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- Lindenberger, Marcus, 1975-
(författare)
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Cardiovascular responses to hypovolemic circulatory stress in women : With special reference to venous compliance and capacitance
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Acute haemorrhage is a leading cause of death in trauma. Young women (YW) seem more susceptible to hypovolemic circulatory stress than young men (YM), but the underlying mechanisms are not clear. Elderly subjects are more vulnerable to haemorrhage, with a decreased defence of central blood volume in elderly men, but the defence has not been evaluated in elderly women (EW). The aims were to assess differences in cardiovascular responses to hypovolemic circulatory stress, emphasizing compensatory mechanisms to maintain central blood volume in YW, EW and in women prone to vaso‐vagal reaction (VW).Lower body negative pressure (LBNP) was used as a model for haemorrhage and to create acute hypovolemic stress. Volumetric techniques were used to assess venous compliance, capacitance and capillary fluid exchange both caused by LBNP in the calf and the response to maintain central blood volume.LBNP induced a comparable hypovolemic stimulus in YW and YM, with lower calf venous compliance and capacitance but higher net capillary fluid filtration in YW. YW responded with smaller vasoconstriction without association between P‐NE and peripheral vascular resistance in contrast to YM. Venous capacitance response was decreased with time in YW. Further, net capillary fluid absorption from peripheral tissues to central circulation was decreased in YW in response to hypovolemic stress. All in all, this indicates less efficiency to defend central blood volume in young women.Calf venous compliance and capacitance was maintained in EW compared to YW but capillary filtration was decreased, implying reduced capillary function with age. With increasing transmural pressures however, filtration and capillary filtration coefficient (CFC) increased indicating increased capillary susceptibility to transmural pressure load in dependent regions with age. Heart rate increase was attenuated in EW while peripheral vascular conductance was maintained suggesting reduced cardiovagal baroreceptor function in response to hypovolemia with age. Venous capacitance response and fluid absorption from peripheral tissues to central circulation were decreased with age, indicating less efficiency to defend central blood volume.LBNP induced a slower hypovolemic stimulus in VW compared with nonvagal women. Further, the cardiopulmonary baroreflex was less efficient, and the venous capacitance response from peripheral tissues to central circulation was decreased, which may explain their susceptibility to orthostatic challenge.
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| 2. |
- Stenborg, Anna, 1967-
(författare)
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Vascular Dysfunction in Stroke and CADASIL
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cerebrovascular disease (CVD) is strongly linked to hypertension and generally occurs later in life than coronary artery disease (CAD). Three quarters of the patients with symptomatic CVD are above 65 years of age. The risk factors are the same for CVD and CAD, but the relative importance of the vascular risk factors differs greatly.Genetic causes of stroke are relatively rare. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) is a hereditary disease which causes CVD in young adults and middle-aged people, with migraine, stroke, psychiatric illness and dementia as clinical manifestations.The subject of this thesis is vascular function in stroke and CADASIL. Endothelium-dependent vasodilation (EDV) and arterial stiffness were investigated by different methods in stroke patients and CADASIL patients compared with healthy controls. Venous occlusion plethysmography with intra-arterial acetylcholine was used to evaluate EDV in the forearm resistance vessels. Flow-mediated vasodilation of the brachial artery was used to evaluate EDV in a conduit artery. Stroke patients displayed reduced EDV in resistance vessels compared with a healthy control group, but this reduction was not significant when, in a larger group of stroke patients, adjustments were made for blood pressure, antihypertensive treatment and other risk factors. Flow mediated vasodilation of the brachial artery was reduced in the stroke patients even after adjustment for risk factors. Compared with controls, the CADASIL patients showed similar EDV in the conduit artery, but reduced EDV in resistance vessels.Arterial compliance was evaluated by augmentation index from pulse wave analysis, by a ratio of cardiac stroke volume and pulse pressure, and by the distensibility of the carotid artery in relation to pulse pressure. Stroke patients and CADASIL patients did not display any significant increase in arterial stiffness when evaluated by these methods.
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| 3. |
- Åstrand, Håkan, 1969-
(författare)
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Regulation of aortic wall mechanics and stress : An experimental study in man
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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