Obligatory role of central aortic blood pressure in pulsatile cerebral hemodynamics
In the human circulatory system, the central aorta is closer to the brain than the radial artery, which is the preferential location for monitoring systemic blood pressure together with intracranial pressure (ICP) for determining cerebral perfusion pressure. The central aortic pressure pulse is different to the peripheral pulse as the pressure alters its morphology and amplifies while propagating from central to the peripheral locations. This alteration in waveform is associated with fundamental hemodynamic phenomena such as peripheral wave reflection and arterial stiffness, parameters which alter with advancing age. Particularly, it is hypothesised that amplified central aortic pulse pressure due to arterial stiffness would cause increased tensile and shear stress to the microvasculature in the brain of elderly people.
This thesis aimed to assess the role of non-invasive central aortic blood pressure in experimental and clinical observations in pulsatile cerebral hemodynamics compared with the use of the radial pressure pulse. Furthermore, the investigation was expanded to include analysis of flow in cerebral arteries to gain additional information on pulsatile cerebral hemodynamics in conjunction with central aortic pressure pulse.
Results suggest that arterial pulse pressure is strongly associated with controlling mean and pulsatile ICP. In particular, central aortic pulse pressure was a major determinant of individual variability of pulsatile ICP. Direct evidence of advancing age was found in features of cerebral blood flow waveforms which is a shared phenomenon with age-related changes in the aortic pressure pulse. Furthermore, the cerebral vasculature is found to be highly dilated, having a relatively low resistance from youth throughout the later stages in life.
Findings of this thesis break new ground in quantifying the role of the aortic pressure pulse in cranial pressure and volume relationship. The findings lead to potential clinical applications such as individual diagnosis for idiopathic normal pressure hydrocephalus (iNPH) patients and treatment of patients with cerebrovascular diseases or neurological disorders with anti-hypertensive drugs in order to control mean and pulsatile ICP. Overall, findings support the hypothesis for causal relation between increase in aortic pulse pressure with advancing age and proportional mechanical stress and longitudinal stress on the fragile cerebral vasculature.