Spontaneous Extension Wave for In Vivo Assessment of Arterial Wall Anisotropy

Another type of natural wave, traced from longitudinal wall motion and propagation along the artery, is unprecedentedly observed in our in vivo human carotid artery experiments. We coin it as extension wave (EW) and hypothesize that EW velocity (EWV) is associated with arterial longitudinal stiffness. The EW is thus assumed to complement the PW, whose velocity (PWV) is tracked from the radial wall displacement and linked to arterial circumferential stiffness through the Moens-Korteweg equation, as indicators for arterial mechanical anisotropy quantification by noninvasive high-frame-rate ultrasound. The relationship between directional arterial stiffnesses and the two natural wave speeds was investigated in wave theory, finite-element simulations based on isotropic and anisotropic arterial models, and in vivo human common carotid artery (N=10) experiments. Excellent agreement between the theory and simulations showed that EWV was 2.57 and 1.03 times higher than PWV in an isotropic and an anisotropic carotid artery model, respectively, while in vivo EWV was consistently lower than PWV in all 10 healthy human subjects. A strong linear correlation was substantiated in vivo between EWV and arterial longitudinal stiffness quantified by a well-validated vascular guided wave imaging technique (VGWI). We thereby proposed a novel index calculated as EWV2/PWV2 as an alternative to assess arterial mechanical anisotropy. Simulations and in vivo results corroborated the effect of mechanical anisotropy on the propagation of spontaneous waves along the arterial wall. The proposed anisotropy index demonstrated the feasibility of the concurrent EW and PW imaged by high frame-rate ultrasound in grading of arterial wall anisotropy.

Temporary cardiac pacing induced electrocardiographic changes simulating myocardial infarction

Temporary transvenous pacing is an immediate lifesaving measure in patients with Stokes-Adams syndrome and in patients with symptomatic bradycardia. Bradyarrhythmias are known to occur in acute myocardial infarction. But in a paced heart, it is difficult to diagnose myocardial infarction from electrocardiogram (ECG) because pacemaker rhythm causes distortion of natural wave forms. On the other hand, remarkable T wave inversions and ST depressions do occur in the ventricular paced ECG as secondary changes. The case report describes a patient who developed profound de novo T wave inversions and ST depressions in the unpaced ECG following temporary transvenous pacing simulating MI.

ELF magnetospheric lines observed by DEMETER

The influence of man-made activity on the ionosphere may be very important. The effects induced by the Power Line Harmonic Radiation (PLHR) may change the natural wave activity and/or the ionospheric plasma components. One goal of the ionospheric satellite DEMETER launched in June 2004 is to study the ionospheric perturbations which could be related to this anthropogenic activity. As the first step, the paper presents Tram Lines (TL) which have been observed on board DEMETER with frequency intervals close to 50 Hz or 16 Hz 2/3 (the current frequency of the railways). When it is observable the frequency drift of these TL is very slow. It is shown that these events occur during periods of strong or moderate magnetic activity. A wave propagation analysis indicates that the TL observed below the low cutoff frequency of the hiss which is simultaneously present are coming from a region below the satellite. The conclusion is that these TL observed by DEMETER are produced by PLHR or radiation of railways lines.

Intracellular Role of Adenylyl Cyclase in Regulation of Lateral Pseudopod Formation during Dictyostelium Chemotaxis

ABSTRACT Cyclic AMP (cAMP) functions as the extracellular chemoattractant in the aggregation phase of Dictyostelium development. There is some question, however, concerning what role, if any, it plays intracellularly in motility and chemotaxis. To test for such a role, the behavior of null mutants of acaA, the adenylyl cyclase gene that encodes the enzyme responsible for cAMP synthesis during aggregation, was analyzed in buffer and in response to experimentally generated spatial and temporal gradients of extracellular cAMP. acaA − cells were defective in suppressing lateral pseudopods in response to a spatial gradient of cAMP and to an increasing temporal gradient of cAMP. acaA − cells were incapable of chemotaxis in natural waves of cAMP generated by majority control cells in mixed cultures. These results indicate that intracellular cAMP and, hence, adenylyl cyclase play an intracellular role in the chemotactic response. The behavioral defects of acaA − cells were surprisingly similar to those of cells of null mutants of regA, which encodes the intracellular phosphodiesterase that hydrolyzes cAMP and, hence, functions opposite adenylyl cyclase A (ACA). This result is consistent with the hypothesis that ACA and RegA are components of a receptor-regulated intracellular circuit that controls protein kinase A activity. In this model, the suppression of lateral pseudopods in the front of a natural wave depends on a complete circuit. Hence, deletion of any component of the circuit (i.e., RegA or ACA) would result in the same chemotactic defect.

Yaw Drift Moment of a Floating Structure in Waves

The wave induced yaw drift moment on floating structures is of particular interest when the lateral yaw motion of the structure should be controlled by moorings and/or active dynamic positioning systems. In the present paper, the estimation of the yaw drift moment in the modeled natural wave environment is conducted by application of a nonlinear time domain numerical method accounting for the motion of arbitrarily shaped floating bodies in waves. The computational method is based on linear potential theory and includes the non-linear hydrostatic terms in an exact way, whereas the higher-order wave-induced effects are partly approximated. Despite the approximate modeling of the second order hydrodynamic forces, the method proved to satisfactorily approach the dominant part of the exerted hydrodynamic forces enabling the calculation of drift forces and of other drift effects in irregular waves. Hence, the subject yaw drift moment in the modeled natural wave environment is derived, resulting to a basic reference for the design of similar type floating structures.