Pressure-independent relationship of aortic characteristic impedance with left ventricular mass and geometry in untreated hypertension

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Abstract

We investigated whether aortic characteristic impedance (Zc), that is, the ratio between the pulsatile change in pressure and flow in the proximal aorta, is related to left ventricular hypertrophy and geometry independently of blood pressure (BP). A total of 438 never-treated hypertensive individuals (men 62%, age 48 ± 11 years, BP 147/90 ± 16/10 mm Hg) underwent echocardiography and 24 h BP monitoring. Aortic pressure waveform was obtained from radial tonometry with a generalized transfer function (SphygmoCor). Using a validated aortic blood flow model based on higher order Windkessel theory (ARCSolver), aortic Zc, forward (Pf) and backward (Pb) wave amplitudes and their ratio (Pb/Pf = reflection magnitude) were calculated from central waveform.

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Prospective evaluation of a method for estimating ascending aortic pressure from the radial artery pressure waveform.

A Pauca, M F O'Rourke, N Kon (2001)

Pressure wave reflection in the upper limb causes amplification of the arterial pulse so that radial systolic and pulse pressures are greater than in the ascending aorta. Wave transmission properties in the upper limbs (in contrast to the descending aorta and lower limbs) change little with age, disease, and drug therapy in adult humans. Such consistency has led to use of a generalized transfer function to synthesize the ascending aortic pressure pulse from the radial pulse. Validity of this approach was tested for estimation of aortic systolic, diastolic, pulse, and mean pressures from the radial pressure waveform. Ascending aortic and radial pressure waveforms were recorded simultaneously at cardiac surgery, before initiation of cardiopulmonary bypass, with matched, fluid-filled manometer systems in 62 patients under control conditions and during nitroglycerin infusion. Aortic pressure pulse waves, generated from the radial pulse, showed agreement with the measured aortic pulse waves with respect to systolic, diastolic, pulse, and mean pressures, with mean differences <1 mm Hg. Control differences in Bland-Altman plots for mean+/-SD in mm Hg were systolic, 0.0+/-4.4; diastolic, 0.6+/-1.7; pulse, -0.7+/-4.2; and mean pressure, -0.5+/-2.0. For nitroglycerin infusion, differences respectively were systolic, -0.2+/-4.3; diastolic, 0.6+/-1.7; pulse, -0.8+/-4.1; and mean pressure, -0.4+/-1.8. Differences were within specified limits of the Association for the Advancement of Medical Instrumentation SP10 criteria. In contrast, differences between recorded radial and aortic systolic and pulse pressures were well outside the criteria (respectively, 15.7+/-8.4 and 16.3+/-8.5 for control and 14.5+/-7.3 and 15.1+/-7.3 mm Hg for nitroglycerin). Use of a generalized transfer function to synthesize radial artery pressure waveforms can provide substantially equivalent values of aortic systolic, pulse, mean, and diastolic pressures.

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Sex differences in arterial stiffness and ventricular-arterial interactions.

Barry Borlaug, Patricia A. Pellikka, Stephen T. Turner … (2013)

This study sought to assess sex differences in ventricular-arterial interactions. Heart failure with preserved ejection fraction is more prevalent in women than in men, but the basis for this difference remains unclear. Echocardiography and arterial tonometry were performed to quantify arterial and ventricular stiffening and interaction in 461 participants without heart failure (189 men, age 67 ± 9 years; 272 women, age 65 ± 10 years). Aortic characteristic impedance (Z(c)), total arterial compliance (pulsatile load), and systemic vascular resistance index (steady load) were compared between men and women, and sex-specific multivariable regression analyses were performed to assess associations of these arterial parameters with diastolic dysfunction and ventricular-arterial coupling (effective arterial elastance/left ventricular end-systolic elastance [Ea/Ees]) after adjustment for potential confounders. Z(c) was higher and total arterial compliance was lower in women, whereas systemic vascular resistance index was similar between sexes. In women but not men, higher log Z(c) was associated with mitral inflow E/A ratio (β ± SE: -0.17 ± 0.07), diastolic dysfunction (odds ratio: 7.8; 95% confidence interval: 2.0 to 30.2) and Ea/Ees (β ± SE: 0.13 ± 0.04) (p ≤ 0.01 for all). Similarly, total arterial compliance was associated with E/A ratio (β ± SE: 0.12 ± 0.04), diastolic dysfunction (odds ratio: 0.33; 95% confidence interval: 0.12 to 0.89), and Ea/Ees (β ± SE: -0.09 ± 0.03) in women only (p ≤ 0.03 for all). Systemic vascular resistance index was not associated with diastolic dysfunction or Ea/Ees. Proximal aortic stiffness (Z(c)) is greater in women than men, and women may be more susceptible to the deleterious effects of greater pulsatile and early arterial load on diastolic function and ventricular-arterial interaction. This may contribute to the greater risk of heart failure with preserved ejection fraction in women. Copyright © 2013 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

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Relationship between short-term blood pressure variability and large-artery stiffness in human hypertension: findings from 2 large databases.

Giuseppe Schillaci, Grzegorz Bilo, Giacomo Pucci … (2012)

Short-term blood pressure (BP) variability predicts cardiovascular complications in hypertension, but its association with large-artery stiffness is poorly understood and confounded by methodologic issues related to the assessment of BP variations over 24 hours. Carotid-femoral pulse wave velocity (cfPWV) and 24-hour ambulatory BP were measured in 911 untreated, nondiabetic patients with uncomplicated hypertension (learning population) and in 2089 mostly treated hypertensive patients (83% treated, 25% diabetics; test population). Short-term systolic BP (SBP) variability was calculated as the following: (1) SD of 24-hour, daytime, or nighttime SBP; (2) weighted SD of 24-hour SBP; and (3) average real variability (ARV), that is, the average of the absolute differences between consecutive SBP measurements over 24 hours. In the learning population, all of the measures of SBP variability showed a direct correlation with cfPWV (SD of 24-hour, daytime, and nighttime SBP, r=0.17/0.19/0.13; weighted SD of 24-hour SBP, r=0.21; ARV, r=0.26; all P<0.001). The relationship between cfPWV and ARV was stronger than that with 24-hour, daytime, or nighttime SBP (all P<0.05) and similar to that with weighted SD of 24-hour SBP. In the test population, ARV and weighted SD of 24-hour SBP had stronger relationships with cfPWV than SD of 24-hour, daytime, or nighttime SBP. In both populations, SBP variability indices independently predicted cfPWV along with age, 24-hour SBP, and other factors. We conclude that short-term variability of 24-hour SBP shows an independent, although moderate, relation to aortic stiffness in hypertension. This relationship is stronger with measures of BP variability focusing on short-term changes, such as ARV and weighted 24-hour SD.