Effect of interelectrode distance on bioelectric parameters of electro-biosystems

Background Supraventricular tachydysrhythmias such as atrial fibrillation frequently complicate the perioperative period. Two electrophysiologic factors critical to the pathogenesis of supraventricular tachydysrhythmias are: 1) atrial wavelength, the product of atrial conduction velocity (CV) and effective refractory period (ERP), and 2) atrioventricular nodal conduction. Modulation of these factors by drugs has important clinical ramifications. The authors studied the effects of propofol, thiopental, and ketamine on atrial wavelength and atrioventricular nodal function in guinea pig isolated atrial trabeculae and hearts, respectively. Methods Electrocardiogram recordings in superfused atrial tissue were obtained using hanging microelectrodes. A stimulating and two recording electrodes were placed on a single atrial trabecula, and the interelectrode distance was measured. Atrial ERP determinations were made using a premature stimulus protocol. The time (t) required for a propagated impulse to traverse the interelectrode distance (d) was measured. Conduction velocity was calculated as d/t. Langendorff-perfused guinea pig hearts were instrumented for low atrial pacing (cycle length = 300 ms) and for measurements of stimulusto-His bundle interval, an index of atrioventricular nodal conduction. To investigate the frequency-dependent behavior of the atrioventricular node, computer-based measurements were made of Wenckebach cycle length (WCL) and atrioventricular nodal ERP. Results Thiopental significantly prolonged atrial ERP in a concentration-dependent manner, whereas propofol and ketamine had no significant effect on atrial refractoriness. In contrast, ketamine caused a dose-dependent decrease in atrial CV, but propofol and thiopental had no significant effect on CV. Therefore, thiopental, ketamine, and propofol caused an increase, a decrease, and no change, respectively, in atrial wavelength. All anesthetics caused a concentration-dependent prolongation of the stimulus-to-His bundle interval, atrioventricular nodal ERP, and WCL. However, on an equimolar basis, significant differences in potencies were found. The concentrations of drug that caused a 20% increase in ERP (ERP20) and WCL (WCL20) for propofol, thiopental, and ketamine were 14 +/- 2 microM, 26 +/- 3 microM, and 62 +/- 11 microM, and 17 +/- 2 microM, 50 +/- 1 microM, and 123 +/- 19 microM (mean +/- SEM), respectively. Therefore, the rank order of potency for frequency-dependent atrioventricular nodal effects is propofol > thiopental > ketamine. Conclusion The authors' results indicate that propofol would be most effective at filtering atrial impulses during supraventricular tachydysrhythmias, whereas thiopental would be most effective at preventing atrial reentrant dysrhythmias. In contrast, ketamine may be most likely to promote atrial reentry while having minimal effect on atrioventricular nodal conduction.

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Interelectrode distance and amplitude of the scalp EEG

Electroencephalography and Clinical Neurophysiology ◽

10.1016/0013-4694(85)90001-x ◽

1985 ◽

Vol 60 (4) ◽

pp. 287-292 ◽

Cited By ~ 9

Author(s):

Charles M. Epstein ◽

Gail P. Brickley

Keyword(s):

Interelectrode Distance ◽

Scalp Eeg

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Effect of interelectrode distance on dc magnetron current–pressure characteristics

Journal of Physics Conference Series ◽

10.1088/1742-6596/946/1/012150 ◽

2018 ◽

Vol 946 ◽

pp. 012150

Author(s):

Yu A Mankelevich ◽

A F Pal ◽

A N Ryabinkin ◽

A O Serov

Keyword(s):

Interelectrode Distance ◽

Pressure Characteristics

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Time-resolved quantification of the dynamic extracellular space in the brain during short-lived event: methodology and simulations

Journal of Neurophysiology ◽

10.1152/jn.00347.2018 ◽

2019 ◽

Vol 121 (5) ◽

pp. 1718-1734 ◽

Cited By ~ 1

Author(s):

Kevin C. Chen ◽

Yi Zhou ◽

Hui-Hui Zhao

Keyword(s):

Extracellular Space ◽

Volume Fraction ◽

Interelectrode Distance ◽

Operating Parameters ◽

High Fidelity ◽

Phase Lag ◽

Time Resolved ◽

Time Pattern ◽

Waveform Amplitude ◽

The Brain

Two macroscopic parameters describe the interstitial diffusion of substances in the extracellular space (ECS) of the brain, the ECS volume fraction α and the diffusion tortuosity λ. Past methods based on sampling the extracellular concentration of a membrane-impermeable ion tracer, such as tetramethylammonium (TMA+), can characterize either the dynamic α( t) alone or the constant α and λ in resting state but never the dynamic α( t) and λ( t) simultaneously in short-lived brain events. In this work, we propose to use a sinusoidal method of TMA+ to provide time-resolved quantification of α( t) and λ( t) in acute brain events. This method iontophoretically injects TMA+ in the brain ECS by a sinusoidal time pattern, samples the resulting TMA+ diffusion waveform at a distance, and analyzes the transient modulations of the amplitude and phase lag of the sampled TMA+ waveform to infer α( t) and λ( t). Applicability of the sinusoidal method was verified through computer simulations of the sinusoidal TMA+ diffusion waveform in cortical spreading depression. Parameter sensitivity analysis identified the sinusoidal frequency and the interelectrode distance as two key operating parameters. Compared with other TMA+-based methods, the sinusoidal method can more accurately capture the dynamic α( t) and λ( t) in acute brain events and is equally applicable to other pathological episodes such as epilepsy, transient ischemic attack, and brain injury. Future improvement of the method should focus on high-fidelity extraction of the waveform amplitude and phase angle. NEW & NOTEWORTHY An iontophoretic sinusoidal method of tetramethylammonium is described to capture the dynamic brain extracellular space volume fraction α and diffusion tortuosity λ. The sinusoidal frequency and interelectrode distance are two key operating parameters affecting the method’s accuracy in capturing α( t) and λ( t). High-fidelity extraction of the waveform amplitude and phase lag is critical to successful sinusoidal analyses.

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