RESUMO
Each artery conduces blood (conduit function, CF) and smoothes out the pulsatility (buffering function, BF), while keeping its wall protected against the high oscillations of the pulse waves (damping function, xi). These functions depend on each segment viscoelasticity and capability to store and dissipate energy. When a graft/prosthesis is implanted, the physiological gradual transition in the viscoelasticity and functionality of adjacent arterial segments is disrupted. It remains to be elucidated if the cryografts would allow keeping the physiological biomechanical transition. The aim of this study was to evaluate the cryografts capability to reproduce the functional, energetic and reflection properties of patients' arteries and fresh homografts. Common carotid's pressure, diameter and wall-thickness were recorded in vivo (15 patients) and in vitro (15 cryografts and 15 fresh homografts from donors). Calculus: elastic (Epd) and viscous (Vpd) indexes, CF, BF, dissipated (WD) and stored (WPS) energy and xi. The graft-patient's artery matching was evaluated using the reflection coefficient (Gamma) and reflected power (WGamma). Cryografts did not show differences in Epd, Vpd, BF, CF, WD, WPS, and xi, in respect to fresh homografts and patients' arteries, ensuring a reduced Gamma and WGamma. Cryografts could be considered as alternatives in arterial reconstructions since they ensure the gradual transition of patients' arteries biomechanical and functional behavior.
Assuntos
Bioprótese , Implante de Prótese Vascular/instrumentação , Prótese Vascular , Artéria Carótida Primitiva/fisiologia , Criopreservação , Fluxo Pulsátil , Adulto , Pressão Sanguínea , Artéria Carótida Primitiva/diagnóstico por imagem , Artéria Carótida Primitiva/transplante , Elasticidade , Frequência Cardíaca , Humanos , Masculino , Teste de Materiais , Pessoa de Meia-Idade , Modelos Cardiovasculares , Desenho de Prótese , Estresse Mecânico , UltrassonografiaRESUMO
AIMS: 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. 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 SS(R) and SS(O) 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 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. CONCLUSION: 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.
Assuntos
Aorta/fisiologia , Balão Intra-Aórtico , Músculo Liso/fisiologia , Ovinos , Vasoconstrição/fisiologia , Animais , Fenômenos Biomecânicos , Resistência ao CisalhamentoRESUMO
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.
Assuntos
Tronco Braquiocefálico/fisiologia , Tecido Conjuntivo/fisiologia , Animais , Tronco Braquiocefálico/anatomia & histologia , Tecido Conjuntivo/anatomia & histologia , Elasticidade , Masculino , Modelos Biológicos , Músculo Liso Vascular/fisiologia , Carneiro Doméstico , Técnicas de Cultura de Tecidos , Transdutores de Pressão , ViscosidadeRESUMO
BACKGROUND: Dynamic aortomyoplasty is an alternative technique to heart transplantation. The goal of our study was to evaluate the benefits of aortic counterpulsation obtained by dynamic thoracic aortomyoplasty in patients with heart failure refractory to pharmacologic treatment and contraindications to heart transplant or cardiomyoplasty. METHODS: In this study we compared preoperative and postoperative data from five out of six carefully selected patients who were treated with dynamic thoracic aortomyoplasty. This surgical technique wraps the right latissimus dorsi muscle flap around the ascending aorta. This muscle flap was electrically stimulated during diastole, following a muscle-conditioning protocol, to obtain diastolic augmentation. At the 6-month follow-up period we evaluated, invasively and noninvasively, the hemodynamic and clinical effects of aortomyoplasty. RESULTS: We observed a significant decrease in the number of hospitalizations (P = 0.01), NYHA functional class (P = 0.01), cardiothoracic ratio (P = 0.02), right ventricular diameter (P = 0.03), left atrial diameter (P = 0.04), and pulmonary artery systolic pressure (P = 0.04); and a significant increase in the 6-minute walking test (P = 0.01), cardiac index (P = 0.04), noninvasive evaluation of diastolic augmentation (P = 0.01), left ventricular shortening fraction (P = 0.01), and radioisotopic left ventricular ejection fraction (P = 0.02). We also found a nonsignificant decrease in the left ventricular diameter (P = 0.08) and wedge pressure (P = 0.19); and a nonsignificant increase in peak oxygen consumption (P = 0.13). CONCLUSIONS: Dynamic thoracic aortomyoplasty in heart failure resulted in an important improvement of hemodynamic parameters, heart functional data, and clinical functional class, when comparing preoperative data with the 6-month follow-up data.
Assuntos
Aorta Torácica/cirurgia , Contrapulsação/métodos , Insuficiência Cardíaca/terapia , Músculo Esquelético/transplante , Retalhos Cirúrgicos , Procedimentos Cirúrgicos Vasculares/métodos , Adulto , Idoso , Aorta Torácica/diagnóstico por imagem , Cateterismo Cardíaco , Cineangiografia , Estimulação Elétrica , Feminino , Seguimentos , Insuficiência Cardíaca/diagnóstico por imagem , Insuficiência Cardíaca/fisiopatologia , Humanos , Masculino , Pessoa de Meia-Idade , Contração Miocárdica , Período Pós-Operatório , Pressão Propulsora Pulmonar , Volume Sistólico , Resultado do TratamentoRESUMO
BACKGROUND: Aortic counterpulsation, either biologic or mechanical, is a useful technique to support circulation during left ventricular dysfunction. METHODS: In this study we used an induced cardiac failure model in acute open chest sheep to compare hemodynamic improvements between thoracic and abdominal aortic counterpulsation. This was achieved with left latissimus dorsi and left hemidiaphragm muscle flaps. RESULTS: Thoracic and abdominal aortic counterpulsation in heart failure resulted in a significant improvement of hemodynamic parameters. Subendocardial viability index, defined as diastolic pressure-time index to systolic tension-time index, in thoracic and abdominal aortomyoplasty showed significant improvement (p<0.05) when cardiac assistance was performed by electrical stimulation of each muscle flap. A new counterpulsation index derived from diastolic and systolic areas beneath the aortic pressure curve was tested, obtaining a correlation coefficient with the subendocardial viability index of 0.758 (p<0.001). Values of subendocardial viability index and counterpulsation index showed minimal variability. CONCLUSIONS: Treatment of experimentally induced cardiac failure with dynamic abdominal aortic counterpulsation allows an effective hemodynamic improvement in open chest sheep. Furthermore, this diastolic arterial pressure augmentation could be evaluated through a new counterpulsation index derived from diastolic and systolic areas beneath the aortic pressure curve.
Assuntos
Aorta Abdominal/cirurgia , Aorta Torácica/cirurgia , Contrapulsação/métodos , Insuficiência Cardíaca/terapia , Animais , Hemodinâmica , Músculo Esquelético/transplante , Ovinos , Retalhos CirúrgicosRESUMO
Dynamic aortomyoplasty has been the subject of experimentation for the treatment of congestive heart failure during the last few years. This method consists of diastolic counterpulsation of the ascending aorta through the stimulation of the latissimus dorsi wrapped around it. This report describes the results of aortomyoplasty in a patient with dilated cardiomyopathy resulting from Chagas' disease and contraindications for heart transplantation or cardiomyoplasty.
Assuntos
Aorta/cirurgia , Cardiomioplastia/métodos , Contrapulsação/métodos , Insuficiência Cardíaca/cirurgia , Aorta/fisiopatologia , Cardiomiopatia Dilatada/fisiopatologia , Cardiomiopatia Dilatada/cirurgia , Cardiomiopatia Chagásica/fisiopatologia , Cardiomiopatia Chagásica/cirurgia , Contraindicações , Insuficiência Cardíaca/fisiopatologia , Transplante de Coração , Hemodinâmica/fisiologia , Humanos , Masculino , Pessoa de Meia-Idade , Complicações Pós-Operatórias/fisiopatologiaRESUMO
The influence of the renin-angiotensin system (RAS) on the aortic wall mechanical properties under angiotensin I converting enzyme inhibition (enalaprilat, 0.3 mg/kg iv) or angiotensin II receptor (AT1) blockade (E-3174, 1 mg/kg iv) was examined in eight normotensive and eight renovascular hypertensive conscious dogs. Aortic diameter (D; sonomicrometry)-pressure (P; microtransducer) hysteresis loops during steady state and during rapid distal aortic occlusion allowed (after hysteresis elimination) calculation of the aortic wall viscosity index, the purely elastic P-D relationship, and derivation into compliance-pressure curves. At the early stage ofrenovascular hypertension when activation of RAS is more pronounced, aortic wall stiffness and wall viscosity were increased as compared with normotensive states. Blood pressure remained unchanged in normotensive animals and was reduced during hypertension after antihypertensive treatments. In hypertensive animals, enalaprilat and E-3174 decreased viscosity index and shifted the compliance-pressure curve upward with respect to pretreatment conditions. In normotensive dogs, whereas E-3174 did not change the compliance-pressure curve and viscosity index, enalaprilat increased compliance and reduced viscosity index. We concluded that in normotensive dogs converting enzyme inhibition modifies arterial viscoelastic parameters by angiotensin-independent mechanisms that contribute to the modulation of the buffering function of large arteries.
Assuntos
Antagonistas de Receptores de Angiotensina , Inibidores da Enzima Conversora de Angiotensina/farmacologia , Aorta/efeitos dos fármacos , Aorta/fisiologia , Angiotensina I/antagonistas & inibidores , Animais , Anti-Hipertensivos/farmacologia , Aorta/metabolismo , Pressão Sanguínea/efeitos dos fármacos , Cães , Elasticidade , Enalaprilato/farmacologia , Hipertensão Renovascular/fisiopatologia , Imidazóis/farmacologia , Losartan , Masculino , Valores de Referência , Tetrazóis/farmacologia , ViscosidadeRESUMO
Knowledge about the viscoelastic behaviour of the arterial wall has been proved to have physiological importance and clinical usage. Our purpose was to study the changes of the systemic arterial wall's elastic properties non-invasively, in patients with established essential and with borderline hypertension, and to evaluate its possible determinants. Three groups of normotensive, borderline and established essential hypertensive patients were evaluated. Arterial pulse wave velocity (PWV) was measured and arterial compliance (Cm) was derived in all patients. Pulse wave velocity was obtained from the pressure values of digitized carotid and radial arteries. Arterial compliance (Cm = dD/dP with P pressure and D diameter) was calculated using a formula derived from the Bramwell and Hill equation: Cm = (1,334 x D)/(2 rho x PWV2), where for D humeral diameter was used as measured by high resolution echograph, and rho is the blood density (rho = 1.06). Pulse wave velocity was significantly higher in established essential hypertensive patients with respect to normotensive patients (p < 0.05). Arterial compliance was significantly diminished in established and in borderline hypertensive patients with respect to normotensive patients (p < 0.05), which implies early alterations in hypertensive cardiovascular disease. Multiple regression analysis of the cofactors showed that age and diastolic pressure are independent determinants of Cm. Impairment of the arterial wall's intrinsic elastic properties was demonstrated in established essential hypertension, independent of age and diastolic pressure.
Assuntos
Artérias/fisiopatologia , Hipertensão/fisiopatologia , Adolescente , Adulto , Fatores Etários , Idoso , Algoritmos , Artérias/diagnóstico por imagem , Artérias/patologia , Velocidade do Fluxo Sanguíneo/fisiologia , Pressão Sanguínea/fisiologia , Viscosidade Sanguínea/fisiologia , Artéria Carótida Primitiva/diagnóstico por imagem , Artéria Carótida Primitiva/patologia , Artéria Carótida Primitiva/fisiopatologia , Diástole , Elasticidade , Feminino , Frequência Cardíaca/fisiologia , Humanos , Úmero/irrigação sanguínea , Úmero/diagnóstico por imagem , Modelos Lineares , Masculino , Pessoa de Meia-Idade , Fluxo Pulsátil/fisiologia , Artéria Radial/diagnóstico por imagem , Artéria Radial/patologia , Artéria Radial/fisiopatologia , Ultrassonografia , Capacitância Vascular/fisiologia , ViscosidadeRESUMO
The aim of our work was to study the hemodynamic effects of dynamic cardiomyoplasty on an acute animal model of atrial fibrillated heart failure. Eight anesthetized open chest dogs suffering from atrial fibrillation and heart failure, obtained by topic acetylcholine and propranolol, were treated by a cardiomyoplasty procedure performed with an electrostimulated latissimus dorsi muscle flap (LDMF). Values considered for analysis during LDMF stimulation were selected from cardiac cycles with R-R intervals similar to those when the LDMF was not stimulated (+/- 20 ms). Atrial fibrillated heart failure showed a significant increase of systemic vascular resistance, end diastolic left ventricular pressure (EDLVP) and right atrial pressure (p < 0.05), and a significant decrease in cardiac output, systolic left ventricular pressure (SLVP), and mean aortic pressure (p < 0.05) compared with control values. LDMF stimulation in atrial fibrillated heart failure resulted in a significant increase of SLVP, cardiac output, and mean aortic pressure (p < 0.05) and a significant decrease of systemic vascular resistance, EDLVP, and right atrial pressure (p < 0.05) compared with nonstimulated values. The highest LVP values were obtained with R-R intervals long enough to allow an adequate LV filling. We conclude that dynamic cardiomyoplasty provides an appropriate recovery in this animal model of atrial fibrillated heart failure. Cardiomyoplasty is an appropriate procedure for cardiac assist when R-R intervals allow an adequate LV filling.
Assuntos
Fibrilação Atrial/cirurgia , Pressão Sanguínea/fisiologia , Débito Cardíaco/fisiologia , Insuficiência Cardíaca/cirurgia , Resistência Vascular/fisiologia , Acetilcolina/toxicidade , Animais , Fibrilação Atrial/induzido quimicamente , Cardiomioplastia , Modelos Animais de Doenças , Cães , Estimulação Elétrica , Feminino , Insuficiência Cardíaca/induzido quimicamente , Masculino , Propranolol/toxicidade , Resultado do Tratamento , Função Ventricular Esquerda/fisiologiaRESUMO
PURPOSE: To study the hemodynamic effects of latissimus dorsi dynamic pulmonaroplasty in open chest animals. METHODS: Six anesthetized mongrel dogs were subjected to diastolic counterpulsation using electrically stimulated latissimus dorsi muscle flap wrapped around the aortic and pulmonary arteries roots and gated to the surface electrocardiogram. Aortic and Pulmonanary pressures as well as cardiac output and cardiac index were measured. RESULTS: Diastolic counterpulsation resulted in a significant increase in cardiac output (from 2.35 +/- 0.26 to 2.45 +/- 0.28 l/min) (p < 0.005) and cardiac index (from 0.108 +/- 0.020 to 0.113 +/- 0.020 l/min/kg) (p < 0.05). The diastolic pulmonary arterial efficiency index showed a significant increase when latissimus dorsi stimulation was on (from 8.37 +/- 0.60 to 11.65 +/- 0.83 mmHg); (p < 0.005). CONCLUSION: Latissimus dorsi dynamic pulmonaroplasty provides an effective means of arterial counter pulsation in open chest dogs.
Assuntos
Aorta/cirurgia , Contrapulsação/métodos , Artéria Pulmonar/cirurgia , Disfunção Ventricular Direita/terapia , Animais , Pressão Sanguínea , Cães , Eletrocardiografia , Retalhos Cirúrgicos , Disfunção Ventricular Direita/fisiopatologiaRESUMO
A description of the arterial wall elastic properties comprehends both collagen and elastin, clearly shown in a biphasic stress-strain relationship. From chronically instrumented conscious dogs, aortic pressure-diameter curves can be obtained in a single beat, which is impossible to perform in human beings. In control conditions, the collagen fibers are almost not distended and the resistance to stretch is mainly supported by the elastin fibers. Therefore, the mechanical properties of the aorta are almost purely elastic in the basal beat to beat conditions. In this study we propose and test five indexes, which include as variables: systolic, diastolic and mean arterial pressure and diameter; besides, arterial compliance and pressure-strain elastic modulus as suggested to evaluate the elastic behaviour of the elastic fibers. This data can be easily obtained by non-invasive methods, such as Doppler-ultrasound techniques and auscultative esphygmomanometrical measurements, while the indexes evaluated can be retrieved from a single beat evaluation. Of three measurements performed in chronically instrumented conscious dogs on different days, one of these indexes, the ME5 = [formula: see text] x Rdias proved to be an accurate and reliable parameter to evaluate the mechanical behaviour of arteries. This kind of parameter may be useful for research and evaluation of several diseases that markedly alter the arterial wall compliance.
Assuntos
Aorta/fisiologia , Elasticidade , Algoritmos , Animais , Pressão Sanguínea , Colágeno/fisiologia , Diástole/fisiologia , Cães , Elastina/fisiologia , Masculino , Modelos Cardiovasculares , Análise de Regressão , Processamento de Sinais Assistido por Computador , Estresse Mecânico , Sístole/fisiologiaRESUMO
We describe a technique for mechanical cardiac assistance in an acute model of severe cardiac failure. Cardiac dysfunction was induced by a high dose of halothane in 13 dogs. Seven served as controls. Following median sternotomy, a pneumatically driven device was implanted in the other six dogs in a para-aortic position, using a simple surgical technique without cardiopulmonary bypass. The aorta was cross-clamped during cardiac assistance. During hemodynamic studies, the seven control animals with induced cardiac failure showed high end-diastolic left ventricular and right atrial pressures with low cardiac index and systolic left ventricular and aortic pressures. All dogs in this group died within 30 minutes. Use of a monovalvular cardiac assist device in the experimental group of six dogs to pump blood from the aortic root to the descending aorta in a counterpulsation manner, confirmed good preservation of systemic hemodynamic parameters after induction of heart failure. All animals in this treated group survived more than 45 minutes. Hemodynamically, the device acts as a new ventricle and the impaired left ventricle functionally becomes a left atrium. This condition is clinically appropriate for recovery of left ventricular function in severe acute myocardial failure.
Assuntos
Contrapulsação/instrumentação , Insuficiência Cardíaca/terapia , Coração Auxiliar , Hemodinâmica/fisiologia , Animais , Cães , Desenho de Equipamento , Halotano , Insuficiência Cardíaca/induzido quimicamenteRESUMO
Nine adult mongrel dogs were instrumented with ultrasonic microcrystals to measure left ventricular basal anteroposterior diameter and midwall myocardial segment length near the cardiac apex. Pneumatic cuff occluders were positioned around the left circumflex coronary artery near its origin and around the left anterior descending coronary artery two thirds of the way along its length. A pressure microtransducer was implanted into the left ventricle. Ten days after instrumentation the animals were anaesthetised with morphine chlorhydrate and pentobarbital sodium. An eight electrode catheter was advanced into the left ventricle to measure ventricular apical and basal regional and total electrical conductance. Minor ischaemia caused by occlusion of the left anterior descending artery was detected only by the electrode pair located near the apex, as decreased local ejection fraction. Major ischaemia caused by left circumflex artery occlusion was detected by both apical and basal electrode pairs and by total conductance, the three conductance signals indicating reduced ejection fractions compared with control values. The basal diameter signal indicated that basal regional motility changed only during major ischaemia, thus confirming the specificity of the changes in the basal conductance signals. The apical segment length signal confirmed the altered motility indicated by the apical conductance signal. These results suggest that regional wall motion abnormalities may be detected by the use of a multielectrode conductance catheter.
Assuntos
Cateterismo Cardíaco/métodos , Doença das Coronárias/diagnóstico , Condutividade Elétrica , Animais , Pressão Sanguínea , Doença das Coronárias/patologia , Doença das Coronárias/fisiopatologia , Cães , Eletrodos , Ventrículos do Coração/fisiopatologia , Miocárdio/patologiaRESUMO
We tested the ability of the slope (Emax) and the volume intercept (Vo) of the end-systolic pressure-volume relationship (ESPVR) to indicate contractility changes in conscious dogs instrumented with sonomicrometers measuring left ventricular diameter in three orthogonal axes and a left ventricular pressure microtransducer. ESPVRs were generated by inferior vena caval occlusion under control conditions (C1 and C2) and during enhanced (I+) and depressed (I-) inotropic states achieved by infusion of dobutamine and injection of propranolol, respectively. No significant difference between the first control (C1) and I+ or between the second control (C2) and I- were found for either Emax (C1, 5.31 +/- 1.68 mm Hg/ml, mean +/- SD; I+, 5.37 +/- 1.44; C2, 5.20 +/- 1.62; I-, 4.18 +/- 1.32) or Vo (C1, 10.3 +/- 9.6 ml; I+, 7.3 +/- 9.1; C2, 9.9 +/- 9.0; I-, 12.7 +/- 12.5), despite significant changes in other indexes of contractility. Comparison of changes in Emax in individual animals in response to I+ and I- revealed that 63% were nonsignificant, 28% were significant and expected, and 9% were significant and paradoxical. Within defined volume limits and irrespective of individual changes in Emax and Vo, in all animals I+ shifted the ESPVR above and to the left of C1 and I- shifted the ESPVR below and to the right of C2. We thus integrated the changes in Emax and Vo by measuring the area beneath each ESPVR between defined limits of end-systolic volume. The values for area were: C1, 612 +/- 150 mm Hg.ml; I+, 745 +/- 191 (p less than .001); C2, 520 +/- 198; I-, 420 +/- 139 (p less than .001). We conclude that (1) neither Emax nor Vo are individually reliable indexes of changed contractility, and (2) the area beneath the ESPVR between defined end-systolic volume limits is a consistent indicator of variations in inotropic state.