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  • 1. Beställ onlineKöp publikationen >>
    Karlsson, Jerker
    Linköpings universitet, Institutionen för hälsa, medicin och vård, Avdelningen för diagnostik och specialistmedicin. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Hjärtcentrum, Fysiologiska kliniken US.
    Abdominal Aortic Wall Mechanics - Stress, Strain and Stiffness in A Medical Perspective: An Experimental Study in Man2024Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Background:  

    The stiffness of the abdominal aorta is considered a significant factor affecting the morbidity and mortality of cardiovascular disease. Estimating vascular stiffness is an integral part in cardiovascular risk assessment. Wall stress of the abdominal aorta appears to be a crucial factor in the remodeling of the arterial wall and the growth of aneurysms. Consequently, arterial mechanics plays a vital role in the function of the cardiovascular system. Therefore, there is a need for comprehensive studies of mechanical forces in the vessel wall to better understand the mechanisms behind normal and pathological changes that are significant for hypertension, atherosclerosis, and the development of arterial aneurysms. The aim of this study was to explore the blood pressure-induced forces in the aortic wall using a computational mechanical model, with particular attention to the effects of age, sex, and blood pressure on the remodeling process of the vessel wall.  

    Methods:  

    A computational model, comprising a solid mechanical model and a parameter identification process known as the Parameter Identification Method for Mechanical Parameters (PIMMP), was used to investigate the mechanical properties of the abdominal aortic vessel wall. Data for the model were obtained from the human abdominal aorta of volunteers: 30 healthy individuals, females (n=15) and males, divided into three age groups with an equal number of females and males (n=5 in each age group). Invasive blood pressure, measured via catheter, and diameter variation in the abdominal aorta, measured via ultrasound, were acquired to be used as input data for PIMMP. This dataset was utilized in Papers I, III, and IV. In Paper II, 24 datasets were generated, based on model parameters presented in the scientific literature.   

    Results:  

    Paper I reveals that elderly males exhibit both higher aortic wall stress and higher isotropic stress component, than females. With age, males show an increase in isotropic load-bearing fraction and a decrease in anisotropic load-bearing fraction, a trend not observed in females.  

    Paper II validates an in silico aortic model against a computerized membrane model of an abdominal aorta. The membrane model accurately predicts stress states as well as the load-bearing fraction of anisotropic material across all blood pressure levels, independent of the transmural stress gradient. However, the model’s accuracy is limited due to insufficient in vivo axial loading information.  

    Paper III demonstrates that changes in circumferential stretch have a more pronounced effect on longitudinal stress than the other way around. Both circumferential and longitudinal stiffnesses increase with age, irrespective of sex. However, sex-based differences in stiffness are observed when comparing younger and older groups.  

    Paper IV investigates pulse wave velocity (PWV) calculations using the Moens-Korteweg equation and the Bramwell-Hill equation. PWV shows a positive association with both isotropic and anisotropic material properties, with a transition zone observed between diastolic and systolic blood pressures, to a positive association with anisotropic properties at systolic blood pressure. Furthermore, an increase in PWV with age, with no significant difference between sexes, is observed.  

    The Extra Material suggests a deficiency in age-related wall stress regulation in males, potentially due to insufficient stiffness of anisotropic materials such as collagen. In contrast, females show an age-related increase in abdominal aortic wall thickness and anisotropic material stiffness, indicating adequate wall stress regulation.  

    Conclusions:  

    This doctoral dissertation focused on the effects of age and sex on the abdominal aortic wall. Overall, the findings suggest potential alterations in the collagen and elastin content during the remodeling of the abdominal aorta, which may differ between sexes. These alterations could be induced chemically or mechanically. The model has shown potential in identifying healthy individuals within a population. These insights may contribute to the understanding of cardiovascular health and disease progression. 

    Delarbeten
    1. An in vivo study of isotropic and anisotropic wall stress in a hyperelastic holzapfel-gasser-ogden model in the human abdominal aorta: Effects of age and sex
    Öppna denna publikation i ny flik eller fönster >>An in vivo study of isotropic and anisotropic wall stress in a hyperelastic holzapfel-gasser-ogden model in the human abdominal aorta: Effects of age and sex
    Visa övriga...
    2023 (Engelska)Ingår i: Frontiers in Physiology, E-ISSN 1664-042X, Vol. 14, artikel-id 1128131Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Background: Wall stress of the abdominal aorta (AA) appears to be an important factor in the assessment of risk for rupture based on the relationship between blood pressure and aortic diameter. We therefore investigated peak wall stress as well as isotropic and anisotropic wall stress of AA.Methods: Thirty healthy adults (male = 15) were included. Pulsatile diameter changes were determined non-invasively by an echo-tracking system, and intra-aortic pressure was measured simultaneously. A computer based mechanical model was used to compute the isotropic and anisotropic components of circumferential and longitudinal stresses.Results: Elderly males had higher total wall stress and a higher isotropic stress component in the circumferential direction and higher total longitudinal wall stress than elderly females. The isotropic component increased with age in males but not in females, whereas the anisotropic component decreased with age in both sexes.Conclusion: We found that isotropic and anisotropic properties of the abdominal aortic wall differ between young and elderly participants and between the sexes. A possible explanation could relate to chemical alterations (e.g., due to sex hormones) and changes over time in the physical distribution of fibers. Modeling of wall stress components of the human AA may contribute to a better understanding of elastin-collagen interactions during remodeling of the aortic wall.

    Ort, förlag, år, upplaga, sidor
    FRONTIERS MEDIA SA, 2023
    Nyckelord
    abdominal aorta, remodeling, wall stress, sex, age
    Nationell ämneskategori
    Klinisk medicin
    Identifikatorer
    urn:nbn:se:liu:diva-192572 (URN)10.3389/fphys.2023.1128131 (DOI)000958802000001 ()
    Anmärkning

    Funding: Region OEstergoetland [ROE-965959]; Medical Faculty Linkoeping University; Swedish Research Council [12,661]; Swedish Heart-Lung Foundation

    Tillgänglig från: 2023-03-22 Skapad: 2023-03-22 Senast uppdaterad: 2024-02-23
    2. Abdominal Aortic Wall Cross-coupled Stiffness Could Potentially Contribute to Aortic Length Remodeling
    Öppna denna publikation i ny flik eller fönster >>Abdominal Aortic Wall Cross-coupled Stiffness Could Potentially Contribute to Aortic Length Remodeling
    Visa övriga...
    2022 (Engelska)Ingår i: Artery Research, ISSN 1872-9312, Vol. 28, s. 113-127Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Background: Wall stiffness of the abdominal aorta is an important factor in the cardiovascular risk assessment. We investigated abdominal aortic wall stiffness divided in direct and cross‑coupled stiffness components with respect to sex and age.Methods: Thirty healthy adult males (n = 15) and females were recruited and divided into three age groups: young, middle aged and elderly. Pulsatile diameter changes were determined noninvasively by an echo‑tracking system, and intra‑aortic pressure was measured simultaneously. A mechanical model was used to compute stress and stiffness in circumferential and longitudinal directions.Results: Circumferential stretch had a higher impact on longitudinal wall stress than longitudinal stretch had on circumferential wall stress. Furthermore, there were an age‑related and sex‑independent increase in circumferential and longitudinal direct and cross‑coupled stiffnesses and a decrease in circumferential and longitudinal stretch of the abdominal aortic wall. For the young group, females had a stiffer wall compared to males, while the male aortic wall grew stiffer with age at a higher rate, reaching a similar level to that of the females in the elderly group.Conclusion: Temporal changes in aortic stiffness suggest an age‑related change in wall constituents that is expressed in terms of circumferential remodeling impacting longitudinal stress. These mechanisms may be active in the development of aortic tortuosity. We observed an age‑dependent increase in circumferential and longitudinal stiffnesses as well as decrease in stretch. A possible mechanism related to the observed changes could act via chemi‑cal alterations of wall constituents and changes in the physical distribution of fibers. Furthermore, modeling of force distribution in the wall of the human abdominal aorta may contribute to a better understanding of elastin–collagen interactions during remodeling of the aortic wall.

    Ort, förlag, år, upplaga, sidor
    BioMed Central (BMC), 2022
    Nyckelord
    Abdominal aorta, cardiovascular disease, wall stress, cross-coupled stiffness, sex, age, remodeling
    Nationell ämneskategori
    Klinisk medicin
    Identifikatorer
    urn:nbn:se:liu:diva-190181 (URN)10.1007/s44200-022-00022-0 (DOI)000888711800001 ()
    Forskningsfinansiär
    Vetenskapsrådet, 12661Hjärt-LungfondenLinköpings universitetVetenskapsrådet, 12661
    Anmärkning

    Funding: Linkoping University; Region Ostergotland; Medical Faculty Linkoping University; Swedish Research Council [12661]; Swedish Heart-Lung Foundation

    Tillgänglig från: 2022-11-28 Skapad: 2022-11-28 Senast uppdaterad: 2024-02-23Bibliografiskt granskad
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  • 2.
    Karlsson, Jerker
    et al.
    Linköpings universitet, Institutionen för hälsa, medicin och vård, Avdelningen för diagnostik och specialistmedicin. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Hjärtcentrum, Fysiologiska kliniken US.
    Stålhand, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Carlhäll, Carl-Johan
    Linköpings universitet, Institutionen för hälsa, medicin och vård, Avdelningen för diagnostik och specialistmedicin. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Region Östergötland, Hjärtcentrum, Fysiologiska kliniken US.
    Länne, Toste
    Linköpings universitet, Institutionen för hälsa, medicin och vård. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Hjärtcentrum, Thorax-kärlkliniken i Östergötland.
    Engvall, Jan
    Linköpings universitet, Institutionen för hälsa, medicin och vård, Avdelningen för diagnostik och specialistmedicin. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Region Östergötland, Hjärtcentrum, Fysiologiska kliniken US.
    Abdominal Aortic Wall Cross-coupled Stiffness Could Potentially Contribute to Aortic Length Remodeling2022Ingår i: Artery Research, ISSN 1872-9312, Vol. 28, s. 113-127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Wall stiffness of the abdominal aorta is an important factor in the cardiovascular risk assessment. We investigated abdominal aortic wall stiffness divided in direct and cross‑coupled stiffness components with respect to sex and age.Methods: Thirty healthy adult males (n = 15) and females were recruited and divided into three age groups: young, middle aged and elderly. Pulsatile diameter changes were determined noninvasively by an echo‑tracking system, and intra‑aortic pressure was measured simultaneously. A mechanical model was used to compute stress and stiffness in circumferential and longitudinal directions.Results: Circumferential stretch had a higher impact on longitudinal wall stress than longitudinal stretch had on circumferential wall stress. Furthermore, there were an age‑related and sex‑independent increase in circumferential and longitudinal direct and cross‑coupled stiffnesses and a decrease in circumferential and longitudinal stretch of the abdominal aortic wall. For the young group, females had a stiffer wall compared to males, while the male aortic wall grew stiffer with age at a higher rate, reaching a similar level to that of the females in the elderly group.Conclusion: Temporal changes in aortic stiffness suggest an age‑related change in wall constituents that is expressed in terms of circumferential remodeling impacting longitudinal stress. These mechanisms may be active in the development of aortic tortuosity. We observed an age‑dependent increase in circumferential and longitudinal stiffnesses as well as decrease in stretch. A possible mechanism related to the observed changes could act via chemi‑cal alterations of wall constituents and changes in the physical distribution of fibers. Furthermore, modeling of force distribution in the wall of the human abdominal aorta may contribute to a better understanding of elastin–collagen interactions during remodeling of the aortic wall.

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  • 3.
    Åstrand, Håkan
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Fysiologi. Linköpings universitet, Hälsouniversitetet.
    Stålhand, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Karlsson, Jerker
    Linköpings universitet, Institutionen för medicin och hälsa, Fysiologi. Linköpings universitet, Hälsouniversitetet.
    Karlsson, Matts
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Sonesson, B.
    Malmö University Hospital, Sweden.
    Länne, Toste
    Linköpings universitet, Institutionen för medicin och hälsa, Fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Thorax-kärlkliniken i Östergötland.
    In vivo estimation of the contribution of elastin and collagen on the mechanical properties in the abdominal aorta of man: effect of age and gender2011Ingår i: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 110, nr 1, s. 8750-8757Artikel i tidskrift (Refereegranskat)
    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.

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