Age and sex-dependent sensitivity analysis of a common carotid artery model.

The common carotid artery (CCA) is an accessible and informative site for assessing cardiovascular function which makes it a prime candidate for clinically relevant computational modelling. The interpretation of supplemental information possible through modelling is encumbered by measurement uncertainty and population variability in model parameters. The distribution of model parameters likely depends on the specific sub-population of interest and delineation based on sex, age or health status may correspond to distinct ranges of typical parameter values. To assess this impact in a 1D-CCA-model, we delineated specific sub-populations based on age, sex and health status and carried out uncertainty quantification and sensitivity analysis for each sub-population. We performed a structured literature review to characterize sub-population-specific variabilities for eight model parameters without consideration of health status; variations for a healthy sub-populations were based on previously established references values. The variabilities of diameter and distensibility found in the literature review differed from those previously established in a healthy population. Model diameter change and pulse pressure were most sensitive to variations in distensibility, while pressure was most sensitive to resistance in the Windkessel model for all groups. Uncertainties were lower when variabilities were based on a healthy sub-population; however, the qualitative distribution of sensitivity indices was largely similar between the healthy and general population. Average sensitivity of the pressure waveform showed a moderate dependence on age with decreasing sensitivity to distal resistance and increasing sensitivity to distensibility and diameter. The female population was less sensitive to variations in diameter but more sensitive to distensibility coefficient than the male population. Overall, as hypothesized input variabilities differed between sub-populations and resulted in distinct uncertainties and sensitivities of the 1D-CCA-model outputs, particularly over age for the pressure waveform and between males and females for pulse pressure.

Interstitial flow, pressure and residual stress in the aging carotid artery model in FEBio.

Vascular smooth muscle cells (VSMCs) are subject to interstitial flow-induced shear stress, which is a critical parameter in cardiovascular disease progression. Transmural pressure loading and residual stresses alter the hydraulic conductivity of the arterial layers and modulate the interstitial fluid flux through the arterial wall. In this paper, a biphasic multilayer model of a common carotid artery (CCA) with anisotropic fiber-reinforced soft tissue and strain-dependent permeability is developed in FEBio software. After the verification of the numerical predictions, age-related arterial thickening and stiffening effects on arterial deformation and interstitial flow are computed under physiological geometry and physical parameters. We found that circumferential residual stress shifts outward in each layer and its gradient increases up to 6 times with aging. Internally pressurized CCA displays nonlinear deformation. In the aged artery, the circumferential stress becomes greater on the media layer (82-158 kPa) and lower on the intima and adventitia (19-23 kPa and 25-28 kPa, respectively). The radial compression of the intima reduces the total hydraulic conductivity by 48% in the young and 16% in the aged arterial walls. Consequently, the average radial interstitial flux increases with pressure by 14% in the young and 91% in the aged arteries. Accordingly, the flow shear stress experienced by the VSMCs becomes more significant for aged arteries, which may accelerate cardiovascular disease progression compared to young arteries.

Effect of left paratracheal pressure on left carotid blood flow.

INTRODUCTION: Gautier et al. demonstrated that a compression in the left paratracheal region (left paratracheal pressure, LPP) can be used to seal the oesophagus. However, at this level, the left common carotid artery is very close to the carotid that could be affected during the manipulation. This study aimed to assess the hemodynamic effects of LPP on the carotid blood flow. METHODS: We prospectively included 47 healthy adult volunteers. We excluded pregnant women and people with anomalies of the carotid arteries. The common and internal carotid arteries were preliminarily studied with ultrasounds to exclude atheromatous plaques or vascular malformation. A planimetry of the common and internal carotid arteries was performed. Doppler echography served to measure the peak systolic (PSV) and end-diastolic velocities (EDV) in the common and internal carotid arteries. All measurements were repeated while applying LPP. RESULTS: Forty-seven participants were enrolled (32 women; mean [SD] age: 42 [13] years). The mean PSV difference [95% CI] in the left common carotid artery before and after LPP at the group level was -15.30 [-31.09 to 0.48] cm s-1 (p = .14). The mean surface difference [95% CI] in the left common carotid artery before and after LPP was 24.52 [6.11-42.92] mm2 (p = .11). Similarly, the same surface at the level of the left internal carotid artery changed by -18.89 [-51.59 to 13.80] mm2 after LPP (p = .58). CONCLUSIONS: Our results suggest that LPP does not have a significant effect on carotid blood flow in individuals without a carotid pathology. However, the safety of the manoeuvre should be evaluated in patients at risk of carotid anomalies.

In Vivo Material Properties of Human Common Carotid Arteries: Trends and Sex Differences.

INTRODUCTION: In vivo estimation of material properties of arterial tissue can provide essential insights into the development and progression of cardiovascular diseases. Furthermore, these properties can be used as an input to finite element simulations of potential medical treatments. MATERIALS AND METHODS: This study uses non-invasively measured pressure, diameter and wall thickness of human common carotid arteries (CCAs) acquired in 103 healthy subjects. A non-linear optimization was performed to estimate material parameters of two different constitutive models: a phenomenological, isotropic model and a structural, anisotropic model. The effect of age, sex, body mass index and blood pressure on the parameters was investigated. RESULTS AND CONCLUSION: Although both material models were able to model in vivo arterial behaviour, the structural model provided more realistic results in the supra-physiological domain. The phenomenological model predicted very high deformations for pressures above the systolic level. However, the phenomenological model has fewer parameters that were shown to be more robust. This is an advantage when only the physiological domain is of interest. The effect of stiffening with age, BMI and blood pressure was present for women, but not always for men. In general, sex had the biggest effect on the mechanical properties of CCAs. Stiffening trends with age, BMI and blood pressure were present but not very strong. The intersubject variability was high. Therefore, it can be concluded that finding a representative set of parameters for a certain age or BMI group would be very challenging. Instead, for purposes of patient-specific modelling of surgical procedures, we currently advise the use of patient-specific parameters.

Response of the carotid artery longitudinal motion to submaximal physical activity in healthy humans-Marked changes already at low workload.

The longitudinal motion of the arterial wall, that is, the displacement of the arterial wall along the artery, parallel to blood flow, is still largely unexplored. The magnitude and nature of putative changes in longitudinal motion of the arterial wall in response to physical activity in humans remain unknown. The aim of this study was therefore to study the longitudinal motion of the carotid artery wall during physical activity in healthy humans. Using in-house developed non-invasive ultrasonic methods, the longitudinal motion of the intima-media complex and the diameter changes of the right common carotid artery (CCA) in 40 healthy volunteers (20 volunteers aged 22-35 years; 20 volunteers aged 55-68 years) were assessed at rest and during submaximal supine bicycle exercise. In a subset of the subjects (n = 18) also intramural shear strain were analyzed. The longitudinal motion of the intima-media complex underwent marked changes in response to physical activity, already at low workload; with most evident a marked increase of the first antegrade displacement (p < 0.001) in early systole. Likewise, the corresponding shear strain also increased significantly (p = 0.004). The increase in longitudinal motion showed significant correlation to increase in blood pressure, but not to blood flow velocity or wall shear stress. In conclusion, physical activity markedly influences the longitudinal motion of the carotid artery wall in healthy humans already at low load. A possible "cushioning" function as well as possible implications for the function of the vasa vasorum, endothelium, and smooth muscle cells and extracellular matrix of the media, are discussed.

The effect of aging on carotid artery wall mechanics during maximal resistance exercise.

INTRODUCTION: Age-related stiffening of the large elastic arteries (e.g., common carotid artery [CCA]) may impair wall dynamics (i.e., strain) and amplify transmission of pulsatile blood flow into the brain with large increases in pressure that occur during maximal resistance exercise (RE). The purpose of this study was to compare CCA arterial wall dynamics, central hemodynamics, and cerebral blood velocity responses during maximal RE between young and older adults. METHODS: Thirty-one young (YA; 26 ± 5 yrs; 23.8 ± 3.3 kg/m2) and 25 older adults (OA; 60 ± 6 yrs; 30.0 ± 5.5 kg/m2) performed a unilateral maximal isokinetic knee flexion/extension exercise protocol (i.e., maximal RE). All measures were recorded at baseline and during the last 10 s of maximal RE. Common carotid artery strain, CCA strain time to peak, and CCA strain rate (i.e., variables of arterial wall dynamics) were analyzed using 2D speckle tracking software from circumferential ultrasound images. Transcranial Doppler was used to measure right middle cerebral artery (MCA) blood velocity. Non-invasive arterial blood pressure measurements were obtained using finger photoplethysmography. RESULTS: Older adults had greater reductions in CCA strain time to peak from baseline to maximal RE (345 ± 39 to 242 ± 52 ms) than YA (308 ± 35 to 247 ± 42 ms; interaction effect, p < 0.01). MCA velocity was similar between YA and OA during maximal RE (p = 0.48), despite a greater arterial pressor response in OA (p < 0.01). CONCLUSION: These data suggest cerebral blood velocity responds similarly during maximal RE among OA compared to YA, despite subtle age-related differences in the pressor and extracranial vascular response during maximal RE.

Reduced Smooth Muscle Contractile Capacity Facilitates Maladaptive Arterial Remodeling.

Albeit seldom considered explicitly, the vasoactive state of a central artery can contribute to luminal control and thereby affect the in vivo values of flow-induced wall shear stress and pressure-induced intramural stress, which in turn are strong determinants of wall growth and remodeling. Here, we test the hypothesis that diminished vasoactive capacity compromises effective mechano-adaptations of central arteries. Toward this end, we use consistent methods to re-interpret published data on common carotid artery remodeling in a nonpharmacologic mouse model of induced hypertension and a model of connective tissue disorder that results in Marfan syndrome. The mice have identical genetic backgrounds and, in both cases, the data are consistent with the hypothesis considered. In particular, carotid arteries with strong (normal) vasoactive capacity tend to maintain wall thickness and in vivo axial stretch closer to homeostatic, thus resulting in passive circumferential wall stress and energy storage close to normal. We conclude that effective vasoactivity helps to control the biomechanical state in which the cells and matrix turnover, thus helping to delineate mechano-adaptive from maladaptive remodeling. Future analyses of experimental data and computational models of growth and remodeling should account for this strong coupling between smooth muscle contractile capacity and central arterial remodeling.

Brachial and carotid hemodynamic response to hot water immersion in men and women.

This study sought to compare the brachial and carotid hemodynamic response to hot water immersion (HWI) between healthy young men and women. Ten women (W) and 11 men (M) (24 ± 4 yr) completed a 60-min HWI session immersed to the level of the sternum in 40°C water. Brachial and carotid artery hemodynamics (Doppler ultrasound) were measured at baseline (seated rest) and every 15 min throughout HWI. Within the brachial artery, total shear rate was elevated to a greater extent in women [+479 (+364, +594) s-1] than in men [+292 (+222, +361) s-1] during HWI (P = 0.005). As shear rate is inversely proportional to blood vessel diameter and directly proportional to blood flow velocity, the sex difference in brachial shear response to HWI was the result of a smaller brachial diameter among women at baseline (P < 0.0001) and throughout HWI (main effect of sex, P < 0.0001) and a greater increase in brachial velocity seen in women [+48 (+36, +61) cm/s] compared with men [+35 (+27, +43) cm/s] with HWI (P = 0.047) which allowed for a similar increase in brachial blood flow between sexes [M: +369 (+287, +451) mL/min, W: +364 (+243, +486) mL/min, P = 0.943]. In contrast, no differences were seen between sexes in carotid total shear rate, flow, velocity, or diameter at baseline or throughout HWI. These data indicate the presence of an artery-specific sex difference in the hemodynamic response to a single bout of HWI.

Spontaneous extension wave for in vivo assessment of arterial wall anisotropy.

Another type of natural wave, traced from longitudinal wall motion and propagation along the artery, is observed in our in vivo human carotid artery experiments. We coin it as extension wave (EW) and hypothesize that EW velocity (EWV) is associated with arterial longitudinal stiffness. The EW is thus assumed to complement the pulse wave (PW), whose velocity (PWV) is tracked from the radial wall displacement and linked to arterial circumferential stiffness through the Moens-Korteweg equation, as indicators for arterial mechanical anisotropy quantification by noninvasive high-frame-rate ultrasound. The relationship between directional arterial stiffnesses and the two natural wave speeds was investigated in wave theory, finite-element simulations based on isotropic and anisotropic arterial models, and in vivo human common carotid artery (n = 10) experiments. Excellent agreement between the theory and simulations showed that EWV was 2.57 and 1.03 times higher than PWV in an isotropic and an anisotropic carotid artery model, respectively, whereas in vivo EWV was consistently lower than PWV in all 10 healthy human subjects. A strong linear correlation was substantiated in vivo between EWV and arterial longitudinal stiffness quantified by a well-validated vascular-guided wave imaging technique (VGWI). We thereby proposed a novel index calculated as EWV2/PWV2 as an alternative to assess arterial mechanical anisotropy. Simulations and in vivo results corroborated the effect of mechanical anisotropy on the propagation of spontaneous waves along the arterial wall. The proposed anisotropy index demonstrated the feasibility of the concurrent EW and PW imaged by high frame-rate ultrasound in grading of arterial wall anisotropy.NEW & NOTEWORTHY An extension wave formed by longitudinal wall displacements was observed by high-frame-rate ultrasound in the human common carotid artery in vivo. A strong correlation between extension wave velocity and arterial longitudinal stiffness complements the well-established pulse wave, which is linked to circumferential stiffness, to noninvasively assess direction-dependent wall elasticity of the major artery. The proposed anisotropy index, which directly reflects arterial wall microstructure and function, might be a potential risk factor for screening (sub-) clinical cardiovascular diseases.

Greater arterial wall viscosity in endurance-trained men.

PURPOSE: The age-associated increase in arterial wall viscosity (AWV) is attenuated by high cardiorespiratory fitness level. However, AWV in endurance-trained athletes have not been determined. We designed a cross sectional study to compare central AWV and compliance between endurance-trained young athletes and age-matched control men. METHODS: Twenty-one endurance-trained men (age 20.7 ± 0.3 years) and 20 age-matched healthy control men (age 21.6 ± 0.4 years) were studied. The common carotid artery was measured noninvasively by tonometry and automatic tracking of B-mode images to obtain instantaneous pressure and diameter hysteresis loops, and we calculated the dynamic carotid arterial compliance, static (effective and isobaric) compliance, and viscosity index. RESULTS: The AWV index in the endurance-trained men was larger than the control peers (2285 ± 181 vs. 1429 ± 124 mmHg·s/mm: P < 0.001). In addition, dynamic and static compliance were not statistically different between both groups. CONCLUSION: The present study indicated that the central AWV in endurance-trained athletes was greater than age-matched healthy control men. We believe that the AWV, as well as arterial compliance, is an important element for assessing vascular adaptation to endurance training.

A framework for incorporating 3D hyperelastic vascular wall models in 1D blood flow simulations.

We present a novel framework for investigating the role of vascular structure on arterial haemodynamics in large vessels, with a special focus on the human common carotid artery (CCA). The analysis is carried out by adopting a three-dimensional (3D) derived, fibre-reinforced, hyperelastic structural model, which is coupled with an axisymmetric, reduced order model describing blood flow. The vessel transmural pressure and lumen area are related via a Holzapfel-Ogden type of law, and the residual stresses along the thickness and length of the vessel are also accounted for. After a structural characterization of the adopted hyperelastic model, we investigate the link underlying the vascular wall response and blood-flow dynamics by comparing the proposed framework results against a popular tube law. The comparison shows that the behaviour of the model can be captured by the simpler linear surrogate only if a representative value of compliance is applied. Sobol's multi-variable sensitivity analysis is then carried out in order to identify the extent to which the structural parameters have an impact on the CCA haemodynamics. In this case, the local pulse wave velocity (PWV) is used as index for representing the arterial transmission capacity of blood pressure waveforms. The sensitivity analysis suggests that some geometrical factors, such as the stress-free inner radius and opening angle, play a major role on the system's haemodynamics. Subsequently, we quantified the differences in haemodynamic variables obtained from different virtual CCAs, tube laws and flow conditions. Although each artery presents a distinct vascular response, the differences obtained across different flow regimes are not significant. As expected, the linear tube law is unable to accurately capture all the haemodynamic features characterizing the current model. The findings from the sensitivity analysis are further confirmed by investigating the axial stretching effect on the CCA fluid dynamics. This factor does not seem to alter the pressure and flow waveforms. On the contrary, it is shown that, for an axially stretched vessel, the vascular wall exhibits an attenuation in absolute distension and an increase in circumferential stress, corroborating the findings of previous studies. This analysis shows that the new model offers a good balance between computational complexity and physics captured, making it an ideal framework for studies aiming to investigate the profound link between vascular mechanobiology and blood flow.

Non-invasive evaluation of the common carotid artery in normal adults using ultrasound radiofrequency data technology.

AIM: To evaluate the changes in CCA-IMT and vascular elasticity in healthy subjects in relation to age using radiofrequency data technology, to produce reference values for potential clinical applications. MATERIALS AND METHODS: The following variables were measured in 160 subjects using radiofrequency data techniques: CCA-IMT, carotid distensibility (CD), local pulse-wave velocity (PWVß), and stiffness (ß). The subjects were divided into four age groups (30-39, 40-49, 50-59, and 60-69 years), with 20 men and 20 women in each group. The above parameters were compared among the different age groups. RESULTS: CCA-IMT increased significantly with age (p<0.05). CD decreased significantly in the 40-49-years compared with the 30-39-years age group (p<0.05). PWVß showed a significant increase in the 30-39-, 40-49-, and 50-59-years age groups (p<0.05). ß increased significantly in the 50-59- compared with the 40-49-years age group (p<0.05). Compared with the 50-59-years age group, CD, PWVß, and ß showed no significant changes in the 60-69-years age group (p>0.05), with mean values of 329.39 ± 102.06 µm, 7.22 ± 1.91 m/s, and 10.04 ± 4.91, respectively. CONCLUSION: Ultrasound radiofrequency data technology provides a non-invasive method for quantitatively and accurately assessing increased CCA-IMT and reduced vascular elasticity in healthy subjects in different age groups. The reference values produced in this study will be useful in clinical practice.

Rabbit Elastase Aneurysm: Imaging and Histology Correlates for Inflammation and Healing.

OBJECTIVE: Aneurysmal subarachnoid hemorrhage remains a devastating event with poorly understood pathophysiology. Previous studies have suggested that aneurysm wall inflammation may play a part in the development and potential rupture of aneurysms. The rabbit elastase aneurysm model is a well-established model, which produces aneurysms closely mimicking human cerebral aneurysms in flow dynamics and histopathology. The primary aim of this study was to correlate inflammatory changes after aneurysm formation using sequential vessel wall imaging with histopathologic analysis. A secondary aim was to evaluate the potential effect of gender and anti-inflammatory treatment with aspirin on this inflammatory response. METHODS: Twenty-seven New Zealand rabbits underwent surgery to create an aneurysm using elastase infusion at the right common carotid artery origin. Vessel wall imaging and histopathologic analysis was obtained at different time points after aneurysm creation. The rabbits were also randomized by gender and to treatment groups with or without aspirin. RESULTS: Histopathologic analysis revealed 3 distinct phases after aneurysm formation. These phases were an initial inflammatory phase, followed by a regeneration phase, and finally a connective tissue deposition phase. Vessel wall imaging demonstrated 2 distinct imaging patterns. No appreciable differences were seen in histology or imaging when comparing gender or treatment with aspirin. CONCLUSIONS: Inflammatory changes induced by the rabbit elastase aneurysm model can be correlated with histopathologic findings and observed on noninvasive vessel wall imaging. This may provide a method to study the inflammatory pathway as it pertains to aneurysmal development and subsequent rupture.

Vasoreactivity of the Murine External Jugular Vein and Carotid Artery.

INTRODUCTION: Impaired venous reactivity has potential to contribute to clinically significant pathologies such as arteriovenous fistula (AVF) maturation failure. Vascular segments commonly used in murine preclinical models of AVF include the carotid artery and external jugular vein. Detailed descriptions of isometric procedures to evaluate function of murine external jugular vein ex vivo have not been previously published. OBJECTIVE: To establish isometric procedures to measure naive murine external jugular vein reactivity ex vivo. METHODS: Vasomotor responses of external jugular veins and ipsilateral common carotid arteries from C57BL/6 mice were evaluated using isometric tension procedures. RESULTS: External jugular veins developed tension (p < 0.05) to potassium chloride and U-46619, but not to phenylephrine, whereas common carotid arteries responded to all 3 agents (p < 0.05). While maximal responses to acetylcholine (ACh) were similar between the venous and arterial segments, the dose required to achieve this value was lower (p < 0.05) in the artery versus vein. Nitric oxide synthase inhibition attenuated (p < 0.05) but did not abolish ACh-evoked vasorelaxation in both vascular segments, whereas cyclooxygenase blockade had no effect. Endothelium-independent vasorelaxation to sodium nitroprusside was similar in the artery and vein. CONCLUSION: Vasorelaxation and vasocontraction can be reliably assessed in the external jugular vein in C57BL/6 mice using isometric procedures.

The influence of habitual endurance exercise on carotid artery strain and strain rate in young and middle-aged men.

NEW FINDINGS: What is the central question of this study? Carotid artery peak circumferential strain (PCS) and strain rate attenuate with age, but appear to be modulated by cardiorespiratory fitness status in young males. However, the relationship between habitual endurance exercise (running) and these parameters has not been studied in young and middle-aged men. What is the main finding and its importance? Young and middle-aged runners exhibited elevated PCS and systolic strain rate (S-SR) compared with non-runners, but habitual running did not influence diastolic strain rate (D-SR). Habitual exercise is associated with comparable improvements in carotid strain parameters in young and middle-aged men, but the age-related decline in PCS and S-SR might be more amenable to habitual endurance exercise than D-SR. ABSTRACT: Central arterial stiffness is an independent predictor of cardiovascular risk that can be modified by exercise training. However, conventional local measures of carotid artery stiffness display conflicting responses to habitual endurance exercise in young and older adults. Two-dimensional (2D)-Strain imaging of the common carotid artery (CCA) quantifies circumferential deformation (strain) of the arterial wall across the cardiac cycle, which is more sensitive at detecting age-related alterations in CCA stiffness than conventional methods. Therefore, the study was designed to examine the relationship between habitual endurance exercise (running) and CCA 2D-Strain parameters in young and middle-aged men. Short-axis ultrasound images of the CCA were obtained from 13 young non-runners [23 years of age (95% confidence interval: 21, 26 years of age)], 19 young runners [24 (22, 26) years of age], 13 middle-aged non-runners [54 (52, 56) years of age] and 19 middle-aged runners [56 (54, 58) years of age]. Images were analysed for peak circumferential strain (PCS; magnitude of deformation) and systolic and diastolic strain rates (S-SR and D-SR; deformation velocity), and group differences were examined via two-way ANOVA. PCS, S-SR and D-SR were attenuated in middle-aged men compared with young men (all P ≤ 0.001). PCS and S-SR were elevated in young and middle-aged runners when compared with non-runners (P = 0.002 and P = 0.009, respectively), but no age × training status interaction was observed. In contrast, there was no influence of habitual running on D-SR. Habitual exercise is associated with comparable improvements in CCA 2D-Strain parameters in young and middle-aged men, but the age-related decline in PCS and S-SR might be more amenable to habitual endurance exercise than D-SR.

Early life factors and their relevance to intima-media thickness of the common carotid artery in early adulthood.

BACKGROUND: Early life factors may predispose an offspring to cardiovascular disease in later life; relevance of these associations may extend to ?healthy" people in Western populations. We examined the prospective associations between early life factors and adult carotid intima-media thickness (IMT), a surrogate marker of atherosclerosis, in a healthy German population. METHODS: We studied term participants (n = 265) of the DONALD Study, with bilateral sonographic measurements of IMT (4-8 measurements on both left and right carotid artery) at age 18-40 years and prospectively collected data on early life factors (maternal and paternal age at child birth, birth weight, gestational weight gain and full breastfeeding (>17weeks). Mean IMT values were averaged from mean values of both sides. Associations between early life factors and adult IMT were analyzed using multivariable linear regression models with adjustment for potential confounders. RESULTS: Adult mean IMT was 0.56mm, SD 0.03, (range: 0.41 mm-0.78 mm). Maternal age at child birth was of relevance for adult IMT, which was sex specific: Advanced maternal age at child birth was associated with an increased adult IMT among female offspring only (ß 0.03, SE 0.009 mm/decade, P = 0.003), this was not affected by adult waist circumference, BMI or blood pressure. Other early life factors were not relevant for IMT levels in males and females. CONCLUSION: This study suggests that advanced maternal age at child birth is of prospective relevance for adult IMT levels in a healthy German population and this association may be of adverse relevance for females only.

Fingerprinting of Doppler audio signals from the common carotid artery.

Audio fingerprinting involves extraction of quantitative frequency descriptors that can be used for indexing, search and retrieval of audio signals in sound recognition software. We propose a similar approach with medical ultrasonographic Doppler audio signals. Power Doppler periodograms were generated from 84 ultrasonographic Doppler signals from the common carotid arteries in 22 dogs. Frequency features were extracted from each periodogram and included in a principal component analysis (PCA). From this 10 audio samples were pairwise classified as being either similar or dissimilar. These pairings were compared to a similar classification based on standard quantitative parameters used in medical ultrasound and to classification performed by a panel of listeners. The ranking of sound files according to degree of similarity differed between the frequency and conventional classification methods. The panel of listeners had an 88% agreement with the classification based on quantitative frequency features. These findings were significantly different from the score expected by chance (p < 0.001). The results indicate that the proposed frequency based classification has a perceptual relevance for human listeners and that the method is feasible. Audio fingerprinting of medical Doppler signals is potentially useful for indexing and search for similar and dissimilar audio samples in a dataset.

Differences in ultrasound-derived arterial wall stiffness parameters and noninvasive blood pressure between Friesian horses and Warmblood horses.

BACKGROUND: Aortic rupture is more common in Friesians compared to Warmbloods, which might be related to differences in arterial wall composition and, as such, arterial wall stiffness (AWS). Currently, nothing is known about differences in AWS between these breeds. OBJECTIVES: Comparison of AWS parameters and noninvasive blood pressure between Friesians and Warmbloods. ANIMALS: One hundred one healthy Friesians and 101 age-matched healthy Warmbloods. METHODS: Two-dimensional and pulsed-wave Doppler ultrasound examination was performed of the aorta, common carotid artery, and external iliac artery to define local and regional AWS parameters. Regional aortic AWS was estimated using aortic-to-external iliac artery pulse wave velocity (PWVa-e ) and carotid-to-external iliac artery pulse wave velocity (PWVc-e ). Noninvasive blood pressure and heart rate were recorded simultaneously. RESULTS: Systolic, diastolic, and mean arterial blood pressure and pulse pressure were significantly higher in Friesians compared to Warmbloods. No significant difference in heart rate was found. Most local AWS parameters (diameter change, compliance coefficient, distensibility coefficient) were significantly lower in Friesians compared to Warmbloods, indicating a stiffer aorta in Friesians. This difference could be confirmed by the regional stiffness parameters. A higher PWVa-e and PWVc-e was found in Friesians. For the cranial and caudal common carotid artery and external iliac artery, most local AWS parameters were not significantly different. CONCLUSIONS AND CLINICAL IMPORTANCE: Results indicate that aortic AWS differs between Friesian and Warmblood horses. Friesians seem to have a stiffer aorta, which might be related to the higher incidence of aortic rupture in Friesians.

Determining the Optimal Normalization Factor of Different Target Arteries for ex vivo Vascular Function Experiments: A New Standardized Procedure.

The standardization of resistance vessel preparation is crucial to compare physiologic vascular reactivity under different experimental conditions. Here, we describe a generalizable experimental setup for ex vivo vascular function experiments and their mathematical basis. Porcine basilar arteries and chicken common carotid arteries were isolated post mortem via standardized surgical approaches. The inner circumference of these vessels with a passive wall tension corresponding to 100 mm Hg (IC100) as well as the circumference at which the active force production of the vessel is maximal (IC1) were determined systematically. The IC1/IC100 ratio (also referred to as factor k), a value that is believed to be constant for a defined vessel type in one species, was calculated by a novel mathematical approach. Here, we present an easy-to-use toolbox for the systematic and computer-based calculation of factor k and simplified optimal pre-stretching of any vascular segments for wire myography experiments.

Computational hemodynamics in arteries with the one-dimensional augmented fluid-structure interaction system: viscoelastic parameters estimation and comparison with in-vivo data.

Mathematical models are widely recognized as a valuable tool for cardiovascular diagnosis and the study of circulatory diseases, especially to obtain data that require otherwise invasive measurements. To correctly simulate body hemodynamics, the viscoelastic properties of vessels walls are a key aspect to be taken into account as they play an essential role in cardiovascular behavior. The present work aims to apply the augmented fluid-structure interaction system of blood flow to real case studies to assess the validity of the model as a valuable resource to improve cardiovascular diagnostics and the treatment of pathologies. Main contributions of the paper include the evaluation of viscoelastic tube laws, estimation of viscoelastic parameters and comparison of models with literature results and in-vivo experiments. The ability of the model to correctly simulate pulse waveforms in single arterial segments is verified using literature benchmark test cases, designed taking into account a simple elastic behavior of the wall in the upper thoracic aorta and in the common carotid artery. Furthermore, in-vivo pressure waveforms, extracted from tonometric measurements performed on four human common carotid arteries and two common femoral arteries, are compared to numerical solutions. It is highlighted that the viscoelastic damping effect of arterial walls is required to avoid an overestimation of pressure peaks. Finally, an effective procedure to estimate the viscoelastic parameters of the model is herein proposed, which returns hysteresis curves of the common carotid arteries dissipating energy fractions in line with values calculated from literature hysteresis loops in the same vessel.