| Summary: | <p>Lower indices of ideal cardiovascular health, such as hypertension, obesity, smoking, alcohol consumption and physical inactivity, are known risk factors for midlife cardiovascular and cerebrovascular disease. Whether modifiable cardiovascular risk factors, and novel early life exposures such as preterm birth, influence the structure and integrity of the heart-brain axis in young adults is less well studied. </p>
<p>This thesis investigates the heart-brain axis using detailed brain and cardiac imaging, exercise testing and ambulatory monitoring. Purposive recruitment established a cohort of young adults with a range of gestational ages and blood pressures. The detailed phenotypic measures were used to investigate associations between cardiac measures, brain volumes, brain cortical thickness, white matter hyperintensity lesions and brain vascular measures to understand factors influencing the heart-brain axis in early life. </p>
<p>It was demonstrated that cardiovascular risk profiles are associated with structural differences across the heart-brain axis. Healthier profiles of ideal cardiovascular health indices are associated with lower left ventricular mass to left ventricular end diastolic volume ratios, higher left ventricular stroke volumes and higher brain vessel density and vessel calibre. In addition, healthier cardiovascular profiles were associated with lower number of white matter hyperintensity lesions and higher brain blood flow. In addition, there was evidence of cortical-thalamic associations with cardiac function at rest. These associations were then tested under exercise stress and found evidence that cortical-thalamic structures are associated with indicators of peak exercise performance. There was also evidence of cortico-thalamic associations with submaximal cardiac output and myocardial strain.</p>
<p>The thesis then adopts best practice guidelines to design intervention strategies to promote ideal cardiovascular health in young adults. A systemic review of randomised control trials demonstrated an evidence gap, making it difficult to recommend specific lifestyle interventions for sustained cardiovascular risk reduction in young adults. However, beneficial short-term reduction in clinic blood pressures was shown to be associated with exercise intervention. Meta-analysis demonstrated supervised, moderate-to-high intensity exercise and frequent contact between participants and intervention teams as the most effective intervention components. </p>
<p>The preliminary data on the heart-brain axis and evidence assimilated in the systematic review have informed development of a randomized control trial to test the effectiveness of exercise intervention on ambulatory blood pressure and remodelling across the heart-brain axis. The combined work will inform future primary prevention strategies and identify biomarkers of heart-brain health to track in young adults.</p>
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