Spectral analysis of electrograms during ventricular tachycardia in a canine model: relation with epicardial isochronal maps

The purpose of this study was to assess the capability of magnitude-squared coherence and bicoherence to differentiate monomorphic ventricular tachycardia (MVT) and polymorphic ventricular tachycardia (PVT) in a canine model and to relate these results to the epicardial isochronal maps on a beat-to-beat basis. Unipolar electrograms were simultaneously recorded from the surface of both ventricles with a 127-lead sock electrode array in 12 open-chest anesthetized dogs. The sampling frequency was 500 Hz. Atrioventricular block was induced by formaldehyde injection into the atrioventricular node. The left anterior descending coronary artery was occluded for 60 minutes under ventricular pacing (140 beats/min). During reperfusion, 12 MVT episodes lasting more than 42 seconds were recorded. Left stellate ganglion stimulation induced five PVT episodes lasting more than 42 seconds. Each of these recordings was divided into seven segments of 3,072 points (6.144 seconds). After visual selection, 104 segments were extracted and classified as 73 MVT and 31 PVT segments. Magnitude-squared coherence was estimated as the cross-spectrum from two epicardial signals (on the right and left ventricles, respectively), normalized with the respective autopower spectrum. Bicoherence was estimated as the bispectrum normalized with the autopower spectrum. Magnitude-squared coherence correctly identified 96% of MVT and 81% of PVT segments for a total accuracy of 91%. Bicoherence estimated with the left ventricular lead correctly identified 100% of MVT and 77% of PVT segments with an accuracy of 93%. Beat-to-beat epicardial maps of MVT displayed a cluster of sites of origin close to the reperfusion area, while the sites of origin from beats during PVT were much more dispersed over both ventricles. A strong and significant correlation was found between the number of electrodes with the earliest epicardial activation and coherence (r = .76, P < .0001) and bicoherence (r = .68, P < .0001), respectively. A high and significant correlation was also found between both spectral estimators (r = .74, P < .0001). Coherence and bicoherence discriminated accurately between MVT and PVT. Coherence achieved better results compared with bicoherence. Coherence and bicoherence measurements showed a quantitative relation with the spatial dispersion of the sites of origin. Both spectral techniques seemed powerful enough to be used in the development of implantable devices.     

Timing error estimation for baseband multicarrier modulation

In this paper, the topic of timing error estimation for baseband discrete multitone modulation is addressed in the context of high‐speed digital subscriber line applications. To the authors' best knowledge, this problem is sparsely and not in depth treated in the literature. In this study the modified Cramer–Rao lower bound is derived, two conventional estimators are considered and a new one is proposed. Behavior of these estimators is evaluated in terms of bias, variance and computational complexity in a wide variety of scenarios, concluding that the proposed estimator appears to be superior in all instances. Copyright © 2008 John Wiley & Sons, Ltd.     

Optimal allocation of bioassays in the case of parametrized covariance functions: an application to Lung’s retention of radioactive particles

In this paper, we investigate the effect of employing a parametrized covariance function in a regression experiment on corresponding optimum designs. We demonstrate these effects in the framework of a real example for measuring the lung’s retention of radioactive particles. Also, two different covariance functions are considered, and it is shown that this choice can play a crucial role.      

Effect of treatment with α‐galactosidase,tannase or a cell‐wall‐degrading enzyme complex on the nutritive utilisation of protein and carbohydrates from pea (Pisum sativum L.) flour

The effect of treatment with α‐galactosidase, tannase or a cell‐wall‐degrading enzyme complex under optimal conditions of pH, temperature and length of incubation time on the chemical composition and nutritive utilisation of protein and carbohydrates from pea (Pisum sativum L.) flour was studied. Soaking of pea flours in combination with enzyme treatment led to reductions of 77–90% in the levels of α‐galactosides, and of 60–80% in the levels of trypsin inhibitor activity, increasing the content of total available sugars, which was highest in the pea flour treated with the cell‐wall‐degrading enzyme complex. All the treatments assayed caused a significant improvement in daily food intake, whereas the nutritive utilisation of protein was not increased in any of the pea products tested when compared to the raw pea flour. However, all the soaking and enzymatic treatments led to a significant improvement in daily weight gain associated with a higher dietary intake of food and total available sugars. Copyright © 2007 Society of Chemical Industry     

Carbon source utilization‐based metabolic activity of Salmonella Oranienburg and Salmonella Saintpaul in river water

The presence of introduced or non‐native bacteria in river water can create a selective pressure due to their ability to overcome fluctuations in physicochemical conditions and carbon source availability. The carbon source concentrations (monosaccharides and polysaccharides), physicochemical parameters (turbidity, total dissolved solids, biochemical oxygen demand, temperature and pH) and metabolic activity of Salmonella Oranienburg and Saintpaul were determined in water from the central Sinaloa state rivers. This study's results revealed that the carbohydrate availability and physicochemical conditions of river water make it a suitable niche for the establishment of Salmonella serotypes. Metabolic profiles showed that Salmonella Typhimurium could consume a wide variety of carbon sources but only at moderate levels; in contrast, Salmonella Oranienburg and Salmonella Saintpaul demonstrated intense carbon source utilization of a limited diversity of carbon sources. Carbohydrates, amino acids and carboxylic acids were the metabolites most utilized by the environmental Salmonella strains, demonstrating their superior ability to adapt to and survive in river water.     

Antimicrobial peptides and their superior fluorinated analogues: structure-activity relationships as revealed by NMR spectroscopy and MD calculations

The conformations of two synthetic pentapeptides with antimicrobial activity and their 4-fluorophenylalanine (Pff)-containing analogues (ArXArXAr-NH(2); Ar=Phe, Pff; X=Lys, Arg) have been studied. NMR experiments carried out both in aqueous fluoroalcohol solutions and SDS micelles permitted their interactions with membrane-like environments to be explored. WaterLOGSY experiments and Mn(2+)-based paramagnetic probes were also applied to assess their orientations with respect to the SDS micelles. In addition, pulse-field gradient (PFG) diffusion NMR spectroscopy studies were conducted, under different experimental conditions (i.e., concentration, temperature) to characterize the possible changes in the peptides' aggregation states as a putative critical factor for their antimicrobial activity. Finally, molecular dynamics simulations on a variety of conformations showed the intrinsic flexibility of these peptides in both aqueous solutions and membrane-mimetic systems.     

Synthesis of Fatty Acid Amides of Catechol Metabolites that Exhibit Antiobesity Properties

A series of fatty acid amides of 3,4‐methylenedioxymethamphetamine (MDMA) catechol metabolites were synthesized in order to evaluate their biological activities. Upon administration, all synthesized compounds resulted in negative modulation of food intake in rats. The most active compounds have affinity for the CB₁ receptor and/or PPAR‐α; part of their biological activity may be caused by these double interactions.     

Soil degradation in the tropical forests of the Dominican Republic's Pedernales province in relation to heavy metal contents

Two of the National Parks of the only Biosphere Reserve in the Caribbean Islands, the Jaragua-Bahoruco-Enriquillo reserve, occur mostly within the Pedernales province (Dominican Republic). In these National Parks, Jaragua and Bahoruco, almost every tropical forest ecosystem is represented, as are the land uses most common to the Dominican Republic. Despite soil being a key natural resource that needs to be considered in any sustainable development programme, the literature contains very little information on the soils of this region. In this study, we analysed 41 topsoil samples representing the main forest types and land uses of the province. The factors examined were fertility (OM, N, P, K) and heavy metal contents (Cu, Cr, Pb, Cd, Ni, Zn). Mean OM, N and total and available metal levels were almost invariably higher in the natural forest soils compared to those given over to human activities, especially cultivated soils. This difference suggests the uptake of metals by the crops and, to a lesser extent, by animals feeding on crop remains and grassland plants. This hypothesis is supported by high total and available metal contents, especially of Zn, Cu, Pb and, in smaller measure, of Cr recorded in the solid waste landfill of the city of Pedernales. It appears that the cutting down and burning practices of a nomad type of cultivation, as well as the pressures of intensive agriculture and livestock rearing have resulted in heavy metals bound to the soil's OM. We propose this is an important point to consider for the management of these lands.