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J M Rogers

Publications and source records attributed to J M Rogers.

At least 37 records · Page 2Linked to original sources
PubMed2000

Modeling the cardiac action potential using B-spline surfaces.

This paper presents a new method for constructing empirical, two-state-variable models of cardiac cell membrane kinetics. The formulation is based on nonuniform rational B-spline surfaces that can be manipulated interactively to produce desired action potential (AP) properties. Using this new methodology, a model of the guinea pig ventricular action potential was constructed that reproduces experimentally measured relationships between pacing cycle length and action potential duration and conduction velocity. The model is computationally efficient, requiring about sixfold less CPU time than the Beeler-Reuter ionic model and only about twice as much time as a FitzHugh-Nagumo type empirical model. Thus, for modeling propagation phenomena, this method can produce models that improve on the quantitative accuracy of both simple empirical models and elaborate ionic models, with computational cost comparable to the simplest of empirical models.

Action Potentials↗
PubMed2000

Distributed computing for membrane-based modeling of action potential propagation.

Action potential propagation simulations with physiologic membrane currents and macroscopic tissue dimensions are computationally expensive. We, therefore, analyzed distributed computing schemes to reduce execution time in workstation clusters by parallelizing solutions with message passing. Four schemes were considered in two-dimensional monodomain simulations with the Beeler-Reuter membrane equations. Parallel speedups measured with each scheme were compared to theoretical speedups, recognizing the relationship between speedup and code portions that executed serially. A data decomposition scheme based on total ionic current provided the best performance. Analysis of communication latencies in that scheme led to a load-balancing algorithm in which measured speedups at 89 +/- 2% and 75 +/- 8% of theoretical speedups were achieved in homogeneous and heterogeneous clusters of workstations. Speedups in this scheme with the Luo-Rudy dynamic membrane equations exceeded 3.0 with eight distributed workstations. Cluster speedups were comparable to those measured during parallel execution on a shared memory machine.

Action Potentials↗
PubMed2000

Functional reentry's influence on intracellular calcium in the LRd membrane equations.

This paper examines relationships between transmembrane potential (Vm), [Ca2+]i dependent membrane ionic currents, and [Ca2+]i handling by the sarcoplasmic reticulum (SR) in a two-dimensional model of cardiac tissue. Luo-Rudy dynamic (LRd) membrane equations were used because they include detailed formulations for triggered SR Ca2+ release dependent on membrane Ca2+ influx (CICR) and for spontaneous SR Ca2+ release following calsequestrin buffer overload (SCR). Reentry's rapid rate (110-ms cycle length) elevated [Ca2+]i and limited CICR, which in turn promoted SCR that occurred at intervals of 320-350 ms, was preferential at sites located inside the functional center, and destabilized the reentrant activation sequence. Although adjustment of LRd parameters for SR Ca2+ modified SCR interval and peak [Ca2+]i in voltage clamp simulations with a command waveform representing Vm time course within the functional center, SCR persisted. Using the same command waveform, SCR also occurred with an alternate SR Ca2+ formulation that represented subcellular details underlying CICR. LRd parameter adjustments to promote CICR and limit SCR in subsequent reentry simulations failed to eliminate SCR completely, as they modulated SCR intervals in a manner consistent with the voltage clamp simulations. Taken together, our findings support a destabilizing influence of functional reentry on [Ca2+]i handling. However, [Ca2+]i instabilities did not always fractionate depolarization wavefronts during reentry. Fractionation depended, in part, upon CICR and SCR parameters in the LRd formulation for SR Ca2+ release.

Animals↗
PubMed2000

Recombinant cell bioassays for endocrine disruptors: development of a stably transfected human ovarian cell line for the detection of estrogenic and anti-estrogenic chemicals.

The ability of a variety of compounds to disrupt normal endocrine homeostasis, and potentially, the physiological and reproductive capacity of an organism, has gained worldwide attention in recent years. In an attempt to identify such compounds, and to examine the mechanism(s) by which they may exert their actions, we have constructed reporter plasmid vectors that contain the firefly luciferase gene under hormone-inducible control of estrogen-, androgen-, or retinoic acid-responsive DNA enhancer elements. Transient transfection of these vectors into appropriate receptor-containing cell lines revealed their ability to respond to their respective hormones with the induction of luciferase. Here, we describe development and optimization of a recombinant human ovarian carcinoma (BG-1) line, which has been stably transfected with the estrogen responsive luciferase reporter plasmid. The resulting recombinant cell line (BG1Luc4E(2)) responds to 17beta-estradiol at concentrations as low as 1 pM. The utility of BG1Luc4E(2) cells as a bioassay screening system for environmental estrogens was demonstrated by their response to known xenoestrogens, and also by the putative identification of two polychlorinated biphenyls (2,3',4, 4,'-tetrachlorobiphenyl and 2,2',3,5',6-pentachlorobiphenyl) as novel estrogenic chemicals. These cell bioassay systems have applications for rapid screening, identification, and characterization of endocrine disrupting chemicals.

Androgens↗
PubMed2000

Novel methods to evaluate controlled reperfusion techniques in cardiac surgery.

BACKGROUND: This manuscript describes two novel techniques that may be useful for comparing methods to reperfuse the heart during cardiac operations. These techniques are based on measurements of intra-myocyte ion content and the analysis of reperfusion arrhythmias. METHODS: Myocyte ion content was measured in normal porcine hearts before and after ischemia (cardioplegic arrest, CP arrest) using atomic absorption spectroscopy. A cobalt-EDTA complex served as the extra-cellular marker. Cobalt-EDTA was infused into the aorta together with blood or cardioplegia (CP) solution. Myocardial biopsies were taken prior to CP arrest and upon successful defibrillation 5 min after initiating reperfusion. Ventricular fibrillation (VF) was recorded prior to ischemia, and then during reperfusion. VF wavefront (WF) morphology and propagation patterns were analyzed using computer algorithms. Electrophysiologic variables for measuring VF included the multiplicity index (a descriptor of VF organization), the number of WFs detected (nwaves/s) and the mean peak first derivative of electrogram voltage with respect to time (mp d V/dt). RESULTS: Intra-cellular sodium content increased, while intra-cellular magnesium content decreased between control and reperfusion measurements (p < 0.05). Electrophysiologic recovery was characterized by increasingly rapid depolarization (i.e. more negative mp d V/dt) and an increasing nwaves/s during the first minute of post-CP reperfusion. CONCLUSIONS: Atomic absorption spectroscopy and computer-based analysis of reperfusion VF successfully measured metabolic and electrophysiologic events that occurred during controlled reperfusion. These methods may be useful for comparing controlled reperfusion techniques.

Animals↗
PubMed1999

Incidence, evolution, and spatial distribution of functional reentry during ventricular fibrillation in pigs.

Functional reentry has been hypothesized to be an underlying mechanism of ventricular fibrillation (VF); however, its contribution to activation patterns during fully developed VF is unclear. We applied new quantitative pattern analysis techniques to mapping data acquired from a 21 x 24 unipolar electrode array (2-mm spacing) located on the ventricular epicardium of 7 open-chest, unsupported pigs. Data epochs 4 seconds long beginning 1, 10, 20, 30, and 40 seconds after electrical induction were analyzed. Reentrant circuits were automatically identified and quantified. We found that 2.3% of activation pathways could unambiguously be classified as reentrant. From scaling analysis, an additional 28% of the pathways may also have been reentrant. Reentry was short-lived with 1.5+/-1.5 (mean+/-SD) complete cycles per circuit. The fraction of reentrant pathways, number of cycles per circuit, cycle duration, and area and perimeter of the cores all increased significantly as VF progressed. Core drift speed decreased significantly. Neither the orientation of the cores nor the direction of drift was well predicted by the epicardial fiber orientation (r2=0.108 and 0.138, respectively, by linear regression). Reentrant circuits were clustered in regions of the epicardium. We conclude the following: (1) Epicardial reentry is relatively uncommon and short-lived during VF, suggesting either that sustained reentry is transmural or that mechanisms governing sustained reentry are relatively unimportant to the dynamics of VF. (2) Reentrant circuits become more common, larger, and longer-lived as VF progresses, which may explain a recently observed increase in VF organization during the first minute of VF. (3) The conditions necessary to induce and sustain reentry are distributed nonuniformly.

Animals↗
PubMed1999

Apoptosis and morphology in mouse embryos by confocal laser scanning microscopy.

Confocal laser scanning microscopy combined with a vital stain was used to study apoptosis in organogenesis-stage mouse embryos. Apoptosis has previously been visualized in whole embryos using the vital dyes acridine orange, Nile blue sulfate, and neutral red. In the present study, mouse embryos were harvested on Gestation Day 9 and stained with the vital lysosomal dye LysoTracker Red. Following incubation in the stain, embryos were fixed overnight in 4% paraformaldehyde, dehydrated in a graded methanol series, and cleared in benzyl alcohol/benzyl benzoate. The resulting embryo is almost transparent and retains specific LysoTracker Red staining. To achieve optical sectioning through embryos, it was necessary to use low-power objectives. With this procedure, the entire embryo can be optically sectioned and reconstructed in three dimensions to reveal areas of dye staining. Our results demonstrate specific regions undergoing programmed cell death in normal development and increased LysoTracker staining in embryos exposed to hydroxyurea. This procedure allows for the optical imaging of whole Day 9 ( approximately 22 somites) embryos that were greater than 700 microm thick in the z axis and can be applied to studies involving neural tube formation or other aspects of organogenesis.

Aldehydes↗
PubMed1999

Automatic detection of conduction block based on time-frequency analysis of unipolar electrograms.

UNLABELLED: It is commonly thought that lethal tachyarrhythmias, such as ventricular fibrillation (VF), are perpetuated by functional reentry, which occurs when an activation wave blocks and rotates around tissue that is excitable (i.e., functional block). Electrograms recorded near these regions typically contain two sequential deflections representing activation on either side of the block. By detecting these "double potentials," we hypothesize that functional block can be detected by a single electrode. METHODS: Unipolar electrograms were recorded from a 24 x 21 mapping array on the intact ventricular epicardium of five pigs during electrically-induced VF. The short time Fourier Transform (STFT) of each electrogram was analyzed to identify double potentials. To evaluate the performance of the STFT algorithm, conduction block was located in activation maps using a minimum conduction velocity criterion (10 cm/s) and then compared to the results of the STFT algorithm. RESULTS: The STFT algorithm detected conduction block with a sensitivity of 0.74 +/- 0.12 and a specificity of 0.99 +/- 0.00. CONCLUSION: We have developed an automated algorithm that can detect functional block during VF from a single electrode recording. Possible applications include fast, objective identification of block in mapping data and realtime localization of reentrant substrates using mapping catheters.

Algorithms↗
PubMed1998

Confocal laser scanning microscopy of apoptosis in organogenesis-stage mouse embryos.

Confocal laser scanning microscopy combined with a vital stain has been used to study apoptosis in organogenesis-stage mouse embryos. In order to achieve optical sectioning through embryos, it was necessary to use low power objectives and to prepare the sample appropriately. Mouse embryos were harvested on gestation day 8 or 9 and stained with the vital lysosomal dye, LysoTracker Red. Following incubation in the stain, embryos were fixed in 2% paraformaldehyde overnight, dehydrated in a graded methanol series, and cleared in benzyl alcohol/benzyl benzoate. The resulting embryo is almost transparent and retains specific LysoTracker Red staining. The entire embryo can be optically sectioned and reconstructed in three dimensions to reveal areas of dye staining. To test this approach, the chemotherapeutic drug hydroxyurea was added to day 8 embryos in vitro to induce apoptosis. Our results demonstrated specific regions undergoing programmed cell death in normal development and increased apoptosis in embryos exposed to hydroxyurea. The observed patterns of LysoTracker Red staining correlate well with previous studies of cell death using other lysosomotropic dyes such as Nile blue sulfate, acridine orange, or neutral red. LysoTracker Red has the advantages of being aldehyde-fixable and highly fluorescent (bleaching was not observed even after multiple scans). This procedure allows for the optical imaging of whole day 9 (approximately 22 somites) embryos that were greater than 500 microns thick in the Z-axis.

Animals↗
PubMed1998

Locally propagated activation immediately after internal defibrillation.

BACKGROUND: Electrical mapping studies indicate an interval of 40 to 100 ms between a defibrillation shock and the earliest activation that propagates globally over the ventricles (globally propagated activation, GPA). This study determined whether activation occurs during this interval but propagates only locally before being blocked (locally propagated activation, LPA). METHODS AND RESULTS: In five anesthetized pigs, the heart was exposed and a 504-electrode sock with 4-mm interelectrode spacing was pulled over the ventricles. Ten biphasic shocks of a strength near the defibrillation threshold (DFT) were delivered via intracardiac catheter electrodes, and epicardial activation sequences were mapped before and after attempted defibrillation. Local activation was defined as dV/dt < or =-0.5 V/s. Postshock activation times and wave-front interaction patterns were determined with an animated display of dV/dt at each electrode in a computer representation of the ventricular epicardium. LPAs were observed after 40 of the 50 shocks. A total of 173 LPA regions were observed, each of which involved 2+/-2 (mean+/-SD) electrodes. LPAs were observed after both successful and failed shocks but occurred earlier (P<.0001) after failed (35+/-8 ms) than successful (41+/-16 ms) shocks, although the times at which the GPA appeared were not significantly different. On reaching the LPA region, the GPA front either propagated through it (n=135) or was blocked (n=38). The time from the onset of the LPA until the GPA front propagated to reach the LPA region was shorter (P<.01) when the GPA front was blocked (32+/-12 ms) than when it propagated through the LPA region (63+/-20 ms). CONCLUSIONS: LPAs exist after successful and failed shocks near the DFT. Thus, the time from the shock to the GPA is not totally electrically silent.

Animals↗
PubMed1998

Use of USPIO-induced magnetic susceptibility artifacts to identify sentinel lymph nodes and lymphatic drainage patterns. I. Dependence of artifact size with subcutaneous Combidex dose in rats.

Subcutaneously administered Combidex contrast agent produced characteristic magnetic susceptibility artifacts in gradient-echo (GE) images of rat brachial and axillary lymph nodes. These artifacts were useful in the rapid location and identification of normal sentinel lymph nodes. A linear dose response was observed with maximum artifact size in transverse images and was used noninvasively to study lymphatic drainage patterns.

Animals↗
PubMed1998

Estimation of conduction velocity vector fields from epicardial mapping data.

An automated method to estimate vector fields of propagation velocity from observed epicardial extracellular potentials is introduced. The method relies on fitting polynomial surfaces T(x, y) to the space-time (x, y, t) coordinates of activity. Both speed and direction of propagation are computed from the gradient of the local polynomial surface. The components of velocity, which are total derivatives, are expressed in terms of the partial derivatives which comprise the gradient of T. The method was validated on two-dimensional (2-D) simulations of propagation and then applied to cardiac mapping data. Conduction velocity was estimated at multiple epicardial locations during sinus rhythm, pacing, and ventricular fibrillation (VF) in pigs. Data were obtained via a 528-channel mapping system from 23 x 22 and 24 x 21 arrays of unipolar electrodes sutured to the right ventricular epicardium. Velocity estimates are displayed as vector fields and are used to characterize propagation qualitatively and quantitatively during both simple and complex rhythms.

Animals↗
PubMed1998

Evolution of the organization of epicardial activation patterns during ventricular fibrillation.

INTRODUCTION: This study quantified how the organization of epicardial activation changes during the first 40 seconds of ventricular fibrillation (VF). METHODS AND RESULTS: Unipolar potentials were mapped from a 504 (24 x 21) electrode array (2-mm interelectrode spacing) on the anterior right ventricle (RV) and left ventricle (LV) epicardium. The array covered approximately 20% of the epicardial surface. In each of seven pigs, six episodes of VF were induced by premature stimulation. One-half second epochs of VF were analyzed, starting 0, 10, 20, 30, and 40 seconds post induction and using novel pattern analysis algorithms. Eight parameters were quantified: (1) the number of wavefronts; (2) the epicardial area activated by wavefronts; (3) the fraction of wavefronts arising from epicardial breakthrough or from a focus; (4) the fraction of wavefronts terminated by conduction block; (5) the multiplicity index (number of distinct activation pathways in the rhythm); (6) the repeatability index (number of times activation pathways are traversed); (7) the activation rate; and (8) the wavefront propagation velocity. The results showed that VF patterns were less organized at 10 than at 0 seconds, with more, smaller wavefronts traversing a larger variety of pathways for fewer repetitions. VF activation patterns then gradually reorganized up to 40 seconds, but by a different mechanism: the spatial size of subpatterns grew, but the dynamics otherwise appeared unchanged. During both transitions, both activation rate and propagation velocity slowed monotonically. CONCLUSION: Thus, changes in organization during VF can occur by multiple mechanisms.

Action Potentials↗
PubMed1998

MR in temporal lobe epilepsy: analysis with pathologic confirmation.

PURPOSE: We evaluated the MR findings in patients with temporal lobe epilepsy to determine the predictive value of MR imaging in assessing patient outcome. METHODS: MR studies from 186 of 274 consecutive patients who underwent temporal lobectomy for intractable epilepsy were reviewed retrospectively. Images were interpreted by an experienced neuroradiologist, who was blinded to the side of seizure activity and to pathologic findings. RESULTS: MR imaging exhibited 93% sensitivity and 83% specificity in detecting hippocampal/amygdalar abnormalities (n = 121), and 97% sensitivity and 97% specificity in detecting abnormalities in the rest of the temporal lobe (n = 60). Abnormal high signal of the hippocampus on T2-weighted images had a sensitivity of 93% and specificity of 74% in predicting mesial temporal sclerosis (n = 115). The presence of hippocampal atrophy on MR correlated with the duration of seizures. Sensitivity and specificity of MR imaging in detecting temporal lobe tumors (n = 42) were 83% and 97%, respectively, based on abnormal signal and mass effect. After surgery, 63% of patients were seizure free and 28% had a significant reduction of seizure frequency at an average of 24 months (range, 12 to 78 months) after surgery. Patients with a single lesion in the anterior temporal lobe or hippocampus/amygdala had a better outcome than patients with multiple lesions (n = 22). Interrater agreement varied from 0.4 to 0.93, with best agreement for tumors or abnormal hippocampal signal on T2-weighted images. CONCLUSION: MR imaging is highly sensitive in detecting and locating abnormalities in the temporal lobe and the hippocampus/amygdala in patients with temporal lobe epilepsy. Hippocampal atrophy appears to correspond to the duration of seizure disorder.

Adult↗