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The aims of our work were to determine normal aging rates for structural and functional arterial parameters in healthy children, adolescents, and young adults and to identify gender-related differences in these aging rates. Methods. 161 subjects (mean: 15 years (range: 4–28 years), 69 females) were studied. Subjects included had no congenital or chronic diseases, nor had they been previously exposed to traditional cardiovascular risk factors. Arterial parameters assessed were (1) central blood pressure (BP) and aortic pulse wave analysis, (2) arterial local (pressure-strain elastic modulus) and regional (pulse wave velocity, PWV) stiffness, and (3) arterial diameters and carotid intima-media thickness (CIMT). Simple linear regression models (age as the independent variable) were obtained for all the parameters and the resulting rates of change were compared between genders. Results. No gender-related differences were found in mean values of arterial structural and functional parameters in prepubertal ages (4–8 years), but they started to appear at ~15 years. Boys showed a greater rate of change for central systolic BP, central pulse pressure, CIMT, and carotid-femoral PWV. Conclusion. Gender-related differences in arterial characteristics of adults can be explained on the basis of different growing-related patterns between boys and girls, with no existing differences in prepubertal ages. [ABSTRACT FROM AUTHOR]

Aims: The intra-aortic balloon pumping (IABP) changes pressure and increases the aorta shear stress reversal (SSR) and oscillatory (SSO) components. Hence, IABP-dependent changes in aortic biomechanics would be expected, because of vascular smooth muscle (VSM) tone (i.e. flow-induced endothelium-dependent response, related to SSR and SSO variations) and/or pressure changes. To characterize: (i) the IABP effects on the aortic and global (systemic circulation) biomechanics, analysing their dependence on pressure and VSM basic tone changes and (ii) the relation between the SSR and SSO and the aortic biomechanical changes associated with the VSM tone variations. Methods: Aortic flow, pressure and diameter were measured in eight sheep during basal, augmented and assisted beats (1 : 1 and 1 : 2 IABP modalities). Calculations: (i) aortic effective and isobaric elasticity, viscosity, circumferential stress, pulse wave velocity, shear stress and buffer and conduit functions, (ii) peripheral resistance, global compliance, reflection coefficient and wave propagation times and (iii) the relation between SSR and SSO and biomechanical changes associated with variations in the aortic VSM tone. Results: Augmented and assisted beats showed: global VSM relaxation pattern (reduced peripheral resistance and reflection coefficient; increased propagation times) and local VSM contraction pattern (increased viscosity; reduced diameter, elasticity and circumferential stress), associated with SSR and SSO, levels and changes. The vascular changes reduced the ventricle afterload determinants, increased the vascular buffer performance and kept the conduit capability. Conclusion: In addition to pressure-dependent changes, IABP determined biomechanical changes related to variations in the VSM tone. The increased SSR and SSO were associated with the aortic VSM contraction pattern and biomechanical changes. [ABSTRACT FROM AUTHOR]

Aim: An adventitia dependent regulation of the vascular smooth muscle tone has been described. However, if the adventitia plays an active role on arterial wall biomechanical behaviour and functions remains to be established. Our aim was to characterize the influence of adventitia on arterial wall mechanical properties and the arterial conduit and buffer functions. Methods: Ovine brachiocephalic arteries were studied in vivo ( n = 8) and in vitro (with null tone) in a circulation mock ( n = 8). Isobaric, isoflow and isofrequency studies were performed. In each segment, pressure and diameter waves were assessed before and after adventitia removal. From the arterial stress–strain relationship, we derived the elastic and the viscous modulus. The buffering and conduit functions were calculated using the Kelvin–Voigt's time constant and the inverse of the characteristic impedance, respectively. Results: In in vivo studies arterial diameter decreased after adventitia removal ( P < 0.05). Elastic and viscous modulus in in vivo studies were significantly higher in adventitia-removed arteries, compared with values in intact vessels ( P < 0.05). This behaviour was not observed in in vitro experiments. An impairment of buffer and conduit functions was observed in vivo after adventitia removal ( P < 0.05), while both functions remain unchanged in in vitro studies ( P > 0.05). Conclusions: Arterial wall viscosity and elasticity were influenced by adventitia removal in in vivo studies, possibly by a smooth muscle-dependent mechanism, since it was not present in in vitro experiments. Adventitia would be involved in a physiological mechanism of arterial wall viscous and elastic properties regulation, that could influence arterial buffering and conduit functions. [ABSTRACT FROM AUTHOR]

We determined the wall mechanical response of the pulmonary artery (PA) to acute pulmonary hypertension induced pharmacologically and by an occlusion maneuver, to study the vascular response of the local segment and its influence in the whole pulmonary circulation. Pulmonary pressure and diameter were measured in six anaesthetized sheep under steady-state conditions. Transient hypertension in the PA was induced by phenylephrine (PHE) and a high pressure (HP) mechanical occlusion aimed at producing the same pulse and mean pressure responses. A viscoelastic arterial wall model was applied and the elastic ( Epd) and viscous ( μ) indexes were obtained. The μ/ Epd ratio was adopted to quantify the damping performance of the arterial wall segment. The diastolic time constant was used as an indicator of the whole pulmonary buffering function. The systemic pressure was always measured. The pulmonary mean, systolic and pulse pressure increases ( P < 0.05) were similar during PHE and HP, with respect to control. PHE also induced a systemic pressure rise ( P < 0.05). The Epd elastic index increased during HP ( P < 0.05) and tended to increase during PHE with respect to control. The viscous index μ only increased with PHE ( P < 0.05) with respect to control and occlusion. The diastolic time constant increased with PHE with respect to control ( P < 0.05). A pressure rise in the PA, induced by an occlusion maneuver, increased local stiffness. Similar pressure rises with smooth muscle activation (PHE), produced both a stiffness and viscous index increase. In PHE resistance increases more than compliance decreases so that the global net effect is a longer decay time. Smooth-muscle activation enhances the local damping effect ( μ/ Epd), concomitant with the buffering function improvement. [ABSTRACT FROM AUTHOR]

Background: Despite the clinical utility of echocardiography to measure left atrial (LA) structure and function, there are scarcities of data about the percentiles of LA diameter (LA D ), LA volume (LA VOL ), and LA volume indexed by body surface area (LA VOL / BSA ) from prospective population-based studies in healthy children and adolescents from the Southern Cone of Latin America., Methods: Echocardiographic studies were obtained in 1095 healthy subjects nonexposed to cardiovascular risk factors (5-24 years). Age- and sex-specific reference values of LA D , LA VOL , and LA VOL / BSA were generated using parametric regression based on fractional polynomials., Results: After covariate analysis (ie, adjusting by age, body surface area), specific sex-specific percentiles were evidenced as necessaries. Age- and sex-specific 1st, 2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, 97.5th, and 99th percentile and curves were reported. Our percentiles showed high concordance and complementarity with what was previously reported for the population of North American, European, and Asiatic Populations., Conclusions: In children and adolescents, the interpretation of the LA size requires sex-related percentiles. This study provides the largest Argentinean database concerning percentile curves of LA D , LA VOL , and LA VOL / BSA obtained in healthy children and adolescents. These data are valuable in that they provide values with which data of populations of children, adolescents, and young adults can be compared., (© 2019 Wiley Periodicals, Inc.)

Background: Echocardiographic reference intervals (RIs) for left ventricular outflow tract (LVOT) and velocity time integral (VTI) are scarce in pediatrics., Aims: (a) to generate RIs and percentiles for LVOT, VTI, and hemodynamic variables in healthy children and adolescents from Argentina; (b) to analyze the equivalence between stroke volume (SV), cardiac output (CO), and cardiac index (CI) obtained from two-dimensional echocardiography (2D) and LVOT-VTI analysis with pulsed wave Doppler (PWD); and (c) to analyze the association between subjects' characteristics and VTI and LVOT-VTI-derived parameters., Methods: Two-dimensional and PWD studies were done in 385 subjects (5-24 years). Mean and standard deviation age-related and body surface area (BSA)-related equations were obtained for VTI and LVOT-VTI-derived parameters (parametric regression methods based on fractional polynomials). BSA- and age-specific percentiles were determined., Results: Pulsed wave Doppler- and 2D-derived parameters were positively correlated. However, PWD values were always lower than those from 2D. Specific RIs for PWD and 2D data were necessary. Covariance analysis showed that sex-specific RIs were required for LVOT, but not for VTI, VTI-derived CO and CI. Age-related RIs were obtained for LVOT, LVOT-VTI, and VTI-derived CO and CI. BSA-related RIs for VTI-derived CO and CI were obtained., Conclusions: Stroke volume, CO, and CI data from 2D and PWD are not equivalent. An accurate analysis of LVOT-VTI-derived parameters requires considering age and BSA. In this study, age- and BSA-related RIs and percentiles for LVOT, VTI, and hemodynamic parameters in healthy children and adolescents were determined, discriminating data according to the methodological approach (2D or PWD)., (© 2018 Wiley Periodicals, Inc.)

There is a relationship between the intra-aortic balloon pumping (IABP) benefits and the dynamic behavior of muscular arteries, which is associated with induced changes on the vessel walls through an endothelial-dependent mechanism. The arterial wall elastic behavior is influenced by adventitial function; however, no studies were performed in order to elucidate if this layer plays a role in the changes determined by IABP. Our aim was to quantify acute IABP effects on the mechanical properties of muscular arteries in induced acute heart failure (AHF), before and after adventitia removal. Pressure and diameter were recorded in the iliac arteries (IA) of sheep (n = 7), before and during 1:2 IABP: (i) in control state (CS) with intact IA, (ii) in CS after IA adventitia removal, and (iii) in de-adventitialized IA after AHF. Conduit function, compliance and arterial distensibility were calculated in each state. During CS, IABP resulted in intact IA dilatation and in an increase in conduit function, compliance and distensibility; adventitial removal determined an increase of arterial stiffness with respect to the CS, which decreased when IABP was used; the increase in arterial stiffness observed after adventitia removal was also detected in AHF state; IABP improves conduit function and arterial stiffness in de-adventitialized arteries, both before and during AHF. However, the improvement in these properties was lower than in intact arteries. Before and after AHF induction, the improvements of conduit function and arterial distensibility determined by IABP in intact IA were significantly reduced after adventitia removal. Adventitial layer integrity would be necessary to maximize IABP-related beneficial effects on arterial system properties., (© 2013 Wiley Periodicals, Inc. and International Center for Artificial Organs and Transplantation.)

Intra-aortic balloon pump (IABP) benefits could depend on variations in the cardiovascular biomechanical properties associated with blood flow-induced endothelium-dependent changes. However, if IABP results in changes in the peripheral artery biomechanics and if the endothelium plays a role in these potential changes remains unknown. The aim of this study is to characterize acute IABP effects on peripheral artery biomechanics in control and acute heart failure (AHF) states and the role of the endothelium in IABP effects on peripheral artery biomechanics. Pressure and diameter were recorded in sheep (n= 7) iliac arteries (IAs), before and during 1:2 IABP, during four states: (i) control with intact IA; (ii) AHF with intact IA; (iii) control with de-endothelialized (DE) (mechanical rubbing) IA; and (iv) AHF with DE IA. Arterial distensibility, elastic modulus, and conduit function (CF) (1/characteristic impedance) were calculated. The results of this study include: (i) during control conditions, IABP resulted in intact IA dilatation, stiffness reduction, and CF increase; (ii) AHF induction determined a reduction in intact IA diameter and CF, and a stiffness increase. These changes reverted during IABP; (iii) the increase in IA stiffness observed after DE remained unchanged during IABP; (iv) in DE IA, AHF did not result in diameter or stiffness changes; and (v) IABP during AHF did not associate changes in diameter or stiffness in the DE IA. In conclusion, during control and AHF states, IABP results in IA dilatation and stiffness reduction. The integrity of the endothelial layer would be critical for the IABP-associated changes in IA biomechanics., (© 2011, Copyright the Authors. Artificial Organs © 2011, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

This study aimed to characterize the following: (i) in chronically hemodialyzed subjects (CHDSs), with and without diabetic nephropathy (DN), and in healthy subjects (non-CHDSs) different arterial pathways stiffness to determine potential pathology-dependent, etiology- and/or pathway-dependent differences; and (ii) the biomechanical mismatch (BM) between arteries from non-CHDSs or CHDSs (with and without DN) and arterial cryografts, venous cryografts, and synthetic prosthesis to determine arterial pathway, pathology, and/or etiology-related differences in the substitute of election in terms of BM. Carotid-femoral and carotid-brachial pulse wave velocity (PWV) were measured in 30 non-CHDSs and 71 CHDSs (11 with DN). In addition, PWV was measured in arterial (elastic and muscular) and venous cryografts and in expanded polytetrafluorethylene prosthesis. The arterial pathways regional differences and the subjects' arterial pathways-substitutes BM were calculated. Arterial stiffness levels and regional differences were higher in CHDS than in non-CHDS. Among CHDS, those with DN showed higher stiffness in the aorto-femoral pathway and larger regional differences. Cryografts showed always the least BM. Non-CHDS and CHDS differed in the cryograft of election. In CHDS, the BM was related with the cryograft type, arterial pathway, and renal disease etiology. The BM could be minimized, selecting the most adequate cryograft type, taking into account the recipient specific characteristic (i.e., arterial pathway and renal disease etiology).

While the situation of tissue donation and transplantation differs between Latin American and European countries, a common problem is tissue deficiency. Hence, at present, there is a pressing need to generate alternatives so as to increase the possibilities of obtaining the requested materials. Consequently, it would be of significant interest to establish an intercontinental network for tissue exchange, to improve international cooperation, and to help patients that need tissue transplantation, and to evaluate the feasibility of using an intercontinental network for the exchange of cryopreserved arteries (cryografts), preserving the arterial distensibility and ensuring a reduced native artery-cryograft biomechanical mismatch. Distensibility was studied in ovine arteries divided into three groups: intact (in vivo tests, conscious animals), fresh control (in vitro tests immediately after the artery excision, Uruguay), and cryografts (in vitro tests of cryopreserved-transported-defrosted arteries, Spain). Histological studies were performed so as to analyze changes in the endothelial layer and elastic components. The comparison between fresh control and cryografts showed that neither the cryopreservation nor the exchange network impaired the distensibility, despite the expected histological changes found in the cryografts. The comparison between intact and cryografts showed that the cryografts would be capable of ensuring a reduced biomechanical mismatch. The cryopreservation and the intercontinental network designed for artery exchange preserved the arterial distensibility. It could be possible to transfer cryografts between Latin America and Europe to be used in cardiovascular surgeries and/or for tissue banking reprocessing, with basic biomechanical properties similar to those of the fresh and/or native arteries.

In several physiological, pathological, and therapeutic circumstances, the arterial blood flow is acutely modified, increasing, in some vascular segments the reversal (SSR) and oscillatory (SSO) components of the shear stress. Recently, in an in vivo model we found a relationship between acute changes in SSR and SSO, and variations in the arterial viscoelasticity. As the arterial viscoelasticity and diameter are the main determinants of the arterial buffering (BF) and conduit (CF) functions, changes in those functions could be expected associated with variations in SSR and SSO. The aim was to analyze the association between acute increases in SSR and SSO, and changes in the aortic CF and BF. Aortic flow, pressure, and diameter were measured in 16 sheep under basal and high reversal and oscillatory flow conditions (high SSR and SSO). Aortic BF and CF were quantified, and their potential association with the SSR and SSO components were analyzed. During high reversal flow rate conditions, a smooth muscle contraction-pattern was evidenced, with an increase in BF and a decrease in CF. Changes in BF and CF were associated with the changes in SSR and SSO. The acute effects on the arterial wall biomechanics of variations in SSR and SSO could contribute to comprehend their chronic effects, and the meaning of the acute vascular effects of changes in SSR and SSO would depend on the situation. Increases in SSR and SSO could be associated with smooth muscle tone increase-dependent changes in arterial BF and CF.

The aim of this study was to characterize and compare human great saphenous veins (HGSVs), HGSV cryoallografts, expanded polytetrafluoroethylene (ePTFE) segments, and elastic and muscular arteries' biomechanics, so as to identify if the biomechanical coupling and the HGSV advantages with respect to ePTFE depend on the arterial type and/or on the biomechanical property considered. Pressure and diameter were measured in vitro, under arterial hemodynamic conditions, in elastic and muscular arteries, and in vascular substitutes: fresh and cryopreserved HGSV and ePTFE segments. The wall's dynamics (compliance, viscosity, and inertia), energy dissipation, and buffering were calculated. The coupling was quantified for each biomechanical parameter. Cryopreservation preserved HGSV biomechanics. The HGSV cryoallografts' dynamics, energetics, and buffering were lesser with respect to both arteries, but were higher than the ePTFE. The coupling differed, depending on the arterial type and property considered. The biomechanical coupling depended on the artery and property considered. HGSV cryoallograft advantages over ePTFE were arterial type and property independent.

The causes of the regional differences in venous grafts patency rates are partially understood. Differences in vein dynamics during physiological situations could determine differences in veins' capability to face arterial conditions and could contribute to the dissimilar performance of veins as arterial grafts. In vitro pressure and diameter were measured in four different veins during physiological and arterial (graft) pressure conditions. A diameter-pressure transfer function was designed. Compliance, viscous and inertial properties; circumferential stresses and deformation; and buffering function were calculated. Regional differences in veins' dynamics, but not in buffering function were found during physiological and arterial conditions. The back vein (femoral) showed the least changes when submitted to arterial conditions. Arterial conditions represent different changes in vein dynamics depending on the segment considered. The regional differences in vein dynamics, both at physiological and graft conditions, could contribute to explain the dissimilar results of venous grafts.