Cerebral Autoregulation: An Overview of Current Concepts and Methodology with Special Focus on the Elderly

Abstract

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.

Hemodynamics and brain blood flow during posture change in younger women and postmenopausal women compared with age-matched men

“…There was, however, higher CVRi with age, which likely reflects the higher MAP, considering that there were no age effects on either systolic or diastolic MCA velocity. As expected due to intact cerebral autoregulation with age (66), there were no changes in the response of mean MCA velocity to sitting and standing with age; however, with more erect posture, systolic MCA velocity decreased more in the younger groups. Many researchers have observed lower MCA velocity in participants over 70 yr old (35,48,57), and Sorond et al (57) observed a greater decrease in MCA velocity in participants over 70 yr old during standing.…”

The Leicester cerebral haemodynamics database: normative values and the influence of age and sex

“…Although two other parameters derived from TFA showed an association with age (LF coherence and LF gain, Table 4), this does not imply that dynamic CA is age dependent since these parameters lack consistency to express dynamic CA effectiveness (Panerai 2008, van Beek et al 2008. The observation that RAP is not influenced by age either, is also noteworthy since changes in RAP have been associated with the myogenic control of small blood vessels as one of the main mechanisms responsible for an active CA (Panerai et al 2005).…”

“…Due to the highly effective control exerted by the mechanism of pressure-autoregulation, CBF is normally maintained within narrow limits for mean blood pressures (MBP) in the range 60-150 mm Hg (Paulson, Strandgaard & Edvinsson 1990). Not surprisingly, it is the CBF autoregulation mechanism itself that has been shown to be impaired in a number of conditions such as ischaemic stroke, severe head injury, carotid artery disease, intracranial hypertension, diabetes and liver failure (Aries et al 2010, Czosnyka et al 1996, Dawson et al 2000, Hauerberg, Juhler 1994, Kim et al 2008, Lagi et al 2002, Panerai 2008, White, Markus 1997, van Beek et al 2008.…”

Aging blunts hyperventilation-induced hypocapnia and reduction in cerebral blood flow velocity during maximal exercise

“…Although we did not measure cerebral autoregulation (CA; i.e. the ability of the brain to regulate CBF relatively independent of changes in BP (Panerai et al 1999;Brys et al 2003;Paulson et al 1990)), CA is maintained during mildto-moderate exercise in YA (Ogoh et al 2005a), at rest in OA (reviewed in van Beek et al 2008) and during mild exercise in middle-aged OA (Ogoh et al 2005a;Fisher et al 2008). Some additional insight into CA may be provided from consideration of cerebrovascular resistance or conductance (Table 1).…”