Sıvı yakıtlı roket motorlarında rejeneratif soğutma analizleri.

High combustion temperatures and long operation durations require the use of cooling techniques in liquid propellant rocket engines. For high-pressure and high-thrust rocket engines, regenerative cooling is the most preferred cooling method. In regenerative cooling, a coolant flows through passages formed either by constructing the chamber liner from tubes or by milling channels in a solid liner. Traditionally, approximately square cross sectional channels have been used. However, recent studies have shown that by increasing the coolant channel height-to-width aspect ratio and changing the cross sectional area in non-critical regions for heat flux, the rocket combustion chamber gas side wall temperature can be reduced significantly without an increase in the coolant pressure drop. In this study, the regenerative cooling of a liquid propellant rocket engine has been numerically simulated. The engine has been modeled to operate on a LOX/Kerosene mixture at a chamber pressure of 60 bar with 300 kN thrust and kerosene is considered as the coolant. A numerical investigation was performed to determine the effect of different aspect ratio cooling channels and different number of cooling channels on gas-side wall and coolant temperature and pressure drop in cooling channel.M.S. - Master of Scienc

Bivalirudin for cardiopulmonary bypass in a patient with heparin allergy

Abstract Background Hypersensitivity reactions to heparin are uncommon conditions but pose a serious clinical problem for patients requiring cardiopulmonary bypass. Bivalirudin is a reversible direct thrombin inhibitor that can be used instead of heparin. Case Report A 49-year-old male patient was admitted to our hospital for coronary artery bypass graft operation with mitral insufficiency and tricuspid valve insufficiency. Heparin allergy was confirmed by skin biopsy and skin tests. Due to this allergy, we used bivalirudin (Bivacard VEM drug, Turkey) during the surgery. A loading dose of 1.0 mg/kg (100 mg) bivalirudin was administered through the central line and a continuous infusion of 2.5 mg/kg/h of the anticoagulant was initiated following the approved protocol. Serial ACTs were obtained at 15-minute intervals during the procedure and the measurements were 330s, 320s, 350s, 360s, and 340s consecutively. Additional boluses of 0.5 mg/kg (50 mg) were administered for each measurement. Left anterior descending, obtuse marginal arteries and the right coronary artery were grafted with the left internal mammary and saphenous veins. Also, mitral valve replacement with St Jude mechanical heart valve and tricuspid ring annuloplasty was performed with Medtronic Duran ring. After the surgery, the patient had an uneventful period in the postoperative intensive care unit with a total of 600ml and 300ml chest tube drainage for two days and was discharged on the 7th day. Conclusion Alternative anticoagulation strategies are needed for cardiopulmonary bypass in patients unable to use heparin. Bivalirudin may be recommended as a viable alternative anticoagulant in patients with heparin allergy during cardiopulmonary bypass. However, each patient should be evaluated individually and it should not be forgotten that more than recommended doses may be needed

286 Original Investigation Diagnostic accuracy of Doppler ultrasonography for assessment of internal thoracic artery graft patency

Objective: The main purpose of this study was to assess the patency of left internal thoracic artery (LITA) graft by using color Doppler ultrasonography (CDUSG) and furthermore to determine the sensitivity and specificity of CDUSG for patency by using coronary angiography as the reference standard. Methods: This study is an observational cohort study on diagnostic accuracy that was held between August 2008 and October 2009. CDUSG was performed in 138 consecutive patients who had angina symptom or positive ischemic findings following coronary artery bypass surgery. LITA blood flow velocity at peak-systole (PSV), diastole (PDV) and end-diastole (EDV) was recorded. All patients were also assessed by coronary angiography for LITA graft patency. Statistical analysis was performed by using independent samples t-test, Mann-Whitney-U test, chisquare test and receiver operating curve analyses (ROC). Results: Seventy-eight of all patients had functional LITA grafts and 59 patients had dysfunctional LITA grafts according to CDUSG-derived parameters, whereas we cannot conclude about one patient’s LITA graft functionality. The LITA grafts were visualized angiographically in all cases. Of all 138 patients, 60 patients had dysfunctional LITA grafts after angiographic evaluation. The ROC analyses showed that PDV (AUC=0.899, 95 % CI 0.844 to 0.953; p<0.001) and EDV (AUC=0.900; 95 % CI 0.847 to 0.953; p<0.001) values were also strongly associated with graft functionality. We found out that CDUSG predicts LITA graft functionality with a sensitivity and specificity of 100 % and 98.4 % respectively. The accuracy of the CDUSG was calculated as 99.3%. Conclusion: CDUSG is a reliable non-invasive method for assessment of LITA graft patency. (Anadolu Kardiyol Derg 2014; 14: 286-91) Key words: blood flow velocity, coronary artery bypass grafting, internal thoracic artery, color Doppler ultrasonography, sensitivity and specificity, diagnostic accurac

Risk Factors for Survival following Open Surgical Repair of Ruptured Abdominal Aortic Aneurysms: A 13-Year Experience

Background: Surgical treatment of a ruptured abdominal aorta aneurysm (RAAA) continues to present a significant challenge to surgeons. There are some patient factors such as age and gender that cannot be changed, and comorbid conditions can be optimized but not eliminated.  The purpose of this study was to identify the risk factors affecting high mortality after the surgical repair of an RAAA. Methods: Data on 121 patients who underwent surgical repair for RAAAs between January 1997 and June 2011 in our institution were collected retrospectively. All the patients had been diagnosed by computed tomography (CT) scans, and intraoperative extra-luminal blood was visualized intraoperatively. Variables studied comprised demographic data; preoperative, operative, and postoperative data; and the causes of mortality. Multivariate regression analysis was used to determine the predictors of mortality. Results: One hundred eight (89.2%) patients were male and 13 (10.7%) were female at an average age of 68.9 ± 10.5 years. Totally, 121 patients underwent surgery for RAAAs. Fifty-four patients had aortic tube grafts, 32 aortobiiliac grafts, 20 aortobifemoral grafts, 1 aortoiliac graft, and 1 aortofemoral graft for the replacement of the RAAAs. Seven patients had only surgical exploration. Operative mortality was 41.3% (50 patients). The factors associated with mortality were preoperative shock, free blood, positive inotropic agent, hematocrit value, and need for blood and plasma. In the multivariate analysis, preoperative shock and positive inotropic agents were found to be significant as the predictors of death (OR: 19.8, 95%CI: 3.2-122.8 and OR: 8.6, 95% CI: 2.9-26.3, respectively). Conclusion: This study revealed that the preoperative clinical findings affected the mortality associated with RAAAs

Impact of Obesity on the Metabolic Control of Type 2 Diabetes: Results of the Turkish Nationwide Survey of Glycemic and Other Metabolic Parameters of Patients with Diabetes Mellitus (TEMD Obesity Study)

Background: Obesity is the main obstacle for metabolic control in patients with type 2 diabetes. Turkey has the highest prevalence of obesity and type 2 diabetes in Europe. The effect of obesity on the metabolic control, and the macro-and microvascular complications of patients are not apparent. Objectives: This nationwide survey aimed to investigate the prevalence of overweight and obesity among patients with type 2 diabetes and to search for the impact of obesity on the metabolic control of these patients. We also investigated the independent associates of obesity in patients with type 2 diabetes. Methods: We consecutively enrolled patients who were under follow-up for at least 1 year in 69 tertiary healthcare units in 37 cities. The demographic, anthropometric, and clinical data including medications were recorded. Patients were excluded if they were pregnant, younger than 18 years, had decompensated liver disease, psychiatric disorders interfering with cognition or compliance, had bariatric surgery, or were undergoing renal replacement therapy. Results: Only 10% of patients with type 2 diabetes (n = 4,648) had normal body mass indexes (BMI), while the others were affected by overweight (31%) or obesity (59%). Women had a significantly higher prevalence of obesity (53.4 vs. 40%) and severe obesity (16.6 vs. 3.3%). Significant associations were present between high BMI levels and lower education levels, intake of insulin, antihypertensives and statins, poor metabolic control, or the presence of microvascular complications. Age, gender, level of education, smoking, and physical inactivity were the independent associates of obesity in patients with type 2 diabetes. Conclusion: The TEMD Obesity Study shows that obesity is a major determinant of the poor metabolic control in patients with type 2 diabetes. These results underline the importance of prevention and management of obesity to improve health care in patients with type 2 diabetes. Also, the results point out the independent sociodemographic and clinical associates of obesity, which should be the prior targets to overcome, in the national fight with obesity. (c) 2019 The Author(s) Published by S. Karger AG, Base

Turkish nationwide survEy of glycemic and other Metabolic parameters of patients with Diabetes mellitus (TEMD study)

Aims: Turkey has the highest prevalence of diabetes in Europe. It is therefore essential to know the overall cardiovascular risk and reveal the predictors of metabolic control in Turkish adults with diabetes mellitus