title: Cerebral blood volume and vasodilation are independently diminished by aging and hypertension: a near infrared spectroscopy study.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Neuroscience and Aging laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, USA.
authors.forename: Merav E
authors.initials: ME
authors.lastname: Shaul
authors.affiliation: Department of Biomedical Engineering, Tufts University, Medford, MA, USA.
authors.forename: Bertan
authors.initials: B
authors.lastname: Hallacoglu
authors.affiliation: Department of Biomedical Engineering, Tufts University, Medford, MA, USA.
authors.forename: Angelo
authors.initials: A
authors.lastname: Sassaroli
authors.affiliation: Neuroscience and Aging laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, USA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Shukitt-Hale
authors.affiliation: Department of Biomedical Engineering, Tufts University, Medford, MA, USA.
authors.forename: Sergio
authors.initials: S
authors.lastname: Fantini
authors.affiliation: Neuroscience and Aging laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, USA.
authors.forename: Irwin H
authors.initials: IH
authors.lastname: Rosenberg
authors.affiliation: Neuroscience and Aging laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, USA Institute of Biochemistry, Food Science and Nutrition, Faculty of Agriculture, Hebrew University of Jerusalem, Israel.
authors.forename: Aron M
authors.initials: AM
authors.lastname: Troen
mesh_terms: D000367:Age Factors; D000375:Aging / Q000502:physiology*; D000818:Animals; D001810:Blood Volume / Q000502:physiology*; D004195:Disease Models, Animal; D006454:Hemoglobins / Q000378:metabolism; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D051381:Rats; D011918:Rats, Inbred SHR; D017208:Rats, Wistar; D012039:Regional Blood Flow / Q000502:physiology; D019265:Spectroscopy, Near-Infrared; D014664:Vasodilation / Q000502:physiology*
chemical_list: D006454:Hemoglobins
keywords: Aging; cerebral blood volume; hypertension; near infrared spectroscopy; vasodilation