Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Martin Raymond Prince. / M.S.

Bibliography: leaves 261-337. / xxii, 340 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The natural history of air embolism of the brain was studied by observing bubbles in the pial vessels of rabbits and the effect of different doses of air on brain function and blood flow. A new model for the pathophysiological basis of CAGE is proposed. / Thesis (Ph.D.)--University of Adelaide, Dept. of Anaesthesia and Intensive Care, 1994

Various techniques are used to transect the liver. With increase in laparoscopic liver resections (LLR), it is of even more interest to develop surgical techniques to minimize bleeding and the risk for gas embolism during transection. Instrument like argon enhanced coagulator provides good hemostasis but increases the danger of gas embolism. The CO2 pneumoperitoneum that is routinely used in most types of laparoscopic surgery can be modified by the use of different gas pressure. It can be assumed that different pressure influences bleeding but also the risk for gas embolism. In presented porcine studies, three instrumental combinations have been studied. In study I sixteen piglets were randomized to LLR with either the cavitron ultrasonic aspirator (CUSA™) in combination with vessels sealing system (Ligasure™) or with CUSA™ and ultrascision scissors (Autosonix™), with the endpoints of intra-operative bleeding and gas embolism.  In study IV sixteen piglets were randomized to LLR either with staple device (Endo-GIA™) or the Ligasure™ - CUSA™ combination with same primary endpoints and additionally secondary endpoints of effect on gas-exchange, systemic- and pulmonary hemodynamic. Focusing on intra-abdominal pressure (IAP) in study II, sixteen piglets were randomized to LLR with an IAP of either 8 or 16 mmHg.  Primary endpoints were bleeding and gas embolism and secondary endpoints, effect on gas-exchange, systemic- and pulmonary hemodynamic. In study III effect of argon gas was tested during LLR. Sixteen piglets were randomized to either argon pneumoperitoneum or CO2 pneumoperitoneum. Primary endpoints were effect on gas-exchange, systemic- and pulmonary hemodynamic. In presented studies, we tested efficacy and safety of different techniques for LLR. CUSA™ can be used in combination with either Ligasure™ or Autosonix™. However, Ligasure™ reduces the amount of bleeding. The recent introduction of staplers seems promising with a further reduction in bleeding, gas embolism, and operating time. The IAP influences both the amount of bleeding as well as gas embolism. It seems reasonable to use a higher IAP to decrease bleeding with caution and with close monitoring for gas embolism. Argon gas embolism gives more extensive effect on gas-exchange and hemodynamic and should probably be avoided in this type of surgery.

Laparoscopic liver surgery is complicated due to the structure of this organ with open sinusoids. A serious disadvantage is the risk of gas embolism (GE) due to CO2 pneumoperitoneum. CO2 can enter the vascular system through a wounded vein. A common opinion is that gas fluxes along a pressure gradient, e.g. CVP-intra abdominal pressure (IAP). The occurrence of GE could also be eased by entrainment, a ‘Venturi-like’ effect, due to cyclic differences in thoracic pressure and blood flow caused by mechanical ventilation at normal frequency. The aims of these studies were to survey, in a porcine model, the influence on respiratory and haemodynamic variables by GE, to determine at what frequency, severity and duration GE occurs during laparoscopic liver resection (LLR) and whether there are methods to influence the occurrence or severity of GE. Pulmonary and circulatory variables were monitored and measured as well as continuous blood gas monitoring. Transoesophageal echocardiogram was used to identify GE and, according to the amount of bubbles in the right outflow tract of the heart, GE was graded as 0, 1 and 2. Pneumoperitoneum was created by using CO2and IAP was set to 16 mm Hg. A single bolus dose of CO2 influenced respiratory and haemodynamic variables for at least 4 h. During LLR GE occurred in 65-70% of the animals, of which the more serious caused negative influence on cardiopulmonary variables. Elevated PEEP (15 cm H2O) increased CVP but GE occurred irrespective if CVP was lower than or exceeded IAP. In two last studies, a hepatic vein was cut and left open for 3 m before it was clipped. Interestingly, no signs of GE were seen despite an open vein and IAP > CVP in 8 of 20 animals. In the last study high frequency jet ventilation was used in order to minimise the risk of entrainment. The duration of GE was shortened. The occurrence of GE seemed to be influenced by several different factors. The physiological reaction of a GE is impossible to predict for a specific patient, and depends among other factors on comorbidity, and amount, site and entrance rate of GE.

Introduction: Neurological complications and stroke in association with cardiac surgery is a serious problem. The stroke event can occur during surgery (early stroke) or in the postoperative period with a symptom free interval (delayed stroke). Particle embolization due to aortic manipulation during surgery has been suspected as a mechanism for early stroke. The present thesis address mechanisms and survival effects of stroke both clinically (I-III) and experimentally (IV-V). Methods: Study I) Within a cohort of 2641 consecutive cases, a group of cardiac surgery patients with stroke and evaluated by computed tomography (CT) were studied (n=77). CT-findings were analyzed in relation to stroke symptoms. Study II) Data from 9122 patients undergoing coronary surgery were analyzed. Records of patients with any signs of neurological complications were reviewed to extract 149 subjects with stroke at extubation (early, 1.6%) versus 99 patients having a free interval (delayed, 1.1%). Early and delayed stroke were evaluated separately. Independent risk factors for stroke were analyzed by logistic regression and survival by Cox regression (9.3 years median follow-up). Study III) Patients with early (n=223) and delayed stroke (n=116) were identified among 10809 patients undergoing cardiac and aortic surgery, both groups exposed to cardiopulmonary bypass. Stroke patients were subdivided by the hemispheric location of lesions. Subgroups were compared and their associated pre- and peroperative variables and survival were analyzed. Study IV) Aortic cross-clamp manipulation was studied in a human cadaveric perfusion model. The pressurized aorta was repeatedly cross-clamped and washout samples were collected before and after clamp maneuvers. Particles in the washout samples were evaluated by microscopy and by digital image analysis. Study V) Pig aortas were pressurized and cannulated. Washout samples were collected before and after cannulation (n = 40). Particles were deposited onto a 10-μm filter to be evaluated by microscopy and digital image analysis. Results: Study I) In the group of patients exposed to routine cardiac surgery (i.e., clamping and cannulation) and with early stroke, right-hemispheric lesions were more frequent than of the contra-lateral side (P=0.005). Patients with aortic dissections had a strong dominance of bilateral findings, which was different from the unilateral pattern in the routine-surgery group (P<0.001). Study II) Early and delayed stroke did not share any risk factors. Both early and delayed stroke explained mortality in the early postoperative period (P<0.001, P<0.001 respectively) but also at long term follow-up (P=0.008, P<0.001 respectively). For patients surviving their first postoperative year, delayed but not early stroke influenced long-term mortality (P=0.001 and P=0.695, respectively). Study III) Stroke lesions in association to cardiac surgery were near exclusively ischemic. Early stroke had a preponderance for right-hemispheric lesions (P=0.009). In contrast, patients with early stroke that had undergone surgery of the aorta with circulatory arrest showed a pattern with more bilateral lesions compared to ‘cardiac-type’ operations (P<0.001). Patients with bilateral lesions had a dramatically impaired survival compared to those with unilateral lesions (P<0.001). Study IV) In the cadaveric perfusion model, cross-clamping produced a significant output of particles, which was seen for size intervals of 1 mm and smaller (P=0.002 to P=0.022). In all size intervals the particle output correlated with the degree of overall aortic calcification (P =0.002 to P=0.025). Study V) At cannulation of the pig aorta, more particles were noted after cannulation compared to before the maneuver (P<0.001). This increase included small (<0.1 mm, P<0.001) and intermediate-size particles (0.1-0.5 mm, P< 0.001). Particles above 0.5 mm were few and were not associated with cannulation. Conclusions: The influence of stroke on mortality was devastating, for both early and delayed stroke. These two stroke groups had obvious differences in both their risk factors and their hemispheric distribution. It is here emphasized that early and delayed stroke should be considered as two separate entities with suggested mechanistic differences. Ischemic lesions accounted for near all stroke events seen in association to cardiac surgery. For early stroke, these were mostly located within the right hemisphere. Results from the experimental studies underscore microembolic risks associated with aortic manipulation.

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

Venous thromboembolism (VTE), comprising deep venous thrombosis (DVT) and pulmonary embolism (PE), is a common and preventable cause of morbidity among individuals and hospital in-patient mortality. Further, it imposes a substantial burden upon the community and its health care system and economy. Studies performed in Western societies suggest that the annual incidence of DVT is about 0.8 to 1.2 per 1,000, PE about 0.3 to 0.6 per 1,000, and VTE about 1.0 to 1.8 per 1,000. However, it is not known if these estimates can be generalised to the Australian population because of differences in ethnic composition and other risk factors for VTE among the different populations. In this thesis, I undertook a prospective, community-based cohort study over a 13-month period in 2003 – 2004 to determine the incidence and crude event rate of symptomatic, objectively verified VTE in north-east metropolitan Perth. The study population was broadly representative of the national Australian population in terms of age, sex and ethnic distribution. Cases were identified through multiple overlapping sources. The incidence of DVT, PE and VTE in the community were 0.52 (95% confidence interval, CI: 0.41 – 0.63), 0.31 (95% CI: 0.22 – 0.40) and 0.83 (95% CI: 0.69 – 0.97) per 1000 per year, respectively. The annual incidence of DVT, adjusted to the World Standard population, was 0.35 (95% CI: 0.26 – 0.44) per 1000, PE 0.21 (95% CI: 0.14 – 0.28) per 1000 and VTE 0.57 (95% CI: 0.47 – 0.67) per 1000. The crude event rate for VTE was 0.85 (95% CI: 0.71 – 0.99) per 1000 per year. These findings suggest that the incidence of DVT, PE and VTE are lower than in other Western societies studied. Possible reasons include a lower prevalence of exposure to causal risk factors (genetic and environmental) and incomplete case ascertainment. Knowledge of the local incidence and event rate allows health planners to allocate appropriate resources and evaluate cost-effective preventive measures.

Thesis (MSc.(Anatomy)--Faculty of Health Sciences)-University of Pretoria, 2008. / Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 64-74).

Made available in DSpace on 2015-12-06T23:06:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2005 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O protocolo de pesquisa "Ecocardiograma transesofágico (ETE) e tratamento com ácido acetil salicílico (AAS) de pacientes com acidente vascular cerebral (AVC) isquêmico” está em andamento e como parte inicial é apresentada nesta tese o artigo "Ecocardiograma transesofágico mostra fonte cardíaca não suspeitada em pacientes com acidente vascular cerebral com mais que 45 anos", já que embolia cerebral de fonte cardíaca é frequentemente relacionada a AVC em jovem. OBJETIVO: descrever achados ecocardiográficos em jovens e não-jovens com AVC isquêmico, sem suspeita de fonte cardíaca. MÉTODO: estudo prospectivo. 523 pacientes (267 homens e 256 mulheres) com AVC isquêmico sem evidência de fonte cardíaca submeteram-se ao ecocardiograma transesofágico (ETE). RESULTADOS: 10% dos pacientes tinha 45 anos ou menos. Hipertrofia do ventrículo esquerdo, aumento do átrio esquerdo, contraste espontâneo na aorta, aneurisma do septo interatrial, calcificação da válvula mitral e aórtica, insuficiência aórtica e placas de ateroma na aorta foram significantemente mais freqüentes nos pacientes com mais que 45 anos; 2.8% dos não-jovens apresentaram trombo nas câmaras esquerdas. CONCLUSÃO: ETE é amplamente sugerido na investigação de embolia em pacientes jovens, porém parece ser tão importante também no grupo de pacientes mais velhos, nos quais o risco de embolia cerebral é subestimado; etiologia cardioembólica e aterosclerótica coexistem, e ambas devem ser identificadas e tratadas para melhor prognóstico. / The clinical protocol "Transesophageal echocardiography and treatment with aspirin in patients with ischemic stroke" is going on, and, as an inicial part of it, we present the article "Transesophageal echocardiography discloses unexpected cardiac sources of embolus in stroke patients aged more than 45 years". Cerebral embolism from cardiac source is an important cause of stroke, specially in patients younger than 45 years old. Objective: to describe the TEE findings in young and no-young stroke patients without any prior evidence of cardiac source for cerebral embolism. Method: Transversal study. 523 patients (267 men and 256 women) with ischemic stroke, without any evidence of cardiac abnormality, underwent to transesophageal echocardiography (TEE). Results: Ten percent were aged 45 years or less. Left ventricle hypertrophy, left atrial enlargement, spontaneous contrast in aorta, interatrial septum aneurysm, mitral and aortic valve calcification, aortic valve regurgitation, and atherosclerotic plaques in aorta were significantly more frequent in patients aged more than 45 years. 2.8% of no-young patients had thrombus in left heart. Conclusion: TEE is widely used to diagnose cardiac source of cerebral embolism in young patients, but it seems to be as useful for older ones, in whom cerebral embolism risk is underestimated; atherogenic and cardioembolic causes may actually coexist, and both should be treated. / BV UNIFESP: Teses e dissertações