Daniela Valdez-Jasso

University of Pittsburgh, Pittsburgh, Pennsylvania, United States

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Publications (7)11.34 Total impact

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    ABSTRACT: Key points  Right-ventricular (RV) function is an important determinant of cardio-pulmonary performance. How and when RV failure occurs in disease is poorly understood. RV biomechanics provides a means to understand tissue level behavior that links cellular mechanisms to organ level phenotype. RV biomechanics has received little attention.  We developed 1) rat model for quantifying the structure and biomechanical behavior of viable and transmurally intact RV tissue, and 2) a novel analysis method for obtaining representative scalar strain-energy function from stress-controlled biaxial experiments.  The mechanical testing revealed a marked mechanical tissue anisotropy with the apex-to-outflow tract direction being the stiffer direction.  The myo- and collagen fibers show a preferential alignment from the apex to the RV outflow tract direction with little transmural variation.  We found a strong relationship between normal tissue microstructure and biomechanical behavior, which lays the foundation for a detailed understanding of RV remodeling in response to disease.
    The Journal of Physiology 07/2012; 590(Pt 18):4571-84. · 4.38 Impact Factor
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    ABSTRACT: A better understanding of the biomechanical properties of the arterial wall provides important insight into arterial vascular biology under normal (healthy) and pathological conditions. This insight has potential to improve tracking of disease progression and to aid in vascular graft design and implementation. In this study, we use linear and nonlinear viscoelastic models to predict biomechanical properties of the thoracic descending aorta and the carotid artery under ex vivo and in vivo conditions in ovine and human arteries. Models analyzed include a four-parameter (linear) Kelvin viscoelastic model and two five-parameter nonlinear viscoelastic models (an arctangent and a sigmoid model) that relate changes in arterial blood pressure to the vessel cross-sectional area (via estimation of vessel strain). These models were developed using the framework of Quasilinear Viscoelasticity (QLV) theory and were validated using measurements from the thoracic descending aorta and the carotid artery obtained from human and ovine arteries. In vivo measurements were obtained from 10 ovine aortas and 10 human carotid arteries. Ex vivo measurements (from both locations) were made in 11 male Merino sheep. Biomechanical properties were obtained through constrained estimation of model parameters. To further investigate the parameter estimates, we computed standard errors and confidence intervals and we used analysis of variance to compare results within and between groups. Overall, our results indicate that optimal model selection depends on the artery type. Results showed that for the thoracic descending aorta (under both experimental conditions), the best predictions were obtained with the nonlinear sigmoid model, while under healthy physiological pressure loading the carotid arteries nonlinear stiffening with increasing pressure is negligible, and consequently, the linear (Kelvin) viscoelastic model better describes the pressure-area dynamics in this vessel. Results comparing biomechanical properties show that the Kelvin and sigmoid models were able to predict the zero-pressure vessel radius; that under ex vivo conditions vessels are more rigid, and comparatively, that the carotid artery is stiffer than the thoracic descending aorta; and that the viscoelastic gain and relaxation parameters do not differ significantly between vessels or experimental conditions. In conclusion, our study demonstrates that the proposed models can predict pressure-area dynamics and that model parameters can be extracted for further interpretation of biomechanical properties.
    Annals of Biomedical Engineering 01/2011; 39(5):1438-56. · 3.23 Impact Factor
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    ABSTRACT: This paper combines a generalized viscoelastic model with a one-dimensional (1D) fluid dynamics model for the prediction of blood flow, pressure, and vessel area in systemic arteries. The 1D fluid dynamics model is derived from the Navier—Stokes equations for an incompressible Newtonian flow through a network of cylindrical vessels. This model predicts pressure and flow and is combined with a viscoelastic constitutive equation derived using the quasilinear viscoelasticity theory that relates pressure and vessel area. This formulation allows for inclusion of an elastic response as well as an appropriate creep function allowing for the description of the viscoelastic deformation of the arterial wall. Three constitutive models were investigated: a linear elastic model and two viscoelastic models. The Kelvin and sigmoidal viscoelastic models provide linear and nonlinear elastic responses, respectively. For the fluid domain, the model assumes that a given flow profile is prescribed at the inlet, that flow is conserved and pressure is continuous across vessel junctions, and that it incorporates a multiscale boundary condition (a three element Windkessel model) at each outlet. This outlet boundary condition allows prediction of the overall impact on the flow and pressure generated by the downstream vasculature. The coupled fluid structure interaction model is solved using a finite element method that is adapted to account for time history of the viscoelastic model. Results of this study demonstrate that incorporation of a viscoelastic wall model allows more physiologic prediction of arterial blood pressure and vessel deformation, which often is overestimated with the simple elastic wall models, while blood flow does not differ significantly between models.
    SIAM Journal on Applied Mathematics 01/2011; 71:1123-1143. · 1.58 Impact Factor
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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: In this paper, we analyze how elastic and viscoelastic properties differ across seven locations along the large arteries in 11 sheep. We employ a two-parameter elastic model and a four-parameter Kelvin viscoelastic model to analyze experimental measurements of vessel diameter and blood pressure obtained in vitro at conditions mimicking in vivo dynamics. Elastic and viscoelastic wall properties were assessed via solutions to the associated inverse problem. We use sensitivity analysis to rank the model parameters from the most to the least sensitive, as well as to compute standard errors and confidence intervals. Results reveal that elastic properties in both models (including Young's modulus and the viscoelastic relaxation parameters) vary across locations (smaller arteries are stiffer than larger arteries). We also show that for all locations, the inclusion of viscoelastic behavior is important to capture pressure-area dynamics.
    IEEE transactions on bio-medical engineering 03/2009; 56(2):210-9. · 2.15 Impact Factor
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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: 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.

Publication Stats

32 Citations
11.34 Total Impact Points


  • 2012
    • University of Pittsburgh
      • Bioengineering
      Pittsburgh, Pennsylvania, United States
    • University of Texas at Austin
      • Department of Biomedical Engineering
      Austin, Texas, United States
  • 2007–2011
    • North Carolina State University
      • Department of Mathematics
      Raleigh, NC, United States