Effects of Diabetes and Gender on Mechanical Properties of the Arterial System in Rats: Aortic Impedance Analysis1

2003 ◽  
Vol 228 (1) ◽  
pp. 70-78 ◽  
Author(s):  
Kuo-Chu Chang ◽  
Kwan-Lih Hsu ◽  
Yung-Zu Tseng
Keyword(s):  
Transit Time ◽  
Input Impedance ◽  
Wave Reflection ◽  
Characteristic Impedance ◽  
Aortic Distensibility ◽  
Aortic Pressure ◽  
Diabetic Rats ◽  
Arterial System ◽  
Reflection Factor ◽  
Aortic Input Impedance

We determined the effects of diabetes and gender on the physical properties of the vasculature in streptozotocin (STZ)-treated rats based on the aortic input impedance analysis. Rats given STZ 65 mg/kg i.v. were compared with untreated age-matched controls. Pulsatile aortic pressure and flow signals were measured and were then subjected to Fourier transformation for the analysis of aortic input impedance. Wave transit time was determined using the impulse response function of the filtered aortic input impedance spectra. Male but not female diabetic rats exhibited an increase in cardiac output in the absence of any significant changes in arterial blood pressure, resulting in a decline in total peripheral resistance. However, in each gender group, diabetes contributed to an increase in wave reflection factor, from 0.47 ± 0.04 to 0.84 ± 0.03 in males and from 0.46 ± 0.03 to 0.81 ± 0.03 in females. Diabetic rats had reduced wave transit time, at 18.82 ± 0.60 vs 21.34 ± 0.51 msec in males and at 19.63 ± 0.37 vs 22.74 ± 0.57 msec in females. Changes in wave transit time and reflection factor indicate that diabetes can modify the timing and magnitude of the wave reflection in the rat arterial system. Meanwhile, diabetes produced a fall in aortic characteristic impedance from 0.023 ± 0.002 to 0.009 ± 0.001 mmHg/min/kg/ml in males and from 0.028 ± 0.002 to 0.014 ± 0.001 mmHg/min/kg/ml in females. With unaltered aortic pressure, both the diminished aortic characteristic impedance and wave transit time suggest that the muscle inactivation in diabetes may occur in aortas and large arteries and may cause a detriment to the aortic distensibility in rats with either sex. We conclude that only rats with male gender diabetes produce a detriment to the physical properties of the resistance arterioles. In spite of male or female gender, diabetes decreases the aortic distensibility and impairs the wave reflection phenomenon in the rat arterial system.

Differential Effects of Isoflurane and Halothane on Aortic Input Impedance Quantified Using a Three-element Windkessel Model

1995 ◽  
Vol 83 (2) ◽  
pp. 361-373. ◽  
Author(s):  
Douglas A. Hettrick ◽  
Paul S. Pagel ◽  
David C. Warltier
Keyword(s):  
Blood Flow ◽  
Input Impedance ◽  
Wave Reflection ◽  
Conscious State ◽  
Left Ventricular ◽  
Arterial System ◽  
Windkessel Model ◽  
Frequency Dependent ◽  
Aortic Input Impedance ◽  
Arterial Wave Reflection

Background Systemic vascular resistance (the ratio of mean aortic pressure [AP] and mean aortic blood flow [AQ]) does not completely describe left ventricular (LV) afterload because of the phasic nature of pressure and blood flow. Aortic input impedance (Zin) is an established experimental description of LV afterload that incorporates the frequency-dependent characteristics and viscoelastic properties of the arterial system. Zin is most often interpreted through an analytical model known as the three-element Windkessel. This investigation examined the effects of isoflurane, halothane, and sodium nitroprusside (SNP) on Zin. Changes in Zin were quantified using three variables derived from the Windkessel: characteristic aortic impedance (Zc), total arterial compliance (C), and total arterial resistance (R). Methods Sixteen experiments were conducted in eight dogs chronically instrumented for measurement of AP, LV pressure, maximum rate of change in left ventricular pressure, subendocardial segment length, and AQ. AP and AQ waveforms were recorded in the conscious state and after 30 min equilibration at 1.25, 1.5, and 1.75 minimum alveolar concentration (MAC) isoflurane and halothane. Zin spectra were obtained by power spectral analysis of AP and AQ waveforms and corrected for the phase responses of the transducers. Zc and R were calculated as the mean of Zin between 2 and 15 Hz and the difference between Zin at zero frequency and Zc, respectively. C was determined using the formula C = (Ad.MAP).[MAQ.(Pes-Ped)]-1, where Ad = diastolic AP area; MAP and MAQ = mean AP and mean AQ, respectively; and Pes and Ped = end-systolic and end-diastolic AP, respectively. Parameters describing the net site and magnitude of arterial wave reflection were also calculated from Zin. Eight additional dogs were studied in the conscious state before and after 15 min equilibration at three equihypotensive infusions of SNP. Results Isoflurane decreased R (3,205 +/- 315 during control to 2,340 +/- 2.19 dyn.s.cm-5 during 1.75 MAC) and increased C(0.55 +/- 0.02 during control to 0.73 +/- 0.06 ml.mmHg-1 during 1.75 MAC) in a dose-related manner. Isoflurane also increased Zc at the highest dose. Halothane increased C and Zc but did not change R. Equihypotensive doses of SNP decreased R and produced marked increases in C without changing Zc. No changes in the net site or the magnitude of arterial wave reflection were observed with isoflurane and halothane, in contrast to the findings with SNP. Conclusions The major difference between the effects of isoflurane and halothane on LV afterload derived from the Windkessel model of Zin was related to R, a property of arteriolar resistance vessels, and not to Zc or C, the mechanical characteristics of the aorta. No changes in arterial wave reflection patterns determined from Zin spectra occurred with isoflurane and halothane. These results indicate that isoflurane and halothane have no effect on frequency-dependent arterial properties.

scholarly journals Longitudinal Changes of Input Impedance, Pulse Wave Velocity, and Wave Reflection in a Middle-Aged Population

Hypertension ◽  
2021 ◽  
Author(s):  
Daime Campos-Arias ◽  
Marc L. De Buyzere ◽  
Julio A. Chirinos ◽  
Ernst R. Rietzschel ◽  
Patrick Segers
Keyword(s):  
Pulse Wave Velocity ◽  
Wave Velocity ◽  
Input Impedance ◽  
Wave Reflection ◽  
Pulse Wave ◽  
Characteristic Impedance ◽  
Arterial System ◽  
Middle Aged ◽  
Cross Sectional ◽  
Aged Population

The changes experienced by the arterial system due to the aging process have been extensively studied but are incompletely understood. Within-subject patterns of changes in regards to input impedance and wave reflection parameters have not been assessed. The Asklepios study is a longitudinal population study including healthy (at onset) middle-aged subjects, with 974 males and 1052 females undergoing 2 rounds of measurements of applanation tonometry and ultrasound, 10.15±1.40 years apart. Carotid-femoral pulse wave velocity, aortic input impedance, and wave reflection parameters were assessed, and linear mixed-effects models were used to evaluate their longitudinal trajectories and determinants. Overall, the effective 10-year increase in pulse wave velocity was less than expected from first round cross-sectional data, and pulse wave velocity was found to accelerate more in women than in men. Interestingly, the increase in pulse wave velocity was not paralleled by a decrease in arterial volume compliance, particularly in younger males. Aortic root characteristic impedance decreased with age in younger subjects while it increased for the older subjects in the study. These changes suggest that aortic dilation and elongation may play an important role determining the longitudinal age-related changes in impedance parameters in middle-age. Wave reflection decreased with aging, whereas resistance increased in women and decreased in men. We conclude that the effective impact of aging on arterial system properties, in a middle-aged population, is not well reflected by cross-sectional studies. Future studies should assess the interaction between geometric remodeling and wall stiffening as determinants of pulsatile hemodynamics.

scholarly journals -154-THE RELATIONSHIP BETWEEN AORTIC INPUT IMPEDANCE (CHARACTERISTIC IMPEDANCE) AND SYSTOLIC AORTIC PRESSURE

1986 ◽  
Vol 50 (6) ◽  
pp. 504
Author(s):  
Shigeki Morita ◽  
Izumi Kuboyama ◽  
Toshihide Asou ◽  
Jiro Tanaka ◽  
Kouichi Tokunaga ◽  
...  
Keyword(s):  
Input Impedance ◽  
Characteristic Impedance ◽  
Aortic Pressure ◽  
Impedance Characteristic ◽  
Aortic Input Impedance ◽  
The Relationship

Empirical estimates of mean aortic pressure: advantages, drawbacks and implications for pressure redundancy

2002 ◽  
Vol 103 (1) ◽  
pp. 7-13 ◽  
Author(s):  
Denis CHEMLA ◽  
Jean-Louis HÉBERT ◽  
Eduardo APTECAR ◽  
Jean-Xavier MAZOIT ◽  
Karen ZAMANI ◽  
...  
Keyword(s):  
Form Factor ◽  
Pulse Pressure ◽  
Wave Reflection ◽  
Diastolic Pressure ◽  
Augmentation Index ◽  
Aortic Pressure ◽  
Arterial System ◽  
Wave Amplification ◽  
Empirical Estimates ◽  
Alternative Formula

Mean arterial pressure (MAP) is estimated at the brachial artery level by adding a fraction of pulse pressure (form factor; = 0.33) to diastolic pressure. We tested the hypothesis that a fixed form factor can also be used at the aortic root level. We recorded systolic aortic pressure (SAP) and diastolic aortic pressure (DAP), and we calculated aortic pulse pressure (PP) and the time-averaged MAP in the aorta of resting adults (n = 73; age 43±14 years). Wave reflection was quantified using the augmentation index. The aortic form factor (range 0.35-0.53) decreased with age, MAP, PP and augmentation index (each P<0.001). The mean form factor value (0.45) gave a reasonable estimation of MAP (MAP = DAP+0.45PP; bias = 0±2mmHg), and the bias increased with MAP (P<0.001). An alternative formula (MAP = DAP+PP/3+5mmHg) gave a more precise estimation (bias = 0±1mmHg), and the bias was not related to MAP. This latter formula was consistent with the previously reported mean pulse wave amplification of 15mmHg, and with unchanged MAP and diastolic pressure from aorta to periphery. Multiple linear regression showed that 99% of the variability of MAP was explained by the combined influence of DAP and SAP, thus confirming major pressure redundancy. Results were obtained irrespective of whether the marked differences in heart period and extent of wave reflection between subjects were taken into account. In conclusion, the aortic form factor was strongly influenced by age, aortic pressure and wave reflection. An empirical formula (MAP = DAP+PP/3+5mmHg) that is consistent with mechanical principles in the arterial system gave a more precise estimate of MAP in the aorta of resting humans. Only two distinct pressure-powered functions were carried out in the (SAP, DAP, MAP, PP) four-pressure set.

A novel servo-control system that imposes desired aortic input impedance on in situ rat heart

2000 ◽  
Vol 278 (3) ◽  
pp. H998-H1007 ◽  
Author(s):  
Hiroshi Miyashita ◽  
Masaru Sugimachi ◽  
Takayuki Sato ◽  
Toru Kawada ◽  
Toshiaki Shishido ◽  
...  
Keyword(s):  
Control System ◽  
Characteristic Impedance ◽  
Aortic Pressure ◽  
Side Branch ◽  
Aortic Flow ◽  
Aortic Input Impedance ◽  
Aortic Impedance ◽  
The Difference ◽  
Flow Waveforms

To clarify the pathophysiological role of dynamic arterial properties in cardiovascular diseases, we attempted to develop a new control system that imposes desired aortic impedance on in situ rat left ventricle. In 38 anesthetized open-chest rats, ascending aortic pressure and flow waveforms were continuously sampled (1,000 Hz). Desired flow waveforms were calculated from measured aortic pressure waveforms and target impedance. To minimize the difference between measured and desired aortic flow waveforms, the computer generated commands to the servo-pump, connected to a side branch of the aorta. By iterating the process, we could successfully control aortic impedance in such a way as to manipulate compliance and characteristic impedance between 60 and 160% of their respective native values. The error between desired and measured aortic flow waveforms was 70 ± 34 μl/s (root mean square; 4.4 ± 1.4% of peak flow), indicating reasonable accuracy in controlling aortic impedance. This system enables us to examine the importance of dynamic arterial properties independently of other hemodynamic and neurohumoral factors in physiological and clinical settings.

Normalized input impedance and arterial decay time over heart period are independent of animal size

1991 ◽  
Vol 261 (1) ◽  
pp. R126-R133 ◽  
Author(s):  
N. Westerhof ◽  
G. Elzinga
Keyword(s):  
Heart Rate ◽  
Decay Time ◽  
Input Impedance ◽  
Diastolic Pressure ◽  
Arterial Compliance ◽  
Characteristic Impedance ◽  
Peripheral Resistance ◽  
Arterial System ◽  
Heart Period ◽  
Arterial Tree

The arterial system of mammals in the weight range from 0.6 to 70 kg is characterized by the three-element windkessel, a succinct representation of the arterial tree consisting of the parameters peripheral resistance (Rp), total arterial compliance (C), and aortic characteristic impedance (Zc). The values of these parameters in resting conditions are related to body mass (M). The time constant, or decay time (tau), of the arterial system (defining rate of decay of aortic pressure in diastole), the product of Rp and C, is also evaluated. The dependencies of the heart period (T, inverse of heart rate), and durations of ejection (Ts) and of diastole (Td) in resting conditions are also determined as a function of M. It is found that Rp = Rp0M-0.93; Zc = Zc0M-0.97; and C = C0M+1.23, where Rp0, Zc0, and C0 are proportionality constants. Zc is thus a constant fraction of Rp in all mammals. tau is related to M as tau = tau 0M+0.29; T and Td are related to M as T = T0M+0.27 and Td = Td0M+0.30, where tau 0, T0, and Td0 are proportionality constants. The duration of diastole is thus a constant fraction of T, and the ratios T/tau and Td/tau are independent of M. The findings indicate that arterial input impedance, normalized to aortic Zc and plotted as a function of frequency normalized to heart rate, is similar for all mammals. The finding that the ratio Td/tau is the same in mammals (and Ts/T and stroke volume/M are constant) explains the constancy of pulse pressure (systolic minus diastolic pressure).(ABSTRACT TRUNCATED AT 250 WORDS)

Repeated reflection of waves in the systemic arterial system

1993 ◽  
Vol 264 (1) ◽  
pp. H269-H281 ◽  
Author(s):  
D. S. Berger ◽  
J. K. Li ◽  
W. K. Laskey ◽  
A. Noordergraaf
Keyword(s):  
Wave Reflection ◽  
Aortic Pressure ◽  
Arterial System ◽  
Tube Length ◽  
Pharmacological Intervention ◽  
Forward Wave ◽  
Heart Tube ◽  
Complex Load ◽  
Backward Wave ◽  
Reflection Theory

Traditional analysis of pulse-wave propagation and reflection in the arterial system treats measured pressure and flow waves as the sum of a single forward wave (traveling away from the heart) and a single backward wave (traveling toward the heart). The purpose of this study was to develop a more general wave reflection theory that allows repeated reflection of these waves. The arterial system was modeled as a uniform viscoelastic tube terminating in a complex load with reflections occurring at the tube load interface and the heart tube interface. The resulting framework considers the forward wave to be the sum of an initial wave plus a series of antegrade waves. Similarly, the backward wave is the sum of a series of retrograde waves. This repeated reflection theory contains within it the traditional forward/backward wave reflection analysis as a special case. In addition, the individual antegrade and retrograde waves, at the tube entrance, are shown to be independent of the tube length. Aortic pressure and flow data, from dog experiments, were used to illustrate the phenomenon of repeated reflections. Alteration of the arterial system loading conditions, brought about through pharmacological intervention, affected the number and morphology of repeated waves. These results are compared with those found in traditional forward/backward reflection analysis.

Response of systemic arterial input impedance to volume expansion and hemorrhage

1980 ◽  
Vol 238 (6) ◽  
pp. H902-H908 ◽  
Author(s):  
J. P. Dujardin ◽  
D. N. Stone ◽  
L. T. Paul ◽  
H. P. Pieper
Keyword(s):  
Blood Volume ◽  
Volume Expansion ◽  
Characteristic Impedance ◽  
Aortic Pressure ◽  
Arterial System ◽  
Aortic Smooth Muscle ◽  
Direct Measurements ◽  
Dextran 70 ◽  
Anesthetized Dogs ◽  
The Mean

Experiments on 12 anesthetized dogs were performed to study the effects of changes in blood volume on the pulsatile hemodynamics of the arterial system as seen from its input. Pressure and flow were measured in the ascending aorta under control conditions, after volume expansion with dextran 70 (+30% of estimated blood volume), and after hemorrhage (-15% of estimated blood volume). The input inpedance of the arterial system was calculated for each condition. It was found that after volume expansion the characteristic impedance of the proximal aorta, Zc, was decreased by 26.6 +/- 5.1% (SE) (P less than 0.01). After hemorrhage Zc was increased by 30.4 +/- 3.4% (P less than 0.01). Since it is well known that Zc is a very weak function of the mean arterial pressure, it is concluded that the changes in Zc seen with volume expansion or hemorrhage are caused mainly by changes in aortic smooth muscle activity. This conclusion is also supported by direct measurements of aortic pressure diameter relationships in earlier work from our lab.

Assessment of Windkessel as a model of aortic input impedance

1988 ◽  
Vol 255 (4) ◽  
pp. H742-H753 ◽  
Author(s):  
D. Burkhoff ◽  
J. Alexander ◽  
J. Schipke
Keyword(s):  
Input Impedance ◽  
Impedance Spectrum ◽  
Aortic Pressure ◽  
Stroke Work ◽  
Windkessel Model ◽  
The Real ◽  
Wide Range ◽  
Aortic Input Impedance ◽  
Coupling Variables ◽  
Best Fit

To facilitate the analysis of aortic-ventricular coupling, simplified models of aortic input properties have been developed, such as the three-element Windkessel. Even though the impedance spectrum of the Windkessel reproduces the gross features of the real aortic input impedance, it fails to reproduce many of its details. In the present study we assessed the physiological significance of the differences between real and Windkessel impedance. We measured aortic input impedance spectra from five anesthetized open-chest dogs under a wide range of conditions. For each experimentally determined spectrum we estimated the corresponding values of the best-fit Windkessel parameters. By computer simulation we imposed both the real and best-fit Windkessel impedances on a model left ventricle and assessed the differences in seven different coupling variables. The analysis indicated that the Windkessel model provides a reasonable representation of afterload for purposes of predicting stroke volume, stroke work, oxygen consumption, and systolic and diastolic aortic pressures. However, the Windkessel model significantly underestimates peak aortic flow, slightly underestimates mean arterial pressure, and, of course, does not provide realistic aortic pressure and flow waveforms.

Derivation of the ascending aortic-carotid pressure transfer function with an arterial model

1996 ◽  
Vol 271 (6) ◽  
pp. H2399-H2404 ◽  
Author(s):  
M. Karamanoglu ◽  
M. P. Feneley
Keyword(s):  
Characteristic Impedance ◽  
Aortic Pressure ◽  
Arterial System ◽  
Model Parameters ◽  
Pressure Waveform ◽  
Mean Square ◽  
Arterial Waveform ◽  
Arterial Model ◽  
Viscoelastic Tube ◽  
Carotid Arterial

To devise a method of deriving the ascending aortic pressure waveform from the noninvasively determined carotid arterial waveform, ascending aortic and carotid arterial pressures were recorded in 13 patients aged 58.5 +/- 10.0 (SD) yr. A single viscoelastic tube terminated with a modified windkessel was used to model the carotid arterial system. For each patient the model parameters, characteristic impedance of the tube (Z0), reflection coefficient at the termination (gamma), and time constant of the windkessel (tau), were estimated by minimizing the root-mean-square error between the measured and predicted carotid waveforms, with the ascending aortic pressure waveform as input. The resulting arterial parameters were realistic: Z0 = 729.5 +/- 246.8 dyn.s.cm-3, gamma = 0.75 +/- 0.19, and tau = 0.16 +/- 0.17 s. A generalized model constructed with these mean parameters yielded a smaller error between predicted and measured carotid arterial pressures (3.4 +/- 1.3 mmHg) than between ascending aortic pressure and measured carotid arterial pressure (4.4 +/- 1.6 mmHg, P < 0.01) and also reproduced the carotid wave contour indexed by the ratio of late systolic to early systolic peak amplitude: predicted = 1.26 +/- 0.05 and measured = 1.24 +/- 0.16 vs. aortic = 1.55 +/- 0.19.

Sign in / Sign up

Export Citation Format

Share Document