The Effect of Age on Residual Strain in the Rat Aorta

1996 ◽  
Vol 118 (4) ◽  
pp. 440-444 ◽  
Author(s):  
A. Badreck-Amoudi ◽  
C. K. Patel ◽  
T. P. C. Kane ◽  
S. E. Greenwald
Keyword(s):  
Residual Stress ◽  
Wall Thickness ◽  
Residual Strain ◽  
Normal Growth ◽  
Rat Aorta ◽  
Opening Angle ◽  
Steady Increase ◽  
The Relationship ◽  
Effect Of Age ◽  
Intravascular Pressure

Residual stress is observed in many parts of the cardiovascular system and is thought to reduce transmural stress gradients due to intravascular pressure. Its development is closely associated with normal growth and pathological remodeling, although there appear to be few previous reports of the relationship between aging and residual stress. We have estimated residual strain (an indicator of the magnitude of residual stress) at ten sites along the aorta of rats aged 2.5 to 56 weeks by measuring the degree to which rings of vessel spring open when cut (opening angle). At all ages the opening angle decreased along the aorta, reaching a minimum near the renal arteries and increasing toward the aorto-iliac bifurcation, a result that confirms previous studies. During growth, although the unloaded circumference of the aorta increased steadily, the wall thickness and medial surface area fell to a minimum at the age of 6 weeks before continuing a steady increase. Similarly, the opening angle decreased between the ages of 2.5 and 6 weeks, thereafter increasing with age. In the abdominal aorta, a strong correlation between opening angle and wall thickness relative to midwall radius (h/R) was seen; whereas in the thoracic segment, in which no increase in h/R with age occurred, no such relationship was found. These observations are in keeping with a recently proposed hypothesis that residual stress will change in response to growth-related changes in vessel geometry driven by a tendency to minimize the nonuniform stress distribution inevitably found in pressurized thick-walled cylinders.

Left Ventricular Geometric Remodeling and Residual Stress in the Rat Heart

1998 ◽  
Vol 120 (6) ◽  
pp. 715-719 ◽  
Author(s):  
J. H. Omens ◽  
S. M. Vaplon ◽  
B. Fazeli ◽  
A. D. McCulloch
Keyword(s):  
Residual Stress ◽  
Wall Thickness ◽  
Residual Strain ◽  
Left Ventricular ◽  
Radius Ratio ◽  
Area Fraction ◽  
Heart Weight ◽  
Left Ventricular Geometry ◽  
Opening Angle ◽  
Internal Radius

Theoretical considerations and observations of residual stress suggest that geometric remodeling in the heart may also alter residual stress and strain. We investigated whether changes in left ventricular geometry during physiologic growth were associated with corresponding changes in myocardial residual strain. In anesthetized rats from eight age groups ranging from 2–25+ weeks, the heart was arrested and isolated, and equatorial slices were obtained. The geometry of the intact, unloaded state was recorded, as well as the “opening angle” of the stress-free configuration after radial resection of the tissue slice. The tissue was fixed and embedded for histological examination of collagen area fraction. Heart weight increased 10-fold with age and unloaded internal radius increased almost 4-fold. However, wall thickness increased only 66 percent, so that the ratio of wall thickness to internal radius decreased significantly from 2.22 ± 0.29 (mean ± SD) at 2 weeks to 0.81 ± 0.47 at 25 weeks. Opening angle of the stress-free slice decreased significantly from 87 ± 16 deg at 2 weeks to 51 ± 16 deg, and correlated linearly with wall thickness/radius ratio. Collagen area fraction increased with age. Hence physiologic ventricular remodeling in rats decreases myocardial residual strain in proportion to the relative reduction in wall thickness–radius ratio.

Experimental Investigation of the Distribution of Residual Strains in the Artery Wall

1997 ◽  
Vol 119 (4) ◽  
pp. 438-444 ◽  
Author(s):  
S. E. Greenwald ◽  
J. E. Moore ◽  
A. Rachev ◽  
T. P. C. Kane ◽  
J.-J. Meister
Keyword(s):  
Smooth Muscle ◽  
Stress State ◽  
Smooth Muscle Cells ◽  
Residual Strain ◽  
Arterial Wall ◽  
Normal Growth ◽  
Muscle Cells ◽  
Opening Angle ◽  
Artery Wall ◽  
Residual Strains

Arterial wall stresses are thought to be a major determinant of vascular remodeling both during normal growth and throughout the development of occlusive vascular disease. A completely physiologic mechanical model of the arterial wall should account not only for its residual strains but also for its structural nonhomogeneity. It is known that each layer of the artery wall possesses different mechanical properties, but the distribution of residual strain among the different mechanical components, and thus the true zero stress state, remain unknown. In this study, two different sets of experiments were carried out in order to determine the distribution of residual strains in artery walls, and thus the true zero stress state. In the first, collagen and elastin were selectively eliminated by chemical methods and smooth muscle cells were destroyed by freezing. Dissolving elastin provoked a decrease in the opening angle, while dissolving collagen and destroying smooth muscle cells had no effect. In the second, different wall layers of bovine carotid arteries were removed from the exterior or luminal surfaces by lathing or drilling frozen specimens, and then allowing the frozen material to thaw before measuring residual strain. Lathing material away from the outer surface caused the opening angle of the remaining inner layers to increase. Drilling material from the inside caused the opening angle of the remaining outer layers to decrease. Mechanical nonhomogeneity, including the distribution of residual strains, should thus be considered as an important factor in determining the distribution of stress in the artery wall and the configuration of the true zero stress state.

Regional arterial stress-strain distributions referenced to the zero-stress state in the rat

2002 ◽  
Vol 282 (2) ◽  
pp. H622-H629 ◽  
Author(s):  
Jingbo Zhao ◽  
Judd Day ◽  
Zhuang Feng Yuan ◽  
Hans Gregersen
Keyword(s):  
Stress State ◽  
Pulmonary Artery ◽  
Thoracic Aorta ◽  
Wall Thickness ◽  
Femoral Artery ◽  
Residual Strain ◽  
Mechanical Test ◽  
Opening Angle ◽  
Outer Diameter ◽  
Stress Strain

Morphometric and stress-strain properties were studied in isolated segments of the thoracic aorta, abdominal aorta, left common carotid artery, left femoral artery, and the left pulmonary artery in 16 male Wistar rats. The mechanical test was performed as a distension experiment where the proximal end of the arterial segment was connected via a tube to the container used for applying pressures to the segment and the distal end was left free. Outer wall dimensions were obtained from digitized images of the arterial segments at different pressures as well as at no-load and zero-stress states. The results showed that the morphometric data, such as inner and outer circumference, wall and lumen area, wall thickness, wall thickness-to-inner radius ratio, and normalized outer diameter, as a function of the applied pressures, differed between the five arteries ( P < 0.01). The opening angle was largest in the pulmonary artery and smallest in thoracic aorta ( P < 0.01). The absolute value of both the inner and outer residual strain and the residual strain gradient were largest in the femoral artery and smallest in the thoracic aorta ( P < 0.01). In the circumferential and longitudinal direction, the arterial wall was stiffest in the femoral artery and in the thoracic aorta, respectively, and most compliant in the pulmonary artery. These results show that the morphometric and biomechanical properties referenced to the zero-stress state differed between the five arterial segments.

Regional and age-dependent residual strains, curvature, and dimensions of the human ureter

2017 ◽  
Vol 232 (2) ◽  
pp. 149-162 ◽  
Author(s):  
Despoina C Petsepe ◽  
Stavros K Kourkoulis ◽  
Stavroula A Papadodima ◽  
Dimitrios P Sokolis
Keyword(s):  
Lamina Propria ◽  
Wall Thickness ◽  
Residual Strain ◽  
Strain Difference ◽  
Biomechanical Properties ◽  
Muscle Layer ◽  
Opening Angle ◽  
Human Cadavers ◽  
Residual Strains ◽  
Human Ureter

The ureters are retroperitoneal structures controlling urine transport from the kidneys to the bladder. Because of the relative scarcity of data on the biomechanical properties of human ureter and the established importance of knowing these properties for understanding its physiology, we initiated biomechanical studies in cadaveric tissue. Herein, we report definite zero-stress/no-load geometrical characterization at 15 regions along the ureter of human cadavers aged 23–82 years, estimating the opening angle, circumferential residual strains, axial curvature, and dimensional parameters. Opening angle decreased along the proximal 25% of ureter, increased and reached a maximum near the mid-ureter, and then gradually decreased toward the vesicoureteral junction (young: p < 0.05; middle-aged: p < 0.05; old: p > 0.05; males: p < 0.05; females: p < 0.05). Similar were the regional distributions of residual strain at the interface between epithelium–lamina propria and muscle and of internal but not external residual strain. Wall thickness increased steadily with aging ( p < 0.05 at few regions), while ureteral circumference did not ( p > 0.05 at most regions) and opening angle decreased ( p < 0.05 at several regions). Consistent with Fung’s stress-growth law, the muscle layer thickened with age unlike the epithelium–lamina propria that thinned ( p < 0.05 at most regions for both thicknesses). Moderate-to-strong direct correlations of residual strain difference (= external – internal) with opening angle, wall thickness, and curvature were found in most ureters. The presented data will provide insight into the biomechanical response of ureter under zero/low-stress conditions and the relationship between ureteral remodeling and aging. Importantly, they may also be used to inform finite element models and computational studies simulating the ureter.

Effect of residual stress on transmural sarcomere length distributions in rat left ventricle

1993 ◽  
Vol 264 (4) ◽  
pp. H1048-H1056 ◽  
Author(s):  
E. K. Rodriguez ◽  
J. H. Omens ◽  
L. K. Waldman ◽  
A. D. McCulloch
Keyword(s):  
Residual Stress ◽  
Left Ventricle ◽  
Wall Thickness ◽  
Sarcomere Length ◽  
Equatorial Region ◽  
Analysis Of Covariance ◽  
Opening Angle ◽  
Cross Sectional ◽  
Rat Hearts ◽  
Stress Free State

It has been previously shown that the myocardium in the walls of the unloaded passive left ventricle (LV) is not stress free. To assess the functional significance of residual stress in the ventricular wall, we compared the transmural distributions of sarcomere length (SL) in specimens of rat LV myocardium fixed in the unloaded (residually stressed) and stress-free states. When a cross-sectional ring cut from the equatorial region of the freshly arrested rat hearts was cut radially to relieve residual stress, it sprang open into an arc with a mean opening angle of 45 +/- 15 degrees (SD) (n = 8). During immersion fixation in glutaraldehyde, the opening angle increased 9.3 +/- 7.1 degrees (SD) overall. SLs were measured at 16 equally spaced transmural locations from the free wall in the stress-free tissue sections and were compared with control measurements from adjacent cross-sectional rings in which residual stress had not been relieved. Average SL for the stress-free tissue (n = 11) was 1.84 +/- 0.05 (SD) microns and for the unloaded tissue was 1.83 +/- 0.06 (SD) microns. However, analysis of covariance on the pooled data showed that the transmural distributions were significantly different (P < 0.0001). Whereas SL was uniform across the wall in the stress-free state with a mean gradient of -0.014 +/- 0.044 (SD) microns/total wall thickness, there was a significant decrease (P = 0.001) in SL from epicardium to endocardium in the intact unloaded tissue [slope = -0.114 +/- 0.054 (SD) microns/total wall thickness].(ABSTRACT TRUNCATED AT 250 WORDS)

The Impact of Financial Literacy on Financial Preparedness for Retirement in the Small and Medium Enterprises Sector in Uganda

2020 ◽  
Vol 9 (3) ◽  
pp. 26-41
Author(s):  
Colin Agabalinda ◽  
Alain Vilard Ndi Isoh
Keyword(s):  
Financial Literacy ◽  
Small And Medium Enterprises ◽  
Group Analysis ◽  
Moderating Effect ◽  
Primary Data ◽  
Retirement Preparedness ◽  
Medium Enterprises ◽  
The Impact ◽  
The Relationship ◽  
Effect Of Age

The study investigated the direct effects of financial literacy (knowledge, skills, and attitudes) on financial preparedness for retirement and the moderating effect of age among the small and medium enterprises in Uganda. Primary data was collected from a sample of n = 380 selected from the SME workforce. Descriptive analysis was run on SPSS, while validity and reliability of the measurement items yielded satisfactory composite reliability scores and average variance explained (AVE) scores for all items. Structural equation modelling (SEM) was used to test the hypotheses and multi-group analysis conducted to test for the moderating effect of age on the relationship between financial literacy and retirement preparedness. The results revealed that knowledge and skills were significant predictors of retirement preparedness. However, ‘attitude' was not a significant predictor, and age had no moderating effect on the relationship between the study variables. These findings present practical implications for policymakers and financial educators in a developing country context.

scholarly journals Influence of Preaging Temperature on the Indentation Strength of 3Y-TZP Aged in Ambient Atmosphere

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2767
Author(s):  
Ki-Won Jeong ◽  
Jung-Suk Han ◽  
Gi-Uk Yang ◽  
Dae-Joon Kim
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Low Temperature ◽  
Compressive Residual Stress ◽  
Yttria Stabilized Zirconia ◽  
Ambient Atmosphere ◽  
Aged Specimen ◽  
Stabilized Zirconia ◽  
M Phase ◽  
The Relationship

Yttria-stabilized zirconia (3Y-TZP) containing 0.25% Al2O3, which is resistant to low temperature degradation (LTD), was aged for 10 h at 130–220 °C in air. The aged specimens were subsequently indented at loads ranging from 9.8 to 490 N using a Vickers indenter. The influence of preaging temperature on the biaxial strength of the specimens was investigated to elucidate the relationship between the extent of LTD and the strength of zirconia restorations that underwent LTD. The indented strength of the specimens increased as the preaging temperature was increased higher than 160 °C, which was accompanied by extensive t-ZrO2 (t) to m-ZrO2 (m) and c-ZrO2 (c) to r-ZrO2 (r) phase transformations. The influence of preaging temperature on the indented strength was rationalized by the residual stresses raised by the t→m transformation and the reversal of tensile residual stress on the aged specimen surface due to the indentation. The results suggested that the longevity of restorations would not be deteriorated if the aged restorations retain compressive residual stress on the surface, which corresponds to the extent of t→m phase transformation less than 52% in ambient environment.

scholarly journals The Effect of Sex and Age on Bone Morphology and Strength in the Metacarpus and Humerus in Beef-Cross-Dairy Cattle

Animals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 694
Author(s):  
Michaela Gibson ◽  
Rebecca Hickson ◽  
Penny Back ◽  
Keren Dittmer ◽  
Nicola Schreurs ◽  
...  
Keyword(s):  
Dairy Cattle ◽  
Quantitative Computed Tomography ◽  
Live Weight ◽  
Peripheral Quantitative Computed Tomography ◽  
Bone Size ◽  
Limited Data ◽  
Bone Morphology ◽  
Relationship Of ◽  
The Relationship ◽  
Effect Of Age

In cattle, limited data have been reported about the relationship between live weight, bone size, and strength and how this relationship can be altered by factors such as sex and age. The aim of this study was to describe the relationship of peripheral quantitative computed tomography (pQCT)-derived parameters of bone strength and morphology with live weight, age and sex in beef-cross-dairy cattle. All animals were weighed the day before slaughter. The metacarpus and humerus were collected at slaughter and scanned at the mid-diaphysis using pQCT. Live weight was the primary explanatory variable for bone size and strength in all cohorts. However, the effect of age was significant, such that magnitude of response to liveweight was less in the 24-month-old cohort. Sex was significant within cohorts in that bulls had a shorter metacarpus than steers and heifers had a shorter metacarpus than steers at age of slaughter.

The Materials Science of “Permeable Polysilicon” Thin Films

2001 ◽  
Vol 687 ◽  
Author(s):  
George M Dougherty ◽  
Timothy Sands ◽  
Albert P. Pisano
Keyword(s):  
Thin Films ◽  
Residual Stress ◽  
Materials Science ◽  
Single Step ◽  
Process Window ◽  
Silicon Thin Films ◽  
Growth Regime ◽  
Deposition Parameters ◽  
Simple Kinetic Model ◽  
The Relationship

AbstractPolycrystalline silicon thin films that are permeable to fluids, known as permeable polysilicon, have been reported by several researchers. Such films have great potential for the fabrication of difficult to make MEMS structures, but their use has been hampered by poor process repeatability and a lack of physical understanding of the origin of film permeability and how to control it. We have completed a methodical study of the relationship between process, microstructure, and properties for permeable polysilicon thin films. As a result, we have determined that the film permeability is caused by the presence of nanoscale pores, ranging from 10-50 nm in size, that form spontaneously during LPCVD deposition within a narrow process window. The unusual microstructure within this process window corresponds to the transition between a semicrystalline growth regime, exhibiting tensile residual stress, and a columnar growth regime exhibiting compressive residual stress. A simple kinetic model is proposed to explain the unusual morphology within this transition regime. It is determined that measurements of the film residual stress can be used to tune the deposition parameters to repeatably produce permeable films for applications. The result is a convenient, single-step process that enables the elegant fabrication of many previously challenging structures.

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