Mechanical Properties Of Carotid Artery Research Articles

An intravascular optical coherence tomography technique for in vivo carotid intima-media thickness measurement and mechanical characterization

Arterial characteristic parameters including the intima-media thickness (IMT), strain, strain rate, elastic modulus, and compliance may be unevenly distributed due to local lesion growth. Thus, a combination of the full-field distribution of these parameters may provide more effective guidance for the diagnosis and treatment of vascular diseases than either one of them. Here, we develop an intravascular coherence tomography (IVOCT) based full-field measurement method to characterize the mechanical properties of carotid artery in vivo. Image processing methods are proposed based on U-Net model and centroid detection for accurate IMT measurement. The strain, strain rate, incremental elastic modulus and volumetric compliance are obtained based on the geometric changes of intima-media. Ex vivo silica gel phantom tests demonstrate the accuracy of the vascular wall segmentation by the U-Net based method is greater than 92%, and the error for elastic modulus measurement is less than 2%. A porcine carotid artery was imaged by IVOCT in vivo, and the IMT and the mechanical characteristics during cardiac cycle were measured. The proposed method facilitates the study of the uneven pathological evolution of the vascular wall and provides an effective measurement method for the study of vascular mechanical properties in vivo.

Alterations in mechanical properties of carotid artery in overweight and obese children

Abstract Background Atherosclerosis begins at a young age in a process that is clinically silent before events occur. Obesity in childhood has been associated with the alterations of vascular properties. Purpose The aim of this study was to investigate the subtle changes of mechanical properties of carotid artery (CA) in overweight and obese children. Methods We prospectively recruited a cohort of overweight (n=25) and obese (n=176) children aged 7–17 years and non-obese children with same age and gender (controls, n=31). Overweight is defined as a body mass index (BMI) at or above the 85th percentile and below the 95th percentile and obesity as a BMI at or above the 95th percentile for children of the same age and gender. The mechanical properties of carotid artery were directly measured in a cross-sectional image of common carotid artery using a velocity-vector imaging (VVI) analysis including instantaneous vessel area and deformation parameters as fractional area change (FAC), circumferential strain, and strain rate (SR). Results Compared to controls, obese children had higher blood pressures and serum glucose and worse lipid profiles than controls, whereas overweight children showed no any difference in blood pressure and laboratory findings. Among vascular properties, there were no differences in carotid intima-media thickness (cIMT) between the three groups. However, obese children showed larger vessel area and higher arterial stiffness presented as lower FAC, circumferential strain and SR than controls, whereas overweight children showed no difference in vascular properties with obese children and with controls except for circumferential SR. Circumferential SR in overweight children was significantly reduced than controls (0.47±0.19 cm/s, 0.75±0.22 cm/s, respectively, p<0.001) and was the only vascular parameter distinguishing overweight children from controls. In multiple linear regression analysis, independent determining factors of the circumferential SR of carotid artery were age (β=−0.13, p=0.03), serum triglycerides (β=−0.14, p=0.01) and BMI (β=−0.37, p<0.001) in this population. Conclusions In overweight and obese children, a decrease in circumferential SR of carotid artery precedes the changes of vessel wall thickness and vessel area. We demonstrated the subtle changes of mechanical properties of carotid artery precede the changes of structural properties in overweight and obese children. Funding Acknowledgement Type of funding source: None

Abstract 123: Subtle Changes in Mechanical Properties of Carotid Artery in Overweight and Obese Children

Objective: Obesity in childhood has also been associated with the development of cardiovascular abnormalities. The aim of this study was to investigate the subtle changes of mechanical properties of carotid artery in overweight and obese children. Methods: We prospectively recruited a cohort of overweight (n=25) and obese (n=176) children aged 7 - 17 years and non-obese children with same age and gender (controls, n=31). Overweight is defined as a body mass index (BMI) at or above the 85th percentile and below the 95th percentile and obesity as a BMI at or above the 95th percentile for children of the same age and gender. The mechanical properties of carotid artery were directly measured in a cross-sectional image of common carotid artery using a velocity-vector imaging (VVI) analysis including instantaneous vessel area and deformation parameters as fractional area change (FAC), circumferential strain, and strain rate (SR). Results: Compared to controls, obese children had higher blood pressures and serum glucose and worse lipid profiles than controls, whereas overweight children showed no any difference in blood pressure and laboratory findings. Among vascular properties, there were no differences in carotid intima-media thickness between the three groups. However, obese children showed larger vessel area and higher arterial stiffness as lower FAC, circumferential strain and SR than controls, whereas overweight children showed no difference in vascular properties with obese children and with controls except for circumferential SR. Circumferential SR in overweight children was significantly reduced than controls (0.47±0.19 cm/s, 0.75±0.22 cm/s, respectively, p<0.001) and was the only vascular parameter distinguishing overweight children from controls. In linear regression analysis, age (β=-0.13, p=0.03), BMI (β=- 0.37, p<0.001), and serum triglycerides (β=-0.14, p=0.01) were independent determinants predicting the circumferential SR of carotid artery in this population. Conclusion: A decrease in circumferential SR of carotid artery precedes the changes of other vascular properties as well as blood pressure and laboratory findings in overweight and obese children.

Carotid artery stiffness is related to hyperinsulinemia and insulin-resistance in middle-aged, non-diabetic hypertensive patients

Background and aimsGlycometabolic abnormalities are frequently found in hypertension and could affect the mechanical properties of carotid arteries. The aim of the study was to investigate the relationship of glucose tolerance, plasma insulin, and insulin sensitivity with carotid distensibility in middle-aged, non-diabetic hypertensive patients free of cardiac and vascular complications. Method and resultsIn 93 patients with grade 1–2, uncomplicated, primary hypertension and 68 matched normotensive controls we measured plasma glucose and insulin at fast and after an oral glucose load (OGTT), calculated the HOMA-index as a marker of insulin sensitivity, and assessed distensibility of common carotid arteries by B-mode ultrasonography. Hypertensive patients were hyperinsulinemic and insulin-resistant as compared to normotensive controls. Hypertensive patients with impaired fasting glucose and/or impaired glucose tolerance had comparable distensibility of carotid arteries. Patients with decreased carotid distensibility were older and had higher body mass, fasting and post-OGTT plasma insulin, HOMA-index, and carotid IMT than the remaining patients, but no differences in glycated hemoglobin, and fasting or post-OGTT plasma glucose. Carotid coefficient of distensibility was inversely related and β-stiffness directly related with fasting and post-OGTT plasma insulin, and HOMA-index. Multivariate logistic regression showed that age and post-OGTT plasma insulin levels predicted carotid artery stiffening independent of body mass index, sex, blood pressure, and plasma glucose levels. ConclusionsThe study demonstrates that decreased insulin sensitivity and the related hyperinsulinemia but not hyperglycemia could contribute to carotid artery stiffening in middle-aged, non-diabetic hypertensive patients free of cardiovascular complications.

PP.20.36

Objective: Fibromuscular dysplasia (FD) is a rare idiopathic, segmental, non-atherosclerotic, non-inflammatory vascular disease, which occurs mostly in middle-aged patients and affects medium-sized arteries (renal and carotid arteries). We previously showed that renal FD is associated with supernumerary echo interfaces (triple signal pattern) detectable on echotracking tracings of the carotid artery (CA) compared to healthy subjects (HS), but we did not study patients with essential hypertension (EH). Design and method: In a cross sectional study, we compared the geometry and the mechanical properties of CA between 50 patients with multifocal FD of renal/carotid arteries, 50 patients with EH matched for age, sex, ethnicity and BP and 50 HS matched for age, sex and ethnicity. We used 1) a high-resolution radiofrequency–based echotracking system to perform a semiquantitative arterial phenotypic scoring and to detect additional interface at the level of the CA wall, and 2) Sphygmocor® to measure carotid-to-femoral pulse wave velocity (PWV). All measurements were performed blind to the diagnosis. Results: FD, EH and HS were well matched (52yrs, 85% women, 80%caucasian). SBP was higher in FD (125 ± 15 mmHg) and EH (121 ± 12 mmHg) than EH (113 ± 10 mmHg) despite antihypertensive treatments. The FD score was significantly higher and the triple signal pattern was observed more frequently in both FD and EH than in HS, with no difference between FD and EH. This was also the case for PWV. All other parameters (CA diameter, distensibility and intima-media thickness [IMT]) did not significantly differ between the 3 groups.Conclusions: In conclusion, even though the FD score is much higher and the prevalence of the triple signal is largely more frequent at the level of CA and PWV is higher in FD than in age, sex-, ethnicity-matched HS, this arterial phenotype is not specific for FD when compared to age-, sex- and BP-matched EH.

The relationship between mechanical properties of carotid artery and coronary artery disease

Carotid intima-media thickness (CIMT) is a useful indicator of coronary artery disease (CAD). The relation between functional changes of the common carotid artery (CCA) and CAD is unclear. This study investigated the relationship between CCA strain and CIMT in the assessment of CAD. Within a 1-month period, 121 patients underwent coronary angiography and ultrasonography of the CCA. Circumferential strain and strain rate were measured in the left CCA by 2D ultrasonography with a speckle tracking method and CIMT was measured using standard techniques. Adequate images were obtained in 104 patients (59 ± 11 years, 39 females), of which 46 had CAD. Strain and strain rate were negatively correlated with CIMT and were positively correlated with the number of risk factors. CIMT was significantly higher, and strain and strain rate were significantly lower in the CAD group (OR, 95% CI, P-value, CIMT: 23.23, 2.03-265.30, 0.011; strain: 0.51, 0.31-0.82, 0.006; strain rate: 0.01, 0.00-0.13, 0.001). However, after adjustment for cardiovascular risk factors, only strain and strain rate were significantly associated with CAD (OR, 95% CI, P-value, CIMT: 5.28, 0.28-99.84, 0.267; strain: 0.51, 0.30-0.88, 0.014; strain rate: 0.01, 0.00-0.42, 0.014). CAD severity, assessed by the number of stenosed coronary arteries, was also significantly correlated with strain and strain rate, but was not significantly correlated with CIMT. Both CIMT and CCA strain were associated with CAD. CAD severity and extent were correlated with strain and strain rate, but were not correlated with CIMT. The evaluation of mechanical properties of CCA by ultrasonographic 2D strain imaging could therefore be more effective than that by CIMT for the assessment of CAD.

Two-dimensional speckle-tracking strain imaging in the assessment of mechanical properties of carotid arteries: feasibility and comparison with conventional markers of subclinical atherosclerosis

The aim of our study was to assess the two-dimensional carotid strain as an index of arterial stiffness in a population of patients without carotid atherosclerotic plaques. Two-dimensional carotid strain, carotid intima-media thickness (CIMT), stiffness index (β), Peterson's elastic modulus, and distensibility coefficient were evaluated in 47 patients. For all patients, cardiovascular risk scores were calculated. Peak systolic circumferential strain was significantly correlated with conventional indices of arterial stiffness and with the CIMT. Peak systolic circumferential strain adjusted for pulse pressure was the only parameter that showed a significant difference between the three cardiovascular risk groups in which patients were classified. Two-dimensional carotid strain showed an excellent reproducibility. The two-dimensional strain allows the assessment of carotid arterial mechanics. Probably the assessment of arterial stiffness allows a better risk stratification of patients.

Performance evaluation of different implementations of the Lagrangian speckle model estimator for non-invasive vascular ultrasound elastography

Non-invasive vascular ultrasound elastography (NIVE) was recently introduced to characterize mechanical properties of carotid arteries for stroke prevention. Using the Lagrangian speckle model estimator (LSME), the four components of the 2D deformation matrix (delta), which are the axial strain (delta(yy)) and shear (delta(yx)) and the lateral strain (delta(xx)) and shear (delta(xy)), can be computed. This paper overviews four different implementations of the LSME and addresses their reliability. These implementations include two unconstrained (L&M and L&M+) and one constrained (ITER(c)) iterative algorithms, and one optical flow-based (OF-based) algorithm. The theoretical frameworks were supported by biomechanical simulations of a pathology-free vessel wall and by one single layer vessel-mimicking phantom study. Regarding simulations, the four LSME implementations provided similar biases on axial motion parameters, except the L&M that outperformed other methods with a minimum strain bias of -3%. LSME axial motion estimates showed good consistence with theory, namely the OF-based algorithm that in a specific instance estimated delta(yy) with no relative error on the standard deviation. With regards to lateral motion parameters, ITER(c) exhibited a minimum strain bias of -8.5% when ultrasound beam and motion mostly run parallel, whereas L&M performs strain and shear estimates with less than 23% bias independently of orientations. The in vitro vessel phantom data showed LSME delta(yy) and delta(yx) maps that were qualitatively equivalent to theory, and noisy delta(xx) and delta(xy) elastograms. In summary, the authors propose to promote the OF-based LSME as an optimal choice for further applications of NIVE, because of its reliability to compute both axial strain and shear motion parameters and because it outperformed the other implementations by a factor of 30 or more in terms of processing time.

Biaxial Mechanical Properties of Carotid Arteries From Normotensive and Hypertensive Rats

Hypertension is known to decrease arterial distensibility and volumetric compliance, as reported from pressure-volume experiments and ring and strip studies of human and animal large arteries. However, recent data using noninvasive in vivo recording of vessel diameter suggest that the cross-sectional compliance of large arteries can be unchanged or even increased in hypertensive subjects. The present study was performed to test the hypothesis that differences between volumetric and cross-sectional compliance could be related to differences in biaxial mechanical properties in normotensive and hypertensive rats. In normotensive (Wistar-Kyoto [WKY]) rats and spontaneously hypertensive rats (SHR) we measured the simultaneous changes in length and diameter of in situ isolated carotid arteries submitted to static pressures (50 to 200 mm Hg by steps of 25 mm Hg each). Carotid artery diameters and lengths were determined by video microscopy and computer-assisted image analysis. At low transmural pressure (50 mm Hg), carotid artery diameter was 710 +/- 41 microns in WKY rats and 980 +/- 31 microns in SHR (P < .01). In response to pressure increases, the carotid diameter increased by 91 +/- 6% in WKY rats and by 41 +/- 4% in SHR (P < .01). In parallel, the percent increase in carotid length was much larger in WKY rats than in SHR (31 +/- 2% versus 7 +/- 1%, respectively; P < .01). In WKY rats, longitudinal distensibility causes significantly larger volumetric values than cross-sectional compliance values; in contrast, because of the very small longitudinal distensibility, volumetric and cross-sectional compliances are almost identical in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chronic dihydropyridine (isradipine) on the large arterial walls of spontaneously hypertensive rats.

The effect of genetic hypertension and of chronic therapy by calcium entry blocker (CEB, isradipine) on the function and structure of large arteries has been studied in adult spontaneously hypertensive rats (SHR, n = 30) and in their normotensive control Wistar-Kyoto (WKY) rats (n = 30). Fifteen-week-old rats were randomly allocated to treatment with isradipine (3 mg/kg subcutaneously once a day) or to placebo and followed for 12 weeks. Hemodynamic parameters, including instantaneous pressure and aortic velocity, were recorded under anesthesia at the end of the treatment period. Passive mechanical properties of carotid arteries were measured in situ in the presence or the absence of smooth muscle cell activity (potassium cyanide poisoning). Histomorphometric parameters of the carotid and aortic media, including cross-sectional area, medial thickness, nucleus density and size, and medial contents of proteins of interstitial matrix, were measured by an automated morphometric system. Untreated SHRs had greater peripheral resistance, stiffer and thicker arterial walls because of smooth muscle cell hyperplasia (thoracic aorta and carotid artery) and/or hypertrophy (thoracic aorta), and increased collagen content than did normotensive control rats. SHRs showed a significant left ventricular hypertrophy. For the whole duration of treatment, treatment with CEB normalized the arterial pressure in SHRs. We observed a significant decrease in peripheral resistance, increased cardiac output, and left ventricular contractility without significant reduction in left ventricular hypertrophy. Increases in diuresis and natriuresis were associated during the last week of treatment in both treated strains with marked increase in plasma renin activity; in contrast, urinary aldosterone was increased by treatment in WKY rats but not in SHRs. Arterial compliance was significantly increased by CEB under control and passive conditions. CEB induced a significant reduction in the medial hypertrophy of the aortic walls of SHRs and WKY rats associated with a reduction in medial hyperplasia. In the carotid artery, CEB reduced smooth muscle cell hypertrophy but did not affect the smooth muscle cell hyperplasia. Isradipine significantly reduced the arterial wall collagen contents in both strains, with marked increases in the elastin content in the carotid but not in the aortic wall. These results suggest that (1) despite normalization of arterial pressure, chronic treatment with CEB in SHRs does not significantly reduce left ventricular hypertrophy, probably because of increase in myocardial contractility and/or increase in plasma renin activity; (2) mechanical properties of the arterial wall are normalized by treatment; and (3) remodeling of the arterial wall by CEB is not uniform according to the studied vessel.

The renin-angiotensin system and arterial wall behavior.

To assess the behavior of the arterial wall in hypertensive patients, we developed a noninvasive ultrasonic device. Simultaneous recordings of internal diameter and blood pressure over the whole cardiac cycle are used to establish compliance-pressure curves. Blood pressure, which is a co-determinant of compliance, is thus taken into account. This method allows one to compare arteries from patients with different blood pressures. Arterial compliance and distensibility were first investigated in healthy young volunteers administered either lisinopril (20 mg), atenolol (100 mg) or nitrendipine (20 mg) once a day. After 8 days of treatment, only lisinopril was found to increase arterial compliance. Subsequently, we compared arterial diameter- and distensibility-pressure curves from newly diagnosed and untreated hypertensive patients with those of matched normotensive control patients. Diameter-pressure curves did not differ significantly between the groups and distensibility was not reduced. Similar findings were later obtained in an animal model, when mechanical properties of carotid arteries were compared between spontaneously hypertensive rats and normotensive counterparts (Wistar-Kyoto rats). These results, although interesting by providing noninvasive information on the elastic response of the wall, call for further development of the technique to be able to measure arterial wall thickness. Stress-strain relationship could ultimately be established to thoroughly characterize physical properties of blood vessel walls.

In vitro assessment of diameter-pressure relationship in carotid arteries from normotensive and spontaneously hypertensive rats

To compare the mechanical properties of carotid arteries from normotensive and spontaneously hypertensive rats. The pressure-diameter relationships of carotid arteries from nine normotensive adult Wistar-Kyoto (WKY) and nine spontaneously hypertensive rats (SHR) were measured in vitro under control conditions and after poisoning the smooth muscle cells with potassium cyanide. Changes in diameter due to changes in transmural pressure were determined with an ultrasonic dimensiometer (12 MHz). The diameter values were determined from the transit times of the pair of echoes given by the proximal and distal walls. The carotid artery was submitted to stepwise increases in pressure of 25 mmHg, from 0 to 200 mmHg; each pressure level was maintained for 5 min before the arterial diameter was recorded. The carotid artery pressure-diameter relationship was a sigmoid curve in both strains. At the same level of pressure, the diameter of the carotid artery from SHR was significantly larger than that from normotensive rats (P < 0.05). Furthermore, the diameter values measured at the operating mean arterial pressure (roughly 100 mmHg for WKY rats and 150 mmHg for SHR) were markedly different (P < 0.001). In both strains, the diameter under passive conditions (with potassium cyanide) was significantly larger than that measured under control conditions (P < 0.01). Carotid arteries from SHR were significantly stiffer than those from WKY rats. Due to the pressure-dependency of the arterial wall stiffness, the increased arterial stiffness reported in hypertensive rats in vivo is related to an increase in distending arterial pressure and also to a significant reduction in the intrinsic compliance of the arterial wall.

Effect of chronic treatment by atrial natriuretic peptide on hemodynamic parameters and mechanical properties of carotid arteries in normotensive and spontaneously hypertensive rats: M.C. Mourlon-Le Grand, P. Poitevin, B. Lévy. INSERM U141, Hoˆpital Lariboisière, 41 bd de la Chapelle, 75010 Paris, France

Effect of chronic treatment by atrial natriuretic peptide on hemodynamic parameters and mechanical properties of carotid arteries in normotensive and spontaneously hypertensive rats: M.C. Mourlon-Le Grand, P. Poitevin, B. Lévy. INSERM U141, Hoˆpital Lariboisière, 41 bd de la Chapelle, 75010 Paris, France

Mechanical properties of carotid arteries from DOCA hypertensive swine.

Carotid arteries from control and deoxycorticosterone acetate (DOCA) hypertensive swine were examined for alterations in structure and in contractile properties. Vessels were excised 7 weeks after subcutaneous implantation of the steroid and subsequent elevation in mean arterial pressure from 102 to 133 mm Hg. The carotid media was 1.8 times thicker in arteries from hypertensive animals than in arteries from control animals. This enlargement was associated with an increase in muscle mass, as the fraction of the media composed of smooth muscle cells remained unchanged. Maximal active stress induced by several agonists normalized for cell cross-sectional area was unaltered. No change was observed in sensitivity or maximal response to norepinephrine, histamine, or KCl depolarization. Isotonic shortening rates were also comparable, as was the time course of shortening velocity to a constant afterload during tonic contractions. It is concluded that an enlargement of the carotid media develops in this model of hypertension. However, this response is not associated with detectable alterations in contractile system function.

Effects of chronic inhibition of converting enzyme on mechanical and structural properties of arteries in rat renovascular hypertension.

The effect of hypertension and of therapy by converting enzyme inhibitor (S 9490-3, perindopril) on the function and structure of large arteries has been studied in two-kidney, one-clip Goldblatt hypertensive rats. After one month without treatment, clipped hypertensive rats (n = 24) and sham-operated rats (n = 24) were randomly allocated to treatment by S 9490, 1 mg/kg once a day (n = 24) or to placebo (n = 24) and pursued for 4 weeks. Hemodynamic parameters, including instantaneous pressure and aortic velocity measured by Döppler, were recorded under anesthesia at the end of the treatment period. Passive mechanical properties of carotid arteries were recorded in situ in the presence or the absence of smooth muscle cell activity (potassium cyanide poisoning). Morphological parameters of the aortic media, including medial thickness, nucleus density, and cross sectional area and relative density in proteins of interstitial matrix, were recorded by an automated morphometrical system. Hypertension was associated with an increase in characteristic impedance of the aorta and a decrease in compliance of the arterial system. Treatment with converting enzyme inhibitors completely reversed these in vivo markers of the rigidity of large arteries. Hypertension was associated with a shift of the passive pressure-volume relation in the carotid. Treatment with converting enzyme inhibitors normalized the carotid pressure-volume relation, whereas poisoning smooth muscle cells induced a disappearance of the curve differences between hypertensive and normotensive animals. Morphometric analysis of aortic walls permits us to report this functional change to structural modification of the arterial wall. Aortic media thickness was increased by hypertension; this phenomenon was reversed by treatment. Modification of aortic thickness was due to hypertrophy of smooth muscle cells with parallel modifications of absolute amount of collagen, whereas absolute amount of elastin did not change in this early phase of renovascular hypertension in young rats. Treatment with converting enzyme inhibitors reversed the thickness of aortic media without regression of the increase in absolute amount of collagen content whereas absolute amount of elastin content did not change.

Effects of sex hormones on the passive mechanical properties of rat carotid artery.

The effects of chronic administration of estradiol and testosterone on the passive mechanical properties of carotid arteries were determined using castrated and noncastrated male rats. Blood vessel segments were removed from the animals and mounted in a bath at &lt;i&gt;in vivo&lt;/i&gt; length. Measurements of external diameter and transmural pressure were made in response to inflation in the presence of smooth muscle inhibitors. These data were used to determine stress-strain relations and values of incremental elastic moduli for the various arteries. Relative to arteries from control animals, passive tangential stress-strain curves for arteries from estradiol treated rats were found to be shifted significantly to the right, i.e., to larger strains. Similar data for testosterone-treated arteries were shifted to the left, but the effect was smaller than the former one and only significant for values of tangential stress greater than 2 × 10&lt;sup&gt;–6&lt;/sup&gt; dyn/cm&lt;sup&gt;2&lt;/sup&gt;. At specific values of wall strain, estradiol produced a decrease in incremental elastic modulus relative to the arteries from control animals, while testosterone produced an increase in elastic modulus which was only significant for strains &gt; 0.7. Quantitatively, similar results were found in castrated and noncastrated rats. These results are consistent with the concepts that estradiol decreases the stiffness of arteries while testosterone to a smaller degree increases the latter through the effects of these steroids on connective tissue accumulation in the arterial wall.