Tuning electrical and thermal conductivities of the two-dimensional electron gas in AlN/GaN heterostructures by piezoelectricity.

We investigate the electrical and thermal conductivities of the two-dimensional electron gas (2DEG) confined in the quantum well formed at the heterojunction between a thin GaN layer and an AlN layer strained by an Al x Ga1-x N capping layer in the temperature range from 10 to 360 K. The experimental protocol developed to deduce from calorimetric and Hall-effect measurements at a variable temperature the critical characteristics and transport properties of the confined 2DEG is presented. It is found that, in the measured temperature range (10-360 K), the electrical conductivity of the 2DEG is temperature-independent, due to the predominance of scattering processes by interface defects. However, the thermal conductivity shows a linear temperature dependence, mirroring the specific heat of free electrons. The temperature-independent relaxation time associated with the overall electron scattering means that the values obtained for electrical and thermal conductivities are in excellent agreement with those stipulated by the Weidemann-Franz law. It is also found that for weak strain fields in the AlN layer, both the electrical and thermal conductivities of the two-dimensional interfacial electrons increase exponentially with strain. The importance of 2DEG in AlN/GaN quantum wells lies in the fact that the strong piezoelectricity of AlN allows the transport properties of the 2DEG to be tuned or modulated by a weak electric field even with the high density of lattice mismatch induced defects at the AlN-GaN interface .

Acute kidney injury following coronary artery bypass graft surgery in a tertiary public hospital in Malaysia: an analysis of 1228 consecutive cases.

BACKGROUND: Acute kidney injury (AKI) following cardiac surgery is well established but the reported incidence is variable due to varying definitions and criteria. Furthermore there is a paucity of such data from Southeast Asia. OBJECTIVES: To determine the incidence of AKI, the associated risk factors, and its impact on early mortality and intensive care unit/hospital stay. METHOD: This is a single centre retrospective observational study to evaluate outcomes on 1260 consecutive patients from a multi-ethnic Southeast Asian population who underwent a primary isolated coronary artery bypass graft (CABG) operation. Data was collected from the hospital's electronic database and analysed using basic descriptive statistics and logistic regression. RESULTS: Overall incidence was 36.2% including 5.5% of patients who required renal replacement therapy (RRT). Multivariate analysis identified age, insulin-dependent diabetes mellitus (IDDM), baseline serum creatinine level (SCr), recent myocardial infarction (MI), cardiopulmonary bypass (CPB) time and intra-aortic balloon pump (IABP) use as independent risk factors for AKI. For patients who required RRT, the SCr and IDDM remained independent predictors. Early 30-day mortality (11.5% vs 0.9%) was significantly higher in patients who developed AKI following CABG. Similarly, AKI was associated with a slight but statistically significant increase in intensive care unit (ICU) and hospital stay. CONCLUSION: Better prognostication and preventative strategies are required to better risk stratify patients undergoing CABG and optimise utilisation of limited healthcare resources.

Rare Intracardiac Tumor: Primary Cardiac Lymphoma Presenting as Atypical Angina.

Primary lymphomas of the heart are extremely rare, accounting for 2% of all primary cardiac tumors. Due to the rare presentation, there is no proper consensus available on treatment strategy. Preoperative confirmation of the pathology is fundamental in guiding an early treatment plan, which allows for improved prognosis. Unfortunately, in most cases, primary cardiac lymphoma is only identified on postoperative histopathological analyses, which affect the treatment plan and outcome. Here, we report a unique case of primary cardiac lymphoma presented with dyspnea and reduced effort tolerance. Young age, rapid onset of symptom, and absence of cardiac risk factors prompted us towards further imaging and emergency resection. The patient received a course of postoperative chemotherapy and was disease-free on six months of follow-up.

A case of successful extracorporeal membrane oxygenation for right ventricular failure following pericardiectomy.

Extracorporeal membrane oxygenation (ECMO) is a useful but less commonly used technique in right ventricular failure post cardiac surgery in our region. We report a case of successful use of ECMO for right ventricular failure post cardiac surgery. Our patient is a 27-year-old male presented with constrictive pericarditis post completion of treatment for disseminated Tuberculosis. He underwent pericardiectomy that was complicated with acute right ventricular failure. He was placed on extracorporeal membrane oxygenation after few hours post op that lasted for five days. The patient survived to hospital discharge and remained well on follow-up. From our experience, this aggressive management approach is beneficial in right ventricular failure and can be safely utilised in all cardiothoracic centres.

Association of calcium concentration with pulse pressure in older women: data from a large population-based multicentric study.

OBJECTIVE: High arterial pulse pressure is a predictor of cardiovascular morbimortality. Mineral metabolism has been associated with blood pressure regulation. Our objective was to determine which variable among serum calcium, parathyroid hormone and 25-hydroxyvitamin D concentrations, was associated with pulse pressure among older adults. DESIGN: Cross-sectional study corresponding to the baseline assessment of the EPIDOS study. SETTING: Five French cities including Amiens, Lyon, Montpellier, Paris and Toulouse. PARTICIPANTS: Randomized sample of 610 community-dwelling older women (mean age 80.2±3.5years) using no antihypertensive drugs. MEASUREMENTS: Serum calcium, parathyroid hormone and 25-hydroxyvitamin D concentrations; supine pulse pressure after 15 minutes of rest (hypertension defined as pulse pressure >50mmHg). Age, body mass index, the number of morbidities and of drugs daily taken, diabetes mellitus, dysthyroidy, the use of estrogenic drugs, smoking, alcohol consumption, practice of a regular physical activity, creatinine clearance, and the effects of season and study centers were used as potential confounders. RESULTS: Hypertensive participants (n=539) had higher calcium concentrations than normotensive ones (94.33±4.12mg/L versus 93.28±3.36mg/L respectively, P=0.040). There were no between-group differences for serum parathyroid hormone and 25-hydroxyvitamin D concentrations. The multiple logistic regressions examining the serum calcium, parathyroid hormone and 25-hydroxyvitamin D concentrations as predictors of hypertension found an association only with calcium (adjusted odds ratio=1.19, P=0.015), but not with parathyroid hormone (adjusted OR=1.01, P=0.349) or 25-hydroxyvitamin D concentration (adjusted OR=0.99, P=0.971). CONCLUSION: Increased serum calcium concentration was independently and positively associated with high pulse pressure in our study, possibly due to increased arterial stiffness. Interventions aimed at normalizing calcaemia may be attractive to prevent hypertension and cardiovascular risk in older adults.

Protective role of selenium supplementation against cardiac lesions induced by the combination of levomepromazine and risperidone in the rabbit.

Neuroleptics are a suspected cause of sudden death in psychiatric patients, especially in those with pre-existing cardiac lesions. As these lesions were previously shown to be associated with selenium (Se) deficiency, the aim of the present study was to evidence the possible protective effect of Se supplementation against cardiac lesions induced by the combination of the neuroleptic drugs levomepromazine and risperidone in the rabbit. Two groups of 6 rabbits were treated with 3 mg/kg of levomepromazine daily intramuscularly combined with 1 mg/kg of risperidone intramuscularly every other week for 3 consecutive months, and one group additionally received a solution of sodium selenite (2 microg/kg/day) intramuscularly during the whole treatment period. Furthermore, one group of six untreated animals was given the Se supplementation and another group of six control animals received saline daily. Blood samples were drawn before and at the end of the treatment period for the measurement of serum Se levels. At the end of the study, all animals were sacrificed and their hearts were removed for the measurement of tissue Se concentrations. In addition, the hearts were prepared for histopathological examination. A variety of cardiac lesions was found in the neuroleptics-treated animals without supplementation and to a lesser extent in the control and Se-supplemented untreated animals. Importantly, only rare cardiac lesions were observed in neuroleptics-Se-treated animals. The most striking differences in Se concentrations were noted in the myocardium: as compared to controls, there was a 43% reduction in neuroleptics-treated, but non-Se-supplemented animals (p < .01), at the end of the treatment period, whereas only a 14% reduction (p < .05) was noted in the neuroleptics-Se-treated animals. These results confirm that neuroleptics induce cardiac lesions associated with Se deficiency. Selenium supplementation markedly decreased the incidence and severity of neuroleptics-induced cardiac lesions and these findings may serve as a basis for further evaluation of the protective role of Se supplementation in neuroleptics-treated patients. However, Se supplementation in normal animals without Se deficiency was also shown to be cardiotoxic.

[Bidirectional Glenn shunt without cardiopulmonary bypass].

From April 2002 to March 2005, 18 patients having undergone bidirectional Glenn shunt (BDG) without cardiopulmonary bypass (CPB) [off-pump BDG] were retrospectively reviewed. During BDG anastomosis, a temporary bypass was established between superior vena cava (15) or innominate vein (3) and main pulmonary artery (16) or right atrium (2). Hemodynamics and oxygenation were maintained well throughout the temporary bypass time. There was no emergent use of CPB. Mean transpulmonary pressure gradient immediately after and 24 hours after the BDG were 6.7 and 5.6 mmHg, respectively. Echocardiography showed mild flow turbulence at the anastomosis in 1 case. This simple and inexpensive technique provided good surgical view with stable hemodynamics enabling satisfactory BDG in selected cases. Furthermore, it could avoid adverse effects of CPB such as lung injury and possible blood transfusion. This experience would encourage off-pump BDG combined with more challenging procedures.