Key result
Older subjects had significantly increased cerebral arterial stiffness and reduced neurovascular- and hypercapnia-mediated cerebral blood flow responses compared to younger subjects.
Why the study?
Does aging reduce cerebrovascular responses to visual stimulation and hypercapnia, and is this associated with increased arterial stiffness?
Cross-Sectional (n=30)
No
Does aging reduce cerebrovascular responses to visual stimulation and hypercapnia, and is this associated with increased arterial stiffness?
Aging is associated with reduced hypercapnia-evoked cerebral blood flow responses through the middle cerebral artery, which appears to be secondary to increased vascular stiffening.
Answers are grounded in this paper and cite their sources.
Caution against inferring causality from cross-sectional data; leaves open whether stiffness mediates age-related CBF impairment.
Aging is associated with decreased vascular compliance and diminished neurovascular- and hypercapnia-evoked cerebral blood flow (CBF) responses. However, the interplay between arterial stiffness and reduced CBF responses is poorly understood. It was hypothesized that increased cerebral arterial stiffness is associated with reduced evoked responses to both, a flashing checkerboard visual stimulation (i.e., neurovascular coupling), and hypercapnia. To test this hypothesis, 20 older (64 ± 8 year; mean ± SD) and 10 young (30 ± 5 year) subjects underwent a visual stimulation (VS) and a hypercapnic test. Blood velocity through the posterior (PCA) and middle cerebral (MCA) arteries was measured concurrently using transcranial Doppler ultrasound (TCD). Cerebral and systemic vascular stiffness were calculated from the cerebral blood velocity and systemic blood pressure waveforms, respectively. Cerebrovascular (MCA: young = 76 ± 15%, older = 98 ± 19%, p = 0.004; PCA: young = 80 ± 16%, older = 106 ± 17%, p < 0.001) and systemic (young = 59 ± 9% and older = 80 ± 9%, p < 0.001) augmentation indices (AI) were higher in the older group. CBF responses to VS (PCA: p < 0.026) and hypercapnia (PCA: p = 0.018; MCA: p = 0.042) were lower in the older group. A curvilinear model fitted to cerebral AI and age showed AI increases until ~60 years of age, after which the increase levels off (PCA: R (2) = 0.45, p < 0.001; MCA: R (2) = 0.31, p < 0.001). Finally, MCA, but not PCA, hypercapnic reactivity was inversely related to cerebral AI (MCA: R (2) = 0.28, p = 0.002; PCA: R (2) = 0.10, p = 0.104). A similar inverse relationship was not observed with the PCA blood flow response to VS (R (2) = 0.06, p = 0.174). In conclusion, older subjects had reduced neurovascular- and hypercapnia-mediated CBF responses. Furthermore, lower hypercapnia-mediated blood flow responses through the MCA were associated with increased vascular stiffness. These findings suggest the reduced hypercapnia-evoked CBF responses through the MCA, in older individuals may be secondary to vascular stiffening.
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Flück et al. (2014) conducted a cross-sectional in Healthy aging (n=30). Older age vs. Younger age was evaluated on Posterior cerebral artery (PCA) augmentation index (AI) (p=<0.001). Older subjects had significantly increased cerebral arterial stiffness and reduced neurovascular- and hypercapnia-mediated cerebral blood flow responses compared to younger subjects.
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