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Cerebral autoregulation

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https://www.readbyqxmd.com/read/28821991/transcranial-doppler-in-autonomic-testing-standards-and-clinical-applications
#1
REVIEW
Lucy Norcliffe-Kaufmann, Brahyan Galindo-Mendez, Ana-Lucia Garcia-Guarniz, Estibaliz Villarreal-Vitorica, Vera Novak
When cerebral blood flow falls below a critical limit, syncope occurs and, if prolonged, ischemia leads to neuronal death. The cerebral circulation has its own complex finely tuned autoregulatory mechanisms to ensure blood supply to the brain can meet the high metabolic demands of the underlying neuronal tissue. This involves the interplay between myogenic and metabolic mechanisms, input from noradrenergic and cholinergic neurons, and the release of vasoactive substrates, including adenosine from astrocytes and nitric oxide from the endothelium...
August 18, 2017: Clinical Autonomic Research: Official Journal of the Clinical Autonomic Research Society
https://www.readbyqxmd.com/read/28819737/further-controversies-about-brain-tissue-oxygenation-pressure-reactivity-after-traumatic-brain-injury
#2
Morten Andresen, Joseph Donnelly, Marcel Aries, Marianne Juhler, David Menon, Pja Hutchinson, Peter Smielewski
BACKGROUND: Continuous monitoring of cerebral autoregulation is considered clinically useful due to its ability to warn against brain ischemic insults, which may translate to a relationship with adverse outcome. It is typically performed using the pressure reactivity index (PRx) based on mean arterial pressure and intracranial pressure. A new ORx index based on brain tissue oxygenation and cerebral perfusion pressure (CPP) has been proposed that similarly allows for evaluation of cerebrovascular reactivity...
August 17, 2017: Neurocritical Care
https://www.readbyqxmd.com/read/28818140/dynamic-cerebral-autoregulation-during-the-combination-of-mild-hypercapnia-and-cephalad-fluid-shift
#3
Takuya Kurazumi, Yojiro Ogawa, Ryo Yanagida, Hiroshi Morisaki, Ken-Ichi Iwasaki
BACKGROUND: Mild hypercapnia combined with a cephalad fluid shift [e.g., that occurring during spaceflight or laparoscopic surgery with head-down tilt (HDT)] might affect cerebral autoregulation. However, no reports have described the effects of the combination on dynamic cerebral autoregulation. Therefore, we tested the hypothesis that the combination of mild hypercapnia and a cephalad fluid shift would attenuate dynamic cerebral autoregulation. METHODS: There were 15 healthy male volunteers who were exposed to 4 10-min protocols in which they received air in the supine position (Placebo/Supine), 3% carbon dioxide (CO2) in the supine position (CO2/Supine), air with -10° HDT (Placebo/HDT) and 3% CO2 with -10° HDT (CO2/HDT)...
September 1, 2017: Aerospace Medicine and Human Performance
https://www.readbyqxmd.com/read/28816837/individualizing-thresholds-of-cerebral-perfusion-pressure-using-estimated-limits-of-autoregulation
#4
Joseph Donnelly, Marek Czosnyka, Hadie Adams, Chiara Robba, Luzius A Steiner, Danilo Cardim, Brenno Cabella, Xiuyun Liu, Ari Ercole, Peter John Hutchinson, David Krishna Menon, Marcel J H Aries, Peter Smielewski
OBJECTIVES: In severe traumatic brain injury, cerebral perfusion pressure management based on cerebrovascular pressure reactivity index has the potential to provide a personalized treatment target to improve patient outcomes. So far, the methods have focused on identifying "one" autoregulation-guided cerebral perfusion pressure target-called "cerebral perfusion pressure optimal". We investigated whether a cerebral perfusion pressure autoregulation range-which uses a continuous estimation of the "lower" and "upper" cerebral perfusion pressure limits of cerebrovascular pressure autoregulation (assessed with pressure reactivity index)-has prognostic value...
September 2017: Critical Care Medicine
https://www.readbyqxmd.com/read/28782872/the-role-of-vascular-resistance-in-bold-responses-to-progressive-hypercapnia
#5
James Duffin, Olivia Sobczyk, Adrian Crawley, Julien Poublanc, Lashmi Venkatraghavan, Kevin Sam, Alan Mutch, David Mikulis, Joseph Fisher
The ability of the cerebral vasculature to regulate vascular diameter, hence resistance and cerebral blood flow (CBF), in response to metabolic demands (neurovascular coupling), and perfusion pressure changes (autoregulation) may be assessed by measuring the CBF response to carbon dioxide (CO2 ). In healthy individuals, the CBF response to a ramp CO2 stimulus from hypocapnia to hypercapnia is assumed sigmoidal or linear. However, other response patterns commonly occur, especially in individuals with cerebrovascular disease, and these remain unexplained...
August 7, 2017: Human Brain Mapping
https://www.readbyqxmd.com/read/28750024/applying-time-frequency-analysis-to-assess-cerebral-autoregulation-during-hypercapnia
#6
Michał M Placek, Paweł Wachel, D Robert Iskander, Peter Smielewski, Agnieszka Uryga, Arkadiusz Mielczarek, Tomasz A Szczepański, Magdalena Kasprowicz
OBJECTIVE: Classic methods for assessing cerebral autoregulation involve a transfer function analysis performed using the Fourier transform to quantify relationship between fluctuations in arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV). This approach usually assumes the signals and the system to be stationary. Such an presumption is restrictive and may lead to unreliable results. The aim of this study is to present an alternative method that accounts for intrinsic non-stationarity of cerebral autoregulation and the signals used for its assessment...
2017: PloS One
https://www.readbyqxmd.com/read/28727580/increase-in-intracranial-pressure-by-application-of-a-rigid-cervical-collar-a-pilot-study-in-healthy-volunteers
#7
Iscander M Maissan, Rein Ketelaars, Boris Vlottes, Sanne E Hoeks, Dennis den Hartog, Robert J Stolker
OBJECTIVES: Rigid cervical collars are known to increase intracranial pressure (ICP) in severe traumatic brain injury (TBI). Cerebral blood flow might decrease according to the Kellie Monroe doctrine. For this reason, the use of the collar in patients with severe TBI has been abandoned from several trauma protocols in the Netherlands. There is no evidence on the effect of a rigid collar on ICP in patients with mild or moderate TBI or indeed patients with no TBI. As a first step we tested the effect in healthy volunteers with normal ICPs and intact autoregulation of the brain...
July 19, 2017: European Journal of Emergency Medicine: Official Journal of the European Society for Emergency Medicine
https://www.readbyqxmd.com/read/28719038/static-cerebrovascular-pressure-autoregulation-remains-intact-during-deep-hypothermia
#8
Dheeraj Goswami, Katherine McLeod, Samantha Leonard, Kathleen Kibler, Ronald Blaine Easley, Charles D Fraser, Dean Andropoulos, Ken Brady
BACKGROUND: Clinical studies measuring cerebral blood flow in infants during deep hypothermia have demonstrated diminished cerebrovascular pressure autoregulation. The coexistence of hypotension in these cohorts confounds the conclusion that deep hypothermia impairs cerebrovascular pressure autoregulation. AIM: We sought to compare the lower limit of autoregulation and the static rate of autoregulation between normothermic and hypothermic piglets. METHODS: Twenty anesthetized neonatal piglets (5-7 days old; 10 normothermic and 10 hypothermic to 20°C) had continuous measurements of cortical red cell flux using laser Doppler flowmetry, while hemorrhagic hypotension was induced without cardiopulmonary bypass...
September 2017: Paediatric Anaesthesia
https://www.readbyqxmd.com/read/28699412/pressure-autoregulation-measurement-techniques-in-adult-tbi-part-ii-a-scoping-review-of-continuous-methods
#9
Frederick Adam Zeiler, Joseph Donnelly, Leanne Calviello, Peter Smieleweski, David Menon, Marek Czosnyka
To perform systematically a scoping review of the literature on commonly described continuous autoregulation measurement techniques in adult TBI. The goal was to provide an overview of methodology and comprehensive reference library of the available literature for each technique. Five separate small systematic reviews were conducted for each of the continuous techniques: pressure reactivity index (PRx), laser Doppler flowmetry (LDF), near infrared spectroscopy (NIRS) techniques, brain tissue oxygen tension (PbtO2), and thermal diffusion (TD) techniques...
July 12, 2017: Journal of Neurotrauma
https://www.readbyqxmd.com/read/28694108/increased-blood-pressure-variability-upon-standing-up-improves-reproducibility-of-cerebral-autoregulation-indices
#10
Adam Mahdi, Dragana Nikolic, Anthony A Birch, Mette S Olufsen, Ronney B Panerai, David M Simpson, Stephen J Payne
Dynamic cerebral autoregulation, that is the transient response of cerebral blood flow to changes in arterial blood pressure, is currently assessed using a variety of different time series methods and data collection protocols. In the continuing absence of a gold standard for the study of cerebral autoregulation it is unclear to what extent does the assessment depend on the choice of a computational method and protocol. We use continuous measurements of blood pressure and cerebral blood flow velocity in the middle cerebral artery from the cohorts of 18 normotensive subjects performing sit-to-stand manoeuvre...
July 7, 2017: Medical Engineering & Physics
https://www.readbyqxmd.com/read/28694107/effects-of-non-physiological-blood-pressure-artefacts-on-cerebral-autoregulation
#11
Adam Mahdi, Erica M Rutter, Stephen J Payne
Cerebral autoregulation refers to the brain's regulation mechanisms that aim to maintain the cerebral blood flow approximately constant. It is often assessed by the autoregulation index (ARI). ARI uses arterial blood pressure and cerebral blood flow velocity time series to produce a ten-scale index of autoregulation performance (0 denoting the absence of and 9 the strongest autoregulation). Unfortunately, data are rarely free from various artefacts. Here, we consider four of the most common non-physiological blood pressure artefacts (saturation, square wave, reduced pulse pressure and impulse) and study their effects on ARI for a range of different artefact sizes...
July 7, 2017: Medical Engineering & Physics
https://www.readbyqxmd.com/read/28681121/indexes-of-cerebral-autoregulation-do-not-reflect-impairment-in-syncope-insights-from-head-up-tilt-test-of-vasovagal-and-autonomic-failure-subjects
#12
Pedro Castro, João Freitas, Rosa Santos, Ronney Panerai, Elsa Azevedo
PURPOSE: The study of dynamic cerebral autoregulation (CA), which adapts cerebral blood flow to arterial blood pressure (ABP) fluctuations, has been limited in orthostatic intolerance syndromes, mainly due to its stationary prerequisites hardly to meet during maneuvers to provoke syncope itself. New techniques of continuous estimates of CA could overcome this pitfall. We aimed to evaluate CA during head-up tilt test in common conditions causing syncope. METHODS: We compared three groups: eight controls; eight patients with autonomic failure due to familial amyloidotic polyneuropathy; eight patients with vasovagal syncope (VVS)...
July 5, 2017: European Journal of Applied Physiology
https://www.readbyqxmd.com/read/28674514/aspects-on-the-physiological-and-biochemical-foundations-of-neurocritical-care
#13
REVIEW
Carl-Henrik Nordström, Lars-Owe Koskinen, Magnus Olivecrona
Neurocritical care (NCC) is a branch of intensive care medicine characterized by specific physiological and biochemical monitoring techniques necessary for identifying cerebral adverse events and for evaluating specific therapies. Information is primarily obtained from physiological variables related to intracranial pressure (ICP) and cerebral blood flow (CBF) and from physiological and biochemical variables related to cerebral energy metabolism. Non-surgical therapies developed for treating increased ICP are based on knowledge regarding transport of water across the intact and injured blood-brain barrier (BBB) and the regulation of CBF...
2017: Frontiers in Neurology
https://www.readbyqxmd.com/read/28673505/the-first-sign-of-loss-of-consciousness
#14
Typ Whinnery, Estrella M Forster
The first clinically observable sign of an unconsciousness episode (UNCE) serves as the temporal sequence (kinetics) onset point for neurological events occurring during the loss of consciousness, unconsciousness and recovery of consciousness phases of the UNCE. The initial neurologic signs of 212 individuals exposed to gradual (N=114) and rapid (N=98) onset +Gz acceleration stress, inducing the ischemic LOC phase in 83.3±18.6s and 8.89±1.52s; p<0.001 respectively, were determined. The duration of the unconscious phase (considered absolute incapacitation) was 10...
July 1, 2017: Physiology & Behavior
https://www.readbyqxmd.com/read/28673382/rational-use-of-dopamine-in-hypotensive-newborns-improving-our-understanding-of-the-effect-on-cerebral-autoregulation
#15
Vibeke Ramsgaard Eriksen
Hypotension in critically ill newborn infants is associated with higher mortality and higher risk of cerebral injuries. Yet treating hypotension has never been shown to improve outcomes. In fact, some studies have found that hypotensive newborn infants who were treated with dopamine fared worse than a comparable group of newborn infants who were not. Therefore, a concern has been raised that dopamine might cause the observed adverse outcomes. Cerebral autoregulation is a protective mechanism that maintains a fairly constant cerebral blood flow despite fluctuations in blood pressure...
July 2017: Danish Medical Journal
https://www.readbyqxmd.com/read/28668343/changes-in-arterial-cerebral-blood-volume-during-lower-body-negative-pressure-measured-with-mri
#16
Joseph R Whittaker, Molly G Bright, Ian D Driver, Adele Babic, Sharmila Khot, Kevin Murphy
Cerebral Autoregulation (CA), defined as the ability of the cerebral vasculature to maintain stable levels of blood flow despite changes in systemic blood pressure, is a critical factor in neurophysiological health. Magnetic resonance imaging (MRI) is a powerful technique for investigating cerebrovascular function, offering high spatial resolution and wide fields of view (FOV), yet it is relatively underutilized as a tool for assessment of CA. The aim of this study was to demonstrate the potential of using MRI to measure changes in cerebrovascular resistance in response to lower body negative pressure (LBNP)...
June 28, 2017: NeuroImage
https://www.readbyqxmd.com/read/28664392/validation-of-near-infrared-spectroscopy-for-monitoring-cerebral-autoregulation-in-comatose-patients
#17
Lucia Rivera-Lara, Romergryko Geocadin, Andres Zorrilla-Vaca, Ryan Healy, Batya R Radzik, Caitlin Palmisano, Marek Mirski, Wendy C Ziai, Charles Hogue
BACKGROUND: Transcranial Doppler (TCD) noninvasively measures cerebral blood flow (CBF) velocity and is a well-studied method to monitor cerebral autoregulation (CA). Near-infrared spectroscopy (NIRS) has emerged as a promising noninvasive method to determine CA continuously by using regional cerebral oxygen saturation (rSO2) as a surrogate for CBF. Little is known about its accuracy to determine CA in patients with intracranial lesions. The purpose of this study was to assess the accuracy of rSO2-based CA monitoring with TCD methods in comatose patients with acute neurological injury...
June 29, 2017: Neurocritical Care
https://www.readbyqxmd.com/read/28657491/novel-noninvasive-method-of-cerebrovascular-blood-volume-assessment-using-brain-bioimpedance
#18
Mohamad H Tiba, Brendan M McCracken, Sardar Ansari, Ashwin Belle, Brandon C Cummings, Venkatakrishna Rajajee, Parag G Patil, Hasan B Alam, Kevin R Ward
Cerebrovascular autoregulation (CAR) is the ability of vessels to modulate their tone in response to changes in pressure. As an auto-protective mechanism, CAR is critical in preventing secondary brain injury post-trauma. Monitoring of changes in cerebral blood volume might be valuable in evaluating CAR and response to various therapies. In this study, we utilized an ocular-brain bioimpedance interface to assess real time changes in cerebral blood volume in response to a number of physiological challenges. We hypothesize that changes in brain bioimpedance (dz) would track changes in cerebral blood volume...
August 4, 2017: Journal of Neurotrauma
https://www.readbyqxmd.com/read/28656320/rho-kinase-and-the-nitric-oxide-pathway-modulate-basilar-arterial-reactivity-to-acetylcholine-and-angiotensin-ii-in-streptozotocin-induced-diabetic-mice
#19
Md Zahorul Islam, Cuong Van Dao, Atsushi Miyamoto, Mitsuya Shiraishi
Diabetes mellitus comprises a heterogeneous group of metabolic disorders with underlying hyperglycemia and secondary cardiovascular complications. Growing evidence suggests that vascular dysfunction is among the most important causes of diabetic cardiovascular disease. Therefore, we determined whether streptozotocin (STZ)-induced diabetes in mice affects blood pressure and cerebral arterial responsiveness to angiotensin (Ang) II and acetylcholine (ACh), which are important modulators of cerebrovascular autoregulation...
June 27, 2017: Naunyn-Schmiedeberg's Archives of Pharmacology
https://www.readbyqxmd.com/read/28655446/cerebral-autoregulation-making-sense-of-the-nonsensical
#20
EDITORIAL
Ken M Brady, Carlos M Mery
No abstract text is available yet for this article.
May 31, 2017: Journal of Thoracic and Cardiovascular Surgery
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