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In a case of aortic insufficiency, increased snaking occured with very pulse wave coming through the retinal arteries. When photographs taken at diastolic and systolic culminations were compared, with the haploscope, when stereoscopically seen, they clearly showed the subtile deformation of the vessels under a stereoscopic effect.
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Ventricular tachycardia and fibrillation are potentially lethal cardiac arrhythmias generated by high frequency, irregular spatio-temporal electrical activity. Re-entrant propagation has been demonstrated as a mechanism generating these arrhythmias in computational and in vitro animal models of these arrhythmias. Re-entry can be idealised in homogenous isotropic virtual cardiac tissues as spiral and scroll wave solutions of reaction-diffusion equations. A spiral wave in a bounded medium can be terminated if its core reaches a boundary. Ventricular tachyarrhythmias in patients are sometimes observed to spontaneously self-terminate. One possible mechanism for self-termination of a spiral wave is meander of its core to an inexcitable boundary. We have previously proposed the hypothesis that the spatial extent of meander of a re-entrant wave in the heart can be directly related to its probability of self-termination, and so inversely related to its lethality. Meander in two-dimensional virtual ventricular tissues based on the Oxsoft family of cell models, with membrane excitation parameters simulating the inherited long Q-T syndromes has been shown to be consistent with this hypothesis: the largest meander is seen in the syndrome with the lowest probability of death per arrhythmic episode. Here we extend our previous results to virtual tissues based on the Luo-Rudy family of models. Consistent with our hypothesis, for both families of models, whose different ionic mechanisms produce different patterns of meander, the LQT virtual tissue with the larger meander simulates the syndrome with the lower probability of death per episode. Further, we search the parameter space of the repolarizing currents to find their conductance parameter values that give increased meander of spiral waves. These parameters may provide targets for antiarrhythmic drugs designed to act by increasing the likelihood of self-termination of re-entrant arrhythmias. (c) 2002 American Institute of Physics.
This contribution represents a continuation of our studies of a gradient in convergent cell movement in the germ ring (GR) during Fundulus gastrulation (Trinkaus et al. [1992] J. Exp. Zool., 261:40-61). In our previous study, we discovered that cells in the dorsal GR nearest the embryonic shield (ES) move toward the ES at a net faster rate than those farther away and that this is due to less meandering. Those farther away meander more. These data suggest the hypothesis that there is a gradient of cues that direct cells to the ES. If so, cells in the ventral GR, farthest from the ES, should meander even more and hence show little or no convergence toward the ES. To test this hypothesis, we have traced the trajectories of individual cells in the midventral GR during midepiboly and have found that, although the general motile behavior of ventral GR cells is the same as that of dorsal cells, they do indeed meander much more and, as a result, show little or no directional movement toward the ES. Taken together, these results indicate that cells of the germ ring move up a gradient in directionality as they converge toward their target, the embryonic shield. One possible explanation for this is that the embryonic shield attracts cells to itself.
In support of the spiral wave theory of reentry, simulation studies and animal models have been utilized to show various patterns of spiral wave tip motion such as meandering and drifting. However, the demonstration of these or any other patterns in cardiac tissues have been limited. Whether such patterns of spiral tip motion are commonly observed in fibrillating cardiac tissues is unknown, and whether such patterns form the basis of ventricular tachycardia or fibrillation remain debatable. Using a computerized dynamic activation display, 108 episodes of atrial and ventricular tachycardia and fibrillation in isolated and intact canine cardiac tissues, as well as in vitro swine and myopathic human cardiac tissues, were analyzed for patterns of nonstationary, spiral wave tip motion. Among them, 46 episodes were from normal animal myocardium without pharmacological perturbations, 50 samples were from normal animal myocardium, either treated with drugs or had chemical ablation of the subendocardium, and 12 samples were from diseased human hearts. Among the total episodes, 11 of them had obvious nonstationary spiral tip motion with a life span of >2 cycles and with consecutive reentrant paths distinct from each other. Four patterns were observed: (1) meandering with an inward petal flower in 2; (2) meandering with outward petals in 5; (3) irregularly concentric in 3 (core moving about a common center); and (4) drift in 1 (linear core movement). The life span of a single nonstationary spiral wave lasted no more than 7 complete cycles with a mean of 4.6+/-4.3, and a median of 4.5 cycles in our samples. Conclusion: (1) Patently evident nonstationary spiral waves with long life spans were uncommon in our sample of mostly normal cardiac tissues, thus making a single meandering spiral wave an unlikely major mechanism of fibrillation in normal ventricular myocardium. (2) A tendency toward four patterns of nonstationary spiral tip motion was observed. (c) 1998 American Institute of Physics.
Mainly because of its transparency, the Fundulus gastrula constitutes ideal material for direct study of morphogenetic cell movements in vivo. Marking studies show that deep cells of the germ ring converge toward and enter the embryonic shield, where they undergo extension. Those close to the shield move faster. Analysis of videotapes reveals that all deep cells of the dorsal germ ring move toward the shield. But none moves in a direct line. All meander considerably. Germ ring cells nearer the shield move toward it at a higher net rate than those farther away because they meander less. This suggests that exogenous factors promote their directionality. Cells in the prospective yolk sac adjacent to the germ ring also show net convergence, but they meander more. Directional forces are apparently stronger in the germ ring. Converging deep cells move both by filolamellipodia and, less frequently, by blebs. However, there is very little individual cell movement; all cells are almost always in adhesive contact with other cells in moving cell clusters. Clusters vary constantly in size, continually aggregating with other cells and other clusters and splitting. Filolamellipodial cells show contact inhibition of cell movement. Nevertheless, they move and do so directionally, presumably in part because, as members of cell clusters, much of their movement is passive. They also show intercalation or invasive activity, but, consistent with their contact-inhibiting properties, only when neighboring cells separate and provide free space. Cells moving by blebbing locomotion are non-contact inhibiting and intercalate readily. Cell division continues during convergence. Although this temporarily arrests their movement, the daughter cells soon join in the mass convergent movement.
Russian olive (Elaeagnus angustifolia L.) was introduced in 1950 onto one site on the Milk River floodplain, northern Montana, 10 km downstream from the Canada/United States border. To analyze dispersal of Russian olive from the point source between 1950 and 1999, we compared distribution, numbers, size structure, and mortality of Russian olive and plains cottonwood (Populus deltoides Marsh:) on an unregulated reach of the Milk River floodplain in southeastern Alberta and north-central Montana. Within 50 years, Russian olive in this reach has moved upriver into Alberta and downriver to the Fresno Reservoir. It is now present on 69 of the 74 meander lobes sampled, comprising 34%, 62%, and 61% of all Russian olive and plains cottonwood seedlings, saplings, and trees, respectively. On some meander lobes, Russian olive has colonized similar elevations on the floodplain as plains cottonwood and is oriented in rows paralleling the river channel, suggesting that recruitment may be related to river processes. Breakup ice had killed 400 Russian olive saplings and trees and damaged >1000 others on 30 of the meander lobes in 1996. Nevertheless, Russian olive now outnumbers cottonwood on many sites on the Milk River floodplain because its seeds can be dispersed by wildlife (particularly birds) and probably by flood water and ice rafts; seeds are viable for up to 3 years and germination can take place on bare and well-vegetated soils; and saplings and trees are less palatable to livestock and beaver than plains cottonwood. Without control, Russian olive could be locally dominant on the Milk River floodplain in all age classes within 10 years and replace plains cottonwood within this century.
In this paper a micromachined electrochemically driven pump capable of dosing precise nanoliter amounts of liquid is presented. The pump consists of a micromachined channel structure realized in silicon by reactive ion etching. On top of this structure a Pyrex((R)) cover piece with noble metal electrodes was bonded. The fluid to be dispensed is stored in a meander shaped reservoir which is part of the channel structure. This meander starts in an electrolyte solution containing reservoir, on top of which two noble metal electrodes are positioned. By the electrochemical production of gas bubbles by electrolysis of water at these electrodes, liquid can be driven out of the meander. The measured volume displacements were in close agreement with theory. Pump rates as low as a few nl/s could accurately be controlled via the actuation current through the electrodes. By applying current pulses rather than a continuous current, preset amounts of fluid in the nanoliter range could be dosed successfully. Because the resulting device consists of simple channel structures and metal electrodes it can easily be integrated in miniaturized chemical analysis systems to dose reagents or calibration solutions.
A jet of fluid flowing down a partially wetting, inclined plane usually meanders but--by maintaining a constant flow rate--meandering can be suppressed, leading to the emergence of a beautiful braided structure. Here we show that this flow pattern can be explained by the interplay between surface tension, which tends to narrow the jet, and fluid inertia, which drives the jet to widen. These observations dispel misconceptions about the relationship between braiding and meandering that have persisted for over 20 years.
This paper evaluates the application of dispersion models to estimate near-field pollutant concentrations in two case studies. The Industrial Source Complex Short-Term Model (ISCST3) was evaluated with hexavalent chromium measurements collected within 100 m of two facilities in Barrio Logan, San Diego, CA. ISCST3 provided reasonable estimates for higher pollutant concentrations but underestimated lower concentrations. To understand the observed distribution of concentrations in Barrio Logan, a recently conducted tracer experiment was analyzed. The tracer, sulfur hexafluoride, was released at ambient temperature from an urban facility at the University of California at Riverside, and concentrations were measured within 20 m of the source. Modeling results indicated that Industrial Source Complex-Plume Rise Model Enhancement and American Meteorological Society/U.S. Environmental Protection Agency Regulatory Model-Plume Rise Model Enhancement overestimated high concentrations and underestimated low concentrations. A diagnostic study with a simple Gaussian dispersion model that incorporated site-specific meteorology was used to evaluate model results. This study found that incorporating lateral meandering for nonbuoyant urban plumes in Gaussian dispersion models could improve concentration estimates even when downwash is not considered. Incorporating a meandering component in ISCST3 resulted in improvements in estimating hexavalent chromium concentrations in Barrio Logan. Credible near-source concentration estimates depend on accurate characterization of emissions, onsite micrometeorology, and a method to account for lateral meandering in the near field.
Steady collisionless driven reconnection in an open system is investigated by means of a new two-dimensional full-particle simulation. The reconnection rate is controlled by an external driving electric field. Ion-meandering motion plays an important role in ion dynamics which controls the spatial structures of ion quantities. Although the electric current is predominantly carried by electrons, the current layer has the half-width of the ion-meandering orbit scale because the density profile is controlled by massive-ion motion. Thus, the global dynamic behavior of reconnection is dominantly controlled by ion dynamics. An electrostatic field generated through the finite-Larmor-radius effect leads to electron acceleration in the equilibrium current direction in the ion-dissipation region and ion heating by intensifying meandering motion. Our results are in agreement with the recent experimental results of Yamada et al. [Phys. Plasmas 7, 1781 (2000)] and of Hus et al. [Phys. Rev. Lett. 84, 3859 (2000)].
Feedback control of spiral waves by the phases of the spiral tip is investigated experimentally in a light-sensitive Belousov-Zhabotinsky reaction. The phases of rotation (Psi(r)) and meandering (Psi(m)) of the spiral tip are obtained in real time during experiments. It is found that, for both meandering and rigid rotating spirals, one can manipulate the spirals to move with any arbitrary paths by the feedback signals derived from Psi(r). Synchronization between meandering and rotation dynamics can be induced when both Psi(m) and Psi(r) are used simultaneously as control signals. Experimental findings are compared well with numerical simulations of the Oregonator model.
The formation of an ion-dissipation region, in which motions of electrons and ions decouple and fast magnetic reconnection occurs, is demonstrated during a steady state of two-dimensional collisionless driven reconnection by means of full-particle simulations. The Hall-term effect is suppressed due to the gyroviscous cancellation at scales between the ion-skin depth and ion-meandering-orbit scale, and thus ions are tied to the magnetic field. The ion frozen-in constraint is strongly broken by nongyrotropic pressure tensor effects due to ion-meandering motion, and thus the ion-dissipation region is formed at scales below the ion-meandering-orbit scale. A similar process is observed in the formation of an electron-dissipation region. These two dissipation regions are clearly observed in an out-of-plane current density profile.
The mechanisms of Wiggers' stage II ventricular fibrillation (VF) are poorly understood. Using computerized mapping techniques, we studied the patterns of activation during Wiggers' stage II VF in 13 open-chest dogs. In 7 of the 13 dogs, the right ventricular Purkinje fibers and adjacent subendocardial myocytes were ablated with Lugol solution. VF was induced electrically, and 3 to 5 seconds of data were obtained beginning approximately 2.5 seconds after the onset of VF. Dynamic displays of the activation patterns and isochronal maps revealed the presence of reentrant wave fronts in 17 of 33 runs of VF in ablated ventricles and in 12 of 45 runs of VF in intact ventricles. The incidence of reentry was not different between the subendocardium-ablated group versus the nonablated group (1.7 +/- 1.6 versus 1.2 +/- 1.6 rotations per episode of VF, P = .19). There were no differences in the core size (25 +/- 19 versus 29 +/- 18 mm2), life span (3.4 +/- 1.1 versus 3.2 +/- 1.2 rotations), or cycle length (111 +/- 12 versus 107 +/- 8 ms) in ablated ventricles versus intact ventricles, respectively. The core was unstable as it meandered within the mapped area displacing the entire reentrant wave front. In all episodes, the reentrant wave fronts were spontaneously initiated by an interaction between two propagating wave fronts roughly perpendicular to each other. The second wave front met the tail of the first wave front 69 +/- 11 ms (range, 40 to 90 ms) after its latest activation, indicating that the interaction occurred during a vulnerable period. The reentrant wave fronts terminated spontaneously (n = 7), as the result of interference by an invading wave front (n = 19 or meandered off the mapped region (n = 3). We conclude the following: (1) Reentrant activities with short life spans and meandering cores are present during Wiggers' stage II VF in dogs. (2) New reentrant wave fronts are generated when one wave front interacts with another wave front during its vulnerable period. (3) The reentrant wave fronts terminate spontaneously or as the result of interference. (4) Chemical subendocardial ablation does not affect the incidence, life span, cycle length, or core size of the reentrant wave fronts.
Although wide range investigations on the heart and great vessels have been reported in acromegaly, the field of microcirculation is still largely vacant. The nailfold is a window through which we can observe in vivo the vascular bed. This study investigates through nailfold capillaroscopy the morphology of cutaneous microcirculation in acromegaly in relationship with the usual hormonal parameters of disease activity. Twenty-five acromegalic patients and 26 normal subjects, age and sex matched, were studied. A subgroup of acromegalics (8 patients) was considered in stable remission, and the remaining 17 had active disease. Capillaroscopy was performed in each subject by in vivo computer aided stereomicroscopy (magnification, x400). The following morphological parameters were calculated: the number of tortuous loops, meandering capillaries, and capillaries per millimeter; avascular areas; visibility of subpapillary plexus; the capillary length; and intercapillary distance. We were unable to perform the exam in 4 of 25 patients because visibility was poor. The capillary number and length were significantly reduced in acromegalics compared to controls [8.9 +/- 1.5 vs. 10.3 +/- 1.2 no./mm (P = 0.0010) and 174 +/- 49 vs. 255 +/- 24 microm (P < 0.0001)]. Moreover, in acromegalics, the numbers of tortuous loops and meandering capillaries were significantly increased [19 +/- 8 vs. 13 +/- 5 (P = 0.0027) and 10 +/- 12 vs. 0.7 +/- 1.1 (P < 0.0001)]. The capillaroscopic alterations were still observed in a smaller group of 8 nondiabetic and nonhypertensive acromegalics. We found branch-like capillaries in 4 acromegalic patients, but not in the control group. Finally, we observed a meaningful different and ameliorated capillaroscopic morphology in acromegalic patients in stable remission compared to active disease patients as far as the total number (density) and meandering capillaries were concerned. In conclusion, our study shows that in acromegaly, morphological alterations also affect the peripheral microcirculation, which seems to be influenced by the activity of the disease. We believe that nailfold capillaroscopy may represent an additional useful tool in the follow-up of acromegalic patients.
Recent studies suggest that atrial fibrillation (AF) is maintained by fibrillatory conduction emanating from a small number of high-frequency reentrant sources (rotors). Our goal was to study the ionic correlates of a rotor during simulated chronic AF conditions. We utilized a two-dimensional (2-D), homogeneous, isotropic sheet (5 x 5 cm(2)) of human atrial cells to create a chronic AF substrate, which was able to sustain a stable rotor (dominant frequency approximately 5.7 Hz, rosette-like tip meander approximately 2.6 cm). Doubling the magnitude of the inward rectifier K(+) current (I(K1)) increased rotor frequency ( approximately 8.4 Hz), and reduced tip meander (approximately 1.7 cm). This rotor stabilization was due to a shortening of the action potential duration and an enhanced cardiac excitability. The latter was caused by a hyperpolarization of the diastolic membrane potential, which increased the availability of the Na(+) current (I(Na)). The rotor was terminated by reducing the maximum conductance (by 90%) of the atrial-specific ultrarapid delayed rectifier K(+) current (I(Kur)), or the transient outward K(+) current (I(to)), but not the fast or slow delayed rectifier K(+) currents (I(Kr)/I(Ks)). Importantly, blockade of I(Kur)/I(to) prolonged the atrial action potential at the plateau, but not at the terminal phase of repolarization, which led to random tip meander and wavebreak, resulting in rotor termination. Altering the rectification profile of I(K1) also slowed down or abolished reentrant activity. In combination, these simulation results provide novel insights into the ionic bases of a sustained rotor in a 2-D chronic AF substrate.