Exercise intensity as a mediator of central and peripheral vascular integrity

Vascular homeostasis is a vital element of health. Exercise plays a role in maintaining the integrity of the vascular endothelium via transient increases in endothelial shear stress that accompany exercise-induced hyperaemia. This hyperaemia and stimulus it presents to the vasculature is governed by exercise intensity. Exercise is the primary therapy in cardiac rehabilitation contexts, a population with typically elevated cardiovascular risk factors and compromised vascular integrity. In the UK, cardiac rehabilitation may be ineffective for improving long-term health outcomes. This thesis demonstrates that the exercise intensities achieved by patients in UK cardiac rehabilitation were variable and generally low. The exercise performed had no impact upon indices of peripheral vascular structure or function and little effect upon short-term health outcomes. A service-level intervention was implemented to increase the dose of exercise achieved by patients via an increase in intensity and examine its effects upon the vasculature. In a subsequent cohort, the intervention was unsuccessful at modifying the exercise intensities that were achieved or indices of peripheral vascular structure or function. However, a positive relationship between the intensity achieved at the end of the programme and changes in vascular function was found. Although peripheral vascular integrity is easily studied it is perhaps less relevant to health compared to central vascular integrity. Assessments of the central circulation during exercise have previously relied upon high-risk, invasive techniques. Therefore, to understand the stimulus presented to the central vasculature by exercise at intensities akin to those achieved in cardiac rehabilitation, a novel technique was applied: using cardiac magnetic resonance imaging during cycling in a healthy cohort. This technique was unable to capture the changes in perfusion of the central circulation that should have occurred with exercise at different intensities but successfully demonstrated reproducible assessments of cardiac dynamics during exercise of different intensities.