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

Lucas, Carol L.; Wilcox, Benson R.; Ha, Belinda; Henry, George W.

doi:10.1109/10.1337

Cited by 48 publications

(40 citation statements)

References 16 publications

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“…Second, the characteristic impedance was calculated based on the time domain rather than the conventional frequency domain analysis, although these analyses are known to yield comparable results. [29][30][31] The descending aortic impedance was calculated from the estimated central pressure instead of the actual descending aortic pressure values, but the pressure waveforms can be regarded as virtually identical between the ascending and descending aorta. 31 The use of flow data in the impedance calculation might have had partial influence on the observed association between aortic impedance and reverse/forward flow ratio.…”

Section: Discussionmentioning

confidence: 99%

Aortic Stiffness Determines Diastolic Blood Flow Reversal in the Descending Thoracic Aorta

2013

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Abstract-Aortic stiffening often precedes cardiovascular diseases, including stroke, but the underlying pathophysiological mechanisms remain obscure. We hypothesized that such abnormalities could be attributable to altered central blood flow dynamics. In 296 patients with uncomplicated hypertension, Doppler velocity pulse waveforms were recorded at the proximal descending aorta and carotid artery to calculate the reverse/forward flow ratio and diastolic/systolic flow index, respectively. Tonometric waveforms were recorded on the radial artery to estimate aortic pressure and characteristic impedance (Z 0 ) and to determine carotid-femoral (aortic) and carotid-radial (peripheral) pulse wave velocities. In all subjects, the aortic flow waveform was bidirectional, comprising systolic forward and diastolic reverse flows. The aortic reverse/forward flow ratio (35±10%) was positively associated with parameters of aortic stiffness (including pulse wave velocity, Z 0 , and aortic/peripheral pulse wave velocity ratio), independent of age, body mass index, aortic diameter, and aortic pressure. The carotid flow waveform was unidirectional and bimodal with systolic and diastolic maximal peaks. There was a positive relationship between the carotid diastolic/systolic flow index (28±9%) and aortic reverse/ forward flow ratio, which remained significant after adjustment for aortic stiffness and other related parameters. The Bland-Altman plots showed a close time correspondence between aortic reverse and carotid diastolic flow peaks. In conclusion, aortic stiffness determines the extent of flow reversal from the descending aorta to the aortic arch, which contributes to the diastolic antegrade flow into the carotid artery. This hemodynamic relationship constitutes a potential mechanism linking increased aortic stiffness, altered flow dynamics, and increased stroke risk in hypertension.

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Section: Discussionmentioning

confidence: 99%

Aortic Stiffness Determines Diastolic Blood Flow Reversal in the Descending Thoracic Aorta

2013

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“…Finally the characteristic impedance Z o can be estimated from the early ejection phase of systole, as before (Li 1986;Lucas et al 1988),…”

Section: Theoretical Analysismentioning

confidence: 99%

Pulse Pressure, Arterial Compliance and Wave Reflection Under Differential Vasoactive and Mechanical Loading

Zhu

Geipel

2010

Cardiovasc Eng

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Similar pulse pressure increases and flow reductions have been reported by many investigators, despite dissimilar forms of arterial loading applied. Increased vascular load is most commonly observed due to mechanical and vasoactive interventions. The present study intended to differentiate the hemodynamic contributions of these two forms of arterial loading at closely matched blood pressure levels. To accomplish this, proximal aortic characteristic impedance (Z(o)), total arterial compliance (C), peripheral vascular resistance (R(s)) and time-domain resolved forward (P(f)) and reflected (P(r)) waves were obtained in six anesthetized, thoracotomized and ventilated dogs. Acute loading was accomplished by brief descending thoracic aorta (DTA) occlusion or by intravenous bolus infusion of methoxamine (MTX:5 mg/ml) Systolic pressure increases were matched to a similar extent. Results showed that pulse pressures were drastically increased, reflecting large increases in wave reflections and decreases in arterial compliances. Changes in Z(o), R(s) and C were quantitatively different between the two forms of loading. DTA occlusion primarily increased Z(o) and R(s) with a concurrently large reduction in C. MTX infusion significantly increased small vessel R(s) to the same extent as DTA occlusion, but with a slight decrease in C secondary to an increase in pressure, with Z(o) unchanged. Examination of dynamic loading showed similar increases in reflection coefficients, but P(f) and P(r) were qualitatively different. We conclude that vasoactive methoxamine infusion provides primarily an increased resistive load, while mechanical DTA occlusion provides an increased complex load to the left ventricle. These loads also occur earlier and variably during ventricular ejection.

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“…Z c was estimated in the time domain as described previously. 20,26,27 Pressure waveforms were decomposed into forward (P f ) and backward (P b ) waves in the time domain 28 ; the ratio of their amplitudes was taken as an index of global reflection, and the extent of their temporal overlap, expressed as a percentage of systolic ejection period, was taken as an index of abnormal reflected wave timing. Proximal aortic compliance per unit length was calculated as described previously.…”

Section: Discussionmentioning

confidence: 99%

Determinants of Elevated Pulse Pressure in Middle-Aged and Older Subjects With Uncomplicated Systolic Hypertension

et al. 2003

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Background-Elevated pulse pressure (PP) is associated with increased cardiovascular risk and is thought to be secondary to elastin fragmentation with secondary collagen deposition and stiffening of the aortic wall, leading to a dilated, noncompliant vasculature. Methods and Results-By use of calibrated tonometry and pulsed Doppler, arterial stiffness and pulsatile hemodynamics were assessed in 128 subjects with uncomplicated systolic hypertension (supine systolic pressure Ն140 mm Hg off medication) and 30 normotensive control subjects of comparable age and gender. Pulse-wave velocity was assessed from tonometry and body surface measurements. Characteristic impedance (Z c ) was calculated from the ratio of change in carotid pressure and aortic flow in early systole. Effective aortic diameter was assessed by use of the water hammer equation. Hypertensives were heavier (PϽ0.001) and had higher PP (PϽ0.001), which was attributable primarily to higher Z c (PϽ0.001), especially in women. Pulse-wave velocity was higher in hypertensives (Pϭ0.001); however, this difference was not significant after adjustment for differences in mean arterial pressure (MAP) (PϾ0.153), whereas increased Z c remained highly significant (PϽ0.001). Increased Z c in women and in hypertensive men was attributable to decreased effective aortic diameter, with no difference in wall stiffness at comparable MAP and body weight. Conclusions-Elevated PP in systolic hypertension was independent of MAP and was attributable primarily to elevated Z c and reduced effective diameter of the proximal aorta. These findings are not consistent with the hypothesis of secondary aortic degeneration, dilation, and wall stiffening but rather suggest that aortic function may play an active role in the pathophysiology of systolic hypertension.

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

Cited by 48 publications

References 16 publications

Aortic Stiffness Determines Diastolic Blood Flow Reversal in the Descending Thoracic Aorta

Aortic Stiffness Determines Diastolic Blood Flow Reversal in the Descending Thoracic Aorta

Pulse Pressure, Arterial Compliance and Wave Reflection Under Differential Vasoactive and Mechanical Loading

Determinants of Elevated Pulse Pressure in Middle-Aged and Older Subjects With Uncomplicated Systolic Hypertension

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