A Multi-Parametric Investigation of Vascular Alterations in Elderly with Hypertension
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BACKGROUND: Along with aging comes many cardiovascular and cerebral changes that impact a person's health. These changes manifest as variances in blood pressure, brain volume, cerebral blood flow (CBF), oxygen metabolism, and neurological functioning. OBJECTIVE: The purpose of this study is to provide evidence to support new or previously known biomarkers for declining cerebrovascular health, such as cerebral arterial stiffness, reduced vessel capacity, and thickening of the extracellular matrix. METHODS: 45 participants ranging from the ages of 61 to 79 with a mean of 67 were studied using a 3 Tesla MRI. Several MRI techniques were employed to acquire and analyze data. Phase-contrast (PC) MRI was used for acquiring images of moving fluid, so that arteries containing blood flow to the brain could be isolated in order to calculate total CBF. Blood-oxygen-level dependent contrast images and end-tidal CO2 and O2 measurements were also obtained using MRI after the participants were given a different sequence of gases to breathe containing varying amounts of oxygen, carbon dioxide, and nitrogen. This allowed the cerebrovascular reactivity (CVR) and venous cerebral volume (vCBV) of the vessels to be determined. Venous oxygenation (Yv) was assessed using T2-relaxation-under-spin-tagging (TRUST) MRI technique. Linear regressions were performed to account for age, sex, and blood pressure. Data were also analyzed by putting participants with a systolic blood pressure greater than 140 into a hypertensive category for comparison. Other data acquired during or immediately prior to the MRI scans include systolic and diastolic blood pressure, brain volume, and the oxygen saturation level of venous and arterial blood. RESULTS: A p-value of <0.05 was used to determine significance. The CVR for the hypertensive group was lower than that of the non-hypertensive group (p<0.01) and CVR decreased as systolic blood pressure increased (p=0.02). CVR also decreased with increasing age (p=0.02) and was higher in males than in females (p<0.01). CBF increased with systolic blood pressure (p=0.03) and was higher in females (p=0.03). Yv also increased with systolic blood pressure (p=0.02) and correlated strongly with CBF values (p<0.001). CONCLUSION: These results support certain relationships between blood pressure and the vascular markers within the brain, which may appear before cognitive decline or clinical symptoms emerge. This study is an early step on the path to discovering easily identifiable precursors to neurological changes that take place as normal aging processes occur.