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Regulation of aortic wall mechanics and stress: An experimental study in man
Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The abdominal aorta (AA) in man is a vulnerable artery prone to atherosclerosis as well as aneurysmatic dilation. The underlying aortic composition, mechanical properties as well as the mechanisms responsible for age-related changes and vascular disease are however largely unknown. The aims of this study were 1) to characterize the age- and gender-related changes of the aortic wall components in vivo, using a mechanical model based on ultrasound measurements of pulsatile aortic diameter changes combined with intra-arterial pressure; 2) to validate ultrasound measurements of diameter and intima-media thickness (IMT) of the AA in order to calculate wall stress; 3) to study the stress driven remodeling response of the aortic wall in healthy individuals and the influence of age and gender; and 4) to study wall stress and remodeling of the AA in diabetic patients in order to elucidate the protective influence of diabetes on abdominal aortic aneurysm formation.

The stiffness of the isotropic material (mainly elastin) increased in males despite the known decrease in elastin content with age. Further, an exponential increase in stiffness of the anisotropic material (mainly collagen) in males at high physiological pressure was found. This might be due to changed isoforms of collagen and increased glycation with age. Females were less affected than males.

The reproducibility of the ultrasound measurements of diameter and IMT in the AA was acceptable (CV; 4% and 11% respectively), making it possible to calculate circumferential aortic wall stress in vivo. The age-related remodeling of the arterial wall led to increased diameter, and compensatory thickening of the wall preventing the circumferential wall stress from increasing in the common carotid artery of males and females, and the AA of females. However, the compensatory increase in wall thickness was defect in the male AA, where stress increased with age. Pulsatile stress influenced the material parameters of the AA, leading to increased stiffness of anisotropic material (mainly collagen), whereas stiffness of isotropic material (mainly elastin) was unaffected.

Patients with diabetes mellitus had increased aortic wall thickness than controls, generating less circumferential stress. This coincides with the known reduction of abdominal aortic aneurysms in diabetic patients and may act as a protective factor.

Place, publisher, year, edition, pages
Institutionen för medicin och hälsa , 2008. , 74 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1053
Keyword [en]
Aorta, wall stress, remodeling, IMT, gender, diabetes mellitus, aging, collagen, elastin
National Category
Surgery
Identifiers
URN: urn:nbn:se:liu:diva-11556ISBN: 9789173939447 (print)OAI: oai:DiVA.org:liu-11556DiVA: diva2:17986
Public defence
2008-05-16, Originalet, Qulturum, Hus B4, Länssjukhuset Ryhov, Jönköping, 09:00 (English)
Opponent
Supervisors
Available from: 2008-04-14 Created: 2008-04-14 Last updated: 2017-12-08
List of papers
1. Noninvasive ultrasound measurements of aortic intima-media thickness: Implications for in vivo study of aortic wall stress
Open this publication in new window or tab >>Noninvasive ultrasound measurements of aortic intima-media thickness: Implications for in vivo study of aortic wall stress
2003 (English)In: Journal of Vascular Surgery, ISSN 0741-5214, Vol. 37, no 6, 1270-1276 p.Article in journal (Refereed) Published
Abstract [en]

Object: The abdominal aorta (AA) has a predilection for aneurysm formation. An etiologic factor may be underlying aortic wall stress. The purpose of this study was to examine whether the intima-media thickness (IMT) of the AA, as a surrogate to arterial wall thickness, can be measured noninvasively with satisfactory results to calculate circumferential wall stress, and to evaluate regional and gender differences in wall stress.

Methods: Sixty-five middle-aged healthy subjects were examined with B-mode ultrasound to determine the diameter and IMT in the infrarenal AA, common carotid artery (CCA), common femoral artery (CFA), and popliteal artery (PA). Blood pressure was measured noninvasively in the brachial artery. Wall stress was calculated according to the law of LaPlace.

Results: Intraobserver variability for the IMT in the AA showed a coefficient of variation of 11%. IMT was thickest in the AA compared with the CCA, CFA, and PA (P < .001). There was a gender difference in IMT in the CFA (P < .05) and PA (P < .01) but not in the AA. Greater wall stress was found in the AA than in the CCA (P < .001) and PA (P < .001), with men having greater wall stress in all studied arterial regions.

Conclusions: Aortic IMT can be satisfactorily studied in vivo with noninvasive B-mode ultrasound. There are gender differences in IMT and wall stress, and the largest wall stress is found in the AA in men, which might be important in aneurysm development.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-13178 (URN)10.1016/S0741-5214(02)75344-5 (DOI)
Available from: 2008-04-14 Created: 2008-04-14 Last updated: 2017-03-27
2. Age-related increase in wall stress of the human abdominal aorta: An in vivo study
Open this publication in new window or tab >>Age-related increase in wall stress of the human abdominal aorta: An in vivo study
2005 (English)In: Journal of Vascular Surgery, ISSN 0741-5214, Vol. 42, no 5, 926-931 p.Article in journal (Refereed) Published
Abstract [en]

Background

The regulation of wall stress in the abdominal aorta (AA) of humans might be of specific interest, because the AA is the most common site for aneurysm formation in which wall stress seems to be an important pathophysiological factor. We studied the age-related changes in wall stress of the AA in healthy subjects, with the common carotid artery (CCA) as a comparison.

Methods

A total of 111 healthy subjects were examined with B-mode ultrasonography to determine the lumen diameter and intima-media thickness (IMT) in the AA and the CCA.

Results

Aortic IMT was affected by age in men and by both age and lumen diameter in women. Carotid IMT was affected by age and pulse pressure in both men and women. Wall stress was higher in the AA than in the CCA (P < .001), and men had higher wall stress than women in both the AA (P < .001) and the CCA (P < .05). Furthermore, wall stress was constant during life in the CCA of men and women and in the AA of women. In the male aorta, however, wall stress increased with age (P < 0.01).

Conclusions

Arterial diameters increase with age, and a compensatory thickening of the arterial wall prevents the circumferential wall stress from increasing. However, this compensatory response is insufficient in the male AA and results in an increase in stress with age. These findings might explain the propensity for aneurysms to develop in the AA of men.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-13179 (URN)10.1016/j.jvs.2005.07.010 (DOI)
Available from: 2008-04-14 Created: 2008-04-14 Last updated: 2017-03-27
3. In vivo estimation of the contribution of elastin and collagen on the mechanical properties in the abdominal aorta of man: effect of age and gender
Open this publication in new window or tab >>In vivo estimation of the contribution of elastin and collagen on the mechanical properties in the abdominal aorta of man: effect of age and gender
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2011 (English)In: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 110, no 1, 8750-8757 p.Article in journal (Refereed) Published
Abstract [en]

The mechanical properties of the aorta affect cardiac function and are related to cardiovascular morbidity/mortality. This study was designed to evaluate the isotropic (mainly elastin, elastiniso) and anisotropic (mainly collagen, collagenani) material parameters within the human aorta in vivo. Thirty healthy men and women in three different age categories (23–30, 41–54, and 67–72 yr) were included. A novel mechanical model was used to identify the mechanical properties and the strain field with aid of simultaneously recorded pressure and radius in the abdominal aorta. The magnitudes of the material parameters relating to both the stiffness of elastiniso and collagenani were in agreement with earlier in vitro studies. The load-bearing fraction attributed to collagenani oscillated from 10 to 30% between diastolic and systolic pressures during the cardiac cycle. With age, stiffness of elastiniso increased in men, despite the decrease in elastin content that has been found due to elastolysis. Furthermore, an increase in stiffness of collagenani at high physiological pressure was found. This might be due to increased glycation, as well as changed isoforms of collagen in the aortic wall with age. A marked sex difference was observed, with a much less age-related effect, both on elastiniso and collagenani stiffness in women. Possible factors of importance could be the effect of sex hormones, as well as differing collagen isoforms, between the sexes.

Place, publisher, year, edition, pages
AMER PHYSIOLOGICAL SOC, 2011
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-13180 (URN)10.1152/japplphysiol.00579.2010 (DOI)000286140900022 ()
Available from: 2008-04-14 Created: 2008-04-14 Last updated: 2017-03-27
4. Reduced aortic wall stress in diabetes mellitus
Open this publication in new window or tab >>Reduced aortic wall stress in diabetes mellitus
Show others...
2007 (English)In: European Journal of Vascular and Endovascular Surgery, ISSN 1078-5884, Vol. 33, no 5, 592-598 p.Article in journal (Refereed) Published
Abstract [en]

Objective: Most risk factors are similar for abdominal aortic aneurysm (AAA) and atherosclerosis, e.g. smoking, male gender, age, high blood pressure, hyperlipidemia. Diabetes mellitus however, is a risk factor for atherosclerosis, but diabetic patients seldom develop AAA. The reason for this discrepancy is unknown. Increased aortic wall stress seems to be an etiologic factor in the formation, growth and rupture of AAA in man. The aim of our study was to study the wall stress in the abdominal aorta in diabetic patients compared with healthy controls.

Methods: 39 patients with diabetes mellitus and 46 age – and sex matched healthy subjects were examined with B-mode ultrasound to determine the lumen diameter (LD) and intima-media thickness (IMT) in the abdominal aorta (AA) and the common carotid artery (CCA). Diastolic blood pressure (DBP) was measured non-invasively in the brachial artery. LaPlace law was used to calculate circumferential wall stress.

Results: Age, DBP, and LD in the abdominal aorta were not significantly different in the diabetic patients compared to controls. IMT in the AA was larger in the diabetic patients, 0.89 ± 0.17 vs 0.73 ± 0.11 mm (p < .001). Accordingly aortic wall stress was reduced in the diabetics, 7.8 ± 1.7 × 105 vs 9.7 ± 1.9 × 105 dynes/cm2 (p < .001).

Conclusions: Wall stress in the abdominal aorta is reduced in diabetes mellitus. This is mainly due to a thicker aortic wall compared to healthy controls. The reduced aortic wall stress coincides with the fact that epidemiological studies have shown a decreased risk of aneurysm development in diabetic patients.

Keyword
Abdominal aorta, Diabetes mellitus, Intima-media thickness, Wall stress, Wall tension, Aneurysm
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-13181 (URN)10.1016/j.ejvs.2006.11.011 (DOI)
Available from: 2008-04-14 Created: 2008-04-14 Last updated: 2017-03-27

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