Nonlinear ac response of anisotropic composites

When a suspension consisting of dielectric particles having nonlinear characteristics is subjected to a sinusoidal (ac) field, the electrical response will in general consist of ac fields at frequencies of the higher-order harmonics. These ac responses will also be anisotropic. In this work, a self-consistent formalism has been employed to compute the induced dipole moment for suspensions in which the suspended particles have nonlinear characteristics, in an attempt to investigate the anisotropy in the ac response. The results showed that the harmonics of the induced dipole moment and the local electric field are both increased as the anisotropy increases for the longitudinal field case, while the harmonics are decreased as the anisotropy increases for the transverse field case. These results are qualitatively understood with the spectral representation. Thus, by measuring the ac responses both parallel and perpendicular to the uniaxial anisotropic axis of the field-induced structures, it is possible to perform a real-time monitoring of the field-induced aggregation process.Comment: 14 pages and 4 eps figure

Dynamic three-dimensional echocardiography combined with semi-automated border detection offers advantages for assessment of resynchronization therapy

Simultaneous electrical stimulation of both ventricles in patients with interventricular conduction disturbance and advanced heart failure improves hemodynamics and results in increased exercise tolerance, quality of life. We have developed a novel technique for the assessment and optimization of resynchronization therapy. Our approach is based on transthoracic dynamic three-dimensional (3D) echocardiography and allows determination of the most delayed contraction site of the left ventricle (LV) together with global LV function data. Our initial results suggest that fast reconstruction of the LV is feasible for the selection of the optimal pacing site and allows identifying LV segments with dyssynchrony

Hemodialysis Complications of Hydroxocobalamin: A Case Report

Hydroxocobalamin is a new antidote approved by the FDA for the treatment of cyanide poisoning. Our report describes a patient with cyanide poisoning who survived after treatment with hydroxocobalamin and complications we encountered with hemodialysis. A 34-year-old female presented to the emergency department after a syncopal event and seizures. Her systolic blood pressure was 75 mmHg, her QRS complex progressively widened, and pulses were lost. She was intubated and resuscitated with fluids, sodium bicarbonate for her QRS widening and vasopressors. Venous blood gas demonstrated a pH of 6.36 with an O2 saturation of 99%. Due to the acidemia with a normal pulse oximetry, simultaneous venous and arterial blood gases were obtained. Venous gas demonstrated a pH of 6.80 with a PO2 of 222 mmHg, an O2 saturation of 99%. The arterial blood gas showed a pH of 6.82, a PO2 518 mmHg, an O2 saturation of 100%. Cyanide was suspected and hydroxocobalamin and sodium thiosulfate were given. Within 40 min of hydroxocobalamin administration, vasopressors were discontinued. Initially, nephrology attempted dialysis for metabolic acidosis; however, the dialysis machine repeatedly shut down due to a “blood leak”. This was an unforeseen effect attributed to hydroxocobalamin. Cyanide level, drawn 20 min after the antidote was completed, was elevated at 22 mcg/dL. Her urinary thiocyanate level could not be analyzed due to an “interfering substance”. Hydroxocobalamin is an effective antidote. However, clinicians must be aware of its effects on hemodialysis machines which could delay the initiation of this important treatment modality in the severely acidemic patient

Evidence regarding clinical use of microvolt T-wave alternans

Background: Microvolt T-wave alternans (MTWA) testing in many studies has proven to be a highly accurate predictor of ventricular tachyarrhythmic events (VTEs) in patients with risk factors for sudden cardiac death (SCD) but without a prior history of sustained VTEs (primary prevention patients). In some recent studies involving primary prevention patients with prophylactically implanted cardioverter-defibrillators (ICDs), MTWA has not performed as well. Objective: This study examined the hypothesis that MTWA is an accurate predictor of VTEs in primary prevention patients without implanted ICDs, but not of appropriate ICD therapy in such patients with implanted ICDs. Methods: This study identified prospective clinical trials evaluating MTWA measured using the spectral analytic method in primary prevention populations and analyzed studies in which: (1) few patients had implanted ICDs and as a result none or a small fraction (≤15%) of the reported end point VTEs were appropriate ICD therapies (low ICD group), or (2) many of the patients had implanted ICDs and the majority of the reported end point VTEs were appropriate ICD therapies (high ICD group). Results: In the low ICD group comprising 3,682 patients, the hazard ratio associated with a nonnegative versus negative MTWA test was 13.6 (95% confidence interval [CI] 8.5 to 30.4) and the annual event rate among the MTWA-negative patients was 0.3% (95% CI: 0.1% to 0.5%). In contrast, in the high ICD group comprising 2,234 patients, the hazard ratio was only 1.6 (95% CI: 1.2 to 2.1) and the annual event rate among the MTWA-negative patients was elevated to 5.4% (95% CI: 4.1% to 6.7%). In support of these findings, we analyzed published data from the Multicenter Automatic Defibrillator Trial II (MADIT II) and Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) trials and determined that in those trials only 32% of patients who received appropriate ICD therapy averted an SCD. Conclusion: This study found that MTWA testing using the spectral analytic method provides an accurate means of predicting VTEs in primary prevention patients without implanted ICDs; in particular, the event rate is very low among such patients with a negative MTWA test. In prospective trials of ICD therapy, the number of patients receiving appropriate ICD therapy greatly exceeds the number of patients who avert SCD as a result of ICD therapy. In trials involving patients with implanted ICDs, these excess appropriate ICD therapies seem to distribute randomly between MTWA-negative and MTWA-nonnegative patients, obscuring the predictive accuracy of MTWA for SCD. Appropriate ICD therapy is an unreliable surrogate end point for SCD