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ABSTRACT: Traditional methods used to assess cardiovascular risk (i.e., the Framingham Risk Score) exhibit clear limitations. To aid in patient-specific risk stratification and diagnosis it has been proposed to evaluate noninvasively structural and functional arterial parameters. A National Public University Center (CUiiDARTE) was created in Uruguay with the aim of developing and applying strategies to improve cardiovascular risk stratification and subclinical vascular disease detection. To this end a health informatics approach and tool was designed, developed, and implemented in CUiiDARTE. Its goals were to: 1) promote screening for subclinical atherosclerosis, 2) develop a centralized database to store information obtained noninvasively from anywhere in our country, 3) develop a biomathematical model integrating values for arterial structure and function into traditional cardiovascular risk assessment, 4) generate a detailed and comprehensive report for the specialist comparing patient data with reference data from the healthy population, 5) generate a similar report (using a structural and functional arterial age calculator) for the patients assessing the state of their arteries. In this paper, we present the main characteristics of the CUiiDARTE health informatics development.
IEEE transactions on information technology in biomedicine: a publication of the IEEE Engineering in Medicine and Biology Society 03/2012; 16(5):943-51. · 1.69 Impact Factor
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ABSTRACT: 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.
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.
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").
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.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2011; 2011:6458-61.
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ABSTRACT: 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.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:2865-8.
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ABSTRACT: This study uses linear and nonlinear viscoelastic models to describe the dynamic distention of the aorta induced by time-varying arterial blood pressure. We employ an inverse mathematical modeling approach on a four-parameter (linear) Kelvin viscoelastic model and two five-parameter nonlinear viscoelastic models (arctangent and sigmoid) to infer vascular biomechanical properties under in vivo and ex vivo experimental conditions in ten and eleven male Merino sheep, respectively. We used the Akaike Information Criterion (AIC) as a goodness-of-fit measure. Results show that under both experimental conditions, the nonlinear models generally outperform the linear Kelvin model, as judged by the AIC. Furthermore, the sigmoid nonlinear viscoelastic model consistently achieves the lowest AIC and also matches the zero-stress vessel radii measured ex vivo. Based on these observations, we conclude that the sigmoid nonlinear viscoelastic model best describes the biomechanical properties of ovine large arteries under both experimental conditions considered in this study.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:2634-7.
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ABSTRACT: The cardiac resynchronization therapy (CRT) effects on the arterial load components, the mechanisms (i.e. haemodynamic changes-dependence) involved in the load reduction and the factors (i.e. basal load conditions) associated with the load changes after CRT, are to be evaluated. Aims: a) to analyze the potential changes in the arterial load components (peripheral resistances, arterial compliance and impedance) associated with the CRT, b) to determine if the load components changes are associated with variations in haemodynamic variables (pressure, heart rate or blood flow), c) to analyze the relationship between the load components basal state and their changes after CRT. To fulfill these aims cardiac and arterial structural and mechanical parameters were non-invasively evaluated in 8 heart failure patients, pre- and post-CRT (23plusmn8 days). The main results were that short-term after CRT: 1) there were changes in the static and dynamic determinants of the arterial load; 2) the changes in the load components were not associated with heart rate or pressure variations, but with blood flow changes, and 3) the load components basal levels and their changes after CRT were associated.
Engineering in Medicine and Biology Society, 2009. EMBC 2009. Annual International Conference of the IEEE; 10/2009
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ABSTRACT: Ergometric exercise stress tests (EST) give important information about the cardiovascular (CV) response to increased demands. The expected EST-related changes in variables like blood pressure and heart rate are known, but those in the arterial biomechanics are controversial and incompletely characterized. Aims: a) to characterize the regional and local arterial biomechanical behavior in response to EST, and its temporal profile in the post-EST recovery phase and (b) to compare different arteries biomechanical response to EST. Methods: In 16 non-trained healthy young subjects the carotid-femoral pulse wave velocity and the carotid, femoral and brachial arterial distensibility were non-invasively evaluated before (Rest) and after EST. Post exercise recordings were obtained 0-1, 4-5, and 9-10 minutes after exercise. The EST resulted in an early increase in the arterial stiffness, evidenced by regional and local parameters. There were quali-quantitative differences among the arterial local stiffness response to EST, when analyzing conjunctly the different postEST recovery stages. The biomechanical changes could not be explained only by blood pressure variations.
Engineering in Medicine and Biology Society, 2009. EMBC 2009. Annual International Conference of the IEEE; 10/2009
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F.P. Salvucci,
D. Bia,
R.L. Armentano,
J.G. Barra,
D. Craiem, Y. Zocalo,
J.D. Fernandez,
F. Baguear,
J.M. Atienza,
F.J. Rojo,
G.V. Guinea
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ABSTRACT: 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.
Engineering in Medicine and Biology Society, 2009. EMBC 2009. Annual International Conference of the IEEE; 10/2009
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ABSTRACT: Current methods used to evaluate the endothelial function have limitations. The analysis of the pulse wave velocity (PWV) response to transient ischaemia could be an alternative to evaluate the endothelial dynamics. Aims: To analyze (a) the carotid-radial PWV temporal profile during flow mediated dilatation test, and (b) the PWV changes considering its main vascular geometrical (diameter) and intrinsic (elastic modulus) determinants. Methods: Sixteen healthy young adults were included. The carotid-radial PWV (strain gauge mechano-transducers), wall thickness and brachial diameter (B-mode ultrasound) were measured before (basal state), during a forearm cuff inflation (5 minutes) and after its deflation (10 minutes). The PWV, brachial diameter and elastic modulus changes and temporal profile were analyzed (basal state, 15, 30, 45, and 60 seconds after cuff deflation). Results: Transient ischaemia was associated with arterial stiffness changes, evidenced by carotid-radial PWV variations. The PWV and diastolic diameter changes, and temporal profiles differed. The arterial stiffness changes could not be explained only by geometrical (diameter) changes. Conclusion: The carotid-radial PWV analysis, evaluated using robust and simple available techniques, could be used in the clinical practice to study the vascular response to transient ischaemia and the endothelial function.
Engineering in Medicine and Biology Society, 2009. EMBC 2009. Annual International Conference of the IEEE; 10/2009
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F P Salvucci,
D Bia,
R L Armentano,
J G Barra,
D Craiem, Y Zócalo,
J D Fernández,
F Baguear,
J M Atienza,
F J Rojo,
G V Guinea
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ABSTRACT: 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.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2009; 2009:4258-61.
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ABSTRACT: This paper compares two models predicting elastic and viscoelastic prop-erties of large arteries. Models compared include a Kelvin (standard linear) model and an extended 2-term exponential linear viscoelastic model. Models were vali-dated against in-vitro data from the ovine thoracic descending aorta and the carotid artery. Measurements of blood pressure data were used as an input to predict ves-sel cross-sectional area. Material properties were predicted by estimating a set of model parameters that minimize the difference between computed and measured values of the cross-sectional area. The model comparison was carried out using generalized analysis of variance type statistical tests. For the thoracic descending aorta, results suggest that the extended 2-term exponential model does not improve the ability to predict the observed cross-sectional area data, while for the carotid artery the extended model does statistically provide an improved fit to the data. This is in agreement with the fact that the aorta displays more complex nonlinear viscoelastic dynamics, while the stiffer carotid artery mainly displays simpler linear viscoelastic dynamics.
Adv. Appl. Math. Mech. 01/2009; 1:151-165.
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ABSTRACT: Objectives: Mechanisms underlying the circadian profile of cardiovascular events (CE) are not totally understood. Whether circadian changes in arterial stiffness (AS) could be related to the circadian profile of CE remains to be investigated. As yet, there is no accepted way to measure circadian profiles or nocturnal-related and/or morning-related changes in cardiovascular variables. The aim of this study was to characterize the circadian pattern and day-night and night-day changes of AS in untreated hypertensive (HG) and healthy subjects (NG), using a recently developed non-symmetrical six-parameter double-logistic model. Methods: Seven hypertensive and seven normotensive subjects underwent 24 hour ambulatory recordings of blood pressure (BP), heart rate (HR) and aorto-brachial pulse transit time (PTT AB ) and pulse transit velocity index (PTV AB ). PTT AB and PTV AB are inversely and directly related to AS, respectively. The circadian profile and transitional periods (day-night and night-day) were analyzed using a model described by a six-parameter double logistic equation. Conclusions: The model was adequate to characterize the circadian pattern of AS. We provide the first evidence that AS in humans follows an asymmetric circadian pattern and that this differs between NG and HG. In both NG and HG, AS had a circadian profile, with the highest levels in the night. HG showed larger levels of AS, larger BP variations and rate of change and minor changes in AS during transitional periods.
Engineering in Medicine and Biology Society, 2008. EMBS 2008. 30th Annual International Conference of the IEEE; 09/2008
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ABSTRACT: Mechanisms underlying the circadian profile of cardiovascular events (CE) are not totally understood. Whether circadian changes in arterial stiffness (AS) could be related to the circadian profile of CE remains to be investigated. As yet, there is no accepted way to measure circadian profiles or nocturnal-related and/or morning-related changes in cardiovascular variables. The aim of this study was to characterize the circadian pattern and day-night and night-day changes of AS in untreated hypertensive (HG) and healthy subjects (NG), using a recently developed non-symmetrical six-parameter double-logistic model.
Seven hypertensive and seven normotensive subjects underwent 24 hour ambulatory recordings of blood pressure (BP), heart rate (HR) and aorto-brachial pulse transit time (PTT(AB)) and pulse transit velocity index (PTV(AB)). PTT(AB) and PTV(AB) are inversely and directly related to AS, respectively. The circadian profile and transitional periods (day-night and night-day) were analyzed using a model described by a six-parameter double logistic equation.
The model was adequate to characterize the circadian pattern of AS. We provide the first evidence that AS in humans follows an asymmetric circadian pattern and that this differs between NG and HG. In both NG and HG, AS had a circadian profile, with the highest levels in the night. HG showed larger levels of AS, larger BP variations and rate of change and minor changes in AS during transitional periods.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2008; 2008:809-12.
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ABSTRACT: Recently, it has been proposed the use of speckle- tracking echography (STE) to study the left ventricle (LV) torsion dynamics, which would make LV torsion assessment more available in clinical and research cardiology. LV torsion has been described during exercise and in some sportsmen, but so far, its dynamics has not been studied in soccer players. The aims were to characterize and to compare LV apical and basal rotation, and to analyze LV torsion in professional soccer players using STE, and to determine the main differences in torsion between soccer players and age-matched non-trained individuals. The STE allowed characterizing LV rotation and torsion in both groups. LV torsion level and velocities were lesser in soccer players than in non-trained individuals. Changes in torsion in soccer players could represent physiological adaptations to training.
Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th Annual International Conference of the IEEE; 09/2007
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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.
Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th Annual International Conference of the IEEE; 09/2007
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ABSTRACT: The mechanics of the arterial wall is complex, due to its material structure and load conditions, which influence the hemodynamic properties as well as the growth and remodeling process of the cardiovascular system. Arterial remodeling can be found both locally and globally. Local remodeling is typically a result of disease, while global remodeling can be found even for healthy arteries. In this study we have analyzed how elastic and viscoelastic properties differ across 7 locations along the large ovine arteries in 11 sheep. We combined the Kelvin model with experimental measurements of vessel diameter and pressure obtained in-vitro at conditions mimicking the in-vivo dynamics. Elastic and viscoelastic wall-properties were assessed by analyzing values of four model parameters across the 7 locations. To do so we solved an inverse problem, resulting in computed estimates for each of the four parameter values that minimize the residual between the data and the model. We used sensitivity analysis to compute standard errors, and confidence intervals for all model parameters. Results showed that while elastic properties including Young's modulus and the vessel wall thickness varied across locations (smaller arteries were stiffer than larger arteries) viscoelastic relaxation parameters did not differ significantly across locations. We also showed that for all locations, the inclusion of viscoelastic behavior, e.g., using the Kelvin model, is important to capture pressure-area dynamics.
04/2007;
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ABSTRACT: The viscoelastic properties of the arterial wall are responsible for their functional role in the arterial system. Cryopreservation is widely used to preserve blood vessels for vascular reconstruction but is controversially suspected to affect the dynamic behaviour of these allografts. The aim of this study was to determine whether differences in the dynamic behaviour exist or not between fresh and cryopreserved human common carotid arteries (CCA). Using a previously developed mock circulation system, dynamic pressure-diameter tests were performed on segments of human fresh (n=10) and cryopreserved arteries (n=7). A diameter-pressure transfer function was designed to evaluate the wall dynamics. An adaptive model was fit to obtain its frequency response. Three models were tested. Results show that non-significant differences exist between wall dynamics of fresh and cryopreserved segments of human CCA.
Engineering in Medicine and Biology Society, 2004. IEMBS '04. 26th Annual International Conference of the IEEE; 10/2004
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ABSTRACT: The viscoelastic properties of the arterial wall are responsible for their functional role in the arterial system. Cryopreservation is widely used to preserve blood vessels for vascular reconstruction but is controversially suspected to affect the dynamic behaviour of these allografts. The aim of this study was to determine whether differences in the dynamic behaviour exist or not between fresh and cryopreserved human common carotid arteries (CCA). Using a previously developed mock circulation system, dynamic pressure-diameter tests were performed on segments of human fresh (n=10) and cryopreserved arteries (n=7). A diameter-pressure transfer function was designed to evaluate the wall dynamics. An adaptive model was fit to obtain its frequency response. Three models were tested. Results show that non-significant differences exist between wall dynamics of fresh and cryopreserved segments of human CCA.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2004; 1:730-3.
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ABSTRACT: Recent non-invasive studies in humans have shown the relationship between venous compliance and pressure within the physiological range to be best described by a biphasic model. This model sets a breakpoint pressure that splits the pressure range in two different linear compliance phases. Six ovine internal jugular vein segments were studied in-vitro under pulsatile pressure and flow conditions achieved by a mock circulation loop. Instantaneous pressure (Konigsberg) and diameter (sonomicrometry) signals were assessed in a wide range (0 to 60 mmHg) of intravascular pressure. For each segment the low pressure range was set between 0 mmHg and the breakpoint pressure and the high pressure range from the breakpoint pressure to 60 mmHg. The mean venous negative slope δC/δP for low pressures was significantly steeper than for high pressures (p<0.01). The calculated r for the linear trend lines resulted r =0.96±0.03 (p<0.01) for low pressures and r =0.79±0.07 (p<0.05) for high pressures, validating the biphasic model in-vitro. The δC/δP would describe a compliance change following a pressure variation and might be adopted as a compliance sensibility index.
Engineering in Medicine and Biology Society, 2003. Proceedings of the 25th Annual International Conference of the IEEE; 10/2003
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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.
Engineering in Medicine and Biology Society, 2003. Proceedings of the 25th Annual International Conference of the IEEE; 10/2003
