Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation.

Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.

Divergent Associations of Slow-Wave Sleep versus Rapid Eye Movement Sleep with Plasma Amyloid-Beta.

OBJECTIVE: Recent evidence shows that during slow-wave sleep (SWS), the brain is cleared from potentially toxic metabolites, such as the amyloid-beta protein. Poor sleep or elevated cortisol levels can worsen amyloid-beta clearance, potentially leading to the formation of amyloid plaques, a neuropathological hallmark of Alzheimer disease. Here, we explored how nocturnal neural and endocrine activity affects amyloid-beta fluctuations in the peripheral blood. METHODS: We acquired simultaneous polysomnography and all-night blood sampling in 60 healthy volunteers aged 20-68 years. Nocturnal plasma concentrations of amyloid-beta-40, amyloid-beta-42, cortisol, and growth hormone were assessed every 20 minutes. Amyloid-beta fluctuations were modeled with sleep stages, (non)oscillatory power, and hormones as predictors while controlling for age and participant-specific random effects. RESULTS: Amyloid-beta-40 and amyloid-beta-42 levels correlated positively with growth hormone concentrations, SWS proportion, and slow-wave (0.3-4Hz) oscillatory and high-band (30-48Hz) nonoscillatory power, but negatively with cortisol concentrations and rapid eye movement sleep (REM) proportion measured 40-100 minutes previously (all t values > |3|, p values < 0.003). Older participants showed higher amyloid-beta-40 levels. INTERPRETATION: Slow-wave oscillations are associated with higher plasma amyloid-beta levels, whereas REM sleep is related to decreased amyloid-beta plasma levels, possibly representing changes in central amyloid-beta production or clearance. Strong associations between cortisol, growth hormone, and amyloid-beta presumably reflect the sleep-regulating role of the corresponding releasing hormones. A positive association between age and amyloid-beta-40 may indicate that peripheral clearance becomes less efficient with age. ANN NEUROL 2024;96:46-60.

Longitudinal changes in cerebral blood flow and their relation with cognitive decline in patients with dementia: Current knowledge and future directions.

The pathophysiology underlying cognitive decline is multifactorial, with increasing literature suggesting a role for cerebrovascular health. Cerebral blood flow (CBF) is an important element of cerebrovascular health, which raises questions regarding the relation between CBF and cognitive decline. Cross-sectional studies demonstrate lower CBF in patients with cognitive decline compared to healthy age-matched peers. Remarkably, longitudinal studies do not support a link between CBF reductions and cognitive decline. These studies, however, are often limited by small sample sizes and may therefore be underpowered to detect small effect sizes. Therefore, through a systematic review and meta-analysis of longitudinal studies, we examined whether longitudinal changes in global CBF are related to cognitive decline in subjects with Alzheimer's disease, and qualitatively described findings on regional CBF. Considering the growing impact of dementia and the lack of treatment options, it is important to understand the role of CBF as a prognostic biomarker and/or treatment target in dementia.

On the use and misuse of cerebral hemodynamics terminology using transcranial Doppler ultrasound: a call for standardization.

Cerebral hemodynamics, e.g., cerebral blood flow, can be measured and quantified using many different methods, with transcranial Doppler ultrasound (TCD) being one of the most commonly used approaches. In human physiology, the terminology used to describe metrics of cerebral hemodynamics are inconsistent and in some instances technically inaccurate; this is especially true when evaluating, reporting, and interpreting measures from TCD. Therefore, this perspective article presents recommended terminology when reporting cerebral hemodynamic data. We discuss the current use and misuse of the terminology in the context of using TCD to measure and quantify cerebral hemodynamics and present our rationale and consensus on the terminology that we recommend moving forward. For example, one recommendation is to discontinue the use of the term "cerebral blood flow velocity" in favor of "cerebral blood velocity" with precise indication of the vessel of interest. We also recommend clarity when differentiating between discrete cerebrovascular regulatory mechanisms, namely, cerebral autoregulation, neurovascular coupling, and cerebrovascular reactivity. This will be a useful guide for investigators in the field of cerebral hemodynamics research.

Genome-wide meta-analysis for Alzheimer's disease cerebrospinal fluid biomarkers.

Amyloid-beta 42 (Aß42) and phosphorylated tau (pTau) levels in cerebrospinal fluid (CSF) reflect core features of the pathogenesis of Alzheimer's disease (AD) more directly than clinical diagnosis. Initiated by the European Alzheimer & Dementia Biobank (EADB), the largest collaborative effort on genetics underlying CSF biomarkers was established, including 31 cohorts with a total of 13,116 individuals (discovery n = 8074; replication n = 5042 individuals). Besides the APOE locus, novel associations with two other well-established AD risk loci were observed; CR1 was shown a locus for Aß42 and BIN1 for pTau. GMNC and C16orf95 were further identified as loci for pTau, of which the latter is novel. Clustering methods exploring the influence of all known AD risk loci on the CSF protein levels, revealed 4 biological categories suggesting multiple Aß42 and pTau related biological pathways involved in the etiology of AD. In functional follow-up analyses, GMNC and C16orf95 both associated with lateral ventricular volume, implying an overlap in genetic etiology for tau levels and brain ventricular volume.

The impact of age, sex, cardio-respiratory fitness, and cardiovascular disease risk on dynamic cerebral autoregulation and baroreflex sensitivity.

BACKGROUND: Humans display an age-related decline in cerebral blood flow and increase in blood pressure (BP), but changes in the underlying control mechanisms across the lifespan are less well understood. We aimed to; (1) examine the impact of age, sex, cardiovascular disease (CVD) risk, and cardio-respiratory fitness on dynamic cerebral autoregulation and cardiac baroreflex sensitivity, and (2) explore the relationships between dynamic cerebral autoregulation (dCA) and cardiac baroreflex sensitivity (cBRS). METHODS: 206 participants aged 18-70 years were stratified into age categories. Cerebral blood flow velocity was measured using transcranial Doppler ultrasound. Repeated squat-stand manoeuvres were performed (0.10 Hz), and transfer function analysis was used to assess dCA and cBRS. Multivariable linear regression was used to examine the influence of age, sex, CVD risk, and cardio-respiratory fitness on dCA and cBRS. Linear models determined the relationship between dCA and cBRS. RESULTS: Age, sex, CVD risk, and cardio-respiratory fitness did not impact dCA normalised gain, phase, or coherence with minimal change in all models (P > 0.05). cBRS gain was attenuated with age when adjusted for sex and CVD risk (young-older; ß = - 2.86 P < 0.001) along with cBRS phase (young-older; ß = - 0.44, P < 0.001). There was no correlation between dCA normalised gain and phase with either parameter of cBRS. CONCLUSION: Ageing was associated with a decreased cBRS, but dCA appears to remain unchanged. Additionally, our data suggest that sex, CVD risk, and cardio-respiratory fitness have little effect.

Orthostatic blood pressure recovery in older males using alpha-blockers for lower urinary tract symptoms, an explorative study in a urology outpatient clinic.

WHAT IS KNOWN AND OBJECTIVE: Alpha-blockers have been associated with orthostatic hypotension (OH). We aimed to assess the prevalence of OH measured with beat-to-beat blood pressure monitoring in older male outpatients who used alpha-blockers for lower urinary tract symptoms (LUTS). In addition, we investigated associations of OH with duration of alpha-blocker use, concomitant medication use and comorbidity. METHODS: Cross-sectional explorative study in a urology outpatient clinic. Older white males ≥65 years using alpha-blockers for LUTS were included. Blood pressure responses to standing up from supine were recorded using a validated beat-to-beat blood pressure device (Finapres). Prevalence rates were derived from the beat-to-beat data to include OH measured between 60-110 s (OH), impaired recovery OH at 40 s (OH[40]), initial OH (IOH) and normal orthostatic response. Subgroups were defined based on duration of alpha-blocker use, polypharmacy, and Charlson comorbidity index (CCI), to obtain relative risks. RESULTS AND DISCUSSION: Sixty-five patients were included. Median age was 75 years (range 65-92). The prevalence of OH was 7.7% (n = 5). The prevalence of OH(40) was 16.9% (n = 11) and of IOH 38.5% (n = 25). Thirty-six patients (55.4%) had a normal orthostatic response. The relative risk of OH for the subgroup using ≥ 10 medications (n = 13) was 6.0 (95%CI 1.1-32.3). For the subgroup with multimorbidity (CCI ≥3, n = 11) this was 7.4 (95%CI 1.4-39.0). Recent initiation of alpha-blocker use (<3 months) did not increase OH risk (RR 0.6 [95%CI 0.1-5.1]). WHAT IS NEW AND CONCLUSION: The overall prevalence of OH was low and comparable to age-matched population prevalence, suggesting that the relative contribution of alpha-blockers to OH was small. However, OH risk significantly increased in patients with multimorbidity or polypharmacy. For these patients, the benefits of starting alpha-blockers for LUTS should be weighed against the increased risk of OH.

Normal cerebrospinal fluid concentrations of PDGFRß in patients with cerebral amyloid angiopathy and Alzheimer's disease.

BACKGROUND: Cerebrospinal fluid (CSF) platelet-derived growth factor receptor-ß (PDGFRß) has been proposed as a biomarker of blood-brain barrier (BBB) breakdown. We studied PDGFRß levels as a biomarker for cerebral amyloid angiopathy (CAA), amnestic mild cognitive impairment (aMCI), or Alzheimer's disease (AD). METHODS: CSF PDGFRß levels were quantified by enzyme-linked immunosorbent assay in patients with CAA, patients with aMCI/AD, and in matched controls. In aMCI/AD we evaluated CSF PDGFRß both by clinical phenotype and by using the AT(N) biomarker classification system defined by CSF amyloid (A), tau (T), and neurodegeneration (N) biomarkers. RESULTS: PDGFRß levels were similar in CAA patients and controls (P = .78) and in aMCI/AD clinical phenotype and controls (P = .91). aMCI/AD patients with an AD+ biomarker profile (A+T+[N+]) had increased PDGFRß levels compared to (A-T-[N-]) controls (P = .006). CONCLUSION: Our findings indicate that PDGFRß levels are associated with an AD+ biomarker profile but are not a suitable biomarker for CAA or aMCI/AD clinical syndrome.

Post-exercise intramuscular O2 supply is tightly coupled with a higher proximal-to-distal ATP synthesis rate in human tibialis anterior.

KEY POINTS: The post-exercise recovery of phosphocreatine, a measure of the oxidative capacity of muscles, as assessed by 31 P MR spectroscopy, shows a striking increase from distal to proximal along the human tibialis anterior muscle. To investigate why this muscle exhibits a greater oxidative capacity proximally, we tested whether the spatial variation in phosphocreatine recovery rate is related to oxygen supply, muscle fibre type or type of exercise. We revealed that oxygen supply also increases from distal to proximal along the tibialis anterior, and that it strongly correlated with phosphocreatine recovery. Carnosine level, a surrogate measure for muscle fibre type was not different between proximal and distal, and type of exercise did not affect the gradient in phosphocreatine recovery rate. Taken together, the findings of this study suggest that the post-exercise spatial gradients in oxygen supply and phosphocreatine recovery are driven by a higher intrinsic mitochondrial oxidative capacity proximally. ABSTRACT: Phosphorus magnetic resonance spectroscopy (31 P MRS) of human tibialis anterior (TA) revealed a strong proximo-distal gradient in the post-exercise phosphocreatine (PCr) recovery rate constant (kPCr ), a measure of muscle oxidative capacity. The aim of this study was to investigate whether this kPCr gradient is related to O2 supply, resting phosphorylation potential, muscle fibre type, or type of exercise. Fifteen male volunteers performed continuous isometric ankle dorsiflexion at 30% maximum force until exhaustion. At multiple locations along the TA, we measured the oxidative PCr resynthesis rate (VPCr = kPCr × PCr depletion) by 31 P MRS, the oxyhaemoglobin recovery rate constant (kO2Hb ) by near infrared spectroscopy, and muscle perfusion with MR intravoxel incoherent motion imaging. The kO2Hb , kPCr , VPCr and muscle perfusion depended on measurement location (P < 0.001, P < 0.001, P = 0.032 and P = 0.003, respectively), all being greater proximally. The kO2Hb and muscle perfusion correlated with kPCr (r = 0.956 and r = 0.852, respectively) and VPCr (r = 0.932 and r = 0.985, respectively), the latter reflecting metabolic O2 consumption. Resting phosphorylation potential (PCr/inorganic phosphate) was also higher proximally (P < 0.001). The surrogate for fibre type, carnosine content measured by 1 H MRS, did not differ between distal and proximal TA (P = 0.884). Performing intermittent exercise to avoid exercise ischaemia, still led to larger kPCr proximally than distally (P = 0.013). In conclusion, the spatial kPCr gradient is strongly associated with the spatial variation in O2 supply. It cannot be explained by exercise-induced ischaemia nor by fibre type. Our findings suggest it is driven by a higher proximal intrinsic mitochondrial oxidative capacity, apparently to support contractile performance of the TA.

Shift-work-related sleep disruption and the risk of decline in cognitive function: The CRUISE Study.

Acute total sleep deprivation and partial sleep deprivation have negative impacts on cognitive performance. Studies in subjects who regularly experience sleep loss, however, are rare and often restricted to examination of internal sleeping disorders. To address this issue, we set up a pilot study to explore the effects of a week characterized by sleep disruption on cognitive functioning, using a case-control setting in a maritime pilot group with chronic exposure to intermittent extrinsic, work-related sleep disruption. Twenty maritime pilots (aged 30-50 years) were compared to sex- and education-matched controls with normal sleep behaviour, from the same age range. We assessed subjective and objective cognitive function, including attention, psychomotor speed, memory and executive function using the Cambridge Neuropsychological Test Automated Battery (CANTAB). Although we were able to confirm poorer sleep in maritime pilots and subjective complaints in some cognitive domains, we did not find objective cognitive deficits in the maritime pilot group compared to controls without sleep disruption. This could suggest that in this group of healthy, young maritime pilots, exposure to sleep disruption resulted in some subjective cognitive complaints, but objective deficits of cognitive function were not detected in comparison with a non-pilot control group. However, given the small sample size, the absence of an effect does not exclude the possibility that sleep disruption could result in cognitive deficits in general. Therefore, our findings have to be confirmed in future prospective studies with a larger sample size and matched controls, regarding age, education and work history.

Cerebral autoregulation assessed by near-infrared spectroscopy: validation using transcranial Doppler in patients with controlled hypertension, cognitive impairment and controls.

PURPOSE: Cerebral autoregulation (CA) aims to attenuate the effects of blood pressure variation on cerebral blood flow. This study assessed the criterion validity of CA derived from near-infrared spectroscopy (NIRS) as an alternative for Transcranial Doppler (TCD). METHODS: Measurements of continuous blood pressure (BP), oxygenated hemoglobin (O2Hb) using NIRS and cerebral blood flow velocity (CBFV) using TCD (gold standard) were performed in 82 controls, 27 patients with hypertension and 94 cognitively impaired patients during supine rest (all individuals) and repeated sit to stand transitions (cognitively impaired patients). The BP-CBFV and BP-O2Hb transfer function phase shifts (TFφ) were computed as CA measures. Spearman correlations (ρ) and Bland Altman limits of agreement (BAloa) between NIRS- and TCD-derived CA measures were computed. BAloa separation < 50° was considered a high absolute agreement. RESULTS: NIRS- and TCD-derived CA estimates were significantly correlated during supine rest (ρ = 0.22-0.30, N = 111-120) and repeated sit-to-stand transitions (ρ = 0.46-0.61, N = 19-32). BAloa separation ranged between 87° and 112° (supine rest) and 65°-77° (repeated sit to stand transitions). CONCLUSION: Criterion validity of NIRS-derived CA measures allows for comparison between groups but was insufficient for clinical application in individuals.

The Association Between Biomarkers and Neuropsychiatric Symptoms Across the Alzheimer's Disease Spectrum.

OBJECTIVE: To investigate the relationship between Alzheimer's disease biomarkers and neuropsychiatric symptoms. METHODS: Data from two large cohort studies, the Dutch Parelsnoer Institute - Neurodegenerative Diseases and the Alzheimer's Disease Neuroimaging Initiative was used, including subjects with subjective cognitive decline (N = 650), mild cognitive impairment (N = 887), and Alzheimer's disease dementia (N = 626). Cerebrospinal fluid (CSF) levels of Aß42, t-tau, p-tau, and hippocampal volume were associated with neuropsychiatric symptoms (measured with the Neuropsychiatric Inventory) using multiple logistic regression analyses. The effect of the Mini-Mental State Examination (as proxy for cognitive functioning) on these relationships was assessed with mediation analyses. RESULTS: Alzheimer's disease biomarkers were not associated with depression, agitation, irritability, and sleep disturbances. Lower levels of CSF Aß42, higher levels of t- and p-tau were associated with presence of anxiety. Lower levels of CSF Aß42 and smaller hippocampal volumes were associated with presence of apathy. All associations were mediated by cognitive functioning. CONCLUSION: The association between Alzheimer's disease pathology and anxiety and apathy is partly due to impairment in cognitive functioning.

Long-Term Occupational Sleep Loss and Post-Retirement Cognitive Decline or Dementia.

INTRODUCTION: Recent evidence suggests that poor sleep is a risk factor that contributes to the development of Alzheimer's disease (AD). Most studies have focused on short-term effects of sleep deprivation on cognitive function, whereas longitudinal studies are limited to self-reported sleep and the risk of later-life dementia. Because sleep loss could be an early manifestation of neurodegenerative disease, reverse causality in these studies cannot be excluded. OBJECTIVE: In this explorative, observational study, we investigated the effects of extended periods of extrinsically (work-related) caused sleep loss on later-life cognitive function, early dementia symptoms, and current sleep quality. METHODS: We approached a community of retired male maritime pilots (approx. n = 500) through a newsletter. We investigated 50 respondents (mean age 71.7 years ± 7.7), with a history of >25 years of work on irregular schedules, which resulted in extended periods of sleep loss. Validated questionnaires on cognitive complaints (Cognitive Failure Questionnaire [CFQ]), early dementia symptoms (Early Dementia Questionnaire [EDQ]), current sleep quality (Pittsburgh Sleep Quality Index [PSQI] and sleep-wake diaries), quality of life (QoL, EQ-5D), and mood (Hospital Anxiety and Depression Scale [HADS]) were administered by a single investigator (J.T.), who also completed an observer rating of cognitive function. RESULTS: Scores on the CFQ, EDQ, PSQI, EQ-5D, and HADS were within normal ranges adjusted for age, sex, and education. The observer rating was not indicative of cognitive decline. CONCLUSION: We found no evidence that long-term exposure to work-related sleep loss had resulted in cognitive decline or early dementia symptoms in this sample of retired maritime pilots.

Plasma Aß (Amyloid-ß) Levels and Severity and Progression of Small Vessel Disease.

BACKGROUND AND PURPOSE: Cerebral small vessel disease (SVD) is a frequent pathology in aging and contributor to the development of dementia. Plasma Aß (amyloid ß) levels may be useful as early biomarker, but the role of plasma Aß in SVD remains to be elucidated. We investigated the association of plasma Aß levels with severity and progression of SVD markers. METHODS: We studied 487 participants from the RUN DMC study (Radboud University Nijmegen Diffusion Tensor and Magnetic Resonance Imaging Cohort) of whom 258 participants underwent 3 MRI assessments during 9 years. We determined baseline plasma Aß38, Aß40, and Aß42 levels using ELISAs. We longitudinally assessed volume of white matter hyperintensities semiautomatically and manually rated lacunes and microbleeds. We analyzed associations between plasma Aß and SVD markers by ANCOVA adjusted for age, sex, and hypertension. RESULTS: Cross-sectionally, plasma Aß40 levels were elevated in participants with microbleeds (mean, 205.4 versus 186.4 pg/mL; P<0.01) and lacunes (mean, 194.8 versus 181.2 pg/mL; P<0.05). Both Aß38 and Aß40 were elevated in participants with severe white matter hyperintensities (Aß38, 25.3 versus 22.7 pg/mL; P<0.01; Aß40, 201.8 versus 183.3 pg/mL; P<0.05). Longitudinally, plasma Aß40 levels were elevated in participants with white matter hyperintensity progression (mean, 194.6 versus 182.9 pg/mL; P<0.05). Both Aß38 and Aß40 were elevated in participants with incident lacunes (Aß38, 24.5 versus 22.5 pg/mL; P<0.05; Aß40, 194.9 versus 181.2 pg/mL; P<0.01) and Aß42 in participants with incident microbleeds (62.8 versus 60.4 pg/mL; P<0.05). CONCLUSIONS: Plasma Aß levels are associated with both presence and progression of SVD markers, suggesting that Aß pathology might contribute to the development and progression of SVD. Plasma Aß levels might thereby serve as inexpensive and noninvasive measure for identifying individuals with increased risk for progression of SVD.

Memory Strategy Training in Older Adults with Subjective Memory Complaints: A Randomized Controlled Trial.

OBJECTIVES: Subjective memory complaints (SMC) in older adults are associated with a decline in everyday functioning and an increased risk for future cognitive decline. This study examines the effect of a memory strategy training compared to a control memory training on memory functioning in daily life. METHODS: This was a randomized controlled trial with baseline, post-treatment, and 6-month follow-up assessments conducted in 60 older adults (50-87 years) with SMC. Participants were randomly assigned to either seven sessions of memory strategy training or seven sessions of control memory training. Both interventions were given in small groups and included psycho-education. Primary outcome measure was memory functioning in daily life. Objective measures of memory performance and self-reported measures of strategy use were included as secondary outcome measures. RESULTS: Participants in each intervention group reported an improvement in personal memory goals (p<.0005), up to 6 months after training. An interaction effect showed that participants following memory strategy training reported a larger improvement in personal memory goals (p=.002). Both intervention groups improved on two memory tests (p<.001 and p<.01). In the memory strategy training group, an increase in strategy use in daily life was the strongest predictor (p<.05) of improvement in subjective memory functioning. CONCLUSIONS: Older adults with subjective memory complaints benefit from memory strategy training, especially in their memory functioning in daily life. (JINS, 2018, 24, 1110-1120).

Slow wave sleep disruption increases cerebrospinal fluid amyloid-ß levels.

See Mander et al. (doi:10.1093/awx174) for a scientific commentary on this article.Sleep deprivation increases amyloid-ß, suggesting that chronically disrupted sleep may promote amyloid plaques and other downstream Alzheimer's disease pathologies including tauopathy or inflammation. To date, studies have not examined which aspect of sleep modulates amyloid-ß or other Alzheimer's disease biomarkers. Seventeen healthy adults (age 35-65 years) without sleep disorders underwent 5-14 days of actigraphy, followed by slow wave activity disruption during polysomnogram, and cerebrospinal fluid collection the following morning for measurement of amyloid-ß, tau, total protein, YKL-40, and hypocretin. Data were compared to an identical protocol, with a sham condition during polysomnogram. Specific disruption of slow wave activity correlated with an increase in amyloid-ß40 (r = 0.610, P = 0.009). This effect was specific for slow wave activity, and not for sleep duration or efficiency. This effect was also specific to amyloid-ß, and not total protein, tau, YKL-40, or hypocretin. Additionally, worse home sleep quality, as measured by sleep efficiency by actigraphy in the six nights preceding lumbar punctures, was associated with higher tau (r = 0.543, P = 0.045). Slow wave activity disruption increases amyloid-ß levels acutely, and poorer sleep quality over several days increases tau. These effects are specific to neuronally-derived proteins, which suggests they are likely driven by changes in neuronal activity during disrupted sleep.

Lack of linear correlation between dynamic and steady-state cerebral autoregulation.

KEY POINTS: For correct application and interpretation of cerebral autoregulation (CA) measurements in research and in clinical care, it is essential to understand differences and similarities between dynamic and steady-state CA. The present study found no correlation between dynamic and steady-state CA indices in healthy older adults. There was variability between individuals in all (steady-state and dynamic) autoregulatory indices, ranging from low (almost absent) to highly efficient CA in this healthy population. These findings challenge the assumption that assessment of a single CA parameter or a single set of parameters can be generalized to overall CA functioning. Therefore, depending on specific research purposes, the choice for either steady-state or dynamic measures or both should be weighed carefully. ABSTRACT: The present study aimed to investigate the relationship between dynamic (dCA) and steady-state cerebral autoregulation (sCA). In 28 healthy older adults, sCA was quantified by a linear regression slope of proportionate (%) changes in cerebrovascular resistance (CVR) in response to proportionate (%) changes in mean blood pressure (BP) induced by stepwise sodium nitroprusside (SNP) and phenylephrine (PhE) infusion. Cerebral blood flow (CBF) was measured at the internal carotid artery (ICA) and vertebral artery (VA) and CBF velocity at the middle cerebral artery (MCA). With CVR = BP/CBF, Slope-CVRICA , Slope-CVRVA and Slope-CVRiMCA were derived. dCA was assessed (i) in supine rest, analysed with transfer function analysis (gain and phase) and autoregulatory index (ARI) fit from spontaneous oscillations (ARIBaseline ), and (ii) with transient changes in BP using a bolus injection of SNP (ARISNP ) and PhE (ARIPhE ). Comparison of sCA and dCA parameters (using Pearson's r for continuous and Spearman's ρ for ordinal parameters) demonstrated a lack of linear correlations between sCA and dCA measures. However, comparisons of parameters within dCA and within sCA were correlated. For sCA slope-CVRVA with Slope-CVRiMCA (r = 0.45, P < 0.03); for dCA ARISNP with ARIPhE (ρ = 0.50, P = 0.03), ARIBaseline (ρ = 0.57, P = 0.03) and PhaseLF (ρ = 0.48, P = 0.03); and for GainVLF with GainLF (r = 0.51, P = 0.01). By contrast to the commonly held assumption based on an earlier study, there were no linear correlations between sCA and dCA. As an additional observation, there was strong inter-individual variability, both in dCA and sCA, in this healthy group of elderly, in a range from low to high CA efficiency.

Memory strategy use in older adults with subjective memory complaints.

BACKGROUND: Subjective memory complaints (SMC) are common among older adults, but it is unclear to what extent adults with SMC spontaneously use memory strategies to compensate for their memory problems. As SMC may be a risk factor for memory decline later, it is important to extend our knowledge about spontaneous compensatory mechanisms in older adults with SMC. METHOD: Self-reported strategy use and observed strategy use were assessed in 38 adults with and 38 without SMC. RESULTS: Adults with SMC used more strategies in daily life than those without. In the SMC group, memory complaints were positively correlated with strategy use. Only in adults without SMC, a significant correlation was found between observed strategy use and task performance. CONCLUSION: Strategy use in older adults with SMC may be compensatory in nature, but did not increase their objective memory performance. Therefore, older adults with SMC might benefit from interventions aimed at optimizing strategy use.