Cerebral blood volume and vasodilation are independently diminished by aging and hypertension: A near infrared spectroscopy study

Senescent changes in brain microvascular circulation may cause or contribute to age-related cognitive decline. Such changes are promoted partly by aging, but also by chronic hypertension, a leading treatable cause of cognitive decline. We aimed to non-invasively detect in vivo the senescent changes in brain microvascular circulation associated with age and hypertension, and inquired whether decrements driven by aging would be exacerbated by chronic hypertension. In this longitudinal study, absolute near infrared spectroscopy (NIRS) was used to quantify in vivo cerebral blood volume (CBV) and assess the hemodynamic response to a hypercapnic respiratory challenge in normotensive Wistar-Kyoto (WKY) and spontaneous-hypertensive (SHR) rats. The impact of age and hypertension were evaluated by repeating these measurements on the same animals at 4-and 16-months of age. CBV decreased markedly with age in both strains, from 4.5 ± 0.2 to 2.6 ± 0.1 ml/100g tissue, on average. Chronic hypertension, however, did not significantly exacerbate this age-related decrease in CBV (-48.1 ± 3.7% in WKYs versus-53.3 ± 5.4% in SHRs). In contrast, vasoreactivity was already impaired in the young hypertensive rats (ΔVMR 0.017 ± 0.014 in young SHRs versus 0.042 ± 0.005 in young WKYs) and further worsened by middle-age (ΔVMR 0.011 ± 0.017 middle-aged SHRs). Conclusion: Whereas a decrease in brain blood volume correlated with age but not hypertension, vasodilatory capacity was diminished due to hypertension but did not appear affected by age alone. The ability of absolute NIRS to distinguish between such senescent changes in brain (micro)vascular circulation in life may allow early detection and intervention to preserve cerebrovascular health with age.