Effects of removing the adventitia on the mechanical properties of ovine femoral arteries in vivo and in vitro.

BACKGROUND: The aims were to characterize in muscular arteries (a) the passive and active effects of the adventitia on vessel biomechanical properties and conduit function (CF), and (b) potential differences between the adventitial role in elastic and muscular arteries. METHODS AND RESULTS: Ovine femoral arteries were studied in vivo and in vitro (reduced smooth muscle-tone) in a circulation mock-up during hemodynamic conditions similar to those found in vivo. Pressure and diameter were assessed before and after removing the adventitia. The arterial compliance, distensibility, stiffness beta-index and CF were quantified. Results were compared with those obtained in brachiocephalic trunks. In vivo, after removing the adventitia there was a nonsignificant diameter reduction and an increase in stiffness (P<0.05). The CF decreased in the early recordings (P<0.02). In vitro, there were no biomechanical changes but vascular dilatation after the adventitia removal. Biomechanical changes associated with the adventitia removal were higher in muscular arteries, whereas diameter changes were major in elastic vessels. CONCLUSIONS: After removing the adventitia, (a) the arterial stiffness and CF were modified in vivo only, suggesting the changes could be ascribed to variations in smooth muscle tone, and (b) changes in elastic and muscular arteries were quantitatively different.

Reversal blood flow component as determinant of the arterial functional capability: theoretical implications in physiological and therapeutic conditions.

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.

Effects of intra-aortic counterpulsation on aortic wall energetics and damping: in vivo experiments.

Intra-aortic balloon pumping (IABP) could modify the arterial biomechanics; however, its effects on arterial wall properties have not been fully explored. This dynamical study was designed to characterize the pressure-dependent and smooth muscle-dependent effects of IABP on aortic wall energetics in an in vivo animal model. Intra-aortic balloon pumping (1:2) was performed in six anesthetized sheep in which aortic pressure and diameter signals were measured in basal, augmented (during balloon inflation), and assisted (postaugmented) beats. Energy dissipation values in augmented and assisted beats were significantly higher than those observed in basal state (p < 0.05). Assisted beats showed a significant increase of wall damping with respect to basal and augmented beats (p < 0.05). Intra-aortic balloon pumping resulted in a significant increase of pulse wave velocity (p < 0.05) in augmented beats with respect to basal state (6.3 +/- 0.8 vs. 5.2 +/- 0.5 m x s(-1)); whereas values observed in assisted beats were significantly (p < 0.05) lower than those observed in augmented beats (4.9 +/- 0.5 vs. 6.3 +/- 0.8 m x s(-1)). Our findings show that IABP determined the pressure and smooth muscle-dependent changes in arterial wall energetics and damping properties in this animal model.

Acute increase in reversal blood flow during counterpulsation is associated with vasoconstriction and changes in the aortic mechanics.

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.

[The adventitia reduces left ventricular dynamic afterload via smooth muscle activation-dependent mechanisms]. / La adventicia reduce la poscarga dinámica ventricular izquierda mediante mecanismos dependientes de la activación muscular lisa.

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 muscle-dependent mechanisms, in determining dynamic afterload. METHODS: 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. RESULTS: 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. CONCLUSIONS: The adventitia may contribute to the control of ventricular dynamic afterload by means of mechanisms dependent on muscular tone.

Efectos de la contrapulsación intra-aórtica sobre las propiedades mecánicas de la pared aórtica / Effects of intra-aortic counter pulsation on the mechanical properties of the aortic wall

La contrapulsación intra-aórtica (CIAO) produce cambios en las propiedades vasculares que pueden ser cuantificadas. El objetivo de este trabajo es caracterizar los efectos de la CIAO (1:2) sobre las propiedades mecánicas de la pared aórtica(AU)

Efectos de la contrapulsación intra-aórtica sobre las propiedades mecánicas de la pared aórtica / Effects of intra-aortic counter pulsation on the mechanical properties of the aortic wall

La contrapulsación intra-aórtica (CIAO) produce cambios en las propiedades vasculares que pueden ser cuantificadas. El objetivo de este trabajo es caracterizar los efectos de la CIAO (1:2) sobre las propiedades mecánicas de la pared aórtica

Juxtaaortic counterpulsation: comparison with intraaortic counterpulsation in an animal model of acute heart failure.

This study was designed to compare the effects of juxtaaortic balloon counterpulsation (JABC), performed in ascending aorta and the aortic arch, with those yielded by intraaortic balloon counterpulsation (IABC) in descending aorta, in experimental animals during induced cardiac failure. JABC was achieved with a manufactured Dacron prosthesis and a balloon pump placed between the prosthesis and the wrapped aorta. JABC resulted in a significant increase of cardiac output (from 2.33+/-0.82 to 2.61+/-1.12 L/min, p < 0.05), cardiac index (from 0.071+/-0.025 to 0.080+/-0.033 L/min/kg, p < 0.05) and diastolic pressure augmentation evaluated through diastolic and systolic areas beneath the aortic pressure curve (DABAC/SABAC) index (from 0.94+/-0.21 to 1.10+/-0.33, p < 0.01). End diastolic aortic pressure showed a significant decrease with JABC (from 31.90+/-7.09 to 27.83+/-9.72 mm Hg, p < 0.05). A close association between percentage of DABAC/SABAC increases obtained with IABC and JABC was observed (r2 = 0.67; p < 0.001). Counterpulsation obtained by a juxtaaortic catheter placed in the arch and the ascending wrapped aorta results in an effective hemodynamic improvement comparable with that achieved by an intraaortic catheter in open chest sheep.

A new approach to assist postoperative heart failure in an animal model: juxta-aortic counterpulsation.

Aortic counterpulsation is a useful technique frequently used in postcardiotomy heart failure. An acute heart failure model in open chest sheep was chosen to evaluate hemodynamic improvement with a counterpulsation balloon pump in juxta-aortic position. This was achieved with a manufactured Dacron prosthesis and a balloon pump placed between the prosthesis and the aorta. Juxta-aortic balloon pump counterpulsation in acute experimental heart failure resulted in a significant improvement of hemodynamic parameters: increase of cardiac output (from 0.86 +/- 0.04 to 1.29 +/- 0.09 L/min, p < 0.05) and cardiac index (from 0.03 +/- 0.01 to 0.04 +/- 0.01 L/min per kg, p < 0.05), and decrease of systemic vascular resistance (from 89.76 +/- 6.69 to 66.56 +/- 6.02 mm Hg/L per min, p < 0.05). The extent of aortic diastolic pressure change evaluated through the diastolic and systolic areas beneath the aortic pressure curve (DABAC/SABAC) index before cardiac failure induction showed a significant increase compared with unassisted values (from 0.81 +/- 0.10 to 1.12 +/- 0.09, p < 0.05). Assisted values of DABAC/SABAC index after heart failure induction also showed a significant increase compared with unassisted values (from 0.78 +/- 0.21 to 1.17 +/- 0.38, p < 0.05). Treatment of experimental acute heart failure by juxta-aortic balloon pump counterpulsation allows an effective hemodynamic improvement in open chest sheep.

Contrapulsación aortica experimental y clínica: su evaluación por medio de un nuevo índice no invasivo / Experimental and clinical aortic contrapulsation: its evaluation by means of a new noninvasive index

La insuficiencia cardíaca refractaria al tratamiento médico tiene el carácter de epidemia y afecta a grandes masas de la población del planeta. La asistencia circulatoria es un área de desarrollo de la bioingeniería que trata de encontrar la solución ocasionada por el síndrome de insuficiencia cardíaca intratable. La asistencia circulatoria puede ser estudiada de dos maneras, mediante dispositivos mecánicos o mediante bioasistencia circulatoria usando colgajos musculares electroestimulados. Existe una forma de asistencia mecánica que puede ser lograda tanto por dispositivos como por bioasistencia: la contrapulsación aórtica, ya sea mecánica o biológica, es una técnica eficaz en el tratamiento de la insuficiencia cardíaca. En este estudio se utilizó un modelo animal de insuficiencia cardíaca en ovejas para comparar los resultados obtenidos mediante contrapulsación biológica torácica y abdominal realizadas con colgajos de músculo dorsal ancho y diafragma, respectivamente. La contrapulsación biológica torácica y abdominal deteminaron una significativa mejoría hemodinámica en insuficiencia cardíaca inducida. El índice de viabilidad subendocárdiaca utilizado para evaluar el grado de contrapulsación abdominal como en la torácica (p<0.05). En esta serie experimental se incluyó la utilización de un nuevo índice no invasivo de contrapulsación que utiliza las áreas bajo el perfil de presión aórtica... (TRUNCADO)

Contrapulsación aortica experimental y clínica: su evaluación por medio de un nuevo índice no invasivo / Experimental and clinical aortic contrapulsation: its evaluation by means of a new noninvasive index

La insuficiencia cardíaca refractaria al tratamiento médico tiene el carácter de epidemia y afecta a grandes masas de la población del planeta. La asistencia circulatoria es un área de desarrollo de la bioingeniería que trata de encontrar la solución ocasionada por el síndrome de insuficiencia cardíaca intratable. La asistencia circulatoria puede ser estudiada de dos maneras, mediante dispositivos mecánicos o mediante bioasistencia circulatoria usando colgajos musculares electroestimulados. Existe una forma de asistencia mecánica que puede ser lograda tanto por dispositivos como por bioasistencia: la contrapulsación aórtica, ya sea mecánica o biológica, es una técnica eficaz en el tratamiento de la insuficiencia cardíaca. En este estudio se utilizó un modelo animal de insuficiencia cardíaca en ovejas para comparar los resultados obtenidos mediante contrapulsación biológica torácica y abdominal realizadas con colgajos de músculo dorsal ancho y diafragma, respectivamente. La contrapulsación biológica torácica y abdominal deteminaron una significativa mejoría hemodinámica en insuficiencia cardíaca inducida. El índice de viabilidad subendocárdiaca utilizado para evaluar el grado de contrapulsación abdominal como en la torácica (p<0.05). En esta serie experimental se incluyó la utilización de un nuevo índice no invasivo de contrapulsación que utiliza las áreas bajo el perfil de presión aórtica... (TRUNCADO)(AU)

Fibrinolisis local en un modelo canino de tromboembolismo pulmonar / Local fibrinolysis in a canine model of pulmonary thromboembolism

El tromboembolismo pulmonar agudo y masivo tiene una alta mortalidad dentro de las primeras horas. Las intervenciones quirúrgicas pueden solo remover grandes trombos y por otro lado el tratamiento fibrinolítico sistémico requiere de cierto tiempo para asegurar una resolución completa del cuadro clínico. En este trabajo se describe un modelo canino, bajo anestesia general, de tromboembolismo pulmonar diseminado, agudo y masivo que se logró con la inyección de 1.7 mls/kg de peso de trombos de 1 hora de edad. Los mismos fueron inyectados directamente en la arteria pulmonar. En todos los casos se realizaron mediciones de índice cardíaco, presión auricular izquierda, presión aórtica, presión pulmonar y resistencias vasculares pulmonares. El grupo de animales tratado contó con su correspondiente grupo testigo. Los émbolos fueron lisados usando 50.000 U.I. de Estreptoquinasa recirculado durante 20 minutos a través del circuito vascular pulmonar usando una bomba a rodillos de circulación extracorpórea a la manera tradicional. Luego del tratamiento instituído, los parámetros hemodinámicos retornaron a valores basales en el grupo tratado. El éxito del tratamiento fue histológicamente confirmado y se efectuó un estudio completo del sistema fibrinolítico en todos los casos usando sangre extraída de los canes al principio y al final del experimento. Los animales del grupo testigo a los que la perfusión pulmonar se les realizó sin usar Estreptoquinasa empeoraron desde el punto de vista hemodinámico en comparación con el otro grupo.

Fibrinolisis local en un modelo canino de tromboembolismo pulmonar / Local fibrinolysis in a canine model of pulmonary thromboembolism

El tromboembolismo pulmonar agudo y masivo tiene una alta mortalidad dentro de las primeras horas. Las intervenciones quirúrgicas pueden solo remover grandes trombos y por otro lado el tratamiento fibrinolítico sistémico requiere de cierto tiempo para asegurar una resolución completa del cuadro clínico. En este trabajo se describe un modelo canino, bajo anestesia general, de tromboembolismo pulmonar diseminado, agudo y masivo que se logró con la inyección de 1.7 mls/kg de peso de trombos de 1 hora de edad. Los mismos fueron inyectados directamente en la arteria pulmonar. En todos los casos se realizaron mediciones de índice cardíaco, presión auricular izquierda, presión aórtica, presión pulmonar y resistencias vasculares pulmonares. El grupo de animales tratado contó con su correspondiente grupo testigo. Los émbolos fueron lisados usando 50.000 U.I. de Estreptoquinasa recirculado durante 20 minutos a través del circuito vascular pulmonar usando una bomba a rodillos de circulación extracorpórea a la manera tradicional. Luego del tratamiento instituído, los parámetros hemodinámicos retornaron a valores basales en el grupo tratado. El éxito del tratamiento fue histológicamente confirmado y se efectuó un estudio completo del sistema fibrinolítico en todos los casos usando sangre extraída de los canes al principio y al final del experimento. Los animales del grupo testigo a los que la perfusión pulmonar se les realizó sin usar Estreptoquinasa empeoraron desde el punto de vista hemodinámico en comparación con el otro grupo. (AU)