Feasibility of cardiac microimpedance measurement using multisite interstitial stimulation

2004 ◽  
Vol 287 (6) ◽  
pp. H2402-H2411 ◽  
Author(s):  
Andrew E. Pollard ◽  
William M. Smith ◽  
Roger C. Barr
Keyword(s):  
Electrophysiological Study ◽  
Independent Measurement ◽  
Dynamic Membrane ◽  
One Dimensional ◽  
Routine Measurement ◽  
Close Proximity ◽  
Comparable Accuracy ◽  
Gap Junctional ◽  
Junctional Resistance ◽  
Interstitial Potential

This study was designed to test the hypothesis that analyses of central interstitial potential differences recorded during multisite stimulation with a set of interstitial electrodes provide sufficient data for accurate measurement of cardiac microimpedances. On theoretical grounds, interstitial current injected and removed using electrodes in close proximity does not cross the membrane, whereas equilibration of intracellular and interstitial potentials occurs distant from electrodes widely separated. Multisite interstitial stimulation should therefore give rise to interstitial potential differences recorded centrally that depend on intracellular and interstitial microimpedances, allowing independent measurement. Simulations of multisite stimulation with fine (25 μm) and wide (400 μm) spacing in one-dimensional models that included Luo-Rudy dynamic membrane equations were performed. Constant interstitial and intracellular microimpedances were prescribed for initial analyses. Discrete myoplasmic and gap-junctional components were prescribed intracellularly in later simulations. With constant microimpedances, multisite stimulation using 29 total electrode combinations allowed interstitial and intracellular microimpedance measurements at errors of 0.30% and 0.34%, respectively, with errors of 0.05% and 0.40% achieved using 6 combinations and 10 total electrodes. With discrete myoplasmic and junctional components, comparable accuracy was maintained following adjustments to the junctions to reflect uncoupling. This allowed uncoupling to be quantified as relative increases in total junctional resistance. Our findings suggest development of microfabricated devices to implement the procedure would facilitate routine measurement as a component of cardiac electrophysiological study.

Cardiac microimpedance measurement in two-dimensional models using multisite interstitial stimulation

2006 ◽  
Vol 290 (5) ◽  
pp. H1976-H1987 ◽  
Author(s):  
Andrew E. Pollard ◽  
Roger C. Barr
Keyword(s):  
Test Data ◽  
Ventricular Myocytes ◽  
Electrophysiological Study ◽  
Two Dimensional ◽  
Dynamic Membrane ◽  
Anisotropic Models ◽  
Wide Range ◽  
Dimensional Models ◽  
Generate Test Data ◽  
Interstitial Potential

We analyzed central interstitial potential differences during multisite stimulation to assess the feasibility of using those recordings to measure cardiac microimpedances in multidimensional preparations. Because interstitial current injected and removed using electrodes with different proximities allows modulation of the portion of current crossing the membrane, we hypothesized that multisite interstitial stimulation would give rise to central interstitial potential differences that depend on intracellular and interstitial microimpedances, allowing measurement of those microimpedances. Simulations of multisite stimulation with fine and wide spacing in two-dimensional models that included dynamic membrane equations for guinea pig ventricular myocytes were performed to generate test data (∂φo). Isotropic interstitial and intracellular microimpedances were prescribed for one set of simulations, and anisotropic microimpedances with unequal ratios (intracellular to interstitial) along and across fibers were prescribed for another set of simulations. Microimpedance measurements were then obtained by making statistical comparisons between ∂φo values and interstitial potential differences from passive bidomain simulations (Δφo) in which a wide range of possible microimpedances were considered. Possible microimpedances were selected at 25% increments. After demonstrating the effectiveness of the overall method with microimpedance measurements using one-dimensional test data, we showed microimpedance measurements within 25% of prescribed values in isotropic and anisotropic models. Our findings suggest that development of microfabricated devices to implement the procedure would facilitate routine measurement as a component of cardiac electrophysiological study.

Effects of octanol on canine subendocardial Purkinje-to-ventricular transmission

1985 ◽  
Vol 249 (6) ◽  
pp. H1228-H1231 ◽  
Author(s):  
R. W. Joyner ◽  
E. D. Overholt
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Current Flow ◽  
Conduction Delay ◽  
Papillary Muscles ◽  
Maximal Rate ◽  
Gap Junctional ◽  
Junctional Resistance ◽  
P Cells

The effects of 0.2 mM octanol on action potential propagation were investigated using in vitro preparations of canine papillary muscles. In these preparations an action potential initiated in the superficial Purkinje (P) layer propagates across specific Purkinje-ventricular junction (PVJ) sites into the underlying ventricular (V) layer. The conduction delay at PVJ sites increased from 4.85 +/- 1.55 to 8.85 +/- 3.34 (mean +/- SD) ms (n = 10, P less than 0.005), an 82% increase. However, propagation within the V syncytium was much less affected, with a decrease of conduction velocity by only 10% and a decrease in the maximal rate of rise of the action potential of 23%. The results indicate that octanol, which has previously been shown to increase gap junctional resistance, has a preferential effect on PVJ sites, as predicted by the hypothesis that there is a restricted pathway for intracellular current flow from P cells to V cells at these sites.

scholarly journals Post-cardiac injury syndrome triggered by radiofrequency ablation for AVNRT

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Florian A. Wenzl ◽  
Martin Manninger ◽  
Stefanie Wunsch ◽  
Daniel Scherr ◽  
Egbert H. Bisping
Keyword(s):  
Pericardial Effusion ◽  
Electrophysiological Study ◽  
Cardiac Injury ◽  
Myocardial Damage ◽  
Slow Pathway ◽  
Atrioventricular Nodal Reentrant Tachycardia ◽  
Rf Ablation ◽  
Close Proximity ◽  
History Of

Abstract Background Post-cardiac injury syndrome (PCIS) is an inflammatory condition following myocardial or pericardial damage. In response to catheter ablation, PCIS most frequently occurs after extensive radiofrequency (RF) ablation of large areas of atrial myocardium. Minor myocardial injury from right septal slow pathway ablation for atrioventricular nodal reentrant tachycardia (AVNRT) is not an established cause of the syndrome. Case presentation A 62-year-old women with a 6-year history of symptomatic narrow-complex tachycardia was referred to perform an electrophysiological study. During the procedure AVNRT was recorded and a total of two RF burns were applied to the region between the coronary sinus and the tricuspid annulus. Pericardial effusion was routinely ruled out by focused cardiac ultrasound. In the following days, the patient developed fever, elevated inflammatory and cardiac markers, new-onset pericardial effusion, characteristic ECG changes, and complained of pleuritic chest pain. An extensive workup for infectious, metabolic, rheumatologic, neoplastic, and toxic causes of pericarditis and myocarditis was unremarkable. Cardiac magnetic resonance imaging showed no signs of ischemia, infiltrative disease or structural abnormalities. The patient was diagnosed with PCIS and initiated on aspirin and low-dose colchicine. At a 1-month follow-up visit the patient was free of symptoms but still had a small pericardial effusion. After three  months of treatment the pericardial effusion had resolved completely. Conclusions Inflammatory pericardial reactions can occur after minor myocardial damage from RF ablation without involvement of structures in close proximity to the pericardium.

scholarly journals Directional luminescence of the diamond NV center via Bloch surface waves in one-dimensional photonic crystals

2021 ◽  
Vol 2015 (1) ◽  
pp. 012022
Author(s):  
A A Bragina ◽  
K R Safronov ◽  
V O Bessonov ◽  
A A Fedyanin
Keyword(s):  
Angular Distribution ◽  
Photonic Crystal ◽  
Surface Wave ◽  
Photonic Crystals ◽  
Surface Waves ◽  
Coupling Efficiency ◽  
One Dimensional ◽  
Close Proximity ◽  
Nv Center ◽  
Bloch Surface Wave

Abstract In this work, we numerically study the luminescence of nanodiamonds with NV centres embedded in a polymer layer on the surface of one-dimensional photonic crystal. The interaction of NV center spontaneous emission with the Bloch surface wave (BSW) is demonstrated. The presence of a photonic crystal leads to a change in the angular distribution of the emitter radiation due to the coupling of luminescence to BSW. We show that the best coupling efficiency of 71% is observed when NV centres are located in the close proximity to the BSW field maximum.

scholarly journals The turbulence boundary of a temporal jet

2013 ◽  
Vol 739 ◽  
pp. 254-275 ◽  
Author(s):  
Maarten van Reeuwijk ◽  
Markus Holzner
Keyword(s):  
Average Distance ◽  
One Dimensional ◽  
Entrainment Velocity ◽  
Buffer Region ◽  
Close Proximity ◽  
Reynolds Number Effects ◽  
Integral Rate ◽  
Plane Jet ◽  
Viscous Transport ◽  
Good Agreement

AbstractWe examine the structure of the turbulence boundary of a temporal plane jet at$\mathit{Re}= 5000$using statistics conditioned on the enstrophy. The data is obtained by direct numerical simulation and threshold values span 24 orders of magnitude, ranging from essentially irrotational fluid outside the jet to fully turbulent fluid in the jet core. We use two independent estimators for the local entrainment velocity${v}_{n} $based on the enstrophy budget. The data show clear evidence for the existence of a viscous superlayer (VSL) that envelopes the turbulence. The VSL is a nearly one-dimensional layer with low surface curvature. We find that both its area and viscous transport velocity adjust to the imposed rate of entrainment so that the integral entrainment flux is independent of threshold, although low-Reynolds-number effects play a role for the case under consideration. This threshold independence is consistent with the inviscid nature of the integral rate of entrainment. A theoretical model of the VSL is developed that is in reasonably good agreement with the data and predicts that the contribution of viscous transport and dissipation to interface propagation have magnitude$2{v}_{n} $and$- {v}_{n} $, respectively. We further identify a turbulent core region (TC) and a buffer region (BR) connecting the VSL and the TC. The BR grows in time and inviscid enstrophy production is important in this region. The BR shows many similarities with the turbulent–non-turbulent interface (TNTI), although the TNTI seems to extend into the TC. The average distance between the TC and the VSL, i.e. the BR thickness is about 10 Kolmogorov length scales or half a Taylor length scale, indicating that intense turbulent flow regions and viscosity-dominated regions are in close proximity.

Elevational Spatial Compounding

1994 ◽  
Vol 16 (3) ◽  
pp. 176-189 ◽  
Author(s):  
Pai-Chi Li ◽  
M. O'Donnell
Keyword(s):  
Spatial Resolution ◽  
Image Plane ◽  
Speckle Noise ◽  
Lateral Resolution ◽  
Medical Ultrasound ◽  
Two Dimensional ◽  
Independent Measurement ◽  
Contrast Resolution ◽  
Spatial Compounding ◽  
One Dimensional

Spatial compounding has long been explored to reduce coherent speckle noise in medical ultrasound. By laterally translating a one-dimensional array, partially correlated measurements made at different look directions can be obtained and incoherently averaged. The lateral resolution, however, is limited by the sub-array length used for each independent measurement. To reduce speckle contrast without compromising lateral resolution, a new spatial compounding technique using two-dimensional, anisotropic arrays is proposed. This technique obtains partially correlated measurements by steering the image plane elevationally with small inclinations. Incoherent averaging is then performed by adding image magnitudes. Therefore, contrast resolution is improved only at the price of a slightly wider elevational beam. Note that although anisotropic arrays have limited steering capability in elevation, grating lobes are not considered influential since only small inclinations are needed between measurements. Simulations have been performed to show both the change in spatial resolution and the improvement in contrast resolution. Results indicated minimal increase in the correlation length both laterally and axially. It was also shown that detectability can be significantly enhanced by increasing the number of measurements or increasing the differential inclination between measurements. This technique is therefore effective for reducing speckle noise while maintaining in-plane spatial resolution. Furthermore, it demonstrates a new application of two-dimensional anisotropic arrays in spite of their limited elevational steering capability.

scholarly journals Extracellular sodium dependence of the conduction velocity-calcium relationship: evidence of ephaptic self-attenuation

2016 ◽  
Vol 310 (9) ◽  
pp. H1129-H1139 ◽  
Author(s):  
Sharon A. George ◽  
Mohammad Bonakdar ◽  
Michael Zeitz ◽  
Rafael V. Davalos ◽  
James W. Smyth ◽  
...  
Keyword(s):  
Conduction Velocity ◽  
Ionic Currents ◽  
Electrical Impedance Spectroscopy ◽  
Cardiac Conduction ◽  
Cx43 Expression ◽  
Transmission Electron ◽  
Theoretical Predictions ◽  
Gap Junctional ◽  
Extracellular Sodium ◽  
Junctional Resistance

Our laboratory previously demonstrated that perfusate sodium and potassium concentrations can modulate cardiac conduction velocity (CV) consistent with theoretical predictions of ephaptic coupling (EpC). EpC depends on the ionic currents and intercellular separation in sodium channel rich intercalated disk microdomains like the perinexus. We suggested that perinexal width (WP) correlates with changes in extracellular calcium ([Ca2+]o). Here, we test the hypothesis that increasing [Ca2+]o reduces WP and increases CV. Mathematical models of EpC also predict that reducing WP can reduce sodium driving force and CV by self-attenuation. Therefore, we further hypothesized that reducing WP and extracellular sodium ([Na+]o) will reduce CV consistent with ephaptic self-attenuation. Transmission electron microscopy revealed that increasing [Ca2+]o (1 to 3.4 mM) significantly decreased WP. Optically mapping wild-type (WT) (100% Cx43) mouse hearts demonstrated that increasing [Ca2+]o increases transverse CV during normonatremia (147.3 mM), but slows transverse CV during hyponatremia (120 mM). Additionally, CV in heterozygous (∼50% Cx43) hearts was more sensitive to changes in [Ca2+]o relative to WT during normonatremia. During hyponatremia, CV slowed in both WT and heterozygous hearts to the same extent. Importantly, neither [Ca2+]o nor [Na+]o altered Cx43 expression or phosphorylation determined by Western blotting, or gap junctional resistance determined by electrical impedance spectroscopy. Narrowing WP, by increasing [Ca2+]o, increases CV consistent with enhanced EpC between myocytes. Interestingly, during hyponatremia, reducing WP slowed CV, consistent with theoretical predictions of ephaptic self-attenuation. This study suggests that serum ion concentrations may be an important determinant of cardiac disease expression.

NMR Characterisation of the Organic/SiO2 Interfaces in Templated Porous Silica.

2006 ◽  
Vol 984 ◽  
Author(s):  
Niki Baccile ◽  
Guillaume Laurent ◽  
Thierry Azaïs ◽  
Florence Babonneau
Keyword(s):  
Mesoporous Silica ◽  
Benzoic Acid ◽  
Porous Silica ◽  
Polarization Transfer ◽  
Transfer Efficiency ◽  
One Dimensional ◽  
Surface Sites ◽  
Close Proximity ◽  
Lower Temperature

AbstractThis paper illustrates the use of a 1H-29Si-1H double CP sequence to investigate different organic/SiO2 interfaces in templated porous silica. The advantage of this sequence is to selectively edit, in a one-dimensional experiment, the protons that are in close proximity with the Si surface sites. In order to maximize the polarization transfer efficiency, some experiments have been recorded at lower temperature (238 K). Examples will concern surfactant/silica interactions in mesostructured silicas and the behavior of benzoic acid and 4-methoxychlorophenol, a common pesticide, encapsulated in mesoporous silica.

Coarse Coding Resource-Allocating Network

1993 ◽  
Vol 5 (1) ◽  
pp. 105-114 ◽  
Author(s):  
Gustavo Deco ◽  
Jürgen Ebmeyer
Keyword(s):  
Learning Process ◽  
Network Architecture ◽  
Receptive Fields ◽  
One Dimensional ◽  
Learning Speed ◽  
Output Mapping ◽  
Input Layer ◽  
Comparable Accuracy ◽  
The Subject ◽  
Coarse Coding

In recent years localized receptive fields have been the subject of intensive research, due to their learning speed and efficient reconstruction of hypersurfaces. A very efficient implementation for such a network was proposed recently by Platt (1991). This resource-allocating network (RAN) allocates a new neuron whenever an unknown pattern is presented at its input layer. In this paper we introduce a new network architecture and learning paradigm. The aim of our approach is to incorporate "coarse coding" to the resource-allocating network. The network presented here provides for each input coordinate a separate layer, which consists of one-dimensional, locally tuned gaussian neurons. In the following layer multidimensional receptive fields are built by using pi-neurons. Linear neurons aggregate the outputs of the pi-neurons in order to approximate the required input-output mapping. The learning process follows the ideas of the resource-allocating network of Platt but due to the extended architecture of our network other improvements of the learning process had to be defined. Compared to the resource-allocating network a more compact network with comparable accuracy is obtained.

scholarly journals The effect of bowl-in-piston geometry layout on fluid flow pattern

2011 ◽  
Vol 15 (3) ◽  
pp. 817-832 ◽  
Author(s):  
Zoran Jovanovic ◽  
Zlatomir Zivanovic ◽  
Zeljko Sakota ◽  
Miroljub Tomic ◽  
Velimir Petrovic
Keyword(s):  
Fluid Flow ◽  
Flow Pattern ◽  
Moving Objects ◽  
Three Dimensional ◽  
Exhaust Valve ◽  
Intake Valve ◽  
Combustion Chambers ◽  
Arbitrary Geometry ◽  
One Dimensional ◽  
Close Proximity

In this paper some results concerning the evolution of 3D fluid flow pattern through all four strokes in combustion chambers with entirely different bowl-in-piston geometry layouts ranging from ?omega? to ?simple cylinder? were presented. All combustion chambers i.e. those with ?omega? bowls, with different profiles, and those with ?cylinder? bowls, with different squish area ranging from 44% to 62%, were with flat head, vertical valves and identical elevation of intake and exhaust ports. A bunch of results emerged by dint of multidimensional modeling of nonreactive fluid flow in arbitrary geometry with moving objects and boundaries. The fluid flow pattern during induction and compression in all cases was extremely complicated and entirely three-dimensional. It should be noted that significant differences due to geometry of the bowl were encountered only in the vicinity of TDC. Namely, in the case of ?omega? bowl all three types of organized macro flows were observed while in the case of ?cylinder? bowl no circumferential velocity was registered at all. On the contrary, in the case of ?cylinder? bowl some interesting results concerning reverse tumble and its center of rotation shifting from exhaust valve zone to intake valve zone during induction stroke and vice-verse from intake valve zone to exhaust valve zone during compression were observed while in the case of ?omega? bowl no such a displacement was legible. During expansion the fluid flow pattern is fully controlled by piston motion and during exhaust it is mainly one-dimensional, except in the close proximity of exhaust valve. For that reason it is not affected by the geometry of the bowl.

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