem ou surgissem sintomas, independentemente da FNL inicial, realizava-se laringoscopia sob anestesia geral. Após a extubação, verificou-se diariamente a ocorrência de estridor, classificado como presente ou ausente. Resultados: Foram acompanhados, de novembro de 2005 a agosto de 2012, 194 pacientes. A incidência de estridor pós-extubação foi de 43,81%. O estridor apresentou uma sensibilidade de 77,78% (IC 95%: 51,9 – 92,6) e especificidade de 59,66% (IC 95%: 52,0 – 66,9) em detectar ESG nessa amostra, o valor preditivo positivo (VPP) foi de 16,47% (IC 95%: 9,6 – 26,4) e o valor preditivo negativo (VPN) foi de 96,33% (IC 95%: 90,3 – 98,8). O estridor quando presente por mais de 72 horas ou quando esse surgiu após as primeiras 72 horas da extubação apresentou uma sensibilidade de 66,67% (IC 95%: 41,2 – 85,6) e especificidade de 88,5% (IC 95%: 83,1 – 93,1). O VPP foi de 38,8% (IC 95%: 22,4 – 57,7) e o VPN foi de 96,23 (IC 95%: 91,6 – 98,5). A área da curva ROC foi 0,78 (IC 95%: 0,65 – 0,91). Conclusões: A ausência de estridor mostrou-se adequada para afastar o diagnóstico de ESG por intubação em pacientes pediátricos após o período neonatal. Melhor especificidade foi encontrada quando o estridor ocorreu por mais de 72 horas após a extubação ou quando teve o início depois desse período. A partir desse estudo, parece adequado indicar endoscopia de via aérea, para a confirmação de ESG, apenas naqueles pacientes que apresentarem estridor após 72 horas da extubação. / Objective: To determine the accuracy of stridor in predicting the occurrence of postintubation subglottic stenosis (SGS) in pediatric patients when compared with endoscopy airway diagnosis. Design: Prospective cohort. Methods: Children aged 28 days to four years admitted to the Pediatric Intensive Care Unit of Hospital de Clinicas de Porto Alegre who required endotracheal intubation for more than 24 hours were eligible for study. Patients with previous intubation, history of laryngeal disease, current or past tracheostomy, presence of craniofacial malformations and those considered terminal by the staff were excluded from the study. Children were monitored daily and underwent flexible fiberoptic laryngoscopy (FFL) after extubation. Those who presented moderate to severe abnormalities in this first examination underwent another FFL between 7 and 10 days later. If these lesions persisted or symptoms developed, regardless of the findings in initial examination, laryngoscopy under general anesthesia was warranted. Occurrence of stridor was verified daily after extubation and classified as either present or absent. Results: We followed 194 children between November 2005 and August 2012. The incidence of post-extubation stridor was 43.81 per cent. Stridor had a sensitivity of 77.78% (CI 95%: 51.9 – 92.6) and specificity of 59.66% (CI 95%: 52.0 – 66.9) to detect SGS in this sample. The positive predictive value (PPV) was 16.47% (CI 95%: 9.6 – 26.4) and the negative predictive value was 96.33% (CI 95%: 90.3 – 98.8). Stridor, when present more than 72 hours or when started after these first 72 hours after extubation, showed a sensitivity of 66.67% (CI 95%: 41.2 – 85.6), specificity of 88.5% (CI 95%: 83.1 – 93.1), PPV of 38.8% (CI 95%: 22.4 – 57.7) and NPV of 96.23% (CI 95%: 91,6 – 98,5). ROC curve area was 0,78 (CI 95%: 0.65 – 0.91). Conclusions: Absence of stridor proved to be adequate to rule out the diagnosis of post-intubation SGS in pediatric patients. Improved specificity was found when stridor occurred for more than 72 hours after extubation or when started after that. From this study, it seems appropriate to indicate airway endoscopy under general anesthesia for the confirmation of SGS only in those patients who present stridor after 72 hours following extubation.

Objetivos: Determinar a acurácia do estridor em predizer a ocorrência de estenose subglótica (ESG) por intubação em pacientes pediátricos quando comparado ao seu diagnóstico por endoscopia de via aérea. Delineamento: Coorte Prospectiva. Métodos: Foram elegíveis todas as crianças de 28 dias a quatro anos de idade internadas na Unidade de Terapia Intensiva Pediátrica do Hospital de Clínicas de Porto Alegre que necessitaram de intubação endotraqueal por mais de 24 horas. Foram excluídas as com história de intubação, doença laríngea prévia, presença de traqueostomia atual ou no passado, presença de malformações craniofaciais e aquelas consideradas portadoras de doença terminal. Foram acompanhadas diariamente e, após a extubação, submetidas à fibronasolaringoscopia (FNL). Novo exame era realizado em sete a dez dias naquelas com alterações moderadas a graves no primeiro. Se essas persistissem ou surgissem sintomas, independentemente da FNL inicial, realizava-se laringoscopia sob anestesia geral. Após a extubação, verificou-se diariamente a ocorrência de estridor, classificado como presente ou ausente. Resultados: Foram acompanhados, de novembro de 2005 a agosto de 2012, 194 pacientes. A incidência de estridor pós-extubação foi de 43,81%. O estridor apresentou uma sensibilidade de 77,78% (IC 95%: 51,9 – 92,6) e especificidade de 59,66% (IC 95%: 52,0 – 66,9) em detectar ESG nessa amostra, o valor preditivo positivo (VPP) foi de 16,47% (IC 95%: 9,6 – 26,4) e o valor preditivo negativo (VPN) foi de 96,33% (IC 95%: 90,3 – 98,8). O estridor quando presente por mais de 72 horas ou quando esse surgiu após as primeiras 72 horas da extubação apresentou uma sensibilidade de 66,67% (IC 95%: 41,2 – 85,6) e especificidade de 88,5% (IC 95%: 83,1 – 93,1). O VPP foi de 38,8% (IC 95%: 22,4 – 57,7) e o VPN foi de 96,23 (IC 95%: 91,6 – 98,5). A área da curva ROC foi 0,78 (IC 95%: 0,65 – 0,91). Conclusões: A ausência de estridor mostrou-se adequada para afastar o diagnóstico de ESG por intubação em pacientes pediátricos após o período neonatal. Melhor especificidade foi encontrada quando o estridor ocorreu por mais de 72 horas após a extubação ou quando teve o início depois desse período. A partir desse estudo, parece adequado indicar endoscopia de via aérea, para a confirmação de ESG, apenas naqueles pacientes que apresentarem estridor após 72 horas da extubação. / Objective: To determine the accuracy of stridor in predicting the occurrence of postintubation subglottic stenosis (SGS) in pediatric patients when compared with endoscopy airway diagnosis. Design: Prospective cohort. Methods: Children aged 28 days to four years admitted to the Pediatric Intensive Care Unit of Hospital de Clinicas de Porto Alegre who required endotracheal intubation for more than 24 hours were eligible for study. Patients with previous intubation, history of laryngeal disease, current or past tracheostomy, presence of craniofacial malformations and those considered terminal by the staff were excluded from the study. Children were monitored daily and underwent flexible fiberoptic laryngoscopy (FFL) after extubation. Those who presented moderate to severe abnormalities in this first examination underwent another FFL between 7 and 10 days later. If these lesions persisted or symptoms developed, regardless of the findings in initial examination, laryngoscopy under general anesthesia was warranted. Occurrence of stridor was verified daily after extubation and classified as either present or absent. Results: We followed 194 children between November 2005 and August 2012. The incidence of post-extubation stridor was 43.81 per cent. Stridor had a sensitivity of 77.78% (CI 95%: 51.9 – 92.6) and specificity of 59.66% (CI 95%: 52.0 – 66.9) to detect SGS in this sample. The positive predictive value (PPV) was 16.47% (CI 95%: 9.6 – 26.4) and the negative predictive value was 96.33% (CI 95%: 90.3 – 98.8). Stridor, when present more than 72 hours or when started after these first 72 hours after extubation, showed a sensitivity of 66.67% (CI 95%: 41.2 – 85.6), specificity of 88.5% (CI 95%: 83.1 – 93.1), PPV of 38.8% (CI 95%: 22.4 – 57.7) and NPV of 96.23% (CI 95%: 91,6 – 98,5). ROC curve area was 0,78 (CI 95%: 0.65 – 0.91). Conclusions: Absence of stridor proved to be adequate to rule out the diagnosis of post-intubation SGS in pediatric patients. Improved specificity was found when stridor occurred for more than 72 hours after extubation or when started after that. From this study, it seems appropriate to indicate airway endoscopy under general anesthesia for the confirmation of SGS only in those patients who present stridor after 72 hours following extubation.