[Show abstract][Hide abstract]ABSTRACT: The purposes of this work were to perform in sheep a quantification of the elastic, viscous, and inertial moduli obtained in carotid and aortic artery segments during in vitro dynamic studies that mimic the normal circulatory function; a quantitative determination of collagen, elastin, and vascular smooth muscle of the carotid and aortic segments analyzed in vitro; the correlation between the amounts of each arterial wall constituent and the viscoelastic properties. To this end, nine healthy sheep were included. One artery was selected from each animal to evaluate its biomechanical properties: (a) in three sheep the ascending aorta, (b) in three the thoracic descending aorta, and (c) in the remaining three the proximal segments of the carotid artery. Each selected artery was instrumented with pressure and diameter sensors. After excision, a small ring-shaped sample was set apart from each segment for histological analysis. In conclusion, (a) the arterial compliance showed a positive association with the absolute and relative amount of the parietal elastin, and (b) arterial viscosity was positively associated with the relative amount of smooth muscle, and this association was increased when the correlation was calculated considering the amount of collagen as well as the amount of smooth muscle.
[Show abstract][Hide abstract]ABSTRACT: 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.
[Show abstract][Hide abstract]ABSTRACT: The aims of this work were (1) to analyze the viscoelastic behavior of different venous segments and their differences, considering the structural characteristics (elastin, collagen, and smooth muscle content) of the venous wall; (2) to analyze the venous biomechanical behavior by means of the histological characteristics of the veins. Nine healthy male Corriedale sheep were included. One vein was selected from each animal to evaluate its biomechanical properties: (a) anterior vena cava, (b) right jugular vein, and (c) right femoral vein. Each selected vein was instrumented with pressure and diameter sensors. After excision, a small ring-shaped sample was set apart from each segment for histological analysis. The amounts of elastin, collagen and smooth muscle were correlated to calculated biomechanical parameters (high- and low-pressure compliance and viscosity). Conclusions are the following: (1) the viscoelastic behavior of the venous wall varies depending on the vascular territory, and it is associated with the variation of the histological structure. These differences involve muscle (both smooth and striated), elastin, and collagen contents. (2) In addition, the quantity of collagen was negatively correlated with high- and low-pressure compliances, and (3) the smooth muscle content was higher in peripheral veins and is positively correlated with venous wall viscosity.
[Show abstract][Hide abstract]ABSTRACT: Purpose. To evaluate in chronically haemodialysed patients (CHPs), if: (1) the vascular access (VA) position (upper arm or forearm) is associated with differential changes in upper limb arterial stiffness; (2) differences in arterial stiffness exist between genders associated with the VA; (3) the vascular substitute (VS) of choice, in biomechanical terms, depends on the previous VA location and CHP gender. Methods. 38 CHPs (18 males; VA in upper arm: 18) were studied. Left and right carotid-brachial pulse wave velocity (PWV(c-b)) was measured. In in vitro studies, PWV was obtained in ePTFE prostheses and in several arterial and venous homografts obtained from donors. The biomechanical mismatch (BM) between CHP native vessel (NV) and VS was calculated. Results/Conclusions. PWV(c-b) in upper limbs with VA was lower than in the intact contralateral limbs (P < 0.05), and differences were higher (P < 0.05) when the VA was performed in the upper arm. Differences between PWV(c-b) in upper limbs with VA (in the upper arm) with respect to intact upper limbs were higher (P < 0.05) in males. Independently of the region in which the VA was performed, the homograft that ensured the minimal BM was the brachial artery. The BM was highly dependent on gender and the location in the upper limb in which the VA was performed.
[Show abstract][Hide abstract]ABSTRACT: The mechanisms that explain intra-aortic balloon pumping (IABP) effects are not completely understood, and attributing them only to pressure-associated changes in cardiac function would be an oversimplification. Since IABP modifies the aortic and systemic blood-flow pattern, flow-related effects could be expected. To characterize effects of acute heart failure (AHF) on the arterial biomechanics; IABP effects on the arterial biomechanics during AHF, and their potential time-dependence; the association between hemodynamics and biomechanical changes during AHF and IABP. Sheep (n = 6) aortic pressure, flow, and diameter were measured: (1) before (Basal) and (2) 1-3 (HF(1-3)) and 28-30 (HF(28-30)) min after starting halothane to induce AHF; and (3) at specific times (1-3, 14-15 and 28-30 min) during IABP assistance. Calculus: aortic characteristic impedance (Z (c)), beta stiffness (β), incremental (E (INC)) and pressure-strain elastic modulus (E (P)); total arterial compliance (C (G)), total systemic vascular resistance and wave propagation parameters. (1) AHF resulted in an acute increase in aortic and systemic stiffness (HF(28-30) % changes with respect to Basal conditions: β +217%, E (P) +143%, E (INC) +101%, Z (c) +52%, C (G) -13%), associated with the reduction in the aortic blood flow; (2) during AHF IABP resulted in acute beneficial changes aortic and systemic biomechanics (% changes in IABP(1-3) with respect HF(28-30): β -62%, E (P) -68%, E (INC) -66%, Z (c) -38%, C (G) 66%), and in wave propagation parameters, (3) IABP-related changes were time-dependent and associated with changes in aortic blood flow. Aortic and systemic biomechanical and impedance properties are detrimentally modified during AHF, being the changes rapidly reverted during IABP. IABP-related beneficial changes in arterial biomechanics were time-dependent and associated with IABP capability to increase blood flow.
[Show abstract][Hide abstract]ABSTRACT: 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.
[Show abstract][Hide abstract]ABSTRACT: 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).
[Show abstract][Hide abstract]ABSTRACT: 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.
[Show abstract][Hide abstract]ABSTRACT: The intra-aortic balloon pumping (IABP) changes pressure and increases the aorta shear stress reversal (SS(R)) and oscillatory (SS(O)) 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 SS(R) and SS(O) 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 SS(R) and SS(O) and the aortic biomechanical changes associated with the VSM tone variations.
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 SS(R) and SS(O) and biomechanical changes associated with variations in the aortic VSM tone.
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 SS(R) and SS(O), levels and changes. The vascular changes reduced the ventricle afterload determinants, increased the vascular buffer performance and kept the conduit capability.
In addition to pressure-dependent changes, IABP determined biomechanical changes related to variations in the VSM tone. The increased SS(R) and SS(O) were associated with the aortic VSM contraction pattern and biomechanical changes.
[Show abstract][Hide abstract]ABSTRACT: Ventricular dynamic afterload depends on arterial viscoelastic and geometric properties. Vasoactive factors produced in the adventitia modulate arterial tone. However, it is still not known whether the adventitia is involved in determining the magnitude of the dynamic afterload. The aim of this study was to investigate the role played by the adventitia, via smooth muscle-dependent mechanisms, in determining dynamic afterload.
The diameter, pressure and flow in brachiocephalic trunks from sheep were measured before and after removal of the adventitia, both in vivo with muscular reactivity preserved (n=8) and in vitro with muscular reactivity abolished (n=8). All studies were performed under similar hemodynamic conditions. Dynamic afterload was determined from elastic and viscous arterial responses, elastic and viscous work, arterial characteristic impedance, and pulse wave velocity. Comparison of in vivo and in vitro findings enabled smooth muscle-dependent changes to be evaluated.
Only in vivo, did removal of the adventitia lead to a reduction in vessel diameter (17.32 [2.02] vs 15.46 [1.28] mm) and to increases in elastic (7.21 [1.39] vs 15.59 [3.00] x 10(6) dyn.cm(-2)) and viscous (5.16 [2.04] vs 9.87 [2.00] x 10(5) dyn.s.cm(-2)) arterial responses, elastic (6.15 [1.08] vs 9.20 [0.76] x 10(-2) J/m2) and viscous work (11.61 [2.25] vs 15.20 [2.37] x 10(-3) J/m2), impedance (223.97 [136.11] vs 396.33 [182.27] dyn x s x cm(-3)), and pulse wave velocity (397.70 [31.21] vs 598.78 [28.04] cm.s(-1)) (P<.05). The reduction in diameter and the increases in elastic and viscous responses are evidence of muscular activation.
The adventitia may contribute to the control of ventricular dynamic afterload by means of mechanisms dependent on muscular tone.
Full-text Article · Jun 2007 · Revista Espa de Cardiologia
[Show abstract][Hide abstract]ABSTRACT: Introduction and objectives
Ventricular dynamic afterload depends on arterial viscoelastic and geometric properties. Vasoactive factors produced in the adventitia modulate arterial tone. However, it is still not known whether the adventitia is involved in determining the magnitude of the dynamic afterload. The aim of this study was to investigate the role played by the adventitia, via smooth muscledependent mechanisms, in determining dynamic afterload.
The diameter, pressure and flow in brachiocephalic trunks from sheep were measured before and after removal of the adventitia, both in vivo with muscular reactivity preserved (n=8) and in vitro with muscular reactivity abolished (n=8). All studies were performed under similar hemodynamic conditions. Dynamic afterload was determined from elastic and viscous arterial responses, elastic and viscous work, arterial characteristic impedance, and pulse wave velocity. Comparison of in vivo and in vitro findings enabled smooth muscledependent changes to be evaluated.
Only in vivo, did removal of the adventitia lead to a reduction in vessel diameter (17.32 [2.02] vs 15.46 [1.28] mm) and to increases in elastic (7.21 [1.39] vs 15.59 [3.00] x 106 dyn.cm-2) and viscous (5.16 [2.04] vs 9.87 [2.00] × 105 dyn.s.cm-2) arterial responses, elastic (6.15 [1.08] vs 9.20 [0.76] × 10-2 J/m2) and viscous work (11.61 [2.25] vs 15.20 [2.37] × 10-3 J/m2), impedance (223.97 [136.11] vs 396.33 [182.27] dyn · s · cm-3), and pulse wave velocity (397.70 [31.21] vs 598.78 [28.04] cm.s-1) (P<.05). The reduction in diameter and the increases in elastic and viscous responses are evidence of muscular activation.
The adventitia may contribute to the control of ventricular dynamic afterload by means of mechanisms dependent on muscular tone.
[Show abstract][Hide abstract]ABSTRACT: While the effects of increases in forward blood flow on the arterial diameter and elasticity are known, the effects of reversal flow on the arterial properties remain to be characterized. The intra-aortic balloon pumping (IABP), the device most frequently used in circulatory support, acts generating changes in aortic flow (i.e. increasing reversal flow). Recently, in vitro studies showed that flow reversion reduces the endothelial release of relaxing factors. Hence, vascular smooth muscle (VSM) dependent changes in the aortic properties would be expected during IABP. The aim was to analyze the changes in flow during IABP and to characterize the potential effects of reversal blood flow on the aortic biomechanics. Pressure, flow and diameter were measured in sheep, before and during IABP circulatory support. Potential effects of IABP-dependent high reversal flow conditions on viscous and elastic aortic modulus were analyzed, using isobaric analysis. Flow and pressure waveforms were analyzed in the time domain, and the contribution of oscillatory forward and backward waves to the IABP-dependent changes in flow patterns were evaluated. We found that IABP changed mainly diastolic blood flow, with an increase in the reversal flow, secondary to an increase in the oscillatory backward wave amplitude. The acute increase in reversal flow during IABP was associated with vasoconstriction and changes in the aortic mechanics, possibly due to VSM activation.
Article · Feb 2007 · Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference
[Show abstract][Hide abstract]ABSTRACT: RESUMEN Introducción: Las propiedades geométricas y la viscosidad (V) y elasticidad (E) arteriales son deter-minantes de la función de conducción (FC) y amorti-guamiento arterial (FA), así como del trabajo elástico (WE) y viscoso (WV) desarrollado por el ventrículo du-rante la eyección (poscarga dinámica externa). Se desconoce el rol endotelial en el control de la V, FC, FA, WE y WV, y resta por establecerse si el endotelio controla la poscarga dinámica de manera frecuen-cia-dependiente. Objetivo: Caracterizar el rol endotelial en la regula-ción de la V, FC, FA, WE y WV, y analizar el control en-dotelial de la poscarga dinámica ante aumentos de frecuencia de estimulación. Material y método: Arterias braquiocefálicas ovi-nas (n=9) se estudiaron en un simulador circulatorio en condiciones hemodinámicas símil fisiológicas. Se midió flujo, presión y diámetro arterial a 60, 80 y 100 latidos/minuto. Para cada frecuencia se calculó E, V, FC, FA, WE y Wv, antes y luego de remover el endote-lio. La adecuada eliminación endotelial se comprobó mediante estudios histológicos. Resultados: La presencia de endotelio permitió man-tener reducidos E, V, WE y WV, y elevada la FC (p<0,05). La reducción de los determinantes de la poscarga fue mayor a elevados niveles de frecuencia de estimulación (p<0,05). Conclusiones: El endotelio regula la viscoelasticidad arterial, reduciendo la pos-carga dinámica, a la vez que permite mantener eleva-da la FC y no modifica la capacidad de la arteria de autoprotegerse. La mayor reducción de la poscarga a mayor frecuencia (mayor consumo de oxígeno), supo-ne un beneficio adicional sobre la función ventricu-lar.
[Show abstract][Hide abstract]ABSTRACT: An arterial bypass might be either carried out with a venous segment or using a polytetrafluoroethylene (ePTFE) graft. Different patency rates were reported depending on the chosen method. Our objective was to compare the elastic properties of three different segment: A) expanded synthetic polytetrafluoroethylene (ePTFE) grafts, B) jugular veins, and C) systemic arteries (femoral artery). Pressure (P) and diameter signals were measured in six ovine venous, arterial, and ePTFE segments, mounted in a circulation mock and perfused at systemic pressure and stretch rate. Elastic modulus (E<sub>inc</sub>) was calculated at 100 mmHg using a pressure and diameter analysis. At systemic P level, both venous and ePTFE were suffer than the artery (p<0.05), but venous E<sub>inc</sub> was more compliant than the ePTFE (p<0.05). The elastic mismatch was higher (p<0.05) between a ePTFE graft and the artery than between the vein and the artery. This could explain the major incidence of arterial by-pass failure reported when a ePTFE graft is chosen.
[Show abstract][Hide abstract]ABSTRACT: A telemetric method has been designed for continuous measurement of intra-arterial aortic blood pressure in the unrestrained dog. The system used a Konigsberg P7 transducer, a temperature-compensated voltage-controlled oscillator, an FM transmitter, and an FM tuner to convert the signal received into a voltage proportional to aortic blood pressure. The method was validated by comparison with a standard direct method (using cables for transmission). Over a wide range of blood pressure obtained by hypotensive and hypertensive drugs (in total about 2500 data points, ranging from 40 to 200 mmHg), the telemetric method gave almost the same result as the direct method. Absolute error (telemetric measure minus standard measure) was normally distributed, with a mean value of -0.44 mmHg, and a standard deviation of 3.37 mmHg. The telemetric method was designed for future studies on the chronobiology of blood pressure in normal condition, in stress conditions and under drugs.
Article · Feb 1990 · Medical Progress Through Technology