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The relationship between arterial blood pressure and cerebral blood flow : insights into aging, altitude and exercise

University of British Columbia

The majority of previous research on the relationship between blood pressure and cerebral blood flow (CBF) through the application of transfer function analysis (TFA) has been performed under spontaneous conditions. Under these circumstances, there is little input signal power (blood pressure), which makes linear interpretation of the output (CBF) results tenuous. In five experimental studies, the general aim of this thesis was to provide new insights on the relationship(s) between blood pressure and CBF throughout the aging spectrum. The first study determined the reproducibility of TFA metrics during spontaneous and driven blood pressure oscillations. The results revealed that squat-stand maneuvers were the most robust and reliable method to evaluate this relationship throughout aging. Consequently, this methodology was employed for the research studies. The second study examined the pressure-flow response in younger adults with acutely elevated cerebrovascular resistance index (CVRi). Augmenting CVRi, even without changes in CO₂, resulted in increased phase lead and reduced amplitude modulation; therefore, the impact of CVRi needs to be considered for the parsimonious interpretation of TFA metrics. The third experiment examined the pressure-flow relationship in three adult populations: young and old healthy adults, and heart transplant recipients. Findings revealed comparable cerebral pressure-flow responses in all groups, despite elevated CVRi (older groups), and blunted cardiac baroreceptors (long-term heart transplant recipients). Thus, it appears the acutely increased phase and decreased gain noted in the second study may not accurately reflect the chronic elevations in CVRi in older adults. Through the unique approach of oscillating blood pressure during exercise, the fourth study demonstrated that the cerebrovasculature high-pass filter model is intact in both young and older populations. The final study at high-altitude (5050m) explored the cerebral pressure-flow relationship prior to, during acclimatization, and return from high-altitude. Despite the marked oxygen desaturation, there were no changes to the pressure-flow response across the entire range of exposure acclimatization timelines. In conclusion: 1) squat-stand maneuvers provide a meritorious way to examine cerebral-pressure flow responses; and 2) effective pressure-flow relationships are maintained during healthy aging and exercise, and persist despite blunting of cardiac baroreflexes and reductions in arterial oxygen saturation.

Text

2015-07-06

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/54000

Interdisciplinary Studies

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/