Impedance of arterial system simulated by viscoelastic t tubes terminated in windkessels

1989 ◽  
Vol 256 (4) ◽  
pp. H1087-H1099 ◽  
Author(s):  
Z. R. Liu ◽  
F. Shen ◽  
F. C. Yin
Keyword(s):  
Input Impedance ◽  
Low Frequency ◽  
Arterial System ◽  
Tube Model ◽  
Impedance Spectra ◽  
Peripheral Vasculature ◽  
Very Low Frequency ◽  
T Tube ◽  
Typical Data ◽  
The Individual

An improved asymmetric t-tube model of the arterial system is proposed. The model consists of two viscoelastic tubes of differing lengths, each terminated in a modified windkessel with inductance as well as resistance and compliance. Equations for calculating the input impedance of this model are presented. Using typical data from the literature, the model predicts a more realistic impedance modulus and phase than previous models of the circulation. Parametric analysis shows that when peripheral compliances are altered, sharp peaks in the very low frequency portions of the impedance spectra are produced, whereas alterations of either the characteristic impedances or inductances of the terminations have little effect on input impedance. Alteration of the elasticity or relative lengths of the tubes results in shifts in the positions of the maxima and minima akin to those observed experimentally. Change in the viscosity of the walls or of the blood only affects the fluctuations of the impedance spectra without affecting the positions of the maxima and minima. Thus, with this still simple model, very realistic impedance spectra are obtainable. The model provides more insight than previously proposed models into the individual influence of various parameters of the proximal and peripheral vasculature on central hemodynamics.

Full Parametric Characterization of LSM/LSM-YSZ Cathodes by Electrochemical Impedance Spectroscopy

2013 ◽  
Vol 11 (1) ◽  
Author(s):  
Rui Antunes ◽  
Janusz Jewulski ◽  
Tomasz Golec
Keyword(s):  
Layer Thickness ◽  
Electrochemical Impedance ◽  
Low Frequency ◽  
Contact Layer ◽  
Gas Diffusion ◽  
Impedance Spectra ◽  
Ohmic Resistance ◽  
The Individual ◽  
Ysz Electrolyte ◽  
Thickness Function

The contributions of the individual process steps of the cathode resistance were determined experimentally, directly from impedance spectra obtained from symmetrical cells. The symmetrical cells have architecture/structure consisting of YSZ electrolyte and a double layer cathode LSM-LSM/YSZ. The investigations were carried out in the temperature interval from 650 to 900 °C. The cathode processes steps activation energies obtained were 1.16 eV, 1.1 eV, and 0.09 eV (diffusion), respectively, which is in relatively good agreement with literature values. To understand the role of layer cathode thickness on electrochemical performance, electrical impedance spectra from symmetric LSM/YSZ/LSM cells were deconvoluted to obtain the key electrochemical components of electrode performance, namely ohmic resistance (RΩ), two low frequency processes related with chemical adsorption and dissociative reaction of O2 (Rp1 and Rp2), and bulk gas diffusion (W, finite warburg) through the electrode pores. The model used has Voight structure with three times constant. These parameters were then related to features, such as contact layer thickness, function layer thickness, and temperature. It was found that polarization resistance is highly dependent on the thickness of the contact layer (Rp1 and Rp2). All deconvoluted parameters are validated by using the appropriate physicochemical model.

Time-domain formulation of asymmetric T-tube model of arterial system

1990 ◽  
Vol 258 (6) ◽  
pp. H1761-H1774 ◽  
Author(s):  
K. B. Campbell ◽  
R. Burattini ◽  
D. L. Bell ◽  
R. D. Kirkpatrick ◽  
G. G. Knowlen
Keyword(s):  
Left Ventricle ◽  
Time Domain ◽  
Arterial Compliance ◽  
Aortic Flow ◽  
Arterial System ◽  
Tube Model ◽  
Pressure Waveform ◽  
Windkessel Model ◽  
Flow Measurements ◽  
T Tube

An asymmetric T-tube model of the arterial system with complex terminal loads was formulated in the time domain. The model was formulated to allow it to be fitted to the aortic pressure waveform, the aortic flow waveform, or simultaneously to both the aortic and descending aortic flow waveforms. Pressure and flow measurements were taken in anesthetized open-chest dogs under basal, vasoconstricted, and vasodilated states. It was found that the T-tube model fitted the data well in all formulations and in all vasoactive states. However, all parameters were estimated accurately in all vasoactive states only with the formulation that fitted to both aortic and descending aortic flow simultaneously. The T-tube model was compared with the three-element windkessel model with regard to the respective models' ability to recreate specific aspects of the pressure waveform and with regard to the estimates of global arterial parameters. The T-tube model recremated those features of the pressure waveform, such as diastolic waves, that the windkessel model could not. Also, the T-tube model systematically estimated lower global arterial compliance and higher characteristic impedance than the windkessel. It was argued that the T-tube model accurately represented important wave transmission features of the arterial loading system. The model is recommended for use in characterizing the arterial load and for merging with representations of the left ventricle in studies of left ventricle-systemic arterial interaction.

Exponentially tapered t-tube model of systemic arterial system in dogs

1994 ◽  
Vol 16 (5) ◽  
pp. 370-378 ◽  
Author(s):  
K.C. Chang ◽  
Y.Z. Tseng ◽  
Y.J. Lin ◽  
T.S. Kuo ◽  
H.I. Chen
Keyword(s):  
Arterial System ◽  
Tube Model ◽  
T Tube

Comments on “Exponentially tapered t-tube model of systemic arterial system in dogs”

1996 ◽  
Vol 18 (4) ◽  
pp. 333-335 ◽  
Author(s):  
Roberto Burattini ◽  
Roberto Fogliardi ◽  
Rita Gobbi
Keyword(s):  
Arterial System ◽  
Tube Model ◽  
T Tube

The Attenuation of Very Low Frequency Brain Oscillations in Transitions from a Rest State to Active Attention

2009 ◽  
Vol 23 (4) ◽  
pp. 191-198 ◽  
Author(s):  
Suzannah K. Helps ◽  
Samantha J. Broyd ◽  
Christopher J. James ◽  
Anke Karl ◽  
Edmund J. S. Sonuga-Barke
Keyword(s):  
Brain Activity ◽  
Sampling Rate ◽  
Low Frequency ◽  
Future Research ◽  
Adhd Symptoms ◽  
Default Mode ◽  
Very Low Frequency ◽  
Wide Range ◽  
Interference Hypothesis ◽  
Mode Interference

Background: The default mode interference hypothesis ( Sonuga-Barke & Castellanos, 2007 ) predicts (1) the attenuation of very low frequency oscillations (VLFO; e.g., .05 Hz) in brain activity within the default mode network during the transition from rest to task, and (2) that failures to attenuate in this way will lead to an increased likelihood of periodic attention lapses that are synchronized to the VLFO pattern. Here, we tested these predictions using DC-EEG recordings within and outside of a previously identified network of electrode locations hypothesized to reflect DMN activity (i.e., S3 network; Helps et al., 2008 ). Method: 24 young adults (mean age 22.3 years; 8 male), sampled to include a wide range of ADHD symptoms, took part in a study of rest to task transitions. Two conditions were compared: 5 min of rest (eyes open) and a 10-min simple 2-choice RT task with a relatively high sampling rate (ISI 1 s). DC-EEG was recorded during both conditions, and the low-frequency spectrum was decomposed and measures of the power within specific bands extracted. Results: Shift from rest to task led to an attenuation of VLFO activity within the S3 network which was inversely associated with ADHD symptoms. RT during task also showed a VLFO signature. During task there was a small but significant degree of synchronization between EEG and RT in the VLFO band. Attenuators showed a lower degree of synchrony than nonattenuators. Discussion: The results provide some initial EEG-based support for the default mode interference hypothesis and suggest that failure to attenuate VLFO in the S3 network is associated with higher synchrony between low-frequency brain activity and RT fluctuations during a simple RT task. Although significant, the effects were small and future research should employ tasks with a higher sampling rate to increase the possibility of extracting robust and stable signals.

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