Aortic Compliance Research Articles

Aortic compliance in healthy subjects: evaluation of tissue Doppler imaging

Increased compliance of abdominal aortic aneurysms at maximum diameter over time might be related to rupture. Compliance could, therefore, be valuable in their management. However, such measurement requires a sophisticated system. An original arterial wall-motion measurement technique, based on tissue Doppler imaging (TDI) and providing segmental exploration, was applied to the study of aorta walls. We report its validation in healthy subjects. Technical feasibility was reliable. The time required for sequence acquisition and transfer was suitable for routine clinical use and the quality of the sequences provided precise identification of the aorta wall/lumen interface and accurate segmentation. The values characterising normal aortic compliance were similar to those previously published, and the initial results concerning reproducibility were appropriate for clinical studies. Further refinements may improve it. This study validates the TDI system for measurement of abdominal aortic compliance in healthy subjects. Study of application to aneurysm compliance is in progress. (E-mail: anne.long@hop.egp.ap-hop-paris.fr)

Ultrasonic delineation of aortic microstructure: the relative contribution of elastin and collagen to aortic elasticity.

Aortic elasticity is an important factor in hemodynamic health, and compromised aortic compliance affects not only arterial dynamics but also myocardial function. A variety of pathologic processes (e.g., diabetes, Marfan's syndrome, hypertension) can affect aortic elasticity by altering the microstructure and composition of the elastin and collagen fiber networks within the tunica media. Ultrasound tissue characterization techniques can be used to obtain direct measurements of the stiffness coefficients of aorta by measurement of the speed of sound in specific directions. In this study we sought to define the contributions of elastin and collagen to the mechanical properties of aortic media by measuring the magnitude and directional dependence of the speed of sound before and after selective isolation of either the collagen or elastin fiber matrix. Formalin-fixed porcine aortas were sectioned for insonification in the circumferential, longitudinal, or radial direction and examined using high-frequency (50 MHz) ultrasound microscopy. Isolation of the collagen or elastin fiber matrices was accomplished through treatment with NaOH or formic acid, respectively. The results suggest that elastin is the primary contributor to aortic medial stiffness in the unloaded state, and that there is relatively little anisotropy in the speed of sound or stiffness in the aortic wall.

Aortic adaptation to pregnancy: elevated expression of matrix metalloproteinases-2 and -3 in rat gestation.

The maternal aorta undergoes substantial functional and structural adaptation in pregnancy. Both aortic diameter and compliance are increased and studies of animal and human gestation indicate that these changes are initiated in early pregnancy and maintained until delivery. The mechanisms underlying aortic adaptation in normal pregnancy remain largely unknown but matrix metalloproteinase enzymes (MMP) are likely to play a key role. Gene expression of candidate MMP and specific tissue inhibitors of MMP (TIMP) were investigated in non-pregnant, pregnant (days 7, 14, 21) and postpartum (day 7) rat aorta using real-time PCR. Of the gene transcripts studied (MMP-2, -3, -7, -9, -12, -13, MT1MMP, TIMP-1, -2) in rat aorta, only MMP-3 was significantly elevated with a 24-fold increase observed in late gestation compared to virgin control (P = 0.0001). MMP-2 mRNA appeared constitutively expressed and unchanged at time-points studied, but MMP-2 activity as assessed by gelatin zymography suggested further modulation after transcription and/or post-translation in rat aorta with activity increased in early pregnancy (P < 0.01, compared to virgin control). These data suggest that MMP-2 and MMP-3 may contribute to adaptive processes in the maternal rat aorta at different gestations and further support a role for this family of enzymes in physiological vascular remodelling.

Contractile Responses of Aortae from WKY and SHR to Vasoconstrictors

Aortae taken from spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats aged 4, 8 and 16 weeks were prepared as rings and used to measure the effects of five vasoconstrictors. The endothelium was removed in order to measure selectively the contractile responses induced by potassium chloride (KCl), phenylephrine (PHE), angiotensin‐II (Ang II), endothelin‐1 (ET‐1) and human urotensin‐II (U‐II). These responses were assumed to derive from the activation of specific receptors (namely α1, AT1, ETA and UT‐II) or from depolarization of the smooth muscle fibers by KCl. Specific antagonists prazosin, losartan, BQ‐123 and [Orn8]‐UII were used at various concentrations for a pharmacological characterization of these latter receptor systems. The primary purpose of the study was to explore mechanisms or factors that may intervene in the development and maintenance of high blood pressure in SHR. Results indicate that isolated aortae of SHR and WKY contain contractile sites (receptors) whose pharmacological profiles (pEC50 for agonists, pA2 for antagonists) are very similar to those of other biological systems and should be considered as typical for the α1, AT1, ETA and UT‐II receptor types. Aortae taken from SHR 4 (non hypertensive), 8 and 16 weeks old (hypertensive) responded to the vasoconstrictors with reduced maximal contractions compared to those of age‐matched WKY. These unexpected reduced responses of aortae, observed with the five vasoconstrictors, may be attributed to a non specific lesions. Maximal contraction of aortae from SHR increased from 4 to 16 weeks for KCl, PHE and U‐II, decreased for Ang II, and remained stable for ET‐1. There was also an age‐dependent increase of maximal contraction induced by U‐II in WKY. It is suggested that aortae from SHR undergo early remodelling that leads to reduced contractility in vitro and possibly to vessel rigidity in vivo. The factors involved in this process appear to be of genetic origin since they are present before hypertension: they may contribute to modify aortic compliance and perhaps vascular resistance in hypertensive animals and thus being the cause and not the consequence of high blood pressure.

Severely elevated intrarenal arterial impedance and abnormal venous flow pattern in a normal functioning kidney graft

Serial Doppler sonographic impedance measurements represent the most common diagnostic method for noninvasive monitoring of kidney grafts. Severely elevated arterial impedance is almost always associated with graft dysfunction. However, we describe in the present work a renal transplant recipient with optimal graft function despite permanently elevated arterial impedance (pulsatility index (PI) ranging from 2.9–3.0, and resistive index (RI) = 1.0 as well as an abnormal venous flow pattern. In contrast, the contralateral graft from the same cadaver donors transplanted into a 17-year-old female patient displayed normal range PI and RI values in conjunction with a normal serum creatinine. Known causes of arterial impedance elevation such as rejection, cyclosporine, urinary obstruction, and external graft compression were excluded. Other extrarenal causes of high impedance, such as aortic insufficiency and reduced aortic compliance, were also excluded. No evidence of impaired venous outflow at the site of the anastomosis of the main renal vein to the iliac vein was found. Those findings support the view that impedance indexes are hemodynamic rather than functional parameters.

Relation between conduit vessel stiffness (assessed by tonometry) and endothelial function (assessed by flow-mediated dilatation) in patients with and without coronary heart disease

Endothelial dysfunction and large artery stiffness occur in patients with risk factors for coronary artery disease (CAD) and in those with established CAD. We evaluated the relation between endothelial function and conduit vessel distensibility in normal subjects, in patients with documented stable CAD, and in patients demonstrating only risk factors but no overt atherosclerosis. Endothelium-dependent dilatation was evaluated by way of flow-mediated dilatation of the brachial artery using high-resolution ultrasound. Large artery stiffness was assessed using tonometry. After adjusting for age and intergroup differences, percent flow-mediated dilatation showed statistically significant correlations with several measures of stiffness, including central pulse pressure (r = −0.457, p = 0.019), central systolic pressure (r = −0.442, p = 0.024), peripheral pulse pressure (r = −0.393, p = 0.039), peripheral systolic pressure (r = −0.398, p = 0.036), and proximal aortic compliance (r = 0.390, p = 0.049). Measures of arterial stiffness correlate significantly with those of endothelial function. An increase in large conduit vessel stiffness may represent either a cause or consequence of endothelial dysfunction and may explain why elevated pulse pressure is a new cardiovascular risk factor.

Volume status and blood pressure during long-term hemodialysis: role of ventricular stiffness.

The importance of volume status on blood pressure in hemodialysis patients has long been recognized. We hypothesized that the enhanced volume dependency of blood pressure is partly determined by ventricular stiffness at end systole. A total of 115 long-term hemodialysis patients were invited to receive a comprehensive, noninvasive cardiovascular examination. End-systolic elastance was determined by using a novel, noninvasive echo-Doppler technique. The positive ratios of the interdialytic systolic blood pressure change vs weight gain during the subsequent 25 hemodialysis sessions were averaged to obtain the volume sensitivity index (mm Hg/kg). The averaged interdialytic weight gain per fat-free mass was correlated significantly with averaged percent change in systolic blood pressure (r=0.45, P<0.001). The estimated end-systolic elastance at baseline was significantly correlated with subsequently observed volume sensitivity index (volume sensitivity index=[1.17xend-systolic elastance]+6.4; r=0.34, P=0.001). End-systolic elastance was also significantly correlated with various vascular function parameters, including effective arterial elastance (r=0.48, P<0.001), pulse wave velocity (r=0.30, P=0.001), carotid augmentation index (r=0.31, P<0.001), and aortic compliance (r=-0.49, P<0.001). The results suggest that end-systolic elastance, a direct measure of left ventricular mechanical properties at end systole, is coupled to arterial mechanical properties and predicts the extent of subsequent interdialytic systolic blood pressure rise relative to weight gain. Therefore, ventricular stiffness at end systole is a determinant of the enhanced volume sensitivity of blood pressure in hemodialysis patients.

Determination of aortic compliance from magnetic resonance images using an automatic active contour model

The possibility of monitoring changes in aortic elasticity in humans has important applications for clinical trials because it estimates the efficacy of plaque-reducing therapies. The elasticity is usually quantified by compliance measurements. Therefore, the relative temporal change in the vessel cross-sectional area throughout the cardiac cycle has to be determined. In this work we determined and compared the compliance between three magnetic resonance (MR) methods (FLASH, TrueFISP and pulse-wave). Since manual outlining of the aortic wall area is a very time-consuming process and depends on an operator's variability, an algorithm for the automatic segmentation of the artery wall from MR images through the entire heart cycle is presented. The reliable detection of the artery cross-sectional area over the whole heart cycle was possible with a relative error of about 1%. Optimizing the temporal resolution to 60 ms we obtained a relative error in compliance of about 7% from TrueFISP (1.0 × 1.0 × 10 mm3, signal-to-noise ratio (SNR) > 12) and FLASH (0.7 × 0.7 × 10 mm3, SNR > 12) measurements in volunteers. Pulse-wave measurements yielded an error of more than 9%. In a study of ten volunteers, a compliance between C = 3 × 10−5 Pa−1 and C = 8 × 10−5 Pa−1 was determined, depending on age. The results of the TrueFISP and the pulse-wave measurements agreed very well with one another (confidence interval of 1 × 10−5 Pa−1) while the results of the FLASH method more clearly deviated from the TrueFISP and pulse-wave (confidence interval of more than 2 × 10−5 Pa−1).

Progesterone attenuates the beneficial effects of hormone replacement therapy on large artery elasticity in hypertensive postmenopausal women

Nowadays, based mainly on the results of the Heart and Estrogen/progestin Replacement Study (HERS), the cardiovascular beneficial effects of hormonal replacement therapy (HRT) on cardiovascular morbidity and mortality, are in doubt. In the present study we sought to define the possible differential effects of combined and uncombined HRT on large artery elastic properties in hypertensive postmenopausal women. Towards this end, we studied aortic compliance in 56 postmenopausal women (aged 52 years, 3.4years after menopause) with untreated, mild essential hypertension. Our pooled population was randomized to conjugated estrogen alone (n=20), estrogen plus medroxyprogesterone (n=20) or placebo (n=16) and classified into three groups respectively. At baseline and after 12 weeks of treatment, we evaluated the aortic elasticity non-invasively on the basis of pulse wave velocity (PWV) measurements. In the entire study population BMI was 27.2 Kgr/m2, office BP146/93 mmHg, left ventricular mass index (LVMI) 104±26 gr/m2, and mean plasma levels of total cholesterol 230mg/d. At baseline the three groups were matched for age, time since menopause, smoking status, office blood pressure, BMI, LVMI and PWV values. At 12 weeks of treatment, in the women receiving estrogen alone, aortic PWV was significantly reduced (231 vs 209 cm/sec, p<0.005), while in the women receiving combined HRT or placebo, PWV did not change (232 vs 228 and 233 vs 230 cm/sec, respectively, p=NS for both cases). In all three groups, blood pressure and heart rate values did not change significantly after treatment. At baseline, aortic PWV had a positive correlation with the age of women (r=0.32, p<0.05) and LVMI (r=0.29, p<0.05). In conclusion, long-term combined HRT has no beneficial effects on the augmented large artery stiffness in hypertensive postmenopausal women. These findings confirms the view that progesterone may attenuate the beneficial effects of unopposed HRT on vascular function in the above-mentioned essential hypertensive patients.

Hemodynamics induced after acute reduction of proximal thoracic aorta compliance

Objective: to investigate the affect of reduced aortic compliance on cardiovascular hemodynamics. Materials and Method: fourteen Yucatan miniature swine were divided into two equal groups, a Sham Operated Group and a Banding Group. A Teflon prosthesis was wrapped around the aortic arc in order to limit proximal aortic compliance (Banding Group). Data were recorded operatively (after implantation of a pressure sensor and a flow probe in the ascending aorta), after banding (only in the Banding Group) and at 2 days postoperatively. Results: after banding, compliance decreased by 52 ± 13% (X̄ ± SEM) (p < 0.01) while systolic and pulse pressure increased by 37 ± 8% (p < 0.05) and 87 ± 31% (p < 0.01), respectively. Diastolic pressure, mean blood pressure, cardiac output and systemic vascular resistance did not change significantly. Aortic characteristic impedance increased nearly 2.5 times. Amplitudes of forward and reflected pressure waves (derived from the aortic pressure wave) increased by 96 ± 41% and 174 ± 46%, respectively (p < 0.05), while the time delay between the two decreased by 36 ± 7% (p < 0.05). Conclusions: about half of the total arterial compliance is located in the proximal thoracic aorta. Arterial reconstruction of the proximal aorta with a non-compliant graft results in a significant decrease in systemic arterial compliance, which in turn increases systolic and pulse pressure. The development of more compliant prosthesis, which matches the host artery compliance, is expected to reduce the hemodynamic changes induced after their implantation.Eur J Vasc Endovasc Surg 26, 195-204 (2003)

A computational fluid-structure interaction analysis of a fiber-reinforced stentless aortic valve

The importance of the aortic root compliance in the aortic valve performance has most frequently been ignored in computational valve modeling, although it has a significant contribution to the functionality of the valve. Aortic root aneurysm or (calcific) stiffening severely affects the aortic valve behavior and, consequently, the cardiovascular regulation. The compromised mechanical and hemodynamical performance of the valve are difficult to study both ‘in vivo’ and ‘in vitro’. Computational analysis of the valve enables a study on system responses that are difficult to obtain otherwise. In this paper a numerical model of a fiber-reinforced stentless aortic valve is presented. In the computational evaluation of its clinical functioning the interaction of the valve with the blood is essential. Hence, the blood–tissue interaction is incorporated in the model using a combined fictitious domain/arbitrary Lagrange–Euler formulation, which is integrated within the Galerkin finite element method. The model can serve as a diagnostic tool for clinical purposes and as a design tool for improving existing valve prostheses or developing new concepts. Structural mechanical and fluid dynamical aspects are analyzed during the systolic course of the cardiac cycle. Results show that aortic root compliance largely influences the valve opening and closing configurations. Stresses in the delicate parts of the leaflets are substantially reduced if fiber-reinforcement is applied and the aortic root is able to expand.

Ultrasonic tissue characterization defines the specific role of elastin in maintaining aortic structural integrity and compliance

Ultrasonic tissue characterization defines the specific role of elastin in maintaining aortic structural integrity and compliance

P1692 Aortic compliance correlated with left-ventricular function in patients with coronary heart disease

P1692 Aortic compliance correlated with left-ventricular function in patients with coronary heart disease

Comparison of Aortic Elasticity in Patients With the Marfan Syndrome With and Without Aortic Root Replacement

Aortic elasticity has been identified as a potential risk factor for aortic complications. 1 Imawaki S. Maeta H. Shiraishi Y. Arioka I. Karasawa Y. Shinohara T. Tanaka S. Decrease in aortic distensibility after an extended aortic reconstruction for Marfan’s syndrome as a cause of postoperative acute aortic dissection DeBakey type I a report of two cases. Surg Today. 1993; 23: 1010-1013 Crossref PubMed Scopus (3) Google Scholar , 2 Westaby S. Aortic dissection in Marfan’s syndrome. Ann Thorac Surg. 1999; 67: 1861-1863 Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar , 3 Maeta H. Hori M. Sakai A. Okamura K. Ijima H. Mitsui T. The importance of aortic compliance as a prognostic factor after aortic valve replacement. Nippon Kyobu Geka Gakkai Zasshi. 1989; 37: 2275-2280 PubMed Google Scholar Groenink et al 4 Groenink M. de Roos A. Mulder B.J.M. Verbeeten B. Timmermans J. Zwinderman A.H. Spaan J.A. Van der Wall E.E. Biophysical properties of the normal-sized aorta in patients with Marfan syndrome evaluation with MR flow mapping. Radiology. 2001; 219: 535-540 Crossref PubMed Scopus (120) Google Scholar demonstrated decreased aortic elasticity determined by measurement of local distensibility and flow wave velocity (FWV) with magnetic resonance imaging (MRI) in patients with the Marfan syndrome who did not undergo operation. Aortic elasticity after aortic root replacement (ARR) has not yet been investigated, but Imawaki et al 1 Imawaki S. Maeta H. Shiraishi Y. Arioka I. Karasawa Y. Shinohara T. Tanaka S. Decrease in aortic distensibility after an extended aortic reconstruction for Marfan’s syndrome as a cause of postoperative acute aortic dissection DeBakey type I a report of two cases. Surg Today. 1993; 23: 1010-1013 Crossref PubMed Scopus (3) Google Scholar demonstrated decreased aortic distensibility in patients with the Marfan syndrome after surgery of the abdominal and thoracic aorta. This study investigates the feasibility of MRI for assessing aortic elasticity in patients with the Marfan syndrome after elective ARR, and compares aortic elasticity in these patients with the aortic elasticity of patients with the Marfan syndrome who did not undergo surgery using MRI.

Insights into the effect of aortic compliance on Doppler diastolic flow patterns seen in coarctation of the aorta: A numeric study

Background: In the echocardiographic evaluation of coarctation of the aorta, the degree of antegrade diastolic flow (diastolic runoff) noted on spectral Doppler tracings traditionally was thought to be solely dependent on lesion severity. However, recent in vitro experiments suggest the presence of this spectral Doppler pattern is as much related to the severity of coarctation as it is with changes in aortic compliance. Using state-of-the-art, multidisciplinary, numeric analysis tools, the purpose of this study was to investigate the specific fluid and wall mechanics present in coarctation of the aorta to further understand these relationships. Methods: Three computational numeric models of coarctation were developed with high, low, and no wall compliance. Flow simulations were run representing high- and low-flow states. Results: In both the low- and high-flow states, the degree of diastolic runoff increased with increasing vessel compliance. The high compliance model had larger changes in aortic dilatation in the precoarctation region compared with the low compliance model. Conclusions: Increased aortic compliance brings about greater dilatation of the precoarctation aorta in systole, resulting in a persistence of stored upstream energy. This stored energy, released downstream in diastole as the precoarctation aortic walls contract, leads to increased degrees of diastolic runoff. Numeric methods offer a unique perspective into the mechanisms behind such clinical measures. (J Am Soc Echocardiogr 2003;16:162-9.)

The clinical significance of aortic compliance and its assessment with magnetic resonance imaging.

The biophysical properties of the aortic wall seems to play a significant role in the pathogenesis of cardiovascular disease such as atherosclerosis, hypertension, aneurysm formation, Marfan's syndrome, and in normal aging. The presence and the proportion of smooth muscle, collagen, and elastin proteins contribute to the compliance of the vessel wall with the latter being the most extensible component. However, elastin fibers fracture at low stresses contributing to a decrease of the aortic compliance and consequently to an elevation of the pulse pressure, which is a risk factor of cardiovascular disease. Early detection of a decrease in the aortic compliance could help to identify early cardiovascular disease in asymptomatic patients and monitor the results of the therapeutic interventions. Therefore, estimation of the aortic compliance can be used for both screening as well as long-term follow-up. Magnetic resonance imaging which is a noninvasive, accurate, and reproducible method can estimate the compliance of the aortic wall either by measuring the relative change in cross sectional area of a chosen segment using ECG-triggered spin echo or gradient echo sequences or by measuring the pulse wave velocity through the aorta using the phase contrast-magnetic resonance imaging (PC-MRI) technique. Both techniques have been validated and many sudies suggest MRI as a valuable tool for evaluating aortic wall function. However, large prospective studies are mandatory for the method to be established as a screening tool.

Automatic determination of aortic compliance with cine-magnetic resonance imaging: an application of fuzzy logic theory.

Aortic compliance is defined as the relative change in aortic cross-sectional area divided by the change in arterial pressure. Magnetic resonance imaging (MRI) is a useful imaging modality for the noninvasive evaluation of aortic compliance. However, manual tracing of the aortic contour is subject to important interobserver variations. To estimate the aortic compliance from cine-MRI, a method based on fuzzy logic theory was elaborated. Seven healthy volunteers and eight patients with Marfan syndrome were examined using an ECG gated cine-MRI sequence. The aorta was imaged in the transverse plane at the level of the pulmonary trunk. A method based on fuzzy logic was developed to automatically detect the aortic contour. Through our robust automatic contouring method, the calculation of aortic cross-sectional areas allows an estimation of the aortic compliance. The aortic compliance can be obtained from a fuzzy logic based automatic contouring method, thereby avoiding the important interobserver variation often associated with manual tracing.

Automatic determination of aortic compliance with cine-magnetic resonance imaging - An application of fuzzy logic theory

Automatic determination of aortic compliance with cine-magnetic resonance imaging - An application of fuzzy logic theory

Relation of aortic distensibility determined by magnetic resonance imaging in patients ≥60 years of age to systolic heart failure and exercise capacity

Aortic stiffness increases with advancing age and is associated with the age-related decline in exercise capacity in healthy persons. Previous studies have suggested that aortic compliance is reduced in heart failure (HF). Older persons with systolic HF can have particularly severe exercise intolerance. However, the relation between increased aortic stiffness and exercise intolerance in elderly patients with systolic HF has not been examined. Therefore, aortic distensibility of the proximal ascending aorta (assessed by magnetic resonance imaging) and exercise tolerance (assessed by maximal exercise ergometry with expired gas analysis) was measured in 28 subjects (10 healthy subjects aged 20 to 30 years, 10 healthy subjects aged ≥60 years, and 8 subjects aged ≥60 years with systolic HF). Compared with healthy older subjects, patients with systolic HF had markedly decreased distensibility of the proximal aorta (0.5 ± 0.4 vs 2.2 ± 1.2 10 −3 mm Hg −1, p <0.002), decreased peak exercise volume of oxygen consumption (VO 2) (858 ± 248 vs 1,436 ± 344 ml/min, p <0.001), and increased aortic wall thickness (3.6 ± 0.7 vs 2.9 ± 0.4 mm, p <0.04). Aortic distensibility was significantly correlated with peak VO 2 (r = 0.80, p <0.0001) and remained so even after being adjusted for age and left ventricular (LV) ejection fraction. These data suggest that decreased aortic distensibility may contribute to exercise intolerance in older patients with HF due to LV systolic dysfunction.

Online parameter identification of second-order systemic circulation model using the delta operator.

To develop effective medical care with the artificial heart, we proposed a new method that can calculate the time varying and unmeasured hemodynamics of the human body from measured physiological data: aortic pressure, aortic flow, and pump flow in real time. This method comprises first, the second order of systemic circulation model, which consists of aortic compliance (Ca), aortic resistance (Ra), aortic inertia (L), and total peripheral resistance (Rp); and second, system identification using the delta operator. In the computer simulation, we confirmed the effectiveness of this method. During the animal experiment with the left ventricular assist system, the physiological parameters could be identified online: mean Ra = 0.04 mm Hg s/ml, mean Ca = 0.65 mm Hg/ml, mean L = 0.004 mm Hg s(2)/ml, and mean Rp = 0.3 mm Hg s/ml. This new method efficiently identified the physiological parameters, which are important not only to support the medical care but also to develop the control method adapted to the physiological behavior.