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Burma JS, Roy MA, Kennedy CM, Labrecque L, Brassard P, Smirl JD. A systematic review, meta-analysis, and meta-regression amalgamating the driven approaches used to quantify dynamic cerebral autoregulation. J Cereb Blood Flow Metab 2024:271678X241235878. [PMID: 38635887 DOI: 10.1177/0271678x241235878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 04/20/2024]
Abstract
Numerous driven techniques have been utilized to assess dynamic cerebral autoregulation (dCA) in healthy and clinical populations. The current review aimed to amalgamate this literature and provide recommendations to create greater standardization for future research. The PubMed database was searched with inclusion criteria consisting of original research articles using driven dCA assessments in humans. Risk of bias were completed using Scottish Intercollegiate Guidelines Network and Methodological Index for Non-Randomized Studies. Meta-analyses were conducted for coherence, phase, and gain metrics at 0.05 and 0.10 Hz using deep-breathing, oscillatory lower body negative pressure (OLBNP), sit-to-stand maneuvers, and squat-stand maneuvers. A total of 113 studies were included, with 40 of these incorporating clinical populations. A total of 4126 participants were identified, with younger adults (18-40 years) being the most studied population. The most common techniques were squat-stands (n = 43), deep-breathing (n = 25), OLBNP (n = 20), and sit-to-stands (n = 16). Pooled coherence point estimates were: OLBNP 0.70 (95%CI:0.59-0.82), sit-to-stands 0.87 (95%CI:0.79-0.95), and squat-stands 0.98 (95%CI:0.98-0.99) at 0.05 Hz; and deep-breathing 0.90 (95%CI:0.81-0.99); OLBNP 0.67 (95%CI:0.44-0.90); and squat-stands 0.99 (95%CI:0.99-0.99) at 0.10 Hz. This review summarizes clinical findings, discusses the pros/cons of the 11 unique driven techniques included, and provides recommendations for future investigations into the unique physiological intricacies of dCA.
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Affiliation(s)
- Joel S Burma
- Cerebrovascular Concussion Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
- Integrated Concussion Research Program, University of Calgary, Calgary, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Canada
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada
| | - Marc-Antoine Roy
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada
| | - Courtney M Kennedy
- Cerebrovascular Concussion Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
- Integrated Concussion Research Program, University of Calgary, Calgary, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Canada
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada
| | - Lawrence Labrecque
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada
| | - Patrice Brassard
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada
| | - Jonathan D Smirl
- Cerebrovascular Concussion Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
- Integrated Concussion Research Program, University of Calgary, Calgary, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Canada
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada
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2
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Butters E, Srinivasan S, O'Brien JT, Su L, Bale G. A promising tool to explore functional impairment in neurodegeneration: A systematic review of near-infrared spectroscopy in dementia. Ageing Res Rev 2023; 90:101992. [PMID: 37356550 DOI: 10.1016/j.arr.2023.101992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Revised: 06/15/2023] [Accepted: 06/22/2023] [Indexed: 06/27/2023]
Abstract
This systematic review aimed to evaluate previous studies which used near-infrared spectroscopy (NIRS) in dementia given its suitability as a diagnostic and investigative tool in this population. From 800 identified records which used NIRS in dementia and prodromal stages, 88 studies were evaluated which employed a range of tasks testing memory (29), word retrieval (24), motor (8) and visuo-spatial function (4), and which explored the resting state (32). Across these domains, dementia exhibited blunted haemodynamic responses, often localised to frontal regions of interest, and a lack of task-appropriate frontal lateralisation. Prodromal stages, such as mild cognitive impairment, revealed mixed results. Reduced cognitive performance accompanied by either diminished functional responses or hyperactivity was identified, the latter suggesting a compensatory response not present at the dementia stage. Despite clear evidence of alterations in brain oxygenation in dementia and prodromal stages, a consensus as to the nature of these changes is difficult to reach. This is likely partially due to the lack of standardisation in optical techniques and processing methods for the application of NIRS to dementia. Further studies are required exploring more naturalistic settings and a wider range of dementia subtypes.
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Affiliation(s)
- Emilia Butters
- Department of Electrical Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UK; Department of Psychiatry, School of Clinical Medicine, University of Cambridge, Cambridge, UK.
| | - Sruthi Srinivasan
- Department of Electrical Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UK
| | - John T O'Brien
- Department of Psychiatry, School of Clinical Medicine, University of Cambridge, Cambridge, UK
| | - Li Su
- Department of Psychiatry, School of Clinical Medicine, University of Cambridge, Cambridge, UK; Department of Neuroscience, University of Sheffield, 385a Glossop Rd, Broomhall, Sheffield S10 2HQ, UK
| | - Gemma Bale
- Department of Physics, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0FA, UK
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Heutz R, Claassen J, Feiner S, Davies A, Gurung D, Panerai RB, Heus RD, Beishon LC. Dynamic cerebral autoregulation in Alzheimer's disease and mild cognitive impairment: A systematic review. J Cereb Blood Flow Metab 2023:271678X231173449. [PMID: 37125762 PMCID: PMC10369144 DOI: 10.1177/0271678x231173449] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Dynamic cerebral autoregulation (dCA) is a key mechanism that regulates cerebral blood flow (CBF) in response to transient changes in blood pressure (BP). Impairment of dCA could increase vulnerability to hypertensive vascular damage, but also to BP lowering effects of antihypertensive treatment. The literature remains conflicted on whether dCA is altered in Alzheimer's disease (AD) and mild cognitive impairment (MCI). We summarized available data on dCA in AD and MCI, by searching PubMed, Embase, PsycINFO and Web of Science databases (inception-January 2022). Eight studies (total n = 443) were included in the qualitative synthesis of which seven were eligible for meta-analysis. All studies used Transcranial Doppler (TCD) ultrasonography and transfer function analysis or the autoregulatory index to assess dCA during spontaneous or induced BP fluctuations. Meta-analysis indicated no significant difference between AD, MCI and healthy controls in dCA parameters for spontaneous fluctuations. For induced fluctuations, the available data were limited, but indicative of at least preserved and possibly better autoregulatory functioning in AD and MCI compared to controls. In summary, current evidence does not suggest poorer dCA efficiency in AD or MCI. Further work is needed to investigate dCA in dementia with induced fluctuations controlling for changes in end-tidal carbon dioxide.
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Affiliation(s)
- Rachel Heutz
- Radboud University Medical Center, Donders Institute for Brain Cognition and Behaviour, Department of Geriatric Medicine, Radboudumc Alzheimer Center, Nijmegen, The Netherlands
| | - Jurgen Claassen
- Radboud University Medical Center, Donders Institute for Brain Cognition and Behaviour, Department of Geriatric Medicine, Radboudumc Alzheimer Center, Nijmegen, The Netherlands
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
| | - Sanne Feiner
- Radboud University Medical Center, Donders Institute for Brain Cognition and Behaviour, Department of Geriatric Medicine, Radboudumc Alzheimer Center, Nijmegen, The Netherlands
| | - Aaron Davies
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
| | - Dewakar Gurung
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
| | - Ronney B Panerai
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
- NIHR Leicester Biomedical Research Centre, British Heart Foundation Cardiovascular Research Centre, Glenfield Hospital, Leicester, UK
| | - Rianne de Heus
- Radboud University Medical Center, Donders Institute for Brain Cognition and Behaviour, Department of Geriatric Medicine, Radboudumc Alzheimer Center, Nijmegen, The Netherlands
| | - Lucy C Beishon
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
- NIHR Leicester Biomedical Research Centre, British Heart Foundation Cardiovascular Research Centre, Glenfield Hospital, Leicester, UK
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Kapadia A, Billimoria K, Desai P, Grist JT, Heyn C, Maralani P, Symons S, Zaccagna F. Hypoperfusion Precedes Tau Deposition in the Entorhinal Cortex: A Retrospective Evaluation of ADNI-2 Data. J Clin Neurol 2023; 19:131-137. [PMID: 36647226 PMCID: PMC9982189 DOI: 10.3988/jcn.2022.0088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 08/01/2022] [Accepted: 08/03/2022] [Indexed: 01/28/2023] Open
Abstract
BACKGROUND AND PURPOSE Tau deposition in the entorhinal cortex is the earliest pathological feature of Alzheimer's disease (AD). However, this feature has also been observed in cognitively normal (CN) individuals and those with mild cognitive impairment (MCI). The precise pathophysiology for the development of tau deposition remains unclear. We hypothesized that reduced cerebral perfusion is associated with the development of tau deposition. METHODS A subset of the Alzheimer's Disease Neuroimaging Initiative data set was utilized. Included patients had undergone arterial spin labeling perfusion MRI along with [18F]flortaucipir tau PET at baseline, within 1 year of the MRI, and a follow-up at 6 years. The association between baseline cerebral blood flow (CBF) and the baseline and 6-year tau PET was assessed. Univariate and multivariate linear modeling was performed, with p<0.05 indicating significance. RESULTS Significant differences were found in the CBF between patients with AD and MCI, and CN individuals in the left entorhinal cortex (p=0.013), but not in the right entorhinal cortex (p=0.076). The difference in maximum standardized uptake value ratio between 6 years and baseline was significantly and inversely associated with the baseline mean CBF (p=0.042, R²=0.54) in the left entorhinal cortex but not the right entorhinal cortex. Linear modeling demonstrated that CBF predicted 6-year tau deposition (p=0.015, R²=0.11). CONCLUSIONS The results of this study suggest that a reduction in CBF at the entorhinal cortex precedes tau deposition. Further work is needed to understand the mechanism underlying tau deposition in aging and disease.
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Affiliation(s)
- Anish Kapadia
- Division of Neuroradiology, Department of Medical Imaging, University of Toronto, Toronto, ON, Canada.,Division of Neuroradiology, Department of Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, ON, Canada.
| | - Krish Billimoria
- MD Program, Temetry Faculty of Medicine, University of Toronto, Toronto, ON, Canada
| | - Prarthna Desai
- Department of Medicine, Maharaja Sayajirao University of Baroda, Vadodara, India
| | - James T. Grist
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, UK.,Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, Oxford, UK.,Department of Radiology, Oxford University Hospitals Trust, Oxford, UK.,Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham, UK
| | - Chris Heyn
- Division of Neuroradiology, Department of Medical Imaging, University of Toronto, Toronto, ON, Canada.,Division of Neuroradiology, Department of Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, ON, Canada
| | - Pejman Maralani
- Division of Neuroradiology, Department of Medical Imaging, University of Toronto, Toronto, ON, Canada.,Division of Neuroradiology, Department of Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, ON, Canada
| | - Sean Symons
- Division of Neuroradiology, Department of Medical Imaging, University of Toronto, Toronto, ON, Canada.,Division of Neuroradiology, Department of Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, ON, Canada
| | - Fulvio Zaccagna
- Division of Neuroradiology, Department of Medical Imaging, University of Toronto, Toronto, ON, Canada
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5
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Keles HO, Karakulak EZ, Hanoglu L, Omurtag A. Screening for Alzheimer's disease using prefrontal resting-state functional near-infrared spectroscopy. Front Hum Neurosci 2022; 16:1061668. [PMID: 36518566 PMCID: PMC9742284 DOI: 10.3389/fnhum.2022.1061668] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Accepted: 11/01/2022] [Indexed: 08/10/2023] Open
Abstract
INTRODUCTION Alzheimer's disease (AD) is neurodegenerative dementia that causes neurovascular dysfunction and cognitive impairment. Currently, 50 million people live with dementia worldwide, and there are nearly 10 million new cases every year. There is a need for relatively less costly and more objective methods of screening and early diagnosis. METHODS Functional near-infrared spectroscopy (fNIRS) systems are a promising solution for the early Detection of AD. For a practical clinically relevant system, a smaller number of optimally placed channels are clearly preferable. In this study, we investigated the number and locations of the best-performing fNIRS channels measuring prefrontal cortex activations. Twenty-one subjects diagnosed with AD and eighteen healthy controls were recruited for the study. RESULTS We have shown that resting-state fNIRS recordings from a small number of prefrontal locations provide a promising methodology for detecting AD and monitoring its progression. A high-density continuous-wave fNIRS system was first used to verify the relatively lower hemodynamic activity in the prefrontal cortical areas observed in patients with AD. By using the episode averaged standard deviation of the oxyhemoglobin concentration changes as features that were fed into a Support Vector Machine; we then showed that the accuracy of subsets of optical channels in predicting the presence and severity of AD was significantly above chance. The results suggest that AD can be detected with a 0.76 sensitivity score and a 0.68 specificity score while the severity of AD could be detected with a 0.75 sensitivity score and a 0.72 specificity score with ≤5 channels. DISCUSSION These scores suggest that fNIRS is a viable technology for conveniently detecting and monitoring AD as well as investigating underlying mechanisms of disease progression.
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Affiliation(s)
- Hasan Onur Keles
- Department of Biomedical Engineering, Ankara University, Ankara, Turkey
| | | | - Lutfu Hanoglu
- Department of Neurology, School of Medicine, Istanbul Medipol University, Istanbul, Turkey
| | - Ahmet Omurtag
- Department of Engineering, Nottingham Trent University, Nottingham, United Kingdom
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6
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Anderson GK, Rickards CA. The potential therapeutic benefits of low frequency haemodynamic oscillations. J Physiol 2022; 600:3905-3919. [PMID: 35883272 PMCID: PMC9444954 DOI: 10.1113/jp282605] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Accepted: 07/22/2022] [Indexed: 11/08/2022] Open
Abstract
Haemodynamic oscillations occurring at frequencies below the rate of respiration have been observed experimentally for more than a century. Much of the research regarding these oscillations, observed in arterial pressure and blood flow, has focused on mechanisms of generation and methods of quantification. However, examination of the physiological role of these oscillations has been limited. Multiple studies have demonstrated that oscillations in arterial pressure and blood flow are associated with the protection in tissue oxygenation or functional capillary density during conditions of reduced tissue perfusion. There is also evidence that oscillatory blood flow can improve clearance of interstitial fluid, with a growing number of studies demonstrating a role for oscillatory blood flow to aid in clearance of debris from the brain. The therapeutic potential of these haemodynamic oscillations is an important new area of research which may have beneficial impact in treating conditions such as stroke, cardiac arrest, blood loss injuries, sepsis, or even Alzheimer's disease and vascular dementia.
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Affiliation(s)
- Garen K Anderson
- Cerebral & Cardiovascular Physiology Laboratory, Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Caroline A Rickards
- Cerebral & Cardiovascular Physiology Laboratory, Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
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7
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Gruszecka A, Waskow M, Malkiewicz MA, Neary JP, Singh J, Teckchandani T, Kratzig GP, Wszedybyl-Winklewska M, Frydrychowski AF, Rumiński J, Głowacka N, Lass P, Winklewski PJ, Gruszecki M. Mild poikilocapnic hypoxia increases very low frequency haemoglobin oxygenation oscillations in prefrontal cortex. Biol Res 2021; 54:39. [PMID: 34906247 PMCID: PMC8669425 DOI: 10.1186/s40659-021-00362-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Accepted: 11/30/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The aim of the study was to investigate the effect of mild cerebral hypoxia on haemoglobin oxygenation (HbO2), cerebrospinal fluid dynamics and cardiovascular physiology. To achieve this goal, four signals were recorded simultaneously: blood pressure, heart rate / electrocardiogram, HbO2 from right hemisphere and changes of subarachnoid space (SAS) width from left hemisphere. Signals were registered from 30 healthy, young participants (2 females and 28 males, body mass index = 24.5 ± 2.3 kg/m2, age 30.8 ± 13.4 years). RESULTS We analysed the recorded signals using wavelet transform and phase coherence. We demonstrated for the first time that in healthy subjects exposed to mild poikilokapnic hypoxia there were increases in very low frequency HbO2 oscillations (< 0.052 Hz) in prefrontal cortex. Additionally, SAS fluctuation diminished in the whole frequency range which could be explained by brain oedema. CONCLUSIONS Consequently the study provides insight into mechanisms governing brain response to a mild hypoxic challenge. Our study supports the notion that HbO2 and SAS width monitoring might be beneficial for patients with acute lung disease.
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Affiliation(s)
- Agnieszka Gruszecka
- Department of Radiology Informatics and Statistics, Medical University of Gdansk, Tuwima Str. 15, 80-210, Gdansk, Poland
| | - Monika Waskow
- Institute of Health Sciences, Pomeranian University of Slupsk, Slupsk, Poland
| | - Marta A Malkiewicz
- Department of Human Physiology, Applied Cognitive Neuroscience Lab, Medical University of Gdansk, Gdansk, Poland.,Department of Psychiatry, Medical University of Gdansk, Gdansk, Poland
| | - J Patrick Neary
- Faculty of Kinesiology and Health Studies, University of Regina, Regina, Canada
| | - Jyotpal Singh
- Faculty of Kinesiology and Health Studies, University of Regina, Regina, Canada
| | - Taylor Teckchandani
- Faculty of Kinesiology and Health Studies, University of Regina, Regina, Canada
| | | | | | | | - Jacek Rumiński
- Department of Biomedical Engineering, Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Poland
| | - Natalia Głowacka
- Department of Biomedical Engineering, Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Poland
| | - Piotr Lass
- Department of Nuclear Medicine, Medical University of Gdansk, Gdansk, Poland
| | - Pawel J Winklewski
- Department of Human Physiology, Medical University of Gdansk, Gdansk, Poland
| | - Marcin Gruszecki
- Department of Radiology Informatics and Statistics, Medical University of Gdansk, Tuwima Str. 15, 80-210, Gdansk, Poland. .,Department of Biomedical Engineering, Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Poland.
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8
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Kalaria RN, Sepulveda-Falla D. Cerebral Small Vessel Disease in Sporadic and Familial Alzheimer Disease. THE AMERICAN JOURNAL OF PATHOLOGY 2021; 191:1888-1905. [PMID: 34331941 PMCID: PMC8573679 DOI: 10.1016/j.ajpath.2021.07.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Revised: 06/15/2021] [Accepted: 07/02/2021] [Indexed: 01/26/2023]
Abstract
Alzheimer disease (AD) is the most common cause of dementia. Biological definitions of AD are limited to the cerebral burden of amyloid β plaques, neurofibrillary pathology, and neurodegeneration. However, current evidence suggests that various features of small vessel disease (SVD) are part of and covertly modify both sporadic and familial AD. Neuroimaging studies suggest that white matter hyperintensities explained by vascular mechanisms occurs frequently in the AD spectrum. Recent advances have further emphasized that frontal periventricular and posterior white matter hyperintensities are associated with cerebral amyloid angiopathy in familial AD. Although whether SVD markers precede the classically recognized biomarkers of disease is debatable, post-mortem studies show that SVD pathology incorporating small cortical and subcortical infarcts, microinfarcts, microbleeds, perivascular spacing, and white matter attenuation is commonly found in sporadic as well as in mutation carriers with confirmed familial AD. Age-related cerebral vessel pathologies such as arteriolosclerosis and cerebral amyloid angiopathy modify progression or worsen risk by shifting the threshold for cognitive impairment and AD dementia. The incorporation of SVD as a biomarker is warranted in the biological definition of AD. Therapeutic interventions directly reducing the burden of brain amyloid β have had no major impact on the disease or delaying cognitive deterioration, but lowering the risk of vascular disease seems the only rational approach to tackle both early- and late-onset AD dementia.
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Affiliation(s)
- Rajesh N Kalaria
- Neurovascular Research Group, Translational and Clinical Research Institute, Newcastle University, Newcastle upon Tyne, United Kingdom; Department of Human Anatomy, College of Health Sciences, University of Nairobi, Nairobi, Kenya.
| | - Diego Sepulveda-Falla
- Institute of Neuropathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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9
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Nardelli M, Catrambone V, Grandi G, Banfi T, Bruno RM, Scilingo EP, Faraguna U, Valenza G. Activation of brain-heart axis during REM sleep: a trigger for dreaming. Am J Physiol Regul Integr Comp Physiol 2021; 321:R951-R959. [PMID: 34704848 DOI: 10.1152/ajpregu.00306.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dreams may be recalled after awakening from sleep following a defined electroencephalographic pattern that involves local decreases in low-frequency activity in the posterior cortical regions. While a dreaming experience implies bodily changes at many organ-, system-, and timescale-levels, the entity and causal role of such peripheral changes in a conscious dream experience are unknown. We performed a comprehensive, causal, multivariate analysis of physiological signals acquired during REM sleep at night, including high-density EEG and peripheral dynamics including electrocardiography and blood pressure. In this preliminary study, we investigated multiple recalls and non-recalls of dream experiences using data from nine healthy volunteers. The aim was not only to investigate the changes in central and autonomic dynamics associated with dream recalls and non-recalls, but also to characterize the central-peripheral dynamical and (causal) directional interactions, and the temporal relations of the related arousals upon awakening. We uncovered a brain-body network that drives a conscious dreaming experience that acts with specific interaction and time delays. Such a network is sustained by the blood pressure dynamics and the increasing functional information transfer from the neural heartbeat regulation to the brain. We conclude that bodily changes play a crucial and causative role in a conscious dream experience during REM sleep.
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Affiliation(s)
- Mimma Nardelli
- Bioengineering and Robotics Research Centre E. Piaggio and Department of Information Engineering, University of Pisa, Italy
| | - Vincenzo Catrambone
- Bioengineering and Robotics Research Centre E. Piaggio and Department of Information Engineering, University of Pisa, Italy
| | - Giulia Grandi
- Department of Translational Research and of New Surgical and Medical Technologies, University of Pisa, Italy
| | - Tommaso Banfi
- Department of Translational Research and of New Surgical and Medical Technologies, University of Pisa, Italy
| | - Rosa Maria Bruno
- INSERM U970 Team 7, Paris Cardiovascular Research Centre - PARCC, University Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Enzo Pasquale Scilingo
- Bioengineering and Robotics Research Centre E. Piaggio and Department of Information Engineering, University of Pisa, Italy
| | - Ugo Faraguna
- Department of Translational Research and of New Surgical and Medical Technologies, University of Pisa, Italy.,Department of Developmental Neuroscience, IRCCS Fondazione Stella Maris, Pisa, Italy
| | - Gaetano Valenza
- Bioengineering and Robotics Research Centre E. Piaggio and Department of Information Engineering, University of Pisa, Italy
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10
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Claassen JAHR, Thijssen DHJ, Panerai RB, Faraci FM. Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation. Physiol Rev 2021; 101:1487-1559. [PMID: 33769101 PMCID: PMC8576366 DOI: 10.1152/physrev.00022.2020] [Citation(s) in RCA: 275] [Impact Index Per Article: 91.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
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.
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Affiliation(s)
- Jurgen A H R Claassen
- Department of Geriatrics, Radboud University Medical Center, Donders Institute for Brain, Cognition, and Behaviour, Nijmegen, The Netherlands
| | - Dick H J Thijssen
- Department of Physiology, Radboud Institute for Health Sciences, Nijmegen, The Netherlands
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
| | - Ronney B Panerai
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
- >National Institute for Health Research Leicester Biomedical Research Centre, University of Leicester, Leicester, United Kingdom
| | - Frank M Faraci
- Departments of Internal Medicine, Neuroscience, and Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, Iowa
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11
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Matsukawa K, Asahara R, Uzumaki M, Hashiguchi Y, Ishii K, Wang J, Smith SA. Central command-related increases in blood velocity of anterior cerebral artery and prefrontal oxygenation at the onset of voluntary tapping. Am J Physiol Heart Circ Physiol 2021; 321:H518-H531. [PMID: 34328343 DOI: 10.1152/ajpheart.00062.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The anterior cerebral artery (ACA) supplies blood predominantly to the frontal lobe including the prefrontal cortex. Our laboratory reported that prefrontal oxygenated-hemoglobin concentration (Oxy-Hb) increased before and at exercise onset, as long as exercise is arbitrarily started. Moreover, the increased prefrontal oxygenation seems independent of both exercise intensity and muscle mass. If so, mean blood velocity of the ACA (ACABV) should increase with "very light motor effort," concomitantly with the preexercise and initial increase in prefrontal Oxy-Hb. This study aimed to examine the responses in ACABV and vascular conductance index (ACAVCI) of the ACA as well as prefrontal Oxy-Hb during arbitrary or cued finger tapping in 12 subjects, an activity with a Borg scale perceived exertion rating of 7 (median). With arbitrary start, ACABV increased at tapping onset (14 ± 9%) via an elevation in ACAVCI. Likewise, prefrontal Oxy-Hb increased at the onset of tapping with a time course resembling that of ACABV. A positive cross correlation between the initial changes in ACABV and prefrontal Oxy-Hb was found significant in 67% of subjects, having a time lag of 2 s, whereas a positive linear regression between them was significant in 75% of subjects. When tapping was forced to start by cue, the initial increases in ACABV, ACAVCI, and prefrontal Oxy-Hb were delayed and blunted as compared with an arbitrary start. Thus, active vasodilatation of the ACA vascular bed occurs at tapping onset, as long as tapping is arbitrarily started, and contributes to immediate increases in blood flow and prefrontal oxygenation.NEW & NOTEWORTHY Anterior cerebral artery blood velocity and vascular conductance index along with prefrontal oxygenated-hemoglobin concentration all increased at the onset of finger tapping, peaking immediately after tapping onset, as long as tapping was arbitrarily started. Positive cross correlation and linear regression between the increases in ACABV and prefrontal Oxy-Hb were significant in 67%-75% of subjects. Active vasodilatation of the ACA vascular bed occurs with arbitrary tapping onset and contributes to increased ACABV and prefrontal oxygenation.
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Affiliation(s)
- Kanji Matsukawa
- Department of Integrative Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan.,Department of Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Ryota Asahara
- Human Informatics and Interaction Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
| | - Minami Uzumaki
- Department of Integrative Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Yoshiki Hashiguchi
- Department of Integrative Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Kei Ishii
- Human Informatics and Interaction Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
| | - Jijia Wang
- Department of Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Scott A Smith
- Department of Applied Clinical Research, University of Texas Southwestern Medical Center, Dallas, Texas
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12
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Palmer JC, Tayler HM, Dyer L, Kehoe PG, Paton JFR, Love S. Zibotentan, an Endothelin A Receptor Antagonist, Prevents Amyloid-β-Induced Hypertension and Maintains Cerebral Perfusion. J Alzheimers Dis 2021; 73:1185-1199. [PMID: 31903990 PMCID: PMC7081103 DOI: 10.3233/jad-190630] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Cerebral blood flow is reduced in Alzheimer’s disease (AD), which is associated with mid-life hypertension. In people with increased cerebral vascular resistance due to vertebral artery or posterior communicating artery hypoplasia, there is evidence that hypertension develops as a protective mechanism to maintain cerebral perfusion. In AD, amyloid-β (Aβ) accumulation may similarly raise cerebral vascular resistance by upregulation of the cerebral endothelin system. The level of endothelin-1 in brain tissue correlates positively with Aβ load and negatively with markers of cerebral hypoperfusion such as increased vascular endothelial growth factor. We previously showed that cerebroventricular infusion of Aβ40 exacerbated pre-existing hypertension in Dahl rats. We have investigated the effects of 28-day cerebral infusion of Aβ40 on blood pressure and heart rate and their variability; carotid flow; endothelin-1; and markers of cerebral oxygenation, in the (normotensive) Wistar rat, and the modulatory influence of the endothelin A receptor antagonist Zibotentan (ZD4054). Cerebral infusion of Aβ caused progressive rise in blood pressure (p < 0.0001) (paired t-test: increase of 3 (0.1–5.6) mmHg (p = 0.040)), with evidence of reduced baroreflex responsiveness, and accumulation of Aβ and elevated endothelin-1 in the vicinity of the infusion. Oral Zibotentan (3 mg/kg/d, administered for 31 d) abrogated the effects of Aβ40 infusion on baroreflex responsiveness and blood pressure, which declined, although without reduction in carotid blood flow, and Zibotentan caused uncoupling of the positive linear relationship between endothelin-1 and vascular endothelial growth factor, which as a sensor of tissue oxygenation would be expected to increase if there were hypoperfusion.
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Affiliation(s)
- Jennifer C Palmer
- Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
| | - Hannah M Tayler
- Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
| | - Laurence Dyer
- Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
| | - Patrick G Kehoe
- Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
| | - Julian F R Paton
- Department of Physiology, Faculty of Medical & Health Sciences, University of Auckland, New Zealand
| | - Seth Love
- Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
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13
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Liu X, Akiyoshi K, Nakano M, Brady K, Bush B, Nadkarni R, Venkataraman A, Koehler RC, Lee JK, Hogue CW, Czosnyka M, Smielewski P, Brown CH. Determining Thresholds for Three Indices of Autoregulation to Identify the Lower Limit of Autoregulation During Cardiac Surgery. Crit Care Med 2021; 49:650-660. [PMID: 33278074 PMCID: PMC7979429 DOI: 10.1097/ccm.0000000000004737] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES Monitoring cerebral autoregulation may help identify the lower limit of autoregulation in individual patients. Mean arterial blood pressure below lower limit of autoregulation appears to be a risk factor for postoperative acute kidney injury. Cerebral autoregulation can be monitored in real time using correlation approaches. However, the precise thresholds for different cerebral autoregulation indexes that identify the lower limit of autoregulation are unknown. We identified thresholds for intact autoregulation in patients during cardiopulmonary bypass surgery and examined the relevance of these thresholds to postoperative acute kidney injury. DESIGN A single-center retrospective analysis. SETTING Tertiary academic medical center. PATIENTS Data from 59 patients was used to determine precise cerebral autoregulation thresholds for identification of the lower limit of autoregulation. These thresholds were validated in a larger cohort of 226 patients. METHODS AND MAIN RESULTS Invasive mean arterial blood pressure, cerebral blood flow velocities, regional cortical oxygen saturation, and total hemoglobin were recorded simultaneously. Three cerebral autoregulation indices were calculated, including mean flow index, cerebral oximetry index, and hemoglobin volume index. Cerebral autoregulation curves for the three indices were plotted, and thresholds for each index were used to generate threshold- and index-specific lower limit of autoregulations. A reference lower limit of autoregulation could be identified in 59 patients by plotting cerebral blood flow velocity against mean arterial blood pressure to generate gold-standard Lassen curves. The lower limit of autoregulations defined at each threshold were compared with the gold-standard lower limit of autoregulation determined from Lassen curves. The results identified the following thresholds: mean flow index (0.45), cerebral oximetry index (0.35), and hemoglobin volume index (0.3). We then calculated the product of magnitude and duration of mean arterial blood pressure less than lower limit of autoregulation in a larger cohort of 226 patients. When using the lower limit of autoregulations identified by the optimal thresholds above, mean arterial blood pressure less than lower limit of autoregulation was greater in patients with acute kidney injury than in those without acute kidney injury. CONCLUSIONS This study identified thresholds of intact and impaired cerebral autoregulation for three indices and showed that mean arterial blood pressure below lower limit of autoregulation is a risk factor for acute kidney injury after cardiac surgery.
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Affiliation(s)
- Xiuyun Liu
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Kei Akiyoshi
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Mitsunori Nakano
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- Saitama Medical Center, Jichi Medical University, Saitama, Japan 330-8503
| | - Ken Brady
- Northwestern University, Ann & Robert H. Lurie Children’s Hospital of Chicago, Department of Anesthesiology, Chicago, Illinois, USA
| | - Brian Bush
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Rohan Nadkarni
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, USA
| | - Archana Venkataraman
- Department of Electrical and Computer Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, Maryland, USA
| | - Raymond C. Koehler
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Jennifer K. Lee
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Charles W. Hogue
- Department of Anesthesiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Marek Czosnyka
- Brain Physics Laboratory, Division of Neurosurgey, Cambridge University Hospitals, University of Cambridge, Cambridge, UK
- Institute of Electronic Systems, Warsaw University of Technology, Warsaw, Poland
| | - Peter Smielewski
- Brain Physics Laboratory, Division of Neurosurgey, Cambridge University Hospitals, University of Cambridge, Cambridge, UK
| | - Charles H. Brown
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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14
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Kapadia A, Mirrahimi A, Dmytriw AA. Intersection between sleep and neurovascular coupling as the driving pathophysiology of Alzheimer’s disease. Med Hypotheses 2020; 144:110283. [DOI: 10.1016/j.mehy.2020.110283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2020] [Revised: 09/05/2020] [Accepted: 09/13/2020] [Indexed: 10/23/2022]
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15
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Bonilauri A, Sangiuliano Intra F, Pugnetti L, Baselli G, Baglio F. A Systematic Review of Cerebral Functional Near-Infrared Spectroscopy in Chronic Neurological Diseases-Actual Applications and Future Perspectives. Diagnostics (Basel) 2020; 10:E581. [PMID: 32806516 PMCID: PMC7459924 DOI: 10.3390/diagnostics10080581] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 08/06/2020] [Accepted: 08/07/2020] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND The management of people affected by age-related neurological disorders requires the adoption of targeted and cost-effective interventions to cope with chronicity. Therapy adaptation and rehabilitation represent major targets requiring long-term follow-up of neurodegeneration or, conversely, the promotion of neuroplasticity mechanisms. However, affordable and reliable neurophysiological correlates of cerebral activity to be used throughout treatment stages are often lacking. The aim of this systematic review is to highlight actual applications of functional Near-Infrared Spectroscopy (fNIRS) as a versatile optical neuroimaging technology for investigating cortical hemodynamic activity in the most common chronic neurological conditions. METHODS We reviewed studies investigating fNIRS applications in Parkinson's Disease (PD), Alzheimer's Disease (AD) and Mild Cognitive Impairment (MCI) as those focusing on motor and cognitive impairment in ageing and Multiple Sclerosis (MS) as the most common chronic neurological disease in young adults. The literature search was conducted on NCBI PubMed and Web of Science databases by PRISMA guidelines. RESULTS We identified a total of 63 peer-reviewed articles. The AD spectrum is the most investigated pathology with 40 articles ranging from the traditional monitoring of tissue oxygenation to the analysis of functional resting-state conditions or cognitive functions by means of memory and verbal fluency tasks. Conversely, applications in PD (12 articles) and MS (11 articles) are mainly focused on the characterization of motor functions and their association with dual-task conditions. The most investigated cortical area is the prefrontal cortex, since reported to play an important role in age-related compensatory mechanism and neurofunctional changes associated to these chronic neurological conditions. Interestingly, only 9 articles applied a longitudinal approach. CONCLUSION The results indicate that fNIRS is mainly employed for the cross-sectional characterization of the clinical phenotypes of these pathologies, whereas data on its utility for longitudinal monitoring as surrogate biomarkers of disease progression and rehabilitation effects are promising but still lacking.
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Affiliation(s)
- Augusto Bonilauri
- Department of Electronics, Information and Bioengineering, Politecnico di Milano, 20133 Milan, Italy; (A.B.); (G.B.)
| | - Francesca Sangiuliano Intra
- IRCCS Fondazione Don Carlo Gnocchi ONLUS, CADITER, 20148 Milan, Italy; (L.P.); (F.B.)
- Faculty of Education, Free University of Bozen-Bolzano, 39100 Bolzano, Italy
| | - Luigi Pugnetti
- IRCCS Fondazione Don Carlo Gnocchi ONLUS, CADITER, 20148 Milan, Italy; (L.P.); (F.B.)
| | - Giuseppe Baselli
- Department of Electronics, Information and Bioengineering, Politecnico di Milano, 20133 Milan, Italy; (A.B.); (G.B.)
| | - Francesca Baglio
- IRCCS Fondazione Don Carlo Gnocchi ONLUS, CADITER, 20148 Milan, Italy; (L.P.); (F.B.)
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16
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Han D, Li H, Pan S, Xie S, Deryck Y, Luo Y, Li J, Ou-Yang C. Measuring Cerebral Carbon Dioxide Reactivity With Transcranial Doppler and Near-Infrared Spectroscopy in Children With Ventricular Septal Defect. J Cardiothorac Vasc Anesth 2020; 34:344-348. [DOI: 10.1053/j.jvca.2019.06.040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2019] [Revised: 06/22/2019] [Accepted: 06/26/2019] [Indexed: 11/11/2022]
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17
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Sanders ML, Elting JWJ, Panerai RB, Aries M, Bor-Seng-Shu E, Caicedo A, Chacon M, Gommer ED, Van Huffel S, Jara JL, Kostoglou K, Mahdi A, Marmarelis VZ, Mitsis GD, Müller M, Nikolic D, Nogueira RC, Payne SJ, Puppo C, Shin DC, Simpson DM, Tarumi T, Yelicich B, Zhang R, Claassen JAHR. Dynamic Cerebral Autoregulation Reproducibility Is Affected by Physiological Variability. Front Physiol 2019; 10:865. [PMID: 31354518 PMCID: PMC6634255 DOI: 10.3389/fphys.2019.00865] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 06/20/2019] [Indexed: 11/24/2022] Open
Abstract
Parameters describing dynamic cerebral autoregulation (DCA) have limited reproducibility. In an international, multi-center study, we evaluated the influence of multiple analytical methods on the reproducibility of DCA. Fourteen participating centers analyzed repeated measurements from 75 healthy subjects, consisting of 5 min of spontaneous fluctuations in blood pressure and cerebral blood flow velocity signals, based on their usual methods of analysis. DCA methods were grouped into three broad categories, depending on output types: (1) transfer function analysis (TFA); (2) autoregulation index (ARI); and (3) correlation coefficient. Only TFA gain in the low frequency (LF) band showed good reproducibility in approximately half of the estimates of gain, defined as an intraclass correlation coefficient (ICC) of >0.6. None of the other DCA metrics had good reproducibility. For TFA-like and ARI-like methods, ICCs were lower than values obtained with surrogate data (p < 0.05). For TFA-like methods, ICCs were lower for the very LF band (gain 0.38 ± 0.057, phase 0.17 ± 0.13) than for LF band (gain 0.59 ± 0.078, phase 0.39 ± 0.11, p ≤ 0.001 for both gain and phase). For ARI-like methods, the mean ICC was 0.30 ± 0.12 and for the correlation methods 0.24 ± 0.23. Based on comparisons with ICC estimates obtained from surrogate data, we conclude that physiological variability or non-stationarity is likely to be the main reason for the poor reproducibility of DCA parameters.
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Affiliation(s)
- Marit L Sanders
- Department of Geriatric Medicine, Radboudumc Alzheimer Center, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, Netherlands
| | - Jan Willem J Elting
- Department of Neurology, University Medical Center Groningen, Groningen, Netherlands
| | - Ronney B Panerai
- Department of Cardiovascular Sciences, NIHR Leicester Biomedical Research Centre, Glenfield Hospital, Leicester, United Kingdom
| | - Marcel Aries
- Department of Intensive Care, University of Maastricht, Maastricht University Medical Center, Maastricht, Netherlands
| | - Edson Bor-Seng-Shu
- Department of Neurology, Faculty of Medicine, Hospital das Clinicas University of São Paulo, São Paulo, Brazil
| | - Alexander Caicedo
- Department of Applied Mathematics and Computer Science, Faculty of Natural Sciences and Mathematics, Universidad del Rosario, Bogotá, Colombia
| | - Max Chacon
- Department of Engineering Informatics, Institute of Biomedical Engineering, University of Santiago, Santiago, Chile
| | - Erik D Gommer
- Department of Clinical Neurophysiology, Maastricht University Medical Centre, Maastricht, Netherlands
| | - Sabine Van Huffel
- Department of Electronic Engineering (ESAT), Stadius Center for Dynamical Systems, Signal Processing and Data Analytics, Katholieke Universiteit Leuven, Leuven, Belgium.,Interuniversity Microelectronics Centre, Leuven, Belgium
| | - José L Jara
- Department of Engineering Informatics, Institute of Biomedical Engineering, University of Santiago, Santiago, Chile
| | - Kyriaki Kostoglou
- Department of Electrical, Computer and Software Engineering, McGill University, Montreal, QC, Canada
| | - Adam Mahdi
- Department of Engineering Science, University of Oxford, Oxford, United Kingdom
| | - Vasilis Z Marmarelis
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States
| | - Georgios D Mitsis
- Department of Bioengineering, McGill University, Montreal, QC, Canada
| | - Martin Müller
- Department of Neurology, Luzerner Kantonsspital, Luzern, Switzerland
| | - Dragana Nikolic
- Faculty of Engineering and the Environment, Institute of Sound and Vibration Research, University of Southampton, Southampton, United Kingdom
| | - Ricardo C Nogueira
- Department of Neurology, Faculty of Medicine, Hospital das Clinicas University of São Paulo, São Paulo, Brazil
| | - Stephen J Payne
- Department of Engineering Science, University of Oxford, Oxford, United Kingdom
| | - Corina Puppo
- Departamento de Emergencia, Hospital de Clínicas, Universidad de la República, Montevideo, Uruguay
| | - Dae C Shin
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States
| | - David M Simpson
- Faculty of Engineering and the Environment, Institute of Sound and Vibration Research, University of Southampton, Southampton, United Kingdom
| | - Takashi Tarumi
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Bernardo Yelicich
- Departamento de Emergencia, Hospital de Clínicas, Universidad de la República, Montevideo, Uruguay
| | - Rong Zhang
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Jurgen A H R Claassen
- Department of Geriatric Medicine, Radboudumc Alzheimer Center, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, Netherlands
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18
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Reduced spontaneous low frequency oscillations as measured with functional near-infrared spectroscopy in mild cognitive impairment. Brain Imaging Behav 2019; 13:283-292. [PMID: 29362991 DOI: 10.1007/s11682-018-9827-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Spontaneous low frequency oscillations (LFO) in functional imaging data have gained increased interest in the study of cognitive decline. Persons diagnosed with mild cognitive impairment (MCI) and Alzheimer's disease (AD) display alterations in their amount of LFO in various brain regions. This is commonly interpreted as disruptions in the autoregulation of the cerebral microvascular system. In the present study LFO (0,07-0,11 Hz) were measured with 52-channel near-infrared spectroscopy (NIRS) in 61 healthy elderly persons (70-76 years), 54 MCI subjects (70-76 years) and 25 healthy young controls (21-48 years) during rest over the frontal and the parietal cortex. Both MCI and healthy elderly controls showed less LFO in the frontal cortex as compared to young subjects. For the parietal cortex a decrease in LFO could be observed for the MCI group in comparison to healthy elderly subjects. Correlations of more LFO with worse performance in neuropsychological tests point to compensatory processes. LFO measured with NIRS might be especially suited for longitudinal studies aiming at predicting cognitive decline.
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19
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Sanders ML, Claassen JAHR, Aries M, Bor-Seng-Shu E, Caicedo A, Chacon M, Gommer ED, Van Huffel S, Jara JL, Kostoglou K, Mahdi A, Marmarelis VZ, Mitsis GD, Müller M, Nikolic D, Nogueira RC, Payne SJ, Puppo C, Shin DC, Simpson DM, Tarumi T, Yelicich B, Zhang R, Panerai RB, Elting JWJ. Reproducibility of dynamic cerebral autoregulation parameters: a multi-centre, multi-method study. Physiol Meas 2018; 39:125002. [PMID: 30523976 DOI: 10.1088/1361-6579/aae9fd] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
OBJECTIVE Different methods to calculate dynamic cerebral autoregulation (dCA) parameters are available. However, most of these methods demonstrate poor reproducibility that limit their reliability for clinical use. Inter-centre differences in study protocols, modelling approaches and default parameter settings have all led to a lack of standardisation and comparability between studies. We evaluated reproducibility of dCA parameters by assessing systematic errors in surrogate data resulting from different modelling techniques. APPROACH Fourteen centres analysed 22 datasets consisting of two repeated physiological blood pressure measurements with surrogate cerebral blood flow velocity signals, generated using Tiecks curves (autoregulation index, ARI 0-9) and added noise. For reproducibility, dCA methods were grouped in three broad categories: 1. Transfer function analysis (TFA)-like output; 2. ARI-like output; 3. Correlation coefficient-like output. For all methods, reproducibility was determined by one-way intraclass correlation coefficient analysis (ICC). MAIN RESULTS For TFA-like methods the mean (SD; [range]) ICC gain was 0.71 (0.10; [0.49-0.86]) and 0.80 (0.17; [0.36-0.94]) for VLF and LF (p = 0.003) respectively. For phase, ICC values were 0.53 (0.21; [0.09-0.80]) for VLF, and 0.92 (0.13; [0.44-1.00]) for LF (p < 0.001). Finally, ICC for ARI-like methods was equal to 0.84 (0.19; [0.41-0.94]), and for correlation-like methods, ICC was 0.21 (0.21; [0.056-0.35]). SIGNIFICANCE When applied to realistic surrogate data, free from the additional exogenous influences of physiological variability on cerebral blood flow, most methods of dCA modelling showed ICC values considerably higher than what has been reported for physiological data. This finding suggests that the poor reproducibility reported by previous studies may be mainly due to the inherent physiological variability of cerebral blood flow regulatory mechanisms rather than related to (stationary) random noise and the signal analysis methods.
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Affiliation(s)
- Marit L Sanders
- Department of Geriatric Medicine, Radboudumc Alzheimer Centre and Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands
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20
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Khaksari K, Blaney G, Sassaroli A, Krishnamurthy N, Pham T, Fantini S. Depth dependence of coherent hemodynamics in the human head. JOURNAL OF BIOMEDICAL OPTICS 2018; 23:1-9. [PMID: 30444084 PMCID: PMC6318717 DOI: 10.1117/1.jbo.23.12.121615] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Accepted: 10/29/2018] [Indexed: 05/03/2023]
Abstract
We report a near-infrared spectroscopy (NIRS) study of coherent hemodynamic oscillations measured on the human forehead at multiple source-detector distances (1 to 4 cm). The physiological source of the coherent hemodynamics is arterial blood pressure oscillations at a frequency of 0.1 Hz, induced by cyclic inflation (to a pressure of 200 mmHg) and deflation of two thigh cuffs wrapped around the subject's thighs. To interpret our results, we use a recently developed hemodynamic model and a phasor representation of the oscillations of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin concentrations in the tissue (phasors O, D, and T, respectively). The increase in the phase angle between D and O at larger source-detector separations is assigned to greater flow versus volume contributions and to a stronger blood flow autoregulation in deeper tissue (brain cortex) with respect to superficial tissue (scalp and skull). The relatively constant phase lag of T versus arterial blood pressure oscillations at all source-detector distances was assigned to competing effects from stronger autoregulation and smaller arterial-to-venous contributions in deeper tissue with respect to superficial tissue. We demonstrate the application of a hemodynamic model to interpret coherent hemodynamics measured with NIRS and to assess the different nature of shallow (extracerebral) versus deep (cerebral) tissue hemodynamics.
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Affiliation(s)
- Kosar Khaksari
- Tufts University, Department of Biomedical Engineering, Medford, Massachusetts, United States
| | - Giles Blaney
- Tufts University, Department of Biomedical Engineering, Medford, Massachusetts, United States
| | - Angelo Sassaroli
- Tufts University, Department of Biomedical Engineering, Medford, Massachusetts, United States
| | - Nishanth Krishnamurthy
- Tufts University, Department of Biomedical Engineering, Medford, Massachusetts, United States
| | - Thao Pham
- Tufts University, Department of Biomedical Engineering, Medford, Massachusetts, United States
| | - Sergio Fantini
- Tufts University, Department of Biomedical Engineering, Medford, Massachusetts, United States
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21
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Montoro CI, Duschek S, Schuepbach D, Gandarillas M, Reyes del Paso GA. Cerebral blood flow variability in fibromyalgia syndrome: Relationships with emotional, clinical and functional variables. PLoS One 2018; 13:e0204267. [PMID: 30235315 PMCID: PMC6147545 DOI: 10.1371/journal.pone.0204267] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Accepted: 09/04/2018] [Indexed: 01/04/2023] Open
Abstract
OBJECTIVE This study analyzed variability in cerebral blood flow velocity (CBFV) and its association with emotional, clinical and functional variables and medication use in fibromyalgia syndrome (FMS). METHODS Using transcranial Doppler sonography, CBFV were bilaterally recorded in the anterior (ACA) and middle (MCA) cerebral arteries of 44 FMS patients and 31 healthy individuals during a 5-min resting period. Participants also completed questionnaires assessing pain, fatigue, insomnia, anxiety, depression and health-related quality of life (HRQoL). RESULTS Fast Fourier transformation revealed a spectral profile with four components: (1) a first very low frequency (VLF) component with the highest amplitude at 0.0024 Hz; (2) a second VLF component around 0.01-to-0.025 Hz; (3) a low frequency (LF) component from 0.075-to-0.11 Hz; and (4) a high frequency (HF) component with the lowest amplitude from 0.25-to-0.35 Hz. Compared to controls, FMS patients exhibited lower LF and HF CBFV variability in the MCAs (p < .005) and right ACA (p = .03), but higher variability at the first right MCA (p = .04) and left ACA (p = .005) VLF components. Emotional, clinical and functional variables were inversely related to LF and HF CBFV variability (r≥-.24, p≤.05). However, associations for the first VLF component were positive (r≥.28, p≤.05). While patients´ medication use was associated with lower CBFV variability, comorbid depression and anxiety disorders were unrelated to variability. CONCLUSIONS Lower CBFV variability in the LF and HF ranges were observed in FMS, suggesting impaired coordination of cerebral regulatory systems. CBFV variability was differentially associated with clinical variables as a function of time-scale, with short-term variability being related to better clinical outcomes. CBFV variability analysis may be a promising tool to characterize FMS pathology and it impact on facets of HRQoL.
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Affiliation(s)
| | - Stefan Duschek
- UMIT—University for Health Sciences Medical Informatics and Technology, Hall in Tirol, Austria
| | - Daniel Schuepbach
- Klinikum am Weissenhof, Zentrum für Psychiatrie Weinsberg, Weinsberg, Germany
- University of Heidelberg, Department of General Psychiatry, Center of Psychosocial Medicine, Heidelberg, Germany
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Affiliation(s)
- Daniel A Nation
- From the Department of Psychology and Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles.
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de Heus RA, de Jong DL, Sanders ML, van Spijker GJ, Oudegeest-Sander MH, Hopman MT, Lawlor BA, Olde Rikkert MG, Claassen JA. Dynamic Regulation of Cerebral Blood Flow in Patients With Alzheimer Disease. Hypertension 2018; 72:139-150. [DOI: 10.1161/hypertensionaha.118.10900] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Revised: 02/09/2018] [Accepted: 04/05/2018] [Indexed: 01/18/2023]
Abstract
Cerebral autoregulation and baroreflex sensitivity are key mechanisms that maintain cerebral blood flow. This study assessed whether these control mechanisms are affected in patients with dementia and mild cognitive impairment due to Alzheimer disease, as this would increase the risks of antihypertensive treatment. We studied 53 patients with dementia (73.1 years [95% confidence interval (CI), 71.4–74.8]), 37 patients with mild cognitive impairment (69.2 years [95% CI, 66.4–72.0]), and 47 controls (69.4 years [95% CI, 68.3–70.5]). Beat-to-beat blood pressure (photoplethysmography), heart rate, and cerebral blood flow velocity (transcranial Doppler) were measured during 5-minute rest (sitting) and 5 minutes of orthostatic challenges, using repeated sit-to-stand maneuvers. Cerebral autoregulation was assessed using transfer function analysis and the autoregulatory index. Baroreflex sensitivity was estimated with transfer function analysis and by calculating the heart rate response to blood pressure changes during the orthostatic challenges. Dementia patients had the lowest cerebral blood flow velocity (
P
=0.004). During rest, neither transfer function analysis nor the autoregulatory index indicated impairments in cerebral autoregulation. During the orthostatic challenges, higher autoregulatory index (
P
=0.011) and lower transfer function gain (
P
=0.017), indicating better cerebral autoregulation, were found in dementia (4.56 arb. unit [95% CI, 4.14–4.97]; 0.59 cm/s per mm Hg [95% CI, 0.51–0.66]) and mild cognitive impairment (4.59 arb. unit [95% CI, 4.04–5.13]; 0.51 cm/s per mm Hg [95% CI, 0.44–0.59]) compared with controls (3.71 arb. unit [95% CI, 3.35–4.07]; 0.67 cm/s per mm Hg [95% CI, 0.59–0.74]). Baroreflex sensitivity measures did not differ between groups. In conclusion, the key mechanisms to control blood pressure and cerebral blood flow are not reduced in 2 stages of Alzheimer disease compared with controls, both in rest and during orthostatic changes that reflect daily life challenges.
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Affiliation(s)
- Rianne A.A. de Heus
- From the Department of Geriatric Medicine, Radboud Alzheimer Centre (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
- Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
| | - Daan L.K. de Jong
- From the Department of Geriatric Medicine, Radboud Alzheimer Centre (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
- Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
| | - Marit L. Sanders
- From the Department of Geriatric Medicine, Radboud Alzheimer Centre (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
- Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
| | - Gerrita J. van Spijker
- From the Department of Geriatric Medicine, Radboud Alzheimer Centre (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
- Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
| | - Madelijn H. Oudegeest-Sander
- From the Department of Geriatric Medicine, Radboud Alzheimer Centre (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
- Department of Physiology (M.H.O.-S., M.T.H.), Radboud University Medical Center, Nijmegen, The Netherlands
- Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
| | - Maria T. Hopman
- Department of Physiology (M.H.O.-S., M.T.H.), Radboud University Medical Center, Nijmegen, The Netherlands
| | - Brian A. Lawlor
- Mercer's Institute for Research on Ageing, St. James's Hospital and Global Brain Health Institute, Trinity College Dublin, Ireland (B.A.L.)
| | - Marcel G.M. Olde Rikkert
- From the Department of Geriatric Medicine, Radboud Alzheimer Centre (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
- Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
| | - Jurgen A.H.R. Claassen
- From the Department of Geriatric Medicine, Radboud Alzheimer Centre (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
- Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands (R.A.A.d.H., D.L.K.d.J., M.L.S., G.J.v.S., M.H.O.-S., M.G.M.O.R., J.A.H.R.C.)
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Andersen AV, Simonsen SA, Schytz HW, Iversen HK. Assessing low-frequency oscillations in cerebrovascular diseases and related conditions with near-infrared spectroscopy: a plausible method for evaluating cerebral autoregulation? NEUROPHOTONICS 2018; 5:030901. [PMID: 30689678 PMCID: PMC6156398 DOI: 10.1117/1.nph.5.3.030901] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Accepted: 08/02/2018] [Indexed: 05/08/2023]
Abstract
BACKGROUND Cerebral autoregulation (CA) is the brain's ability to always maintain an adequate and relatively constant blood supply, which is often impaired in cerebrovascular diseases. Near-infrared spectroscopy (NIRS) examines oxygenated hemoglobin (OxyHb) in the cerebral cortex. Low- and very low-frequency oscillations ( LFOs ≈ 0.1 Hz and VLFOs ≈ 0.05 to 0.01 Hz) in OxyHb have been proposed to reflect CA. AIM To systematically review published results on OxyHb LFOs and VLFOs in cerebrovascular diseases and related conditions measured with NIRS. APPROACH A systematic search was performed in the MEDLINE database, which generated 36 studies relevant for inclusion. RESULTS Healthy people have relatively stable LFOs. LFO amplitude seems to reflect myogenic CA being decreased by vasomotor paralysis in stroke, by smooth muscle damage or as compensatory action in other conditions but can also be influenced by the sympathetic tone. VLFO amplitude is believed to reflect neurogenic and metabolic CA and is lower in stroke, atherosclerosis, and with aging. Both LFO and VLFO synchronizations appear disturbed in stroke, while the former is also altered in internal carotid stenosis and hypertension. CONCLUSION We conclude that amplitudes of LFOs and VLFOs are relatively robust measures for evaluating mechanisms of CA and synchronization analyses can show temporal disruption of CA. Further research and more coherent methodologies are needed.
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Affiliation(s)
- Adam Vittrup Andersen
- Rigshospitalet, Department of Neurology, Glostrup, Denmark
- University of Copenhagen, Department of Clinical Medicine, Copenhagen, Denmark
- Address all correspondence to: Adam Vittrup Andersen, E-mail:
| | - Sofie Amalie Simonsen
- Rigshospitalet, Department of Neurology, Glostrup, Denmark
- University of Copenhagen, Department of Clinical Medicine, Copenhagen, Denmark
| | - Henrik Winther Schytz
- Rigshospitalet, Department of Neurology, Glostrup, Denmark
- University of Copenhagen, Department of Clinical Medicine, Copenhagen, Denmark
| | - Helle Klingenberg Iversen
- Rigshospitalet, Department of Neurology, Glostrup, Denmark
- University of Copenhagen, Department of Clinical Medicine, Copenhagen, Denmark
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Agbangla NF, Audiffren M, Albinet CT. Use of near-infrared spectroscopy in the investigation of brain activation during cognitive aging: A systematic review of an emerging area of research. Ageing Res Rev 2017; 38:52-66. [PMID: 28755870 DOI: 10.1016/j.arr.2017.07.003] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2017] [Revised: 07/18/2017] [Accepted: 07/19/2017] [Indexed: 01/24/2023]
Abstract
The cognitive neuroscience of aging is a growing and stimulating research area. The development of neuroimaging techniques in the past two decades has considerably increased our understanding of the brain mechanisms that might underlie cognitive performance and resulting changes due to normal aging. Beside traditional metabolic neuroimaging techniques, such as Positron Emission Tomography and functional Magnetic Resonance Imaging, near infrared spectroscopy (NIRS), an optical imaging technique allowing to monitor real-time cerebral blood oxygenation, has gained recent interest in this field. The aim of the present review paper, after briefly presenting the NIRS technique, is to review and to summarize the recent results of neuroimaging studies using this technique in the field of cognitive aging. The reviewed literature shows that, despite low spatial resolution and cerebral depth penetration, this technique provides consistent findings on the reduced hemodynamic activity as a function of chronological age, mainly in the prefrontal cortex. Important moderators of brain hemodynamics, such as cognitive load, subjects' characteristics and experimental conditions, for which the NIRS technique is sensitive, are discussed. Strengths and weaknesses of functional NIRS in the field of cognitive aging are presented and finally, novel perspectives of research are proposed.
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27
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Madureira J, Castro P, Azevedo E. Demographic and Systemic Hemodynamic Influences in Mechanisms of Cerebrovascular Regulation in Healthy Adults. J Stroke Cerebrovasc Dis 2017; 26:500-508. [DOI: 10.1016/j.jstrokecerebrovasdis.2016.12.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 08/24/2016] [Accepted: 12/05/2016] [Indexed: 01/05/2023] Open
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28
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Malojcic B, Giannakopoulos P, Sorond FA, Azevedo E, Diomedi M, Oblak JP, Carraro N, Boban M, Olah L, Schreiber SJ, Pavlovic A, Garami Z, Bornstein NM, Rosengarten B. Ultrasound and dynamic functional imaging in vascular cognitive impairment and Alzheimer's disease. BMC Med 2017; 15:27. [PMID: 28178960 PMCID: PMC5299782 DOI: 10.1186/s12916-017-0799-3] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 01/21/2017] [Indexed: 01/03/2023] Open
Abstract
BACKGROUND The vascular contributions to neurodegeneration and neuroinflammation may be assessed by magnetic resonance imaging (MRI) and ultrasonography (US). This review summarises the methodology for these widely available, safe and relatively low cost tools and analyses recent work highlighting their potential utility as biomarkers for differentiating subtypes of cognitive impairment and dementia, tracking disease progression and evaluating response to treatment in various neurocognitive disorders. METHODS At the 9th International Congress on Vascular Dementia (Ljubljana, Slovenia, October 2015) a writing group of experts was formed to review the evidence on the utility of US and arterial spin labelling (ASL) as neurophysiological markers of normal ageing, vascular cognitive impairment (VCI) and Alzheimer's disease (AD). Original articles, systematic literature reviews, guidelines and expert opinions published until September 2016 were critically analysed to summarise existing evidence, indicate gaps in current knowledge and, when appropriate, suggest standards of use for the most widely used US and ASL applications. RESULTS Cerebral hypoperfusion has been linked to cognitive decline either as a risk or an aggravating factor. Hypoperfusion as a consequence of microangiopathy, macroangiopathy or cardiac dysfunction can promote or accelerate neurodegeneration, blood-brain barrier disruption and neuroinflammation. US can evaluate the cerebrovascular tree for pathological structure and functional changes contributing to cerebral hypoperfusion. Microvascular pathology and hypoperfusion at the level of capillaries and small arterioles can also be assessed by ASL, an MRI signal. Despite increasing evidence supporting the utility of these methods in detection of microvascular pathology, cerebral hypoperfusion, neurovascular unit dysfunction and, most importantly, disease progression, incomplete standardisation and missing validated cut-off values limit their use in daily routine. CONCLUSIONS US and ASL are promising tools with excellent temporal resolution, which will have a significant impact on our understanding of the vascular contributions to VCI and AD and may also be relevant for assessing future prevention and therapeutic strategies for these conditions. Our work provides recommendations regarding the use of non-invasive imaging techniques to investigate the functional consequences of vascular burden in dementia.
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Affiliation(s)
- Branko Malojcic
- Department of Neurology, University Hospital Center Zagreb, Zagreb School of Medicine, Kispaticeva 12, 10000, Zagreb, Croatia.
| | | | - Farzaneh A Sorond
- Department of Neurology, Northwestern University Feinberg School of Medicine Chicago, Chicago, IL, USA
| | - Elsa Azevedo
- Department of Neurology, São João Hospital Center and Faculty of Medicine of University of Porto, Porto, Portugal
| | - Marina Diomedi
- Cerebrovascular Disease Center, Stroke Unit, University of Rome Tor Vergata, Rome, Italy
| | - Janja Pretnar Oblak
- Department of Vascular Neurology and Intensive Therapy, University Medical Center Ljubljana, Ljubljana, Slovenia
| | - Nicola Carraro
- Department of Medical Sciences, Clinical Neurology-Stroke Unit, University Hospital, University of Trieste, Trieste, Italy
| | - Marina Boban
- Department of Neurology, University Hospital Center Zagreb, Zagreb School of Medicine, Kispaticeva 12, 10000, Zagreb, Croatia
| | - Laszlo Olah
- Department of Neurology, University of Debrecen, Debrecen, Hungary
| | - Stephan J Schreiber
- Department of Neurology, Charite - Universitätsmedizin Berlin, Berlin, Germany
| | - Aleksandra Pavlovic
- Neurology Clinic, Clinical Center of Serbia, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
| | - Zsolt Garami
- Methodist DeBakey Heart and Vascular Center, Houston, TX, USA
| | - Nantan M Bornstein
- Neurology Department, Tel Aviv Sourasky Medical Centre, Tel Aviv, Israel
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Vermeij A, Kessels RPC, Heskamp L, Simons EMF, Dautzenberg PLJ, Claassen JAHR. Prefrontal activation may predict working-memory training gain in normal aging and mild cognitive impairment. Brain Imaging Behav 2017; 11:141-154. [PMID: 26843001 PMCID: PMC5415588 DOI: 10.1007/s11682-016-9508-7] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Cognitive training has been shown to result in improved behavioral performance in normal aging and mild cognitive impairment (MCI), yet little is known about the neural correlates of cognitive plasticity, or about individual differences in responsiveness to cognitive training. In this study, 21 healthy older adults and 14 patients with MCI received five weeks of adaptive computerized working-memory (WM) training. Before and after training, functional Near-Infrared Spectroscopy (fNIRS) was used to assess the hemodynamic response in left and right prefrontal cortex during performance of a verbal n-back task with varying levels of WM load. After training, healthy older adults demonstrated decreased prefrontal activation at high WM load, which may indicate increased processing efficiency. Although MCI patients showed improved behavioral performance at low WM load after training, no evidence was found for training-related changes in prefrontal activation. Whole-group analyses showed that a relatively strong hemodynamic response at low WM load was related to worse behavioral performance, while a relatively strong hemodynamic response at high WM load was related to higher training gain. Therefore, a 'youth-like' prefrontal activation pattern at older age may be associated with better behavioral outcome and cognitive plasticity.
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Affiliation(s)
- Anouk Vermeij
- Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, The Netherlands
- Department of Geriatric Medicine, Radboud University Medical Center, Route 925, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Roy P C Kessels
- Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, The Netherlands
- Department of Medical Psychology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Linda Heskamp
- Department of Geriatric Medicine, Radboud University Medical Center, Route 925, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Esther M F Simons
- Department of Geriatric Medicine, Radboud University Medical Center, Route 925, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Paul L J Dautzenberg
- Department of Geriatric Medicine, Jeroen Bosch Hospital, 's-Hertogenbosch, The Netherlands
| | - Jurgen A H R Claassen
- Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, The Netherlands.
- Department of Geriatric Medicine, Radboud University Medical Center, Route 925, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands.
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Marmarelis VZ, Shin DC, Tarumi T, Zhang R. Comparison of Model-Based Indices of Cerebral Autoregulation and Vasomotor Reactivity Using Transcranial Doppler versus Near-Infrared Spectroscopy in Patients with Amnestic Mild Cognitive Impairment. J Alzheimers Dis 2017; 56:89-105. [PMID: 27911329 PMCID: PMC5240580 DOI: 10.3233/jad-161004] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/17/2016] [Indexed: 01/24/2023]
Abstract
We recently introduced model-based "physiomarkers" of dynamic cerebral autoregulation and CO2 vasomotor reactivity as an aid for diagnosis of early-stage Alzheimer's disease (AD) [1], where significant impairment of dynamic vasomotor reactivity (DVR) was observed in early-stage AD patients relative to age-matched controls. Milder impairment of DVR was shown in patients with amnestic mild cognitive impairment (MCI) using the same approach in a subsequent study [2]. The advocated approach utilizes subject-specific data-based models of cerebral hemodynamics to quantify the dynamic effects of resting-state changes in arterial blood pressure and end-tidal CO2 (the putative inputs) upon cerebral blood flow velocity (the putative output) measured at the middle cerebral artery via transcranial Doppler (TCD). The obtained input-output models are then used to compute model-based indices of DCA and DVR from model-predicted responses to an input pressure pulse or an input CO2 pulse, respectively. In this paper, we compare these model-based indices of DVR and DCA in 46 amnestic MCI patients, relative to 20 age-matched controls, using TCD measurements with their counterparts using Near-Infrared Spectroscopy (NIRS) measurements of blood oxygenation at the lateral prefrontal cortex in 43 patients and 22 age-matched controls. The goal of the study is to assess whether NIRS measurements can be used instead of TCD measurements to obtain model-based physiomarkers with comparable diagnostic utility. The results corroborate this view in terms of the ability of either output to yield model-based physiomarkers that can differentiate the group of aMCI patients from age-matched healthy controls.
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Affiliation(s)
- Vasilis Z. Marmarelis
- Biomedical Simulations Resource Center, University of Southern California, Los Angeles, CA, USA
| | - Dae C. Shin
- Biomedical Simulations Resource Center, University of Southern California, Los Angeles, CA, USA
| | - Takashi Tarumi
- Exercise Physiology & Rehabilitation Center, UT Southwestern Medical Center, Dallas, TX, USA
| | - Rong Zhang
- Exercise Physiology & Rehabilitation Center, UT Southwestern Medical Center, Dallas, TX, USA
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Phillips AA, Chan FH, Zheng MMZ, Krassioukov AV, Ainslie PN. Neurovascular coupling in humans: Physiology, methodological advances and clinical implications. J Cereb Blood Flow Metab 2016; 36:647-64. [PMID: 26661243 PMCID: PMC4821024 DOI: 10.1177/0271678x15617954] [Citation(s) in RCA: 252] [Impact Index Per Article: 31.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Revised: 10/22/2015] [Accepted: 10/23/2015] [Indexed: 12/16/2022]
Abstract
Neurovascular coupling reflects the close temporal and regional linkage between neural activity and cerebral blood flow. Although providing mechanistic insight, our understanding of neurovascular coupling is largely limited to non-physiologicalex vivopreparations and non-human models using sedatives/anesthetics with confounding cerebrovascular implications. Herein, with particular focus on humans, we review the present mechanistic understanding of neurovascular coupling and highlight current approaches to assess these responses and the application in health and disease. Moreover, we present new guidelines for standardizing the assessment of neurovascular coupling in humans. To improve the reliability of measurement and related interpretation, the utility of new automated software for neurovascular coupling is demonstrated, which provides the capacity for coalescing repetitive trials and time intervals into single contours and extracting numerous metrics (e.g., conductance and pulsatility, critical closing pressure, etc.) according to patterns of interest (e.g., peak/minimum response, time of response, etc.). This versatile software also permits the normalization of neurovascular coupling metrics to dynamic changes in arterial blood gases, potentially influencing the hyperemic response. It is hoped that these guidelines, combined with the newly developed and openly available software, will help to propel the understanding of neurovascular coupling in humans and also lead to improved clinical management of this critical physiological function.
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Affiliation(s)
- Aaron A Phillips
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada International Collaboration on Repair Discoveries (ICORD), UBC, Vancouver, Canada Experimental Medicine Program, Faculty of Medicine, UBC, Vancouver, Canada
| | - Franco Hn Chan
- International Collaboration on Repair Discoveries (ICORD), UBC, Vancouver, Canada
| | - Mei Mu Zi Zheng
- International Collaboration on Repair Discoveries (ICORD), UBC, Vancouver, Canada Experimental Medicine Program, Faculty of Medicine, UBC, Vancouver, Canada
| | - Andrei V Krassioukov
- International Collaboration on Repair Discoveries (ICORD), UBC, Vancouver, Canada Experimental Medicine Program, Faculty of Medicine, UBC, Vancouver, Canada Department of Physical Therapy, UBC, Vancouver, Canada GF Strong Rehabilitation Center, Vancouver, Canada Department of Medicine, Division of Physical Medicine and Rehabilitation, UBC, Vancouver, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
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Vascular coupling in resting-state fMRI: evidence from multiple modalities. J Cereb Blood Flow Metab 2015; 35:1910-20. [PMID: 26174326 PMCID: PMC4671123 DOI: 10.1038/jcbfm.2015.166] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Revised: 04/27/2015] [Accepted: 05/26/2015] [Indexed: 01/23/2023]
Abstract
Resting-state functional magnetic resonance imaging (rs-fMRI) provides a potential to understand intrinsic brain functional connectivity. However, vascular effects in rs-fMRI are still not fully understood. Through multiple modalities, we showed marked vascular signal fluctuations and high-level coupling among arterial pressure, cerebral blood flow (CBF) velocity and brain tissue oxygenation at <0.08 Hz. These similar spectral power distributions were also observed in blood oxygen level-dependent (BOLD) signals obtained from six representative regions of interest (ROIs). After applying brain global, white-matter, cerebrospinal fluid (CSF) mean signal regressions and low-pass filtering (<0.08 Hz), the spectral power of BOLD signal was reduced by 55.6% to 64.9% in all ROIs (P=0.011 to 0.001). The coherence of BOLD signal fluctuations between an ROI pair within a same brain network was reduced by 9.9% to 20.0% (P=0.004 to <0.001), but a larger reduction of 22.5% to 37.3% (P=0.032 to <0.001) for one not in a same network. Global signal regression overall had the largest impact in reducing spectral power (by 52.2% to 61.7%) and coherence, relative to the other three preprocessing steps. Collectively, these findings raise a critical question of whether a large portion of rs-fMRI signals can be attributed to the vascular effects produced from upstream changes in cerebral hemodynamics.
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Smirl JD, Hoffman K, Tzeng YC, Hansen A, Ainslie PN. Methodological comparison of active- and passive-driven oscillations in blood pressure; implications for the assessment of cerebral pressure-flow relationships. J Appl Physiol (1985) 2015; 119:487-501. [PMID: 26183476 DOI: 10.1152/japplphysiol.00264.2015] [Citation(s) in RCA: 96] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Accepted: 07/15/2015] [Indexed: 11/22/2022] Open
Abstract
We examined the between-day reproducibility of active (squat-stand maneuvers)- and passive [oscillatory lower-body negative pressure (OLBNP) maneuvers]-driven oscillations in blood pressure. These relationships were examined in both younger (n = 10; 25 ± 3 yr) and older (n = 9; 66 ± 4 yr) adults. Each testing protocol incorporated rest (5 min), followed by driven maneuvers at 0.05 (5 min) and 0.10 (5 min) Hz to increase blood-pressure variability and improve assessment of the pressure-flow dynamics using linear transfer function analysis. Beat-to-beat blood pressure, middle cerebral artery velocity, and end-tidal partial pressure of CO2 were monitored. The pressure-flow relationship was quantified in the very low (0.02-0.07 Hz) and low (0.07-0.20 Hz) frequencies (LF; spontaneous data) and at 0.05 and 0.10 Hz (driven maneuvers point estimates). Although there were no between-age differences, very few spontaneous and OLBNP transfer function metrics met the criteria for acceptable reproducibility, as reflected in a between-day, within-subject coefficient of variation (CoV) of <20%. Combined CoV data consist of LF coherence (15.1 ± 12.2%), LF gain (15.1 ± 12.2%), and LF normalized gain (18.5 ± 10.9%); OLBNP data consist of 0.05 (12.1 ± 15.%) and 0.10 (4.7 ± 7.8%) Hz coherence. In contrast, the squat-stand maneuvers revealed that all metrics (coherence: 0.6 ± 0.5 and 0.3 ± 0.5%; gain: 17.4 ± 12.3 and 12.7 ± 11.0%; normalized gain: 16.7 ± 10.9 and 15.7 ± 11.0%; and phase: 11.6 ± 10.2 and 17.3 ± 10.8%) at 0.05 and 0.10 Hz, respectively, were considered biologically acceptable for reproducibility. These findings have important implications for the reliable assessment and interpretation of cerebral pressure-flow dynamics in humans.
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Affiliation(s)
- Jonathan D Smirl
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, British Columbia, Canada; and
| | - Keegan Hoffman
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, British Columbia, Canada; and
| | - Yu-Chieh Tzeng
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, Wellington, New Zealand
| | - Alex Hansen
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, British Columbia, Canada; and
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, British Columbia, Canada; and
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Rickards CA, Sprick JD, Colby HB, Kay VL, Tzeng YC. Coupling between arterial pressure, cerebral blood velocity, and cerebral tissue oxygenation with spontaneous and forced oscillations. Physiol Meas 2015; 36:785-801. [PMID: 25798890 DOI: 10.1088/0967-3334/36/4/785] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We tested the hypothesis that transmission of arterial pressure to brain tissue oxygenation is low under conditions of arterial pressure instability. Two experimental models of hemodynamic instability were used in healthy human volunteers; (1) oscillatory lower body negative pressure (OLBNP) (N = 8; 5 male, 3 female), and; (2) maximal LBNP to presyncope (N = 21; 13 male, 8 female). Mean arterial pressure (MAP), middle cerebral artery velocity (MCAv), and cerebral tissue oxygen saturation (ScO2) were measured non-invasively. For the OLBNP protocol, between 0 and -60 mmHg negative pressure was applied for 20 cycles at 0.05 Hz, then 20 cycles at 0.1 Hz. For the maximal LBNP protocol, progressive 5 min stages of chamber decompression were applied until the onset of presyncope. Spectral power of MAP, mean MCAv, and ScO2 were calculated within the VLF (0.04-0.07 Hz), and LF (0.07-0.2 Hz) ranges, and cross-spectral coherence was calculated for MAP-mean MCAv, MAP-ScO2, and mean MCAv-ScO2 at baseline, during each OLBNP protocol, and at the level prior to pre-syncope during maximal LBNP (sub-max). The key findings are (1) both 0.1 Hz OLBNP and sub-max LBNP elicited increases in LF power for MAP, mean MCAv, and ScO2 (p ≤ 0.08); (2) 0.05 Hz OLBNP increased VLF power in MAP and ScO2 only (p ≤ 0.06); (3) coherence between MAP-mean MCAv was consistently higher (≥0.71) compared with MAP-ScO2, and mean MCAv-ScO2 (≤0.43) during both OLBNP protocols, and sub-max LBNP (p ≤ 0.04). These data indicate high linearity between pressure and cerebral blood flow variations, but reduced linearity between cerebral tissue oxygenation and both arterial pressure and cerebral blood flow. Measuring arterial pressure variability may not always provide adequate information about the downstream effects on cerebral tissue oxygenation, the key end-point of interest for neuronal viability.
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Affiliation(s)
- Caroline A Rickards
- Department of Integrative Physiology & Anatomy, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
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Gao Y, Zhang M, Han Q, Li W, Xin Q, Wang Y, Li Z. Cerebral autoregulation in response to posture change in elderly subjects-assessment by wavelet phase coherence analysis of cerebral tissue oxyhemoglobin concentrations and arterial blood pressure signals. Behav Brain Res 2014; 278:330-6. [PMID: 25453742 DOI: 10.1016/j.bbr.2014.10.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2014] [Revised: 10/07/2014] [Accepted: 10/12/2014] [Indexed: 10/24/2022]
Abstract
This study aims to assess the dynamic cerebral autoregulation (dCA) in response to posture change using wavelet phase coherence (WPCO) of cerebral tissue oxyhemoglobin concentrations (Delta [HbO2]) and arterial blood pressure (ABP) signals in healthy elderly subjects. Continuous recordings of near-infrared spectroscopy (NIRS) and ABP signals were obtained from simultaneous measurements in 16 healthy elderly subjects (age: 68.9±7.1 years) and 19 young subjects (age: 24.9±3.2 years). The phase coherence between Delta [HbO2] and ABP oscillations in six frequency intervals (I, 0.6-2 Hz; II, 0.15-0.6 Hz; III, 0.05-0.15 Hz; IV, 0.02-0.05 Hz, V, 0.0095-0.02 Hz and VI, 0.005-0.0095 Hz) was analyzed using WPCO. The sit-to-stand posture change induces significantly lower WPCO in interval III (F=5.50 p=0.025) in the elderly subjects than in the young subjects. However, the stand-to-sit posture change induces higher WPCO in intervals II (F=5.25 p=0.028) and V (F=6.22 p=0.018) in the elderly subjects than in the young subjects. The difference of WPCO in response to posture change between the elderly and the young subjects indicates an altered CA due to aging. This study provides new insight into the dynamics of CA and may be useful in identifying the risk for dCA processes.
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Affiliation(s)
- Yuanjin Gao
- Key Laboratory of High Efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan 250061, PR China
| | - Ming Zhang
- Interdisciplinary Division of Biomedical Engineering, Faculty of Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, SAR, PR China
| | - Qingyu Han
- Key Laboratory of High Efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan 250061, PR China
| | - Wenhao Li
- Key Laboratory of High Efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan 250061, PR China
| | - Qing Xin
- Hospital of Shandong University, Jinan 250061, PR China
| | - Yan Wang
- Interdisciplinary Division of Biomedical Engineering, Faculty of Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, SAR, PR China
| | - Zengyong Li
- Key Laboratory of High Efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan 250061, PR China.
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Benathan-Tordjmann J, Bailly P, Meyer ME, Daouk J. Cerebral arterial inflow assessment with 18F-FDG PET: methodology and feasibility. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2014; 116:177-183. [PMID: 25015567 DOI: 10.1016/j.cmpb.2014.06.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Revised: 06/12/2014] [Accepted: 06/17/2014] [Indexed: 06/03/2023]
Abstract
Positron emission tomography (PET) with 18fluorodeoxyglucose (18F-FDG) is increasingly used in neurology. The measurement of cerebral arterial inflow (QA) using 18F-FDG complements the information provided by standard brain PET imaging. Here, injections were performed after the beginning of dynamic acquisitions and the time to arrival (t0) of activity in the gantry's field of view was computed. We performed a phantom study using a branched tube (internal diameter: 4mm) and a 18F-FDG solution injected at 240 mL/min. Data processing consisted of (i) reconstruction of the first 3s after t0, (ii) vascular signal enhancement and (iii) clustering. This method was then applied in four subjects. We measured the volumes of the tubes or vascular trees and calculated the corresponding flows. In the phantom, the flow was calculated to be 244.2 mL/min. In each subject, our QA value was compared with that obtained by quantitative cine-phase contrast magnetic resonance imaging; the mean QA value of 581.4±217.5 mL/min calculated with 18F-FDG PET was consistent with the mean value of 593.3±205.8 mL/min calculated with quantitative cine-phase contrast magnetic resonance imaging. Our 18F-FDG PET method constitutes a novel, fully automatic means of measuring QA.
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Affiliation(s)
- Jennifer Benathan-Tordjmann
- Service de médecine nucléaire et de traitement de l'image médicale, Centre Hospitalier Universitaire d'Amiens, Amiens, France
| | - Pascal Bailly
- Service de médecine nucléaire et de traitement de l'image médicale, Centre Hospitalier Universitaire d'Amiens, Amiens, France.
| | - Marc-Etienne Meyer
- Service de médecine nucléaire et de traitement de l'image médicale, Centre Hospitalier Universitaire d'Amiens, Amiens, France; Université de Picardie Jules Verne, Amiens, France
| | - Joël Daouk
- Université de Picardie Jules Verne, Amiens, France
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Marmarelis VZ, Shin DC, Orme ME, Zhang R. Model-based physiomarkers of cerebral hemodynamics in patients with mild cognitive impairment. Med Eng Phys 2014; 36:628-37. [PMID: 24698010 PMCID: PMC4076301 DOI: 10.1016/j.medengphy.2014.02.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Revised: 02/17/2014] [Accepted: 02/26/2014] [Indexed: 02/02/2023]
Abstract
In our previous studies, we have introduced model-based "functional biomarkers" or "physiomarkers" of cerebral hemodynamics that hold promise for improved diagnosis of early-stage Alzheimer's disease (AD). The advocated methodology utilizes subject-specific data-based dynamic nonlinear models of cerebral hemodynamics to compute indices (serving as possible diagnostic physiomarkers) that quantify the state of cerebral blood flow autoregulation to pressure-changes (CFAP) and cerebral CO2 vasomotor reactivity (CVMR) in each subject. The model is estimated from beat-to-beat measurements of mean arterial blood pressure, mean cerebral blood flow velocity and end-tidal CO2, which can be made reliably and non-invasively under resting conditions. In a previous study, it was found that a CVMR index quantifying the impairment in CO2 vasomotor reactivity correlates with clinical indications of early AD, offering the prospect of a potentially useful diagnostic tool. In this paper, we explore the use of the same model-based indices for patients with amnestic Mild Cognitive Impairment (MCI), a preclinical stage of AD, relative to a control subjects and clinical cognitive assessments. It was found that the model-based CVMR values were lower for MCI patients relative to the control subjects.
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Affiliation(s)
- V Z Marmarelis
- Department of Biomedical Engineering & Biomedical Simulations Resource, University of Southern California, United States.
| | - D C Shin
- Department of Biomedical Engineering & Biomedical Simulations Resource, University of Southern California, United States
| | - M E Orme
- Sonovation Imaging & Diagnostics Inc., Los Angeles, CA, United States
| | - R Zhang
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, United States
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Very-low-frequency oscillations of cerebral hemodynamics and blood pressure are affected by aging and cognitive load. Neuroimage 2014; 85 Pt 1:608-15. [DOI: 10.1016/j.neuroimage.2013.04.107] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 04/04/2013] [Accepted: 04/26/2013] [Indexed: 11/22/2022] Open
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Marmarelis VZ, Shin DC, Orme ME, Zhang R. Model-based quantification of cerebral hemodynamics as a physiomarker for Alzheimer's disease? Ann Biomed Eng 2013; 41:2296-317. [PMID: 23771298 PMCID: PMC3992829 DOI: 10.1007/s10439-013-0837-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2013] [Accepted: 05/29/2013] [Indexed: 01/27/2023]
Abstract
Previous studies have found that Alzheimer's disease (AD) impairs cerebral vascular function, even at early stages of the disease. This offers the prospect of a useful diagnostic method for AD, if cerebral vascular dysfunction can be quantified reliably within practical clinical constraints. We present a recently developed methodology that utilizes a data-based dynamic nonlinear closed-loop model of cerebral hemodynamics to compute "physiomarkers" quantifying the state of cerebral flow autoregulation to pressure-changes (CA) and cerebral CO2 vasomotor reactivity (CVMR) in each subject. This model is estimated from beat-to-beat measurements of mean arterial blood pressure, mean cerebral blood flow velocity and end-tidal CO2, which can be made reliably and non-invasively under resting conditions. This model may also take an open-loop form and comparisons are made with the closed-loop counterpart. The proposed model-based physiomarkers take the form of two indices that quantify the gain of the CA and CVMR processes in each subject. It was found in an initial set of clinical data that the CVMR index delineates AD patients from control subjects and, therefore, may prove useful in the improved diagnosis of early-stage AD.
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Affiliation(s)
- V Z Marmarelis
- University of Southern California, Los Angeles, CA, USA,
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40
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Meel-van den Abeelen AS, Lagro J, Gommer ED, Reulen JP, Claassen JA. Baroreflex function is reduced in Alzheimer’s disease: a candidate biomarker? Neurobiol Aging 2013; 34:1170-6. [DOI: 10.1016/j.neurobiolaging.2012.10.010] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 10/10/2012] [Accepted: 10/15/2012] [Indexed: 10/27/2022]
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Vermeij A, van Beek AHEA, Olde Rikkert MGM, Claassen JAHR, Kessels RPC. Effects of aging on cerebral oxygenation during working-memory performance: a functional near-infrared spectroscopy study. PLoS One 2012; 7:e46210. [PMID: 23029437 PMCID: PMC3460859 DOI: 10.1371/journal.pone.0046210] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 08/29/2012] [Indexed: 11/18/2022] Open
Abstract
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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Affiliation(s)
- Anouk Vermeij
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, The Netherlands.
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Cheng R, Shang Y, Hayes D, Saha SP, Yu G. Noninvasive optical evaluation of spontaneous low frequency oscillations in cerebral hemodynamics. Neuroimage 2012; 62:1445-54. [DOI: 10.1016/j.neuroimage.2012.05.069] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Revised: 05/11/2012] [Accepted: 05/24/2012] [Indexed: 01/15/2023] Open
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Quintessential Risk Factors: Their Role in Promoting Cognitive Dysfunction and Alzheimer’s Disease. Neurochem Res 2012; 37:2627-58. [DOI: 10.1007/s11064-012-0854-6] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Accepted: 07/21/2012] [Indexed: 12/13/2022]
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Kolyva C, Kingston H, Tachtsidis I, Mohanty S, Mishra S, Patnaik R, Maude RJ, Dondorp AM, Elwell CE. Oscillations in cerebral haemodynamics in patients with falciparum malaria. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 765:101-107. [PMID: 22879021 PMCID: PMC4038006 DOI: 10.1007/978-1-4614-4989-8_15] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Spontaneous oscillations in cerebral haemodynamics studied with near-infrared spectroscopy (NIRS), become impaired in several pathological conditions. We assessed the spectral characteristics of these oscillations in 20 patients with falciparum malaria admitted to Ispat General Hospital, Rourkela, India. Monitoring included continuous frontal lobe NIRS recordings within 24 h of admission (Day 0), together with single measurements of a number of clinical and chemical markers recorded on admission. Seven patients returned for follow-up measurements on recovery (FU). A 2,048 sampling-point segment of oxygenated haemoglobin concentration ([ΔHbO(2)]) data was subjected to Fourier analysis per patient, and power spectral density was derived over the very low frequency (VLF: 0.02-0.04 Hz), low frequency (LF: 0.04-0.15 Hz) and high frequency (HF: 0.15-0.4 Hz) bands. At Day 0, VLF spectral power was 21.1 ± 16.4, LF power 7.2 ± 4.6 and HF power 2.6 ± 5.0, with VLF power being statistically significantly higher than LF and HF (P < 0.005). VLF power tended to decrease in the severely ill patients and correlated negatively with heart rate (r = 0.57, P < 0.01), while LF power correlated positively with aural body temperature (r = 0.49, P < 0.05). In all but one of the patients who returned for FU measurements, VLF power increased after recovery. This may be related to autonomic dysfunction in severe malaria, a topic of little research to date. The present study demonstrated that application of NIRS in a resource-poor setting is feasible and has potential as a research tool.
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Affiliation(s)
- Christina Kolyva
- grid.83440.3b0000000121901201Department of Medical Physics and Bioengineering, University College London, Malet Place Engineering Building, Gower Street, London, WC1E 6BT UK
| | - Hugh Kingston
- grid.10223.320000 0004 1937 0490Mahidol-Oxford Tropical Medicine Research Unit, Mahidol University, Bangkok, Thailand
| | - Ilias Tachtsidis
- grid.83440.3b0000000121901201Department of Medical Physics and Bioengineering, University College London, Malet Place Engineering Building, Gower Street, London, WC1E 6BT UK
| | - Sanjib Mohanty
- grid.440315.7Department of Internal Medicine, Ispat General Hospital, Rourkela, India
| | - Saroj Mishra
- grid.440315.7Department of Internal Medicine, Ispat General Hospital, Rourkela, India
| | - Rajya Patnaik
- grid.440315.7Department of Internal Medicine, Ispat General Hospital, Rourkela, India
| | - Richard J. Maude
- grid.4991.50000 0004 1936 8948Centre for Tropical Medicine, University of Oxford, Oxford, UK
| | - Arjen M. Dondorp
- grid.10223.320000 0004 1937 0490Mahidol-Oxford Tropical Medicine Research Unit, Mahidol University, Bangkok, Thailand
| | - Clare E. Elwell
- grid.83440.3b0000000121901201Department of Medical Physics and Bioengineering, University College London, Malet Place Engineering Building, Gower Street, London, WC1E 6BT UK
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Rodell AB, Aanerud J, Braendgaard H, Gjedde A. Low Residual CBF Variability in Alzheimer's Disease after Correction for CO(2) Effect. FRONTIERS IN NEUROENERGETICS 2012; 4:8. [PMID: 22783187 PMCID: PMC3389721 DOI: 10.3389/fnene.2012.00008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Accepted: 06/04/2012] [Indexed: 11/13/2022]
Abstract
We tested the claim that inter-individual CBF variability in Alzheimer's disease (AD) is substantially reduced after correction for arterial carbon dioxide tension (PaCO(2)). Specifically, we tested whether the variability of CBF in brain of patients with AD differed significantly from brain of age-matched healthy control subjects (HC). To eliminate the CO(2)-induced variability, we developed a novel and generally applicable approach to the correction of CBF for changes of PaCO(2) and applied the method to positron emission tomographic (PET) measures of CBF in AD and HC groups of subjects. After correction for the differences of CO(2) tension, the patients with AD lost the inter-individual CBF variability that continued to characterize the HC subjects. The difference (ΔK(1)) between the blood-brain clearances (K(1)) of water (the current measure of CBF) and oxygen (the current measure of oxygen clearance) was reduced globally in AD and particularly in the parietal, occipital, and temporal lobes. We then showed that oxygen gradients calculated for brain tissue were similar in AD and HC, indicating that the low residual variability of CBF in AD may be due to low functional demands for oxidative metabolism of brain tissue rather than impaired delivery of oxygen.
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Affiliation(s)
- Anders Bertil Rodell
- Department of Nuclear Medicine and Positron Emission Tomography Centre, Aarhus University HospitalAarhus, Denmark
| | - Joel Aanerud
- Department of Nuclear Medicine and Positron Emission Tomography Centre, Aarhus University HospitalAarhus, Denmark
| | - Hans Braendgaard
- Department of Neurology, Aarhus University HospitalAarhus, Denmark
| | - Albert Gjedde
- Department of Nuclear Medicine and Positron Emission Tomography Centre, Aarhus University HospitalAarhus, Denmark
- Department of Neuroscience and Pharmacology and Center of Healthy Aging, Faculty of Health and Medical Sciences, University of CopenhagenCopenhagen, Denmark
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Keage HAD, Churches OF, Kohler M, Pomeroy D, Luppino R, Bartolo ML, Elliott S. Cerebrovascular function in aging and dementia: a systematic review of transcranial Doppler studies. Dement Geriatr Cogn Dis Extra 2012; 2:258-70. [PMID: 22822408 PMCID: PMC3398823 DOI: 10.1159/000339234] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Background/Aim The contribution of cerebrovascular dysfunction to the manifestation of dementia and cognitive decline in late life is gaining increased attention. We aimed to systematically review evidence for associations between dementia or aging and cerebrovascular function as measured using transcranial Doppler (TCD) examination. Methods A total of 1,172 articles were retrieved from PsychInfo and PubMed searches, and 34 relevant articles were identified using a variety of TCD methods. Results The pulsatility index (vessel resistance), spontaneous emboli and cerebrovascular reactivity to hyper-/hypocapnia appeared good discriminators of dementia. Aging was associated with a slowing in blood flow velocity. Conclusion TCD ultrasonography is inexpensive, portable and well tolerated by aged and demented subjects. The technique stands to make a valuable contribution to the knowledge regarding the underlying functional biology of age-related cognitive change and dementia.
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Affiliation(s)
- Hannah A D Keage
- Cognitive Neuroscience Laboratory, School of Psychology, Social Work and Social Policy, Adelaide, S.A., Australia
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Sabayan B, Jansen S, Oleksik AM, van Osch MJ, van Buchem MA, van Vliet P, de Craen AJ, Westendorp RG. Cerebrovascular hemodynamics in Alzheimer's disease and vascular dementia: a meta-analysis of transcranial Doppler studies. Ageing Res Rev 2012; 11:271-7. [PMID: 22226802 DOI: 10.1016/j.arr.2011.12.009] [Citation(s) in RCA: 125] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2011] [Revised: 12/07/2011] [Accepted: 12/14/2011] [Indexed: 12/11/2022]
Abstract
BACKGROUND AND PURPOSE Alteration in cerebrovascular hemodynamics has reported in both ageing and dementia. However, it is still unclear whether this alteration follows similar pattern in ageing and in different dementia pathologies. The aim of this meta-analysis was to investigate changes in cerebral blood flow velocity and pulsatility index in two most common forms of dementia; Alzheimer's disease and vascular dementia, using transcranial Doppler studies. METHODS A literature search was conducted in Pubmed, EMBASE and Web of Science. After initial screening of 304 articles and removing duplicates, a total of 53 articles, published between 1980 and 2010, were reviewed. Finally 12 articles were included in the meta-analysis. For each study, effect sizes (ES) indicating the standardized mean differences of the hemodynamic measures between two groups were calculated. Using random effect models, pooled estimates of ES were measured. RESULTS Patients with Alzheimer's disease (ES=-1.09, 95% CI -1.77 to -0.44, p=0.004) and vascular dementia (ES=-1.62, 95% CI -2.26 to -0.98, p<0.001) had significantly lower cerebral blood flow velocity compared with healthy aged-matched controls. In addition, pulsatility index was significantly higher in both Alzheimer's disease (ES=0.5, 95% CI 0.28-0.72, p<0.001) and vascular dementia patients (ES=2.34, 95% CI 1.39-3.29, p<0.001). Patients with Alzheimer's disease had lower pulsatility index (ES=-1.22, 95% CI -1.98 to -0.46, p=0.002) compared to subjects with vascular type of dementia. CONCLUSIONS Patients with Alzheimer's disease and vascular dementia have a pronounced disturbance in their cerebrovascular hemodynamics. The severity of disturbances in cerebral hemodynamics is significantly lower in Alzheimer's disease compared to vascular dementia.
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Hansen N. Action mechanisms of transcranial direct current stimulation in Alzheimer's disease and memory loss. Front Psychiatry 2012; 3:48. [PMID: 22615703 PMCID: PMC3351674 DOI: 10.3389/fpsyt.2012.00048] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Accepted: 04/24/2012] [Indexed: 01/01/2023] Open
Abstract
The pharmacological treatment of Alzheimer's disease (AD) is often limited and accompanied by drug side effects. Thus alternative therapeutic strategies such as non-invasive brain stimulation are needed. Few studies have demonstrated that transcranial direct current stimulation (tDCS), a method of neuromodulation with consecutive robust excitability changes within the stimulated cortex area, is beneficial in AD. There is also evidence that tDCS enhances memory function in cognitive rehabilitation in depressive patients, Parkinson's disease, and stroke. tDCS improves working and visual recognition memory in humans and object-recognition learning in the elderly. AD's neurobiological mechanisms comprise changes in neuronal activity and the cerebral blood flow (CBF) caused by altered microvasculature, synaptic dysregulation from ß-amyloid peptide accumulation, altered neuromodulation via degenerated modulatory amine transmitter systems, altered brain oscillations, and changes in network connectivity. tDCS alters (i) neuronal activity and (ii) human CBF, (iii) has synaptic and non-synaptic after-effects (iv), can modify neurotransmitters polarity-dependently, (v) and alter oscillatory brain activity and (vi) functional connectivity patterns in the brain. It thus is reasonable to use tDCS as a therapeutic instrument in AD as it improves cognitive function in manner based on a disease mechanism. Moreover, it could prove valuable in other types of dementia. Future large-scale clinical and mechanism-oriented studies may enable us to identify its therapeutic validity in other types of demential disorders.
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Affiliation(s)
- Niels Hansen
- Department of Neurophysiology, Ruhr University Bochum Bochum, Germany
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Abstract
Cerebral autoregulation aims to stabilize blood flow to the brain during variations in perfusion pressure, thus protecting the brain against the risks of low or high systemic blood pressure. This vital mechanism is severely impaired in the transgenic mouse model of Alzheimer's disease (AD) that abundantly produces amyloid-β peptide β(1-42). These observations have been extrapolated to human AD, wherein impairment of autoregulation could have important implications for the clinical management and prevention of AD. Research on cerebral autoregulation in human AD, however, has only recently become available. Contrary to the animal models, preliminary studies suggest that cerebral autoregulation is preserved in patients with AD. Further research is urgently needed to elucidate this discrepancy in the current literature, given the accumulating evidence that implicates cerebrovascular pathology in AD.
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