Pursell ER, Vélez-Rendón D, Valdez-Jasso D. Biaxial properties of the left and right pulmonary arteries in a monocrotaline rat animal model of pulmonary arterial hypertension. 2016.


In a MCT induced-PAH rat animal model, the dynamic stress-strain relation was investigated in the circumferential and axial direction using a linear elastic response model within the quasi-linear viscoelasticity theory framework. Right and left pulmonary arterial segments (RPA, LPA) were mechanically tested in a tubular biaxial device at the early stage (1 week post-MCT treatment) and at the advanced stage of the disease (4 weeks post-MCT treatment). The vessels were tested circumferentially at the in vivo axial length with matching in vivo measured pressure ranges. Subsequently, the vessels were tested axially at the mean pulmonary arterial pressure by stretching them from in vivo plus 5% of their length. Parameter estimation showed that the LPA and RPA remodel at different rates: axially, both vessels decreased in Young’s modulus at the early stage of the disease, and increased at the advanced disease stage. Circumferentially, the Young’s modulus increased in advanced PAH, but it was only significant in the RPA. The damping properties also changed in PAH; in the circumferential direction, the relaxation times continuously decreased while in the axial direction, they initially increased and then decreased. Our modeling efforts were corroborated by the restructuring organization of the fibers imaged under multiphoton microscopy, where the collagen fibers became strongly aligned to the 45 degree angle in the RPA from an un-crimped and randomly organized state. Additionally, collagen content increased almost 10% in the RPA from the placebo to advanced PAH.


Hill MR, Simon MA, Valdez-Jasso D, Zhang W, Champion HC, Sacks MS. Structural and mechanical adaptations of right ventricular free wall myocardium to pulmonary hypertension induced pressure overload. 2014.


Right ventricular (RV) failure in response to pulmonary hypertension (PH) is a severe disease that remains poorly understood. PH-induced pressure overload leads to changes in the RV free wall (RVFW) that eventually results in RV failure. While the development of computational models can benefit our understanding of the onset and progression of PH-induced pressure overload, detailed knowledge of the underlying structural and biomechanical events remains limited. The goal of the present study was to elucidate the structural and biomechanical adaptations of RV myocardium subjected to sustained pressure overload in a rat model.


Valdez-Jasso D, Simon MA, Champion HC, Sacks MS. A murine experimental model for the mechanical behavior of viable right ventricular myocardium. 2012.


Although right-ventricular function is an important determinant of cardio-pulmonary performance in health and disease, right ventricular myocardium mechanical behaviour has received relatively little attention. We present a novel experimental method for quantifying the mechanical behaviour of transmurally intact, viable right-ventricular myocardium. Seven murine right ventricular free wall (RVFW) specimens were isolated and biaxial mechanical behaviour measured, along with quantification of the local transmural myofibre and collagen fibre architecture. We developed a complementary strain energy function based method to capture the average biomechanical response.


Brooke SN, Valdez-Jasso D, Haider MA, Olufsen MS. Predicting arterial flow and pressure dynamics using a 1d fluid dynamics model with a viscoelastic wall. 2011.


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.

Valdez-Jasso D, Bia D, Zocalo Y, Armentano RL, Haider MA, and Olufsen MS. Linear and nonlinear viscoelastic modeling of aorta and carotid pressure-area dynamics under in vivo and ex vivo conditions. 2011.


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).


Valdez-Jasso D, Haider MA, Banks HT, Bia D, Zocalo Y, Armentano RL, Olufsen MS. Analysis of viscoelastic wall properties in ovine arteries. 2009.


In this study we analyzed how elastic and viscoelastic properties differ across 7 locations along the large arteries in 11 sheep. We employed a 2 parameter elastic model and a 4 parameter Kelvin viscoelastic model to analyze experimental measurements of vessel diameter and blood pressure obtained in-vitro at conditions mimicking the in-vivo dynamics.

Valdez-Jasso D, Banks HT, Haider MA, Bia D, Zocalo Y, Armentano RL, Olufsen MS. Viscoelastic models for passive arterial wall dynamics. 2009.


This paper compares two models predicting elastic and viscoelastic properties of large arteries. Models compared include a Kelvin (standard linear) model and an extended 2-term exponential linear viscoelastic model. Models were validated 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 vessel 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.