351
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Smirl JD, Tzeng YC, Monteleone BJ, Ainslie PN. Influence of cerebrovascular resistance on the dynamic relationship between blood pressure and cerebral blood flow in humans. J Appl Physiol (1985) 2014; 116:1614-22. [PMID: 24744385 DOI: 10.1152/japplphysiol.01266.2013] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined the hypothesis that changes in the cerebrovascular resistance index (CVRi), independent of blood pressure (BP), will influence the dynamic relationship between BP and cerebral blood flow in humans. We altered CVRi with (via controlled hyperventilation) and without [via indomethacin (INDO, 1.2 mg/kg)] changes in PaCO2. Sixteen subjects (12 men, 27 ± 7 yr) were tested on two occasions (INDO and hypocapnia) separated by >48 h. Each test incorporated seated rest (5 min), followed by squat-stand maneuvers to increase BP variability and improve assessment of the pressure-flow dynamics using linear transfer function analysis (TFA). Beat-to-beat BP, middle cerebral artery velocity (MCAv), posterior cerebral artery velocity (PCAv), and end-tidal Pco2 were monitored. Dynamic pressure-flow relations were quantified using TFA between BP and MCAv/PCAv in the very low and low frequencies through the driven squat-stand maneuvers at 0.05 and 0.10 Hz. MCAv and PCAv reductions by INDO and hypocapnia were well matched, and CVRi was comparably elevated (P < 0.001). During the squat-stand maneuvers (0.05 and 0.10 Hz), the point estimates of absolute gain were universally reduced, and phase was increased under both conditions. In addition to an absence of regional differences, our findings indicate that alterations in CVRi independent of PaCO2 can alter cerebral pressure-flow dynamics. These findings are consistent with the concept of CVRi being a key factor that should be considered in the correct interpretation of cerebral pressure-flow dynamics as indexed using TFA metrics.
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Affiliation(s)
- J D Smirl
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada;
| | - Y C Tzeng
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, Wellington, New Zealand; and
| | - B J Monteleone
- Faculty of Medicine, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - P N Ainslie
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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352
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Rickards CA, Tzeng YC. Arterial pressure and cerebral blood flow variability: friend or foe? A review. Front Physiol 2014; 5:120. [PMID: 24778619 PMCID: PMC3985018 DOI: 10.3389/fphys.2014.00120] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2013] [Accepted: 03/13/2014] [Indexed: 01/09/2023] Open
Abstract
Variability in arterial pressure and cerebral blood flow has traditionally been interpreted as a marker of cardiovascular decompensation, and has been associated with negative clinical outcomes across varying time scales, from impending orthostatic syncope to an increased risk of stroke. Emerging evidence, however, suggests that increased hemodynamic variability may, in fact, be protective in the face of acute challenges to perfusion, including significant central hypovolemia and hypotension (including hemorrhage), and during cardiac bypass surgery. This review presents the dichotomous views on the role of hemodynamic variability on clinical outcome, including the physiological mechanisms underlying these patterns, and the potential impact of increased and decreased variability on cerebral perfusion and oxygenation. We suggest that reconciliation of these two apparently discrepant views may lie in the time scale of hemodynamic variability; short time scale variability appears to be cerebroprotective, while mid to longer term fluctuations are associated with primary and secondary end-organ dysfunction.
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Affiliation(s)
- Caroline A Rickards
- Department of Integrative Physiology, Cardiovascular Research Institute, University of North Texas Health Science Center Fort Worth, TX, USA
| | - Yu-Chieh Tzeng
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago Wellington, New Zealand
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353
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Blohm ME, Obrecht D, Hartwich J, Singer D. Effect of cerebral circulatory arrest on cerebral near-infrared spectroscopy in pediatric patients. Paediatr Anaesth 2014; 24:393-9. [PMID: 24354795 DOI: 10.1111/pan.12328] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 11/17/2013] [Indexed: 10/25/2022]
Abstract
BACKGROUND/AIMS The aim was to investigate whether cerebral transcutaneous near-infrared spectroscopy (NIRS) or two-site NIRS is a suitable monitoring tool to detect or confirm a cerebral circulatory arrest in pediatric intensive care unit (PICU) patients. METHODS Prospective single-center pediatric observational study. Simultaneous NIRS measurements over forehead (cNIRS, crS02) and kidney (rNIRS, rrSO2), at the same time, the cardiac output were determined by transthoracic echocardiography. Area under the curve (AUC) in the receiver-operating curve (ROC) was analyzed for NIRS regarding cerebral circulatory arrest. RESULTS There were two groups of patients (weight 2.1-73 kg): Group A: patients with intact cerebral perfusion (n = 36). Group B: patients with cerebral circulatory arrest (n = 8) proven by Doppler ultrasound scan or perfusion scintigraphy. There was no difference in cardiac output between the groups. PICU mortality for Group A was 3/36 (8.3%), for Group B 8/8, (100%). Mean cNIRS values were significantly higher with 68.92 (SEM = 2.54, SD = 15.25) in Group A compared with 34.63 (SEM = 5.36, SD = 15.15) in Group B (P < 0.001). ROC analysis for cNIRS detecting cerebral circulatory arrest was significant (AUC 0.948, 95% confidence interval 0.876-1.000, SE = 0.037, P < 0.001). Discrimination was optimal at 46 for cNIRS, at 36.5 for the difference rNIRS-cNIRS and at 0.5646 for the quotient cNIRS/rNIRS. The probability of a cerebral circulatory arrest was 77.8% (cNIRS) and 87.5% (combinations of cNIRS and rNIRS) at these cutoffs. CONCLUSIONS cNIRS did detect cerebral circulatory arrest with high sensitivity. Specificity was, however, not high enough to confirm a cerebral circulatory arrest.
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Affiliation(s)
- Martin E Blohm
- Department of Pediatrics, Division of Neonatology and Pediatric Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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354
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Perry BG, Mündel T, Cochrane DJ, Cotter JD, Lucas SJE. The cerebrovascular response to graded Valsalva maneuvers while standing. Physiol Rep 2014; 2:e00233. [PMID: 24744902 PMCID: PMC3966248 DOI: 10.1002/phy2.233] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Revised: 01/20/2014] [Accepted: 01/21/2014] [Indexed: 12/02/2022] Open
Abstract
The Valsalva maneuver (VM) produces large and abrupt increases in mean arterial pressure (MAP) at the onset of strain (Phase I), however, hypotension, sufficient to induce syncope, occurs upon VM release (phase III). We examined the effect of VM intensity and duration on middle cerebral artery blood velocity (MCAv) responses. Healthy men (n =10; mean ± SD: 26 ± 4 years) completed 30%, 60%, and 90% of their maximal VM mouth pressure, for 5 and 10 sec (order randomized) while standing. Beat‐to‐beat MCAv and MAP during phase I (peak), at nadir (phase III), and recovery are reported as the change from standing baseline. During phase I, MCAv rose 15 ± 6 cm·s−1 (P <0.001), which was not reliably different between intensities (P =0.11), despite graded increases in MAP (P <0.001; e.g., +12 ± 9 mmHg vs. +35 ± 14 for 5 sec 30% and 90% VM, respectively). During Phase III, the MCAv response was duration‐ (P = 0.045) and intensity dependent (P < 0.001), with the largest decrease observed following the 90% VM (e.g., −19 ± 13 and −15 ± 11 cm·s−1 for 5 and 10 sec VM, respectively) with a concomitant decrease in MAP (P <0.001, −23 ± 11 and −23 ± 9 mmHg). This asymmetric response may be attributable to the differential modulators of MCAv throughout the VM. The mechanical effects of the elevated intrathoracic pressure during phase I may restrain increases in cerebral perfusion via related increases in intracranial pressure; however, during phase III the decrease in MCAv arises from an abrupt hypotension, the extent of which is dependent upon both the duration and intensity of the VM. More intense Valsalva maneuvers when standing are associated with an increase blood pressure response during Phase I of the maneuver although this is not accompanied by changes in cerebral blood flow. However, following the maneuver (phase III) more intense straining is associated with a greater decrease in both blood pressure and cerebral blood flow and in some instances is sufficient to induce syncope.
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Affiliation(s)
- Blake G Perry
- School of Sport and Exercise, Massey University, Palmerston North, New Zealand
| | - Toby Mündel
- School of Sport and Exercise, Massey University, Palmerston North, New Zealand
| | - Darryl J Cochrane
- School of Sport and Exercise, Massey University, Palmerston North, New Zealand
| | - James D Cotter
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand
| | - Samuel J E Lucas
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand ; Department of Physiology, University of Otago, Dunedin, New Zealand ; School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
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355
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Smirl JD, Lucas SJE, Lewis NCS, duManoir GR, Smith KJ, Bakker A, Basnyat AS, Ainslie PN, Ainslie PN. Cerebral pressure-flow relationship in lowlanders and natives at high altitude. J Cereb Blood Flow Metab 2014; 34:248-57. [PMID: 24169852 PMCID: PMC3915197 DOI: 10.1038/jcbfm.2013.178] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Revised: 08/13/2013] [Accepted: 09/09/2013] [Indexed: 12/30/2022]
Abstract
We investigated if dynamic cerebral pressure-flow relationships in lowlanders are altered at high altitude (HA), differ in HA natives and after return to sea level (SL). Lowlanders were tested at SL (n=16), arrival to 5,050 m, after 2-week acclimatization (with and without end-tidal PO2 normalization), and upon SL return. High-altitude natives (n=16) were tested at 5,050 m. Testing sessions involved resting spontaneous and driven (squat-stand maneuvers at very low (VLF, 0.05 Hz) and low (LF, 0.10 Hz) frequencies) measures to maximize blood pressure (BP) variability and improve assessment of the pressure-flow relationship using transfer function analysis (TFA). Blood flow velocity was assessed in the middle (MCAv) and posterior (PCAv) cerebral arteries. Spontaneous VLF and LF phases were reduced and coherence was elevated with acclimatization to HA (P<0.05), indicating impaired pressure-flow coupling. However, when BP was driven, both the frequency- and time-domain metrics were unaltered and comparable with HA natives. Acute mountain sickness was unrelated to TFA metrics. In conclusion, the driven cerebral pressure-flow relationship (in both frequency and time domains) is unaltered at 5,050 m in lowlanders and HA natives. Our findings indicate that spontaneous changes in TFA metrics do not necessarily reflect physiologically important alterations in the capacity of the brain to regulate BP.
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Affiliation(s)
- Jonathan D Smirl
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Samuel J E Lucas
- 1] Department of Physiology, University of Otago, Dunedin, New Zealand [2] School of Physical Education, University of Otago, Dunedin, New Zealand [3] School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Nia C S Lewis
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | | | - Kurt J Smith
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Akke Bakker
- University of Twente, Enschede, The Netherlands
| | | | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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356
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Phillips AA, Krassioukov AV, Ainslie PN, Warburton DER. Perturbed and spontaneous regional cerebral blood flow responses to changes in blood pressure after high-level spinal cord injury: the effect of midodrine. J Appl Physiol (1985) 2014; 116:645-53. [PMID: 24436297 DOI: 10.1152/japplphysiol.01090.2013] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Individuals with spinal cord injury (SCI) above the T6 spinal segment suffer from orthostatic intolerance. How cerebral blood flow (CBF) responds to orthostatic challenges in SCI is poorly understood. Furthermore, it is unclear how interventions meant to improve orthostatic tolerance in SCI influence CBF. This study aimed to examine 1) the acute regional CBF responses to rapid changes in blood pressure (BP) during orthostatic stress in individuals with SCI and able-bodied (AB) individuals; and 2) the effect of midodrine (alpha1-agonist) on orthostatic tolerance and CBF regulation in SCI. Ten individuals with SCI >T6, and 10 age- and sex-matched AB controls had beat-by-beat BP and middle and posterior cerebral artery blood velocity (MCAv, PCAv, respectively) recorded during a progressive tilt-test to quantify the acute CBF response and orthostatic tolerance. Dynamic MCAv and PCAv to BP relationships were evaluated continuously in the time domain and frequency domain (via transfer function analysis). The SCI group was tested again after administration of 10 mg midodrine to elevate BP. Coherence (i.e., linearity) was elevated in SCI between BP-MCAv and BP-PCAv by 35% and 22%, respectively, compared with AB, whereas SCI BP-PCAv gain (i.e., magnitudinal relationship) was reduced 30% compared with AB (all P < 0.05). The acute (i.e., 0-30 s after tilt) MCAv and PCAv responses were similar between groups. In individuals with SCI, midodrine led to improved PCAv responses 30-60 s following tilt (10 ± 3% vs. 4 ± 2% decline; P < 0.05), and a 59% improvement in orthostatic tolerance (P < 0.01). The vertebrobasilar region may be particularly susceptible to hypoperfusion in SCI, leading to increased orthostatic intolerance.
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Affiliation(s)
- Aaron A Phillips
- Cardiovascular Physiology and Rehabilitation Laboratory, Physical Activity Promotion and Chronic Disease Prevention Unit, University of British Columbia, Vancouver, British Columbia, Canada
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357
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Berg RMG, Plovsing RR, Evans KA, Christiansen CB, Bailey DM, Holstein-Rathlou NH, Møller K. Lipopolysaccharide infusion enhances dynamic cerebral autoregulation without affecting cerebral oxygen vasoreactivity in healthy volunteers. Crit Care 2013; 17:R238. [PMID: 24131656 PMCID: PMC4057209 DOI: 10.1186/cc13062] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Accepted: 08/13/2013] [Indexed: 12/23/2022] Open
Abstract
INTRODUCTION Sepsis may be associated with disturbances in cerebral oxygen transport and cerebral haemodynamic function, thus rendering the brain particularly susceptible to hypoxia. The purpose of this study was to assess the impact of isocapnic hypoxia and hyperoxia on dynamic cerebral autoregulation in a human-experimental model of the systemic inflammatory response during the early stages of sepsis. METHODS A total of ten healthy volunteers were exposed to acute isocapnic inspiratory hyperoxia (FIO₂ = 40%) and hypoxia (FIO₂ = 12%) before and after a 4-hour lipopolysaccharide (LPS) infusion (2 ng kg-1). Middle cerebral artery blood follow velocity was assessed using transcranial Doppler ultrasound, and dynamic autoregulation was evaluated by transfer function analysis. RESULTS Transfer function analysis revealed an increase in the phase difference between mean arterial blood pressure and middle cerebral artery blood flow velocity in the low frequency range (0.07-0.20 Hz) after LPS (P<0.01). In contrast, there were no effects of either isocapnic hyperoxia or hypoxia on dynamic autoregulation, and the cerebral oxygen vasoreactivity to both hyperoxia and hypoxia was unaffected by LPS. CONCLUSIONS The observed increase in phase suggests that dynamic cerebral autoregulation is enhanced after LPS infusion and resistant to any effects of acute hypoxia; this may protect the brain from ischaemia and/or blood-brain barrier damage during the early stages of sepsis.
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Affiliation(s)
- Ronan MG Berg
- Centre of Inflammation and Metabolism, Department of Infectious Diseases, section M7641, University Hospital Rigshospitalet, Blegdamsvej 9, DK-2100, Copenhagen Ø, Denmark
- Renal and Vascular Research Section, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen N, Denmark
- Intensive Care Unit 4131, University Hospital Rigshospitalet, Copenhagen Ø, Denmark
| | - Ronni R Plovsing
- Intensive Care Unit 4131, University Hospital Rigshospitalet, Copenhagen Ø, Denmark
| | - Kevin A Evans
- Neurovascular Research Laboratory, Faculty of Health, Science and Sport, University of Glamorgan, South Wales CF374AT, UK
| | - Claus B Christiansen
- Centre of Inflammation and Metabolism, Department of Infectious Diseases, section M7641, University Hospital Rigshospitalet, Blegdamsvej 9, DK-2100, Copenhagen Ø, Denmark
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Health, Science and Sport, University of Glamorgan, South Wales CF374AT, UK
| | - Niels-Henrik Holstein-Rathlou
- Renal and Vascular Research Section, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen N, Denmark
| | - Kirsten Møller
- Centre of Inflammation and Metabolism, Department of Infectious Diseases, section M7641, University Hospital Rigshospitalet, Blegdamsvej 9, DK-2100, Copenhagen Ø, Denmark
- Neurointensive Care Unit 2093, Department of Neuroanaesthesiology, University Hospital Rigshospitalet, Copenhagen Ø, Denmark
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358
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Skow RJ, MacKay CM, Tymko MM, Willie CK, Smith KJ, Ainslie PN, Day TA. Differential cerebrovascular CO2 reactivity in anterior and posterior cerebral circulations. Respir Physiol Neurobiol 2013; 189:76-86. [DOI: 10.1016/j.resp.2013.05.036] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2012] [Revised: 05/30/2013] [Accepted: 05/31/2013] [Indexed: 01/08/2023]
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359
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Bain AR, Smith KJ, Lewis NC, Foster GE, Wildfong KW, Willie CK, Hartley GL, Cheung SS, Ainslie PN. Regional changes in brain blood flow during severe passive hyperthermia: effects of PaCO2 and extracranial blood flow. J Appl Physiol (1985) 2013; 115:653-9. [DOI: 10.1152/japplphysiol.00394.2013] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We investigated 1) the regional distribution of cerebral blood flow (CBF), 2) the influence of end-tidal Pco2 (PetCO2) on CBF, and 3) the potential for an extracranial blood “steal” from the anterior brain region during passive hyperthermia. Nineteen (13 male) volunteers underwent supine passive heating until a steady-state esophageal temperature of 2°C above resting was established. Measurements were obtained 1) during normothermia (Normo), 2) during poikilocapnic hyperthermia (Hyper), and 3) during hyperthermia with PetCO2 and end-tidal Po2 clamped to Normo levels (Hyper-clamp). Blood flow in the internal carotid (Q̇ica), vertebral (Q̇VA), and external carotid (Q̇eca) arteries (Duplex ultrasound), blood velocity of the middle cerebral (MCAv) and posterior cerebral (PCAv) arteries (transcranial Doppler), and cutaneous vascular conductance on the cheek (cheek CVC; Doppler velocimetry) were measured at each stage. During Hyper, PetCO2 was lowered by 7.0 ± 5.2 mmHg, resulting in a reduction in Q̇ica (−18 ± 17%), Q̇va (−31 ± 21%), MCAv (−22 ± 13%), and PCAv (−18 ± 10%) compared with Normo ( P < 0.05). The reduction in Q̇VA was greater than that in Q̇ICA ( P = 0.017), MCAv ( P = 0.047), and PCAv ( P = 0.034). Blood flow/velocity was completely restored in each intracranial vessel (ICA, VA, MCA, and PCA) during Hyper-clamp. Despite a ∼250% increase in Q̇ECA and a subsequent increase in cheek CVC during Hyper compared with Normo, reductions in Q̇ICA were unrelated to changes in Q̇ECA. These data provide three novel findings: 1) hyperthermia attenuates Q̇VA to a greater extent than Q̇ICA, 2) reductions in CBF during hyperthermia are governed primarily by reductions in arterial Pco2, and 3) increased Q̇ECA is unlikely to compromise Q̇ICA during hyperthermia.
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Affiliation(s)
- Anthony R. Bain
- Center for Heart, Lung, and Vascular Health, University of British Columbia, Okanagan, British Columbia, Canada
| | - Kurt J. Smith
- Center for Heart, Lung, and Vascular Health, University of British Columbia, Okanagan, British Columbia, Canada
| | - Nia C. Lewis
- Center for Heart, Lung, and Vascular Health, University of British Columbia, Okanagan, British Columbia, Canada
| | - Glen E. Foster
- Center for Heart, Lung, and Vascular Health, University of British Columbia, Okanagan, British Columbia, Canada
- School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada; and
| | - Kevin W. Wildfong
- Center for Heart, Lung, and Vascular Health, University of British Columbia, Okanagan, British Columbia, Canada
| | - Christopher K. Willie
- Center for Heart, Lung, and Vascular Health, University of British Columbia, Okanagan, British Columbia, Canada
| | - Geoffrey L. Hartley
- Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada
| | - Stephen S. Cheung
- Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada
| | - Philip N. Ainslie
- Center for Heart, Lung, and Vascular Health, University of British Columbia, Okanagan, British Columbia, Canada
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360
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Len TK, Neary JP, Asmundson GJG, Candow DG, Goodman DG, Bjornson B, Bhambhani YN. Serial monitoring of CO2 reactivity following sport concussion using hypocapnia and hypercapnia. Brain Inj 2013; 27:346-53. [PMID: 23438354 DOI: 10.3109/02699052.2012.743185] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PRIMARY OBJECTIVE This study examined the effects of mild traumatic brain injury (mTBI) on cerebrovascular reactivity (CVR). RESEARCH DESIGN A repeated measures design was used to examine serial changes in CVR. METHODS AND PROCEDURES Twenty subjects who recently suffered a mTBI were subjected to a respiratory challenge consisting of repeated 20 s breath-holds (BH) and hyperventilations (HV). Testing occurred on days 2 (D2), 4 (D4) and 8 (D8) post-injury as well as a baseline (BASE) assessment (after return-to-play). Transcranial Doppler was used to assess mean cerebral blood velocity (vMCA) and expired gas analysis provided end-tidal carbon dioxide (PETCO2) levels. RESULTS There was no significant difference in resting vMCA across all testing days for mTBI. No significant differences in PETCO2 were found throughout the testing protocol. A significant effect (p < 0.001) of testing day on vMCA was found during BH and HV challenges for mTBI. Post-hoc analysis revealed significant differences (p < 0.05) in vMCA between D2 and the other testing days. CONCLUSIONS These data suggest that, following mTBI: (1) CVR is not impaired at rest; (2) CVR is impaired in response to respiratory stress; and (3) the impairment may be resolved as early as 4 days post-injury.
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Affiliation(s)
- Trevor K Len
- Faculty of Kinesiology and Health Studies, University of Regina, Saskatchewan, Canada
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361
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Zhu YS, Tarumi T, Tseng BY, Palmer DM, Levine BD, Zhang R. Cerebral vasomotor reactivity during hypo- and hypercapnia in sedentary elderly and Masters athletes. J Cereb Blood Flow Metab 2013; 33:1190-6. [PMID: 23591649 PMCID: PMC3734768 DOI: 10.1038/jcbfm.2013.66] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 03/14/2013] [Accepted: 03/17/2013] [Indexed: 11/09/2022]
Abstract
Physical activity may influence cerebrovascular function. The objective of this study was to determine the impact of life-long aerobic exercise training on cerebral vasomotor reactivity (CVMR) to changes in end-tidal CO2 (EtCO2) in older adults. Eleven sedentary young (SY, 27±5 years), 10 sedentary elderly (SE, 72±4 years), and 11 Masters athletes (MA, 72±6 years) underwent the measurements of cerebral blood flow velocity (CBFV), arterial blood pressure, and EtCO2 during hypocapnic hyperventilation and hypercapnic rebreathing. Baseline CBFV was lower in SE and MA than in SY while no difference was observed between SE and MA. During hypocapnia, CVMR was lower in SE and MA compared with SY (1.87±0.42 and 1.47±0.21 vs. 2.18±0.28 CBFV%/mm Hg, P<0.05) while being lowest in MA among all groups (P<0.05). In response to hypercapnia, SE and MA exhibited greater CVMR than SY (6.00±0.94 and 6.67±1.09 vs. 3.70±1.08 CBFV1%/mm Hg, P<0.05) while no difference was observed between SE and MA. A negative linear correlation between hypo- and hypercapnic CVMR (R(2)=0.37, P<0.001) was observed across all groups. Advanced age was associated with lower resting CBFV and lower hypocapnic but greater hypercapnic CVMR. However, life-long aerobic exercise training appears to have minimal effects on these age-related differences in cerebral hemodynamics.
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Affiliation(s)
- Yong-Sheng Zhu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, USA
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362
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Lucas SJE, Lewis NCS, Sikken ELG, Thomas KN, Ainslie PN. Slow breathing as a means to improve orthostatic tolerance: a randomized sham-controlled trial. J Appl Physiol (1985) 2013; 115:202-11. [DOI: 10.1152/japplphysiol.00128.2013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endogenous oscillations in blood pressure (BP) and cerebral blood flow have been associated with improved orthostatic tolerance. Although slow breathing induces such responses, it has not been tested as a therapeutic strategy to improve orthostatic tolerance. With the use of a randomized, crossover sham-controlled design, we tested the hypothesis that breathing at six breaths/min (vs. spontaneous breathing) would improve orthostatic tolerance via inducing oscillations in mean arterial BP (MAP) and cerebral blood flow. Sixteen healthy participants (aged 25 ± 4 yr; mean ± SD) had continuous beat-to-beat measurements of middle cerebral artery blood velocity (MCAv), BP (finometer), heart rate (ECG), and end-tidal carbon dioxide partial pressure during an incremental orthostatic stress test to presyncope by combining head-up tilt with incremental lower-body negative pressure. Tolerance time to presyncope was improved (+15%) with slow breathing compared with spontaneous breathing (29.2 ± 5.4 vs. 33.7 ± 6.0 min; P < 0.01). The improved tolerance was reflected in elevations in low-frequency (LF; 0.07-0.2 Hz) oscillations of MAP and mean MCAv, improved metrics of dynamic cerebrovascular control (increased LF phase and reduced LF gain), and a reduced rate of decline for MCAv (−0.60 ± 0.27 vs. −0.99 ± 0.51 cm·s−1·min−1; P < 0.01) and MAP (−0.50 ± 0.37 vs. −1.03 ± 0.80 mmHg/min; P = 0.01 vs. spontaneous breathing) across time from baseline to presyncope. Our findings show that orthostatic tolerance can be improved within healthy individuals with a simple, nonpharmacological breathing strategy. The mechanisms underlying this improvement are likely mediated via the generation of negative intrathoracic pressure during slow and deep breathing and the related beneficial impact on cerebrovascular and autonomic function.
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Affiliation(s)
- Samuel J. E. Lucas
- Department of Physiology, University of Otago, Dunedin, New Zealand
- School of Physical Education, University of Otago, Dunedin, New Zealand
- School of Sport and Exercise Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Nia C. S. Lewis
- Centre of Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Vancouver, British Columbia, Canada
- Research Institute of Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom; and
| | - Elisabeth L. G. Sikken
- Department of Physiology, University of Otago, Dunedin, New Zealand
- Department of Physiology, Radboud University, Nijmegen Medical Centre, Nijmegen, the Netherlands
| | - Kate N. Thomas
- Department of Physiology, University of Otago, Dunedin, New Zealand
- School of Physical Education, University of Otago, Dunedin, New Zealand
| | - Philip N. Ainslie
- Centre of Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Vancouver, British Columbia, Canada
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Schlader ZJ, Lucas RAI, Pearson J, Crandall CG. Hyperthermia does not alter the increase in cerebral perfusion during cognitive activation. Exp Physiol 2013; 98:1597-607. [PMID: 23851918 DOI: 10.1113/expphysiol.2013.074104] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This study tested the hypothesis that hyperthermia attenuates the increase in cerebral perfusion during cognitive activation. Mean middle cerebral artery blood velocity (MCAV(mean)) served as an index of cerebral perfusion, while the nBack test (a test of working memory) was the cognitive task. Hyperthermia was characterized by elevations (P < 0.001) in skin (by 5.0 ± 0.8 °C) and intestinal temperatures (by 1.3 ± 0.1 °C) and reductions (P < 0.020) in mean arterial pressure (by 11 ± 10 mmHg), end-tidal CO2 tension (by 3 ± 6 mmHg) and MCAV(mean) (by 10 ± 9 cm s(-1)). Hyperthermia had no influence on nBack test performance (mean difference from normothermia to hyperthermia, -1 ± 11%; P = 0.276) or, counter to the hypothesis, the increase in MCAV(mean) during nBack testing (mean difference from normothermia to hyperthermia: 0 ± 16 cm s(-1); P = 0.608). These findings indicate that the capacity to increase cerebral perfusion during cognitive activation is unaffected by hyperthermia.
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Affiliation(s)
- Zachary J Schlader
- C. G. Crandall: Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, 7232 Greenville Avenue, Dallas, TX 75231, USA.
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364
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An SA, Lee HB, Kim Y, Kim J, Kim HS, Kim WC, Kim OJ, Oh SH. Plasma total homocysteine level is associated with the pulsatility index of cerebral arteries in lacunar infarction. Yonsei Med J 2013; 54:819-24. [PMID: 23709413 PMCID: PMC3663237 DOI: 10.3349/ymj.2013.54.4.819] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
PURPOSE The pulsatility index (PI), measured by transcranial Doppler (TCD), is a surrogate marker for distal vascular resistance in cerebral arteries, and elevated plasma total homocysteine (tHcyt) is regarded as a cause of ischemic stroke, including lacunar infarction. We investigated the relationship between the PI of cerebral arteries and plasma tHcyt in patients with lacunar infarction. MATERIALS AND METHODS Plasma tHcyt level and TCD examination were performed in 94 patients with lacunar infarction. Mean flow velocity (MFV) and PI were assessed at the ipsilateral middle cerebral artery (MCA) and contralateral MCA, relative to the infarction, and the basilar artery (BA). Multivariate regression analysis was conducted between log-transformed tHcyt levels (logHcyt) and the PI of individual arteries. RESULTS There was a significant correlation between logHcyt and the PI in all tested arteries (ipsilateral MCA: r=0.21, p=0.03; contralateral MCA: r=0.21, p=0.04; BA: r=0.35, p=0.01). In multivariate regression analysis, this significance remained unchanged after adjusting for vascular risk factors, creatinine, hematocrit and platelet count (ipsilateral MCA: β=0.26, p=0.01; contralateral MCA: β=0.21, p=0.04; BA: β=0.39, p=0.001). There was no significant association between logHcyt and MFV of individual arteries. CONCLUSION A significant association between plasma tHcyt and the PI of cerebral arteries indicates that homocysteine plays a role in the increase of distal arterial resistance in lacunar infarction.
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Affiliation(s)
- Se-A An
- Department of Neurology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
| | - Han-Bin Lee
- Department of Neurology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
| | - Yoon Kim
- Department of Neurology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
| | - Jinkwon Kim
- Department of Neurology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
| | - Hyun-Sook Kim
- Department of Neurology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
| | - Won-Chan Kim
- Department of Neurology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
| | - Ok-Joon Kim
- Department of Neurology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
| | - Seung-Hun Oh
- Department of Neurology, CHA Bundang Medical Center, CHA University, Seongnam, Korea
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365
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366
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Neurovascular coupling of the posterior cerebral artery in spinal cord injury: a pilot study. Brain Sci 2013; 3:781-9. [PMID: 24961424 PMCID: PMC4061840 DOI: 10.3390/brainsci3020781] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 04/26/2013] [Accepted: 04/29/2013] [Indexed: 11/16/2022] Open
Abstract
PURPOSE To compare neurovascular coupling in the posterior cerebral artery (PCA) between those with spinal cord injury (SCI) and able bodied (AB) individuals. METHODS A total of seven SCI and seven AB were matched for age and sex. Measures included PCA velocity (PCAv), beat-by-beat blood pressure and end-tidal carbon dioxide. Posterior cerebral cortex activation was achieved by 10 cycles of (1) 30 s eyes closed (pre-stimulation), (2) 30 s reading (stimulation). RESULTS Blood pressure was significantly reduced in those with SCI (SBP: 100 ± 13 mmHg; DBP: 58 ± 13 mmHg) vs. AB (SBP 121 ± 12 mmHg; DBP: 74 ± 9 mmHg) during both pre-stimulation and stimulation, but the relative increase was similar during the stimulation period. Changes in PCAv during stimulation were mitigated in the SCI group (6% ± 6%) vs. AB (29% ± 12%, P < 0.001). Heart rate and end-tidal carbon dioxide responded similarly between groups. CONCLUSIONS Clearly, NVC is impaired in those with SCI. This study may provide a link between poor perfusion of the posterior cerebral region (containing the medullary autonomic centres) and autonomic dysfunction after SCI.
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367
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Schlader ZJ, Seifert T, Wilson TE, Bundgaard-Nielsen M, Secher NH, Crandall CG. Acute volume expansion attenuates hyperthermia-induced reductions in cerebral perfusion during simulated hemorrhage. J Appl Physiol (1985) 2013; 114:1730-5. [PMID: 23580601 DOI: 10.1152/japplphysiol.00079.2013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hyperthermia reduces the capacity to withstand a simulated hemorrhagic challenge, but volume loading preserves this capacity. This study tested the hypotheses that acute volume expansion during hyperthermia increases cerebral perfusion and attenuates reductions in cerebral perfusion during a simulated hemorrhagic challenge induced by lower-body negative pressure (LBNP). Eight healthy young male subjects underwent a supine baseline period (pre-LBNP), followed by 15- and 30-mmHg LBNP while normothermic, hyperthermic (increased pulmonary artery blood temperature ~1.1°C), and following acute volume infusion while hyperthermic. Primary dependent variables were mean middle cerebral artery blood velocity (MCAvmean), serving as an index of cerebral perfusion; mean arterial pressure (MAP); and cardiac output (thermodilution). During baseline, hyperthermia reduced MCAvmean (P = 0.001) by 12 ± 9% relative to normothermia. Volume infusion while hyperthermic increased cardiac output by 2.8 ± 1.4 l/min (P < 0.001), but did not alter MCAvmean (P = 0.99) or MAP (P = 0.39) compared with hyperthermia alone. Relative to hyperthermia, at 30-mmHg LBNP acute volume infusion attenuated reductions (P < 0.001) in cardiac output (by 2.5 ± 0.9 l/min; P < 0.001), MAP (by 5 ± 6 mmHg; P = 0.004), and MCAvmean (by 12 ± 13%; P = 0.002). These data indicate that acute volume expansion does not reverse hyperthermia-induced reductions in cerebral perfusion pre-LBNP, but that it does attenuate reductions in cerebral perfusion during simulated hemorrhage in hyperthermic humans.
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Affiliation(s)
- Zachary J Schlader
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital of Dallas, Dallas, Texas 75231, USA
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368
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McDonnell MN, Berry NM, Cutting MA, Keage HA, Buckley JD, Howe PRC. Transcranial Doppler ultrasound to assess cerebrovascular reactivity: reliability, reproducibility and effect of posture. PeerJ 2013; 1:e65. [PMID: 23646284 PMCID: PMC3642776 DOI: 10.7717/peerj.65] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Accepted: 03/20/2013] [Indexed: 11/20/2022] Open
Abstract
Transcranial Doppler ultrasound (TCD) allows measurement of blood flow velocities in the intracranial vessels, and can be used to assess cerebral vasodilator responses to a hypercapnic stimulus. The reliability of this technique has not been established, nor is there agreement about whether the technique should be performed in sitting or lying postures. We tested the intra- and inter-rater reliability of measures of cerebrovascular reactivity (CVR) in 10 healthy adults, in sitting and lying postures. Participants underwent triplicate bilateral ultrasound assessment of flow velocities in the middle cerebral arteries whilst sitting and lying supine prior to and during inhalation of Carbogen (5% CO2, 95% O2) for 2 min. This procedure was performed twice by each of two raters for a total of four sessions. CVR was calculated as the difference between baseline and the peak blood flow velocity attained during CO2 inhalation. Intraclass correlation coefficients (ICCs) for intra-rater reliability were greater sitting than lying for both raters (e.g. Rater 1 ICC sitting = 0.822, lying = 0.734), and inter-rater reliability was also greater in sitting (e.g. sitting ICC = 0.504, lying = 0.081). These results suggest that assessment of CVR using TCD should be performed with participants sitting in order to maximise CVR measurement reliability.
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369
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Mace E, Montaldo G, Osmanski BF, Cohen I, Fink M, Tanter M. Functional ultrasound imaging of the brain: theory and basic principles. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2013; 60:492-506. [PMID: 23475916 DOI: 10.1109/tuffc.2013.2592] [Citation(s) in RCA: 146] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Hemodynamic changes in the brain are often used as surrogates of neuronal activity to infer the loci of brain activity. A major limitation of conventional Doppler ultrasound for the imaging of these changes is that it is not sensitive enough to detect the blood flow in small vessels where the major part of the hemodynamic response occurs. Here, we present a μDoppler ultrasound method able to detect and map the cerebral blood volume (CBV) over the entire brain with an important increase in sensitivity. This method is based on imaging the brain at an ultrafast frame rate (1 kHz) using compounded plane wave emissions. A theoretical model demonstrates that the gain in sensitivity of the μDoppler method is due to the combination of 1) the high signal-to-noise ratio of the gray scale images, resulting from the synthetic compounding of backscattered echoes; and 2) the extensive signal averaging enabled by the high temporal sampling of ultrafast frame rates. This μDoppler imaging is performed in vivo on trepanned rats without the use of contrast agents. The resulting images reveal detailed maps of the rat brain vascularization with an acquisition time as short as 320 ms per slice. This new method is the basis for a real-time functional ultrasound (fUS) imaging of the brain.
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Affiliation(s)
- Emilie Mace
- Institut Langevin, CNRS UMR7587, Inserm U979, Université Paris VII, Ecole Superieure de Physique et de Chimie Industrielles de Paris, Paris, France.
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370
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Schuepbach D, Skotchko T, Duschek S, Theodoridou A, Grimm S, Boeker H, Seifritz E. Gender and rapid alterations of hemispheric dominance during planning. Neuropsychobiology 2013; 66:149-57. [PMID: 22948314 DOI: 10.1159/000339562] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Accepted: 05/21/2012] [Indexed: 11/19/2022]
Abstract
BACKGROUND Mental planning and carrying out a plan provoke specific cerebral hemodynamic responses. Gender aspects of hemispheric laterality using rapid cerebral hemodynamics have not been reported. METHOD Here, we applied functional transcranial Doppler sonography to examine lateralization of cerebral hemodynamics of the middle cerebral arteries of 28 subjects (14 women and 14 men) performing a standard planning task. There were easy and difficult problems, and mental planning without motor activity was separated from movement execution. RESULTS Difficult mental planning elicited lateralization to the right hemisphere after 2 or more seconds, a feature that was not observed during movement execution. In females, there was a dominance to the left hemisphere during movement execution. Optimized problem solving yielded an increased laterality change to the right during mental planning. CONCLUSIONS Gender-related hemispheric dominance appears to be condition-dependent, and change of laterality to the right may play a role in optimized performance. Results are of relevance when considering laterality from a perspective of performance enhancement of higher cognitive functions, and also of psychiatric disorders with cognitive dysfunctions and abnormal lateralization patterns such as schizophrenia.
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Affiliation(s)
- Daniel Schuepbach
- Clinic for Affective Disorders and General Psychiatry, Psychiatric University Hospital Zurich, Zurich, Switzerland.
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371
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Burgess KR, Lucas SJE, Shepherd K, Dawson A, Swart M, Thomas KN, Lucas RAI, Donnelly J, Peebles KC, Basnyat R, Ainslie PN. Worsening of central sleep apnea at high altitude--a role for cerebrovascular function. J Appl Physiol (1985) 2013; 114:1021-8. [PMID: 23429871 DOI: 10.1152/japplphysiol.01462.2012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although periodic breathing during sleep at high altitude occurs almost universally, the likely mechanisms and independent effects of altitude and acclimatization have not been clearly reported. Data from 2005 demonstrated a significant relationship between decline in cerebral blood flow (CBF) at sleep onset and subsequent severity of central sleep apnea that night. We suspected that CBF would decline during partial acclimatization. We hypothesized therefore that reductions in CBF and its reactivity would worsen periodic breathing during sleep following partial acclimatization. Repeated measures of awake ventilatory and CBF responsiveness, arterial blood gases during wakefulness. and overnight polysomnography at sea level, upon arrival (days 2-4), and following partial acclimatization (days 12-15) to 5,050 m were made on 12 subjects. The apnea-hypopnea index (AHI) increased from to 77 ± 49 on days 2-4 to 116 ± 21 on days 12-15 (P = 0.01). The AHI upon initial arrival was associated with marked elevations in CBF (+28%, 68 ± 11 to 87 ± 17 cm/s; P < 0.05) and its reactivity to changes in PaCO2 [>90%, 2.0 ± 0.6 to 3.8 ± 1.5 cm·s(-1)·mmHg(-1) hypercapnia and 1.9 ± 0.4 to 4.1 ± 0.9 cm·s(-1)·mmHg(-1) for hypocapnia (P < 0.05)]. Over 10 days, the increases resolved and AHI worsened. During sleep at high altitude large oscillations in mean CBF velocity (CBFv) occurred, which were 35% higher initially (peak CBFv = 96 cm/s vs. peak CBFv = 71 cm/s) than at days 12-15. Our novel findings suggest that elevations in CBF and its reactivity to CO(2) upon initial ascent to high altitude may provide a protective effect on the development of periodic breathing during sleep (likely via moderating changes in central Pco2).
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Affiliation(s)
- Keith R Burgess
- Peninsula Sleep Laboratory, Sydney, New South Wales, Australia.
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372
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Abstract
Transcranial Doppler (TCD) ultrasound provides rapid, noninvasive, real-time measures of cerebrovascular function. TCD can be used to measure flow velocity in the basal arteries of the brain to assess relative changes in flow, diagnose focal vascular stenosis, or to detect embolic signals within these arteries. TCD can also be used to assess the physiologic health of a particular vascular territory by measuring blood flow responses to changes in blood pressure (cerebral autoregulation), changes in end-tidal CO2 (cerebral vasoreactivity), or cognitive and motor activation (neurovascular coupling or functional hyperemia). TCD has established utility in the clinical diagnosis of a number of cerebrovascular disorders such as acute ischemic stroke, vasospasm, subarachnoid hemorrhage, sickle cell disease, as well as other conditions such as brain death. Clinical indication and research applications for this mode of imaging continue to expand. In this review, the authors summarize the basic principles and clinical utility of TCD and provide an overview of a few TCD research applications.
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373
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Lewis NCS, Ainslie PN, Atkinson G, Jones H, Grant EJM, Lucas SJE. Initial orthostatic hypotension and cerebral blood flow regulation: effect of α1-adrenoreceptor activity. Am J Physiol Regul Integr Comp Physiol 2013; 304:R147-54. [DOI: 10.1152/ajpregu.00427.2012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined the hypothesis that α1-adrenergic blockade would lead to an inability to correct initial orthostatic hypotension (IOH) and cerebral hypoperfusion, leading to symptoms of presyncope. Twelve normotensive humans (aged 25 ± 1 yr; means ± SE) attempted to complete a 3-min upright stand, 90 min after the administration of either α1-blockade (prazosin, 1 mg/20 kg body wt) or placebo. Continuous beat-to-beat measurements of middle cerebral artery velocity (MCAv; Doppler), blood pressure (finometer), heart rate, and end-tidal Pco2were obtained. Compared with placebo, the α1-blockade reduced resting mean arterial blood pressure (MAP) (−15%; P < 0.01); MCAv remained unaltered ( P ≥ 0.28). Upon standing, although the absolute level of MAP was lower following α1-blockade (39 ± 10 mmHg vs. 51 ± 14 mmHg), the relative difference in IOH was negligible in both trials (mean difference in MAP: 2 ± 2 mmHg; P = 0.50). Compared with the placebo trial, the declines in MCAv and PetCO2during IOH were greater in the α1-blockade trial by 12 ± 4 cm/s and 4.4 ± 1.3 mmHg, respectively ( P ≤ 0.01). Standing tolerance was markedly reduced in the α1-blockade trial (75 ± 17 s vs. 180 ± 0 s; P < 0.001). In summary, while IOH was little affected by α1-blockade, the associated decline in MCAv was greater in the blockade condition. Unlike in the placebo trial, the extent of IOH and cerebral hypoperfusion failed to recover toward baseline in the α1-blockade trial leading to presyncope. Although the development of IOH is not influenced by the α1-adrenergic receptor pathway, this pathway is critical in the recovery from IOH to prevent cerebral hypoperfusion and ultimately syncope.
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Affiliation(s)
- Nia C. S. Lewis
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Kelowna, British Columbia, Canada
| | - Philip N. Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Kelowna, British Columbia, Canada
| | - Greg Atkinson
- Health and Social Care Institute, Teesside University, Middlesbrough, United Kingdom
| | - Helen Jones
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
| | - Emily J. M. Grant
- Department of Physiology, University of Otago, Dunedin, New Zealand; and
| | - Samuel J. E. Lucas
- Department of Physiology, University of Otago, Dunedin, New Zealand; and
- School of Physical Education, University of Otago, Dunedin, New Zealand
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374
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Impaired cerebral haemodynamic function associated with chronic traumatic brain injury in professional boxers. Clin Sci (Lond) 2013; 124:177-89. [PMID: 22913765 DOI: 10.1042/cs20120259] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The present study examined to what extent professional boxing compromises cerebral haemodynamic function and its association with CTBI (chronic traumatic brain injury). A total of 12 male professional boxers were compared with 12 age-, gender- and physical fitness-matched non-boxing controls. We assessed dCA (dynamic cerebral autoregulation; thigh-cuff technique and transfer function analysis), CVRCO₂ (cerebrovascular reactivity to changes in CO₂: 5% CO₂ and controlled hyperventilation), orthostatic tolerance (supine to standing) and neurocognitive function (psychometric tests). Blood flow velocity in the middle cerebral artery (transcranial Doppler ultrasound), mean arterial blood pressure (finger photoplethysmography), end-tidal CO₂ (capnography) and cortical oxyhaemoglobin concentration (near-IR spectroscopy) were continuously measured. Boxers were characterized by fronto-temporal neurocognitive dysfunction and impaired dCA as indicated by a lower rate of regulation and autoregulatory index (P<0.05 compared with controls). Likewise, CVRCO₂ was also reduced resulting in a lower CVRCO₂ range (P<0.05 compared with controls). The latter was most marked in boxers with the highest CTBI scores and correlated against the volume and intensity of sparring during training (r=-0.84, P<0.05). These impairments coincided with more marked orthostatic hypotension, cerebral hypoperfusion and corresponding cortical de-oxygenation during orthostatic stress (P<0.05 compared with controls). In conclusion, these findings provide the first comprehensive evidence for chronically impaired cerebral haemodynamic function in active boxers due to the mechanical trauma incurred by repetitive, sub-concussive head impact incurred during sparring training. This may help explain why CTBI is a progressive disease that manifests beyond the active boxing career.
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375
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Ainslie PN. Regional brain blood flow regulation during orthostatic stress: new insights from volumetric brain blood flow measurements. Exp Physiol 2012; 97:1247-8. [DOI: 10.1113/expphysiol.2012.067751] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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376
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Zhang HL, Guo ZN, Yang G, Yang L, Han K, Wu J, Xing Y, Yang Y. Compromised cerebrovascular modulation in chronic anxiety: evidence from cerebral blood flow velocity measured by transcranial Doppler sonography. Neurosci Bull 2012; 28:723-8. [PMID: 23152329 DOI: 10.1007/s12264-012-1282-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 05/01/2012] [Indexed: 12/01/2022] Open
Abstract
OBJECTIVE Cerebral autoregulation (CA) is the mechanism by which constant cerebral blood flow is maintained despite changes in cerebral perfusion pressure. CA can be evaluated by dynamic monitoring of cerebral blood flow velocity (CBFV) with transcranial Doppler sonography (TCD). The present study aimed to explore CA in chronic anxiety. METHODS Subjects with Hamilton anxiety scale scores ≥14 were enrolled and the dynamic changes of CBFV in response to an orthostatic challenge were investigated using TCD. RESULTS In both the anxious and the healthy subjects, the mean CBFV was significantly lower in the upright position than when supine. However, the CBFV changes from supine to upright differed between the anxious and the healthy groups. Anxious subjects showed more pronounced decreases in CBFV with abrupt standing. CONCLUSION Our results indicate that cerebrovascular modulation is compromised in chronic anxiety; anxious subjects have some insufficiency in maintaining cerebral perfusion after postural change. Given the fact that anxiety and impaired CA are associated with cardiovascular disease, early ascertainment of compromised cerebrovascular modulation using TCD might suggest interventional therapies in the anxious population, and improve the primary prevention of cardiovascular disease.
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Affiliation(s)
- Hong-Liang Zhang
- Department of Neurology, The First Norman Bethune Hospital of Jilin University, Changchun 130021, China
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377
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Purkayastha S, Saxena A, Eubank WL, Hoxha B, Raven PB. α1-Adrenergic receptor control of the cerebral vasculature in humans at rest and during exercise. Exp Physiol 2012; 98:451-61. [DOI: 10.1113/expphysiol.2012.066118] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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378
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[Sonographic diagnostics in neurological emergency and intensive care medicine]. Med Klin Intensivmed Notfmed 2012; 108:131-8. [PMID: 23070330 DOI: 10.1007/s00063-012-0146-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Revised: 05/14/2012] [Accepted: 07/03/2012] [Indexed: 11/27/2022]
Abstract
BACKGROUND This article gives an up-to-date overview of neurosonographic emergency and intensive care diagnostics. METHODS Selective literature research from 1984 with critical appraisal and including national and international guidelines. RESULTS Fast and valid diagnostics in acute stroke is the main field of application of neurosonography. Specific monitoring methods bear great advantages for intensive care patients, especially "as-often-as-wanted" repetitive imaging under real-time conditions. A number of new developments make neurosonography an interesting area of research. CONCLUSIONS Neurosonography has played a key role in neurological emergency and intensive care medicine for many years. It remains important to continuously support dissemination of the method.
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379
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Berg RMG, Plovsing RR, Ronit A, Bailey DM, Holstein-Rathlou NH, Møller K. Disassociation of static and dynamic cerebral autoregulatory performance in healthy volunteers after lipopolysaccharide infusion and in patients with sepsis. Am J Physiol Regul Integr Comp Physiol 2012; 303:R1127-35. [PMID: 23076874 DOI: 10.1152/ajpregu.00242.2012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Sepsis is frequently complicated by brain dysfunction, which may be associated with disturbances in cerebral autoregulation, rendering the brain susceptible to hypoperfusion and hyperperfusion. The purpose of the present study was to assess static and dynamic cerebral autoregulation 1) in a human experimental model of the systemic inflammatory response during early sepsis and 2) in patients with advanced sepsis. Cerebral autoregulation was tested using transcranial Doppler ultrasound in healthy volunteers (n = 9) before and after LPS infusion and in patients with sepsis (n = 16). Static autoregulation was tested by norepinephrine infusion and dynamic autoregulation by transfer function analysis (TFA) of spontaneous oscillations between mean arterial blood pressure and middle cerebral artery blood flow velocity in the low frequency range (0.07-0.20 Hz). Static autoregulatory performance after LPS infusion and in patients with sepsis was similar to values in healthy volunteers at baseline. In contrast, TFA showed decreased gain and an increased phase difference between blood pressure and middle cerebral artery blood flow velocity after LPS (both P < 0.01 vs. baseline); patients exhibited similar gain but lower phase difference values (P < 0.01 vs. baseline and LPS), indicating a slower dynamic autoregulatory response. Our findings imply that static and dynamic cerebral autoregulatory performance may disassociate in sepsis; thus static autoregulation was maintained both after LPS and in patients with sepsis, whereas dynamic autoregulation was enhanced after LPS and impaired with a prolonged response time in patients. Hence, acute surges in blood pressure may adversely affect cerebral perfusion in patients with sepsis.
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Affiliation(s)
- Ronan M G Berg
- Centre of Inflammation and Metabolism, Department of Infectious Diseases, University Hospital Rigshospitalet, Copenhagen Ø, Denmark.
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380
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Morrison SA, Ainslie PN, Lucas RAI, Cheung SS, Cotter JD. Compression garments do not alter cerebrovascular responses to orthostatic stress after mild passive heating. Scand J Med Sci Sports 2012; 24:291-300. [DOI: 10.1111/sms.12001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/14/2012] [Indexed: 11/26/2022]
Affiliation(s)
- S. A. Morrison
- School of Physical Education; University of Otago; Dunedin New Zealand
- Jozef Stefan Institute; Ljubljana Slovenia
| | - P. N. Ainslie
- School of Health and Exercise Sciences; University of British Columbia; Kelowna BC Canada
| | - R. A. I. Lucas
- School of Physical Education; University of Otago; Dunedin New Zealand
| | - S. S. Cheung
- Department of Kinesiology; Brock University; St. Catharines ON Canada
| | - J. D. Cotter
- School of Physical Education; University of Otago; Dunedin New Zealand
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381
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Regional cerebral blood flow distribution during exercise: influence of oxygen. Respir Physiol Neurobiol 2012; 184:97-105. [PMID: 22926137 DOI: 10.1016/j.resp.2012.07.014] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Revised: 07/18/2012] [Accepted: 07/19/2012] [Indexed: 11/22/2022]
Abstract
We investigated regional changes in cerebral artery velocity during incremental exercise while breathing normoxia (21% O2), hyperoxia (100% O2) or hypoxia (16% O2) [n=10; randomized cross over design]. Middle cerebral and posterior cerebral arterial velocities (MCAv and PCAv) were measured continuously using transcranial Doppler ultrasound. At rest, only PCAv was reduced (-7%; P=0.016) with hyperoxia. During low-intensity exercise (40% workload maximum [Wmax]) MCAv (+17 cms(-1); +14cms(-1)) and PCAv (+9cms(-1); +14 cms(-1)) were increased above baseline with normoxia and hypoxia, respectively (P<0.05). The absolute increase from rest in MCAv was greater than the increase in PCAv between 40 and 80% Wmax with normoxia; this greater increase in MCAv was also evident at 60% Wmax with hypoxia and hyperoxia. Hyperoxic exercise resulted in larger absolute (+19 cms(-1)) and relative (+40%) increases in PCAv compared with normoxia. Our findings highlight the selective changes in PCAv during hyperoxic incremental exercise.
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382
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Ainslie PN, Lucas SJE, Fan JL, Thomas KN, Cotter JD, Tzeng YC, Burgess KR. Influence of sympathoexcitation at high altitude on cerebrovascular function and ventilatory control in humans. J Appl Physiol (1985) 2012; 113:1058-67. [PMID: 22837165 DOI: 10.1152/japplphysiol.00463.2012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We sought to determine the influence of sympathoexcitation on dynamic cerebral autoregulation (CA), cerebrovascular reactivity, and ventilatory control in humans at high altitude (HA). At sea level (SL) and following 3-10 days at HA (5,050 m), we measured arterial blood gases, ventilation, arterial pressure, and middle cerebral blood velocity (MCAv) before and after combined α- and β-adrenergic blockade. Dynamic CA was quantified using transfer function analysis. Cerebrovascular reactivity was assessed using hypocapnia and hyperoxic hypercapnia. Ventilatory control was assessed from the hypercapnia and during isocapnic hypoxia. Arterial Pco(2) and ventilation and its control were unaltered following blockade at both SL and HA. At HA, mean arterial pressure (MAP) was elevated (P < 0.01 vs. SL), but MCAv remained unchanged. Blockade reduced MAP more at HA than at SL (26 vs. 15%, P = 0.048). At HA, gain and coherence in the very-low-frequency (VLF) range (0.02-0.07 Hz) increased, and phase lead was reduced (all P < 0.05 vs. SL). Following blockade at SL, coherence was unchanged, whereas VLF phase lead was reduced (-40 ± 23%; P < 0.01). In contrast, blockade at HA reduced low-frequency coherence (-26 ± 20%; P = 0.01 vs. baseline) and elevated VLF phase lead (by 177 ± 238%; P < 0.01 vs. baseline), fully restoring these parameters back to SL values. Irrespective of this elevation in VLF gain at HA (P < 0.01), blockade increased it comparably at SL and HA (∼43-68%; P < 0.01). Despite elevations in MCAv reactivity to hypercapnia at HA, blockade reduced (P < 0.05) it comparably at SL and HA, effects we attributed to the hypotension and/or abolition of the hypercapnic-induced increase in MAP. With the exception of dynamic CA, we provide evidence of a redundant role of sympathetic nerve activity as a direct mechanism underlying changes in cerebrovascular reactivity and ventilatory control following partial acclimatization to HA. These findings have implications for our understanding of CBF function in the context of pathologies associated with sympathoexcitation and hypoxemia.
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Affiliation(s)
- P N Ainslie
- Dept. of Human Kinetics, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada.
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383
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Lewis NCS, Ainslie PN, Atkinson G, Jones H, Grant EJM, Lucas SJE. The Effect of Time-of-Day and Sympathetic α1-Blockade on Orthostatic Tolerance. Chronobiol Int 2012; 29:882-90. [DOI: 10.3109/07420528.2012.699121] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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384
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Spronck B, Martens EGHJ, Gommer ED, van de Vosse FN. A lumped parameter model of cerebral blood flow control combining cerebral autoregulation and neurovascular coupling. Am J Physiol Heart Circ Physiol 2012; 303:H1143-53. [PMID: 22777421 DOI: 10.1152/ajpheart.00303.2012] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Cerebral blood flow regulation is based on a variety of different mechanisms, of which the relative regulatory role remains largely unknown. The cerebral regulatory system expresses two regulatory properties: cerebral autoregulation and neurovascular coupling. Since partly the same mechanisms play a role in cerebral autoregulation and neurovascular coupling, this study aimed to develop a physiologically based mathematical model of cerebral blood flow regulation combining these properties. A lumped parameter model of the P2 segment of the posterior cerebral artery and its distal vessels was constructed. Blood flow regulation is exerted at the arteriolar level by vascular smooth muscle and implements myogenic, shear stress based, neurogenic, and metabolic mechanisms. In eight healthy subjects, cerebral autoregulation and neurovascular coupling were challenged by squat-stand maneuvers and visual stimulation using a checkerboard pattern, respectively. Cerebral blood flow velocity was measured using transcranial Doppler, whereas blood pressure was measured by finger volume clamping. In seven subjects, the model proposed fits autoregulation and neurovascular coupling measurement data well. Myogenic regulation is found to dominate the autoregulatory response. Neurogenic regulation, although only implemented as a first-order mechanism, describes neurovascular coupling responses to a great extent. It is concluded that our single, integrated model of cerebral blood flow control may be used to identify the main mechanisms affecting cerebral blood flow regulation in individual subjects.
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Affiliation(s)
- Bart Spronck
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
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385
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Koller A, Toth P. Contribution of flow-dependent vasomotor mechanisms to the autoregulation of cerebral blood flow. J Vasc Res 2012; 49:375-89. [PMID: 22739136 PMCID: PMC3586555 DOI: 10.1159/000338747] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Accepted: 04/04/2012] [Indexed: 11/19/2022] Open
Abstract
Regulation of cerebral blood flow (CBF) is the result of multilevel mechanisms to maintain the appropriate blood supply to the brain while having to comply with the limited space available in the cranium. The latter requirement is ensured by the autoregulation of CBF, in which the pressure-sensitive myogenic response is known to play a pivotal role. However, in vivo increases in pressure are accompanied by increases in flow; yet the effects of flow on the vasomotor tone of cerebral vessels are less known. Earlier studies showed flow-sensitive dilation and/or constriction or both, but no clear picture emerged. Recently, the important role of flow-sensitive mechanism(s) eliciting the constriction of cerebral vessels has been demonstrated. This review focuses on the effect of hemodynamic forces (especially intraluminal flow) on the vasomotor tone of cerebral vessels and the underlying cellular and molecular mechanisms. A novel concept of autoregulation of CBF is proposed, suggesting that (in certain areas of the cerebrovascular tree) pressure- and flow-induced constrictions together maintain an effective autoregulation, and that alterations in these mechanisms may contribute to the development of cerebrovascular disorders. Future studies are warranted to explore the signals, the details of signaling processes and the in vivo importance of these mechanisms.
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Affiliation(s)
- Akos Koller
- Department of Pathophysiology and Gerontology, Medical School, University of Pécs, Pécs, Hungary.
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386
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Assessing Cerebrovascular Reactivity in Carotid Steno-Occlusive Disease Using MRI BOLD and ASL Techniques. Radiol Res Pract 2012; 2012:268483. [PMID: 22919485 PMCID: PMC3388310 DOI: 10.1155/2012/268483] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Revised: 04/17/2012] [Accepted: 04/17/2012] [Indexed: 12/13/2022] Open
Abstract
Impaired cerebrovascular reactivity (CVR), a predictive factor of imminent stroke, has been shown to be associated with carotid steno-occlusive disease. Magnetic resonance imaging (MRI) techniques, such as blood oxygenation level-dependent (BOLD) and arterial spin labeling (ASL), have emerged as promising noninvasive tools to evaluate altered CVR with whole-brain coverage, when combined with a vasoactive stimulus, such as respiratory task or injection of acetazolamide. Under normal cerebrovascular conditions, CVR has been shown to be globally and homogenously distributed between hemispheres, but with differences among cerebral regions. Such differences can be explained by anatomical specificities and different biochemical mechanisms responsible for vascular regulation. In patients with carotid steno-occlusive disease, studies have shown that MRI techniques can detect impaired CVR in brain tissue supplied by the affected artery. Moreover, resulting CVR estimations have been well correlated to those obtained with more established techniques, indicating that BOLD and ASL are robust and reliable methods to assess CVR in patients with cerebrovascular diseases. Therefore, the present paper aims to review recent studies which use BOLD and ASL to evaluate CVR, in healthy individuals and in patients with carotid steno-occlusive disease, providing a source of information regarding the obtained results and the methodological difficulties.
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387
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Marsden KR, Haykowsky MJ, Smirl JD, Jones H, Nelson MD, Altamirano-Diaz LA, Gelinas JC, Tzeng YC, Smith KJ, Willie CK, Bailey DM, Ainslie PN. Aging blunts hyperventilation-induced hypocapnia and reduction in cerebral blood flow velocity during maximal exercise. AGE (DORDRECHT, NETHERLANDS) 2012; 34:725-35. [PMID: 21559869 PMCID: PMC3337932 DOI: 10.1007/s11357-011-9258-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2010] [Accepted: 04/26/2011] [Indexed: 05/22/2023]
Abstract
Cerebral blood flow (CBF) increases from rest to ∼60% of peak oxygen uptake (VO(2peak)) and thereafter decreases towards baseline due to hyperventilation-induced hypocapnia and subsequent cerebral vasoconstriction. It is unknown what happens to CBF in older adults (OA), who experience a decline in CBF at rest coupled with a blunted ventilatory response during VO(2peak). In 14 OA (71 ± 10 year) and 21 young controls (YA; 23 ± 4 years), we hypothesized that OA would experience less hyperventilation-induced cerebral vasoconstriction and therefore an attenuated reduction in CBF at VO(2peak). Incremental exercise was performed on a cycle ergometer, whilst bilateral middle cerebral artery blood flow velocity (MCA V (mean); transcranial Doppler ultrasound), heart rate (HR; ECG) and end-tidal PCO(2) (P(ET)CO(2)) were monitored continuously. Blood pressure (BP) was monitored intermittently. From rest to 50% of VO(2peak), despite greater elevations in BP in OA, the change in MCA V(mean) was greater in YA compared to OA (28% vs. 15%, respectively; P < 0.0005). In the YA, at intensities >70% of VO(2peak), the hyperventilation-induced declines in both P(ET)CO(2) (14 mmHg (YA) vs. 4 mmHg (OA); P < 0.05) and MCA V(mean) (-21% (YA) vs. -7% (OA); P < 0.0005) were greater in YA compared to OA. Our findings show (1), from rest-to-mild intensity exercise (50% VO(2peak)), elevations in CBF are reduced in OA and (2) age-related declines in hyperventilation during maximal exercise result in less hypocapnic-induced cerebral vasoconstriction.
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Affiliation(s)
- K. R. Marsden
- Department of Human Kinetics, University of British Columbia Okanagan, Kelowna, BC Canada V1V 2Y5
| | - M. J. Haykowsky
- Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, AB Canada T6G 2G4
| | - J. D. Smirl
- Department of Human Kinetics, University of British Columbia Okanagan, Kelowna, BC Canada V1V 2Y5
| | - H. Jones
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, L3 3AF UK
| | - M. D. Nelson
- Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, AB Canada T6G 2G4
| | | | - J. C. Gelinas
- Department of Human Kinetics, University of British Columbia Okanagan, Kelowna, BC Canada V1V 2Y5
| | - Y. C. Tzeng
- Cardiovascular Systems Laboratory, Department of Surgery & Anesthesia, University of Otago, Wellington, New Zealand
| | - K. J. Smith
- Department of Human Kinetics, University of British Columbia Okanagan, Kelowna, BC Canada V1V 2Y5
| | - C. K. Willie
- Department of Human Kinetics, University of British Columbia Okanagan, Kelowna, BC Canada V1V 2Y5
| | - D. M. Bailey
- Neurovascular Research Laboratory, Faculty of Health, Science and Sport, University of Glamorgan, Wales, UK
| | - P. N. Ainslie
- Department of Human Kinetics, University of British Columbia Okanagan, Kelowna, BC Canada V1V 2Y5
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388
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Salinet AS, Robinson TG, Panerai RB. Reproducibility of cerebral and peripheral haemodynamic responses to active, passive and motor imagery paradigms in older healthy volunteers: A fTCD study. J Neurosci Methods 2012; 206:143-50. [DOI: 10.1016/j.jneumeth.2012.02.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Accepted: 02/10/2012] [Indexed: 11/29/2022]
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389
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Willie CK, Macleod DB, Shaw AD, Smith KJ, Tzeng YC, Eves ND, Ikeda K, Graham J, Lewis NC, Day TA, Ainslie PN. Regional brain blood flow in man during acute changes in arterial blood gases. J Physiol 2012; 590:3261-75. [PMID: 22495584 DOI: 10.1113/jphysiol.2012.228551] [Citation(s) in RCA: 362] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Despite the importance of blood flow on brainstem control of respiratory and autonomic function, little is known about regional cerebral blood flow (CBF) during changes in arterial blood gases.We quantified: (1) anterior and posterior CBF and reactivity through a wide range of steady-state changes in the partial pressures of CO2 (PaCO2) and O2 (PaO2) in arterial blood, and (2) determined if the internal carotid artery (ICA) and vertebral artery (VA) change diameter through the same range.We used near-concurrent vascular ultrasound measures of flow through the ICA and VA, and blood velocity in their downstream arteries (the middle (MCA) and posterior (PCA) cerebral arteries). Part A (n =16) examined iso-oxic changes in PaCO2, consisting of three hypocapnic stages (PaCO2 =∼15, ∼20 and ∼30 mmHg) and four hypercapnic stages (PaCO2 =∼50, ∼55, ∼60 and ∼65 mmHg). In Part B (n =10), during isocapnia, PaO2 was decreased to ∼60, ∼44, and ∼35 mmHg and increased to ∼320 mmHg and ∼430 mmHg. Stages lasted ∼15 min. Intra-arterial pressure was measured continuously; arterial blood gases were sampled at the end of each stage. There were three principal findings. (1) Regional reactivity: the VA reactivity to hypocapnia was larger than the ICA, MCA and PCA; hypercapnic reactivity was similar.With profound hypoxia (35 mmHg) the relative increase in VA flow was 50% greater than the other vessels. (2) Neck vessel diameters: changes in diameter (∼25%) of the ICA was positively related to changes in PaCO2 (R2, 0.63±0.26; P<0.05); VA diameter was unaltered in response to changed PaCO2 but yielded a diameter increase of +9% with severe hypoxia. (3) Intra- vs. extra-cerebral measures: MCA and PCA blood velocities yielded smaller reactivities and estimates of flow than VA and ICA flow. The findings respectively indicate: (1) disparate blood flow regulation to the brainstem and cortex; (2) cerebrovascular resistance is not solely modulated at the level of the arteriolar pial vessels; and (3) transcranial Doppler ultrasound may underestimate measurements of CBF during extreme hypoxia and/or hypercapnia.
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Affiliation(s)
- C K Willie
- School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Canada, 3333 University Way, Kelowna, BC Canada V1V 1V7.
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390
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Katsogridakis E, Bush G, Fan L, Birch AA, Simpson DM, Allen R, Potter JF, Panerai RB. Random perturbations of arterial blood pressure for the assessment of dynamic cerebral autoregulation. Physiol Meas 2012; 33:103-16. [PMID: 22227772 DOI: 10.1088/0967-3334/33/2/103] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The assessment of cerebral autoregulation (CA) relies mostly on methods that modulate arterial blood pressure (ABP). Despite advances, the gold standard of assessment remains elusive and clinical practicality is limited. We investigate a novel approach of assessing CA, consisting of the intermittent application of thigh cuffs using square wave sequences. Our aim was to increase ABP variability whilst minimizing volunteer discomfort, thus improving assessment acceptability. Two random square wave sequences and two maximum pressure settings (80 and 150 mmHg) were used, corresponding to four manoeuvres that were conducted in random order after a baseline recording. The intermittent application of thigh cuffs resulted in an amplitude dependent increase in ABP (p = 0.001) and cerebral blood flow velocity (CBFV) variability (p = 0.026) compared to baseline. No statistically significant differences in mean heart rate or heart rate variability were observed (p = 0.108 and p = 0.350, respectively), suggesting that no significant sympathetic response was elicited. No significant differences in the CBFV step response were observed, suggesting no distortion of autoregulatory parameters resulted from the use of thigh cuffs. We conclude that pseudorandom binary sequences are an effective and safe alternative for increasing ABP variability. This new approach shows great promise as a tool for the robust assessment of CA.
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391
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Lucas SJE, Ainslie PN, Murrell CJ, Thomas KN, Franz EA, Cotter JD. Effect of age on exercise-induced alterations in cognitive executive function: relationship to cerebral perfusion. Exp Gerontol 2012; 47:541-51. [PMID: 22230488 DOI: 10.1016/j.exger.2011.12.002] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Revised: 12/06/2011] [Accepted: 12/12/2011] [Indexed: 11/29/2022]
Abstract
Regular exercise improves the age-related decline in cerebral blood flow (CBF) and is associated with improved cognitive function; however, less is known about the direct relationship between CBF and cognitive function. We examined the influence of healthy aging on the capability of acute exercise to improve cognition, and whether exercise-induced improvements in cognition are related to CBF and cortical hemodynamics. Middle cerebral artery blood flow velocity (MCAv; Doppler) and cortical hemodynamics (NIRS) were measured in 13 young (24±5 y) and 9 older (62±3 y) participants at rest and during cycling at 30% and 70% of heart rate range (HRR). Cognitive performance was assessed using a computer-adapted Stroop task (i.e., test of executive function cognition) at rest and during exercise. Average response times on the Stroop task were slower for the older compared to younger group for both simple and difficult tasks (P<0.01). Independent of age, difficult-task response times improved during exercise (P<0.01), with the improvement greater at 70% HRR exercise (P=0.04 vs. 30% HRR). Higher MCAv was correlated with faster response times for simple and difficult tasks at rest (R(2)=0.47 and R(2)=0.47, respectively), but this relation uncoupled progressively during exercise. Exercise-induced increases in MCAv were similar and unaltered during cognitive tasks for both age groups. In contrast, prefrontal cortical hemodynamic NIRS measures [oxyhemoglobin (O(2)Hb) and total hemoglobin (tHb)] were differentially affected by exercise intensity, age and cognitive task; e.g., there were smaller increases in [O(2)Hb] and [tHb] in the older group between exercise intensities (P<0.05). These data indicate that: 1) Regardless of age, cognitive (executive) function is improved while exercising; 2) while MCAv is strongly related to cognition at rest, this relation becomes uncoupled during exercise, and 3) there is dissociation between global CBF and regional cortical oxygenation and NIRS blood volume markers during exercise and engagement of prefrontal cognition.
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Affiliation(s)
- Samuel J E Lucas
- Department of Physiology, University of Otago, Dunedin, New Zealand.
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392
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Ross EZ, Cotter JD, Wilson L, Fan JL, Lucas SJE, Ainslie PN. Cerebrovascular and corticomotor function during progressive passive hyperthermia in humans. J Appl Physiol (1985) 2011; 112:748-58. [PMID: 22134692 DOI: 10.1152/japplphysiol.00988.2011] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present study examined the integrative effects of passive heating on cerebral perfusion and alterations in central motor drive. Eight participants underwent passive hyperthermia [0.5°C increments in core temperature (Tc) from normothermia (37 ± 0.3°C) to their limit of thermal tolerance (T-LIM; 39.0 ± 0.4°C)]. Blood flow velocity in the middle cerebral artery (CBFv) and respiratory responses were measured continuously. Arterial blood gases and blood pressure were obtained intermittently. At baseline and each Tc level, supramaximal femoral nerve stimulation and transcranial magnetic stimulation (TMS) were performed to assess neuromuscular and cortical function, respectively. At T-LIM, measures were (in a randomized order) also made during a period of breathing 5% CO(2) gas to restore eucapnia (+5% CO(2)). Mean heating time was 179 ± 51 min, with each 0.5°C increment in Tc taking 40 ± 10 min. CBFv was reduced by ∼20% below baseline from +0.5°C until T-LIM. Maximal voluntary contraction (MVC) of the knee extensors was decreased at T-LIM (-9 ± 10%; P < 0.05), and cortical voluntary activation (VA), assessed by TMS, was decreased at +1.5°C and T-LIM by 11 ± 8 and 22 ± 23%, respectively (P < 0.05). Corticospinal excitability (measured as the EMG response produced by TMS) was unaltered. Reductions in cortical VA were related to changes in ventilation (Ve; R(2) = 0.76; P < 0.05) and partial pressure of end-tidal CO(2) (Pet(CO(2)); R(2) = 0.63; P < 0.05) and to changes in CBFv (R(2) = 0.61; P = 0.067). Interestingly, although CBFv was not fully restored, MVC and cortical VA were restored towards baseline values during inhalation of 5% CO(2). These results indicate that descending voluntary drive becomes progressively impaired as Tc is increased, presumably due, in part, to reductions in CBFv and to hyperthermia-induced hyperventilation and subsequent hypocapnia.
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Affiliation(s)
- Emma Z Ross
- Univ. of Brighton, Chelsea School, Denton Road, Eastbourne BN20 7SR, UK.
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393
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Cochand NJ, Wild M, Brugniaux JV, Davies PJ, Evans KA, Wise RG, Bailey DM. Sea-Level Assessment of Dynamic Cerebral Autoregulation Predicts Susceptibility to Acute Mountain Sickness at High Altitude. Stroke 2011; 42:3628-30. [DOI: 10.1161/strokeaha.111.621714] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Nicholas J. Cochand
- From the School of Medicine (N.J.C.), Cardiff University, Cardiff, UK; the School of Medicine (M.W., P.J.D.), University of Wales, Swansea, UK; the Neurovascular Research Laboratory (J.V.B., K.A.E., D.M.B.), Faculty of Health, Science and Sport, University of Glamorgan, Pontypridd, UK; and the Cardiff University Brain Research Imaging Centre (R.G.W.), School of Psychology, Cardiff University, Cardiff, UK
| | - Michael Wild
- From the School of Medicine (N.J.C.), Cardiff University, Cardiff, UK; the School of Medicine (M.W., P.J.D.), University of Wales, Swansea, UK; the Neurovascular Research Laboratory (J.V.B., K.A.E., D.M.B.), Faculty of Health, Science and Sport, University of Glamorgan, Pontypridd, UK; and the Cardiff University Brain Research Imaging Centre (R.G.W.), School of Psychology, Cardiff University, Cardiff, UK
| | - Julien V. Brugniaux
- From the School of Medicine (N.J.C.), Cardiff University, Cardiff, UK; the School of Medicine (M.W., P.J.D.), University of Wales, Swansea, UK; the Neurovascular Research Laboratory (J.V.B., K.A.E., D.M.B.), Faculty of Health, Science and Sport, University of Glamorgan, Pontypridd, UK; and the Cardiff University Brain Research Imaging Centre (R.G.W.), School of Psychology, Cardiff University, Cardiff, UK
| | - Peter J. Davies
- From the School of Medicine (N.J.C.), Cardiff University, Cardiff, UK; the School of Medicine (M.W., P.J.D.), University of Wales, Swansea, UK; the Neurovascular Research Laboratory (J.V.B., K.A.E., D.M.B.), Faculty of Health, Science and Sport, University of Glamorgan, Pontypridd, UK; and the Cardiff University Brain Research Imaging Centre (R.G.W.), School of Psychology, Cardiff University, Cardiff, UK
| | - Kevin A. Evans
- From the School of Medicine (N.J.C.), Cardiff University, Cardiff, UK; the School of Medicine (M.W., P.J.D.), University of Wales, Swansea, UK; the Neurovascular Research Laboratory (J.V.B., K.A.E., D.M.B.), Faculty of Health, Science and Sport, University of Glamorgan, Pontypridd, UK; and the Cardiff University Brain Research Imaging Centre (R.G.W.), School of Psychology, Cardiff University, Cardiff, UK
| | - Richard G. Wise
- From the School of Medicine (N.J.C.), Cardiff University, Cardiff, UK; the School of Medicine (M.W., P.J.D.), University of Wales, Swansea, UK; the Neurovascular Research Laboratory (J.V.B., K.A.E., D.M.B.), Faculty of Health, Science and Sport, University of Glamorgan, Pontypridd, UK; and the Cardiff University Brain Research Imaging Centre (R.G.W.), School of Psychology, Cardiff University, Cardiff, UK
| | - Damian M. Bailey
- From the School of Medicine (N.J.C.), Cardiff University, Cardiff, UK; the School of Medicine (M.W., P.J.D.), University of Wales, Swansea, UK; the Neurovascular Research Laboratory (J.V.B., K.A.E., D.M.B.), Faculty of Health, Science and Sport, University of Glamorgan, Pontypridd, UK; and the Cardiff University Brain Research Imaging Centre (R.G.W.), School of Psychology, Cardiff University, Cardiff, UK
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394
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Rickards CA, Ryan KL, Cooke WH, Convertino VA. Tolerance to central hypovolemia: the influence of oscillations in arterial pressure and cerebral blood velocity. J Appl Physiol (1985) 2011; 111:1048-58. [DOI: 10.1152/japplphysiol.00231.2011] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Higher oscillations of cerebral blood velocity and arterial pressure (AP) induced by breathing with inspiratory resistance are associated with delayed onset of symptoms and increased tolerance to central hypovolemia. We tested the hypothesis that subjects with high tolerance (HT) to central hypovolemia would display higher endogenous oscillations of cerebral blood velocity and AP at presyncope compared with subjects with low tolerance (LT). One-hundred thirty-five subjects were exposed to progressive lower body negative pressure (LBNP) until the presence of presyncopal symptoms. Subjects were classified as HT if they completed at least the −60-mmHg level of LBNP (93 subjects; LBNP time, 1,880 ± 259 s) and LT if they did not complete this level (42 subjects; LBNP time, 1,277 ± 199 s). Middle cerebral artery velocity (MCAv) was measured by transcranial Doppler, and AP was measured at the finger by photoplethysmography. Mean MCAv and mean arterial pressure (MAP) decreased progressively from baseline to presyncope for both LT and HT subjects ( P < 0.001). However, low frequency (0.04–0.15 Hz) oscillations of mean MCAv and MAP were higher at presyncope in HT subjects compared with LT subjects (MCAv: HT, 7.2 ± 0.7 vs. LT, 5.3 ± 0.6 (cm/s)2, P = 0.075; MAP: HT, 15.3 ± 1.4 vs. 7.9 ± 1.2 mmHg2, P < 0.001). Consistent with our previous findings using inspiratory resistance, high oscillations of mean MCAv and MAP are associated with HT to central hypovolemia.
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Affiliation(s)
- Caroline A. Rickards
- Department of Health and Kinesiology, University of Texas at San Antonio, San Antonio; and
| | - Kathy L. Ryan
- US Army Institute of Surgical Research, Fort Sam Houston, Texas
| | - William H. Cooke
- Department of Health and Kinesiology, University of Texas at San Antonio, San Antonio; and
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395
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Bailey DM, Evans KA, McEneny J, Young IS, Hullin DA, James PE, Ogoh S, Ainslie PN, Lucchesi C, Rockenbauer A, Culcasi M, Pietri S. Exercise-induced oxidative-nitrosative stress is associated with impaired dynamic cerebral autoregulation and blood-brain barrier leakage. Exp Physiol 2011; 96:1196-207. [DOI: 10.1113/expphysiol.2011.060178] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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396
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Nelson MD, Haykowsky MJ, Stickland MK, Altamirano-Diaz LA, Willie CK, Smith KJ, Petersen SR, Ainslie PN. Reductions in cerebral blood flow during passive heat stress in humans: partitioning the mechanisms. J Physiol 2011; 589:4053-64. [PMID: 21690194 DOI: 10.1113/jphysiol.2011.212118] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Cerebral blood flow (CBF) is reduced during passive heat stress, with 50% of this reduction associated with hyperventilatory-induced hypocapnia and subsequent cerebral vasoconstriction. It remains unknown, however, what other factors may contribute to the remaining 50%. We tested the hypothesis that the distribution of cardiac output plays an important role in maintaining cerebral perfusion during mild and severe heat stress. Middle cerebral artery and posterior cerebral artery blood flow velocity (MCAv and PCAv; transcranial Doppler) and left ventricular end-diastolic and end-systolic volumes (2-D echocardiography) were measured under conditions of normothermia and mild and severe passive heat stress (core temperature +0.8 ± 0.1°C (Protocol I; n = 10) and 1.8 ± 0.1°C (Protocol II; n = 8) above baseline). Venous return was manipulated by passive tilt table positioning (30 deg head-down tilt (HDT) and 30 deg head-up tilt (HUT)). Measurements were made under poikilocapnic and isocapnic conditions. Protocol I consisted of mild heat stress which resulted in small reductions in end-tidal CO2 (−5.6 ± 3.5%), MCAv/PCAv (−7.3 ± 2.3% and −10.3 ± 2.9%, respectively) and stroke volume (−8.5 ± 4.2%); while end-diastolic volume was significantly reduced (−16.9 ± 4.0%) and cardiac output augmented (17.2 ± 7.4%). During mild heat stress, CBF was related to left ventricular end-diastolic volume (MCAv, r2 = 0.81; PCAv, r2 = 0.83; P < 0.05) and stroke volume (MCAv, r2 = 0.38; PCAv, r2 = 0.43), but not with cardiac output. Protocol II consisted of severe heat stress which resulted in much greater reductions in end-tidal CO2 (−87.5 ± 31.5%) and CBF (MCAv, −36.4 ± 6.1%; PCAv, −30.1 ± 4.8%; P < 0.01 for all variables), while end-diastolic volume and stroke volume decreased to a similar extent as for mild heat stress. Importantly, isocapnia restored MCAv and PCAv back to normothermic baseline. This investigation therefore produced two novel findings: first, that venous return and stroke volume are related to CBF during mild heat stress; and second, that hyperventilatory hypocapnia has a major influence on CBF during severe passive heat stress.
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Affiliation(s)
- Michael D Nelson
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada.
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397
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Willie CK, Cowan EC, Ainslie PN, Taylor CE, Smith KJ, Sin PYW, Tzeng YC. Neurovascular coupling and distribution of cerebral blood flow during exercise. J Neurosci Methods 2011; 198:270-3. [PMID: 21459113 DOI: 10.1016/j.jneumeth.2011.03.017] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Revised: 03/20/2011] [Accepted: 03/23/2011] [Indexed: 10/18/2022]
Abstract
We examined how cerebral blood flow velocity (CBV) and neurovascular coupling is influenced by exercise. Blood velocities in the posterior and middle cerebral arteries (PCAv and MCAv) during rest and cycling exercise at 60% estimated maximal oxygen consumption were measured. Neurovascular coupling was quantified as the ΔPCAv with visual stimulation. During exercise, despite a 15.2±13.6% and 26.1±22.5% increase from rest in the MCAv and PCAv, respectively, neurovascular coupling was unaltered. Thus, despite regionally heterogeneous elevations in CBV during exercise, neurometabolic coupling is maintained.
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Affiliation(s)
- C K Willie
- Department of Human Kinetics, Faculty of Health and Social Development, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC V1V1V7, Canada.
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