RESUMO
Myocardial perfusion is performed by the left and the right coronary arteries, which deliver blood to the left and right ventricles, respectively. The impairment of arterial flow supply to the cardiac muscle by disease denotes a phenomenon known as ischaemia. Previous studies have demonstrated the ability of fractal dimension (FD) value of a physiological parameter in differentiating healthy/pathological behaviours. The aim of this study consisted in quantifying the loss of ventricular thickness fractal complexity in order to determine if FD is an intrinsic marker of acute coronary ischaemia. Five mongrel dogs weighing 18.8-26.5 kg (24.4 ± 3.3, mean ± SD) were submitted to this studio. A left ventricular pressure transducer and a fluid-filled catheter for later calibration of the pressure transducer were introduced through a stab wound near the apex. Two pairs of ultrasonic microcrystals (5 MHz) for continuous wall thickness measurements were implanted at the anterior and posterior walls of the left ventricle following a previously described technique. During coronary occlusion, the ischemic wall started to thin at the very onset of relaxation (showing abnormal motility), while the normoperfused wall displayed postejective thickening. Concomitantly, posterior ventricular wall thickness and anterior wall ventricular thickness showed a significant decrease in its FD value (P <0.05). In conclusion, loss of time series fractal complexity (waveform fine structure diminution or 'unwrinkling') constitutes a marker of the presence of an ischemic process. As a result, a single scalar value is sufficient to characterize the entire behaviour of the time series. This value manifested a similar trend compared to the most well-known clinical indices of myocardial ischaemia.
Assuntos
Fractais , Ventrículos do Coração/fisiopatologia , Isquemia Miocárdica/fisiopatologia , Animais , Pressão Sanguínea/fisiologia , Cães , Perfusão , Projetos PilotoRESUMO
UNLABELLED: Flow-mediated dilatation (FMD) is the most accepted technique for the evaluation of endothelial function. However, it has been show a great inter-subject variability limiting its clinical use. Carotid-radial pulse wave velocity (PWVcr) was proposed as an alternative tool for the evaluation of endothelial function. At the present, there is no doubt that PWVcr reduces its values in response to reactive hyperemia test (RHT) in healthy subjects. AIMS: a) to determine simultaneously the temporal profile of FMD, PWVcr and shear rate in response to RHT and b) to describe and analyze how subjects "FMD responders" or "non-responders" behave regards to PWVcr changes. METHODS: 34 Healthy young subjects were included. The PWVcr (strain gauge mechanotransducers), brachial diameter (B-Mode ultrasound and blood flow velocity (Doppler ultrasound) were measured before (baseline) the cuff was inflated and after its deflation (5 minutes). 10(th) percentiles FMD and PWVcr changes in the population were used for the definition of the subjects ("responders and non-responders"). RESULTS: Changes in PWVcr, brachial arterial diameter and shear rate were evidenced after the cuff release (p<0.05). There were differences in the PWV and FMD temporal profiles. Within "FMD responders" there were "PWV responders and non-responders". CONCLUSION: Assessing RHT-related changes in PWVcr in the context of a FMD evaluation, could be useful as a discriminator of intrinsic wall alterations giving additional information of vascular dynamics.
Assuntos
Artérias Carótidas/patologia , Adulto , Algoritmos , Velocidade do Fluxo Sanguíneo/fisiologia , Pressão Sanguínea , Artéria Braquial/patologia , Sistema Cardiovascular , Dilatação , Endotélio Vascular/patologia , Feminino , Humanos , Hiperemia/patologia , Masculino , Resistência ao Cisalhamento , Estresse Mecânico , Fatores de Tempo , Vasodilatação/fisiologiaRESUMO
Atherosclerotic plaques form at specific sites of the arterial tree, an observation that has led to the "geometric risk factor" hypothesis for atherogenesis. It is accepted that the location of atherosclerotic plaques is correlated with sites subjected to low abnormal values of wall shear stress (WSS), which is in turn determined by the specific geometry of the arterial segment. In particular, the left coronary artery (LCA) is one of the most important sites of plaque formation and its progression may lead to stroke. However, little is known about hemodynamics and WSS distributions in the LCA. The purpose of this work is to set up a method to evaluate flow patterns and WSS distributions in the human LCA based on real patient-specific geometries reconstructed from medical images.
Assuntos
Artérias/fisiopatologia , Vasos Coronários/fisiopatologia , Estresse Fisiológico , Aterosclerose/fisiopatologia , Humanos , Modelos AnatômicosRESUMO
The early detection of biomechanical modifications in the arterial wall could be used as a predictor factor for various diseases, for example hypertension or atherosclerosis. In this work a transient elastography technique is used for the in vitro evaluation of the arterial wall elasticity. The obtained Young modulus is compared with the one obtained by a more classical approach: pressure-diameter relationships. As a sample an arterial phantom made of PolyVinyl Alcohol (PVA) gel was used. Diameter variation due to pressure variation inside the phantom was recorded by means of ultrasound. Through both techniques similar Young modulus estimations are obtained showing in this way the feasibility of applying transient elastography for the arterial wall elasticity assessment.
Assuntos
Artérias/diagnóstico por imagem , Técnicas de Imagem por Elasticidade/métodos , Processamento de Imagem Assistida por Computador/métodos , Modelos Cardiovasculares , Algoritmos , Módulo de Elasticidade , Estudos de Viabilidade , Imagens de Fantasmas , Álcool de Polivinil , VibraçãoRESUMO
UNLABELLED: The analysis of carotid-radial pulse wave velocity (PWVcr) changes in response to forearm transient ischemia (TI) has been proposed as an alternative approach to evaluate endothelial function. Consider flow mediated dilatation tests, PWVcr changes are characterized after 5 minutes of TI. It is unknown if lower TI times could be used and if different TI times would result in different PWVcr responses (levels and/or kinetics). OBJECTIVE: To determine PWVcr changes associated with the reactive hyperemia in response to 1, 3 or 5 minutes of forearm TI. METHODS: We measured left PWVcr change using mechano-transducers in healthy volunteers (22 ± 2 years old) before (basal) and after 1 (n=14), 3 (n=14) and 5 (n=15) minutes of TI (forearm cuff inflation), respectively. The change of level and rate in PWVcr were recorded at 15, 30, 45 and 60 seconds after cuff release. Right brachial pressure was measured. RESULTS: There were no changes in heart rate or blood pressure during the studies. Regardless of the occlusion length, TI resulted in PWVcr reduction (p < 0.05). The groups showed similar maximum PWVcr reduction. However, there were differences in the immediate PWVcr changes (-4.9 ± 0.2%; -6.8 ± 0.3% and -8.3 ± 0.5% for 1, 3 and 5 minutes of TI, respectively) (p < 0.05). Then, the immediate rate of PWVcr change differed (p < 0.05) among the different ischemia times considered. Thereafter, the differences diminished and a minute after TI the groups showed similar levels and mean rate of PWVcr reduction. CONCLUSION: Similar maximum PWVcr responses can be obtained after 1, 3, or 5 minutes of TI. Different TI times resulted in dissimilar immediate, but not later, PWVcr changes.
Assuntos
Artérias Carótidas/patologia , Hiperemia/diagnóstico , Hiperemia/fisiopatologia , Isquemia , Adulto , Algoritmos , Fenômenos Biomecânicos , Determinação da Pressão Arterial , Frequência Cardíaca , Humanos , Cinética , Processamento de Sinais Assistido por Computador , Software , Esfigmomanômetros , Fatores de Tempo , TransdutoresRESUMO
Atherosclerotic plaque complication is a major cause of vascular accidents. Although a variety of factors have been proposed as key factors in these process, the mechanism that contribute to this problem remain to be characterized. Previously we demonstrated that changes in arterial wall viscous and elastic properties and/or in the filtering function (FF) could be part of the arterial wall alterations basis. If these properties are altered in arteries with atherosclerotic plaques remains to be analyzed. Our aims were 1) to analyze the arterial wall visco-elasticity and FF of carotid and femoral segments with atherosclerotic plaques, 2) to compare them with the mechanical behavior of segments without plaques (from the same artery) and of healthy arteries studied non-invasively. To this end, in each arterial segment, pressure and diameter signals were obtained, in vitro (circulation mock) and in vivo (non-invasive recordings). In atherosclerotic arteries recordings were performed on plaques and near regions without plaques. In each segment, the elasticity, the viscosity, and the wall FF were quantified. Atherosclerotic vessels, and particularly plaque regions, showed a reduced viscosity and FF. At the light of our results, hypothetical links between plaque events and changes in visco-elasticity and FF were discussed.
Assuntos
Aterosclerose/patologia , Artéria Carótida Primitiva/patologia , Artéria Femoral/patologia , Placa Aterosclerótica/patologia , Adulto , Fenômenos Biomecânicos , Elasticidade , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Modelos Cardiovasculares , Modelos Estatísticos , Processamento de Sinais Assistido por Computador , ViscosidadeRESUMO
In several clinical and experimental circumstances, it is widely necessary to characterize the bio-mechanical changes induced by atherosclerosis to the arterial wall. In this context, the purpose of this paper is twofold. Firstly, to propose a low cost ultrasound setup to improve artery radii determination in elasticity experiments, based on two transducers using a single channel ultrasound hardware. Secondly, to present an in vitro artificial heart system developed in our laboratory, which provides a wide range of hemodynamic parameters in arterial elasticity assessment experiments. It can be used in a liquid, stand alone mode or blowing air to a Jarvik device. This system will be integrated in future works with the proposed ultrasound setup to provide real time elasticity measurements.
Assuntos
Artérias/diagnóstico por imagem , Coração Artificial , Ultrassonografia/métodos , Algoritmos , Fenômenos Biomecânicos , Calibragem , Ecocardiografia/métodos , Elasticidade , Técnicas de Imagem por Elasticidade/métodos , Desenho de Equipamento , Hemodinâmica , Humanos , Processamento de Imagem Assistida por Computador , Técnicas In Vitro , Pressão , TransdutoresRESUMO
Although a variety of factors have been proposed as key factors of the atherosclerotic plaque vulnerability, the mechanisms that contribute to this problem are not yet fully characterized. In previous works we demonstrated that changes in arterial wall viscosity and elasticity and/or in the filtering function (FF) could be in the basis of arterial wall alterations. If these properties are altered in arterial wall with atherosclerotic plaques remain to be analyzed. Our aims were to analyze, the arterial wall visco-elasticity and FF of human carotid arteries with atherosclerotic plaques. To this end, instantaneous arterial diameter waveforms were obtained non-invasively (B-Mode Echography), in five sites (S1-S5) on the carotid artery. After that, diameter waveform obtained in S1 (first segment of the common carotid artery) was calibrated using pressure values, and used to quantify the pressure-diameter relationship for each segment. From pressure-diameter relationships, viscosity, elasticity and FF were quantified. Central portions of atherosclerotic plaques showed a reduced FF. At least in theoretical terms, the FF reduction could be related with the plaque vulnerability.
Assuntos
Aterosclerose/diagnóstico , Aterosclerose/patologia , Artérias Carótidas/patologia , Idoso , Calibragem , Ecocardiografia/métodos , Elasticidade , Humanos , Masculino , Pessoa de Meia-Idade , Modelos Estatísticos , Placa Aterosclerótica/diagnóstico , Placa Aterosclerótica/patologia , Pressão , Software , Ultrassonografia/métodos , ViscosidadeRESUMO
Biomechanical and functional properties of tissue engineered vascular grafts must be similar to those observed in native vessels. This supposes a complete mechanical and structural characterization of the blood vessels. To this end, static and dynamic mechanical tests performed in the sheep thoracic and abdominal aorta and the cava vein were contrasted with histological quantification of their main constituents: elastin, collagen and muscle cells. Our results demonstrate that in order to obtain adequate engineered vascular grafts, the absolute amount of collagen fibers, the collagen/elastin ratio, the amount of muscle cells and the muscle cells/elastic fibers ratio are necessary to be determined in order to ensure adequate elastic modulus capable of resisting high stretches, an adequate elastic modulus at low and normal stretch values, the correct viscous energy dissipation, and a good dissipation factor and buffering function, respectively.
Assuntos
Artérias/patologia , Prótese Vascular , Veias/patologia , Animais , Aorta Abdominal/patologia , Aorta Torácica/patologia , Fenômenos Biomecânicos , Soluções Tampão , Colágeno/química , Módulo de Elasticidade , Elastina/química , Masculino , Ovinos , Estresse Mecânico , Resistência à Tração , Engenharia Tecidual/métodos , Veias Cavas/patologiaRESUMO
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.