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- Karlsson, Jerker, 1967-, et al.
(författare)
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Abdominal Aortic Wall Cross-coupled Stiffness Could Potentially Contribute to Aortic Length Remodeling
- 2022
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Ingår i: Artery Research. - : BioMed Central (BMC). - 1872-9312 .- 1876-4401. ; 28, s. 113-127
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 2. |
- Karlsson, Jerker, 1967-
(författare)
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Abdominal Aortic Wall Mechanics - Stress, Strain and Stiffness in A Medical Perspective : An Experimental Study in Man
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 3. |
- Karlsson, Jerker, 1967-, et al.
(författare)
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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
- 2023
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Ingår i: Frontiers in Physiology. - : FRONTIERS MEDIA SA. - 1664-042X. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Nelzén, Oskar, 1984-
(författare)
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Lower limb venous incompetence and the effect of radiofrequency ablation versus open surgery : Focus on haemodynamics, quality of life and health economic aspects
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chronic venous incompetence (CVI) is a common condition, and varicose vein treatment is one of the most-common surgical procedures performed worldwide. Common symptoms of CVI are pain, cramps, itching, feeling of leg heaviness and venous claudication. Advanced CVI can lead to skin changes, eczema and venous ulcers. While the cause of the disease is un-known, it often starts with venous enlargement and valve dysfunction. The overall aims of this thesis are: 1) to develop quantitative diagnostic measurements using strain-gauge plethysmography (SGP) with standardised superficial venous occlusion and duplex ultrasound (DUS); 2) to evaluate the effects of radiofrequency ablation (RFA) and high ligation/stripping (HL/S) for patients with great saphenous vein (GSV) incompetence; and 3) to evaluate the cost-effectiveness of GSV treatment. The first of the four studies involved patients with GSV incompetence. For these patients, SGP with superficial venous occlusion was performed before and after GSV treatment. SGP was able to predict the haemodynamic outcome of the treatment in the majority of the limbs examined. The conclusion is that SGP with standardised superficial venous occlusion may be used for predicting the outcome of GSV treatment. The second study evaluated the short-term outcomes of GSV treatment using RFA and HL/S regarding haemodynamics and quality of life (QoL). Both treatments lead to significant improvements in QoL, with no signifcant differences between the treatments. Despite successful treatment, the majority of the limbs in both treatment groups had significant residual reflux located mainly in the calf (i.e., below the treated area). The residual reflux may be a risk factor for future symptom relapses and need to be examined in more-long-term studies. The third study examined quantitative DUS and SGP parameters in relation to clinical severity and QoL. DUS-derived volume flow and SGP re-flux time showed weak but significant correlations with clinical severity (C in CEAP). The conclusion is that the current gold standard using the qualitative DUS-derived reflux time for CVI diagnostics should be revised and replaced with a more-relevant quantitative parameter. The fourth study evaluated the cost-effectiveness of GSV treatment with 1 year of follow-up. Both RFA and HL/S provided significant improvements in QoL. RFA is very cost-effective and is associated with fewer days missed from work compared to HL/S. Cost-wise, both methods are well be-low the national threshold for cost-effective treatment. Due to its higher cost, HL/S should be reserved for cases that require this method.
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