Five decades of histological, electrophysiological, pharmacological and biochemical investigations exist, but relatively little is known regarding the ionic mechanisms underlying the action potential variations in the...
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Five decades of histological, electrophysiological, pharmacological and biochemical investigations exist, but relatively little is known regarding the ionic mechanisms underlying the action potential variations in the ventricle associated with healthy and disease conditions. The computational modelling in murine ventricular myocytes can complement our knowledge of the experimental data and provide us with more quantitative descriptions in understanding different conditions related to normal and disease conditions. This paper initially reviews the theoretical modelling for cardiac ventricular action potentials of various species and the related experimental work. It then focuses on the progress of computational modelling of cardiac ventricular cells for normal, diabetic and spontaneously hypertensive rats. Also presented is the recent modelling efforts of the action potential in mouse ventricular cells. The computational insights gained into the ionic mechanisms in rodents will enhance our understanding of the heart and provide us with new knowledge for future studies to treat cardiac diseases in children and adults.
This research focuses on developing new implantable cardioverter defibrillator (ICD) dual lead configurations that reduce the defibrillation threshold (DFT) energy by delivering a second threshold shock in the area wh...
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ISBN:
(纸本)0780364651
This research focuses on developing new implantable cardioverter defibrillator (ICD) dual lead configurations that reduce the defibrillation threshold (DFT) energy by delivering a second threshold shock in the area where the conventional shock's electric field is weakest. The objective of this study is to optimize electrode placements for lead systems including left-ventricular (LV) electrodes. A physiologically realistic 3D finite element model of the human thorax is employed to compute DFTs. The lead configurations investigated consist of a conventional lead system (TRIAD/sup TM/, Guidant Corporation) and additional LV shocking electrodes placed in the apical and basal portion of the posteriolateral coronary vein or directly within the TRIAD system's weak field region. The LV electrodes measure 50 mm in length and 1 mm in diameter. The computed DFT energy for the TRIAD is 6.2 J, falling within one standard deviation of the mean DFT reported in clinical studies using the TRIAD leads. LV leads located in the apical and basal portion of the posteriolateral coronary vein result in a DFT of 3.1 J, a 50% reduction from the TRIAD alone. LV leads placed in the anterior, middle, and posterior TRLAD weak field result in a DFT of 2.9 J, 2.7 J., and 3.5 J, respectively, corresponding to a 44-56% reduction in DFT from the TRIAD. The results indicate that an additional electrode placed in the proximity of the TRIAD weak field is just as effective in reducing DFTs as one placed directly within the weak field.
We report resuls of an experimental protocol for determining effective diffusion coefficients in suspension flows in thin channels. The method is based on the first-passage method (FPM), a well-known aspect of probabi...
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We report results of an experimental protocol for determining effective diffusion coefficients in suspension flows in thin channels. The method is based on the first-passage method (FPM), a well-known aspect of probab...
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ISBN:
(纸本)0791816400
We report results of an experimental protocol for determining effective diffusion coefficients in suspension flows in thin channels. The method is based on the first-passage method (FPM), a well-known aspect of probability theory. Images of identifiable individual particles are collected at a regular rate by a video camera. The times needed for individual particles to move selected distances on either side of the original position are measured. Such events are individually the 'first passage' for the selected net distances. Repeated evaluation of this statistic for the same initial conditions is done so that the history of axial motion can be summarized in a statistical manner. All images are collected in a moving frame of reference in order to limit more precisely the initial time and to make observations in a specified region of the flow. The protocol has been used in rectangular channels approximately 50 micrometers high and 500 micrometers wide to collect observations that were located approximately 12 microns in the narrow direction down from the upper surface. The local shear rate is estimated to be 100 inverse seconds. A dilute suspension of beads and a 25% suspension (volume/volume) of erythrocytes was used. Values that were measured compared well with those predicted by the Stokes-Einstein equation and with published data for blood flows.
The sinoatrial node (SAN) model of Demir et al. (Amer. J. Physiol, vol. 266, p. C832-52, 1994) was extended to include two potassium channels. A channel with fast and slow activation components and rapid inactivation ...
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The sinoatrial node (SAN) model of Demir et al. (Amer. J. Physiol, vol. 266, p. C832-52, 1994) was extended to include two potassium channels. A channel with fast and slow activation components and rapid inactivation (I/sub Kr/) and a channel with slow activation (I/sub Ks/) were investigated by Lei & Brown (1996) and Ono & Ito (1995). New K/sup +/ current descriptions were incorporated into the model. The simulated action potentials were in agreement with the action potentials recorded by Irasawa et al. (1993). The sum of I/sub Kr/ and I/sub Ks/ was comparable to the potassium delayed rectifier (I/sub K/) of Demir et al. with the exception that the sum did not totally inactivate. Simulations showed that I/sub Kr/ is essential for pacing, as seen in the experiments of Lei & Brown. Voltage clamp experiments were also accurately simulated. In conclusion, two distinct potassium channels were necessary to accurately simulate the K/sup +/ ionic mechanisms in the rabbit SAN cells.
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