Pressure and Angiotensin II Influence the Mechanical Properties of Aortic Valves

2012 ◽  
Vol 2012 (4) ◽  
pp. 41
Author(s):  
Valtresa Myles ◽  
Jun Liao ◽  
James N. Warnock
Keyword(s):  
Mechanical Properties ◽  
Angiotensin Ii ◽  
Aortic Valves

Stress Dependent Collagen Fibril Diameter Distribution in Human Aortic Valves

2007 ◽  
Author(s):  
Angelique Balguid ◽  
Anita Mol ◽  
Niels Driessen ◽  
Carlijn Bouten ◽  
Frank Baaijens
Keyword(s):  
Mechanical Properties ◽  
Collagen Fibril ◽  
Diameter Distribution ◽  
Connective Tissues ◽  
Aortic Valves ◽  
Cross Links ◽  
Fibril Morphology ◽  
Stress Dependent ◽  
Collagenous Tissues ◽  
Fibril Diameter

The mechanical properties of collagenous tissues are known to depend on a wide variety of factors, such as the type of tissue and the composition of its extracellular matrix. Relating mechanical roles to individual matrix components in such a complex system is difficult, if not impossible. However, as collagen is the main load bearing component in connective tissues, the relation between collagen and tissue biomechanics has been studied extensively in various types of tissues. The type of collagen, the amount and type of inter- and intramolecular covalent cross-links and collagen fibril morphology are involved in the tissues mechanical behavior (Beekman et al., 1997; Parry et al., 1978; Avery and Bailey, 2005). From literature it is known that the the collagen fibril diameter distribution can be directly related to the mechanical properties of the tissue. In particular, the diameter distribution of collagen fibrils is largely determined by the tissues requirement for tensile strength and elasticity (Parry et al., 1978).

Cyclic Pressure and Angiotensin II Influence the Biomechanical Properties of Aortic Valves

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Valtresa Myles ◽  
Jun Liao ◽  
James N. Warnock
Keyword(s):  
Angiotensin Ii ◽  
Aortic Valve ◽  
Biomechanical Properties ◽  
Interstitial Cells ◽  
Collagen Content ◽  
Cell Stiffness ◽  
Ang Ii ◽  
Aortic Valves ◽  
Cyclic Pressure ◽  
Aortic Valve Leaflets

Hypertension is a known risk factor for aortic stenosis. The elevated blood pressure increases the transvalvular load and can elicit inflammation and extracellular matrix (ECM) remodeling. Elevated cyclic pressure and the vasoactive agent angiotensin II (Ang II) both promote collagen synthesis, an early hallmark of aortic sclerosis. In the current study, it was hypothesized that elevated cyclic pressure and/or angiotensin II decreases extensibility of aortic valve leaflets due to an increase in collagen content and/or interstitial cell stiffness. Porcine aortic valve leaflets were exposed to pressure conditions of increasing magnitude (static atmospheric pressure, 80, and 120 mmHg) with and without 10−6 M Ang II. Biaxial mechanical testing was performed to determine extensibility in the circumferential and radial directions and collagen content was determined using a quantitative dye-binding method at 24 and 48 h. Isolated aortic valve interstitial cells exposed to the same experimental conditions were subjected to atomic force microscopy to assess cellular stiffness at 24 h. Leaflet tissue incubated with Ang II decreased tissue extensibility in the radial direction, but not in the circumferential direction. Elevated cyclic pressure decreased extensibility in both the radial and circumferential directions. Ang II and elevated cyclic pressure both increased the collagen content in leaflet tissue. Interstitial cells incubated with Ang II were stiffer than those incubated without Ang II while elevated cyclic pressure caused a decrease in cell stiffness. The results of the current study demonstrated that both pressure and Ang II play a role in altering the biomechanical properties of aortic valve leaflets. Ang II and elevated cyclic pressure decreased the extensibility of aortic valve leaflet tissue. Ang II induced direction specific changes in extensibility, demonstrating different response mechanisms. These findings help to provide a better understanding of the responses of aortic valves to mechanical and biochemical changes that occur under hypertensive conditions.

scholarly journals St Jude Epic heart valve bioprostheses versus native human and porcine aortic valves - comparison of mechanical properties

2009 ◽  
Vol 8 (5) ◽  
pp. 553-556 ◽  
Author(s):  
M. Kalejs ◽  
P. Stradins ◽  
R. Lacis ◽  
I. Ozolanta ◽  
J. Pavars ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Heart Valve ◽  
Aortic Valves

Cyclic Pressure and Angiotensin II Influence the Biomechanical Properties of Aortic Valves

2012 ◽  
Author(s):  
Valtresa Myles ◽  
Jun Liao ◽  
James N. Warnock
Keyword(s):  
Angiotensin Ii ◽  
Collagen Synthesis ◽  
Biomechanical Properties ◽  
Elevated Pressure ◽  
Ang Ii ◽  
Aortic Valves ◽  
Vasoactive Agent ◽  
Ecm Remodeling ◽  
Cyclic Pressure ◽  
Aortic Sclerosis

Hypertension is a known risk factor for aortic valve stenosis. The elevated blood pressure increases the transvalvular load and can elicit inflammation and extra-cellular matrix (ECM) remodeling. Elevated cyclic pressure and the vasoactive agent angiotensin II (Ang II) have both been shown to promote collagen synthesis, one of the early hallmarks of aortic sclerosis [1,2]. In the current study, it was hypothesized that the increased collagen production induced by either elevated pressure conditions or the presence of Ang II would affect the mechanical properties of the tissue by increasing stiffness.

scholarly journals Decellularization Following Fixation of Explanted Aortic Valves as a Strategy for Preserving Native Mechanical Properties and Function

2022 ◽  
Vol 9 ◽  
Author(s):  
Manisha Singh ◽  
Clara Park ◽  
Ellen T. Roche
Keyword(s):  
Mechanical Properties ◽  
Learning Experience ◽  
Fixation Method ◽  
Valvular Regurgitation ◽  
Aortic Valves ◽  
Hands On Learning ◽  
Human Cadavers ◽  
Primary Focus ◽  
Hemodynamic Performance ◽  
And Function

Mechanical or biological aortic valves are incorporated in physical cardiac simulators for surgical training, educational purposes, and device testing. They suffer from limitations including either a lack of anatomical and biomechanical accuracy or a short lifespan, hence limiting the authentic hands-on learning experience. Medical schools utilize hearts from human cadavers for teaching and research, but these formaldehyde-fixed aortic valves contort and stiffen relative to native valves. Here, we compare a panel of different chemical treatment methods on explanted porcine aortic valves and evaluate the microscopic and macroscopic features of each treatment with a primary focus on mechanical function. A surfactant-based decellularization method after formaldehyde fixation is shown to have mechanical properties close to those of the native aortic valve. Valves treated in this method were integrated into a custom-built left heart cardiac simulator to test their hemodynamic performance. This decellularization, post-fixation technique produced aortic valves which have ultimate stress and elastic modulus in the range of the native leaflets. Decellularization of fixed valves reduced the valvular regurgitation by 60% compared to formaldehyde-fixed valves. This fixation method has implications for scenarios where the dynamic function of preserved valves is required, such as in surgical trainers or device test rigs.

scholarly journals Induction of local angiotensin II-producing systems in stenotic aortic valves

2004 ◽  
Vol 44 (9) ◽  
pp. 1859-1866 ◽  
Author(s):  
Satu Helske ◽  
Ken A. Lindstedt ◽  
Mika Laine ◽  
Mikko Mäyränpää ◽  
Kalervo Werkkala ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Aortic Valves

scholarly journals A Biomechanical and Biochemical Synergy Study of Heart Valve Tissue

2012 ◽  
Author(s):  
Hsiao-Ying Shadow Huang ◽  
Brittany N. Balhouse ◽  
Siyao Huang
Keyword(s):  
Mechanical Properties ◽  
Heart Valve ◽  
Heart Valves ◽  
Heart Valve Disease ◽  
Aortic Valves ◽  
Valve Tissue ◽  
Tissue Engineered Heart Valve ◽  
Heart Valve Tissue ◽  
Flow Through ◽  
The Relationship

The function of heart valves is to allow blood to flow through the heart smoothly and to prevent retrograde flow of blood. Previous studies have shown that the mechanical properties of heart valve tissues, microstructures of extracellular matrix, and collagen concentrations are the keys to the healthy heart valves and, therefore, are crucial to the development of viable tissue-engineered heart valve replacements. Therefore, this study investigates the relationship between these factors in native porcine aortic and pulmonary valves and provides insights to the healthy heart valves. Heart valve leaflets are prepared for biaxial stretching to obtain mechanical properties. The average collagen concentrations of heart valve leaflets are determined via an assay kit. The results indicate that aortic valves are stiffer than pulmonary valves macroscopically and stiffness varies more in the circumferential direction for the aortic valve than it does for the pulmonary valve. Microscopically, it is due to collagen fibers in aortic valves are more in alignment than ones in pulmonary valves, which are more randomly in direction. Collagen assay results show that collagen concentrations are higher in the edges of pulmonary valves than in aortic valves. The results also suggest the duration of extraction may have significant affects on the concentration results. This work provides quantified stress and strain environment within heart valve tissues to help further studies on how to treat heart valve disease and create more viable heart valve replacements.

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