Cerebral autoregulation (CA) refers to the properties of the brain vascular bed to maintain cerebral perfusion despite changes in blood pressure (BP). Whereas classic studies have assessed CA during changes in BP that have a gradual onset, dynamic studies quantify the fast modifications in cerebral blood flow (CBF) in relation to rapid alterations in BP. There is a lack of standardization in the assessment of dynamic CA. This review provides an overview of the methods that have been applied, with special focus on the elderly. We will discuss the relative merits and shortcomings of these methods with regard to the aged population. Furthermore, we summarize the effects of variability in BP on CBF in older people. Of the various dynamic assessments of CA, a single sit-tostand procedure is a feasible and physiologic method in the elderly. The collection of spontaneous beat-to-beat changes in BP and CBF allows estimation of CA using the technique of transfer function analysis. A thorough search of the literature yielded eight studies that have measured dynamic CA in the elderly aged < 75 years. Regardless of the methods used, it was concluded from these studies that CA was preserved in this population.

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New Findings r What is the central question in this study?It is unknown to what extent increasing age influences the dynamic adaptations of cerebral blood flow velocity and cortical oxygenation in response to changes in blood pressure (cerebral autoregulation) and to changes in carbon dioxide (cerebrovascular CO 2 reactivity). r What is the main finding and its importance?We have shown that ageing up to 86 years is associated with an overall preservation of dynamic cerebral autoregulation and cerebrovascular CO 2 reactivity, leading to a sufficiency of cerebral cortical oxygenation during daily life activities, despite the decrease in absolute cerebral blood flow velocity and increase in cerebrovascular resistance with advancing age.With ageing, cerebral blood flow velocity (CBFV) decreases; however, to what extent dynamic cerebral autoregulation and cerebrovascular CO 2 reactivity are influenced by ageing is unknown. The aim was to examine the dynamic responses of CBFV and cortical oxygenation to changes in blood pressure (BP) and arterial CO 2 across different ages. Fifty-eight participants in three age groups were included, as follows: young (n = 20, 24 ± 2 years old), elderly (n = 20, 66 ± 1 years old), and older elderly (n = 18, 78 ± 3 years old). The CBFV was measured using transcranial Doppler ultrasound, simultaneously with oxyhaemoglobin (O 2 Hb) using near-infrared spectroscopy and beat-to-beat BP measurements using Finapres. Postural manoeuvres were performed to induce haemodynamic fluctuations. Cerebrovascular CO 2 reactivity was tested with hyperventilation and CO 2 inhalation. With age, CBFV decreased (young 59 ± 12 cm s −1 , elderly 48 ± 7 cm s −1 and older elderly 42 ± 9 cm s −1 , P < 0.05) and cerebrovascular resistance increased (1.46 ± 0.58, 1.81 ± 0.36 and 1.98 ± 0.52 mmHg cm −1 s −1 , respectively, P < 0.05). Normalized gain (autoregulatory damping) increased with age for BP-CBFV (0.88 ± 0.18, 1.31 ± 0.30 and 1.06 ± 0.34, respectively, P < 0.05) and CBFV-O 2 Hb (0.10 ± 0.09, 0.12 ± 0.04 and 0.17 ± 0.08, respectively, P < 0.05) during the repeated sit-stand manoeuvre at 0.05 Hz. Even though the absolute changes in CBFV and cerebrovascular resistance index during the cerebrovascular CO 2 reactivity were higher in the young group, the percentage changes in CBFV, cerebrovascular resistance index and O 2 Hb were similar in all age groups. In conclusion, there was no decline in dynamic cerebral autoregulation and cerebrovascular CO 2 reactivity with increasing age up to 86 years. Despite the decrease in cerebral blood flow * M. H. Oudegeest-Sander and A. H. E. A. van Beek contributed equally to this work.

Working memory is sensitive to aging-related decline. Evidence exists that aging is accompanied by a reorganization of the working-memory circuitry, but the underlying neurocognitive mechanisms are unclear. In this study, we examined aging-related changes in prefrontal activation during working-memory performance using functional Near-Infrared Spectroscopy (fNIRS), a noninvasive neuroimaging technique. Seventeen healthy young (21–32 years) and 17 healthy older adults (64–81 years) performed a verbal working-memory task (n-back). Oxygenated and deoxygenated hemoglobin concentration changes were registered by two fNIRS channels located over the left and right prefrontal cortex. Increased working-memory load resulted in worse performance compared to the control condition in older adults, but not in young participants. In both young and older adults, prefrontal activation increased with rising working-memory load. Young adults showed slight right-hemispheric dominance at low levels of working-memory load, while no hemispheric differences were apparent in older adults. Analysis of the time-activation curve during the high working-memory load condition revealed a continuous increase of the hemodynamic response in the young. In contrast to that, a quadratic pattern of activation was found in the older participants. Based on these results it could be hypothesized that young adults were better able to keep the prefrontal cortex recruited over a prolonged period of time. To conclude, already at low levels of working-memory load do older adults recruit both hemispheres, possibly in an attempt to compensate for the observed aging-related decline in performance. Also, our study shows that aging effects on the time course of the hemodynamic response must be taken into account in the interpretation of the results of neuroimaging studies that rely on blood oxygen levels, such as fMRI.

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