Comparison of time domain algorithms for estimating aortic characteristic impedance in humans

1988 ◽  
Vol 35 (1) ◽  
pp. 62-68 ◽  
Author(s):  
C.L. Lucas ◽  
B.R. Wilcox ◽  
B. Ha ◽  
G.W. Henry
Keyword(s):  
Time Domain ◽  
Characteristic Impedance ◽  
Aortic Characteristic Impedance

1.1 COMPARISON OF VARIOUS METHODS FOR THE ESTIMATION FOR AORTIC CHARACTERISTIC IMPEDANCE IN TIME DOMAIN FROM VELOCITY-ENCODED MAGNETIC RESONANCE AND APPLANATION TONOMETRY DATA

2013 ◽  
Vol 7 (3-4) ◽  
pp. 161
Author(s):  
E. Bollache ◽  
N. Kachenoura ◽  
I. Bargiotas ◽  
A. de Cesare ◽  
M. Bensalah ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Time Domain ◽  
Characteristic Impedance ◽  
Applanation Tonometry ◽  
Aortic Characteristic Impedance

How to estimate aortic characteristic impedance from magnetic resonance and applanation tonometry data?

2015 ◽  
Vol 33 (3) ◽  
pp. 575-583 ◽  
Author(s):  
Emilie Bollache ◽  
Nadjia Kachenoura ◽  
Ioannis Bargiotas ◽  
Alain Giron ◽  
Alain De Cesare ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Characteristic Impedance ◽  
Applanation Tonometry ◽  
Aortic Characteristic Impedance

Effects of blood volume changes on characteristic impedance of the pulmonary artery

1982 ◽  
Vol 242 (2) ◽  
pp. H197-H202 ◽  
Author(s):  
J. P. Dujardin ◽  
D. N. Stone ◽  
C. D. Forcino ◽  
L. T. Paul ◽  
H. P. Pieper
Keyword(s):  
Pulmonary Artery ◽  
Blood Volume ◽  
Time Domain ◽  
Volume Expansion ◽  
Characteristic Impedance ◽  
Main Pulmonary Artery ◽  
Time Domain Method ◽  
Frequency Domain Method ◽  
Domain Method ◽  
The Time Domain

Experiments were performed on eight anesthetized dogs to study the response of the characteristic impedance (Zc) of the main pulmonary artery to changes in circulating blood volume. Pressure and flow were measured in the proximal main pulmonary artery under control conditions, after hemorrhage (-15% of the estimated blood volume), again under control conditions, and finally after volume expansion (+30% of the estimated blood volume). Two different methods were used to determine Zc from these recordings. With the frequency-domain method values for Zc were obtained by averaging the input impedance moduli between 2 and 15 Hz. With the time-domain method Zc was derived as the slope of the early ejection pressure-flow relationship. The values for Zc obtained with the two methods were not statistically different. In the time-domain method the average increase in Zc with hemorrhage was 30.7 +/- 7.4 (SE) %, and the average decrease with volume expansion was -21.1 +/- 5.0 (SE) %. Because the time-domain method allowed the values of Zc during control conditions and after hemorrhage to be obtained in the same pressure range, it was concluded that the observed changes were caused by a change in the activity of the smooth muscle in the pulmonary arterial wall. Similarly, it was concluded that the decrease in Zc after volume expansion was active in nature.

scholarly journals Changes in hemodynamics associated with metabolic syndrome are more pronounced in women than in men

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Pauliina Kangas ◽  
Antti Tikkakoski ◽  
Jarkko Kettunen ◽  
Arttu Eräranta ◽  
Heini Huhtala ◽  
...  
Keyword(s):  
Metabolic Syndrome ◽  
Cardiovascular Risk ◽  
Impedance Cardiography ◽  
Pulse Wave ◽  
Characteristic Impedance ◽  
Whole Body ◽  
Cardiac Work ◽  
Head Up Tilt ◽  
Body Impedance ◽  
Aortic Characteristic Impedance

AbstractThe increase in cardiovascular risk associated with metabolic syndrome (MS) seems higher in women than in men. We examined hemodynamics during head-up tilt in 252 men and 250 women without atherosclerosis, diabetes, or antihypertensive medication, mean age 48 years, using whole-body impedance cardiography and radial pulse wave analysis. MS was defined according to Alberti et al. 2009. Men and women with MS presented with corresponding elevations of systolic and diastolic blood pressure (10-14%, p ≤ 0.001) versus controls. Supine pulse wave velocity (16–17%, p < 0.001) and systemic vascular resistance (7–9%, p ≤ 0.026), and upright cardiac output (6–11%, p ≤ 0.008) were higher in both MS groups than controls. Elevation of supine aortic characteristic impedance was higher in women than in men with MS (16% vs. 8%, p = 0.026), and in contrast to men, no upright impedance reduction was observed in women. When upright, women but not men with MS showed faster return of reflected pressure wave (p = 0.036), and smaller decrease in left cardiac work (p = 0.035) versus controls. The faster upright return of reflected pressure, lower upright decrease in left cardiac work, and higher elevation of aortic characteristic impedance may contribute to the greater increase in MS-related cardiovascular risk in women than in men.

Modeling near‐field GPR in three dimensions using the FDTD method

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1114-1126 ◽  
Author(s):  
Roger L. Roberts ◽  
Jeffrey J. Daniels
Keyword(s):  
Electrical Properties ◽  
Finite Difference ◽  
Time Domain ◽  
Near Field ◽  
Characteristic Impedance ◽  
Fdtd Method ◽  
Three Dimensions ◽  
Field Pattern ◽  
Scattered Fields ◽  
Transmitting Antenna

Complexities associated with the theoretical solution of the near‐field interaction between the fields radiated from dipole antennas placed near a dielectric half‐space and electrical inhomogeneities within the dielectric can be overcome by using numerical techniques. The finite‐difference time‐domain (FDTD) technique implements finite‐difference approximations of Maxwell's equations in a discretized volume that permit accurate computation of the radiated field from a transmitting antenna, propagation through the air‐earth interface, scattering by subsurface targets and reception of the scattered fields by a receiving antenna. In this paper, we demonstrate the implementation of the FDTD technique for accurately modeling near‐field time‐domain ground‐penetrating radar (GPR). This is accomplished by incorporating many of the important GPR parameters directly into the FDTD model. These variables include: the shape of the GPR antenna, feed cables with a fixed characteristic impedance attached to the terminals of the antenna, the height of the antenna above the ground, the electrical properties of the ground, and the electrical properties and geometry of targets buried in the subsurface. FDTD data generated from a 3-D model are compared to experimental antenna impedance data, field pattern data, and measurements of scattering from buried pipes to verify the accuracy of the method.

scholarly journals Characteristic impedance and propagation of the first higher order microstrip mode in frequency and time domain

2002 ◽  
Vol 50 (5) ◽  
pp. 1370-1379 ◽  
Author(s):  
Shyue-Dar Chen ◽  
C.-K.C. Tzuang
Keyword(s):  
Time Domain ◽  
Characteristic Impedance ◽  
Higher Order

Measurements of characteristic impedance of high frequency cables with time domain reflectometry (TDR)

2008 ◽  
Author(s):  
Luis Navarro ◽  
Eugene Mayevskiy ◽  
Timothy Chairet
Keyword(s):  
Time Domain ◽  
High Frequency ◽  
Characteristic Impedance ◽  
Time Domain Reflectometry
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