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Luchkanych AMS, Morse CJ, Boyes NG, Khan MR, Marshall RA, Morton JS, Tomczak CR, Olver TD. Cerebral sympatholysis: experiments on in vivo cerebrovascular regulation and ex vivo cerebral vasomotor control. Am J Physiol Heart Circ Physiol 2024; 326:H1105-H1116. [PMID: 38391313 DOI: 10.1152/ajpheart.00714.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 02/13/2024] [Accepted: 02/19/2024] [Indexed: 02/24/2024]
Abstract
Whether cerebral sympathetic-mediated vasomotor control can be modulated by local brain activity remains unknown. This study tested the hypothesis that the application or removal of a cognitive task during a cold pressor test (CPT) would attenuate and restore decreases in cerebrovascular conductance (CVC), respectively. Middle cerebral artery blood velocity (transcranial Doppler) and mean arterial pressure (finger photoplethysmography) were examined in healthy adults (n = 16; 8 females and 8 males) who completed a control CPT, followed by a CPT coupled with a cognitive task administered either 1) 30 s after the onset of the CPT and for the duration of the CPT or 2) at the onset of the CPT and terminated 30 s before the end of the CPT (condition order was counterbalanced). The major finding was that the CPT decreased the index of CVC, and such decreases were abolished when a cognitive task was completed concurrently and restored when the cognitive task was removed. As a secondary experiment, vasomotor interactions between sympathetic transduction pathways (α1-adrenergic and Y1-peptidergic) and compounds implicated in cerebral blood flow control [adenosine, and adenosine triphosphate (ATP)] were explored in isolated porcine cerebral arteries (wire myography). The data reveal α1-receptor agonism potentiated vasorelaxation modestly in response to adenosine, and preexposure to ATP attenuated contractile responses to α1-agonism. Overall, the data suggest a cognitive task attenuates decreases in CVC during sympathoexcitation, possibly related to an interaction between purinergic and α1-adrenergic signaling pathways.NEW & NOTEWORTHY The present study demonstrates that the cerebrovascular conductance index decreases during sympathoexcitation and this response can be positively and negatively modulated by the application or withdrawal of a nonexercise cognitive task. Furthermore, isolated vessel experiments reveal that cerebral α1-adrenergic agonism potentiates adenosine-mediated vasorelaxation and ATP attenuates α1-adrenergic-mediated vasocontraction.
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Affiliation(s)
- Adam M S Luchkanych
- College of Kinesiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Cameron J Morse
- Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Natasha G Boyes
- College of Kinesiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - M Rafique Khan
- College of Kinesiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Rory A Marshall
- Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Jude S Morton
- Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Corey R Tomczak
- College of Kinesiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - T Dylan Olver
- Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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Stewart JM, Medow MS. Anticipatory central command on standing decreases cerebral blood velocity causing hypocapnia in hyperpneic postural tachycardia syndrome. J Appl Physiol (1985) 2023; 135:26-34. [PMID: 37227184 PMCID: PMC10281786 DOI: 10.1152/japplphysiol.00016.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Revised: 05/16/2023] [Accepted: 05/18/2023] [Indexed: 05/26/2023] Open
Abstract
Fifty percent of patients with postural tachycardia syndrome (POTS) are hypocapnic during orthostasis related to initial orthostatic hypotension (iOH). We determined whether iOH drives hypocapnia in POTS by low BP or decreased cerebral blood velocity (CBv). We studied three groups; healthy volunteers (n = 32, 18 ± 3 yr) were compared with POTS, grouped by presence [POTS-low end-tidal CO2 (↓ETCO2), n = 26, 19 ± 2 yr] or absence [POTS-normal upright end-tidal carbon dioxide (nlCO2), n = 28, 19 ± 3 yr] of standing hypocapnia defined by end-tidal CO2 (ETCO2) ≤ 30 mmHg at steady-state, measuring middle cerebral artery CBv, heart rate (HR), and beat-to-beat blood pressure (BP). After 30 min supine, subjects stood for 5 min. Quantities were measured prestanding, at minimum CBv, minimum BP, peak HR, CBv recovery, BP recovery, minimum HR, steady-state, and 5 min. Baroreflex gain was estimated by α index. iOH occurred with similar frequency and minimum BP in POTS-↓ETCO2 and POTS-nlCO2. Minimum CBv was reduced significantly (P < 0.05) in POTS-↓ETCO2 (48 ± 3 cm/s) preceding hypocapnia compared with POTS-nlCO2 (61 ± 3 cm/s) or Control (60 ± 2 cm/s). The anticipatory increased BP was significantly larger (P < 0.05) in POTS (8 ± 1 mmHg vs. 2 ± 1) and began ∼8 s prestanding. HR increased in all subjects, CBv increased significantly (P < 0.05) in both POTS-nlCO2 (76 ± 2 to 85 ± 2 cm/s) and Control (75 ± 2 to 80 ± 2 cm/s) consistent with central command. CBv decreased in POTS-↓ETCO2 (76 ± 3 to 64 ± 3 cm/s) correlating with decreased baroreflex gain. Cerebral conductance [meanCBv/mean arterial blood pressure (MAP)] was reduced in POTS-↓ETCO2 throughout. Data support the hypothesis that excessively reduced CBv during iOH may intermittently reduce carotid body blood flow, sensitizing that organ and producing postural hyperventilation in POTS-↓ETCO2. Excessive fall in CBv occurs in part during prestanding central command and is a facet of defective parasympathetic regulation in POTS.NEW & NOTEWORTHY Dyspnea is frequent in postural tachycardia syndrome (POTS) and is associated with upright hyperpnea and hypocapnia that drives sinus tachycardia. It is initiated by an exaggerated reduction in cerebral conductance and decreased cerebral blood flow (CBF) that precedes the act of standing. This is a form of autonomically mediated "central command." Cerebral blood flow is further reduced by initial orthostatic hypotension common in POTS. Hypocapnia is maintained during the standing response and might account for persistent postural tachycardia.
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Affiliation(s)
- Julian M Stewart
- Department of Pediatrics, New York Medical College, Valhalla, New York, United States
- Department of Physiology, New York Medical College, Valhalla, New York, United States
| | - Marvin S Medow
- Department of Pediatrics, New York Medical College, Valhalla, New York, United States
- Department of Physiology, New York Medical College, Valhalla, New York, United States
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Marmarelis VZ, Shin DC, Hamner JW, Tan CO. Dynamic effects of cholinergic blockade upon cerebral blood flow autoregulation in healthy adults. Front Physiol 2022; 13:1015544. [PMID: 36406984 PMCID: PMC9666788 DOI: 10.3389/fphys.2022.1015544] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Accepted: 10/05/2022] [Indexed: 01/25/2023] Open
Abstract
Background: Cerebral flow autoregulation (CFA) is a homeostatic mechanism critical for survival. The autonomic nervous system (ANS) plays a key role in maintaining proper CFA function. More quantitative studies of how the ANS influences CFA are desirable. Objective: To discover and quantify the dynamic effects of cholinergic blockade upon CFA in response to changes of arterial blood pressure and blood CO2 tension in healthy adults. Methods: We analyzed time-series data of spontaneous beat-to-beat mean arterial blood pressure (ABP) and cerebral blood flow velocity in the middle cerebral arteries (CFV), as well as breath-to-breath end-tidal CO2 (CO2), collected in 9 adults before and after cholinergic blockade, in order to obtain subject-specific predictive input-output models of the dynamic effects of changes in ABP and CO2 (inputs) upon CFV (output). These models are defined in convolutional form using "kernel" functions (or, equivalently, Transfer Functions in the frequency domain) that are estimated via the robust method of Laguerre expansions. Results: Cholinergic blockade caused statistically significant changes in the obtained kernel estimates (and the corresponding Transfer Functions) that define the linear dynamics of the ABP-to-CFV and CO2-to-CFV causal relations. The kernel changes due to cholinergic blockade reflect the effects of the cholinergic mechanism and exhibited, in the frequency domain, resonant peaks at 0.22 Hz and 0.06 Hz for the ABP-to-CFV and CO2-to-CFV dynamics, respectively. Conclusion: Quantitative estimates of the dynamics of the cholinergic component in CFA are found as average changes of the ABP-to-CFV and CO2-to-CFV kernels, and corresponding Transfer Functions, before and after cholinergic blockade.
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Affiliation(s)
- Vasilis Z. Marmarelis
- Biomedical Engineering, University of Southern CA, Los Angeles, MA, United States,*Correspondence: Vasilis Z. Marmarelis,
| | - Dae C. Shin
- Biomedical Engineering, University of Southern CA, Los Angeles, MA, United States
| | - Jason W. Hamner
- Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, Boston, MA, United States
| | - Can Ozan Tan
- Electrical Engineering Math and Computer Science, University of Twente, Enschede, Netherlands
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Larson S, Anderson L, Thomson S. Effect of phenylephrine on cerebral oxygen saturation and cardiac output in adults when used to treat intraoperative hypotension: a systematic review. JBI Evid Synth 2021; 19:34-58. [PMID: 32941358 DOI: 10.11124/jbisrir-d-19-00352] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
OBJECTIVE The objective of this review was to examine the effect of phenylephrine on cerebral oxygen saturation, cardiac output, and middle cerebral artery blood flow velocity when used to treat intraoperative hypotension. INTRODUCTION While the etiology of postoperative cognitive dysfunction in adults following surgery is likely multifactorial, intraoperative cerebral hypoperfusion is a commonly proposed mechanism. Research evidence and expert opinion are emerging that suggest phenylephrine adversely affects cerebral oxygen saturation and may also adversely affect cerebral perfusion via a reduction in cardiac output or cerebral vascular vasoconstriction. The administration of phenylephrine to treat intraoperative hypotension is common anesthesia practice, despite a lack of evidence to show it improves cerebral perfusion. Therefore, a systematic review of the effect of phenylephrine on cerebral hemodynamics has significant implications for anesthesia practice and future research. INCLUSION CRITERIA Studies of adults 18 years and over undergoing elective, non-neurosurgical procedures involving anesthesia were included. In these studies, participants received phenylephrine to treat intraoperative hypotension. The effect of phenylephrine on cerebral oxygen saturation, cardiac output, or middle cerebral artery blood flow velocity was measured. METHODS Key information sources searched included MEDLINE (Ovid), Embase, CINAHL (EBSCO), and Google Scholar. The scope of the search was limited to English-language studies published from 1999 through 2017. The recommended JBI approach to critical appraisal, study selection, data extraction, and data synthesis were used. RESULTS This systematic review found that phenylephrine consistently decreased cerebral oxygen saturation values despite simultaneously increasing mean arterial pressure to normal range. Results also found that ephedrine and dopamine were superior to phenylephrine in maintaining or increasing values. Phenylephrine was found to be similar to vasopressin in the extent to which both decreased cerebral oxygen saturation values. Results also showed that phenylephrine resulted in statistically significant declines in cardiac output, or failed to improve abnormally low preintervention values. The effect of phenylephrine on middle cerebral artery blood flow velocity was only measured in one study and showed that phenylephrine increased flow velocity by about 20%. Statistical pooling of the study results was not possible due to the gross variation in how the intervention was administered and how effect was measured. CONCLUSIONS This review found that phenylephrine administration resulted in declines in cerebral oxygen saturation and cardiac output. However, the research studies were ineffective in informing phenylephrine's mechanism of action or its impact on postoperative cognitive function. SYSTEMATIC REVIEW REGISTRATION NUMBER PROSPERO (CRD42018100740).
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Affiliation(s)
- Sandra Larson
- Rosalind Franklin University of Medicine and Science: A JBI Affiliated Group, Chicago, IL, USA
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Moerman AT, Vandenheuvel M, Tuybens PJ, Van Gompel C, De Hert SG. Incongruous effect of phenylephrine on changes in cerebral blood volume measured by near-infrared spectroscopy (NIRS) indicating extracranial contamination. J Clin Monit Comput 2021; 36:745-750. [PMID: 33846886 DOI: 10.1007/s10877-021-00702-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 04/01/2021] [Indexed: 11/28/2022]
Abstract
We assessed extracranial contamination of the near-infrared spectroscopy (NIRS) signal during administration of phenylephrine. The study was performed with NIRO 200NX which employs both the Modified Beer-Lambert (MBL) method to measure total hemoglobin (tHb, expressed in µM), and Spatially Resolved Spectroscopy (SRS) to measure total hemoglobin content (nTHI, expressed in arbitrary units (a.u.)). SRS tends to not be affected by extracranial blood flow. As vasoconstriction with phenylephrine mainly occurs in the extracranial area, we hypothesized that if NIRS measurements are indeed prone to extracranial contamination, tHb will be more affected by the administration of phenylephrine than nTHI. After ethical committee approval, 20 consenting cardiac surgery patients were included. Phenylephrine was administered whenever clinically indicated and its effect on nTHI and tHb was evaluated. To adjust for the difference in raw scale units, Z-scores were calculated. Data were analyzed with Wilcoxon Signed Ranks Test and the Hodges-Lehmann method. A total of 191 data sets were obtained in 20 patients (10 male, 65 ± 15 years, 77 ± 16 kg, 166 ± 11 cm). The median difference before and after administration of phenylephrine was - 0.006 a.u. [95%CI - 0.010 to - 0.002] (p < 0.001) and - 0.415 µM [95%CI - 0.665 to - 0.205] (p < 0.001) for nTHI and tHb, respectively. The median difference between the Z-scores of nTHI and tHb was - 0.02 [95%CI - 0.04 to - 0.003] (p = 0.03), with a higher variability in the Z-scores of tHb. Phenylephrine induced significant larger changes in MBL values compared to SRS values, indicating that the MBL method might be more prone to extracranial contamination. Trial and clinical registry: Trial registration number: B670201939459, ethical committee number: 2019/0265, date of approval: March 19, 2019.
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Affiliation(s)
- Annelies T Moerman
- Department of Anesthesia, University Hospital Ghent, Corneel Heymanslaan 10, 9000, Ghent, Belgium.
| | - Michaël Vandenheuvel
- Department of Anesthesia, University Hospital Ghent, Corneel Heymanslaan 10, 9000, Ghent, Belgium
| | - Pieter-Jan Tuybens
- Department of Anesthesia, University Hospital Ghent, Corneel Heymanslaan 10, 9000, Ghent, Belgium
| | - Carla Van Gompel
- Department of Anesthesia, University Hospital Ghent, Corneel Heymanslaan 10, 9000, Ghent, Belgium
| | - Stefan G De Hert
- Department of Anesthesia, University Hospital Ghent, Corneel Heymanslaan 10, 9000, Ghent, Belgium
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Burma JS, Macaulay A, Copeland PV, Khatra O, Bouliane KJ, Smirl JD. Temporal evolution of neurovascular coupling recovery following moderate- and high-intensity exercise. Physiol Rep 2021; 9:e14695. [PMID: 33463899 PMCID: PMC7814491 DOI: 10.14814/phy2.14695] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 11/24/2020] [Accepted: 12/01/2020] [Indexed: 01/13/2023] Open
Abstract
PURPOSE Studies examining neurovascular coupling (NVC) require participants to refrain from exercise for 12-24 hours. However, there is a paucity of empirical evidence for this restriction. The objectives for this study were to delineate the time-course recovery of NVC metrics following exercise and establish the NVC within- and between-day reliability. METHODS Nine participants completed a complex visual search paradigm to assess NVC via transcranial Doppler ultrasound of the posterior cerebral artery blood velocity (PCA). Measurements were performed prior to and throughout the 8-hour recovery period following three randomized conditions: 45 minutes of moderate-intensity exercise (at 50% heart-rate reserve), 30 minutes high-intensity intervals (10, 1-minute intervals at 85% heart-rate reserve), and control (30 minutes quiet rest). In each condition, baseline measures were collected at 8:00am with serial follow-ups at hours zero, one, two, four, six, and eight. RESULTS Area-under-the-curve and time-to-peak PCA velocity during the visual search were attenuated at hour zero following high-intensity intervals (all p < 0.05); however, these NVC metrics recovered at hour one (all p > 0.13). Conversely, baseline PCA velocity, peak PCA velocity, and the relative percent increase were not different following high-intensity intervals compared to baseline (all p > 0.26). No NVC metrics differed from baseline following both moderate exercise and control conditions (all p > 0.24). The majority of the NVC parameters demonstrated high levels of reliability (intraclass correlation coefficient: >0.90). CONCLUSION Future NVC assessments can take place a minimum of one hour following exercise. Moreover, all metrics did not change across the control condition, therefore future studies using this methodology can reliably quantify NVC between 8:00am and 7:00 pm.
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Affiliation(s)
- Joel S. Burma
- Concussion Research LaboratoryFaculty of Health and Exercise ScienceUniversity of British ColumbiaKelownaBCCanada
- Sport Injury Prevention Research CentreFaculty of KinesiologyUniversity of CalgaryCalgaryABCanada
- Human Performance LaboratoryFaculty of KinesiologyUniversity of CalgaryCalgaryABCanada
- Hotchkiss Brain InstituteUniversity of CalgaryCalgaryABCanada
- Alberta Children’s Hospital Research InstituteUniversity of CalgaryCalgaryABCanada
- Libin Cardiovascular Institute of AlbertaUniversity of CalgaryABCanada
| | - Alannah Macaulay
- Concussion Research LaboratoryFaculty of Health and Exercise ScienceUniversity of British ColumbiaKelownaBCCanada
- School of Health Sciences, Nuclear MedicineBritish Columbia Institute of TechnologyBurnabyBCCanada
| | - Paige V. Copeland
- Concussion Research LaboratoryFaculty of Health and Exercise ScienceUniversity of British ColumbiaKelownaBCCanada
| | - Omeet Khatra
- Faculty of MedicineUniversity of British ColumbiaVancouverBCCanada
| | - Kevin J. Bouliane
- Concussion Research LaboratoryFaculty of Health and Exercise ScienceUniversity of British ColumbiaKelownaBCCanada
| | - Jonathan D. Smirl
- Concussion Research LaboratoryFaculty of Health and Exercise ScienceUniversity of British ColumbiaKelownaBCCanada
- Sport Injury Prevention Research CentreFaculty of KinesiologyUniversity of CalgaryCalgaryABCanada
- Human Performance LaboratoryFaculty of KinesiologyUniversity of CalgaryCalgaryABCanada
- Hotchkiss Brain InstituteUniversity of CalgaryCalgaryABCanada
- Alberta Children’s Hospital Research InstituteUniversity of CalgaryCalgaryABCanada
- Libin Cardiovascular Institute of AlbertaUniversity of CalgaryABCanada
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Matsuo N, Matsuo S, Nakamura Y, Ezomo FO, Kawai Y. Regulatory effects of cervical sympathetic trunk and renal sympathetic nerve activities on cerebral blood flow during head-down postural rotations. Auton Neurosci 2020; 229:102738. [PMID: 33197695 DOI: 10.1016/j.autneu.2020.102738] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Revised: 10/28/2020] [Accepted: 10/29/2020] [Indexed: 11/19/2022]
Abstract
This study attempts to clarify the neural control of cerebral blood flow (CBF) during head-down postural rotation, which induces a cephalad fluid shift in urethane-anesthetized rats. The animals were placed on a table, tilted to a 45° head-down position over 5 s and maintained in that position. Head-down rotation (HDR) induced a transient decrease (8 ± 3 mm Hg; mean ± SE) in mean arterial blood pressure (ABP) at 7.3 ± 0.3 s after the onset of HDR. The pressure returned to the pre-HDR level within 1 min in the head-down position. Pretreatment with hexamethonium bromide suppressed the HDR-elicited decrease in ABP, suggesting that the decrease in ABP was induced by the suppression of autonomic neural outflow. The administration of phenoxybenzamine (PB), an α-adrenergic antagonist, also eliminated the HDR-elicited decrease in ABP, suggesting that this decrease was elicited by the suppression of α-adrenergic vascular tone. To test sympathetic outflow during HDR, renal sympathetic nerve activity (RSNA) and cervical sympathetic trunk (CST) activity (CSTA) were recorded. RSNA was transiently suppressed at 2.3 ± 0.4 s after HDR onset, followed by a decrease in ABP, suggesting that this decrease was, at least in part, induced by the suppression of sympathetic nerves. CSTA did not change significantly during HDR. These results suggest that HDR suppresses sympathetic nerves in the lower body rather than in the head, which might result in a decrease in ABP. To test the effect of the decrease in ABP due to sympathetic activity on CBF during HDR, changes in CBF during HDR were measured. CBF did not change significantly during HDR in the control group after the administration of an α-receptor blocker or after denervation of the CSTs. These results suggest that the impact of the CSTs on CBF is likely to be limited by a rapid increase in CBF due to HDR-elicited cephalad fluid shift and that CBF autoregulation proceeds through an alternative mechanism involving the myogenic properties of cerebral vessels.
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Affiliation(s)
- Noriko Matsuo
- Division of Adaptation Physiology, Department of Physiology, Tottori University Faculty of Medicine, 86 Nishi-cho, Yonago 683-8503, Japan
| | - Satoshi Matsuo
- Division of Adaptation Physiology, Department of Physiology, Tottori University Faculty of Medicine, 86 Nishi-cho, Yonago 683-8503, Japan.
| | - Yosuke Nakamura
- Division of Adaptation Physiology, Department of Physiology, Tottori University Faculty of Medicine, 86 Nishi-cho, Yonago 683-8503, Japan
| | - Felix Ojeiru Ezomo
- Division of Adaptation Physiology, Department of Physiology, Tottori University Faculty of Medicine, 86 Nishi-cho, Yonago 683-8503, Japan
| | - Yasuaki Kawai
- Division of Adaptation Physiology, Department of Physiology, Tottori University Faculty of Medicine, 86 Nishi-cho, Yonago 683-8503, Japan
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Immink RV, Sperna Weiland NH, van den Dool REC, van der Ster BJP, Hollmann MW. Cerebral autoregulation: with age comes wisdom. Br J Anaesth 2019; 123:e466-e468. [PMID: 31280889 DOI: 10.1016/j.bja.2019.06.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 06/06/2019] [Accepted: 06/06/2019] [Indexed: 11/24/2022] Open
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Bojić T. Editorial: Neurocardiovascular Diseases: New Aspects of the Old Issues. Front Neurosci 2019; 12:1032. [PMID: 30686991 PMCID: PMC6336917 DOI: 10.3389/fnins.2018.01032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Accepted: 12/20/2018] [Indexed: 11/24/2022] Open
Affiliation(s)
- Tijana Bojić
- Laboratory of Radiobiology and Molecular Genetics, Institute of Nuclear Sciences Vinča, University of Belgrade, Belgrade, Serbia
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Cornwell WK, Tarumi T, Lawley J, Ambardekar AV. CrossTalk opposing view: Blood flow pulsatility in left ventricular assist device patients is not essential to maintain normal brain physiology. J Physiol 2018; 597:357-359. [PMID: 30560586 DOI: 10.1113/jp276730] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Affiliation(s)
- William K Cornwell
- Department of Medicine, Division of Cardiology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Takashi Tarumi
- Human Informatics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
| | - Justin Lawley
- Department of Sports Science, Division of Physiology, University of Innsbruck, Innsbruck, Austria
| | - Amrut V Ambardekar
- Department of Medicine, Division of Cardiology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
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Slupe AM, Kirsch JR. Effects of anesthesia on cerebral blood flow, metabolism, and neuroprotection. J Cereb Blood Flow Metab 2018; 38:2192-2208. [PMID: 30009645 PMCID: PMC6282215 DOI: 10.1177/0271678x18789273] [Citation(s) in RCA: 160] [Impact Index Per Article: 26.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2018] [Revised: 06/11/2018] [Accepted: 06/25/2018] [Indexed: 12/12/2022]
Abstract
Administration of anesthetic agents fundamentally shifts the responsibility for maintenance of homeostasis from the patient and their intrinsic physiological regulatory mechanisms to the anesthesiologist. Continuous delivery of oxygen and nutrients to the brain is necessary to prevent irreversible injury and arises from a complex series of regulatory mechanisms that ensure uninterrupted cerebral blood flow. Our understanding of these regulatory mechanisms and the effects of anesthetics on them has been driven by the tireless work of pioneers in the field. It is of paramount importance that the anesthesiologist shares this understanding. Herein, we will review the physiological determinants of cerebral blood flow and how delivery of anesthesia impacts these processes.
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Affiliation(s)
- Andrew M Slupe
- Department of Anesthesiology and Perioperative Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Jeffrey R Kirsch
- Department of Anesthesiology and Perioperative Medicine, Oregon Health and Science University, Portland, OR, USA
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The pial vasculature of the mouse develops according to a sensory-independent program. Sci Rep 2018; 8:9860. [PMID: 29959346 PMCID: PMC6026131 DOI: 10.1038/s41598-018-27910-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 06/12/2018] [Indexed: 12/15/2022] Open
Abstract
The cerebral vasculature is organized to supply the brain’s metabolic needs. Sensory deprivation during the early postnatal period causes altered neural activity and lower metabolic demand. Neural activity is instructional for some aspects of vascular development, and deprivation causes changes in capillary density in the deprived brain region. However, it is not known if the pial arteriole network, which contains many leptomeningeal anastomoses (LMAs) that endow the network with redundancy against occlusions, is also affected by sensory deprivation. We quantified the effects of early-life sensory deprivation via whisker plucking on the densities of LMAs and penetrating arterioles (PAs) in anatomically-identified primary sensory regions (vibrissae cortex, forelimb/hindlimb cortex, visual cortex and auditory cortex) in mice. We found that the densities of penetrating arterioles were the same across cortical regions, though the hindlimb representation had a higher density of LMAs than other sensory regions. We found that the densities of PAs and LMAs, as well as quantitative measures of network topology, were not affected by sensory deprivation. Our results show that the postnatal development of the pial arterial network is robust to sensory deprivation.
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Larson SL, Anderson LR, Thomson JS. The effect of phenylephrine on cerebral perfusion when used to treat anesthesia-induced hypotension: a systematic review protocol. JBI DATABASE OF SYSTEMATIC REVIEWS AND IMPLEMENTATION REPORTS 2018; 16:1346-1353. [PMID: 29894402 DOI: 10.11124/jbisrir-2017-003426] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
REVIEW QUESTION The question of this review is: What is the effect of intravenous phenylephrine on cerebral perfusion in adult patients when administered to treat anesthesia-induced hypotension?
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Affiliation(s)
- Sandra Louise Larson
- Rosalind Franklin University of Medicine and Science: a Joanna Briggs Institute Affiliated Group, Chicago, USA
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Budidha K, Kyriacou PA. Investigation of photoplethysmography and arterial blood oxygen saturation from the ear-canal and the finger under conditions of artificially induced hypothermia. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2018; 2015:7954-7. [PMID: 26738137 DOI: 10.1109/embc.2015.7320237] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Pulse oximeters relay on the technique of photoplethysmography (PPG) to estimate arterial oxygen saturation (SpO2). In conditions of poor peripheral perfusion such as hypotension, hypothermia, and vasoconstriction, pulse oximeters become inaccurate or provide no reading. This is due to the poor quality of the PPG signals detected at that instance. In order to overcome this problem, the ear canal has been proposed as a alternative measurement site for measuring reliable SpO2. Hence, an ear canal PPG sensor was developed along with a PPG processing system. The performance of the sensor was evaluated by measuring the red and infrared PPGs and SpO2 from 10 healthy volunteers undergoing artificially induced hypothermia. The results from the ear canal sensor were compared with simultaneously acquired results from the finger. Hypothermia was induced by exposing the volunteers to cold temperatures of 10 ± 1°C. The results acquired suggest that the ear canal pulse oximeter endures more in estimating SpO2 values accurately when compared with the more common finger pulse oximeter.
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15
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Goyal D, Goyal R. Developmental Maturation and Alpha-1 Adrenergic Receptors-Mediated Gene Expression Changes in Ovine Middle Cerebral Arteries. Sci Rep 2018; 8:1772. [PMID: 29379105 PMCID: PMC5789090 DOI: 10.1038/s41598-018-20210-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Accepted: 01/15/2018] [Indexed: 11/23/2022] Open
Abstract
The Alpha Adrenergic Signaling Pathway is one of the chief regulators of cerebrovascular tone and cerebral blood flow (CBF), mediating its effects in the arteries through alpha1-adrenergic receptors (Alpha1AR). In the ovine middle cerebral artery (MCA), with development from a fetus to an adult, others and we have shown that Alpha1AR play a key role in contractile responses, vascular development, remodeling, and angiogenesis. Importantly, Alpha1AR play a significant role in CBF autoregulation, which is incompletely developed in a premature fetus as compared to a near-term fetus. However, the mechanistic pathways are not completely known. Thus, we tested the hypothesis that as a function of maturation and in response to Alpha1AR stimulation there is a differential gene expression in the ovine MCA. We conducted microarray analysis on transcripts from MCAs of premature fetuses (96-day), near-term fetuses (145-day), newborn lambs, and non-pregnant adult sheep (2-year) following stimulation of Alpha1AR with phenylephrine (a specific agonist). We observed several genes which belonged to pro-inflammatory and vascular development/angiogenesis pathway significantly altered in all of the four age groups. We also observed age-specific changes in gene expression–mediated by Alpha1AR stimulation in the different developmental age groups. These findings imply complex regulatory mechanisms of cerebrovascular development.
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Affiliation(s)
- Dipali Goyal
- Center for Perinatal Biology, School of Medicine, Loma Linda University, Loma Linda, CA, USA
| | - Ravi Goyal
- Center for Perinatal Biology, School of Medicine, Loma Linda University, Loma Linda, CA, USA.
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16
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Brassard P, Tymko MM, Ainslie PN. Sympathetic control of the brain circulation: Appreciating the complexities to better understand the controversy. Auton Neurosci 2017; 207:37-47. [DOI: 10.1016/j.autneu.2017.05.003] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Revised: 05/03/2017] [Accepted: 05/04/2017] [Indexed: 12/24/2022]
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17
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Verbree J, Bronzwaer A, van Buchem MA, Daemen M, van Lieshout JJ, van Osch M. Middle cerebral artery diameter changes during rhythmic handgrip exercise in humans. J Cereb Blood Flow Metab 2017; 37:2921-2927. [PMID: 27837189 PMCID: PMC5536799 DOI: 10.1177/0271678x16679419] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Transcranial Doppler (TCD) sonography is a frequently employed technique for quantifying cerebral blood flow by assuming a constant arterial diameter. Given that exercise increases arterial pressure by sympathetic activation, we hypothesized that exercise might induce a change in the diameter of large cerebral arteries. Middle cerebral artery (MCA) cross-sectional area was assessed in response to handgrip exercise by direct magnetic resonance imaging (MRI) observations. Twenty healthy subjects (11 female) performed three 5 min bouts of rhythmic handgrip exercise at 60% maximum voluntary contraction, alternated with 5 min of rest. High-resolution 7 T MRI scans were acquired perpendicular to the MCA. Two blinded observers manually determined the MCA cross-sectional area. Sufficient image quality was obtained in 101 MCA-scans of 19 subjects (age-range 20-59 years). Mixed effects modelling showed that the MCA cross-sectional area decreased by 2.1 ± 0.8% (p = 0.01) during handgrip, while the heart rate increased by 11 ± 2% (p < 0.001) at constant end-tidal CO2 (p = 0.10). In conclusion, the present study showed a 2% decrease in MCA cross-sectional area during rhythmic handgrip exercise. This further strengthens the current concept of sympathetic control of large cerebral arteries, showing in vivo vasoconstriction during exercise-induced sympathetic activation. Moreover, care must be taken when interpreting TCD exercise studies as diameter constancy cannot be assumed.
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Affiliation(s)
- J Verbree
- 1 Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Agt Bronzwaer
- 2 Department of Internal Medicine, Academic Medical Center, Amsterdam, The Netherlands.,3 Laboratory for Clinical Cardiovascular Physiology, Academic Medical Center, Amsterdam, The Netherlands
| | - M A van Buchem
- 1 Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Mjap Daemen
- 4 Department of Pathology, Academic Medical Center, Amsterdam, The Netherlands
| | - J J van Lieshout
- 2 Department of Internal Medicine, Academic Medical Center, Amsterdam, The Netherlands.,3 Laboratory for Clinical Cardiovascular Physiology, Academic Medical Center, Amsterdam, The Netherlands.,5 MRC/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Nottingham, UK
| | - Mjp van Osch
- 1 Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
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18
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Flück D, Ainslie PN, Bain AR, Wildfong KW, Morris LE, Fisher JP. Extra- and intracranial blood flow regulation during the cold pressor test: influence of age. J Appl Physiol (1985) 2017; 123:1071-1080. [PMID: 28663374 DOI: 10.1152/japplphysiol.00224.2017] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Revised: 05/30/2017] [Accepted: 06/26/2017] [Indexed: 11/22/2022] Open
Abstract
We determined how the extra- and intracranial circulations respond to generalized sympathetic activation evoked by a cold pressor test (CPT) and whether this is affected by healthy aging. Ten young [23 ± 2 yr (means ± SD)] and nine older (66 ± 3 yr) individuals performed a 3-min CPT by immersing the left foot into 0.8 ± 0.3°C water. Common carotid artery (CCA) and internal carotid artery (ICA) diameter, velocity, and flow were simultaneously measured (duplex ultrasound) along with middle cerebral artery and posterior cerebral artery mean blood velocity (MCAvmean and PCAvmean) and cardiorespiratory variables. The increases in heart rate (~6 beats/min) and mean arterial blood pressure (~14 mmHg) were similar in young and older groups during the CPT (P < 0.01 vs. baseline). In the young group, the CPT elicited an ~5% increase in CCA diameter (P < 0.01 vs. baseline) and a tendency for an increase in CCA flow (~12%, P = 0.08); in contrast, both diameter and flow remained unchanged in the older group. Although ICA diameter was not changed during the CPT in either group, ICA flow increased (~8%, P = 0.02) during the first minute of the CPT in both groups. Whereas the CPT elicited an increase in MCAvmean and PCAvmean in the young group (by ~20 and ~10%, respectively, P < 0.01 vs. baseline), these intracranial velocities were unchanged in the older group. Collectively, during the CPT, these findings suggest a differential mechanism(s) of regulation between the ICA compared with the CCA in young individuals and a blunting of the CCA and intracranial responses in older individuals.NEW & NOTEWORTHY Sympathetic activation evoked by a cold pressor test elicits heterogeneous extra- and intracranial blood vessel responses in young individuals that may serve an important protective role. The extra- and intracranial responses to the cold pressor test are blunted in older individuals.
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Affiliation(s)
- Daniela Flück
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, 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, Kelowna, British Columbia, Canada; and
| | - Anthony R Bain
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada; and
| | - Kevin W Wildfong
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada; and
| | - Laura E Morris
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada; and
| | - James P Fisher
- School of Sport, Exercise, and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
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19
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Whittaker JR, Bright MG, Driver ID, Babic A, Khot S, Murphy K. Changes in arterial cerebral blood volume during lower body negative pressure measured with MRI. Neuroimage 2017; 187:166-175. [PMID: 28668343 PMCID: PMC6414398 DOI: 10.1016/j.neuroimage.2017.06.041] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 06/19/2017] [Indexed: 01/12/2023] Open
Abstract
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). A Pulsed Arterial Spin Labeling (PASL) approach with short inversion times (TI) was used to estimate cerebral arterial blood volume (CBVa) in eight healthy subjects at baseline and −40 mmHg LBNP. We estimated group mean CBVa values of 3.13 ± 1.00 and 2.70 ± 0.38 for baseline and lbnp respectively, which were the result of a differential change in CBVa during −40 mmHg LBNP that was dependent on baseline CBVa. These data suggest that the PASL CBVa estimates are sensitive to the complex cerebrovascular response that occurs during the moderate orthostatic challenge delivered by LBNP, which we speculatively propose may involve differential changes in vascular tone within different segments of the arterial vasculature. These novel data provide invaluable insight into the mechanisms that regulate perfusion of the brain, and establishes the use of MRI as a tool for studying CA in more detail.
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Affiliation(s)
- Joseph R Whittaker
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff CF24 4HQ, United Kingdom; Cardiff University Brain Research Imaging Centre (CUBRIC), School of Physics and Astronomy, Cardiff University, Queen's Buildings, The Parade, Cardiff CF24 3AA, United Kingdom.
| | - Molly G Bright
- Sir Peter Mansfield Imaging Centre, School of Medicine, University of Nottingham, Nottingham NG7 2RD, United Kingdom; Division of Clinical Neurosciences, School of Medicine, University of Nottingham, Nottingham NG7 2UH, United Kingdom
| | - Ian D Driver
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff CF24 4HQ, United Kingdom
| | - Adele Babic
- Department of Anaesthesia and Intensive Care Medicine, Cardiff University School of Medicine, Cardiff CF14 4XN, United Kingdom
| | - Sharmila Khot
- Department of Anaesthesia and Intensive Care Medicine, Cardiff University School of Medicine, Cardiff CF14 4XN, United Kingdom
| | - Kevin Murphy
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff CF24 4HQ, United Kingdom; Cardiff University Brain Research Imaging Centre (CUBRIC), School of Physics and Astronomy, Cardiff University, Queen's Buildings, The Parade, Cardiff CF24 3AA, United Kingdom
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20
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Bruce CD, Steinback CD, Chauhan UV, Pfoh JR, Abrosimova M, Vanden Berg ER, Skow RJ, Davenport MH, Day TA. Quantifying cerebrovascular reactivity in anterior and posterior cerebral circulations during voluntary breath holding. Exp Physiol 2016; 101:1517-1527. [DOI: 10.1113/ep085764] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2016] [Accepted: 09/05/2016] [Indexed: 12/12/2022]
Affiliation(s)
- Christina D. Bruce
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Craig D. Steinback
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Uday V. Chauhan
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Jamie R. Pfoh
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Maria Abrosimova
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Emily R. Vanden Berg
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
- Department of Biology; Faculty of Science; University of Victoria; Victoria BC Canada
| | - Rachel J. Skow
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Margie H. Davenport
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Trevor A. Day
- Department of Biology; Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
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21
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Sperna Weiland NH, Brevoord D, Jöbsis DA, de Beaumont EMFH, Evers V, Preckel B, Hollmann MW, van Dieren S, de Mol BAJM, Immink RV. Cerebral oxygenation during changes in vascular resistance and flow in patients on cardiopulmonary bypass - a physiological proof of concept study. Anaesthesia 2016; 72:49-56. [DOI: 10.1111/anae.13631] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/15/2016] [Indexed: 12/17/2022]
Affiliation(s)
- N. H. Sperna Weiland
- Department of Anaesthesiology; Academic Medical Center; Amsterdam The Netherlands
| | - D. Brevoord
- Department of Anaesthesiology; Academic Medical Center; Amsterdam The Netherlands
| | - D. A. Jöbsis
- Department of Anaesthesiology; Academic Medical Center; Amsterdam The Netherlands
| | | | - V. Evers
- Department of Anaesthesiology; Academic Medical Center; Amsterdam The Netherlands
| | - B. Preckel
- Department of Anaesthesiology; Academic Medical Center; Amsterdam The Netherlands
| | - M. W. Hollmann
- Department of Anaesthesiology; Academic Medical Center; Amsterdam The Netherlands
| | - S. van Dieren
- Department of Anaesthesiology; Academic Medical Center; Amsterdam The Netherlands
| | - B. A. J. M. de Mol
- Department of Cardiothoracic Surgery; Academic Medical Center; Amsterdam The Netherlands
| | - R. V. Immink
- Department of Anaesthesiology; Academic Medical Center; Amsterdam The Netherlands
- Laboratory for Clinical Cardiovascular Physiology; Department of Anatomy and Embryology; Academic Medical Center; Amsterdam The Netherlands
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22
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Volianitis S, Secher NH. Cardiovascular control during whole body exercise. J Appl Physiol (1985) 2016; 121:376-90. [PMID: 27311439 PMCID: PMC5007320 DOI: 10.1152/japplphysiol.00674.2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Accepted: 06/10/2016] [Indexed: 12/25/2022] Open
Abstract
It has been considered whether during whole body exercise the increase in cardiac output is large enough to support skeletal muscle blood flow. This review addresses four lines of evidence for a flow limitation to skeletal muscles during whole body exercise. First, even though during exercise the blood flow achieved by the arms is lower than that achieved by the legs (∼160 vs. ∼385 ml·min(-1)·100 g(-1)), the muscle mass that can be perfused with such flow is limited by the capacity to increase cardiac output (42 l/min, highest recorded value). Secondly, activation of the exercise pressor reflex during fatiguing work with one muscle group limits flow to other muscle groups. Another line of evidence comes from evaluation of regional blood flow during exercise where there is a discrepancy between flow to a muscle group when it is working exclusively and when it works together with other muscles. Finally, regulation of peripheral resistance by sympathetic vasoconstriction in active muscles by the arterial baroreflex is critical for blood pressure regulation during exercise. Together, these findings indicate that during whole body exercise muscle blood flow is subordinate to the control of blood pressure.
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Affiliation(s)
- Stefanos Volianitis
- Department of Health Science and Technology, Aalborg University, Aalborg, Denmark; and
| | - Niels H Secher
- The Copenhagen Muscle Research Center, Department of Anesthesiology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
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23
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Soeding PF, Currigan DA, Mamo Y, Hoy G. Effect of interscalene anaesthesia on cerebral oxygen saturation. Anaesth Intensive Care 2016; 44:359-63. [PMID: 27246935 DOI: 10.1177/0310057x1604400301] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Interscalene blockade (ISB) is commonly associated with Horner's syndrome, indicating spread of injectate to the cervical sympathetic chain. Cervical sympathetic nerve activity (SNA) is believed to influence cerebral autoregulation, and a decrease in sympathetic tone may alter cerebral blood flow (CBF). This study investigated whether ISB influenced CBF in patients undergoing shoulder surgery. Patients (n=30) scheduled for elective shoulder arthroscopy were recruited. Cerebral oxygen saturation (ScO(2)) of the left and right frontal cortices was continuously measured during ISB administration, sedation and anaesthetic induction. Baseline ScO(2) was similar in blocked and unblocked sides (74 ± 5% and 73 ± 5% respectively, P=0.70). ScO(2) decreased with sedation (-3 ± 3% and -4 ± 3%, P=0.93), and increased with pre-oxygenation and general anaesthesia (P <0.01). Following ISB there was no change in ScO(2) between blocked and unblocked sides (P=0.18), or any difference between right- or left-sided ISB. ISB is not associated with an increase in CBF as indicated by ScO(2), despite the presence of Horner's syndrome.
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Affiliation(s)
- P F Soeding
- Visiting Anaesthetist, Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, and Associate Professor, Department of Pharmacology, University of Melbourne, Melbourne, Victoria
| | - D A Currigan
- Fellow, Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Melbourne, Victoria
| | - Y Mamo
- Cardiovascular Therapeutics Unit, Department of Pharmacology and Therapeutics, University of Melbourne, Melbourne, Victoria
| | - G Hoy
- Specialist Surgeon, Melbourne Orthopaedic Group, Windsor, Victoria
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24
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Hilz MJ, Wang R, Marthol H, Liu M, Tillmann A, Riss S, Hauck P, Hösl KM, Wasmeier G, Stemper B, Köhrmann M. Partial pharmacologic blockade shows sympathetic connection between blood pressure and cerebral blood flow velocity fluctuations. J Neurol Sci 2016; 365:181-7. [PMID: 27206903 DOI: 10.1016/j.jns.2016.04.022] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Revised: 03/24/2016] [Accepted: 04/07/2016] [Indexed: 11/18/2022]
Abstract
Cerebral autoregulation (CA) dampens transfer of blood pressure (BP)-fluctuations onto cerebral blood flow velocity (CBFV). Thus, CBFV-oscillations precede BP-oscillations. The phase angle (PA) between sympathetically mediated low-frequency (LF: 0.03-0.15Hz) BP- and CBFV-oscillations is a measure of CA quality. To evaluate whether PA depends on sympathetic modulation, we assessed PA-changes upon sympathetic stimulation with and without pharmacologic sympathetic blockade. In 10 healthy, young men, we monitored mean BP and CBFV before and during 120-second cold pressor stimulation (CPS) of one foot (0°C ice-water). We calculated mean values, standard deviations and sympathetic LF-powers of all signals, and PAs between LF-BP- and LF-CBFV-oscillations. We repeated measurements after ingestion of the adrenoceptor-blocker carvedilol (25mg). We compared parameters before and during CPS, without and after carvedilol (analysis of variance, post-hoc t-tests, significance: p<0.05). Without carvedilol, CPS increased BP, CBFV, BP-LF- and CBFV-LF-powers, and shortened PA. Carvedilol decreased resting BP, CBFV, BP-LF- and CBFV-LF-powers, while PAs remained unchanged. During CPS, BPs, CBFVs, BP-LF- and CBFV-LF-powers were lower, while PAs were longer with than without carvedilol. With carvedilol, CPS no longer shortened resting PA. Sympathetic activation shortens PA. Partial adrenoceptor blockade abolishes this PA-shortening. Thus, PA-measurements provide a subtle marker of sympathetic influences on CA and might refine CA evaluation.
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Affiliation(s)
- Max J Hilz
- Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany.
| | - Ruihao Wang
- Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany.
| | - Harald Marthol
- Department of Psychiatry, Addiction, Psychotherapy and Psychosomatics, Klinikum am Europakanal, Am Europakanal 71, 91056 Erlangen, Germany.
| | - Mao Liu
- Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany.
| | - Alexandra Tillmann
- Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany.
| | - Stephan Riss
- Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany.
| | - Paulina Hauck
- Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany.
| | - Katharina M Hösl
- Department of Psychiatry and Psychotherapy, Paracelsus Medical University Nuremberg, Prof.-Ernst-Nathan-Strasse 1, 90419 Nuremberg, Germany.
| | - Gerald Wasmeier
- Department of Cardiology, Klinik Neustadt a. d. Aisch, Paracelsusstraße 30-36, 91413 Neustadt a. d. Aisch, Germany.
| | - Brigitte Stemper
- Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany; Bayer HealthCare, Bayer Pharma AG, Global Development Specialty Medicine, Müllerstr. 178, Building P300, Room 239, 13353 Berlin, Germany.
| | - Martin Köhrmann
- Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, D-91054 Erlangen, Germany.
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25
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Donnelly J, Budohoski KP, Smielewski P, Czosnyka M. Regulation of the cerebral circulation: bedside assessment and clinical implications. Crit Care 2016; 20:129. [PMID: 27145751 PMCID: PMC4857376 DOI: 10.1186/s13054-016-1293-6] [Citation(s) in RCA: 122] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Regulation of the cerebral circulation relies on the complex interplay between cardiovascular, respiratory, and neural physiology. In health, these physiologic systems act to maintain an adequate cerebral blood flow (CBF) through modulation of hydrodynamic parameters; the resistance of cerebral vessels, and the arterial, intracranial, and venous pressures. In critical illness, however, one or more of these parameters can be compromised, raising the possibility of disturbed CBF regulation and its pathophysiologic sequelae. Rigorous assessment of the cerebral circulation requires not only measuring CBF and its hydrodynamic determinants but also assessing the stability of CBF in response to changes in arterial pressure (cerebral autoregulation), the reactivity of CBF to a vasodilator (carbon dioxide reactivity, for example), and the dynamic regulation of arterial pressure (baroreceptor sensitivity). Ideally, cerebral circulation monitors in critical care should be continuous, physically robust, allow for both regional and global CBF assessment, and be conducive to application at the bedside. Regulation of the cerebral circulation is impaired not only in primary neurologic conditions that affect the vasculature such as subarachnoid haemorrhage and stroke, but also in conditions that affect the regulation of intracranial pressure (such as traumatic brain injury and hydrocephalus) or arterial blood pressure (sepsis or cardiac dysfunction). Importantly, this impairment is often associated with poor patient outcome. At present, assessment of the cerebral circulation is primarily used as a research tool to elucidate pathophysiology or prognosis. However, when combined with other physiologic signals and online analytical techniques, cerebral circulation monitoring has the appealing potential to not only prognosticate patients, but also direct critical care management.
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Affiliation(s)
- Joseph Donnelly
- />Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, Cambridge Biomedical Campus, University of Cambridge, Hills Road, Cambridge, CB2 0QQ UK
| | - Karol P. Budohoski
- />Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, Cambridge Biomedical Campus, University of Cambridge, Hills Road, Cambridge, CB2 0QQ UK
| | - Peter Smielewski
- />Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, Cambridge Biomedical Campus, University of Cambridge, Hills Road, Cambridge, CB2 0QQ UK
| | - Marek Czosnyka
- />Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, Cambridge Biomedical Campus, University of Cambridge, Hills Road, Cambridge, CB2 0QQ UK
- />Institute of Electronic Systems, Warsaw University of Technology, ul. Nowowiejska 15/19, 00-665 Warsaw, Poland
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26
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Steinback CD, Poulin MJ. Influence of Hypoxia on Cerebral Blood Flow Regulation in Humans. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 903:131-44. [PMID: 27343093 DOI: 10.1007/978-1-4899-7678-9_9] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The brain is a vital organ that relies on a constant and adequate supply of blood to match oxygen and glucose delivery with the local metabolic demands of active neurones. It is well established that cerebral blood flow is altered in response to both neural activity and humoral stimuli. Thus, augmented neural activation (e.g. visual stimulation) leads to locally increased cerebral blood flow via functional hyperaemia, whereas humoral stimuli (i.e. alterations in arterial PO2 and PCO2) produce global increases in cerebral blood flow. Perhaps not surprisingly, cerebrovascular responses to neural activity and humoral stimuli may not be highly correlated because they reflect different physiological mechanisms for vasodilation. Exquisite regulation of cerebral blood flow is particularly important under hypoxic conditions when cerebral PO2 can be reduced substantially. Indeed, cerebrovascular reactivity to hypoxia determines the capacity of cerebral vessels to respond and compensate for a reduced oxygen supply. This reactivity is dynamic, changing with prolonged exposure to hypoxic environments, and in patients and healthy individuals exposed to chronic intermittent periods of hypoxia. More recently, a number of animal studies have provided evidence that glial cells (i.e. astrocytes) play an important role in regulating cerebral blood flow under normoxic and hypoxic conditions. This review aims to summarize our current understanding of cerebral blood flow control during hypoxia in humans and put into context the underlying neurovascular mechanisms that may contribute to this regulation.
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Affiliation(s)
- Craig D Steinback
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Marc J Poulin
- Departments of Physiology and Pharmacology and Clinical Neurosciences, Faculty of Medicine, Hotchkiss Brain Institute, The Libin Cardiovascular Institute of Alberta, Calgary, AB, Canada.
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Abstract
Heat stress increases human morbidity and mortality compared to normothermic conditions. Many occupations, disease states, as well as stages of life are especially vulnerable to the stress imposed on the cardiovascular system during exposure to hot ambient conditions. This review focuses on the cardiovascular responses to heat stress that are necessary for heat dissipation. To accomplish this regulatory feat requires complex autonomic nervous system control of the heart and various vascular beds. For example, during heat stress cardiac output increases up to twofold, by increases in heart rate and an active maintenance of stroke volume via increases in inotropy in the presence of decreases in cardiac preload. Baroreflexes retain the ability to regulate blood pressure in many, but not all, heat stress conditions. Central hypovolemia is another cardiovascular challenge brought about by heat stress, which if added to a subsequent central volumetric stress, such as hemorrhage, can be problematic and potentially dangerous, as syncope and cardiovascular collapse may ensue. These combined stresses can compromise blood flow and oxygenation to important tissues such as the brain. It is notable that this compromised condition can occur at cardiac outputs that are adequate during normothermic conditions but are inadequate in heat because of the increased systemic vascular conductance associated with cutaneous vasodilation. Understanding the mechanisms within this complex regulatory system will allow for the development of treatment recommendations and countermeasures to reduce risks during the ever-increasing frequency of severe heat events that are predicted to occur.
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Affiliation(s)
- Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, Texas Marian University College of Osteopathic Medicine, Indianapolis, Indiana
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Lucas SJE, Cotter JD, Brassard P, Bailey DM. High-intensity interval exercise and cerebrovascular health: curiosity, cause, and consequence. J Cereb Blood Flow Metab 2015; 35:902-11. [PMID: 25833341 PMCID: PMC4640257 DOI: 10.1038/jcbfm.2015.49] [Citation(s) in RCA: 136] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 01/25/2015] [Accepted: 03/01/2015] [Indexed: 12/14/2022]
Abstract
Exercise is a uniquely effective and pluripotent medicine against several noncommunicable diseases of westernised lifestyles, including protection against neurodegenerative disorders. High-intensity interval exercise training (HIT) is emerging as an effective alternative to current health-related exercise guidelines. Compared with traditional moderate-intensity continuous exercise training, HIT confers equivalent if not indeed superior metabolic, cardiac, and systemic vascular adaptation. Consequently, HIT is being promoted as a more time-efficient and practical approach to optimize health thereby reducing the burden of disease associated with physical inactivity. However, no studies to date have examined the impact of HIT on the cerebrovasculature and corresponding implications for cognitive function. This review critiques the implications of HIT for cerebrovascular function, with a focus on the mechanisms and translational impact for patient health and well-being. It also introduces similarly novel interventions currently under investigation as alternative means of accelerating exercise-induced cerebrovascular adaptation. We highlight a need for studies of the mechanisms and thereby also the optimal dose-response strategies to guide exercise prescription, and for studies to explore alternative approaches to optimize exercise outcomes in brain-related health and disease prevention. From a clinical perspective, interventions that selectively target the aging brain have the potential to prevent stroke and associated neurovascular diseases.
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Affiliation(s)
- Samuel J E Lucas
- 1] School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK [2] Department of Physiology, University of Otago, Dunedin, New Zealand
| | - James D Cotter
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand
| | - Patrice Brassard
- 1] Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada [2] Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada
| | - Damian M Bailey
- 1] Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, South Wales, UK [2] Université de Provence Marseille, Sondes Moléculaires en Biologie, Laboratoire Chimie Provence UMR 6264 CNRS, Marseille, France
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Braz ID, Scott C, Simpson LL, Springham EL, Tan BWL, Balanos GM, Fisher JP. Influence of muscle metaboreceptor stimulation on middle cerebral artery blood velocity in humans. Exp Physiol 2014; 99:1478-87. [PMID: 25217497 DOI: 10.1113/expphysiol.2014.081687] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Regional anaesthesia to attenuate skeletal muscle afferent feedback abolishes the exercise-induced increase in middle cerebral artery mean blood velocity (MCA Vmean). However, such exercise-related increases in cerebral perfusion are not preserved during post exercise muscle ischaemia (PEMI) where the activation of metabolically sensitive muscle afferents is isolated. We tested the hypothesis that a hyperventilation-mediated decrease in the arterial partial pressure of CO2, hence cerebral vasoconstriction, masks the influence of muscle metaboreceptor stimulation on MCA Vmean during PEMI. Ten healthy men (20 ± 1 years old) performed two trials of fatiguing isometric hand-grip exercise followed by PEMI, in control conditions and with end-tidal CO2 (P ET ,CO2) clamped at ∼1 mmHg above the resting partial pressure. In the control trial, P ET ,CO2 decreased from rest during hand-grip exercise and PEMI, while MCA Vmean was unchanged from rest. By design, P ET ,CO2 remained unchanged from rest throughout the clamp trial, while MCA Vmean increased during hand-grip (+10.6 ±1.8 cm s(-1)) and PEMI (+9.2 ± 1.6 cm s(-1); P < 0.05 versus rest and control trial). Increases in minute ventilation and mean arterial pressure during hand-grip and PEMI were not different in the control and P ET ,CO2 clamp trials (P > 0.05). These findings indicate that metabolically sensitive skeletal muscle afferents play an important role in the regional increase in cerebral perfusion observed in exercise, but that influence can be masked by a decrease in P ET ,CO2 when they are activated in isolation during PEMI.
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Affiliation(s)
- Igor D Braz
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Clare Scott
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Lydia L Simpson
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Emma L Springham
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Beverly W L Tan
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - George M Balanos
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - James P Fisher
- School of Sport, Exercise & Rehabilitation Sciences, College of Life & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
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Trangmar SJ, Chiesa ST, Stock CG, Kalsi KK, Secher NH, González-Alonso J. Dehydration affects cerebral blood flow but not its metabolic rate for oxygen during maximal exercise in trained humans. J Physiol 2014; 592:3143-60. [PMID: 24835170 PMCID: PMC4214665 DOI: 10.1113/jphysiol.2014.272104] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Intense exercise is associated with a reduction in cerebral blood flow (CBF), but regulation of CBF during strenuous exercise in the heat with dehydration is unclear. We assessed internal (ICA) and common carotid artery (CCA) haemodynamics (indicative of CBF and extra-cranial blood flow), middle cerebral artery velocity (MCA Vmean), arterial–venous differences and blood temperature in 10 trained males during incremental cycling to exhaustion in the heat (35°C) in control, dehydrated and rehydrated states. Dehydration reduced body mass (75.8 ± 3 vs. 78.2 ± 3 kg), increased internal temperature (38.3 ± 0.1 vs. 36.8 ± 0.1°C), impaired exercise capacity (269 ± 11 vs. 336 ± 14 W), and lowered ICA and MCA Vmean by 12–23% without compromising CCA blood flow. During euhydrated incremental exercise on a separate day, however, exercise capacity and ICA, MCA Vmean and CCA dynamics were preserved. The fast decline in cerebral perfusion with dehydration was accompanied by increased O2 extraction (P < 0.05), resulting in a maintained cerebral metabolic rate for oxygen (CMRO2). In all conditions, reductions in ICA and MCA Vmean were associated with declining cerebral vascular conductance, increasing jugular venous noradrenaline, and falling arterial carbon dioxide tension () (R2 ≥ 0.41, P ≤ 0.01) whereas CCA flow and conductance were related to elevated blood temperature. In conclusion, dehydration accelerated the decline in CBF by decreasing and enhancing vasoconstrictor activity. However, the circulatory strain on the human brain during maximal exercise does not compromise CMRO2 because of compensatory increases in O2 extraction.
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Affiliation(s)
- Steven J Trangmar
- Centre for Sports Medicine and Human Performance, Brunel University, London, UK
| | - Scott T Chiesa
- Centre for Sports Medicine and Human Performance, Brunel University, London, UK
| | - Christopher G Stock
- Centre for Sports Medicine and Human Performance, Brunel University, London, UK
| | - Kameljit K Kalsi
- Centre for Sports Medicine and Human Performance, Brunel University, London, UK
| | - Niels H Secher
- Centre for Sports Medicine and Human Performance, Brunel University, London, UK Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
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Ainslie PN, Brassard P. Why is the neural control of cerebral autoregulation so controversial? F1000PRIME REPORTS 2014; 6:14. [PMID: 24669295 PMCID: PMC3944747 DOI: 10.12703/p6-14] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Cerebral autoregulation refers to the mechanisms that act to keep cerebral blood flow (CBF) constant during changes in blood pressure. The mechanisms of cerebral autoregulation, especially in humans, are poorly understood but are undoubtedly multifactorial and likely reflect many redundant pathways that potentially differ between species. Whether sympathetic nervous activity influences CBF and/or cerebral autoregulation in humans remains controversial. Following a brief introduction to cerebral autoregulation, this review highlights the likely reasons behind the controversy of the neural control of cerebral autoregulation. Finally, suggestions are provided for further studies to improve the understanding of the neural control of CBF regulation.
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Affiliation(s)
- Philip N. Ainslie
- Center for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia – OkanaganKelowna, British ColumbiaCanada
| | - Patrice Brassard
- Department of Kinesiology, Faculty of Medicine, Université LavalQuébecCanada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de QuébecQuébecCanada
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Tan CO, Taylor JA. Integrative physiological and computational approaches to understand autonomic control of cerebral autoregulation. Exp Physiol 2013; 99:3-15. [PMID: 24097158 DOI: 10.1113/expphysiol.2013.072355] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The brain requires steady delivery of oxygen and glucose, without which neurodegeneration occurs within minutes. Thus, the ability of the cerebral vasculature to maintain relatively steady blood flow in the face of changing systemic pressure, i.e. cerebral autoregulation, is critical to neurophysiological health. Although the study of autoregulation dates to the early 20th century, only the recent availability of cerebral blood flow measures with high temporal resolution has allowed rapid, beat-by-beat measurements to explore the characteristics and mechanisms of autoregulation. These explorations have been further enhanced by the ability to apply sophisticated computational approaches that exploit the large amounts of data that can be acquired. These advances have led to unique insights. For example, recent studies have revealed characteristic time scales wherein cerebral autoregulation is most active, as well as specific regions wherein autonomic mechanisms are prepotent. However, given that effective cerebral autoregulation against pressure fluctuations results in relatively unchanging flow despite changing pressure, estimating the pressure-flow relationship can be limited by the error inherent in computational models of autoregulatory function. This review focuses on the autonomic neural control of the cerebral vasculature in health and disease from an integrative physiological perspective. It also provides a critical overview of the current analytical approaches to understand cerebral autoregulation.
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Affiliation(s)
- Can Ozan Tan
- C. O. Tan: CVLab, SW052, Spaulding Hospital Cambridge, 1575 Cambridge Street, Cambridge, MA 02138, USA.
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35
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Moerman A, Denys W, De Somer F, Wouters P, De Hert S. Influence of variations in systemic blood flow and pressure on cerebral and systemic oxygen saturation in cardiopulmonary bypass patients. Br J Anaesth 2013; 111:619-26. [DOI: 10.1093/bja/aet197] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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ter Laan M, van Dijk J, Elting J, Staal M, Absalom A. Sympathetic regulation of cerebral blood flow in humans: a review. Br J Anaesth 2013; 111:361-7. [DOI: 10.1093/bja/aet122] [Citation(s) in RCA: 208] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Impaired cerebral autoregulation is associated with brain atrophy and worse functional status in chronic ischemic stroke. PLoS One 2012; 7:e46794. [PMID: 23071639 PMCID: PMC3469603 DOI: 10.1371/journal.pone.0046794] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 09/07/2012] [Indexed: 11/30/2022] Open
Abstract
Dynamic cerebral autoregulation (dCA) is impaired following stroke. However, the relationship between dCA, brain atrophy, and functional outcomes following stroke remains unclear. In this study, we aimed to determine whether impairment of dCA is associated with atrophy in specific regions or globally, thereby affecting daily functions in stroke patients. We performed a retrospective analysis of 33 subjects with chronic infarctions in the middle cerebral artery territory, and 109 age-matched non-stroke subjects. dCA was assessed via the phase relationship between arterial blood pressure and cerebral blood flow velocity. Brain tissue volumes were quantified from MRI. Functional status was assessed by gait speed, instrumental activities of daily living (IADL), modified Rankin Scale, and NIH Stroke Score. Compared to the non-stroke group, stroke subjects showed degraded dCA bilaterally, and showed gray matter atrophy in the frontal, parietal and temporal lobes ipsilateral to infarct. In stroke subjects, better dCA was associated with less temporal lobe gray matter atrophy on the infracted side ( = 0.029), faster gait speed ( = 0.018) and lower IADL score (0.002). Our results indicate that better dynamic cerebral perfusion regulation is associated with less atrophy and better long-term functional status in older adults with chronic ischemic infarctions.
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Peebles KC, Ball OG, MacRae BA, Horsman HM, Tzeng YC. Sympathetic regulation of the human cerebrovascular response to carbon dioxide. J Appl Physiol (1985) 2012; 113:700-6. [DOI: 10.1152/japplphysiol.00614.2012] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although the cerebrovasculature is known to be exquisitely sensitive to CO2, there is no consensus on whether the sympathetic nervous system plays a role in regulating cerebrovascular responses to changes in arterial CO2. To address this question, we investigated human cerebrovascular CO2 reactivity in healthy participants randomly assigned to the α1-adrenoreceptor blockade group (9 participants; oral prazosin, 0.05 mg/kg) or the placebo control (9 participants) group. We recorded mean arterial blood pressure (MAP), heart rate (HR), mean middle cerebral artery flow velocity (MCAV mean), and partial pressure of end-tidal CO2 (PetCO2) during 5% CO2 inhalation and voluntary hyperventilation. CO2 reactivity was quantified as the slope of the linear relationship between breath-to-breath PetCO2 and the average MCAvmean within successive breathes after accounting for MAP as a covariate. Prazosin did not alter resting HR, PetCO2, MAP, or MCAV mean. The reduction in hypocapnic CO2 reactivity following prazosin (−0.48 ± 0.093 cm·s−1·mmHg−1) was greater compared with placebo (−0.19 ± 0.087 cm·s−1·mmHg−1; P < 0.05 for interaction). In contrast, the change in hypercapnic CO2 reactivity following prazosin (−0.23 cm·s−1·mmHg−1) was similar to placebo (−0.31 cm·s−1·mmHg−1; P = 0.50 for interaction). These data indicate that the sympathetic nervous system contributes to CO2 reactivity via α1-adrenoreceptors; blocking this pathway with prazosin reduces CO2 reactivity to hypocapnia but not hypercapnia.
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Affiliation(s)
- K. C. Peebles
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - O. G. Ball
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - B. A. MacRae
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - H. M. Horsman
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - Y. C. Tzeng
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
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Someya N, Ikemura T, Hayashi N. Effect of preceding exercise on cerebral and splanchnic vascular responses to mental task. J Physiol Anthropol 2012; 31:17. [PMID: 22738029 PMCID: PMC3423064 DOI: 10.1186/1880-6805-31-17] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Accepted: 05/29/2012] [Indexed: 11/10/2022] Open
Abstract
Background To investigate the effect of preceding acute exercise on the peripheral vascular response to a mental task, we measured splanchnic and cerebral blood flow responses to performing a mental task after exercise and resting. Methods In the exercise trial, 11 males exercised for 30 min on a cycle ergometer with a workload set at 70% of the age-predicted maximal heart rate for each individual. After a 15-min recovery period, the subjects rested for 5 min for pre-task baseline measurement and then performed mental arithmetic for 5 min followed by 5 min of post-task measurement. In the resting trial, they rested for 45 min and pre-task baseline data was obtained for 5 min. Then mental arithmetic was performed for 5 min followed by post-task measurement. We measured the mean blood velocity in the middle cerebral artery and superior mesenteric artery and the mean arterial pressure. Results Mean arterial pressure and mean blood velocity in the middle cerebral artery were significantly higher than the baseline during mental arithmetic in both exercise and resting trials. Mean blood velocity in the middle cerebral artery during mental arithmetic was greater in the control trial than the exercise trial. Mean blood velocity in the superior mesenteric artery showed no significant change during mental arithmetic from baseline in both trials. Conclusion These results suggest that acute exercise can moderate the increase in cerebral blood flow induced by a mental task.
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Affiliation(s)
- Nami Someya
- Graduate School of Human-Environment Studies, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan
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Revel A, Gallet C, Oréa V, Chapuis B, Barrès C, Julien C. Effect of chronic cervical ganglionectomy on the spontaneous variability of internal carotid blood flow in the conscious rat. Exp Physiol 2012; 97:564-71. [PMID: 22308161 DOI: 10.1113/expphysiol.2011.062455] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The role of sympathetic innervation in the control of spontaneous fluctuations of cerebral blood flow is still poorly understood. In conscious, unrestrained rats, blood flow velocity (pulsed Doppler) was measured in both internal carotid arteries 1 week after either excision of the right superior cervical ganglion (n = 8) or sham surgery (n = 6). Using Fourier-based techniques, spectral power of each carotid blood flow (CBF) was computed over the whole recording period (246 min), which was segmented into nine consecutive 27.3 min periods. Variability of CBF (spectral power) was ∼40% higher (P < 0.02) on the denervated than on the intact side at frequencies <1 Hz. Coherence between left and right CBFs was similar in the two groups of rats, except in the 0.01-0.1 Hz frequency range where it was lower (P < 0.05) in rats with unilateral sympathectomy (0.54 ± 0.03) than in intact rats (0.74 ± 0.06). In this frequency range, mathematically removing the influence of arterial pressure had little effect on coherence between CBFs in both groups of rats, so that coherence remained significantly lower in rats with unilateral sympathectomy (0.52 ± 0.03) than in intact rats (0.70 ± 0.06). This study indicates that sympathetic innervation has an overall buffering influence on CBF variability. This modulatory role is especially important in a frequency range corresponding to slow fluctuations of CBF (lasting from 10 to 100 s), which are essentially unrelated to fluctuations of arterial pressure.
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Affiliation(s)
- Aurélia Revel
- Unité de Neurocardiologie, Faculté de Pharmacie, Université Lyon 1, F-69008 Lyon, France
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Purkayastha S, Raven PB. The functional role of the alpha-1 adrenergic receptors in cerebral blood flow regulation. Indian J Pharmacol 2011; 43:502-6. [PMID: 22021989 PMCID: PMC3195116 DOI: 10.4103/0253-7613.84950] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2011] [Revised: 05/11/2011] [Accepted: 07/01/2011] [Indexed: 01/22/2023] Open
Abstract
Cerebral vasculature is richly innervated by the α-1 adrenergic receptors similar to that of the peripheral vasculature. However, the functional role of the α-1adrenergic receptors in cerebral blood flow (CBF) regulation is yet to be established. The traditional thinking being that during normotension and normocapnia sympathetic neural activity does not play a significant role in CBF regulation. Reports in the past have stated that catecholamines do not penetrate the blood brain barrier (BBB) and therefore only influence cerebral vessels from outside the BBB and hence, have a limited role in CBF regulation. However, with the advent of dynamic measurement techniques, beat-to-beat CBF assessment can be done during dynamic changes in arterial blood pressure. Several studies in the recent years have reported a functional role of the α-1adrenergic receptors in CBF regulation. This review focuses on the recent developments on the role of the sympathetic nervous system, specifically that of the α-1 adrenergic receptors in CBF regulation.
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Affiliation(s)
- Sushmita Purkayastha
- Department of Integrative Physiology and the Cardiovascular Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, 76017, USA
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Seifert T, Secher NH. Sympathetic influence on cerebral blood flow and metabolism during exercise in humans. Prog Neurobiol 2011; 95:406-26. [PMID: 21963551 DOI: 10.1016/j.pneurobio.2011.09.008] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2011] [Revised: 09/13/2011] [Accepted: 09/19/2011] [Indexed: 11/26/2022]
Abstract
This review focuses on the possibility that autonomic activity influences cerebral blood flow (CBF) and metabolism during exercise in humans. Apart from cerebral autoregulation, the arterial carbon dioxide tension, and neuronal activation, it may be that the autonomic nervous system influences CBF as evidenced by pharmacological manipulation of adrenergic and cholinergic receptors. Cholinergic blockade by glycopyrrolate blocks the exercise-induced increase in the transcranial Doppler determined mean flow velocity (MCA Vmean). Conversely, alpha-adrenergic activation increases that expression of cerebral perfusion and reduces the near-infrared determined cerebral oxygenation at rest, but not during exercise associated with an increased cerebral metabolic rate for oxygen (CMRO(2)), suggesting competition between CMRO(2) and sympathetic control of CBF. CMRO(2) does not change during even intense handgrip, but increases during cycling exercise. The increase in CMRO(2) is unaffected by beta-adrenergic blockade even though CBF is reduced suggesting that cerebral oxygenation becomes critical and a limited cerebral mitochondrial oxygen tension may induce fatigue. Also, sympathetic activity may drive cerebral non-oxidative carbohydrate uptake during exercise. Adrenaline appears to accelerate cerebral glycolysis through a beta2-adrenergic receptor mechanism since noradrenaline is without such an effect. In addition, the exercise-induced cerebral non-oxidative carbohydrate uptake is blocked by combined beta 1/2-adrenergic blockade, but not by beta1-adrenergic blockade. Furthermore, endurance training appears to lower the cerebral non-oxidative carbohydrate uptake and preserve cerebral oxygenation during submaximal exercise. This is possibly related to an attenuated catecholamine response. Finally, exercise promotes brain health as evidenced by increased release of brain-derived neurotrophic factor (BDNF) from the brain.
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Affiliation(s)
- Thomas Seifert
- Department of Anaesthesia and The Copenhagen Muscle Research Centre, Rigshospitalet 2041, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark.
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Ter Laan M, van Dijk JMC, Staal MJ, Elting JWJ. Electrical modulation of the sympathetic nervous system in order to augment cerebral blood flow: a protocol for an experimental study. BMJ Open 2011; 1:e000120. [PMID: 22021767 PMCID: PMC3191412 DOI: 10.1136/bmjopen-2011-000120] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Introduction Cerebral blood flow (CBF) is regulated by several mechanisms. Neurogenic control has been a matter of debate, even though several publications reported the effects of changes in sympathetic tone on CBF. Transcutaneous electrical nerve stimulation and spinal-cord stimulation have been shown to influence peripheral and cerebral blood flow through a sympathetic pathway. The authors hypothesise that certain pathological conditions result in a relative increase in the neurogenic regulation of CBF and that this regulation can be modulated electrically. Methods and analysis Patients with cerebral vasospasm after subarachnoid haemorrhage will be included. The experimental set-up measures several parameters that are involved in cerebral blood flow regulation in patients with cerebral vasospasm after subarachnoid haemorrhage. Measurements are taken at baseline and with stimulation in several frequencies. An ad hoc statistical analysis is used to evaluate different settings of the electrical stimulation. Autoregulation is evaluated with transfer function analysis and autoregulatory index calculations. Ethics and dissemination Ethical registration was granted by Medical Review Ethics Committee Groningen (ID METc 2010.123). All participants provide written informed consent on participation. Upon finishing a pilot study to investigate feasibility and effect, either future prospective (randomised) studies will be designed, or other modalities of electrical stimulation will be explored using the same set-up. Trial Registration Dutch Trial Registry: NTR2358.
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Affiliation(s)
- Mark Ter Laan
- Department of Neurosurgery, University Medical Center Groningen, Groningen, The Netherlands
| | - J Marc C van Dijk
- Department of Neurosurgery, University Medical Center Groningen, Groningen, The Netherlands
| | - Michiel J Staal
- Department of Neurosurgery, University Medical Center Groningen, Groningen, The Netherlands
| | - Jan-Willem J Elting
- Department of Neurophysiology and Neurology, University of Groningen, Groningen, The Netherlands
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Meng L, Cannesson M, Alexander BS, Yu Z, Kain ZN, Cerussi AE, Tromberg BJ, Mantulin WW. Effect of phenylephrine and ephedrine bolus treatment on cerebral oxygenation in anaesthetized patients. Br J Anaesth 2011; 107:209-17. [PMID: 21642644 DOI: 10.1093/bja/aer150] [Citation(s) in RCA: 155] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND How phenylephrine and ephedrine treatments affect global and regional haemodynamics is of major clinical relevance. Cerebral tissue oxygen saturation (Sct(O2) )-guided management may improve postoperative outcome. The physiological variables responsible for Sct(O2) changes induced by phenylephrine and ephedrine bolus treatment in anaesthetized patients need to be defined. METHODS A randomized two-treatment cross-over trial was conducted: one bolus dose of phenylephrine (100-200 µg) and one bolus dose of ephedrine (5-20 mg) were given to 29 ASA I-III patients anaesthetized with propofol and remifentanil. , mean arterial pressure (MAP), cardiac output (CO), and other physiological variables were recorded before and after treatments. The associations of changes were analysed using linear-mixed models. RESULTS The CO decreased significantly after phenylephrine treatment [▵CO = -2.1 (1.4) litre min(-1), P<0.001], but was preserved after ephedrine treatment [▵CO = 0.5 (1.4) litre min(-1), P>0.05]. The was significantly decreased after phenylephrine treatment [▵ = -3.2 (3.0)%, P<0.01] but preserved after ephedrine treatment [▵ = 0.04 (1.9)%, P>0.05]. CO was identified to have the most significant association with (P<0.001). After taking CO into consideration, the other physiological variables, including MAP, were not significantly associated with (P>0.05). CONCLUSIONS Associated with changes in CO, decreased after phenylephrine treatment, but remained unchanged after ephedrine treatment. The significant correlation between CO and implies a cause-effect relationship between global and regional haemodynamics.
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Affiliation(s)
- L Meng
- Department of Anesthesiology and Perioperative Care, University of California, Irvine Medical Center, 101 The City Drive South, Bldg. 53, Rm 227, Orange, CA 92868, USA.
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Gierthmühlen J, Allardt A, Sawade M, Baron R, Wasner G. Dynamic cerebral autoregulation in stroke patients with a central sympathetic deficit. Acta Neurol Scand 2011; 123:332-8. [PMID: 20809903 DOI: 10.1111/j.1600-0404.2010.01424.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE To investigate the functional role of the sympathetic innervation on cerebral autoregulation. MATERIALS AND METHODS Seventeen patients with infarction of the dorsolateral medulla oblongata affecting central sympathetic pathways (Wallenberg's syndrome) and 21 healthy controls were included in the study. Cerebral blood flow velocity (CBFV) in the medial cerebral artery was investigated using transcranial Doppler ultrasound during decrease in cerebral perfusion pressure induced by leg-cuff test and tilt table. RESULTS Upon leg-cuff test, changes of cerebral blood flow and mean arterial blood pressure as well as autoregulatory index did not differ between patients or controls. No differences were found in changes of CBFV, mean arterial blood pressure and heart rate between patients or controls during the tilt table test. CONCLUSIONS We suggest that the sympathetic nervous system does not have an influence on cerebral autoregulation after decrease in perfusion pressure under normotonous conditions.
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Affiliation(s)
- J Gierthmühlen
- Department of Neurology, Division ofNeurological Pain Research and Therapy, University Hospital Schleswig-Holstein, Campus Kiel, Germany.
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Hartwich D, Fowler KL, Wynn LJ, Fisher JP. Differential responses to sympathetic stimulation in the cerebral and brachial circulations during rhythmic handgrip exercise in humans. Exp Physiol 2011; 95:1089-97. [PMID: 20851860 DOI: 10.1113/expphysiol.2010.054387] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The sympathetic neural regulation of the cerebral circulation remains controversial. The purpose of the present study was to determine how exercise modulates the simultaneous responsiveness of the cerebral and brachial circulations to 'endogenous' sympathetic activation (cold pressor test). In nine healthy subjects, heart rate (HR) and mean arterial blood pressure (MAP) were continuously measured during cold pressor tests (4°C water) conducted at rest and during randomized bouts of rhythmic handgrip of 10, 25 and 40% of maximal voluntary contraction. Doppler ultrasound was used to examine brachial artery blood flow (FBF) and middle cerebral artery (MCA) mean blood velocity (V mean), and indices of vascular conductance were calculated for the brachial artery (forearm vascular conductance, FVC) and MCA (cerebral vascular conductance index, CVCi). End-tidal PCO2 (P ET.CO2) was evaluated on a breath-by-breath basis. Handgrip evoked increases in HR, FBF, FVC and MCA V mean (P < 0.05 versus rest), while MAP and CVCi were unchanged and P ET.CO2 fell slightly (P < 0.05 versus rest). Increases in MAP and HR during the cold pressor test were similar at rest and during all handgrip trials. Forearm vascular conductance was markedly reduced with the cold pressor test at rest (-45 ± 8%), but this vasoconstrictor effect was progressively attenuated with increasing exercise intensity (FVC -17 ± 3% during exercise at 40% of maximal voluntary contraction; P < 0.05). In contrast, the small reduction in CVCi with cold pressor test was similar at rest and during handgrip (approximately -5%). Our data indicate that while the marked vasoconstrictor responses to sympathetic activation in the skeletal muscle vasculature are blunted by handgrip exercise, the modest cerebrovascular responses to a cold pressor test remain unchanged.
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Affiliation(s)
- Doreen Hartwich
- School of Sport and Exercise Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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Abstract
Heat stress, whether passive (i.e. exposure to elevated environmental temperatures) or via exercise, results in pronounced cardiovascular adjustments that are necessary for adequate temperature regulation as well as perfusion of the exercising muscle, heart and brain. The available data suggest that generally during passive heat stress baroreflex control of heart rate and sympathetic nerve activity are unchanged, while baroreflex control of systemic vascular resistance may be impaired perhaps due to attenuated vasoconstrictor responsiveness of the cutaneous circulation. Heat stress improves left ventricular systolic function, evidenced by increased cardiac contractility, thereby maintaining stroke volume despite large reductions in ventricular filling pressures. Heat stress-induced reductions in cerebral perfusion likely contribute to the recognized effect of this thermal condition in reducing orthostatic tolerance, although the mechanism(s) by which this occurs is not completely understood. The combination of intense whole-body exercise and environmental heat stress or dehydration-induced hyperthermia results in significant cardiovascular strain prior to exhaustion, which is characterized by reductions in cardiac output, stroke volume, arterial pressure and blood flow to the brain, skin and exercising muscle. These alterations in cardiovascular function and regulation late in heat stress/dehydration exercise might involve the interplay of both local and central reflexes, the contribution of which is presently unresolved.
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Affiliation(s)
- C G Crandall
- Department of Internal Medicine Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, and University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75231, USA.
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Gierthmühlen J, Allardt A, Sawade M, Wasner G, Baron R. Role of sympathetic nervous system in activity-induced cerebral perfusion. J Neurol 2010; 257:1798-805. [DOI: 10.1007/s00415-010-5613-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2009] [Accepted: 05/23/2010] [Indexed: 11/29/2022]
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Brassard P, Seifert T, Wissenberg M, Jensen PM, Hansen CK, Secher NH. Phenylephrine decreases frontal lobe oxygenation at rest but not during moderately intense exercise. J Appl Physiol (1985) 2010; 108:1472-8. [DOI: 10.1152/japplphysiol.01206.2009] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Whether sympathetic activity influences cerebral blood flow (CBF) and oxygenation remains controversial. The influence of sympathetic activity on CBF and oxygenation was evaluated by the effect of phenylephrine on middle cerebral artery (MCA) mean flow velocity ( Vmean) and the near-infrared spectroscopy-derived frontal lobe oxygenation (ScO2) at rest and during exercise. At rest, nine healthy male subjects received bolus injections of phenylephrine (0.1, 0.25, and 0.4 mg), and changes in mean arterial pressure (MAP), MCA Vmean, internal jugular venous O2 saturation (SjvO2), ScO2, and arterial Pco2 (PaCO2) were measured and the cerebral metabolic rate for O2 (CMRO2) was calculated. In randomized order, a bolus of saline or 0.3 mg of phenylephrine was then injected during semisupine cycling, eliciting a low (∼110 beats/min) or a high (∼150 beats/min) heart rate. At rest, MAP and MCA Vmean increased ∼20% ( P < 0.001) and ∼10% ( P < 0.001 for 0.25 mg of phenylephrine and P < 0.05 for 0.4 mg of phenylephrine), respectively. ScO2 then decreased ∼7% ( P < 0.001). Phenylephrine had no effect on SjvO2, PaCO2, or CMRO2. MAP increased after the administration of phenylephrine during low-intensity exercise (∼15%), but this was attenuated (∼10%) during high-intensity exercise ( P < 0.001). The reduction in ScO2 after administration of phenylephrine was attenuated during low-intensity exercise (−5%, P < 0.001) and abolished during high-intensity exercise (−3%, P = not significant), where PaCO2 decreased 7% ( P < 0.05) and CMRO2 increased 17% ( P < 0.05). These results suggest that the administration of phenylephrine reduced ScO2 but that the increased cerebral metabolism needed for moderately intense exercise eliminated that effect.
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Affiliation(s)
- Patrice Brassard
- Department of Anesthesia, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Thomas Seifert
- Department of Anesthesia, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Mads Wissenberg
- Department of Anesthesia, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Peter M. Jensen
- Department of Anesthesia, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Christian K. Hansen
- Department of Anesthesia, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Niels H. Secher
- Department of Anesthesia, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
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Hamner JW, Tan CO, Lee K, Cohen MA, Taylor JA. Sympathetic control of the cerebral vasculature in humans. Stroke 2009; 41:102-9. [PMID: 20007920 DOI: 10.1161/strokeaha.109.557132] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND AND PURPOSE The role of the sympathetic nervous system in cerebral autoregulation remains poorly characterized. We examined cerebral blood flow responses to augmented arterial pressure oscillations with and without sympathetic blockade and compared them with responses in the forearm circulation. METHODS An oscillatory lower body negative pressure of 40 mm Hg was used at 6 frequencies from 0.03 to 0.08 Hz in 11 healthy subjects with and without alpha-adrenergic blockade by phentolamine. RESULTS Sympathetic blockade resulted in unchanged mean pressure and cerebral flow. The transfer function relationship to arterial pressure at frequencies >0.05 Hz was significantly increased in both the cerebral and brachial circulations, but the coherence of the relation remained weak at the lowest frequencies in the cerebral circulation. CONCLUSIONS Our data demonstrate a strong, frequency-dependent role for sympathetic regulation of blood flow in both cerebral and brachial circulations. However, marked differences in the response to blockade suggest the control of the cerebral circulation at longer time scales is characterized by important nonlinearities and relies on regulatory mechanisms other than the sympathetic system.
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Affiliation(s)
- J W Hamner
- Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, 125 Nashua Street, Boston, MA 02114, USA
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