264 publications from this institution
Coil embolization has become a widely accepted endovascular procedure for intracranial aneurysms, as an alternative to surgical clipping [1,2]. This procedure involves treating an aneurysm from the inside out, whereby metallic coils are placed into the aneurysm to induce thrombosis of the lumen and eliminate the risk of rupture and hemorrhage. Successful endosaccular packing mainly depends on the morphological features and size of the aneurysm, and the relationship of the aneurysm to the cerebral arteries.
Extracellular matrix (ECM) is a key component and regulator of many biological tissues including aorta. Several aortic pathologies are associated with significant changes in the composition of the matrix, especially in the content, quality and type of aortic structural proteins, collagen and elastin. The purpose of this study was to develop an infrared spectroscopic methodology that is comparable to biochemical assays to quantify collagen and elastin in aorta. Enzymatically degraded porcine aorta samples were used as a model of ECM degradation in abdominal aortic aneurysm (AAA). After enzymatic treatment, Fourier transform infrared (FTIR) spectra of the aortic tissue were acquired by an infrared fiber optic probe (IFOP) and FTIR imaging spectroscopy (FT-IRIS). Collagen and elastin content were quantified biochemically and partial least squares (PLS) models were developed to predict collagen and elastin content in aorta based on FTIR spectra. PLS models developed from FT-IRIS spectra were able to predict elastin and collagen content of the samples with strong correlations (RMSE of validation = 8.4% and 11.1% of the range respectively), and IFOP spectra were successfully used to predict elastin content (RMSE = 11.3% of the range). The PLS regression coefficients from the FT-IRIS models were used to map collagen and elastin in tissue sections of degraded porcine aortic tissue as well as a human AAA biopsy tissue, creating a similar map of each component compared to histology. These results support further application of FTIR spectroscopic techniques for evaluation of AAA tissues.
The purpose of this work was to test the effects of diminished pulse on the mechanical properties and vasoresponse of bovine arteries. A segment was harvested at the time of implant of a continuous flow ventricular assist device. The goal was to maintain pump flow ∼ 50% of cardiac output. Another segment was removed at necropsy (after 30 days). The vessels were implanted into an ex-vivo perfusion system. Compliance was assessed by measuring external diameter change over a pressure pulse (P = 120/80 mmHg). The vessels were then tested to failure in a tensile testing device. Young's modulus, yield strength, and ultimate strength were derived from the data. The results of the work do not indicate a statistically significant change in vasoresponse or mechanical properties between arteries removed at baseline and at necropsy from the pump-implanted animals. However, the data suggests several trends occurring in the pump-implanted: the compliance (C) decreases (p < 0.25) the ultimate strength (US) of the tissue increases (p < 0.18) and the % constriction increases (p < 0.25). Statistical comparisons were also made between controls (n=2) and the implanted cows (n=7) at necropsy. The C in the controls is greater than in the implants (p < 0.06) The US of the arteries taken from the implanted cows is significantly greater than the sham controls at necropsy (p < 0.05). Further research i s required to verify if these observed trends are indeed significant.
Abstract Rupture of abdominal aortic aneurysm (AAA) is currently the 13th leading cause of death in the US and represents a mechanical failure of the diseased aortic wall. Therefore, accurate estimation of the wall stress distribution in AAA may be a clinically useful tool to predict their risk of rupture [1]. A necessary precursor to an accurate stress analysis is an appropriate representation of the constitutive behavior of the AAA wall. Many previous biomechanical analyses of AAA have employed a linearly elastic constitutive behavior [2,3]. However, we have shown that the AAA wall is nonlinearly elastic [4] and undergoes large strain in-vivo [5]. With this as motivation, we recently developed an isotropic, nonlinearly elastic, large strain constitutive model for AAA wall based on uniaxial tensile testing data [6]. The assumption of isotropy was not validated, however. Utilization of an isotropic material symmetry in models of anisotropic structures may lead to significant errors in stress distribution [7]. Indeed, experiments suggest that the nonaneurysmal aorta is anisotropic (orthotropic) [8,9], but the material symmetry of AAA is not presently known. Moreover, most of the previous work investigating the material symmetry of aorta has been performed on animal tissue. To evaluate the anisotropy of aortic tissue, biaxial experimentation is necessary. There has been very little published work involving the biaxial experimentation of human aortic tissue, and none for AAA tissue. We present here a preliminary evaluation of the biaxial mechanical behavior of human aneurysmal and nonaneurysmal abdominal aorta.
The biomechanical response of abdominal aortic tissue to uniaxial loading conditions has been reported previously [1]. This testing identified the uniaxial mechanical response of aortic tissue to specimens oriented in the longitudinal and circumferential directions, but did not provide significant evidence for the isotropy or anisotropy of this tissue. The information taken from uniaxial tensile testing is insufficient for the characterization of the multi-axial mechanical response of aortic tissue. In particular, the uniaxial response of a biological tissue in a given direction does not incorporate the effects of loading in an orthogonal direction. For these reasons, there exists a need for an enhanced description of the mechanical response of aortic tissue to loading in multiple planar directions. For the current investigation, biaxial tensile testing was performed on normal abdominal aortic tissue in order to gain insight into the anisotropy and age related differences of the biomechanical response of this tissue.
