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Cardiac surgery is traditionally a heavy user of blood and blood products. Until recently, the benefits of transfusion have been largely assumed and the risks relatively ignored. This has prompted us to examine new ways of minimising patient exposure to donor red blood cells (RBC's). At the present time, most clinical guidelines for RBC transfusion are based mainly upon haemoglobin concentration ([Hb]). As [Hb] may be artificially depressed by the haemodiluting effect of the heavy clear fluid load associated with cardiac surgery, transfusing based upon [Hb] alone may overestimate the requirement for RBC's. Where such haemodilution is present, systemic oxygenation may be maintained through a viscosity mediated patho-physiological response. The work reported in this thesis attempts to explore the relative contribution of both red cell volume (RCV) and plasma volume (PV) to the anaemia encountered following cardiac surgery while also examining factors that may be associated with a low post-operative RCV. In addition, we have explored on a theoretical basis what [Hb] would represent a critical level of systemic oxygen delivery (DO2Crit). Taken together, this has allowed us to develop an RCV based transfusion guideline aimed at reducing the incidence of unnecessary (and potentially counter-productive) RBC transfusion. As RBC's may be associated with pulmonary endothelial damage, we have also studied the impact of the RCV guideline developed on post-operative acute lung injury (ALI). Finally, in a separate study, the merits of a simple activated clotting time (ACT) based system of anti-coagulation management for cardiopulmonary bypass (CPB) versus that of an individualised heparin management system (HMS) are described.

<p>Diss. (sammanfattning) Umeå : Umeå universitet, 1995, härtill 5 uppsatser</p> / digitalisering@umu

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Cardiovascular disease (CVD) is a term used to describe a variety of diseases and events that impact the heart and circulatory system. CVD is the United Kingdom's (UKs) biggest killer, causing more than 50,000 premature deaths each year. Early recognition of the potential for magnetic resonance imaging (MRI) to provide a versatile, non-ionising, non-invasive, technique for the assessment of CVD resulted in the modality becoming an area of intense interest in the research, radiology and cardiology communities. The first half of this thesis reviews some of the key developments in magnetic resonance hardware and software that have led to cardiac magnetic resonance imaging (CMRI) emerging as a reliable and reproducible tool, with a range of applications ideally suited for the evaluation of cardiac morphology, function, viability, valvular disease, perfusion, and congenital cardiomyopathies. In addition to this, the advantages and challenges of imaging at 3.0T in comparison to 1.5T are discussed. The second half of this thesis presents a number of investigations that were specifically designed to explore the capability of CMRI to accurately detect subtle age and disease related changes in the human heart. Our investigations begin with a study at 1.5T that explores the clinical and scientific significance of the less frequently used measure of right ventricular function to test the hypothesis that the inclusion of this data provides a more informative assessment of overall cardiac function. The focus then shifts to imaging at 3.0T and the challenges of optimising cardiac imaging at this field strength are discussed. Normal quantitative parameters of cardiac function are established at this field strength for the left ventricle and the left atrium of local volunteers. These values are used to investigate disease related changes in left ventricle and left atrium of distinct patient cohorts. This work concludes by investigating the impact of gadolinium-based contrast agents on the quantitative parameters of cardiac function.

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.