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Stok WJ, Karemaker JM, Berecki‐Gisolf J, Immink RV, van Lieshout JJ. Slow sinusoidal tilt movements demonstrate the contribution to orthostatic tolerance of cerebrospinal fluid movement to and from the spinal dural space. Physiol Rep 2019; 7:e14001. [PMID: 30810293 PMCID: PMC6391715 DOI: 10.14814/phy2.14001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 01/11/2019] [Indexed: 11/24/2022] Open
Abstract
Standing up elicits a host of cardiovascular changes which all affect the cerebral circulation. Lowered mean arterial blood pressure (ABP) at brain level, change in the cerebral venous outflow path, lowered end-tidal PCO2 (PET CO2 ), and intracranial pressure (ICP) modify cerebral blood flow (CBF). The question we undertook to answer is whether gravity-induced blood pressure (BP) changes are compensated in CBF with the same dynamics as are spontaneous or induced ABP changes in a stable position. Twenty-two healthy subjects (18/4 m/f, 40 ± 8 years) were subjected to 30° and 70° head-up tilt (HUT) and sinusoidal tilts (SinTilt, 0°↨60° around 30° at 2.5-10 tilts/min). Additionally, at those three tilt levels, they performed paced breathing at 6-15 breaths/min to induce larger than spontaneous cardiovascular oscillations. We measured continuous finger BP and cerebral blood flow velocity (CBFv) in the middle cerebral artery by transcranial Doppler to compute transfer functions (TFs) from ABP- to CBFv oscillations. SinTilt induces the largest ABP oscillations at brain level with CBFv gains strikingly lower than for paced breathing or spontaneous variations. This would imply better autoregulation for dynamic gravitational changes. We demonstrate in a mathematical model that this difference is explained by ICP changes due to movement of cerebrospinal fluid (CSF) into and out of the spinal dural sack. Dynamic cerebrovascular autoregulation seems insensitive to how BP oscillations originate if the effect of ICP is factored in. CSF-movement in-and-out of the spinal dural space contributes importantly to orthostatic tolerance by its effect on cerebral perfusion pressure.
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Affiliation(s)
- Wim J. Stok
- Department of Medical BiologySection Systems PhysiologyAmsterdam UMCLocation AMCUniversity of AmsterdamAmsterdamThe Netherlands
- Department of Medical BiologyLaboratory for Clinical Cardiovascular PhysiologyAmsterdam UMCLocation AMCUniversity of AmsterdamAmsterdamThe Netherlands
| | - John M. Karemaker
- Department of Medical BiologySection Systems PhysiologyAmsterdam UMCLocation AMCUniversity of AmsterdamAmsterdamThe Netherlands
| | - Janneke Berecki‐Gisolf
- Department of Medical BiologySection Systems PhysiologyAmsterdam UMCLocation AMCUniversity of AmsterdamAmsterdamThe Netherlands
- Present address:
Monash University Accident Research Centre (Vic Injury Surveillance Unit)Monash University Clayton CampusClaytonVictoriaAustralia
| | - Rogier V. Immink
- Department of AnesthesiologyAmsterdam UMCLocation AMCUniversity of AmsterdamAmsterdamThe Netherlands
| | - Johannes J. van Lieshout
- Department of Medical BiologyLaboratory for Clinical Cardiovascular PhysiologyAmsterdam UMCLocation AMCUniversity of AmsterdamAmsterdamThe Netherlands
- Department of Internal MedicineAmsterdam UMCLocation AMCUniversity of AmsterdamAmsterdamThe Netherlands
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53
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Slupe AM, Kirsch JR. Effects of anesthesia on cerebral blood flow, metabolism, and neuroprotection. J Cereb Blood Flow Metab 2018; 38:2192-2208. [PMID: 30009645 PMCID: PMC6282215 DOI: 10.1177/0271678x18789273] [Citation(s) in RCA: 160] [Impact Index Per Article: 26.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2018] [Revised: 06/11/2018] [Accepted: 06/25/2018] [Indexed: 12/12/2022]
Abstract
Administration of anesthetic agents fundamentally shifts the responsibility for maintenance of homeostasis from the patient and their intrinsic physiological regulatory mechanisms to the anesthesiologist. Continuous delivery of oxygen and nutrients to the brain is necessary to prevent irreversible injury and arises from a complex series of regulatory mechanisms that ensure uninterrupted cerebral blood flow. Our understanding of these regulatory mechanisms and the effects of anesthetics on them has been driven by the tireless work of pioneers in the field. It is of paramount importance that the anesthesiologist shares this understanding. Herein, we will review the physiological determinants of cerebral blood flow and how delivery of anesthesia impacts these processes.
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Affiliation(s)
- Andrew M Slupe
- Department of Anesthesiology and Perioperative Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Jeffrey R Kirsch
- Department of Anesthesiology and Perioperative Medicine, Oregon Health and Science University, Portland, OR, USA
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54
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Chen H, Zhou J, Lin YQ, Zhou JX, Yu RG. Intracranial pressure responsiveness to positive end-expiratory pressure in different respiratory mechanics: a preliminary experimental study in pigs. BMC Neurol 2018; 18:183. [PMID: 30396336 PMCID: PMC6217765 DOI: 10.1186/s12883-018-1191-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2017] [Accepted: 10/28/2018] [Indexed: 12/13/2022] Open
Abstract
Background Respiratory mechanics affects the effect of positive end-expiratory pressure (PEEP) on intracranial pressure (ICP). Respiratory mechanics of the lung and the chest wall was not differentiated in previous studies. In the present study, we investigated the influence of the following possible determinants of ICP responsiveness to PEEP: chest wall elastance (ECW), lung elastance (EL), and baseline ICP. Methods Eight healthy Bama miniature pigs were studied. The increase of EL was induced by instillation of hydrochloride, and the increase of ECW was induced by strapping the animals’ chest wall and abdomen. A balloon-tipped catheter was placed intracranially for inducing intracranial hypertension. Six experimental conditions were investigated in sequence: 1) Normal; 2) Stiff Chest Wall; 3) Lung Injury; 4) Lung Injury + Stiff Chest Wall; 5) Lung Injury + Stiff Chest Wall + Intracranial Hypertension and 6) Lung Injury + Intracranial Hypertension. PEEP was gradually increased in a 5 cm H2O interval from 5 to 25 cm H2O in each condition. Blood pressure, central venous pressure, ICP, airway pressure and esophageal pressure were measured. Results Hydrochloride instillation significantly increased EL in conditions with lung injury. ECW significantly increased in the conditions with chest wall and abdomen strapping (all p < 0.05). ICP significantly increased with increments of PEEP in all non-intracranial hypertension conditions (p < 0.001). The greatest cumulative increase in ICP was observed in the Stiff Chest Wall condition (6 [5.3, 6.8] mm Hg), while the lowest cumulative increase in ICP was observed in the Lung Injury condition (2 [1.3, 3.8] mm Hg). ICP significantly decreased when PEEP was increased in the intracranial hypertension conditions (p < 0.001). There was no significant difference in cumulative ICP change between the two intracranial hypertension conditions (p = 0.924). Conclusions Different respiratory mechanics models can be established via hydrochloride induced lung injury and chest wall and abdominal strapping. The effect of PEEP on ICP is determined by respiratory mechanics in pigs with normal ICP. However, the responsiveness of ICP to PEEP is independent of respiratory mechanics when there is intracranial hypertension.
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Affiliation(s)
- Han Chen
- Surgical Intensive Care Unit, Fujian Provincial Clinical College, Fujian Medical University, No 134, Dongjie Street, Gulou District, Fuzhou, 350001, Fujian, China.
| | - Jing Zhou
- Surgical Intensive Care Unit, Fujian Provincial Clinical College, Fujian Medical University, No 134, Dongjie Street, Gulou District, Fuzhou, 350001, Fujian, China
| | - Yi-Qin Lin
- Surgical Intensive Care Unit, Fujian Provincial Clinical College, Fujian Medical University, No 134, Dongjie Street, Gulou District, Fuzhou, 350001, Fujian, China
| | - Jian-Xin Zhou
- Department of Critical Care Medicine, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
| | - Rong-Guo Yu
- Surgical Intensive Care Unit, Fujian Provincial Clinical College, Fujian Medical University, No 134, Dongjie Street, Gulou District, Fuzhou, 350001, Fujian, China
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55
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Panerai RB, Barnes SC, Nath M, Ball N, Robinson TG, Haunton VJ. Directional sensitivity of dynamic cerebral autoregulation in squat-stand maneuvers. Am J Physiol Regul Integr Comp Physiol 2018; 315:R730-R740. [DOI: 10.1152/ajpregu.00010.2018] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Dynamic cerebral autoregulation (CA), the transient response of cerebral blood flow (CBF) to rapid changes in arterial blood pressure (BP), is usually modeled as a linear mechanism. We tested the hypothesis that dynamic CA can display nonlinear behavior resulting from differential efficiency dependent on the direction of BP changes. Cerebral blood velocity (CBV) (transcranial Doppler), heart rate (HR) (three-lead ECG), continuous BP (Finometer), and end-tidal CO2 (capnograph) were measured in 10 healthy young subjects during 15 squat-stand maneuvers (SSM) with a frequency of 0.05 Hz. The protocol was repeated with a median (interquartile range) of 44 (35–64) days apart. Dynamic CA was assessed with the autoregulation index (ARI) obtained from CBV step responses estimated with an autoregressive moving-average model. Mean BP, HR, and CBV were different (all P < 0.001) between squat and stand, regardless of visits. ARI showed a strong interaction ( P < 0.001) of SSM with the progression of transients; in general, the mean ARI was higher for the squat phase compared with standing. The changes in ARI were partially explained by concomitant changes in CBV ( P = 0.023) and pulse pressure ( P < 0.001), but there was no evidence that ARI differed between visits ( P = 0.277). These results demonstrate that dynamic CA is dependent on the direction of BP change, but further work is needed to confirm if this finding can be generalized to other physiological conditions and also to assess its dependency on age, sex and pathology.
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Affiliation(s)
- Ronney B. Panerai
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
- National Institute for Health Research, Leicester Biomedical Research Centre, University of Leicester, Leicester, United Kingdom
| | - Sam C. Barnes
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
| | - Mintu Nath
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
- National Institute for Health Research, Leicester Biomedical Research Centre, University of Leicester, Leicester, United Kingdom
| | - Naomi Ball
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
| | - Thompson G. Robinson
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
- National Institute for Health Research, Leicester Biomedical Research Centre, University of Leicester, Leicester, United Kingdom
| | - Victoria J. Haunton
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
- National Institute for Health Research, Leicester Biomedical Research Centre, University of Leicester, Leicester, United Kingdom
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Brindle RC, Ginty AT, Whittaker AC, Carroll D, Lucas SJE. Assessment of the cerebral pressure-flow relationship using psychological stress to manipulate blood pressure. Psychophysiology 2018; 55:e13265. [PMID: 30059151 DOI: 10.1111/psyp.13265] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 05/10/2018] [Accepted: 06/11/2018] [Indexed: 01/23/2023]
Abstract
Recent evidence indicates that cerebral autoregulation (CA) might be more pressure passive than previously thought. That is, cerebral blood flow, traditionally thought to be regulated independently of prevailing mean arterial pressure (MAP), might fluctuate, to some extent, as a function of MAP. However, due to limitations associated with experimental usage of pharmaceuticals to manipulate MAP and inconsistent control of arterial carbon dioxide, questions remain regarding the MAP-cerebral blood flow relationship, especially during typical daily activities that alter MAP. Therefore, the current study aimed to assess CA using a nonpharmacological acute psychological stress task to augment MAP, while at the same time controlling for end-tidal carbon dioxide (PET CO2 ). Twenty-five healthy young adults completed a stressful task while continuous measures of MAP, middle cerebral artery blood flow velocity (MCAv), and PET CO2 were recorded. Slope values obtained from hierarchical linear regression were used to assess the strength of the MAP-MCAv relationship and control for PET CO2 . The stress task significantly increased MAP (p < 0.001) and MCAv (p < 0.001), and decreased PET CO2 (p = 0.05). For every 10 mmHg task-induced increase in MAP, MCAv increased by ≈3.5%; task-induced changes in PET CO2 did not appreciably change the MAP-MCAv relationship. Greater task-induced MAP responses were significantly related to decreased MAP-MCAv slope values, consistent with CA. These data support the hypothesis that CA is more pressure passive than previously thought and provide initial evidence indicating that a pressure-passive MAP-MCAv relationship may play a role in the observed associations between MAP stress responses, stroke, and cerebrovascular disease.
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Affiliation(s)
- Ryan C Brindle
- Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Annie T Ginty
- Department of Psychology and Neuroscience, Baylor University, Waco, Texas
| | - Anna C Whittaker
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
| | - Douglas Carroll
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom.,Centre for Human Brain Health, University of Birmingham, Birmingham, United Kingdom
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57
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Olesen ND, Fischer M, Secher NH. Sodium nitroprusside dilates cerebral vessels and enhances internal carotid artery flow in young men. J Physiol 2018; 596:3967-3976. [PMID: 29917239 DOI: 10.1113/jp275887] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 06/12/2018] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Sodium nitroprusside lowers blood pressure by vasodilatation but is reported to reduce cerebral blood flow. In healthy young men sodium nitroprusside reduced blood pressure, total peripheral resistance, and arterial CO2 tension and yet cerebral blood flow was maintained, with an increase in internal carotid artery blood flow and cerebrovascular conductance. Sodium nitroprusside induces both systemic and cerebral vasodilatation affecting internal carotid artery more than vertebral artery flow. ABSTRACT Cerebral autoregulation maintains cerebral blood flow (CBF) despite marked changes in mean arterial pressure (MAP). Sodium nitroprusside (SNP) reduces blood pressure by vasodilatation but is reported to lower CBF, probably by a reduction in its perfusion pressure. We evaluated the influence of SNP on CBF and aimed for a 20% and then 40% reduction in MAP, while keeping MAP ≥ 50 mmHg, to challenge cerebral autoregulation. In 19 healthy men (age 24 ± 4 years; mean ± SD) duplex ultrasound determined right internal carotid (ICA) and vertebral artery (VA) blood flow. The SNP reduced MAP (from 83 ± 8 to 69 ± 8 and 58 ± 4 mmHg; both P < 0.0001), total peripheral resistance, and arterial CO2 tension (P aC O2; 41 ± 3 vs. 39 ± 3 and 37 ± 4 mmHg; both P < 0.01). Yet ICA flow increased with the moderate reduction in MAP but returned to the baseline value with the large reduction in MAP (336 ± 66 vs. 365 ± 69; P = 0.013 and 349 ± 82 ml min-1 ; n.s.), while VA flow (114 ± 34 vs. 112 ± 38 and 110 ± 42 ml min-1 ; both n.s.) and CBF ((ICA + VA flow) × 2; 899 ± 135 vs. 962 ± 127 and 918 ± 197 ml min-1 ; both n.s.) were maintained with increased cerebrovascular conductance. In conclusion, CBF is maintained during SNP-induced reduction in MAP despite reduced P aC O2 and the results indicate that SNP dilates cerebral vessels and increases ICA flow.
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Affiliation(s)
- Niels D Olesen
- Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark.,Department of Biomedical Sciences, University of Copenhagen, Denmark
| | - Mads Fischer
- Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark.,Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark
| | - Niels H Secher
- Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark
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58
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Labrecque L, Rahimaly K, Imhoff S, Paquette M, Le Blanc O, Malenfant S, Lucas SJE, Bailey DM, Smirl JD, Brassard P. Diminished dynamic cerebral autoregulatory capacity with forced oscillations in mean arterial pressure with elevated cardiorespiratory fitness. Physiol Rep 2018; 5:5/21/e13486. [PMID: 29122957 PMCID: PMC5688778 DOI: 10.14814/phy2.13486] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Accepted: 10/07/2017] [Indexed: 12/12/2022] Open
Abstract
The effect that cardiorespiratory fitness has on the dynamic cerebral autoregulatory capacity during changes in mean arterial pressure (MAP) remains equivocal. Using a multiple‐metrics approach, challenging MAP across the spectrum of physiological extremes (i.e., spontaneous through forced MAP oscillations), we characterized dynamic cerebral autoregulatory capacity in 19 male endurance athletes and eight controls via three methods: (1) onset of regulation (i.e., time delay before an increase in middle cerebral artery (MCA) conductance [MCA blood velocity (MCAv)/MAP] and rate of regulation, after transient hypotension induced by sit‐to‐stand, and transfer function analysis (TFA) of MAP and MCAv responses during (2) spontaneous and (3) forced oscillations (5‐min of squat‐stand maneuvers performed at 0.05 and 0.10 Hz). Reductions in MAP and mean MCAv (MCAVmean) during initial orthostatic stress (0‐30 sec after sit‐to‐stand) and the prevalence of orthostatic hypotension were also determined. Onset of regulation was delayed after sit‐to‐stand in athletes (3.1 ± 1.7 vs. 1.5 ± 1.0 sec; P = 0.03), but rate of regulation was not different between groups (0.24 ± 0.05 vs. 0.21 ± 0.09 sec−1; P = 0.82). While both groups had comparable TFA metrics during spontaneous oscillations, athletes had higher TFA gain during 0.10 Hz squat‐stand versus recreational controls (P = 0.01). Reductions in MAP (P = 0.15) and MCAVmean (P = 0.11) during orthostatic stress and the prevalence of initial orthostatic hypotension (P = 0.65) were comparable between groups. These results indicate an intact ability of the cerebral vasculature to react to spontaneous oscillations but an attenuated capability to counter rapid and large changes in MAP in individuals with elevated cardiorespiratory fitness.
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Affiliation(s)
- Lawrence Labrecque
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada.,Research center of the Institut universitaire de cardiologie et de pneumologie de Québec, Québec, Canada
| | - Kevan Rahimaly
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada.,Research center of the Institut universitaire de cardiologie et de pneumologie de Québec, Québec, Canada
| | - Sarah Imhoff
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada.,Research center of the Institut universitaire de cardiologie et de pneumologie de Québec, Québec, Canada
| | - Myriam Paquette
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada.,Research center of the Institut universitaire de cardiologie et de pneumologie de Québec, Québec, Canada
| | - Olivier Le Blanc
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada.,Research center of the Institut universitaire de cardiologie et de pneumologie de Québec, Québec, Canada
| | - Simon Malenfant
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada.,Research center of the Institut universitaire de cardiologie et de pneumologie de Québec, Québec, Canada
| | - Samuel J E Lucas
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom.,Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Damian M Bailey
- Neurovascular Research Laboratory Faculty of Life Sciences and Education University of South Wales, South Wales, United Kingdom.,Faculty of Medicine, Reichwald Health Sciences Centre University of British Columbia-Okanagan, Kelowna British Columbia, Canada
| | - Jonathan D Smirl
- Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Patrice Brassard
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada .,Research center of the Institut universitaire de cardiologie et de pneumologie de Québec, Québec, Canada
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59
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Stembridge M, Hoiland RL, Bain AR, Barak OF, Drvis I, MacLeod DB, MacLeod DM, Madden D, Batinic T, O'Donoghue P, Shave R, Dujic Z, Ainslie PN. Influence of lung volume on the interaction between cardiac output and cerebrovascular regulation during extreme apnoea. Exp Physiol 2018; 102:1288-1299. [PMID: 28762565 DOI: 10.1113/ep086429] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Accepted: 07/20/2017] [Indexed: 12/12/2022]
Abstract
NEW FINDINGS What is the central question of this study? Does the reduction in cardiac output observed during extreme voluntary apnoea, secondary to high lung volume, result in a reduction in cerebral blood flow, perfusion pressure and oxygen delivery in a group of elite free divers? What is the main finding and its importance? High lung volumes reduce cardiac output and ventricular filling during extreme apnoea, but changes in cerebral blood flow are observed only transiently during the early stages of apnoea. This reveals that whilst cardiac output is important in regulating cerebral haemodynamics, the role of mean arterial pressure in restoring cerebral perfusion pressure is of greater significance to the regulation of cerebral blood flow. We investigated the role of lung volume-induced changes in cardiac output (Q̇) on cerebrovascular regulation during prolonged apnoea. Fifteen elite apnoea divers (one female; 185 ± 7 cm, 82 ± 12 kg, 29 ± 7 years old) attended the laboratory on two separate occasions and completed maximal breath-holds at total lung capacity (TLC) and functional residual capacity (FRC) to elicit disparate cardiovascular responses. Mean arterial pressure (MAP), internal jugular venous pressure and arterial blood gases were measured via cannulation. Global cerebral blood flow was quantified by ultrasound and cardiac output was quantified by via photoplethysmography. At FRC, stroke volume and Q̇ did not change from baseline (P > 0.05). In contrast, during the TLC trial stroke volume and Q̇ were decreased until 80 and 40% of apnoea, respectively (P < 0.05). During the TLC trial, global cerebral blood flow was significantly lower at 20%, but subsequently increased so that cerebral oxygen delivery was comparable to that during the FRC trial. Internal jugular venous pressure was significantly higher throughout the TLC trial in comparison to FRC. The MAP increased progressively in both trials but to a greater extent at TLC, resulting in a comparable cerebral perfusion pressure between trials by the end of apnoea. In summary, although lung volume has a profound effect on Q̇ during prolonged breath-holding, these changes do not translate to the cerebrovasculature owing to the greater sensitivity of cerebral blood flow to arterial blood gases and MAP; regulatory mechanisms that facilitate the maintenance of cerebral oxygen delivery.
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Affiliation(s)
- Mike Stembridge
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cardiff, UK
| | - Ryan L Hoiland
- Centre for Heart Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada
| | - Anthony R Bain
- Centre for Heart Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada
| | - Otto F Barak
- School of Medicine, University of Split, Split, Croatia.,Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
| | - Ivan Drvis
- School of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - David B MacLeod
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | | | - Dennis Madden
- School of Medicine, University of Split, Split, Croatia
| | - Tonci Batinic
- School of Medicine, University of Split, Split, Croatia
| | - Peter O'Donoghue
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cardiff, UK
| | - Rob Shave
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cardiff, UK
| | - Zeljko Dujic
- School of Medicine, University of Split, Split, Croatia
| | - Philip N Ainslie
- Centre for Heart Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada
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60
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Payne SJ. Identifying the myogenic and metabolic components of cerebral autoregulation. Med Eng Phys 2018; 58:S1350-4533(18)30078-X. [PMID: 29773488 DOI: 10.1016/j.medengphy.2018.04.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Revised: 04/18/2018] [Accepted: 04/30/2018] [Indexed: 01/15/2023]
Abstract
Cerebral autoregulation is the term used to describe a number of mechanisms that act together to maintain a near constant cerebral blood flow in response to changes in arterial blood pressure. These mechanisms are complex and known to be affected in a range of cerebrovascular diseases. However, it can be difficult to assign an alteration in cerebral autoregulation to one of the underlying physiological mechanisms without the use of a complex mathematical model. In this paper, we thus set out a new approach that enables these mechanisms to be related to the autoregulation behaviour and hence inferred from experimental measurements. We show that the arteriolar response is a function of just three parameters, which we term the elastic, the myogenic and the metabolic sensitivity coefficients, and that the full vascular response is dependent upon only seven parameters. The ratio of the strengths of the myogenic and the metabolic responses is found to be in the range 2.5 to 5 over a wide range of pressure, indicating that the balance between the two appears to lie within this range. We validate the model with existing experimental data both at the level of an individual vessel and across the whole vasculature, and show that the results are consistent with findings from the literature. We then conduct a sensitivity analysis of the model to demonstrate which parameters are most important in determining the strength of static autoregulation, showing that autoregulation strength is predominantly set by the arteriolar sensitivity coefficients. This new approach could be used in future studies to help to interpret the components of the autoregulation response and how they are affected under different conditions, providing a greater insight into the fundamental processes that govern autoregulation.
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Affiliation(s)
- S J Payne
- Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
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61
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A comparison of static and dynamic cerebral autoregulation during mild whole-body cold stress in individuals with and without cervical spinal cord injury: a pilot study. Spinal Cord 2018; 56:469-477. [PMID: 29330514 DOI: 10.1038/s41393-017-0021-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Revised: 09/14/2017] [Accepted: 09/14/2017] [Indexed: 11/09/2022]
Abstract
STUDY DESIGN Experimental study. OBJECTIVES To characterize static and dynamic cerebral autoregulation (CA) of individuals with cervical spinal cord injury (SCI) compared to able-bodied controls in response to moderate increases in mean arterial pressure (MAP) caused by mild whole-body cold stress. SETTING Japan METHODS: Five men with complete autonomic cervical SCI (sustained > 5 y) and six age-matched able-bodied men participated in hemodynamic, temperature, catecholamine and respiratory measurements for 60 min during three consecutive stages: baseline (10 min; 33 °C water through a thin-tubed whole-body suit), mild cold stress (20 min; 25 °C water), and post-cold recovery (30 min; 33 °C water). Static CA was determined as the ratio between mean changes in middle cerebral artery blood velocity and MAP, dynamic CA as transfer function coherence, gain, and phase between spontaneous changes in MAP to middle cerebral artery blood velocity. RESULTS MAP increased in both groups during cold and post-cold recovery (mean differences: 5-10 mm Hg; main effect of time: p = 0.001). Static CA was not different between the able-bodied vs. the cervical SCI group (mean (95% confidence interval (CI)) of between-group difference: -4 (-11 to 3) and -2 (-5 to 1) cm/s/mm Hg for cold (p = 0.22) and post-cold (p = 0.24), respectively). At baseline, transfer function phase was shorter in the cervical SCI group (mean (95% CI) of between-group difference: 0.6 (0.2 to 1.0) rad; p = 0.006), while between-group differences in changes in phase were not different in response to the cold stress (interaction term: p = 0.06). CONCLUSIONS This pilot study suggests that static CA is similar between individuals with cervical SCI and able-bodied controls in response to moderate increases in MAP, while dynamic CA may be impaired in cervical SCI because of disturbed sympathetic control.
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62
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van der Velpen IF, Yancy CW, Sorond FA, Sabayan B. Impaired Cardiac Function and Cognitive Brain Aging. Can J Cardiol 2017; 33:1587-1596. [DOI: 10.1016/j.cjca.2017.07.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2017] [Revised: 07/16/2017] [Accepted: 07/16/2017] [Indexed: 12/25/2022] Open
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63
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Brassard P, Tymko MM, Ainslie PN. Sympathetic control of the brain circulation: Appreciating the complexities to better understand the controversy. Auton Neurosci 2017; 207:37-47. [DOI: 10.1016/j.autneu.2017.05.003] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Revised: 05/03/2017] [Accepted: 05/04/2017] [Indexed: 12/24/2022]
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Smith KJ, Ainslie PN. Regulation of cerebral blood flow and metabolism during exercise. Exp Physiol 2017; 102:1356-1371. [PMID: 28786150 DOI: 10.1113/ep086249] [Citation(s) in RCA: 191] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2017] [Accepted: 07/31/2017] [Indexed: 12/18/2022]
Abstract
NEW FINDINGS What is the topic of this review? The manuscript collectively combines the experimental observations from >100 publications focusing on the regulation of cerebral blood flow and metabolism during exercise from 1945 to the present day. What advances does it highlight? This article highlights the importance of traditional and historical assessments of cerebral blood flow and metabolism during exercise, as well as traditional and new insights into the complex factors involved in the integrative regulation of brain blood flow and metabolism during exercise. The overarching theme is the importance of quantifying cerebral blood flow and metabolism during exercise using techniques that consider multiple volumetric cerebral haemodynamics (i.e. velocity, diameter, shear and flow). Cerebral function in humans is crucially dependent upon continuous oxygen delivery, metabolic nutrients and active regulation of cerebral blood flow (CBF). As a consequence, cerebrovascular function is precisely titrated by multiple physiological mechanisms, characterized by complex integration, synergism and protective redundancy. At rest, adequate CBF is regulated through reflexive responses in the following order of regulatory importance: fluctuating arterial blood gases (in particularly, partial pressure of carbon dioxide), cerebral metabolism, arterial blood pressure, neurogenic activity and cardiac output. Unfortunately, the magnitude that these integrative and synergistic relationships contribute to governing the CBF during exercise remains unclear. Despite some evidence indicating that CBF regulation during exercise is dependent on the changes of blood pressure, neurogenic activity and cardiac output, their role as a primary governor of the CBF response to exercise remains controversial. In contrast, the balance between the partial pressure of carbon dioxide and cerebral metabolism continues to gain empirical support as the primary contributor to the intensity-dependent changes in CBF observed during submaximal, moderate and maximal exercise. The goal of this review is to summarize the fundamental physiology and mechanisms involved in regulation of CBF and metabolism during exercise. The clinical implications of a better understanding of CBF during exercise and new research directions are also outlined.
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Affiliation(s)
- Kurt J Smith
- Cardiovascular Research Group, School of Sports Science, Exercise and Health, University of Western Australia, Crawley, WA, Australia.,Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
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de Jong DLK, Tarumi T, Liu J, Zhang R, Claassen JAHR. Lack of linear correlation between dynamic and steady-state cerebral autoregulation. J Physiol 2017; 595:5623-5636. [PMID: 28597991 PMCID: PMC5556173 DOI: 10.1113/jp274304] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Accepted: 06/06/2017] [Indexed: 01/15/2023] Open
Abstract
Key points For correct application and interpretation of cerebral autoregulation (CA) measurements in research and in clinical care, it is essential to understand differences and similarities between dynamic and steady‐state CA. The present study found no correlation between dynamic and steady‐state CA indices in healthy older adults. There was variability between individuals in all (steady‐state and dynamic) autoregulatory indices, ranging from low (almost absent) to highly efficient CA in this healthy population. These findings challenge the assumption that assessment of a single CA parameter or a single set of parameters can be generalized to overall CA functioning. Therefore, depending on specific research purposes, the choice for either steady‐state or dynamic measures or both should be weighed carefully.
Abstract The present study aimed to investigate the relationship between dynamic (dCA) and steady‐state cerebral autoregulation (sCA). In 28 healthy older adults, sCA was quantified by a linear regression slope of proportionate (%) changes in cerebrovascular resistance (CVR) in response to proportionate (%) changes in mean blood pressure (BP) induced by stepwise sodium nitroprusside (SNP) and phenylephrine (PhE) infusion. Cerebral blood flow (CBF) was measured at the internal carotid artery (ICA) and vertebral artery (VA) and CBF velocity at the middle cerebral artery (MCA). With CVR = BP/CBF, Slope‐CVRICA, Slope‐CVRVA and Slope‐CVRiMCA were derived. dCA was assessed (i) in supine rest, analysed with transfer function analysis (gain and phase) and autoregulatory index (ARI) fit from spontaneous oscillations (ARIBaseline), and (ii) with transient changes in BP using a bolus injection of SNP (ARISNP) and PhE (ARIPhE). Comparison of sCA and dCA parameters (using Pearson's r for continuous and Spearman's ρ for ordinal parameters) demonstrated a lack of linear correlations between sCA and dCA measures. However, comparisons of parameters within dCA and within sCA were correlated. For sCA slope‐CVRVA with Slope‐CVRiMCA (r = 0.45, P < 0.03); for dCA ARISNP with ARIPhE (ρ = 0.50, P = 0.03), ARIBaseline (ρ = 0.57, P = 0.03) and PhaseLF (ρ = 0.48, P = 0.03); and for GainVLF with GainLF (r = 0.51, P = 0.01). By contrast to the commonly held assumption based on an earlier study, there were no linear correlations between sCA and dCA. As an additional observation, there was strong inter‐individual variability, both in dCA and sCA, in this healthy group of elderly, in a range from low to high CA efficiency. For correct application and interpretation of cerebral autoregulation (CA) measurements in research and in clinical care, it is essential to understand differences and similarities between dynamic and steady‐state CA. The present study found no correlation between dynamic and steady‐state CA indices in healthy older adults. There was variability between individuals in all (steady‐state and dynamic) autoregulatory indices, ranging from low (almost absent) to highly efficient CA in this healthy population. These findings challenge the assumption that assessment of a single CA parameter or a single set of parameters can be generalized to overall CA functioning. Therefore, depending on specific research purposes, the choice for either steady‐state or dynamic measures or both should be weighed carefully.
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Affiliation(s)
- Daan L K de Jong
- Donders Institute for Brain, Cognition and Behavior, Radboud Alzheimer Center, and Department of Geriatric Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Takashi Tarumi
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Texas, USA.,Department of Internal Medicine
| | - Jie Liu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Texas, USA.,Department of Internal Medicine
| | - Rong Zhang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Texas, USA.,Department of Internal Medicine.,Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Texas, USA
| | - Jurgen A H R Claassen
- Donders Institute for Brain, Cognition and Behavior, Radboud Alzheimer Center, and Department of Geriatric Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
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Güiza F, Meyfroidt G, Piper I, Citerio G, Chambers I, Enblad P, Nillson P, Feyen B, Jorens P, Maas A, Schuhmann MU, Donald R, Moss L, Van den Berghe G, Depreitere B. Cerebral Perfusion Pressure Insults and Associations with Outcome in Adult Traumatic Brain Injury. J Neurotrauma 2017; 34:2425-2431. [PMID: 28385097 PMCID: PMC5563857 DOI: 10.1089/neu.2016.4807] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The definition of cerebral perfusion pressure (CPP) secondary insults in severe traumatic brain injury remains unclear. The purpose of the present study is to visualize the association of intensity and duration of episodes below or above CPP thresholds and outcome. The analysis was based on prospectively collected minute-by-minute intracranial pressure (ICP) and blood pressure data and outcome from 259 adult patients. The relationship of episodes of CPP below or above a certain threshold for certain duration with the 6-month Glasgow Outcome Score was visualized separately for episodes of active or deficient autoregulation (AR). In adults ≤65 years, an almost exponential transition curve separates the episodes of CPP associated with better outcomes from the episodes of low CPP associated with worse outcomes, indicating that lower CPP could only be tolerated for a brief time. Analysis of episodes of high CPP again showed a time-intensity dependent association with outcome. When combining the two plots, a safe CPP zone between 60 and 70 mm Hg could be delineated-however, only for AR active insults. The AR status predominantly affected the transition curve for insults of low CPP. Episodes with ICP >25 mm Hg were associated with poor outcome regardless of CPP. In the present study, the CPP pressure-time burden associated with poor outcome was visualized. A safe zone between 60 and 70 mm Hg could be identified for adults ≤65 years, provided AR was active and ICP was ≤25 mm Hg. Deficient AR reduces the tolerability for low CPP.
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Affiliation(s)
- Fabian Güiza
- 1 Department of Intensive Care Medicine, University Hospitals Leuven , Leuven, Belgium
| | - Geert Meyfroidt
- 1 Department of Intensive Care Medicine, University Hospitals Leuven , Leuven, Belgium
| | - Ian Piper
- 2 Department of Clinical Physics, Southern General Hospital , Glasgow, United Kingdom
| | - Giuseppe Citerio
- 3 Department of Perioperative Medicine and Intensive Care Medicine, San Gerardo Hospital , Monza, Italy
| | - Iain Chambers
- 4 Medical Physics, James Cook University Hospital , Middlesborough, United Kingdom
| | - Per Enblad
- 5 Department of Neurosciences, Neurosurgery , Uppsala, Sweden
| | - Pelle Nillson
- 5 Department of Neurosciences, Neurosurgery , Uppsala, Sweden
| | - Bart Feyen
- 6 Department of Neurosurgery, Antwerp University Hospital , Edegem, Belgium
| | - Philippe Jorens
- 7 Department of Intensive Care Medicine, Antwerp University Hospital , Edegem, Belgium
| | - Andrew Maas
- 6 Department of Neurosurgery, Antwerp University Hospital , Edegem, Belgium
| | - Martin U Schuhmann
- 8 Klinik für Neurochirurgie, Universitätsklinikum Tübingen , Tübingen, Germany
| | - Rob Donald
- 9 School of Mathematics and Statistics, University of Glasgow , Glasgow, United Kingdom
| | - Laura Moss
- 10 Department of Clinical Physics and Bioengineering, NHS Greater Glasgow & Clyde , Glasgow, United Kingdom
| | - Greet Van den Berghe
- 1 Department of Intensive Care Medicine, University Hospitals Leuven , Leuven, Belgium
| | - Bart Depreitere
- 11 Department of Neurosurgery, University Hospitals Leuven , Leuven, Belgium
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Brassard P, Ferland-Dutil H, Smirl JD, Paquette M, Le Blanc O, Malenfant S, Ainslie PN. Evidence for hysteresis in the cerebral pressure-flow relationship in healthy men. Am J Physiol Heart Circ Physiol 2017; 312:H701-H704. [DOI: 10.1152/ajpheart.00790.2016] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 01/05/2017] [Accepted: 01/17/2017] [Indexed: 11/22/2022]
Abstract
The cerebrovasculature is more efficient at compensating for pharmacologically induced transient hypertension versus transient hypotension. Whether this phenomenon exists during nonpharmacologically induced hypertension and hypotension is currently unknown. We compared the percent change in mean velocity in the middle cerebral artery (MCAvmean) per percent change in mean arterial pressure (MAP) (%ΔMCAVmean/%ΔMAP) during transient hypertension and hypotension induced during squat-stand maneuvers performed at 0.05 Hz (20-s cycles) and 0.10 Hz (10-s cycles) in 58 male volunteers. %ΔMCAvmean/%ΔMAP was attenuated by 25% ( P = 0.03, 0.05 Hz) and 47% ( P < 0.0001, 0.10 Hz) during transient hypertension versus hypotension. Thus, these findings indicate that the brain in healthy men is better adapted to compensate for physiologically relevant transient hypertension than hypotension. NEW & NOTEWORTHY The novel finding of this study is that the change in middle cerebral artery mean flow velocity is attenuated during hypertension compared with hypotension physiologically induced by oscillations in blood pressure in men. These results support that the human brain is more effective at compensating for transient hypertension than hypotension.
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Affiliation(s)
- Patrice Brassard
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec City, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec City, Québec, Canada; and
| | - Hélène Ferland-Dutil
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec City, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec City, Québec, Canada; and
| | - Jonathan D. Smirl
- Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Myriam Paquette
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec City, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec City, Québec, Canada; and
| | - Olivier Le Blanc
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec City, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec City, Québec, Canada; and
| | - Simon Malenfant
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec City, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec City, Québec, Canada; and
| | - Philip N. Ainslie
- Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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68
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Ruesch A, Smith MA, Wollstein G, Sigal IA, Nelson S, Kainerstorfer JM. Correlation between Cerebral Hemodynamic and Perfusion Pressure Changes in Non-Human Primates. PROCEEDINGS OF SPIE--THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING 2017; 10059:100591P. [PMID: 29311754 PMCID: PMC5755600 DOI: 10.1117/12.2252550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The mechanism that maintains a stable blood flow in the brain despite changes in cerebral perfusion pressure (CPP), and therefore guaranties a constant supply of oxygen and nutrients to the neurons, is known as cerebral autoregulation (CA). In a certain range of CPP, blood flow is mediated by a vasomotor adjustment in vascular resistance through dilation of blood vessels. CA is known to be impaired in diseases like traumatic brain injury, Parkinson's disease, stroke, hydrocephalus and others. If CA is impaired, blood flow and pressure changes are coupled and the oxygen supply might be unstable. Lassen's blood flow autoregulation curve describes this mechanism, where a plateau of stable blood flow in a specific range of CPP corresponds to intact autoregulation. Knowing the limits of this plateau and maintaining CPP within these limits can improve patient outcome. Since CPP is influenced by both intracranial pressure and arterial blood pressure, long term changes in either can lead to autoregulation impairment. Non-invasive methods for monitoring blood flow autoregulation are therefore needed. We propose to use Near infrared spectroscopy (NIRS) to fill this need. NIRS is an optical technique, which measures microvascular changes in cerebral hemoglobin concentration. We pe erformed experiments on non-human primates during exsanguination to demonstrate that the limits of blood flow autoregulation can be accessed with NIRS.
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Affiliation(s)
- A Ruesch
- Department of Biomedical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213
| | - M A Smith
- Department of Ophthalmology, University of Pittsburgh, Eye and Ear Institute, 203 Lothrop Street, Pittsburgh, PA 15213
| | - G Wollstein
- NYU Langone Eye Center, New York University School of Medicine, 462 First Avenue, New York, NY 10016
| | - I A Sigal
- Department of Ophthalmology, University of Pittsburgh, Eye and Ear Institute, 203 Lothrop Street, Pittsburgh, PA 15213
| | - S Nelson
- Department of Ophthalmology, University of Pittsburgh, Eye and Ear Institute, 203 Lothrop Street, Pittsburgh, PA 15213
| | - J M Kainerstorfer
- Department of Biomedical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213
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69
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Hoiland RL, Bain AR, Tymko MM, Rieger MG, Howe CA, Willie CK, Hansen AB, Flück D, Wildfong KW, Stembridge M, Subedi P, Anholm J, Ainslie PN. Adenosine receptor-dependent signaling is not obligatory for normobaric and hypobaric hypoxia-induced cerebral vasodilation in humans. J Appl Physiol (1985) 2017; 122:795-808. [PMID: 28082335 DOI: 10.1152/japplphysiol.00840.2016] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Revised: 01/09/2017] [Accepted: 01/09/2017] [Indexed: 01/11/2023] Open
Abstract
Hypoxia increases cerebral blood flow (CBF) with the underlying signaling processes potentially including adenosine. A randomized, double-blinded, and placebo-controlled design, was implemented to determine if adenosine receptor antagonism (theophylline, 3.75 mg/Kg) would reduce the CBF response to normobaric and hypobaric hypoxia. In 12 participants the partial pressures of end-tidal oxygen ([Formula: see text]) and carbon dioxide ([Formula: see text]), ventilation (pneumotachography), blood pressure (finger photoplethysmography), heart rate (electrocardiogram), CBF (duplex ultrasound), and intracranial blood velocities (transcranial Doppler ultrasound) were measured during 5-min stages of isocapnic hypoxia at sea level (98, 90, 80, and 70% [Formula: see text]). Ventilation, [Formula: see text] and [Formula: see text], blood pressure, heart rate, and CBF were also measured upon exposure (128 ± 31 min following arrival) to high altitude (3,800 m) and 6 h following theophylline administration. At sea level, although the CBF response to hypoxia was unaltered pre- and postplacebo, it was reduced following theophylline (P < 0.01), a finding explained by a lower [Formula: see text] (P < 0.01). Upon mathematical correction for [Formula: see text], the CBF response to hypoxia was unaltered following theophylline. Cerebrovascular reactivity to hypoxia (i.e., response slope) was not different between trials, irrespective of [Formula: see text] At high altitude, theophylline (n = 6) had no effect on CBF compared with placebo (n = 6) when end-tidal gases were comparable (P > 0.05). We conclude that adenosine receptor-dependent signaling is not obligatory for cerebral hypoxic vasodilation in humans.NEW & NOTEWORTHY The signaling pathways that regulate human cerebral blood flow in hypoxia remain poorly understood. Using a randomized, double-blinded, and placebo-controlled study design, we determined that adenosine receptor-dependent signaling is not obligatory for the regulation of human cerebral blood flow at sea level; these findings also extend to high altitude.
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Affiliation(s)
- Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada;
| | - Anthony R Bain
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Mathew G Rieger
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Christopher K Willie
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Alex B Hansen
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Daniela Flück
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Kevin W Wildfong
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Mike Stembridge
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cardiff, United Kingdom; and
| | - Prajan Subedi
- VA Loma Linda Healthcare System and Loma Linda University School of Medicine, Loma Linda, California
| | - James Anholm
- VA Loma Linda Healthcare System and Loma Linda University School of Medicine, Loma Linda, California
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
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70
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Bronzwaer ASGT, Verbree J, Stok WJ, Daemen MJAP, van Buchem MA, van Osch MJP, van Lieshout JJ. The cerebrovascular response to lower-body negative pressure vs. head-up tilt. J Appl Physiol (1985) 2017; 122:877-883. [PMID: 28082333 DOI: 10.1152/japplphysiol.00797.2016] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Revised: 01/05/2017] [Accepted: 01/05/2017] [Indexed: 11/22/2022] Open
Abstract
Lower-body negative pressure (LBNP) has been proposed as a MRI-compatible surrogate for orthostatic stress. Although the effects of LBNP on cerebral hemodynamic behavior have been considered to reflect those of orthostatic stress, a direct comparison with actual orthostasis is lacking. We assessed the effects of LBNP (-50 mmHg) vs. head-up tilt (HUT; at 70°) in 10 healthy subjects (5 female) on transcranial Doppler-determined cerebral blood flow velocity (CBFv) in the middle cerebral artery and cerebral perfusion pressure (CPP) as estimated from the blood pressure signal (finger plethysmography). CPP was maintained during LBNP but decreased after 2 min in response to HUT, leading to an ~15% difference in CPP between LBNP and HUT (P ≤ 0.020). Mean CBFv initially decreased similarly in response to LBNP and for HUT, but, from minute 3 on, the decline became ~50% smaller (P ≤ 0.029) during LBNP. The reduction in end-tidal Pco2 partial pressure (PetCO2 ) was comparable but with an earlier return toward baseline values in response to LBNP but not during HUT (P = 0.008). We consider the larger decrease in CBFv during HUT vs. LBNP attributable to the pronounced reduction in PetCO2 and to gravitational influences on CPP, and this should be taken into account when applying LBNP as an MRI-compatible orthostatic stress modality.NEW & NOTEWORTHY Lower-body negative pressure (LBNP) has the potential to serve as a MRI-compatible surrogate of orthostatic stress but a comparison with actual orthostasis was lacking. This study showed that the pronounced reduction in end-tidal Pco2 together with gravitational effects on the brain circulation lead to a larger decline in cerebral blood flow velocity in response to head-up tilt than during lower-body negative pressure. This should be taken into account when employing lower-body negative pressure as MRI-compatible alternative to orthostatic stress.
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Affiliation(s)
- Anne-Sophie G T Bronzwaer
- Department of Internal Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.,Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
| | - Jasper Verbree
- Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| | - Wim J Stok
- Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.,Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
| | - Mat J A P Daemen
- Department of Pathology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands; and
| | - Mark A van Buchem
- Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| | | | - Johannes J van Lieshout
- Department of Internal Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands; .,Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.,Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.,Medical Research Center/Arthritis Research United Kingdom Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom
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71
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McBryde FD, Malpas SC, Paton JFR. Intracranial mechanisms for preserving brain blood flow in health and disease. Acta Physiol (Oxf) 2017; 219:274-287. [PMID: 27172364 DOI: 10.1111/apha.12706] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 02/03/2016] [Accepted: 05/06/2016] [Indexed: 12/19/2022]
Abstract
The brain is an exceptionally energetically demanding organ with little metabolic reserve, and multiple systems operate to protect and preserve the brain blood supply. But how does the brain sense its own perfusion? In this review, we discuss how the brain may harness the cardiovascular system to counter threats to cerebral perfusion sensed via intracranial pressure (ICP), cerebral oxygenation and ischaemia. Since the work of Cushing over 100 years ago, the existence of brain baroreceptors capable of eliciting increases in sympathetic outflow and blood pressure has been hypothesized. In the clinic, this response has generally been thought to occur only in extremis, to perfuse the severely ischaemic brain as cerebral autoregulation fails. We review evidence that pressor responses may also occur with smaller, physiologically relevant increases in ICP. The incoming brain oxygen supply is closely monitored by the carotid chemoreceptors; however, hypoxia and other markers of ischaemia are also sensed intrinsically by astrocytes or other support cells within brain tissue itself and elicit reactive hyperaemia. Recent studies suggest that astrocytic oxygen signalling within the brainstem may directly affect sympathetic nerve activity and blood pressure. We speculate that local cerebral oxygen tension is a major determinant of the mean level of arterial pressure and discuss recent evidence that this may be the case. We conclude that intrinsic intra- and extra-cranial mechanisms sense and integrate information about hypoxia/ischaemia and ICP and play a major role in determining the long-term level of sympathetic outflow and arterial pressure, to optimize cerebral perfusion.
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Affiliation(s)
- F. D. McBryde
- Department of Physiology; Faculty of Medical and Health Sciences; University of Auckland; Auckland New Zealand
- School of Physiology, Pharmacology & Neuroscience; Biomedical Sciences; University of Bristol; Bristol UK
| | - S. C. Malpas
- Department of Physiology; Faculty of Medical and Health Sciences; University of Auckland; Auckland New Zealand
| | - J. F. R. Paton
- Department of Physiology; Faculty of Medical and Health Sciences; University of Auckland; Auckland New Zealand
- School of Physiology, Pharmacology & Neuroscience; Biomedical Sciences; University of Bristol; Bristol UK
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72
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Fantini S, Sassaroli A, Tgavalekos KT, Kornbluth J. Cerebral blood flow and autoregulation: current measurement techniques and prospects for noninvasive optical methods. NEUROPHOTONICS 2016; 3:031411. [PMID: 27403447 PMCID: PMC4914489 DOI: 10.1117/1.nph.3.3.031411] [Citation(s) in RCA: 211] [Impact Index Per Article: 26.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 05/10/2016] [Indexed: 05/23/2023]
Abstract
Cerebral blood flow (CBF) and cerebral autoregulation (CA) are critically important to maintain proper brain perfusion and supply the brain with the necessary oxygen and energy substrates. Adequate brain perfusion is required to support normal brain function, to achieve successful aging, and to navigate acute and chronic medical conditions. We review the general principles of CBF measurements and the current techniques to measure CBF based on direct intravascular measurements, nuclear medicine, X-ray imaging, magnetic resonance imaging, ultrasound techniques, thermal diffusion, and optical methods. We also review techniques for arterial blood pressure measurements as well as theoretical and experimental methods for the assessment of CA, including recent approaches based on optical techniques. The assessment of cerebral perfusion in the clinical practice is also presented. The comprehensive description of principles, methods, and clinical requirements of CBF and CA measurements highlights the potentially important role that noninvasive optical methods can play in the assessment of neurovascular health. In fact, optical techniques have the ability to provide a noninvasive, quantitative, and continuous monitor of CBF and autoregulation.
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Affiliation(s)
- Sergio Fantini
- Tufts University, Department of Biomedical Engineering, 4 Colby Street, Medford, Massachusetts 02155, United States
| | - Angelo Sassaroli
- Tufts University, Department of Biomedical Engineering, 4 Colby Street, Medford, Massachusetts 02155, United States
| | - Kristen T. Tgavalekos
- Tufts University, Department of Biomedical Engineering, 4 Colby Street, Medford, Massachusetts 02155, United States
| | - Joshua Kornbluth
- Tufts University School of Medicine, Department of Neurology, Division of Neurocritical Care, 800 Washington Street, Box #314, Boston, Massachusetts 02111, United States
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73
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Tymko MM. Measuring cerebral auto-variability. J Physiol 2016; 594:3185-6. [DOI: 10.1113/jp272207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Accepted: 02/12/2016] [Indexed: 11/08/2022] Open
Affiliation(s)
- Michael M. Tymko
- Centre for Heart; Lung; and Vascular Health; School of Health and Exercise Science; University of British Columbia; Kelowna Canada
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Bain AR, Nybo L, Ainslie PN. Cerebral Vascular Control and Metabolism in Heat Stress. Compr Physiol 2016; 5:1345-80. [PMID: 26140721 DOI: 10.1002/cphy.c140066] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This review provides an in-depth update on the impact of heat stress on cerebrovascular functioning. The regulation of cerebral temperature, blood flow, and metabolism are discussed. We further provide an overview of vascular permeability, the neurocognitive changes, and the key clinical implications and pathologies known to confound cerebral functioning during hyperthermia. A reduction in cerebral blood flow (CBF), derived primarily from a respiratory-induced alkalosis, underscores the cerebrovascular changes to hyperthermia. Arterial pressures may also become compromised because of reduced peripheral resistance secondary to skin vasodilatation. Therefore, when hyperthermia is combined with conditions that increase cardiovascular strain, for example, orthostasis or dehydration, the inability to preserve cerebral perfusion pressure further reduces CBF. A reduced cerebral perfusion pressure is in turn the primary mechanism for impaired tolerance to orthostatic challenges. Any reduction in CBF attenuates the brain's convective heat loss, while the hyperthermic-induced increase in metabolic rate increases the cerebral heat gain. This paradoxical uncoupling of CBF to metabolism increases brain temperature, and potentiates a condition whereby cerebral oxygenation may be compromised. With levels of experimentally viable passive hyperthermia (up to 39.5-40.0 °C core temperature), the associated reduction in CBF (∼ 30%) and increase in cerebral metabolic demand (∼ 10%) is likely compensated by increases in cerebral oxygen extraction. However, severe increases in whole-body and brain temperature may increase blood-brain barrier permeability, potentially leading to cerebral vasogenic edema. The cerebrovascular challenges associated with hyperthermia are of paramount importance for populations with compromised thermoregulatory control--for example, spinal cord injury, elderly, and those with preexisting cardiovascular diseases.
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Affiliation(s)
- Anthony R Bain
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, Canada
| | - Lars Nybo
- Department of Nutrition, Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Philip N Ainslie
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, Canada
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75
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Hoiland RL, Tymko MM, Bain AR, Wildfong KW, Monteleone B, Ainslie PN. Carbon dioxide-mediated vasomotion of extra-cranial cerebral arteries in humans: a role for prostaglandins? J Physiol 2016; 594:3463-81. [PMID: 26880615 DOI: 10.1113/jp272012] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 02/01/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Cerebral blood flow increases during hypercapnia and decreases during hypocapnia; it is unknown if vasomotion of the internal carotid artery is implicated in these responses. Indomethacin, a non-selective cyclooxygenase inhibitor (used to inhibit prostaglandin synthesis), has a unique ability to blunt cerebrovascular carbon dioxide reactivity, while other cyclooxygenase inhibitors have no effect. We show significant dilatation and constriction of the internal carotid artery during hypercapnia and hypocapnia, respectively. Indomethacin, but not ketorolac or naproxen, reduced the dilatatory response of the internal carotid artery to hypercapnia The differential effect of indomethacin compared to ketorolac and naproxen suggests that indomethacin inhibits vasomotion of the internal carotid artery independent of prostaglandin synthesis inhibition. ABSTRACT Extra-cranial cerebral blood vessels are implicated in the regulation of cerebral blood flow during changes in arterial CO2 ; however, the mechanisms governing CO2 -mediated vasomotion of these vessels in humans remain unclear. We determined if cyclooxygenase inhibition with indomethacin (INDO) reduces the vasomotor response of the internal carotid artery (ICA) to changes in end-tidal CO2 (P ETC O2). Using a randomized single-blinded placebo-controlled study, participants (n = 10) were tested on two occasions, before and 90 min following oral INDO (1.2 mg kg(-1) ) or placebo. Concurrent measurements of beat-by-beat velocity, diameter and blood flow of the ICA were made at rest and during steady-state stages (4 min) of iso-oxic hypercapnia (+3, +6, +9 mmHg P ETC O2) and hypocapnia (-3, -6, -9 mmHg P ETC O2). To examine if INDO affects ICA vasomotion independent of cyclooxygenase inhibition, two participant subsets (each n = 5) were tested before and following oral ketorolac (post 45 min, 0.25 mg kg(-1) ) or naproxen (post 90 min, 4.2 mg kg(-1) ). During pre-drug testing in the INDO trial, the ICA dilatated during hypercapnia at +6 mmHg (4.72 ± 0.45 vs. 4.95 ± 0.51 mm; P < 0.001) and +9 mmHg (4.72 ± 0.45 mm vs. 5.12 ± 0.47 mm; P < 0.001), and constricted during hypocapnia at -6 mmHg (4.95 ± 0.33 vs. 4.88 ± 0.27 mm; P < 0.05) and -9 mmHg (4.95 ± 0.33 vs. 4.82 ± 0.27 mm; P < 0.001). Following INDO, vasomotor responsiveness of the ICA to hypercapnia was reduced by 67 ± 28% (0.045 ± 0.015 vs. 0.015 ± 0.012 mm mmHg P ETC O2(-1) ). There was no effect of the drug in the ketorolac and naproxen trials. We conclude that: (1) INDO markedly reduces the vasomotor response of the ICA to changes in P ETC O2; and (2) INDO may be reducing CO2 -mediated vasomotion via a mechanism(s) independent of cyclooxygenase inhibition.
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Affiliation(s)
- Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Anthony R Bain
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Kevin W Wildfong
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Brad Monteleone
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
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76
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Berg RMG, Plovsing RR. Effects of short-term mechanical hyperventilation on cerebral blood flow and dynamic cerebral autoregulation in critically ill patients with sepsis. Scandinavian Journal of Clinical and Laboratory Investigation 2016; 76:226-33. [PMID: 26935607 DOI: 10.3109/00365513.2015.1137350] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In sepsis, higher PaCO2 levels are associated with impaired dynamic cerebral autoregulation (dCA), which may expose the brain to hypo- and hyperperfusion during acute fluctuations in blood pressure. We hypothesised that short-term mechanical hyperventilation would dCA in critically ill patients with sepsis. Seven mechanically ventilated septic patients were included. We assessed dCA before and after 30 min of mechanical hyperventilation. Transfer function analysis of spontaneous oscillations in transcranial Doppler-based middle cerebral artery blood flow velocity (MCAv) and invasive mean arterial blood pressure was used to assess dCA. Mechanical enhance hyperventilation reduced the median PaCO2 from 5.3 (IQR, 5.0-6.5) to 4.7 (IQR, 4.2-5.1) kPa (p < 0.05). This was associated with a reduction in the median MCAv from 57 (IQR, 33-68) to 32 (IQR, 21-40) cm sec(-1) (p < 0.05). Apart from a small increase in gain in the low frequency range (2.32 [IQR 1.80-2.41] vs. 2.59 (2.40-4.64) cm mmHg(-1) sec(-1); p < 0.05), this was not associated with any enhancement in dCA. In conclusion, cerebral CO2 vasoreactivity was found to be preserved in septic patients; nevertheless, and in contrast to our working hypothesis, short-term mechanical hyperventilation did not enhance dCA.
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Affiliation(s)
- Ronan M G Berg
- a Department of Clinical Physiology and Nuclear Medicine , Bispebjerg and Frederiksberg Hospitals , Copenhagen ;,b Centre of Inflammation and Metabolism , University Hospital Rigshospitalet , Copenhagen
| | - Ronni R Plovsing
- c Department of Intensive Care 4131 , University Hospital Rigshospitalet , Copenhagen ;,d Department of Anaesthesiology , Køge Hospital , Køge , Denmark
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78
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Donnelly J, Aries MJ, Czosnyka M. Further understanding of cerebral autoregulation at the bedside: possible implications for future therapy. Expert Rev Neurother 2015; 15:169-85. [PMID: 25614952 DOI: 10.1586/14737175.2015.996552] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Cerebral autoregulation reflects the ability of the brain to keep the cerebral blood flow (CBF) relatively constant despite changes in cerebral perfusion pressure. It is an intrinsic neuroprotective physiological phenomenon often suggested as part of pathophysiological pathways in brain research. However, despite increasing knowledge of this phenomenon for over 50 years, harnessing cerebral autoregulation as a basis for therapy remains an elegant concept rather than a practical reality. This raises the question is it useful to measure at the bedside or is it merely a scientific curiosity that is too complex and has little pragmatic relevance. In this article, we attempt to answer this question by demonstrating how cerebral autoregulation assessment can have prognostic value, indicate pathological states, and potentially even influence therapy with the use of the 'optimal cerebral perfusion pressure' paradigm. Evidence from the literature is combined with bedside clinical examples to address the following fundamental questions about cerebral autoregulation: What is it? How do we measure it? Why is it important? Can we use it as a basis for therapy?
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Affiliation(s)
- Joseph Donnelly
- Department of Clinical Neurosciences, Division of Neurosurgery, Addenbrooke's Hospital, University of Cambridge, Hills Road, Cambridge, CB2 0QQ, UK
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79
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Mündel T, Perry BG, Ainslie PN, Thomas KN, Sikken ELG, Cotter JD, Lucas SJE. Postexercise orthostatic intolerance: influence of exercise intensity. Exp Physiol 2015; 100:915-25. [DOI: 10.1113/ep085143] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 05/29/2015] [Indexed: 11/08/2022]
Affiliation(s)
- Toby Mündel
- School of Sport and Exercise; Massey University; Palmerston North New Zealand
| | - Blake G. Perry
- School of Sport and Exercise; Massey University; Palmerston North New Zealand
| | - Philip N. Ainslie
- Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia; Okanagan British Columbia Canada
- Department of Physiology; University of Otago; Dunedin New Zealand
| | - Kate N. Thomas
- School of Physical Education, Sport and Exercise Sciences; University of Otago; Dunedin New Zealand
- Department of Surgical Sciences; University of Otago; Dunedin New Zealand
| | - Elisabeth L. G. Sikken
- Department of Physiology; University of Otago; Dunedin New Zealand
- Department of Physiology; Radboud University Nijmegen Medical Centre; The Netherlands
| | - James D. Cotter
- School of Physical Education, Sport and Exercise Sciences; University of Otago; Dunedin New Zealand
| | - Samuel J. E. Lucas
- 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; UK
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80
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Abstract
We examined the impact of progressive hypotension with and without hypocapnia on regional extracranial cerebral blood flow (CBF) and intracranial velocities. Participants underwent progressive lower-body negative pressure (LBNP) until pre-syncope to inflict hypotension. End-tidal carbon dioxide was clamped at baseline levels (isocapnic trial) or uncontrolled (poikilocapnic trial). Middle cerebral artery (MCA) and posterior cerebral artery (PCA) blood velocities (transcranial Doppler; TCD), heart rate, blood pressure and end-tidal carbon dioxide were obtained continuously. Measurements of internal carotid artery (ICA) and vertebral artery (VA) blood flow (ICABF and VABF respectively) were also obtained. Overall, blood pressure was reduced by ~20% from baseline in both trials (P<0.001). In the isocapnic trial, end-tidal carbon dioxide was successfully clamped at baseline with hypotension, whereas in the poikilocapnic trial it was reduced by 11.1 mmHg (P<0.001) with hypotension. The decline in the ICABF with hypotension was comparable between trials (-139 ± 82 ml; ~30%; P<0.0001); however, the decline in the VABF was -28 ± 22 ml/min (~21%) greater in the poikilocapnic trial compared with the isocapnic trial (P=0.002). Regardless of trial, the blood flow reductions in ICA (-26 ± 14%) and VA (-27 ± 14%) were greater than the decline in MCA (-21 ± 15%) and PCA (-19 ± 10%) velocities respectively (P ≤ 0.01). Significant reductions in the diameter of both the ICA (~5%) and the VA (~7%) contributed to the decline in cerebral perfusion with systemic hypotension, independent of hypocapnia. In summary, our findings indicate that blood flow in the VA, unlike the ICA, is sensitive to changes hypotension and hypocapnia. We show for the first time that the decline in global CBF with hypotension is influenced by arterial constriction in the ICA and VA. Additionally, our findings suggest TCD measures of blood flow velocity may modestly underestimate changes in CBF during hypotension with and without hypocapnia, particularly in the posterior circulation.
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81
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Cerebral autoregulation in the microvasculature measured with near-infrared spectroscopy. J Cereb Blood Flow Metab 2015; 35:959-66. [PMID: 25669906 PMCID: PMC4640259 DOI: 10.1038/jcbfm.2015.5] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Revised: 12/17/2014] [Accepted: 01/06/2015] [Indexed: 01/27/2023]
Abstract
Cerebral autoregulation (CA) is the mechanism that allows the brain to maintain a stable blood flow despite changes in blood pressure. Dynamic CA can be quantified based on continuous measurements of systemic mean arterial pressure (MAP) and global cerebral blood flow. Here, we show that dynamic CA can be quantified also from local measurements that are sensitive to the microvasculature. We used near-infrared spectroscopy (NIRS) to measure temporal changes in oxy- and deoxy-hemoglobin concentrations in the prefrontal cortex of 11 human subjects. A novel hemodynamic model translates those changes into changes of cerebral blood volume and blood flow. The interplay between them is described by transfer function analysis, specifically by a high-pass filter whose cutoff frequency describes the autoregulation efficiency. We have used pneumatic thigh cuffs to induce MAP perturbation by a fast release during rest and during hyperventilation, which is known to enhance autoregulation. Based on our model, we found that the autoregulation cutoff frequency increased during hyperventilation in comparison to normal breathing in 10 out of 11 subjects, indicating a greater autoregulation efficiency. We have shown that autoregulation can reliably be measured noninvasively in the microvasculature, opening up the possibility of localized CA monitoring with NIRS.
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82
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Lucas SJE, Cotter JD, Brassard P, Bailey DM. High-intensity interval exercise and cerebrovascular health: curiosity, cause, and consequence. J Cereb Blood Flow Metab 2015; 35:902-11. [PMID: 25833341 PMCID: PMC4640257 DOI: 10.1038/jcbfm.2015.49] [Citation(s) in RCA: 136] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 01/25/2015] [Accepted: 03/01/2015] [Indexed: 12/14/2022]
Abstract
Exercise is a uniquely effective and pluripotent medicine against several noncommunicable diseases of westernised lifestyles, including protection against neurodegenerative disorders. High-intensity interval exercise training (HIT) is emerging as an effective alternative to current health-related exercise guidelines. Compared with traditional moderate-intensity continuous exercise training, HIT confers equivalent if not indeed superior metabolic, cardiac, and systemic vascular adaptation. Consequently, HIT is being promoted as a more time-efficient and practical approach to optimize health thereby reducing the burden of disease associated with physical inactivity. However, no studies to date have examined the impact of HIT on the cerebrovasculature and corresponding implications for cognitive function. This review critiques the implications of HIT for cerebrovascular function, with a focus on the mechanisms and translational impact for patient health and well-being. It also introduces similarly novel interventions currently under investigation as alternative means of accelerating exercise-induced cerebrovascular adaptation. We highlight a need for studies of the mechanisms and thereby also the optimal dose-response strategies to guide exercise prescription, and for studies to explore alternative approaches to optimize exercise outcomes in brain-related health and disease prevention. From a clinical perspective, interventions that selectively target the aging brain have the potential to prevent stroke and associated neurovascular diseases.
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Affiliation(s)
- Samuel J E Lucas
- 1] School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK [2] Department of Physiology, University of Otago, Dunedin, New Zealand
| | - James D Cotter
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand
| | - Patrice Brassard
- 1] Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada [2] Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada
| | - Damian M Bailey
- 1] Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, South Wales, UK [2] Université de Provence Marseille, Sondes Moléculaires en Biologie, Laboratoire Chimie Provence UMR 6264 CNRS, Marseille, France
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83
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Lewis NCS, Bain AR, MacLeod DB, Wildfong KW, Smith KJ, Willie CK, Sanders ML, Numan T, Morrison SA, Foster GE, Stewart JM, Ainslie PN. Impact of hypocapnia and cerebral perfusion on orthostatic tolerance. J Physiol 2014; 592:5203-19. [PMID: 25217373 PMCID: PMC4262334 DOI: 10.1113/jphysiol.2014.280586] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 09/01/2014] [Indexed: 12/25/2022] Open
Abstract
We examined two novel hypotheses: (1) that orthostatic tolerance (OT) would be prolonged when hyperventilatory-induced hypocapnia (and hence cerebral hypoperfusion) was prevented; and (2) that pharmacological reductions in cerebral blood flow (CBF) at baseline would lower the 'CBF reserve', and ultimately reduce OT. In study 1 (n = 24; aged 25 ± 4 years) participants underwent progressive lower-body negative pressure (LBNP) until pre-syncope; end-tidal carbon dioxide (P ET , CO 2) was clamped at baseline levels (isocapnic trial) or uncontrolled. In study 2 (n = 10; aged 25 ± 4 years), CBF was pharmacologically reduced by administration of indomethacin (INDO; 1.2 mg kg(-1)) or unaltered (placebo) followed by LBNP to pre-syncope. Beat-by-beat measurements of middle cerebral artery blood flow velocity (MCAv; transcranial Doppler), heart rate (ECG), blood pressure (BP; Finometer) and end-tidal gases were obtained continuously. In a subset of subjects' arterial-to-jugular venous differences were obtained to examine the independent impact of hypocapnia or cerebral hypoperfusion (following INDO) on cerebral oxygen delivery and extraction. In study 1, during the isocapnic trial, P ET , CO 2 was successfully clamped at baseline levels at pre-syncope (38.3 ± 2.7 vs. 38.5 ± 2.5 mmHg respectively; P = 0.50). In the uncontrolled trial, P ET , CO 2 at pre-syncope was reduced by 10.9 ± 3.9 mmHg (P ≤ 0.001). Compared to the isocapnic trial, the decline in mean MCAv was 15 ± 4 cm s(-1) (35%; P ≤ 0.001) greater in the uncontrolled trial, yet the time to pre-syncope was comparable between trials (544 ± 130 vs. 572 ± 180 s; P = 0.30). In study 2, compared to placebo, INDO reduced resting MCAv by 19 ± 4 cm s(-1) (31%; P ≤ 0.001), but time to pre-syncope remained similar between trials (placebo: 1123 ± 138 s vs. INDO: 1175 ± 212 s; P = 0.53). The brain extracted more oxygen in face of hypocapnia (34% to 53%) or cerebral hypoperfusion (34% to 57%) to compensate for reductions in delivery. In summary, cerebral hypoperfusion either at rest or induced by hypocapnia at pre-syncope does not impact OT, probably due to a compensatory increase in oxygen extraction.
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Affiliation(s)
- Nia C S Lewis
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Canada
| | - Anthony R Bain
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Canada
| | - David B MacLeod
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - Kevin W Wildfong
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Canada
| | - Kurt J Smith
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Canada
| | - Christopher K Willie
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Canada
| | | | - Tianne Numan
- MIRA, University of Twente, Enschede, The Netherlands
| | - Shawnda A Morrison
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Canada Jozef Stefan Institute, Ljubljana, Slovenia
| | - Glen E Foster
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Canada
| | | | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Canada
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