Insular Alzheimer's disease pathology as a cause of "age-related" autonomic dysfunction and mortality in the non-demented elderly

Central autonomic network dysfunction and plasma Alzheimer's disease biomarkers in older adults

BACKGROUND

Higher order regulation of autonomic function is maintained by the coordinated activity of specific cortical and subcortical brain regions, collectively referred to as the central autonomic network (CAN). Autonomic changes are frequently observed in Alzheimer's disease (AD) and dementia, but no studies to date have investigated whether plasma AD biomarkers are associated with CAN functional connectivity changes in at risk older adults.

METHODS

Independently living older adults (N = 122) without major neurological or psychiatric disorder were recruited from the community. Participants underwent resting-state brain fMRI and a CAN network derived from a voxel-based meta-analysis was applied for overall, sympathetic, and parasympathetic CAN connectivity using the CONN Functional Toolbox. Sensorimotor network connectivity was studied as a negative control. Plasma levels of amyloid (Aβ42, Aβ40), neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) were assessed using digital immunoassay. The relationship between plasma AD biomarkers and within-network functional connectivity was studied using multiple linear regression adjusted for demographic covariates and Apolipoprotein E (APOE) genotype. Interactive effects with APOE4 carrier status were also assessed.

RESULTS

All autonomic networks were positively associated with Aβ42/40 ratio and remained so after adjustment for age, sex, and APOE4 carrier status. Overall and parasympathetic networks were negatively associated with GFAP. The relationship between the parasympathetic CAN and GFAP was moderated by APOE4 carrier status, wherein APOE4 carriers with low parasympathetic CAN connectivity displayed the highest plasma GFAP concentrations (B = 910.00, P = .004). Sensorimotor connectivity was not associated with any plasma AD biomarkers, as expected.

CONCLUSION

The present study findings suggest that CAN function is associated with plasma AD biomarker levels. Specifically, lower CAN functional connectivity is associated with decreased plasma Aβ42/40, indicative of cerebral amyloidosis, and increased plasma GFAP in APOE4 carriers at risk for AD. These findings could suggest higher order autonomic and parasympathetic dysfunction in very early-stage AD, which may have clinical implications.

Relationship between Alzheimer dementia and QT interval: A meta-analysis

While the link between aging and mortality from dementia is widely appreciated, the mechanism is not clear. The objective of this study was to determine whether there is a direct relationship between Alzheimer dementia (AD) and the QT interval, because the latter has been related to cardiac mortality. A systematic review and meta-analysis were conducted after a Medline and EMBASE search using terms "Alzheimer disease or Dementia AND QT interval, QT dispersion or cardiac repolarization." Four studies with control groups were identified. There were significant differences in QT interval between individuals with AD vs individuals without dementia (controls) (odds ratio (OR)1.665 [random effects model] and 1.879 [fixed effect model]) (p < 0.001). There were significant differences in QT interval between individuals with AD vs individuals with mild cognitive impairment (MCI) (OR 1.760 [random effects] and 1.810 [fixed effect]) (p < 0.001). A significant (p <0.001) correlation exists between the QTc and the Mini-Mental State Exam (MMSE), a test of cognitive function. Two studies examined QT variability (the difference between the longest and shortest QT interval on a 12 lead ECG); the OR for QT variability AD vs MCI was 3.858 [random effects model] and 3.712 [fixed effects model] (p < 0.001). When compared to the control group, the OR for QT dispersion in AD was 6.358 [random effects model] or 5.143 ( P< 0.001) [fixed effects model]. A qualitative analysis of the data raised questions about paucity of data defining the nature of the control groups, the pathophysiologic mechanism, and the uniform use of a poor QT heart rate correction factor. The longer QT in AD, greater QT variability in AD, and the direct relationship between QT interval and AD severity supports a brain-heart connection in AD that might be fundamental to aging-induced AD and mortality. Issues with defining the control group, limited number of studies, conflicting data in population studies, and the lack of a strong electrophysiological basis underscore the need for additional research in this field.

Obstructive sleep apnea and non-dipper: epiphenomena or risks of Alzheimer's disease?: a review from the HOPE Asia Network

Obstructive sleep apnea (OSA) and associated nocturnal blood pressure (BP) surges is associated with non-dipper. On the other hand, the relationship between neurodegenerative diseases and non-dipper hypertension has been reported. To date, few studies have evaluated the relationships of nocturnal BP dipping patterns and OSA in relation to neurodegenerative diseases, particularly Alzheimer's disease (AD). This review examines the etiology of the association between OSA and the non-dipper pattern of hypertension and how both are involved in the development of AD. To set the stage for this review, we first focus on the pathophysiology of AD, which is interrelated with sleep apnea and non-dipper through dysregulation of central autonomic network.

Heart rate variability during slow wave sleep is linked to functional connectivity in the central autonomic network

Reduced heart rate variability can be an early sign of autonomic dysfunction in neurodegenerative diseases and may be related to brain dysfunction in the central autonomic network. As yet, such autonomic dysfunction has not been examined during sleep-which is an ideal physiological state to study brain-heart interaction as both the central and peripheral nervous systems behave differently compared to during wakefulness. Therefore, the primary aim of the current study was to examine whether heart rate variability during nocturnal sleep, specifically slow wave (deep) sleep, is associated with central autonomic network functional connectivity in older adults 'at-risk' of dementia. Older adults (n = 78; age range = 50-88 years; 64% female) attending a memory clinic for cognitive concerns underwent resting-state functional magnetic resonance imaging and an overnight polysomnography. From these, central autonomic network functional connectivity strength and heart rate variability data during sleep were derived, respectively. High-frequency heart rate variability was extracted to index parasympathetic activity during distinct periods of sleep, including slow wave sleep as well as secondary outcomes of non-rapid eye movement sleep, wake after sleep onset, and rapid eye movement sleep. General linear models were used to examine associations between central autonomic network functional connectivity and high-frequency heart rate variability. Analyses revealed that increased high-frequency heart rate variability during slow wave sleep was associated with stronger functional connectivity (F = 3.98, P = 0.022) in two core brain regions within the central autonomic network, the right anterior insular and posterior midcingulate cortex, as well as stronger functional connectivity (F = 6.21, P = 0.005) between broader central autonomic network brain regions-the right amygdala with three sub-nuclei of the thalamus. There were no significant associations between high-frequency heart rate variability and central autonomic network connectivity during wake after sleep onset or rapid eye movement sleep. These findings show that in older adults 'at-risk' of dementia, parasympathetic regulation during slow wave sleep is uniquely linked to differential functional connectivity within both core and broader central autonomic network brain regions. It is possible that dysfunctional brain-heart interactions manifest primarily during this specific period of sleep known for its role in memory and metabolic clearance. Further studies elucidating the pathophysiology and directionality of this relationship should be conducted to determine if heart rate variability drives neurodegeneration, or if brain degeneration within the central autonomic network promotes aberrant heart rate variability.

The Insular Cortex, Alzheimer Disease Pathology, and Their Effects on Blood Pressure Variability

Recent findings indicate that the human cardiovascular system is regulated by a cortical network comprised of the insular cortex (Ic), anterior cingulate gyrus, and amygdala which is necessary for the regulation of the central autonomic network system. Alzheimer disease (AD) affects the Ic at a preclinical stage. The pathology of AD at the Ic is suggested to predispose the cardiovascular system to detrimental changes such as increased blood pressure variability (BPV). In this review article, we focus on the physiology of the Ic in the relationship between the central autonomic network and BPV. We provide a summary of the published evidence regarding the relationship between Ic damage and exaggerated BPV in the context of AD pathology.

Orthostatic hypotension in patients with Alzheimer's disease: a meta-analysis of prospective studies

BACKGROUND

Orthostatic hypotension (OH) is a clinical sign associated with severe adverse health outcomes in older adults. It has been reported to be common in patients with Alzheimer's disease (AD). The present meta-analysis aimed to investigate the prevalence and risk of OH in AD patients.

METHODS

English-language articles published from January 1990 to August 2020 were searched in PubMed, ScienceDirect, Cochrane, and Web of Science with the keywords "Alzheimer" and "autonomic dysfunction" or "dysautonomia" or "postural hypotension" or "orthostatic hypotension." All prospective clinical studies (case-control, cohort, and cross-sectional studies, and randomized controlled trials) that were regarded as pertinent were included in this study. For quality assessment, the Newcastle-Ottawa Scale was used. Odds ratios (OR) and risk ratios (RR) were extracted with 95% confidence intervals (CI) and combined using the random effects model after logarithmic transformation. The prevalence in the AD patients was also combined using the random effects model.

RESULTS

The meta-analysis involved 11 studies (7 case-control and 4 case series) to assess the risk of OH in AD. It was found that AD increased the risk of OH with an RR of 1.98 (95% CI: 0.97-4.04) and an OR of 2.53 (95% CI:1.10-5.86) compared to healthy controls, and OH was present in 28% (95% CI: 0.17-0.40) of 500 AD patients.

CONCLUSION

There is an elevated risk of OH in AD by nearly 2.5-fold. Therefore, the evaluation of postural blood pressure changes should definitely be among the follow-up and treatment goals of AD.

Orthostatic Blood Pressure Recovery Is Associated With the Rate of Cognitive Decline and Mortality in Clinical Alzheimer's Disease

Background

Impaired recovery of blood pressure (BP) after standing has been shown to be related to cognitive function and mortality in people without dementia, but its role in people with Alzheimer’s disease (AD) is unknown. The aim of this study was to investigate the association of the orthostatic BP response with cognitive decline and mortality in AD.

Methods

In this post hoc analysis of a randomized controlled trial (Nilvad), we measured the beat-to-beat response of BP upon active standing in mild-to-moderate AD. This included the initial drop (nadir within 40 seconds) and recovery after 1 minute, both expressed relative to resting values. We examined the relationship between a small or large initial drop (median split) and unimpaired (≥100%) or impaired recovery (<100%) with 1.5-year change in Alzheimer’s Disease Assessment—cognitive subscale (ADAS-cog) scores and all-cause mortality.

Results

We included 55 participants (age 73.1 ± 6.2 years). Impaired BP recovery was associated with higher increases in ADAS-cog scores (systolic: β [95% confidence interval] = 5.6 [0.4–10.8], p = .035; diastolic: 7.6 [2.3–13.0], p = .006). During a median follow-up time of 49 months, 20 participants died. Impaired BP recovery was associated with increased mortality (systolic: HR [95% confidence interval] = 2.9 [1.1–7.8], p = .039; diastolic: HR [95% confidence interval] = 5.5 [1.9–16.1], p = .002). The initial BP drop was not associated with any outcome. Results were adjusted for age, sex, and intervention group.

Conclusions

Failure to fully recover BP after 1 minute of standing is associated with cognitive decline and mortality in AD. As such, BP recovery can be regarded as an easily obtained marker of progression rate of AD.

Baroreceptor Modulation of the Cardiovascular System, Pain, Consciousness, and Cognition

Baroreceptors are mechanosensitive elements of the peripheral nervous system that maintain cardiovascular homeostasis by coordinating the responses to external and internal environmental stressors. While it is well known that carotid and cardiopulmonary baroreceptors modulate sympathetic vasomotor and parasympathetic cardiac neural autonomic drive, to avoid excessive fluctuations in vascular tone and maintain intravascular volume, there is increasing recognition that baroreceptors also modulate a wide range of non-cardiovascular physiological responses via projections from the nucleus of the solitary tract to regions of the central nervous system, including the spinal cord. These projections regulate pain perception, sleep, consciousness, and cognition. In this article, we summarize the physiology of baroreceptor pathways and responses to baroreceptor activation with an emphasis on the mechanisms influencing cardiovascular function, pain perception, consciousness, and cognition. Understanding baroreceptor-mediated effects on cardiac and extra-cardiac autonomic activities will further our understanding of the pathophysiology of multiple common clinical conditions, such as chronic pain, disorders of consciousness (e.g., abnormalities in sleep-wake), and cognitive impairment, which may result in the identification and implementation of novel treatment modalities. © 2021 American Physiological Society. Compr Physiol 11:1373-1423, 2021.

Association of Heart Rate Variability With Cognitive Performance: The Multi-Ethnic Study of Atherosclerosis

Background Heart rate variability (HRV) is associated with vascular risk factors for dementia, but whether HRV is associated with specific domains of cognitive performance is unclear. Methods and Results In the Multi-Ethnic Study of Atherosclerosis (N=3018; mean age 59.3±9.2 years), we assessed the relationship of 10-second HRV to scores on tests of global cognitive performance (Cognitive Abilities Screening Instrument), processing speed (Digit Symbol Coding), and working memory (Digit Span). HRV was computed as the SD of normal-normal intervals (SDNN) and root mean square of successive differences (RMSSD) at Exam 1 (2000-2002) and Exam 5 (2010-2012). Cognitive tests were administered at Exam 5. We report regression coefficients (β [95% CI]) representing cognitive test score change per 2-fold increase in HRV. After adjustment for age, race/ethnicity, sex, education, apolipoprotein E genotype, and cardiovascular risk factors and incident disease, higher Exam 1 (β=0.37 [0.06, 0.67]) and Exam 5 (β=0.31 [0.04, 0.59]) SDNN were associated with better Cognitive Abilities Screening Instrument performance. Higher Exam 1 (β=0.80 [0.17, 1.43]) and Exam 5 (β=0.63 [0.06, 1.20]) SDNN, and Exam 5 RMSSD (β=0.54 [0.01, 1.08]) were associated with better Digit Symbol Coding performance. Finally, higher Exam 5 SDNN was associated with better Digit Span performance (β=0.17 [0.01, 0.33]). Associations were attenuated after adjustment for resting heart rate. Conclusions Higher HRV is generally associated with better cognitive performance in this multi-ethnic cohort of aging adults, and further study of the relationship of autonomic function to cognition is warranted.

Visit-to-Visit Blood Pressure Variability and Alzheimer's Disease: Links and Risks

While hypertension has been shown to be a risk factor for vascular dementia, several studies have also demonstrated that hypertension also increases the risk of Alzheimer's disease (AD). Although the relationship between visit-to-visit blood pressure variability (VVV) and cognitive impairment, including AD, have been provided, the mechanisms remain poorly understood. This review paper focuses on the relationship of VVV with AD and summarizes the pathophysiology underlying that relationship, which appears to be mediated by arterial stiffness.

Physiological changes in neurodegeneration - mechanistic insights and clinical utility

The effects of neurodegenerative syndromes extend beyond cognitive function to involve key physiological processes, including eating and metabolism, autonomic nervous system function, sleep, and motor function. Changes in these physiological processes are present in several conditions, including frontotemporal dementia, amyotrophic lateral sclerosis, Alzheimer disease and the parkinsonian plus conditions. Key neural structures that mediate physiological changes across these conditions include neuroendocrine and hypothalamic pathways, reward pathways, motor systems and the autonomic nervous system. In this Review, we highlight the key changes in physiological processing in neurodegenerative syndromes and the similarities in these changes between different progressive neurodegenerative brain conditions. The changes and similarities between disorders might provide novel insights into the human neural correlates of physiological functioning. Given the evidence that physiological changes can arise early in the neurodegenerative process, these changes could provide biomarkers to aid in the early diagnosis of neurodegenerative diseases and in treatment trials.

Cognitive Status, Gray Matter Atrophy, and Lower Orthostatic Blood Pressure in Older Adults

BACKGROUND

Associations between orthostatic blood pressure and cognitive status (CS) have been described with conflicting results.

OBJECTIVE

We hypothesize that long-term exposure to lower orthostatic blood pressure is related to having worse CS later in life and that atrophy of regions involved in central regulation of autonomic function mediate these associations.

METHODS

Three-to-four measures of orthostatic blood pressure were obtained from 1997-2003 in a longitudinal cohort of aging, and average systolic orthostatic blood pressure response (ASOBPR) was computed as % change in systolic blood pressure from sit-to-stand measured at one minute post stand. CS was determined in 2010-2012 by clinician-adjudication (n = 240; age = 87.1±2.6; 59% women; 37% black) with a subsample also undergoing concurrent structural neuroimaging (n = 129). Gray matter volume of regions related to autonomic function was measured. Multinomial regression was used to compare ASOBPR in those who were cognitively intact versus those with a diagnosis of mild cognitive impairment or dementia, controlling for demographics, trajectories of seated blood pressure, incident cardiovascular risk/events and medications measured from 1997 to 2012. Models were repeated in the subsample with neuroimaging, before and after adjustment for regional gray matter volume.

RESULTS

There was an inverse association between ASOBPR and probability of dementia diagnosis (9% lower probability for each % point higher ASOBPR: OR 0.91, CI95%  = 0.85-0.98; p = 0.01). Associations were similar in the subgroup with neuroimaging before and after adjustment for regional gray matter volume.

CONCLUSION

ASOBPR may be an early marker of risk of dementia in older adults living in the community.

Sub-clinical orthostatic hypotension is associated with greater subjective memory impairment in older adults

INTRODUCTION

Orthostatic blood pressure (BP) is a measure of cardiovascular autonomic function. Orthostatic BP dysregulation may lie on the causal pathway to dementia. Subjective memory impairment (SMI) is commonly reported by older people some of whom may progress to dementia. We hypothesised that sub-clinical orthostatic hypotension would be associated with SMI and explored these associations according to sex.

METHODS

Cross-sectional analysis of data from 4340 participants aged 50 and over collected during the first wave (2009-2011) of the cohort study, The Irish Longitudinal Study on Ageing. Subjective memory was rated according to a 5-point scale ranging from 'poor' to 'excellent'. BP was measured during orthostatic stress using continuous non-invasive beat-to-beat recording over 2 min.

RESULTS

2% reported 'poor' subjective memory, 12.3% 'fair' , 38% 'good', 33% 'very good' and 14.6% 'excellent'. After controlling for several potential confounding factors including cardiovascular risk, objective cognition, and depressive symptoms mean systolic orthostatic BP was lowest in those with poor subjective memory: 92.2 mmHg (CI95% = 87.1, 97.3) versus excellent 99.3 mmHg (CI95% = 97.4, 101.2); p = 0.011. Further adjustment for supine systolic BP suggested that men with poor subjective memory reached the lowest average systolic orthostatic BP and had the greatest impairment in systolic orthostatic BP stabilisation to baseline levels at 10 s post-stand (-6.64 mmHg; CI95% = -11.49, -1.79; p = 0.007).

CONCLUSIONS

Sub-clinical orthostatic hypotension is associated with SMI, and there are sex-specific relationships evident in this population-based cohort. Subtle cardiovascular autonomic dysfunction may represent a modifiable risk marker at an early stage of cognitive decline in older adults. Copyright © 2016 John Wiley & Sons, Ltd.

Eight-year parallel change in baroreflex sensitivity and memory function in a sample of healthy older adults

OBJECTIVES

To examine whether changes in the cardiac autonomic nervous system (ANS) over time, as expressed by baroreflex sensitivity (BRS), were associated with long-term changes in cognitive performance in elderly individuals without dementia.

DESIGN

Community-based 8-year longitudinal study.

SETTING

Clinical settings.

PARTICIPANTS

Individuals aged 66.9 ± 0.9 (N = 425).

MEASUREMENTS

At baseline and follow-up, subjects underwent a clinical interview, autonomic and vascular measurements, and a neuropsychological evaluation including attentional, executive, and memory tests using standardized Z-scores. BRS was defined as being normal, moderate, or severe alteration at each evaluation. On the basis of the longitudinal changes subjects were stratified as being stable, moderate or improved.

RESULTS

Mean attentional, executive, and memory change Z-scores were -0.41 ± 0.9, -0.15 ± 0.7, and -0.14 ± 0.8, respectively. BRS of 56% of the subjects remained unchanged, of 20% decreased, and of 24% improved. After regression analysis, the worsened BRS group was 1.88 times as likely to have greater memory change as the group with stable BRS (P = .02). No significant association was found between longitudinal change in BRS and attentional and executive changes.

CONCLUSION

In healthy elderly individuals, BRS decrease was associated with a weak but significant decrease in memory function. The long-term effect of BRS on memory changes may suggest a role of the ANS in cognitive decline.

Autonomic dysfunction in mild cognitive impairment: evidence from power spectral analysis of heart rate variability in a cross-sectional case-control study

BACKGROUND

Mild cognitive impairment (MCI) is set to become a major health problem with the exponential ageing of the world's population. The association between MCI and autonomic dysfunction, supported by indirect evidence and rich with clinical implications in terms of progression to dementia and increased risk of mortality and falls, has never been specifically demonstrated.

AIM

To conduct a comprehensive assessment of autonomic function in subjects with MCI by means of power spectral analysis (PSA) of heart rate variability (HRV) at rest and during provocative manoeuvres.

METHODS

This cross-sectional study involved 80 older outpatients (aged ≥ 65) consecutively referred to a geriatric unit and diagnosed with MCI or normal cognition (controls) based on neuropsychological testing. PSA was performed on 5-minute electrocardiographic recordings under three conditions--supine rest with free breathing (baseline), supine rest with paced breathing at 12 breaths/minute (parasympathetic stimulation), and active standing (orthosympathetic stimulation)--with particular focus on the changes from baseline to stimulation of indices of sympathovagal balance: normalized low frequency (LFn) and high frequency (HFn) powers and the LF/HF ratio. Blood pressure (BP) was measured at baseline and during standing. Given its exploratory nature in a clinical population the study included subjects on medications with a potential to affect HRV.

RESULTS

There were no significant differences in HRV indices between the two groups at baseline. MCI subjects exhibited smaller physiological changes in all three HRV indices during active standing, consistently with a dysfunction of the orthosympathetic system. Systolic BP after 10 minutes of standing was lower in MCI subjects, suggesting dysautonomia-related orthostatic BP dysregulation.

CONCLUSIONS

Our study is novel in providing evidence of autonomic dysfunction in MCI. This is associated with orthostatic BP dysregulation and the ongoing follow-up of the study population will determine its prognostic relevance as a predictor of adverse health outcomes.

Cardiovascular manifestations of neurologic disease

Cardiac manifestations of neurologic diseases are common in clinical practice. There are numerous anatomic and pathophysiologic links between the normal and abnormal function of both systems. There are a number of brain-heart interactions which affect the care of patients as well as help guide therapeutic development. This is exemplified in the area of vascular neurology where knowledge of the brain-heart connection is essential not only for bedside management but where collaborative efforts between neurology and cardiology are key in developing new strategies for ischemic stroke prevention and treatment, atrial fibrillation, and interventional techniques. This chapter will focus on cardiac manifestations of neurologic disease, with special emphasis on vascular and intensive care neurology, epilepsy, and neurodegenerative and peripheral nervous system diseases.

QT dispersion in mild cognitive impairment: a possible tool for predicting the risk of progression to dementia?

OBJECTIVE

The aim of this research was to investigate relationships between cognitive function and non-invasive, repeatable cardiac parameters in elderly subjects suffering from mild cognitive impairment (MCI) or Alzheimer's disease (AD).

METHODS

Two hundred and twenty-four community-living elderly subjects, 31 AD patients, 77 MCI patients, and 116 cognitively normal subjects (CNS), were evaluated for cognitive abilities (Mini Mental State Examination score (MMSE)) and for electrocardiographic [corrected heart rate QT interval dispersion (QTcD)] and echocardiographic [Left ventricular ejection fraction (LVEF)] parameters.

RESULTS

Mean values of LVEF were not significantly different between the three groups; QTcD mean values were significantly lower in CNS group than in subjects with MCI and AD. The Pearson Product Moment Correlation test, carried out in the three study groups, showed a significant inverse correlation between QTcD and MMSE score (r = -0.357; p < 0.01) in the group of MCI patients, only. In multivariable-adjusted linear regression tests, QTcD (p = 0.030) and education (p = 0.021) are associated with MMSE score in MCI group. Only the parameter of education appears to predict MMSE in CNS group; none of these parameters appear to predict MMSE in the group of patients with AD.

CONCLUSION

The association between QTcD and MMSE requires cautious interpretation and further extensive investigation. However, if confirmed by longitudinal studies, the finding could play a role in the management of the subjects with MCI.

Autonomic dysfunction in mild cognitive impairment: a transcranial Doppler study

OBJECTIVES

The contribution of early microvascular and autonomic derangements to the pathogenesis of mild cognitive impairment (MCI) is unclear. Aim of this study is to evaluate cerebrovascular reactivity (CVR) and cardiac autonomic function in patients with MCI by means of transcranial Doppler (TCD).

MATERIAL AND METHODS

Fifteen patients with MCI and 28 controls underwent carotid ultrasound and TCD evaluation, including assessment of mean flow velocity (MFV) in the middle cerebral artery at baseline, after CO(2) inhalation and after hyperpnoea. End-tidal CO(2) , mean arterial blood pressure (MAP), heart rate (HR), and respiratory rate were monitored throughout the procedure, and CVR was calculated.

RESULTS

MAP, end-tidal CO(2) , and MFV variations during hypercapnia and hyperventilation showed no between-group differences. CVR was similar in controls and MCI (2.30 vs 2,39, respectively, P = 0.767). HR significantly increased in hypercapnia (+9.4%, P < 0.0001) and hyperventilation (+18.7%, P < 0.0001) in controls, while in MCI it significantly increased in hyperventilation (+10.4%, P = 0.002), but not in hypercapnia (+1.1%, P = 0.635).

CONCLUSIONS

This study demonstrates that patients with MCI have a normal CVR, but they exhibit signs of autonomic dysfunction after CO(2) challenge. Should this finding be confirmed in larger studies, HR response to CO(2) challenge could become a marker of MCI.

Multimodal MRI neuroimaging biomarkers for cognitive normal adults, amnestic mild cognitive impairment, and Alzheimer's disease

Multimodal magnetic resonance imaging (MRI) techniques have been developed to noninvasively measure structural, metabolic, hemodynamic and functional changes of the brain. These advantages have made MRI an important tool to investigate neurodegenerative disorders, including diagnosis, disease progression monitoring, and treatment efficacy evaluation. This paper discusses recent findings of the multimodal MRI in the context of surrogate biomarkers for identifying the risk for AD in normal cognitive (NC) adults, brain anatomical and functional alterations in amnestic mild cognitive impairment (aMCI), and Alzheimer's disease (AD) patients. Further developments of these techniques and the establishment of promising neuroimaging biomarkers will enhance our ability to diagnose aMCI and AD in their early stages and improve the assessment of therapeutic efficacy in these diseases in future clinical trials.

Altered cerebral hemodynamics in early Alzheimer disease: a pilot study using transcranial Doppler

Cerebrovascular disease may contribute to the development and progression of Alzheimer's disease (AD). This study investigated whether impairments in cerebral hemodynamics can be detected in early-stage AD. Nine patients with mild AD and eight cognitively normal controls matched for age underwent brain magnetic resonance imaging and neuropsychological evaluation, followed by assessment of steady-state cerebral blood flow velocity (CBFV, transcranial Doppler), blood pressure (BP, Finapres), and cerebrovascular resistance index (BP/CBFV). Cerebral hemodynamics were quantified using spectral and transfer function analysis of BP and CBFV in rest, during standing up after squat, and during repeated squat-stand maneuvers. Compared to controls, AD patients had lower CBFV and higher cerebrovascular resistance index, unexplained by brain atrophy. Low-frequency variability of BP was enhanced, suggesting impaired arterial baroreflex function. However, CBFV variability was reduced despite enhanced BP variability, and dynamic cerebral autoregulation was not impaired. In conclusion, despite a distinct pattern of altered cerebral hemodynamics, AD patients may have normal autoregulation. However, the challenges for autoregulation in AD are higher, as our data show enhanced BP fluctuations. Increased cerebral vasoconstriction or reduced vasomotion also may attenuate CBFV variability.

Cardiac autonomic modulation and cognitive status in Alzheimer's disease

INTRODUCTION

Although nervous structures affected in Alzheimer's disease are also implicated in autonomic nervous system function, the relationship between autonomic and cognitive functions was not still investigated.

METHODS

The cardiac autonomic modulation of 5-min heart interval variability evaluated by time- and frequency-domain indexes, in supine and standing positions, of 22 Alzheimer's disease patients (90.9% women) aged 79.6 +/- 1.4 years (mean +/- SE) was correlated with mild to severe cognitive impairment scored by the CAMCOG and MMSE subset tests, by the Spearman's correlation analysis.

RESULTS

Age and level of education were not correlated with the heart interval variability indexes and the cognitive scores. Significantly positive (r (s) = 0.43-0.47, P = 0.03-0.04) or trend (r (s) = 0.36-0.40, P = 0.06-0.10) correlation was observed in both positions between the cognitive performance and pNN50%, rMSSD and absolute and normalised high-frequency power, considered to express parasympathetic modulation. Negative trend correlation (r (s) = -0.35 to -0.39, P = 0.07-0.10) was observed between absolute sympathetic modulation (low-frequency power and low-to-high frequency power ratio) in supine posture.

CONCLUSION

The cognitive status and the cardiac sympathovagal modulation appear to be correlated and hypothetically may influence one another in mild to severe Alzheimer's disease. Individuals with more severe cognitive deficiency showed suggestive lower cardiac parasympathetic modulation and trend for higher cardiac sympathetic modulation.

Correlation between cognitive impairment and dependence in hypoxemic COPD

We studied 149 patients with stable chronic obstructive pulmonary disease (COPD). Three clusters were generated (high, mid, and low level of cognitive function) based on 11 neuropsychologic scores; personal independence in basic/instrumental activities of daily living (BADL/IADL) of clusters was compared by discriminant analysis. Pattern of BADL/IADL was cluster-specific in 79.2% of high and 54.9% of low clusters, but only 20.8% of mid cluster. Self-administering drugs, continence, managing money, and dressing items had the greatest discriminatory capacity. Clusters had comparable respiratory function. In older COPD patients, dependence parallels cognitive impairment only to some extent. Indices of COPD severity are poor correlates of dependence.

Asymmetric insular function predicts positional blood pressure in nondemented elderly

Forty percent of nondemented octogenarians have Braak stages consistent with insular involvement, and may be at risk for "age-related" autonomic dysfunction. The authors examined the association between insular resting cerebral blood flow (rCBF) and cardiovascular functions in 29 nondemented elderly subjects who were highly screened to exclude comorbid cardiovascular disease. Mean insular rCBF was significantly higher on the right than left. However, 35.4% of participants had left dominant rCBF (a high-risk group). Right insular rCBF was significantly lower in the high-risk group. This subset had significantly increased positional drops in systolic blood pressure. While these data cannot address Alzheimer's disease as the specific cause, this possibility is being investigated in other cohorts.

Cardiac sympathovagal modulation evaluated by short-term heart interval variability is subtly impaired in Alzheimer's disease

AIM

Alzheimer's disease affects several nervous structures involved with the autonomic nervous system. Therefore, the still scarce evaluation of the cardiac autonomic function in this disease is of great functional, clinical, prognostic and therapeutic relevance.

METHODS

Time- and frequency-domain variability of 5-min R-R interval series in supine and standing positions was comparatively evaluated in 22 Alzheimer's disease subjects, aged 60-87 years (mean +/- standard error of the mean, 79.6 +/- 1.4) with variable cognitive impairment, and 24 healthy individuals, aged 60-91 years (68.6 +/- 1.6). The Student's t-test was used to compare the variability indices between the groups and logistic regression excluded the effects on these indices in the Alzheimer's group of confounding variables different from the control group (age, physical activity and caffeinated intake), at a significance level of P </= 0.05.

RESULTS

No difference was observed between the groups (P = 0.12-0.72) for each time-domain mean indices and for the frequency-domain indices of overall and absolute sympathetic modulation in both positions (P = 0.21-0.78). Absolute parasympathetic modulation showed borderline decrease in supine position (P = 0.07) and was reduced in the standing (P = 0.05). The sympathovagal balance was altered (P = 0.05) toward relative parasympathetic borderline depression (P = 0.07) and sympathetic exacerbation (P = 0.04) only in the supine posture.

CONCLUSION

Data indicate that Alzheimer's disease subjects with mild-to-severe cognitive dysfunction showed subtle, absolute and relative parasympathetic depression and relative sympathetic exacerbation, which may even so contribute to distinctive functional and cognitive disturbances.

Clock-drawing potentially mediates the effect of depression on mortality: replication in three cohorts

OBJECTIVE

Previously studies have associated visuospatial tasks, particularly 'clock-drawing', with mortality. We sought to determine whether clock-drawing also mediates the association between depressive symptoms and mortality.

PARTICIPANTS

Non-institutionalized Hispanic and non-Hispanic White elderly volunteers.

MEASUREMENTS

Survival curves were generated as a function of baseline depressive symptom ratings. Significant models were adjusted for CLOX performance. CLOX is divided into CLOX1, a measure of executive control, and CLOX2, a measure of visuospatial skills.

DESIGN

Retrospective analysis of three longitudinal cohorts.

RESULTS

CLOX2 and depressive symptoms were both associated with mortality in unadjusted models. CLOX2 predicted survival independently of CLOX1 in all three cohorts. CLOX2 also attenuated, and/or mediated the association between depressive symptoms and mortality. These results withstood adjustment for age and education in all three cohorts.

CONCLUSION

Regardless of the sample examined, or the measure of depressive symptoms applied, the association between depressive symptoms and mortality appears to be at least partially mediated by visuospatial skills. This finding supports our hypothesis that right hemisphere structural brain disease, particularly that involving the insula, may mediate depression's effects on mortality.

Voxel-based analysis of 11C-PIB scans for diagnosing Alzheimer's disease

The positron emission tomography (PET) radioligand N-methyl-11C-2-(4-methylaminophenyl)-6-hydroxybenzothiazole (also known as 11C-6-OH-BTA-1 or 11C-PIB) binds to amyloid-beta (Abeta), which accumulates pathologically in Alzheimer's disease (AD). Although 11C-PIB accumulation is greater in patients with AD than in healthy controls at a group level, the optimal method for discriminating between these 2 groups has, to our knowledge, not been established. We assessed the use of data-determined standardized voxels of interest (VOIs) to improve the classification capability of 11C-PIB scans on patients with AD.

METHODS

A total of 16 controls and 14 AD age-matched patients were recruited. All subjects underwent a 11C-PIB scan and structural MRI. Binding potential (a measure of amyloid burden) was calculated for each voxel using the Logan graphical method with cerebellar gray matter as the reference region. Voxel maps were then partial-volume corrected and spatially normalized by MRI onto a standardized template. The subjects were divided into 2 cohorts. The first cohort (control, 12; AD, 9) was used for statistical parametric mapping analysis and delineation of data-based VOIs. These VOIs were tested in the second cohort (control, 4; AD, 5) of subjects.

RESULTS

Statistical parametric mapping analysis revealed significant differences between control and AD groups. The VOI map determined from the first cohort resulted in complete separation between the control and the AD subjects in the second cohort (P < 0.02). Binding potential values based on this VOI were in the same range as other reported individual and mean cortical VOI results.

CONCLUSION

A standardized VOI template that is optimized for control or AD group discrimination provides excellent separation of control and AD subjects on the basis of 11C-PIB uptake. This VOI template can serve as a potential replacement for manual VOI delineation and can eventually be fully automated, facilitating potential use in a clinical setting. To facilitate independent analysis and validation with more and a broader variety of subjects, this VOI template and the software for processing will be made available through the Internet.

Alzheimer disease neuropathology: understanding autonomic dysfunction

Alzheimer's disease is a widely studied disorder with research focusing on cognitive and functional impairments, behavioral and psychological symptoms, and on abnormal motor manifestations. Despite the importance of autonomic dysfunctions they have received less attention in systematic studies. The underlying neurodegenerative process of AD, mainly affecting cortical areas, has been studied for more than one century. However, autonomic-related structures have not been studied neuropathologically with the same intensity. The autonomic nervous system governs normal visceral functions, and its activity is expressed in relation to homeostatic needs of the organism's current physical and mental activities. The disease process leads to autonomic dysfunction or dysautonomy possibly linked to increased rates of morbidity and mortality.

OBJECTIVE

The aim of this review was to analyze the cortical, subcortical, and more caudal autonomic-related regions, and the specific neurodegenerative process in Alzheimer's disease that affects these structures.

METHODS

A search for papers addressing autonomic related-structures affected by Alzheimer's degeneration, and under normal condition was performed through MedLine, PsycInfo and Lilacs, on the bibliographical references of papers of interest, together with a manual search for classic studies in older journals and books, spanning over a century of publications.

RESULTS

The main central autonomic-related structures are described, including cortical areas, subcortical structures (amygdala, thalamus, hypothalamus, brainstem, cerebellum) and spinal cord. They constitute autonomic neural networks that underpin vital functions. These same structures, affected by specific Alzheimer's disease neurodegeneration, were also described in detail. The autonomic-related structures present variable neurodegenerative changes that develop progressively according to the degenerative stages described by Braak and Braak.

CONCLUSION

The neural networks constituted by the central autonomic-related structures, when damaged by progressive neurodegeneration, represent the neuropathological substrate of autonomic dysfunction. The presence of this dysfunction and its possible relationship with higher rates of morbidity, and perhaps of mortality, in affected subjects must be kept in mind when managing Alzheimer's patients.

Atypical early-onset Alzheimer's disease caused by the Iranian APP mutation

BACKGROUND

Approximately 1% of all cases of Alzheimer's disease are inherited autosomal dominantly, and to date, three causative genes have been found, the Presenilin 1 (PSEN1) gene, the Presenilin 2 (PSEN2) gene and the Amyloid precursor protein (APP) gene. We describe atypical phenotypic features in a family with a pathogenic APP gene mutation and discuss possible explanations for these atypical features.

METHODS AND RESULTS

We report a family with a history of dementia compatible with autosomal dominant transmission. The disease course in the proband was not typical for Alzheimer's disease as the diagnosis was preceded by 8 years of an isolated amnesia. Further, the proband had epilepsy with complex partial seizures and central degenerative autonomic failure as determined by clinical physiology. Sequencing the three known causative Alzheimer genes revealed a pathogenic missense mutation, APP Thr714Ala (the Iranian mutation).

CONCLUSIONS

The atypical clinical phenotype with long prodromal phase, autonomic failure and seizures in this new proband with the APP Thr714Ala mutation illustrates the clinical heterogeneity in families with identical pathogenic mutations.

Cognitive predictors of mortality in elderly retirees: results from the Freedom House study

OBJECTIVE

The objective of this longitudinal cohort study was to study the cognitive domains associated with five-year longitudinal survival among healthy, well-educated, noninstitutionalized elderly.

METHODS

Survival curves were generated as a function of cross-sectional baseline cognitive test performance.

RESULTS

Nonverbal tests were significantly associated with survival. This finding was markedly consistent. Several nonverbal tasks were each significantly associated with survival independently of age, gender, baseline level of care, and healthcare utilization. In a multivariate model, copying a clock made the strongest, independent contribution to survival.

CONCLUSIONS

Right hemisphere integrity in general and nonverbal drawing tasks in particular have been associated with survival in conditions as diverse as Alzheimer disease, stroke, and epilepsy. This study extends this association to "normal" aging. The mechanism by which nonverbal cognitive function is related to mortality remains unclear but may be mediated by changes in right hemisphere cortical control of autonomic function. Nondemented older persons may be at risk. Clock drawing may provide a simple means of identifying them.

Drawing impairment predicts mortality in severe COPD

BACKGROUND

Cognitive impairment frequently occurs in elderly COPD patients, but little is known about its prognostic implications. We aimed at evaluating the prognostic role of cognitive impairment in patients with severe COPD.

METHODS

Our series consisted of 149 stable patients (mean [+/- SD] age, 68.7 +/- 8.5 years) with COPD and a Pao(2) of < 57 mm Hg at rest (n = 97) or at the end of the 6-min walking test (n = 37) who were enrolled in a prospective observational study. After a multidimensional baseline assessment, patients were followed up by telephone calls for a mean duration of 32.5 +/- 9.2 months (minimal follow-up duration, 24 months); 134 patients were successfully tracked. We used multivariable Cox proportional hazard analysis to identify predictors of death among clinical/functional variables that previously were shown to have prognostic implications and among neuropsychological indexes selected on the basis of univariate analysis.

RESULTS

We observed 29 deaths over a median follow-up time of 32 months. Only the two following variables were independently associated with the outcome: an abnormal score on the copy with landmark test (hazard ratio [HR], 2.93; 95% confidence interval [CI], 1.34 to 6.39); and a 6-min walk distance of < 300 m (HR, 3.46; 95% CI, 1.15 to 10.5). A Pao(2) of < 57 mm Hg at rest (HR, 2.19; 95% CI, 0.93 to 5.18) and an FEV(1) of < 40% predicted (HR, 2.74; 95% CI, 0.99 to 7.57) were nearly significantly associated with the outcome, while Paco(2), body mass index, physical dependence, comorbid diseases, and the impairment of cognitive domains other than drawing impairment were unrelated to the outcome.

CONCLUSIONS

Drawing impairment is a risk factor for mortality and might improve the assessment of hypoxemic COPD patients.