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Caldwell HG, Hoiland RL, Bain AR, Howe CA, Carr JMJR, Gibbons TD, Durrer CG, Tymko MM, Stacey BS, Bailey DM, Sekhon MS, MacLeod DB, Ainslie PN. Evidence for direct CO 2 -mediated alterations in cerebral oxidative metabolism in humans. Acta Physiol (Oxf) 2024; 240:e14197. [PMID: 38958262 DOI: 10.1111/apha.14197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 06/18/2024] [Accepted: 06/20/2024] [Indexed: 07/04/2024]
Abstract
AIM How the cerebral metabolic rates of oxygen and glucose utilization (CMRO2 and CMRGlc, respectively) are affected by alterations in arterial PCO2 (PaCO2) is equivocal and therefore was the primary question of this study. METHODS This retrospective analysis involved pooled data from four separate studies, involving 41 healthy adults (35 males/6 females). Participants completed stepwise steady-state alterations in PaCO2 ranging between 30 and 60 mmHg. The CMRO2 and CMRGlc were assessed via the Fick approach (CBF × arterial-internal jugular venous difference of oxygen or glucose content, respectively) utilizing duplex ultrasound of the internal carotid artery and vertebral artery to calculate cerebral blood flow (CBF). RESULTS The CMRO2 was altered by 0.5 mL × min-1 (95% CI: -0.6 to -0.3) per mmHg change in PaCO2 (p < 0.001) which corresponded to a 9.8% (95% CI: -13.2 to -6.5) change in CMRO2 with a 9 mmHg change in PaCO2 (inclusive of hypo- and hypercapnia). The CMRGlc was reduced by 7.7% (95% CI: -15.4 to -0.08, p = 0.045; i.e., reduction in net glucose uptake) and the oxidative glucose index (ratio of oxygen to glucose uptake) was reduced by 5.6% (95% CI: -11.2 to 0.06, p = 0.049) with a + 9 mmHg increase in PaCO2. CONCLUSION Collectively, the CMRO2 is altered by approximately 1% per mmHg change in PaCO2. Further, glucose is incompletely oxidized during hypercapnia, indicating reductions in CMRO2 are either met by compensatory increases in nonoxidative glucose metabolism or explained by a reduction in total energy production.
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
- Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Collaborative Entity for REsearching Brain Ischemia (CEREBRI), University of British Columbia, Vancouver, British Columbia, Canada
| | - Anthony R Bain
- Department of Kinesiology, Faculty of Human Kinetics, University of Windsor, Windsor, Ontario, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Travis D Gibbons
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Cody G Durrer
- Centre for Physical Activity Research, Rigshospitalet, Copenhagen, Denmark
| | - Michael M Tymko
- Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Human Cerebrovascular Physiology Laboratory, Department of Human Health and Nutritional Sciences, College of Biological Science, University of Guelph, Guelph, Ontario, Canada
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Mypinder S Sekhon
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Collaborative Entity for REsearching Brain Ischemia (CEREBRI), University of British Columbia, Vancouver, British Columbia, Canada
- Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, British Columbia, Canada
| | - David B MacLeod
- Human Pharmacology and Physiology Lab, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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Kelley EF, Cross TJ, Johnson BD. Expiratory Threshold Loading and Attentional Performance. Aerosp Med Hum Perform 2024; 95:367-374. [PMID: 38915161 DOI: 10.3357/amhp.6383.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/26/2024]
Abstract
INTRODUCTION: While there are numerous factors that may affect pilot attentional performance, we hypothesize that an increased expiratory work of breathing experienced by fighter pilots may impose a "distraction stimulus" by creating an increased expiratory effort sensation. Therefore, the purpose of this study was to determine the extent to which increasing expiratory pressure time product or expiratory effort sensation impacts attentional performance.METHODS: Data was collected on 10 healthy participants (age: 29 ± 6 yr). Participants completed six repetitions of a modified Masked Conjunctive Continuous Performance Task protocol while breathing against four different expiratory threshold loads. Repeated measures analysis of variances and generalized additive mixed effects models were used to investigate the effects of expiratory threshold load conditions on expiratory pressure time product, expiratory effort sensation, and the influence of altered end tidal gases on Masked Conjunctive Continuous Performance Task scores.RESULTS: The overall median hit reaction times were significantly longer as the expiratory threshold loads increased. Specific shape-conjunctive and non-conjunctive median hit reaction times were longer with increased expiratory effort sensation. Additionally, increased expiratory effort sensation did not significantly change commission error rates, but did significantly increase omission error rates.DISCUSSION: The findings of our work suggest that both progressively greater expiratory threshold loads during spontaneous breathing and expiratory effort sensation may impair subjects' attentional performance due to longer reaction times and increased stimuli recognition error rates.Kelley EF, Cross TJ, Johnson BD. Expiratory threshold loading and attentional performance. Aerosp Med Hum Perform. 2024; 95(7):367-374.
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Jimenez JV, Ackrivo J, Hsu JY, Wilson MW, Labaki WW, Hansen-Flaschen J, Hyzy RC, Choi PJ. Lowering P CO2 With Noninvasive Ventilation Is Associated With Improved Survival in Chronic Hypercapnic Respiratory Failure. Respir Care 2023; 68:1613-1622. [PMID: 37137711 PMCID: PMC10676248 DOI: 10.4187/respcare.10813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 05/01/2023] [Indexed: 05/05/2023]
Abstract
BACKGROUND Chronic hypercapnic respiratory failure is associated with high mortality. Although previous work has demonstrated a mortality improvement with high-intensity noninvasive ventilation in COPD, it is unclear whether a PCO2 reduction strategy is associated with improved outcomes in other populations of chronic hypercapnia. METHODS The objective of this study was to investigate the association between PCO2 reduction (by using transcutaneous PCO2 as an estimate for PaCO2 and survival in a broad population of individuals treated with noninvasive ventilation for chronic hypercapnia. We hypothesized that reductions in PCO2 would be associated with improved survival. Therefore, we performed a cohort study of all the subjects evaluated from February 2012 to January 2021 for noninvasive ventilation initiation and/or optimization due to chronic hypercapnia at a home ventilation clinic in an academic center. We used multivariable Cox proportional hazard models with time-varying coefficients and PCO2 as a time-varying covariate to test the association between PCO2 and all-cause mortality and when adjusting for known cofounders. RESULTS The mean ± SD age of 337 subjects was 57 ± 16 years, 37% women, and 85% white. In a univariate analysis, survival probability increased with reductions in PCO2 to < 50 mm Hg after 90 d, and these remained significant after adjusting for age, sex, race, body mass index, diagnosis, Charlson comorbidity index, and baseline PCO2 . In the multivariable analysis, the subjects who had a PaCO2 < 50 mm Hg had a reduced mortality risk of 94% between 90 and 179 d (hazard ratio [HR] 0.06, 95% CI 0.01-0.50), 69% between 180 and 364 d (HR 0.31, 95% CI 0.12-0.79), and 73% for 365-730 d (HR 0.27, 95% CI 0.13-0.56). CONCLUSIONS Reduction in PCO2 from baseline for subjects with chronic hypercapnia treated with noninvasive ventilation was associated with improved survival. Management strategies should target the greatest attainable reductions in PCO2 .
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Affiliation(s)
- Jose Victor Jimenez
- Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, Michigan. Dr Jimenez is affiliated with the Department of Internal Medicine, Yale New Haven Hospital, New Haven, Connecticut
| | - Jason Ackrivo
- Pulmonary, Allergy, and Critical Care Division, Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania
| | - Jesse Y Hsu
- Department of Biostatistics, Epidemiology, and Informatics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania
| | - Mathew W Wilson
- Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, Michigan. Dr Jimenez is affiliated with the Department of Internal Medicine, Yale New Haven Hospital, New Haven, Connecticut
| | - Wassim W Labaki
- Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, Michigan. Dr Jimenez is affiliated with the Department of Internal Medicine, Yale New Haven Hospital, New Haven, Connecticut
| | - John Hansen-Flaschen
- Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, Michigan. Dr Jimenez is affiliated with the Department of Internal Medicine, Yale New Haven Hospital, New Haven, Connecticut
| | - Robert C Hyzy
- Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, Michigan. Dr Jimenez is affiliated with the Department of Internal Medicine, Yale New Haven Hospital, New Haven, Connecticut
| | - Philip J Choi
- Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, Michigan. Dr Jimenez is affiliated with the Department of Internal Medicine, Yale New Haven Hospital, New Haven, Connecticut.
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Desachy M, Alexandre F, Varray A, Molinier V, Four E, Charbonnel L, Héraud N. High Prevalence of Non-Responders Based on Quadriceps Force after Pulmonary Rehabilitation in COPD. J Clin Med 2023; 12:4353. [PMID: 37445388 DOI: 10.3390/jcm12134353] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 06/22/2023] [Accepted: 06/23/2023] [Indexed: 07/15/2023] Open
Abstract
Pulmonary rehabilitation (PR) in patients with COPD improves quality of life, dyspnea, and exercise tolerance. However, 30 to 50% of patients are "non-responders" (NRs) according to considered variables. Surprisingly, peripheral muscle force is never taken into account to attest the efficacy of PR, despite its major importance. Thus, we aimed to estimate the prevalence of force in NRs, their characteristics, and predictors of non-response. In total, 62 COPD patients were included in this retrospective study (May 2019 to December 2020). They underwent inpatient PR, and their quadriceps isometric maximal force (QMVC) was assessed. The PR program followed international guidelines. Patients with a QMVC increase <7.5 N·m were classified as an NR. COPD patients showed a mean improvement in QMVC after PR (10.08 ± 12.97 N·m; p < 0.001). However, 50% of patients were NRs. NRs had lower pre-PR values for body mass, height, body mass index, PaO2, and QMVC. Non-response can be predicted by low QMVC, high PaCO2, and gender (when male). This model has a sensitivity of 74% and specificity of 81%. The study highlights the considerable number of NRs and potential risk factors for non-response. To systematize the effects, it may be interesting to implement blood gas correction and/or optimize the programs to enhance peripheral and central effects.
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Affiliation(s)
- Marion Desachy
- EuroMov Digital Health in Motion, University Montpellier, IMT Mines Ales, Montpellier, France
- Direction de la Recherche et de l'Innovation en Santé (Research and Health Innovation Department), Clariane, France
| | - François Alexandre
- Direction de la Recherche et de l'Innovation en Santé (Research and Health Innovation Department), Clariane, France
| | - Alain Varray
- EuroMov Digital Health in Motion, University Montpellier, IMT Mines Ales, Montpellier, France
| | - Virginie Molinier
- Direction de la Recherche et de l'Innovation en Santé (Research and Health Innovation Department), Clariane, France
| | - Elodie Four
- Clinique du Souffle Les Clarines, Inicea, France
| | | | - Nelly Héraud
- Direction de la Recherche et de l'Innovation en Santé (Research and Health Innovation Department), Clariane, France
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Nakata H, Kakigi R, Kubo H, Shibasaki M. Effects of hypocapnia and hypercapnia on human somatosensory processing. Neurosci Res 2023; 190:29-35. [PMID: 36460201 DOI: 10.1016/j.neures.2022.11.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Revised: 11/21/2022] [Accepted: 11/23/2022] [Indexed: 11/30/2022]
Abstract
The present study investigated the effects of hypocapnia and hypercapnia on human somatosensory processing by utilizing somatosensory evoked magnetic fields (SEFs) with magnetoencephalography (MEG). Thirteen volunteers participated in two experiments separately to measure respiratory and cardiovascular data and SEFs. Both experiments consisted of a combination of normal and rapid respiratory rhythms and two inspiratory gas conditions (air and a hypercapnic gas); normal breathing with air (NB), rapid breathing with air (RB), normal breathing with the hypercapnic gas (NB+Gas), and rapid breathing with gas (RB+Gas). Partial pressures of end-tidal CO2 (PETCO2) increased during inhaling the hypercapnic gas and decreased during RB, but the RB+Gas condition continued to cause elevated PETCO2 compared with the baseline. Subsequently, middle cerebral artery blood (MCA) velocity using transcranial Doppler changed as well, while mean MCA velocity increased under the RB+Gas condition. The peak amplitude of the M60 component in SEFs was also significantly larger under with-gas than without-gas conditions, irrespective of the respiratory frequency. These results suggest that there is a close relationship between cerebral blood flow and neural activity of the M60 component in SEFs. This study provides evidence to further understanding on one of the neural mechanisms of hypercapnia.
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Affiliation(s)
- Hiroki Nakata
- Faculty of Engineering, Nara Women's University, Nara, Japan
| | - Ryusuke Kakigi
- Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Japan
| | - Hiroko Kubo
- Faculty of Engineering, Nara Women's University, Nara, Japan
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Driesen NR, Herman P, Rowland MA, Thompson G, Qiu M, He G, Fineberg S, Barron DS, Helgeson L, Lacadie C, Chow R, Gueorguieva R, Straun TC, Krystal JH, Hyder F. Ketamine Effects on Energy Metabolism, Functional Connectivity and Working Memory in Healthy Humans. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.21.529425. [PMID: 36865249 PMCID: PMC9980048 DOI: 10.1101/2023.02.21.529425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
Working memory (WM) is a crucial resource for temporary memory storage and the guiding of ongoing behavior. N-methyl-D-aspartate glutamate receptors (NMDARs) are thought to support the neural underpinnings of WM. Ketamine is an NMDAR antagonist that has cognitive and behavioral effects at subanesthetic doses. To shed light on subanesthetic ketamine effects on brain function, we employed a multimodal imaging design, combining gas-free calibrated functional magnetic resonance imaging (fMRI) measurement of oxidative metabolism (CMRO 2 ), resting-state cortical functional connectivity assessed with fMRI, and WM-related fMRI. Healthy subjects participated in two scan sessions in a randomized, double-blind, placebo-controlled design. Ketamine increased CMRO 2 and cerebral blood flow (CBF) in prefrontal cortex (PFC) and other cortical regions. However, resting-state cortical functional connectivity was not affected. Ketamine did not alter CBF-CMRO 2 coupling brain-wide. Higher levels of basal CMRO 2 were associated with lower task-related PFC activation and WM accuracy impairment under both saline and ketamine conditions. These observations suggest that CMRO 2 and resting-state functional connectivity index distinct dimensions of neural activity. Ketamine’s impairment of WM-related neural activity and performance appears to be related to its ability to produce cortical metabolic activation. This work illustrates the utility of direct measurement of CMRO 2 via calibrated fMRI in studies of drugs that potentially affect neurovascular and neurometabolic coupling.
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7
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Kelley EF, Cross TJ, Johnson BD. Inspiratory threshold loading negatively impacts attentional performance. Front Psychol 2022; 13:959515. [PMID: 36186373 PMCID: PMC9524251 DOI: 10.3389/fpsyg.2022.959515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 08/26/2022] [Indexed: 11/13/2022] Open
Abstract
RationaleThere are growing concerns over the occurrence of adverse physiologic events (PEs) occurring in pilots during operation of United States Air Force and Navy high-performance aircraft. We hypothesize that a heightened inspiratory work of breathing experienced by jet pilots by virtue of the on-board life support system may constitute a “distraction stimulus” consequent to an increased sensation of respiratory muscle effort. As such, the purpose of this study was to determine whether increasing inspiratory muscle effort adversely impacts on attentional performance.MethodsTwelve, healthy participants (age: 29 ± 6 years) were recruited for this study. Participants completed six repetitions of a modified Masked Conjunctive Continuous Performance Task (MCCPT) protocol while breathing against four different inspiratory threshold loads to assess median reaction times (RTs). A computer-controlled threshold loading device was used to set the inspiratory threshold loads. Repeated measures analysis of variances (ANOVAs) were performed to examine: (i) the efficacy of the threshold loading device to impose significantly higher loading at each loading condition; (ii) the effects of loading condition on respiratory muscle effort sensation; and (iii) the influence of hypercapnia on MCCPT scores during inspiratory threshold loading. Generalized additive mixed effects models (GAMMs) were used to examine the potential non-linear effects of respiratory muscular effort sensation, device loading, and hypercapnia, on MCCPT scores during inspiratory threshold loading.ResultsInspiratory threshold loading significantly augmented (P < 0.05) inspiratory effort sensation and the inspiratory pressure-time product (PTP). Our analyses also revealed that median hit RT was positively associated with inspiratory effort sensation during inspiratory loading trials.ConclusionThe findings of this work suggest that it was not increasing inspiratory muscle effort (i.e., PTP) per se, but rather participant’s subjective perception of inspiratory “load” that impacts negatively on attentional performance; i.e., as the degree of inspiratory effort sensation increased, sotoo did median hit RT. As such, it is reasonable to suggest that minimizing inspiratory effort sensation (independent of the mechanical output of the inspiratory muscles) during high-performance flight operations may prove useful in reducing pilot RTs during complex behavioral tasks.
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Affiliation(s)
- Eli F. Kelley
- Air Force Research Laboratory (AFRL), 711HPW/RHBFP, WPAFB, Dayton, OH, United States
- *Correspondence: Eli F. Kelley,
| | - Troy J. Cross
- Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia
| | - Bruce D. Johnson
- Department of Cardiovascular Diseases, Mayo Clinic, Rochester, MN, United States
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Guilbert J, Légaré A, De Koninck P, Desrosiers P, Desjardins M. Toward an integrative neurovascular framework for studying brain networks. NEUROPHOTONICS 2022; 9:032211. [PMID: 35434179 PMCID: PMC8989057 DOI: 10.1117/1.nph.9.3.032211] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Accepted: 03/11/2022] [Indexed: 05/28/2023]
Abstract
Brain functional connectivity based on the measure of blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals has become one of the most widely used measurements in human neuroimaging. However, the nature of the functional networks revealed by BOLD fMRI can be ambiguous, as highlighted by a recent series of experiments that have suggested that typical resting-state networks can be replicated from purely vascular or physiologically driven BOLD signals. After going through a brief review of the key concepts of brain network analysis, we explore how the vascular and neuronal systems interact to give rise to the brain functional networks measured with BOLD fMRI. This leads us to emphasize a view of the vascular network not only as a confounding element in fMRI but also as a functionally relevant system that is entangled with the neuronal network. To study the vascular and neuronal underpinnings of BOLD functional connectivity, we consider a combination of methodological avenues based on multiscale and multimodal optical imaging in mice, used in combination with computational models that allow the integration of vascular information to explain functional connectivity.
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Affiliation(s)
- Jérémie Guilbert
- Université Laval, Department of Physics, Physical Engineering, and Optics, Québec, Canada
- Université Laval, Centre de recherche du CHU de Québec, Québec, Canada
| | - Antoine Légaré
- Université Laval, Department of Physics, Physical Engineering, and Optics, Québec, Canada
- Centre de recherche CERVO, Québec, Canada
- Université Laval, Department of Biochemistry, Microbiology, and Bioinformatics, Québec, Canada
| | - Paul De Koninck
- Centre de recherche CERVO, Québec, Canada
- Université Laval, Department of Biochemistry, Microbiology, and Bioinformatics, Québec, Canada
| | - Patrick Desrosiers
- Université Laval, Department of Physics, Physical Engineering, and Optics, Québec, Canada
- Centre de recherche CERVO, Québec, Canada
| | - Michèle Desjardins
- Université Laval, Department of Physics, Physical Engineering, and Optics, Québec, Canada
- Université Laval, Centre de recherche du CHU de Québec, Québec, Canada
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Chen JJ, Uthayakumar B, Hyder F. Mapping oxidative metabolism in the human brain with calibrated fMRI in health and disease. J Cereb Blood Flow Metab 2022; 42:1139-1162. [PMID: 35296177 PMCID: PMC9207484 DOI: 10.1177/0271678x221077338] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Conventional functional MRI (fMRI) with blood-oxygenation level dependent (BOLD) contrast is an important tool for mapping human brain activity non-invasively. Recent interest in quantitative fMRI has renewed the importance of oxidative neuroenergetics as reflected by cerebral metabolic rate of oxygen consumption (CMRO2) to support brain function. Dynamic CMRO2 mapping by calibrated fMRI require multi-modal measurements of BOLD signal along with cerebral blood flow (CBF) and/or volume (CBV). In human subjects this "calibration" is typically performed using a gas mixture containing small amounts of carbon dioxide and/or oxygen-enriched medical air, which are thought to produce changes in CBF (and CBV) and BOLD signal with minimal or no CMRO2 changes. However non-human studies have demonstrated that the "calibration" can also be achieved without gases, revealing good agreement between CMRO2 changes and underlying neuronal activity (e.g., multi-unit activity and local field potential). Given the simpler set-up of gas-free calibrated fMRI, there is evidence of recent clinical applications for this less intrusive direction. This up-to-date review emphasizes technological advances for such translational gas-free calibrated fMRI experiments, also covering historical progression of the calibrated fMRI field that is impacting neurological and neurodegenerative investigations of the human brain.
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Affiliation(s)
- J Jean Chen
- Medical Biophysics, University of Toronto, Toronto, Canada.,Rotman Research Institute, Baycrest, Toronto, Canada
| | - Biranavan Uthayakumar
- Medical Biophysics, University of Toronto, Toronto, Canada.,Sunnybrook Research Institute, Toronto, Canada
| | - Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, USA.,Department of Radiology, Yale University, New Haven, Connecticut, USA.,Quantitative Neuroscience with Magnetic Resonance (QNMR) Research Program, Yale University, New Haven, Connecticut, USA.,Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
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Jin RN, Inada H, Négyesi J, Ito D, Nagatomi R. Carbon dioxide effects on daytime sleepiness and EEG signal: A combinational approach using classical frequentist and Bayesian analyses. INDOOR AIR 2022; 32:e13055. [PMID: 35762237 PMCID: PMC9327715 DOI: 10.1111/ina.13055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Revised: 04/29/2022] [Accepted: 05/10/2022] [Indexed: 06/15/2023]
Abstract
Environmental carbon dioxide (CO2 ) could affect various mental and physiological activities in humans, but its effect on daytime sleepiness is still controversial. In a randomized and counterbalanced crossover study with twelve healthy volunteers, we applied a combinational approach using classical frequentist and Bayesian statistics to analyze the CO2 exposure effect on daytime sleepiness and electroencephalogram (EEG) signals. Subjective sleepiness was measured by the Japanese Karolinska Sleepiness Scale (KSS-J) by recording EEG during CO2 exposure at different concentrations: Normal (C), 4000 ppm (Moderately High: MH), and 40 000 ppm (high: H). The daytime sleepiness was significantly affected by the exposure time but not the CO2 condition in the classical statistics. On the other hand, the Bayesian paired t-test revealed that the CO2 exposure at the MH condition might induce daytime sleepiness at the 40-min point compared with the C condition. By contrast, EEG was significantly affected by a short exposure to the H condition but not exposure time. The Bayesian analysis of EEG was primarily consistent with results by the classical statistics but showed different credible levels in the Bayes' factor. Our result suggested that the EEG may not be suitable to detect objective sleepiness induced by CO2 exposure because the EEG signal was highly sensitive to environmental CO2 concentration. Our study would be helpful for researchers to revisit whether EEG is applicable as a judgment indicator of objective sleepiness.
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Affiliation(s)
- Rui Nian Jin
- Division of Biomedical Engineering for Health & WelfareTohoku University Graduate School of Biomedical EngineeringSendaiMiyagiJapan
| | - Hitoshi Inada
- Division of Biomedical Engineering for Health & WelfareTohoku University Graduate School of Biomedical EngineeringSendaiMiyagiJapan
| | - János Négyesi
- Division of Biomedical Engineering for Health & WelfareTohoku University Graduate School of Biomedical EngineeringSendaiMiyagiJapan
| | - Daisuke Ito
- Division of Biomedical Engineering for Health & WelfareTohoku University Graduate School of Biomedical EngineeringSendaiMiyagiJapan
| | - Ryoichi Nagatomi
- Division of Biomedical Engineering for Health & WelfareTohoku University Graduate School of Biomedical EngineeringSendaiMiyagiJapan
- Department of Medicine and Science in Sports and ExerciseTohoku University Graduate School of MedicineSendaiMiyagiJapan
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Deckers PT, Bhogal AA, Dijsselhof MB, Faraco CC, Liu P, Lu H, Donahue MJ, Siero JC. Hemodynamic and metabolic changes during hypercapnia with normoxia and hyperoxia using pCASL and TRUST MRI in healthy adults. J Cereb Blood Flow Metab 2022; 42:861-875. [PMID: 34851757 PMCID: PMC9014679 DOI: 10.1177/0271678x211064572] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Blood oxygenation level-dependent (BOLD) or arterial spin labeling (ASL) MRI with hypercapnic stimuli allow for measuring cerebrovascular reactivity (CVR). Hypercapnic stimuli are also employed in calibrated BOLD functional MRI for quantifying neuronally-evoked changes in cerebral oxygen metabolism (CMRO2). It is often assumed that hypercapnic stimuli (with or without hyperoxia) are iso-metabolic; increasing arterial CO2 or O2 does not affect CMRO2. We evaluated the null hypothesis that two common hypercapnic stimuli, 'CO2 in air' and carbogen, are iso-metabolic. TRUST and ASL MRI were used to measure the cerebral venous oxygenation and cerebral blood flow (CBF), from which the oxygen extraction fraction (OEF) and CMRO2 were calculated for room-air, 'CO2 in air' and carbogen. As expected, CBF significantly increased (9.9% ± 9.3% and 12.1% ± 8.8% for 'CO2 in air' and carbogen, respectively). CMRO2 decreased for 'CO2 in air' (-13.4% ± 13.0%, p < 0.01) compared to room-air, while the CMRO2 during carbogen did not significantly change. Our findings indicate that 'CO2 in air' is not iso-metabolic, while carbogen appears to elicit a mixed effect; the CMRO2 reduction during hypercapnia is mitigated when including hyperoxia. These findings can be important for interpreting measurements using hypercapnic or hypercapnic-hyperoxic (carbogen) stimuli.
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Affiliation(s)
- Pieter T Deckers
- Department of Neurosurgery, University Medical Center Utrecht, Utrecht, Netherlands
| | - Alex A Bhogal
- Department of Radiology, Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands
| | - Mathijs Bj Dijsselhof
- Department of Radiology, Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands.,Department of Radiology and Nuclear Medicine, Amsterdam Neuroscience, Amsterdam UMC (location VUmc), Amsterdam, Netherlands
| | - Carlos C Faraco
- Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Peiying Liu
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Hanzhang Lu
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Manus J Donahue
- Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Jeroen Cw Siero
- Department of Radiology, Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands.,Spinoza Centre for Neuroimaging, Amsterdam, Netherlands
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12
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Turner MP, Zhao Y, Abdelkarim D, Liu P, Spence JS, Hutchison JL, Sivakolundu DK, Thomas BP, Hubbard NA, Xu C, Taneja K, Lu H, Rypma B. Altered linear coupling between stimulus-evoked blood flow and oxygen metabolism in the aging human brain. Cereb Cortex 2022; 33:135-151. [PMID: 35388407 PMCID: PMC9758587 DOI: 10.1093/cercor/bhac057] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Revised: 01/13/2022] [Accepted: 01/14/2022] [Indexed: 11/14/2022] Open
Abstract
Neural-vascular coupling (NVC) is the process by which oxygen and nutrients are delivered to metabolically active neurons by blood vessels. Murine models of NVC disruption have revealed its critical role in healthy neural function. We hypothesized that, in humans, aging exerts detrimental effects upon the integrity of the neural-glial-vascular system that underlies NVC. To test this hypothesis, calibrated functional magnetic resonance imaging (cfMRI) was used to characterize age-related changes in cerebral blood flow (CBF) and oxygen metabolism during visual cortex stimulation. Thirty-three younger and 27 older participants underwent cfMRI scanning during both an attention-controlled visual stimulation task and a hypercapnia paradigm used to calibrate the blood-oxygen-level-dependent signal. Measurement of stimulus-evoked blood flow and oxygen metabolism permitted calculation of the NVC ratio to assess the integrity of neural-vascular communication. Consistent with our hypothesis, we observed monotonic NVC ratio increases with increasing visual stimulation frequency in younger adults but not in older adults. Age-related changes in stimulus-evoked cerebrovascular and neurometabolic signal could not fully explain this disruption; increases in stimulus-evoked neurometabolic activity elicited corresponding increases in stimulus-evoked CBF in younger but not in older adults. These results implicate age-related, demand-dependent failures of the neural-glial-vascular structures that comprise the NVC system.
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Affiliation(s)
- Monroe P Turner
- School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX 75080, USA,Center for BrainHealth, University of Texas at Dallas, Dallas, TX, 75235, USA
| | - Yuguang Zhao
- School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX 75080, USA,Center for BrainHealth, University of Texas at Dallas, Dallas, TX, 75235, USA
| | - Dema Abdelkarim
- School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX 75080, USA,Center for BrainHealth, University of Texas at Dallas, Dallas, TX, 75235, USA
| | - Peiying Liu
- Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD 21287, USA
| | - Jeffrey S Spence
- School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX 75080, USA,Center for BrainHealth, University of Texas at Dallas, Dallas, TX, 75235, USA
| | - Joanna L Hutchison
- School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX 75080, USA,Center for BrainHealth, University of Texas at Dallas, Dallas, TX, 75235, USA
| | - Dinesh K Sivakolundu
- School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX 75080, USA,Department of Biological Sciences, University of Texas at Dallas, Richardson, TX, 75080, USA
| | - Binu P Thomas
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA
| | - Nicholas A Hubbard
- Department of Psychology, Center for Brain, Biology, and Behavior, University of Nebraska, Lincoln, NE 68588, USA
| | - Cuimei Xu
- Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD 21287, USA
| | - Kamil Taneja
- Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD 21287, USA
| | - Hanzhang Lu
- Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD 21287, USA
| | - Bart Rypma
- Corresponding author: School of Behavioral and Brain Sciences, Center for Brain Health, University of Texas at Dallas, 800 West Campbell Road, Richardson, TX 75080, USA.
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13
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Jelinčić V, Van Diest I, Torta DM, von Leupoldt A. The breathing brain: The potential of neural oscillations for the understanding of respiratory perception in health and disease. Psychophysiology 2021; 59:e13844. [PMID: 34009644 DOI: 10.1111/psyp.13844] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 04/21/2021] [Accepted: 04/23/2021] [Indexed: 11/30/2022]
Abstract
Dyspnea or breathlessness is a symptom occurring in multiple acute and chronic illnesses, however, the understanding of the neural mechanisms underlying its subjective experience is limited. In this topical review, we propose neural oscillatory dynamics and cross-frequency coupling as viable candidates for a neural mechanism underlying respiratory perception, and a technique warranting more attention in respiration research. With the evidence for the potential of neural oscillations in the study of normal and disordered breathing coming from disparate research fields with a limited history of interdisciplinary collaboration, the main objective of the review was to converge the existing research and suggest future directions. The existing findings show that distinct limbic and cortical activations, as measured by hemodynamic responses, underlie dyspnea, however, the time-scale of these activations is not well understood. The recent findings of oscillatory neural activity coupled with the respiratory rhythm could provide the solution to this problem, however, more research with a focus on dyspnea is needed. We also touch on the findings of distinct spectral patterns underlying the changes in breathing due to experimental manipulations, meditation and disease. Subsequently, we suggest general research directions and specific research designs to supplement the current knowledge using neural oscillation techniques. We argue for the benefits of interdisciplinary collaboration and the converging of neuroimaging and behavioral methods to best explain the emergence of the subjective and aversive individual experience of dyspnea.
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Affiliation(s)
- Valentina Jelinčić
- Research Group Health Psychology, Department of Psychology, KU Leuven, Leuven, Belgium
| | - Ilse Van Diest
- Research Group Health Psychology, Department of Psychology, KU Leuven, Leuven, Belgium
| | - Diana M Torta
- Research Group Health Psychology, Department of Psychology, KU Leuven, Leuven, Belgium
| | - Andreas von Leupoldt
- Research Group Health Psychology, Department of Psychology, KU Leuven, Leuven, Belgium
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14
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Morelli MS, Vanello N, Callara AL, Hartwig V, Maestri M, Bonanni E, Emdin M, Passino C, Giannoni A. Breath-hold task induces temporal heterogeneity in electroencephalographic regional field power in healthy subjects. J Appl Physiol (1985) 2021; 130:298-307. [PMID: 33300854 DOI: 10.1152/japplphysiol.00232.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We demonstrated that changes in CO2 values cause oscillations in the cortical activity in δ-and α-bands. The analysis of the regional field power (RFP) showed evidence that different cortical areas respond with different time delays to CO2 challenges. An opposite behavior was found for the end-tidal O2. We suppose that the different cortical time delays likely expresse specific ascending pathways to the cortex, generated by chemoreceptor nuclei in the brain stem. Although the brain stem is in charge of the automatic control of ventilation, the cortex is involved in the voluntary control of breathing but also receives inputs from the brain stem, which influences the perception of breathing, the arousal state and sleep architecture in conditions of hypoxia/hypercapnia. We evaluated in 11 healthy subjects the effects of breath hold (BH; 30 s of apneas and 30 s of normal breathing) and BH-related CO2/O2 changes on electroencephalogram (EEG) global field power (GFP) and RFP in nine different areas (3 rostrocaudal sections: anterior, central, and posterior; and 3 sagittal sections: left, middle, and right) in the δ- and α-bands by cross correlation analysis. No significant differences were observed in GFP or RFP when comparing free breathing (FB) with the BH task. Within the BH task, the shift from apnea to normal ventilation was accompanied by an increase in the δ-power and a decrease in the α-power. The end-tidal pressure of CO2 ([Formula: see text]) was positively correlated with the δ-band and negatively with the α- band with a positive time shift, whereas an opposite behavior was found for the end-tidal pressure of O2 ([Formula: see text]). Notably, the time shift between [Formula: see text] / [Formula: see text] signals and cortical activity at RFP was heterogenous and seemed to follow a hierarchical activation, with the δ-band responding earlier than the α-band. Overall, these findings suggest that the effect of BH on the cortex may follow specific ascending pathways from the brain stem and be related to chemoreflex stimulation.NEW & NOTEWORTHY We demonstrated that the end tidal CO2 oscillation causes oscillations of delta and alpha bands. The analysis of the regional field power showed that different cortical areas respond with different time delays to CO2 challenges. An opposite behavior was found for the end-tidal O2. We can suppose that the different cortical time delay response likely expresses specific ascending pathways to the cortex generated by chemoreceptor nuclei in the brainstem.
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Affiliation(s)
- Maria Sole Morelli
- Scuola Superiore Sant'Anna, Pisa, Italy.,Fondazione Toscana Gabriele Monasterio, Pisa, Italy
| | - Nicola Vanello
- Department of Information Engineering, University of Pisa, Pisa, Italy
| | | | - Valentina Hartwig
- Institute of Clinical Physiology, National Council of Research, Pisa, Italy
| | | | - Enrica Bonanni
- Departement of Neuroscience, University of Pisa, Pisa, Italy
| | - Michele Emdin
- Scuola Superiore Sant'Anna, Pisa, Italy.,Fondazione Toscana Gabriele Monasterio, Pisa, Italy
| | - Claudio Passino
- Scuola Superiore Sant'Anna, Pisa, Italy.,Fondazione Toscana Gabriele Monasterio, Pisa, Italy
| | - Alberto Giannoni
- Scuola Superiore Sant'Anna, Pisa, Italy.,Fondazione Toscana Gabriele Monasterio, Pisa, Italy
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15
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Presa JL, Saravia F, Bagi Z, Filosa JA. Vasculo-Neuronal Coupling and Neurovascular Coupling at the Neurovascular Unit: Impact of Hypertension. Front Physiol 2020; 11:584135. [PMID: 33101063 PMCID: PMC7546852 DOI: 10.3389/fphys.2020.584135] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Accepted: 09/04/2020] [Indexed: 12/18/2022] Open
Abstract
Components of the neurovascular unit (NVU) establish dynamic crosstalk that regulates cerebral blood flow and maintain brain homeostasis. Here, we describe accumulating evidence for cellular elements of the NVU contributing to critical physiological processes such as cerebral autoregulation, neurovascular coupling, and vasculo-neuronal coupling. We discuss how alterations in the cellular mechanisms governing NVU homeostasis can lead to pathological changes in which vascular endothelial and smooth muscle cell, pericyte and astrocyte function may play a key role. Because hypertension is a modifiable risk factor for stroke and accelerated cognitive decline in aging, we focus on hypertension-associated changes on cerebral arteriole function and structure, and the molecular mechanisms through which these may contribute to cognitive decline. We gather recent emerging evidence concerning cognitive loss in hypertension and the link with vascular dementia and Alzheimer’s disease. Collectively, we summarize how vascular dysfunction, chronic hypoperfusion, oxidative stress, and inflammatory processes can uncouple communication at the NVU impairing cerebral perfusion and contributing to neurodegeneration.
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Affiliation(s)
- Jessica L Presa
- Department of Physiology, Medical College of Georgia, Augusta University, Augusta, GA, United States.,Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Biología y Medicina Experimental, CONICET, Buenos Aires, Argentina
| | - Flavia Saravia
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Biología y Medicina Experimental, CONICET, Buenos Aires, Argentina
| | - Zsolt Bagi
- Department of Physiology, Medical College of Georgia, Augusta University, Augusta, GA, United States
| | - Jessica A Filosa
- Department of Physiology, Medical College of Georgia, Augusta University, Augusta, GA, United States
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16
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Kato T, Matsumoto T, Yamashiro SM. Effect of 3% CO2 inhalation on respiratory exchange ratio and cardiac output during constant work-rate exercise. J Sports Med Phys Fitness 2020; 61:175-182. [PMID: 32734753 DOI: 10.23736/s0022-4707.20.11012-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND The aim of this study was to examine whether the decrease in respiratory exchange ratio (RER) during constant work-rate exercise (CWE) with 3% carbon dioxide (CO<inf>2</inf>) inhalation could be caused by the combination of the decrease in CO<inf>2</inf> output (V̇CO<inf>2</inf>) and the increase in oxygen uptake (V̇O<inf>2</inf>). In addition, we investigated the effect of 3% CO<inf>2</inf> inhalation on cardiac output (Q̇) during CWE. METHODS Seven males (V̇O<inf>2max</inf>: 44.1±6.4 mL/min/kg) carried out transitions from low-load cycling (baseline; 40w) to light intensity exercise (45% V̇O<inf>2 max</inf>; 89.3±12.5 W) and heavy intensity exercise (80% V̇O<inf>2max</inf>; 186.5±20.2 W) while inhaling normal air (Air) or an enriched CO<inf>2</inf> gas (3% CO<inf>2</inf>, 21% O<inf>2</inf>, balance N<inf>2</inf>). Each exercise session was 6 min, and respiratory responses by Douglas bag technique and cardiac responses by thoracic bio-impedance method were measured during the experiment. RESULTS Ventilation for 3% CO<inf>2</inf> was higher than for air through the experiment (P<0.05). Steady and non-steady state RER and V̇CO<inf>2</inf> for 3% CO<inf>2</inf> were less than for air in both light and heavy intensities (P<0.05), but V̇O<inf>2</inf> and Q̇ did not differ between the two conditions. CONCLUSIONS 3% CO<inf>2</inf> inhalation induced the decrease in RER during CWE at light and heavy intensities, which was due to the decrease in V̇CO<inf>2</inf>. The promoted ventilation with 3% CO<inf>2</inf> did not lead to the increase in V̇O<inf>2</inf>. Moreover, 3% CO<inf>2</inf> inhalation did not affect Q̇ during CWE at light and heavy intensities.
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Affiliation(s)
- Takahide Kato
- Department of General Education, National Institute of Technology, Toyota College, Toyota, Japan -
| | - Takaaki Matsumoto
- Laboratory for Exercise Physiology and Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan
| | - Stanley M Yamashiro
- Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA, USA
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17
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Jiang D, Lin Z, Liu P, Sur S, Xu C, Hazel K, Pottanat G, Yasar S, Rosenberg P, Albert M, Lu H. Normal variations in brain oxygen extraction fraction are partly attributed to differences in end-tidal CO 2. J Cereb Blood Flow Metab 2020; 40:1492-1500. [PMID: 31382788 PMCID: PMC7308520 DOI: 10.1177/0271678x19867154] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Cerebral oxygen extraction fraction is an important physiological index of the brain's oxygen consumption and supply and has been suggested to be a potential biomarker for a number of diseases such as stroke, Alzheimer's disease, multiple sclerosis, sickle cell disease, and metabolic disorders. However, in order for oxygen extraction fraction to be a sensitive biomarker for personalized disease diagnosis, inter-subject variations in normal subjects must be minimized or accounted for, which will otherwise obscure its interpretation. Therefore, it is essential to investigate the physiological underpinnings of normal differences in oxygen extraction fraction. This work used two studies, one discovery study and one verification study, to examine the extent to which an individual's end-tidal CO2 can explain variations in oxygen extraction fraction. It was found that, across normal subjects, oxygen extraction fraction is inversely correlated with end-tidal CO2. Approximately 50% of the inter-subject variations in oxygen extraction fraction can be attributed to end-tidal CO2 differences. In addition, oxygen extraction fraction was found to be positively associated with age and systolic blood pressure. By accounting for end-tidal CO2, age, and systolic blood pressure of the subjects, normal variations in oxygen extraction fraction can be reduced by 73%, which is expected to substantially enhance the utility of oxygen extraction fraction as a disease biomarker.
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Affiliation(s)
- Dengrong Jiang
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Zixuan Lin
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Peiying Liu
- The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Sandeepa Sur
- The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Cuimei Xu
- The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Kaisha Hazel
- The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - George Pottanat
- The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Sevil Yasar
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Paul Rosenberg
- Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Marilyn Albert
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Hanzhang Lu
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,The Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, MD, USA
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18
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Burgraff NJ, Neumueller SE, Buchholz KJ, Hodges MR, Pan L, Forster HV. Midbrain and cerebral inflammatory and glutamatergic adaptations during chronic hypercapnia in goats. Brain Res 2019; 1724:146437. [PMID: 31494104 DOI: 10.1016/j.brainres.2019.146437] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 08/28/2019] [Accepted: 09/04/2019] [Indexed: 11/18/2022]
Abstract
Cognitive impairment is associated with multiple human diseases that have in common chronic hypercapnia. However, the mechanisms leading to chronic hypercapnia-induced cognitive decline are not known. We have previously shown chronic hypercapnia through exposure to increased inspired CO2 (6% InCO2) in conscious goats caused an immediate (within hours) and sustained decline in cognitive performance during a shape discrimination test. Herein, within the same goats, we assessed markers of neuroinflammation and glutamate receptor expression/phosphorylation within CNS regions important for cognitive function following 24 hours (h) or 30 days (d) of chronic hypercapnia. Within 24 h, chronic hypercapnia increased expression of the inflammatory cytokine IL-1β in the orbitofrontal cortex and medial prefrontal cortex, but at 30d IL-1β levels were not different relative to time-matched goats exposed to room-air. Additionally, Iba1 expression (a marker of microglial activation) was unaltered by chronic hypercapnia in all regions tested. Finally, levels of the total and phosphorylated AMPA receptor subunit GluR2 were reduced within the hippocampus at both 24 h and 30 d of hypercapnia, and reduced following 30 d within the anterior insular cortex. These data suggest that chronic hypercapnia leads to CNS site-dependent acute inflammatory responses and shifts in select glutamate receptor expression/phosphorylation in brain regions contributing to cognitive function. Such changes may be indicative of alterations in glutamatergic receptor-mediated signaling and neuronal dysfunction that contribute to declines in cognitive function associated with human diseases defined or marked by chronic CO2 retention.
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Affiliation(s)
- Nicholas J Burgraff
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - Suzanne E Neumueller
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - Kirstyn J Buchholz
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - Matthew R Hodges
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States; Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, WI 53226, United States
| | - Lawrence Pan
- Department of Physical Therapy, Marquette University, Milwaukee, WI 53226, United States
| | - Hubert V Forster
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, United States; Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, WI 53226, United States; Zablocki Veterans Affairs Medical Center, Milwaukee, WI 53226, United States.
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19
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Steinberg F, Doppelmayr M. Neurocognitive Markers During Prolonged Breath-Holding in Freedivers: An Event-Related EEG Study. Front Physiol 2019; 10:69. [PMID: 30792665 PMCID: PMC6374628 DOI: 10.3389/fphys.2019.00069] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Accepted: 01/21/2019] [Indexed: 01/16/2023] Open
Abstract
Since little is known concerning the psychological, cognitive, and neurophysiological factors that are involved in and important for phases of prolonged breath-holding (pBH) in freedivers, the present study uses electroencephalography (EEG) to investigate event-related neurocognitive markers during pBH of experienced freedivers that regularly train pBH. The purpose was to determine whether the well-known neurophysiological modulations elicited by hypoxic and hypercapnic conditions can also be detected during pBH induced hypoxic hypercapnia. Ten experienced free-divers (all male, aged 35.10 ± 7.89 years) were asked to hold their breath twice for 4 min per instance. During the first pBH, a checker board reversal task was presented and in the second four-min pBH phase a classical visual oddball paradigm was performed. A visual evoked potential (VEP) as an index of early visual processing (i.e., latencies and amplitudes of N75, P100, and N145) and the latency and amplitude of a P300 component (visual oddball paradigm) as an index of cognitive processing were investigated. In a counter-balanced cross-over design, all tasks were once performed during normal breathing (B), and once during pBH. All components were then compared between an early pBH (0–2 min) and a later pBH stage (2–4 min) and with the same time phases without pBH (i.e., during normal breathing). Statistical analyses using analyses of variance (ANOVA) revealed that comparisons between B and pBH yielded no significant changes either in the amplitude and latency of the VEP or in the P300. This indicates that neurocognitive markers, whether in an early visual processing stream or at a later cognitive processing stage, were not affected by pBH in experienced free-divers.
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Affiliation(s)
- Fabian Steinberg
- Department of Sport Psychology, Institute of Sport Science, Johannes Gutenberg-University Mainz, Mainz, Germany
| | - Michael Doppelmayr
- Department of Sport Psychology, Institute of Sport Science, Johannes Gutenberg-University Mainz, Mainz, Germany.,Centre of Cognitive Neuroscience, University of Salzburg, Salzburg, Austria
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20
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Holanda MA, Alves-de-Almeida M, Lima JW, Taunay TC, Gondim FA, P.R.Cavalcanti R, Mont’Alverne FJ, Sousa NDS, Oliveira MF, Pereira ED. Short-term effects of non-invasive ventilation on cerebral blood flow and cognitive function in COPD. Respir Physiol Neurobiol 2018; 258:53-59. [DOI: 10.1016/j.resp.2018.05.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Revised: 05/23/2018] [Accepted: 05/28/2018] [Indexed: 11/17/2022]
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21
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Hou X, Liu P, Gu H, Chan M, Li Y, Peng SL, Wig G, Yang Y, Park D, Lu H. Estimation of brain functional connectivity from hypercapnia BOLD MRI data: Validation in a lifespan cohort of 170 subjects. Neuroimage 2018; 186:455-463. [PMID: 30463025 DOI: 10.1016/j.neuroimage.2018.11.028] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Revised: 10/31/2018] [Accepted: 11/16/2018] [Indexed: 01/07/2023] Open
Abstract
Functional connectivity MRI, based on Blood-Oxygenation-Level-Dependent (BOLD) signals, is typically performed while the subject is at rest. On the other hand, BOLD is also widely used in physiological imaging such as cerebrovascular reactivity (CVR) mapping using hypercapnia (HC) as a modulator. We therefore hypothesize that hypercapnia BOLD data can be used to extract FC metrics after factoring out the effects of the physiological modulation, which will allow simultaneous assessment of neural and vascular function and may be particularly important in populations such as aging and cerebrovascular diseases. The present work aims to systematically examine the feasibility of hypercapnia BOLD-based FC mapping using three commonly applied analysis methods, specifically dual-regression Independent Component Analysis (ICA), region-based FC matrix analysis, and graph-theory based network analysis, in a large cohort of 170 healthy subjects ranging from 20 to 88 years old. To validate the hypercapnia BOLD results, we also compared these FC metrics with those obtained from conventional resting-state data. ICA analysis of the hypercapnia BOLD data revealed FC maps that strongly resembled those reported in the literature. FC matrix using region-based analysis showed a correlation of 0.97 on the group-level and 0.54 ± 0.10 on the individual-level, when comparing between hypercapnia and resting-state results. Although the correspondence on the individual-level was moderate, this was primarily attributed to variations intrinsic to FC mapping, because a corresponding resting-vs-resting comparison in a sub-cohort (N = 39) revealed a similar correlation of 0.57 ± 0.09. Graph-theory computations were also feasible in hypercapnia BOLD data and indices of global efficiency, clustering coefficient, modularity, and segregation were successfully derived. Hypercapnia FC results revealed age-dependent differences in which within-network connections generally exhibited an age-dependent decrease while between-network connections showed an age-dependent increase.
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Affiliation(s)
- Xirui Hou
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Peiying Liu
- The Russell H. Morgan Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA
| | - Hong Gu
- Neuroimaging Research Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA
| | - Micaela Chan
- Center for Vital Longevity, School of Behavioral and Brain Sciences, University of Texas at Dallas, Dallas, TX, USA
| | - Yang Li
- The Russell H. Morgan Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Graduate School of Biomedical Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Shin-Lei Peng
- The Russell H. Morgan Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung, Taiwan
| | - Gagan Wig
- Center for Vital Longevity, School of Behavioral and Brain Sciences, University of Texas at Dallas, Dallas, TX, USA; Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yihong Yang
- Neuroimaging Research Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA
| | - Denise Park
- Center for Vital Longevity, School of Behavioral and Brain Sciences, University of Texas at Dallas, Dallas, TX, USA; Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Hanzhang Lu
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA; The Russell H. Morgan Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA.
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22
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Analysis of generic coupling between EEG activity and P ETCO 2 in free breathing and breath-hold tasks using Maximal Information Coefficient (MIC). Sci Rep 2018. [PMID: 29540714 PMCID: PMC5851981 DOI: 10.1038/s41598-018-22573-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Brain activations related to the control of breathing are not completely known. The respiratory system is a non-linear system. However, the relationship between neural and respiratory dynamics is usually estimated through linear correlation measures, completely neglecting possible underlying nonlinear interactions. This study evaluate the linear and nonlinear coupling between electroencephalographic (EEG) signal and variations in carbon dioxide (CO2) signal related to different breathing task. During a free breathing and a voluntary breath hold tasks, the coupling between EEG power in nine different brain regions in delta (1–3 Hz) and alpha (8–13 Hz) bands and end-tidal CO2 (PET CO2) was evaluated. Specifically, the generic associations (i.e. linear and nonlinear correlations) and a “pure” nonlinear correlations were evaluated using the maximum information coefficient (MIC) and MIC-ρ2 between the two signals, respectively (where ρ2 represents the Pearson’s correlation coefficient). Our results show that in delta band, MIC indexes discriminate the two tasks in several regions, while in alpha band the same behaviour is observed for MIC-ρ2, suggesting a generic coupling between delta EEG power and PETCO2 and a pure nonlinear interaction between alpha EEG power and PETCO2. Moreover, higher indexes values were found for breath hold task respect to free breathing.
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23
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Bright MG, Croal PL, Blockley NP, Bulte DP. Multiparametric measurement of cerebral physiology using calibrated fMRI. Neuroimage 2017; 187:128-144. [PMID: 29277404 DOI: 10.1016/j.neuroimage.2017.12.049] [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: 10/03/2017] [Revised: 12/14/2017] [Accepted: 12/15/2017] [Indexed: 02/07/2023] Open
Abstract
The ultimate goal of calibrated fMRI is the quantitative imaging of oxygen metabolism (CMRO2), and this has been the focus of numerous methods and approaches. However, one underappreciated aspect of this quest is that in the drive to measure CMRO2, many other physiological parameters of interest are often acquired along the way. This can significantly increase the value of the dataset, providing greater information that is clinically relevant, or detail that can disambiguate the cause of signal variations. This can also be somewhat of a double-edged sword: calibrated fMRI experiments combine multiple parameters into a physiological model that requires multiple steps, thereby providing more opportunity for error propagation and increasing the noise and error of the final derived values. As with all measurements, there is a trade-off between imaging time, spatial resolution, coverage, and accuracy. In this review, we provide a brief overview of the benefits and pitfalls of extracting multiparametric measurements of cerebral physiology through calibrated fMRI experiments.
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Affiliation(s)
- Molly G Bright
- Sir Peter Mansfield Imaging Centre, School of Medicine, University of Nottingham, Nottingham, UK; Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Paula L Croal
- IBME, Department of Engineering Science, University of Oxford, Oxford, UK
| | - Nicholas P Blockley
- FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Daniel P Bulte
- IBME, Department of Engineering Science, University of Oxford, Oxford, UK; FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
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24
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Bain AR, Ainslie PN, Barak OF, Hoiland RL, Drvis I, Mijacika T, Bailey DM, Santoro A, DeMasi DK, Dujic Z, MacLeod DB. Hypercapnia is essential to reduce the cerebral oxidative metabolism during extreme apnea in humans. J Cereb Blood Flow Metab 2017; 37:3231-3242. [PMID: 28071964 PMCID: PMC5584699 DOI: 10.1177/0271678x16686093] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The cerebral metabolic rate of oxygen (CMRO2) is reduced during apnea that yields profound hypoxia and hypercapnia. In this study, to dissociate the impact of hypoxia and hypercapnia on the reduction in CMRO2, 11 breath-hold competitors completed three apneas under: (a) normal conditions (NM), yielding severe hypercapnia and hypoxemia, (b) with prior hyperventilation (HV), yielding severe hypoxemia only, and (c) with prior 100% oxygen breathing (HX), yielding the greatest level of hypercapnia, but in the absence of hypoxemia. The CMRO2 was calculated from the product of cerebral blood flow (ultrasound) and the radial artery-jugular venous oxygen content difference (cannulation). Secondary measures included net-cerebral glucose/lactate exchange and nonoxidative metabolism. Reductions in CMRO2 were largest in the HX condition (-44 ± 15%, p < 0.05), with the most severe hypercapnia (PaCO2 = 58 ± 5 mmHg) but maintained oxygen saturation. The CMRO2 was reduced by 24 ± 27% in NM ( p = 0.05), but unchanged in the HV apnea where hypercapnia was absent. A net-cerebral lactate release was observed at the end of apnea in the HV and NM condition, but not in the HX apnea (main effect p < 0.05). These novel data support hypercapnia/pH as a key mechanism mediating reductions in CMRO2 during apnea, and show that severe hypoxemia stimulates lactate release from the brain.
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Affiliation(s)
- Anthony R Bain
- 1 Centre for Heart Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada
| | - Philip N Ainslie
- 1 Centre for Heart Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada
| | - Otto F Barak
- 2 School of Medicine, University of Split, Split, Croatia
| | | | - Ivan Drvis
- 4 School of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - Tanja Mijacika
- 2 School of Medicine, University of Split, Split, Croatia
| | - Damian M Bailey
- 5 Faculty of Life Sciences and Education, University of South Wales, Glamorgan, UK
| | | | | | - Zeljko Dujic
- 2 School of Medicine, University of Split, Split, Croatia
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25
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Hoedemaekers CW, Ainslie PN, Hinssen S, Aries MJ, Bisschops LL, Hofmeijer J, van der Hoeven JG. Low cerebral blood flow after cardiac arrest is not associated with anaerobic cerebral metabolism. Resuscitation 2017; 120:45-50. [PMID: 28844934 DOI: 10.1016/j.resuscitation.2017.08.218] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Revised: 08/10/2017] [Accepted: 08/20/2017] [Indexed: 12/21/2022]
Abstract
AIM OF THE STUDY Estimation of cerebral anaerobic metabolism in survivors and non-survivors after cardiac arrest. METHODS We performed an observational study in twenty comatose patients after cardiac arrest and 19 healthy control subjects. We measured mean flow velocity in the middle cerebral artery (MFVMCA) by transcranial Doppler. Arterial and jugular blood samples were used for calculation of the jugular venous-to-arterial CO2/arterial to-jugular venous O2 content difference ratio. RESULTS After cardiac arrest, MFVMCA increased from 26.0[18.6-40.4]cm/sec on admission to 63.9[48.3-73.1]cm/sec after 72h (p<0.0001), with no significant differences between survivors and non-survivors (p=0.4853). The MFVMCA in controls was 59.1[52.8-69.0]cm/sec. The oxygen extraction fraction (O2EF) was 38.9[24.4-47.7]% on admission and decreased significantly to 17.3[12.1-26.2]% at 72h (p<0.0001). The decrease in O2EF was more pronounced in non-survivors (p=0.0173). O2EF in the control group was 35.4[32.4-38.7]%. The jugular bulb-arterial CO2 to arterial-jugular bulb O2 content difference ratio was >1 at all time points after cardiac arrest and did not change during admission, with no differences between survivors and non-survivors. Values in cardiac arrest patients were similar to those in normal subjects. CONCLUSIONS In this study, low CBF after cardiac arrest is not associated with anaerobic metabolism. Hypoperfusion appears to be the consequence of a decrease of neuronal functioning and metabolic needs. Alternatively, hypoperfusion may decrease cerebral metabolism. Subsequently, metabolism increases in survivors, consistent with resumption of neuronal activity, whereas in non-survivors lasting low metabolism reflects irreversible neuronal damage.
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Affiliation(s)
- Cornelia W Hoedemaekers
- Department of Intensive Care Medicine, Radboud University Medical Center, Nijmegen, The Netherlands.
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia, British Columbia, Canada
| | - Stijn Hinssen
- Department of Neurology, Rijnstate Hospital, Arnhem and department of Clinical Neurophysiology, University of Twente, Enschede, The Netherlands
| | - Marcel J Aries
- Department of Intensive Care, University of Maastricht, Maastricht University Medical Center, Maastricht, The Netherlands
| | - Laurens L Bisschops
- Department of Intensive Care Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Jeannette Hofmeijer
- Department of Neurology, Rijnstate Hospital, Arnhem and department of Clinical Neurophysiology, University of Twente, Enschede, The Netherlands
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26
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Nakamura S, Walker DW, Wong FY. Cerebral haemodynamic response to somatosensory stimulation in neonatal lambs. J Physiol 2017. [PMID: 28643877 DOI: 10.1113/jp274244] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Cerebral haemodynamic response to neural stimulation has been extensively studied in adults, but little is known about cerebral haemodynamic response in the fetal and neonatal brain. The present study describes the cerebral haemodynamic response measured by near infrared spectroscopy to somatosensory stimulation in newborn lambs, in comparison to recent findings in fetal sheep. The cerebral haemodynamic responses in the newborn lamb brain can involve an increase in oxyhaemoglobin (oxyHb), or a decrease of oxyHb suggestive of reduced perfusion and oxygenation. Positive correlations between changes in oxyHb and mean arterial blood pressure were found in newborn but not fetal sheep, which suggests the result is unlikely to be due to immature autoregulation alone. In contrast to adult studies, hypercapnia increased the changes in cerebral blood flow and oxyHb in most of the lambs in response to somatosensory stimulation. ABSTRACT The neurovascular coupling response has been defined for the adult brain, but in the neonate non-invasive measurement of local cerebral perfusion using near infrared spectroscopy or blood oxygen level-dependent functional magnetic resonance imaging have yielded variable and inconsistent results, including negative responses suggesting decreased perfusion and localized tissue tissue hypoxia. Also, the impact of permissive hypercapnia (P aC O2 > 50 mmHg) in the management of neonates on cerebrovascular responses to somatosensory input is unknown. Using near infrared spectroscopy to measure changes in cerebral oxy- and deoxyhaemoglobin (ΔoxyHb, ΔdeoxyHb) in eight anaesthetized newborn lambs, we studied the cerebral haemodynamic functional response to left median nerve stimulation using stimulus trains of 1.8, 4.8 and 7.8 s. Stimulation always produced a somatosensory evoked response, and superficial cortical perfusion measured by laser Doppler flowmetry predominantly increased following median nerve stimulation. However, with 1.8 s stimulation, oxyHb responses in the contralateral hemisphere were either positive (i.e. increased oxyHb), negative, or absent; and with 4.8 and 7.8 s stimulations, both positive and negative responses were observed. Hypercapnia increased baseline oxyHb and total Hb consistent with cerebral vasodilatation, and six of seven lambs tested showed increased Δtotal Hb responses after the 7.8 s stimulation, among which four lambs also showed increased ΔoxyHb responses. In two of three lambs, the negative ΔoxyHb response became a positive pattern during hypercapnia. These results show that instead of functional hyperaemia, somatosensory stimulation can evoke negative (decreased oxyHb, total Hb) functional responses in the neonatal brain suggestive of decreased local perfusion and vasoconstriction, and that hypercapnia produces both baseline hyperperfusion and increased functional hyperaemia.
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Affiliation(s)
- Shinji Nakamura
- Department of Pediatrics, Faculty of Medicine, Kagawa University, Kagawa, Japan.,The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Melbourne, Victoria, 3168, Australia
| | - David W Walker
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Melbourne, Victoria, 3168, Australia.,School of Health & Biomedical Sciences, RMIT University, Bundoora, Melbourne, Victoria, 3083, Australia
| | - Flora Y Wong
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Melbourne, Victoria, 3168, Australia.,Department of Paediatrics, Monash University, Clayton, Melbourne, Victoria, 3168, Australia.,Monash Newborn, Monash Medical Centre, Clayton, Melbourne, Victoria, 3168, Australia
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27
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Arterial CO2 Fluctuations Modulate Neuronal Rhythmicity: Implications for MEG and fMRI Studies of Resting-State Networks. J Neurosci 2017; 36:8541-50. [PMID: 27535903 PMCID: PMC4987431 DOI: 10.1523/jneurosci.4263-15.2016] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Accepted: 06/09/2016] [Indexed: 01/25/2023] Open
Abstract
A fast emerging technique for studying human resting state networks (RSNs) is based on spontaneous temporal fluctuations in neuronal oscillatory power, as measured by magnetoencephalography. However, it has been demonstrated recently that this power is sensitive to modulations in arterial CO2 concentration. Arterial CO2 can be modulated by natural fluctuations in breathing pattern, as might typically occur during the acquisition of an RSN experiment. Here, we demonstrate for the first time the fine-scale dependence of neuronal oscillatory power on arterial CO2 concentration, showing that reductions in alpha, beta, and gamma power are observed with even very mild levels of hypercapnia (increased arterial CO2). We use a graded hypercapnia paradigm and participant feedback to rule out a sensory cause, suggesting a predominantly physiological origin. Furthermore, we demonstrate that natural fluctuations in arterial CO2, without administration of inspired CO2, are of a sufficient level to influence neuronal oscillatory power significantly in the delta-, alpha-, beta-, and gamma-frequency bands. A more thorough understanding of the relationship between physiological factors and cortical rhythmicity is required. In light of these findings, existing results, paradigms, and analysis techniques for the study of resting-state brain data should be revisited. SIGNIFICANCE STATEMENT In this study, we show for the first time that neuronal oscillatory power is intimately linked to arterial CO2 concentration down to the fine-scale modulations that occur during spontaneous breathing. We extend these results to demonstrate a correlation between neuronal oscillatory power and spontaneous arterial CO2 fluctuations in awake humans at rest. This work identifies a need for studies investigating resting-state networks in the human brain to measure and account for the impact of spontaneous changes in arterial CO2 on the neuronal signals of interest. Changes in breathing pattern that are time locked to task performance could also lead to confounding effects on neuronal oscillatory power when considering the electrophysiological response to functional stimulation.
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28
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Peng SL, Ravi H, Sheng M, Thomas BP, Lu H. Searching for a truly "iso-metabolic" gas challenge in physiological MRI. J Cereb Blood Flow Metab 2017; 37:715-725. [PMID: 26980756 PMCID: PMC5381460 DOI: 10.1177/0271678x16638103] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/16/2015] [Revised: 01/14/2016] [Accepted: 01/25/2016] [Indexed: 11/16/2022]
Abstract
Hypercapnia challenge (e.g. inhalation of CO2) has been used in calibrated fMRI as well as in the mapping of vascular reactivity in cerebrovascular diseases. An important assumption underlying these measurements is that CO2 is a pure vascular challenge but does not alter neural activity. However, recent reports have suggested that CO2 inhalation may suppress neural activity and brain metabolic rate. Therefore, the goal of this study is to propose and test a gas challenge that is truly "iso-metabolic," by adding a hypoxic component to the hypercapnic challenge, since hypoxia has been shown to enhance cerebral metabolic rate of oxygen (CMRO2). Measurement of global CMRO2 under various gas challenge conditions revealed that, while hypercapnia (P = 0.002) and hypoxia (P = 0.002) individually altered CMRO2 (by -7.6 ± 1.7% and 16.7 ± 4.1%, respectively), inhalation of hypercapnic-hypoxia gas (5% CO2/13% O2) did not change brain metabolism (CMRO2 change: 1.5 ± 3.9%, P = 0.92). Moreover, cerebral blood flow response to the hypercapnic-hypoxia challenge (in terms of % change per mmHg CO2 change) was even greater than that to hypercapnia alone (P = 0.007). Findings in this study suggest that hypercapnic-hypoxia gas challenge may be a useful maneuver in physiological MRI as it preserves vasodilatory response yet does not alter brain metabolism.
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Affiliation(s)
- Shin-Lei Peng
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, USA
- Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, USA
- Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung, Taiwan
| | - Harshan Ravi
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, USA
- Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, USA
- Department of Bioengineering, UT Arlington, Arlington, USA
| | - Min Sheng
- Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, USA
| | - Binu P Thomas
- Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, USA
| | - Hanzhang Lu
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, USA
- Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, USA
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29
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Nakamura S, Walker DW, Wong FY. Cerebral haemodynamic response to somatosensory stimulation in near-term fetal sheep. J Physiol 2016; 595:1289-1303. [PMID: 27805787 DOI: 10.1113/jp273163] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 10/20/2016] [Indexed: 01/03/2023] Open
Abstract
KEY POINTS Cerebral haemodynamic response to neural stimulation has been extensively investigated in animal and clinical studies, in both adult and paediatric populations, but little is known about cerebral haemodynamic functional response in the fetal brain. The present study describes the cerebral haemodynamic response measured by near-infrared spectroscopy to somatosensory stimulation in fetal sheep. The cerebral haemodynamic response in the fetal sheep brain changes from a positive (increase in oxyhaemoglobin (oxyHb)) response pattern to a negative or biphasic response pattern when the duration of somatosensory stimulation is increased, probably due to cerebral vasoconstriction with prolonged stimulations. In contrast to adult studies, we have found that changes in fetal cerebral blood flow and oxyHb are positively increased in response to somatosensory stimulation during hypercapnia. We propose this is related to reduced vascular resistance and recruitment of cerebral vasculature in the fetal brain during hypercapnia. ABSTRACT Functional hyperaemia induced by a localised increase in neuronal activity has been suggested to occur in the fetal brain owing to a positive blood oxygen level-dependent (BOLD) signal recorded by functional magnetic resonance imaging following acoustic stimulation. To study the effect of somatosensory input on local cerebral perfusion we used near-infrared spectroscopy (NIRS) in anaesthetised, partially exteriorised fetal sheep where the median nerve was stimulated with trains of pulses (2 ms, 3.3 Hz) for durations of 1.8, 4.8 and 7.8 s. Signal averaging of cerebral NIRS responses to 20 stimulus trains repeated every 60 s revealed that a short duration of stimulation (1.8 s) increased oxyhaemoglobin in the contralateral cortex consistent with a positive functional response, whereas longer durations of stimulation (4.8, 7.8 s) produced more variable oxyhaemoglobin responses including positive, negative and biphasic patterns of change. Mean arterial blood pressure and cerebral perfusion as monitored by laser Doppler flowmetry always showed small, but coincident increases following median nerve stimulation regardless of the type of response detected by the NIRS in the contralateral cortex. Hypercapnia significantly increased the baseline total haemoglobin and deoxyhaemoglobin, and in 7 of 8 fetal sheep positively increased the changes in contralateral total haemoglobin and oxyhaemoglobin in response to the 7.8 s stimulus train, compared to the response recorded during normocapnia. These results show that activity-driven changes in cerebral perfusion and oxygen delivery are present in the fetal brain, and persist even during periods of hypercapnia-induced cerebral vasodilatation.
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Affiliation(s)
- S Nakamura
- Department of Pediatrics, Faculty of Medicine, Kagawa University, Kagawa, Japan.,The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Melbourne, Victoria, 3168, Australia
| | - D W Walker
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Melbourne, Victoria, 3168, Australia.,Department of Obstetrics and Gynaecology, Monash University, Clayton, Melbourne, Victoria, 3168, Australia
| | - F Y Wong
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Melbourne, Victoria, 3168, Australia.,Department of Paediatrics, Monash University, Clayton, Melbourne, Victoria, 3168, Australia.,Monash Newborn, Monash Medical Centre, Clayton, Melbourne, Victoria, 3168, Australia
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30
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Morelli MS, Valenza G, Greco A, Giannoni A, Passino C, Emdin M, Scilingo EP, Vanello N. Exploratory analysis of nonlinear coupling between EEG global field power and end-tidal carbon dioxide in free breathing and breath-hold tasks. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2016:728-731. [PMID: 28268431 DOI: 10.1109/embc.2016.7590805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Brain activations underlying control of breathing are not completely known. Furthermore, the coupling between neural and respiratory dynamics is usually estimated through linear correlation measures, thus totally disregarding possible underlying nonlinear interactions. To overcome these limitations, in this preliminary study we propose a nonlinear coupling analysis of simultaneous recordings of electroencephalographic (EEG) and respiratory signals at rest and after variation of carbon dioxide (CO2) level. Specifically, a CO2 increase was induced by a voluntary breath hold task. EEG global field power (GFP) in different frequency bands and end-tidal CO2 (PETCO2) were estimated in both conditions. The maximum information coefficient (MIC) and MIC-ρ2 (where ρ represents the Pearson's correlation coefficient) between the two signals were calculated to identify generic associations (i.e. linear and nonlinear correlations) and nonlinear correlations, respectively. With respect to a free breathing state, our results suggest that a breath hold state is characterized by an increased coupling between respiration activity and specific EEG oscillations, mainly involving linear and nonlinear interactions in the delta band (1-4 Hz), and prevalent nonlinear interactions in the alpha band (8-13 Hz).
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31
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Bain AR, Ainslie PN, Hoiland RL, Barak OF, Cavar M, Drvis I, Stembridge M, MacLeod DM, Bailey DM, Dujic Z, MacLeod DB. Cerebral oxidative metabolism is decreased with extreme apnoea in humans; impact of hypercapnia. J Physiol 2016; 594:5317-28. [PMID: 27256521 DOI: 10.1113/jp272404] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Accepted: 05/18/2016] [Indexed: 12/25/2022] Open
Abstract
KEY POINTS The present study describes the cerebral oxidative and non-oxidative metabolism in man during a prolonged apnoea (ranging from 3 min 36 s to 7 min 26 s) that generates extremely low levels of blood oxygen and high levels of carbon dioxide. The cerebral oxidative metabolism, measured from the product of cerebral blood flow and the radial artery-jugular venous oxygen content difference, was reduced by ∼29% at the termination of apnoea, although there was no change in the non-oxidative metabolism. A subset study with mild and severe hypercapnic breathing at the same level of hypoxia suggests that hypercapnia can partly explain the cerebral metabolic reduction near the apnoea breakpoint. A hypercapnia-induced oxygen-conserving response may protect the brain against severe oxygen deprivation associated with prolonged apnoea. ABSTRACT Prolonged apnoea in humans is reflected in progressive hypoxaemia and hypercapnia. In the present study, we explore the cerebral metabolic responses under extreme hypoxia and hypercapnia associated with prolonged apnoea. We hypothesized that the cerebral metabolic rate for oxygen (CMRO2 ) will be reduced near the termination of apnoea, attributed in part to the hypercapnia. Fourteen elite apnoea-divers performed a maximal apnoea (range 3 min 36 s to 7 min 26 s) under dry laboratory conditions. In a subset study with the same divers, the impact of hypercapnia on cerebral metabolism was determined using varying levels of hypercapnic breathing, against the background of similar hypoxia. In both studies, the CMRO2 was calculated from the product of cerebral blood flow (ultrasound) and the radial artery-internal jugular venous oxygen content difference. Non-oxidative cerebral metabolism was calculated from the ratio of oxygen and carbohydrate (lactate and glucose) metabolism. The CMRO2 was reduced by ∼29% (P < 0.01, Cohen's d = 1.18) near the termination of apnoea compared to baseline, although non-oxidative metabolism remained unaltered. In the subset study, in similar backgrounds of hypoxia (arterial O2 tension: ∼38.4 mmHg), severe hypercapnia (arterial CO2 tension: ∼58.7 mmHg), but not mild-hypercapnia (arterial CO2 tension: ∼46.3 mmHg), depressed the CMRO2 (∼17%, P = 0.04, Cohen's d = 0.87). Similarly to the apnoea, there was no change in the non-oxidative metabolism. These data indicate that hypercapnia can partly explain the reduction in CMRO2 near the apnoea breakpoint. This hypercapnic-induced oxygen conservation may protect the brain against severe hypoxaemia associated with prolonged apnoea.
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Affiliation(s)
- Anthony R Bain
- Centre for Heart Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada. ,
| | - Philip N Ainslie
- Centre for Heart Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada
| | - Ryan L Hoiland
- 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, Serbia
| | - Marija Cavar
- School of Medicine, University of Split, Split, Croatia
| | - Ivan Drvis
- School of Kinesiology, University of Zagreb, Zagreb, Croatia
| | | | | | - Damian M Bailey
- Faculty of Life Sciences and Education, University of South Wales, Glamorgan, UK
| | - Zeljko Dujic
- School of Medicine, University of Split, Split, Croatia
| | - David B MacLeod
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
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32
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Wang D, Thomas RJ, Yee BJ, Grunstein RR. Hypercapnia is more important than hypoxia in the neuro-outcomes of sleep-disordered breathing. J Appl Physiol (1985) 2016; 120:1484. [DOI: 10.1152/japplphysiol.01008.2015] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- David Wang
- Sleep & Circadian Group, Woolcock Institute of Medical Research, The University of Sydney, Australia
- Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney Local Health District, Sydney, Australia
- NHMRC Centre of Research Excellence in Sleep Medicine-NeuroSleep, Woolcock Institute of Medical Research, The University of Sydney, Australia
- Central Clinical School, The University of Sydney, Sydney, Australia; and
| | - Robert J. Thomas
- Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts
| | - Brendon J. Yee
- Sleep & Circadian Group, Woolcock Institute of Medical Research, The University of Sydney, Australia
- Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney Local Health District, Sydney, Australia
- NHMRC Centre of Research Excellence in Sleep Medicine-NeuroSleep, Woolcock Institute of Medical Research, The University of Sydney, Australia
- Central Clinical School, The University of Sydney, Sydney, Australia; and
| | - Ronald R. Grunstein
- Sleep & Circadian Group, Woolcock Institute of Medical Research, The University of Sydney, Australia
- Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney Local Health District, Sydney, Australia
- NHMRC Centre of Research Excellence in Sleep Medicine-NeuroSleep, Woolcock Institute of Medical Research, The University of Sydney, Australia
- Central Clinical School, The University of Sydney, Sydney, Australia; and
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33
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Shu CY, Sanganahalli BG, Coman D, Herman P, Hyder F. New horizons in neurometabolic and neurovascular coupling from calibrated fMRI. PROGRESS IN BRAIN RESEARCH 2016; 225:99-122. [PMID: 27130413 DOI: 10.1016/bs.pbr.2016.02.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Neurovascular coupling relates changes in neuronal activity to constriction/dilation of microvessels. However neurometabolic coupling, which is less well known, relates alterations in neuronal activity with metabolic demands. The link between the blood oxygenation level dependent (BOLD) signal and neural activity opened doors for functional MRI (fMRI) to be a powerful neuroimaging tool in the neurosciences. But due to the complex makeup of BOLD contrast, researchers began to investigate the relationship between BOLD signal and blood flow and/or volume changes during functional brain activation, which together provided the tools to measure oxygen consumption on the basis of the biophysical model of BOLD. This field is called calibrated fMRI, thereby allowed probing of both neurometabolic and neurovascular couplings for a variety of health conditions in animals and humans. Calibrated fMRI may provide brain disorder biomarkers that could be used for monitoring effective therapies.
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Affiliation(s)
- C Y Shu
- Yale University, New Haven, CT, United States
| | - B G Sanganahalli
- Yale University, New Haven, CT, United States; Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, United States
| | - D Coman
- Yale University, New Haven, CT, United States; Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, United States
| | - P Herman
- Yale University, New Haven, CT, United States; Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, United States
| | - F Hyder
- Yale University, New Haven, CT, United States; Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, United States.
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Golestani AM, Kwinta JB, Strother SC, Khatamian YB, Chen JJ. The association between cerebrovascular reactivity and resting-state fMRI functional connectivity in healthy adults: The influence of basal carbon dioxide. Neuroimage 2016; 132:301-313. [PMID: 26908321 DOI: 10.1016/j.neuroimage.2016.02.051] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Revised: 12/23/2015] [Accepted: 02/15/2016] [Indexed: 12/28/2022] Open
Abstract
Although widely used in resting-state fMRI (fMRI) functional connectivity measurement (fcMRI), the BOLD signal is only an indirect measure of neuronal activity, and is inherently modulated by both neuronal activity and vascular physiology. For instance, cerebrovascular reactivity (CVR) varies widely across individuals irrespective of neuronal function, but the implications for fcMRI are currently unknown. This knowledge gap compromises our ability to correctly interpret fcMRI measurements. In this work, we investigate the relationship between CVR and resting fcMRI measurements in healthy young adults, in both the motor and the executive-control networks. We modulate CVR within each individual by subtly increasing and decreasing resting vascular tension through baseline end-tidal CO2 (PETCO2), and measure fcMRI during these hypercapnic, hypocapnic and normocapnic states. Furthermore, we assess the association between CVR and fcMRI within and across individuals. Within individuals, resting PETCO2 is found to significantly influence both CVR and resting fcMRI values. In addition, we find resting fcMRI to be significantly and positively associated with CVR across the group in both networks. This relationship is potentially mediated by concomitant alterations in BOLD signal fluctuation amplitude. This work clearly demonstrates and quantifies a major vascular modulator of resting fcMRI, one that is also subject and regional dependent. We suggest that individualized correction for CVR effects in fcMRI measurements is essential for fcMRI studies of healthy brains, and can be even more important in studying diseased brains.
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Affiliation(s)
| | - Jonathan B Kwinta
- Rotman Research Institute at Baycrest Centre, Canada; Department of Medical Biophysics, University of Toronto, Canada
| | - Stephen C Strother
- Rotman Research Institute at Baycrest Centre, Canada; Department of Medical Biophysics, University of Toronto, Canada
| | | | - J Jean Chen
- Rotman Research Institute at Baycrest Centre, Canada; Department of Medical Biophysics, University of Toronto, Canada.
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Whittaker JR, Driver ID, Bright MG, Murphy K. The absolute CBF response to activation is preserved during elevated perfusion: Implications for neurovascular coupling measures. Neuroimage 2016; 125:198-207. [PMID: 26477657 PMCID: PMC4692513 DOI: 10.1016/j.neuroimage.2015.10.023] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Revised: 10/06/2015] [Accepted: 10/08/2015] [Indexed: 12/31/2022] Open
Abstract
Functional magnetic resonance imaging (fMRI) techniques in which the blood oxygenation level dependent (BOLD) and cerebral blood flow (CBF) response to a neural stimulus are measured, can be used to estimate the fractional increase in the cerebral metabolic rate of oxygen consumption (CMRO2) that accompanies evoked neural activity. A measure of neurovascular coupling is obtained from the ratio of fractional CBF and CMRO2 responses, defined as n, with the implicit assumption that relative rather than absolute changes in CBF and CMRO2 adequately characterise the flow-metabolism response to neural activity. The coupling parameter n is important in terms of its effect on the BOLD response, and as potential insight into the flow-metabolism relationship in both normal and pathological brain function. In 10 healthy human subjects, BOLD and CBF responses were measured to test the effect of baseline perfusion (modulated by a hypercapnia challenge) on the coupling parameter n during graded visual stimulation. A dual-echo pulsed arterial spin labelling (PASL) sequence provided absolute quantification of CBF in baseline and active states as well as relative BOLD signal changes, which were used to estimate CMRO2 responses to the graded visual stimulus. The absolute CBF response to the visual stimuli were constant across different baseline CBF levels, meaning the fractional CBF responses were reduced at the hyperperfused baseline state. For the graded visual stimuli, values of n were significantly reduced during hypercapnia induced hyperperfusion. Assuming the evoked neural responses to the visual stimuli are the same for both baseline CBF states, this result has implications for fMRI studies that aim to measure neurovascular coupling using relative changes in CBF. The coupling parameter n is sensitive to baseline CBF, which would confound its interpretation in fMRI studies where there may be significant differences in baseline perfusion between groups. The absolute change in CBF, as opposed to the change relative to baseline, may more closely match the underlying increase in neural activity in response to a stimulus.
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Affiliation(s)
- Joseph R Whittaker
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, CF10 3AT Cardiff, UK
| | - Ian D Driver
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, CF10 3AT Cardiff, UK
| | - Molly G Bright
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, CF10 3AT Cardiff, UK; Sir Peter Mansfield Imaging Centre, Clinical Neurology, School of Medicine, University of Nottingham, Nottingham, UK
| | - Kevin Murphy
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, CF10 3AT Cardiff, UK.
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36
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Morelli MS, Vanello N, Giannoni A, Frijia F, Hartwig V, Maestri M, Bonanni E, Carnicelli L, Positano V, Passino C, Emdin M, Landini L. Correlational analysis of electroencephalographic and end-tidal carbon dioxide signals during breath-hold exercise. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2015:6102-5. [PMID: 26737684 DOI: 10.1109/embc.2015.7319784] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The central mechanism of breathing control is not totally understood. Several studies evaluated the correlation between electroencephalographic (EEG) power spectra and respiratory signals by performing resting state tasks or adopting hypercapnic/hypoxic stimuli. The observation of brain activity during voluntary breath hold tasks, might be an useful approach to highlight the areas involved in mechanism of breath regulation. Nevertheless, studies of brain activity with EEG could present some limitations due to presence of severe artifacts. When artifact rejection methods, as independent component analysis, cannot reliably clean EEG data, it is necessary to exclude noisy segments. In this study, global field power in the delta band and end-tidal CO2 were derived from EEG and CO2 signals respectively in 4 healthy subjects during a breath-hold task. The cross correlation function between the two signals was estimated taking into account the presence of missing samples. The statistical significance of the correlation coefficients at different time lags was assessed using surrogate data. Some simulations are introduced to evaluate the effect of missing data on the correlational analysis and their results are discussed. Results obtained on subjects show a significant correlation between changes in EEG power in the delta band and end-tidal CO2. Moreover, the changes in end-tidal CO2 were found to precede those of global field power. These results might help to better understand the cortical mechanisms involved in the control of breathing.
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37
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Shu CY, Herman P, Coman D, Sanganahalli BG, Wang H, Juchem C, Rothman DL, de Graaf RA, Hyder F. Brain region and activity-dependent properties of M for calibrated fMRI. Neuroimage 2015; 125:848-856. [PMID: 26529646 DOI: 10.1016/j.neuroimage.2015.10.083] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Revised: 10/28/2015] [Accepted: 10/30/2015] [Indexed: 11/28/2022] Open
Abstract
Calibrated fMRI extracts changes in oxidative energy demanded by neural activity based on hemodynamic and metabolic dependencies of the blood oxygenation level-dependent (BOLD) response. This procedure requires the parameter M, which is determined from the dynamic range of the BOLD signal between deoxyhemoglobin (paramagnetic) and oxyhemoglobin (diamagnetic). Since it is unclear if the range of M-values in human calibrated fMRI is due to regional/state differences, we conducted a 9.4T study to measure M-values across brain regions in deep (α-chloralose) and light (medetomidine) anesthetized rats, as verified by electrophysiology. Because BOLD signal is captured differentially by gradient-echo (R2*) and spin-echo (R2) relaxation rates, we measured M-values by the product of the fMRI echo time and R2' (i.e., the reversible magnetic susceptibility component), which is given by the absolute difference between R2* and R2. While R2' mapping was shown to be dependent on the k-space sampling method used, at nominal spatial resolutions achieved at high magnetic field of 9.4T the M-values were quite homogenous across cortical gray matter. However cortical M-values varied in relation to neural activity between brain states. The findings from this study could improve precision of future calibrated fMRI studies by focusing on the global uniformity of M-values in gray matter across different resting activity levels.
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Affiliation(s)
- Christina Y Shu
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA.
| | - Peter Herman
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Daniel Coman
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Basavaraju G Sanganahalli
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Helen Wang
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Christoph Juchem
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA; Department of Neurology, Yale University, New Haven, CT, USA
| | - Douglas L Rothman
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Robin A de Graaf
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Fahmeed Hyder
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA.
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38
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Nasrallah FA, Yeow LY, Biswal B, Chuang KH. Dependence of BOLD signal fluctuation on arterial blood CO2 and O2: Implication for resting-state functional connectivity. Neuroimage 2015; 117:29-39. [PMID: 26003858 DOI: 10.1016/j.neuroimage.2015.05.035] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Revised: 03/22/2015] [Accepted: 05/13/2015] [Indexed: 11/16/2022] Open
Abstract
Blood oxygenation level dependent (BOLD) functional MRI signal is known to be modulated by the CO2 level. Typically only end-tidal CO2, rather than the arterial partial pressure of CO2 (paCO2), was measured while the arterial partial pressure of O2 (paO2) level was not controlled due to free breathing, making their contribution not separable. Especially, the influences of paO2 and paCO2 on resting-state functional connectivity are not well studied. In this study, we investigated the relationship between paCO2 and resting as well as stimulus-evoked BOLD signals under hyperoxic and hypercapnic manipulation with tight control of arterial paO2. Rats under isoflurane anesthesia were subjected to six inspired gas conditions: 47% O2 in air (Normal), adding 1%, 2% or 5% CO2, carbogen (95% O2/5% CO2), and 100% O2. Somatosensory BOLD activation was significantly increased under 100% O2, while reduced with increased paCO2 levels. However, while resting BOLD connectivity pattern expanded and bilateral correlation increased under 100% O2, the correlation coefficient between the left and right somatosensory cortex was generally not dependent on paCO2 or paO2. Interestingly, the correlation in 0.04-0.07Hz range significantly increased with CO2 levels. Intracortical electrophysiological recordings showed a similar trend as the BOLD but the neurovascular coupling varied. The results suggest that paO2 and paCO2 together rather than paCO2 alone alter the BOLD signal. The response is not purely vascular in nature but has strong neuronal origins. This should be taken into consideration when designing calibrated BOLD experiment and interpreting functional connectivity data especially in aging, under drug, or neurological disorders.
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Affiliation(s)
- Fatima A Nasrallah
- Magnetic Resonance Imaging Group, Singapore Bioimaging Consortium, Agency for Science Technology and Research, Singapore
| | - Ling Yun Yeow
- Magnetic Resonance Imaging Group, Singapore Bioimaging Consortium, Agency for Science Technology and Research, Singapore
| | - Bharat Biswal
- Department of Biomedical Engineering, New Jersey Institute of Technology, NJ, USA
| | - Kai-Hsiang Chuang
- Magnetic Resonance Imaging Group, Singapore Bioimaging Consortium, Agency for Science Technology and Research, Singapore; Clinical Imaging Research Centre, National University of Singapore, Singapore; Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
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39
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Wang D, Yee BJ, Wong KK, Kim JW, Dijk DJ, Duffin J, Grunstein RR. Comparing the effect of hypercapnia and hypoxia on the electroencephalogram during wakefulness. Clin Neurophysiol 2015; 126:103-9. [DOI: 10.1016/j.clinph.2014.04.012] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 04/07/2014] [Accepted: 04/12/2014] [Indexed: 01/01/2023]
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40
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Croal PL, Hall EL, Driver ID, Brookes MJ, Gowland PA, Francis ST. The effect of isocapnic hyperoxia on neurophysiology as measured with MRI and MEG. Neuroimage 2015; 105:323-31. [DOI: 10.1016/j.neuroimage.2014.10.036] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 08/27/2014] [Accepted: 10/14/2014] [Indexed: 10/24/2022] Open
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Lu H, Liu P, Yezhuvath U, Cheng Y, Marshall O, Ge Y. MRI mapping of cerebrovascular reactivity via gas inhalation challenges. J Vis Exp 2014. [PMID: 25549106 PMCID: PMC4396915 DOI: 10.3791/52306] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The brain is a spatially heterogeneous and temporally dynamic organ, with different regions requiring different amount of blood supply at different time. Therefore, the ability of the blood vessels to dilate or constrict, known as Cerebral-Vascular-Reactivity (CVR), represents an important domain of vascular function. An imaging marker representing this dynamic property will provide new information of cerebral vessels under normal and diseased conditions such as stroke, dementia, atherosclerosis, small vessel diseases, brain tumor, traumatic brain injury, and multiple sclerosis. In order to perform this type of measurement in humans, it is necessary to deliver a vasoactive stimulus such as CO2 and/or O2 gas mixture while quantitative brain magnetic resonance images (MRI) are being collected. In this work, we presented a MR compatible gas-delivery system and the associated protocol that allow the delivery of special gas mixtures (e.g., O2, CO2, N2, and their combinations) while the subject is lying inside the MRI scanner. This system is relatively simple, economical, and easy to use, and the experimental protocol allows accurate mapping of CVR in both healthy volunteers and patients with neurological disorders. This approach has the potential to be used in broad clinical applications and in better understanding of brain vascular pathophysiology. In the video, we demonstrate how to set up the system inside an MRI suite and how to perform a complete experiment on a human participant.
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Affiliation(s)
- Hanzhang Lu
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center;
| | - Peiying Liu
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center
| | - Uma Yezhuvath
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center
| | - Yamei Cheng
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center
| | - Olga Marshall
- Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine
| | - Yulin Ge
- Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine
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42
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Wang D, Piper AJ, Yee BJ, Wong KK, Kim JW, D'Rozario A, Rowsell L, Dijk DJ, Grunstein RR. Hypercapnia is a key correlate of EEG activation and daytime sleepiness in hypercapnic sleep disordered breathing patients. J Clin Sleep Med 2014; 10:517-22. [PMID: 24910553 PMCID: PMC4046358 DOI: 10.5664/jcsm.3700] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
BACKGROUND The key determinants of daytime drowsiness in sleep disordered breathing (SDB) are unclear. Hypercapnia has not been examined as a potential contributor due to the lack of reliable measurement during sleep. To overcome this limitation, we studied predominantly hypercapnic SDB patients to investigate the role of hypercapnia on EEG activation and daytime sleepiness. METHODS We measured overnight polysomnography (PSG), arterial blood gases, and Epworth Sleepiness Scale in 55 severe SDB patients with obesity hypoventilation syndrome or overlap syndrome (COPD+ obstructive sleep apnea) before and ∼3 months after positive airway pressure (PAP) treatment. Quantitative EEG analyses were performed, and the Delta/ Alpha ratio was used as an indicator of EEG activation. RESULTS After the PAP treatment, these patients showed a significant decrease in their waking pCO(2), daytime sleepiness, as well as all key breathing/oxygenation parameters during sleep. Overnight Delta/Alpha ratio of EEG was significantly reduced. There is a significant cross-correlation between a reduced wake pCO(2), a faster (more activated) sleep EEG (reduced Delta/Alpha ratio) and reduced daytime sleepiness (all p < 0.05) with PAP treatment. Multiple regression analyses showed the degree of change in hypercapnia to be the only significant predictor for both ESS and Delta/ Alpha ratio. CONCLUSIONS Hypercapnia is a key correlate of EEG activation and daytime sleepiness in hypercapnic SDB patients. The relationship between hypercapnia and sleepiness may be mediated by reduced neuro-electrical brain activity.
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Affiliation(s)
- David Wang
- Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed)
- Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia
| | - Amanda J. Piper
- Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed)
- Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia
| | - Brendon J. Yee
- Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed)
- Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia
- Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Sydney, Australia
| | - Keith K. Wong
- Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed)
- Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia
- Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Sydney, Australia
| | - Jong-Won Kim
- Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Sydney, Australia
- School of Physics, University of Sydney, Sydney, Australia
| | - Angela D'Rozario
- Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia
- Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Sydney, Australia
| | - Luke Rowsell
- Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia
| | - Derk-Jan Dijk
- Surrey Sleep Research Centre, University of Surrey, UK
| | - Ronald R. Grunstein
- Department of Respiratory and Sleep Medicine, Royal Prince Alfred Hospital, Sydney, Australia (work performed)
- Woolcock Institute of Medical Research, University of Sydney, Sydney, Australia
- Centre for Integrated Research and Understanding of Sleep (CIRUS), University of Sydney, Sydney, Australia
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Buxton RB. The physics of functional magnetic resonance imaging (fMRI). REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2013; 76:096601. [PMID: 24006360 PMCID: PMC4376284 DOI: 10.1088/0034-4885/76/9/096601] [Citation(s) in RCA: 127] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Functional magnetic resonance imaging (fMRI) is a methodology for detecting dynamic patterns of activity in the working human brain. Although the initial discoveries that led to fMRI are only about 20 years old, this new field has revolutionized the study of brain function. The ability to detect changes in brain activity has a biophysical basis in the magnetic properties of deoxyhemoglobin, and a physiological basis in the way blood flow increases more than oxygen metabolism when local neural activity increases. These effects translate to a subtle increase in the local magnetic resonance signal, the blood oxygenation level dependent (BOLD) effect, when neural activity increases. With current techniques, this pattern of activation can be measured with resolution approaching 1 mm(3) spatially and 1 s temporally. This review focuses on the physical basis of the BOLD effect, the imaging methods used to measure it, the possible origins of the physiological effects that produce a mismatch of blood flow and oxygen metabolism during neural activation, and the mathematical models that have been developed to understand the measured signals. An overarching theme is the growing field of quantitative fMRI, in which other MRI methods are combined with BOLD methods and analyzed within a theoretical modeling framework to derive quantitative estimates of oxygen metabolism and other physiological variables. That goal is the current challenge for fMRI: to move fMRI from a mapping tool to a quantitative probe of brain physiology.
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Affiliation(s)
- Richard B Buxton
- Department of Radiology, University of California, San Diego, USA
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44
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Blockley NP, Griffeth VEM, Simon AB, Buxton RB. A review of calibrated blood oxygenation level-dependent (BOLD) methods for the measurement of task-induced changes in brain oxygen metabolism. NMR IN BIOMEDICINE 2013; 26:987-1003. [PMID: 22945365 PMCID: PMC3639302 DOI: 10.1002/nbm.2847] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Revised: 07/17/2012] [Accepted: 08/02/2012] [Indexed: 05/23/2023]
Abstract
The dynamics of the blood oxygenation level-dependent (BOLD) response are dependent on changes in cerebral blood flow, cerebral blood volume and the cerebral metabolic rate of oxygen consumption. Furthermore, the amplitude of the response is dependent on the baseline physiological state, defined by the haematocrit, oxygen extraction fraction and cerebral blood volume. As a result of this complex dependence, the accurate interpretation of BOLD data and robust intersubject comparisons when the baseline physiology is varied are difficult. The calibrated BOLD technique was developed to address these issues. However, the methodology is complex and its full promise has not yet been realised. In this review, the theoretical underpinnings of calibrated BOLD, and issues regarding this theory that are still to be resolved, are discussed. Important aspects of practical implementation are reviewed and reported applications of this methodology are presented.
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Affiliation(s)
- Nicholas P Blockley
- Center for Functional Magnetic Resonance Imaging, Department of Radiology, University of California San Diego, La Jolla, CA, USA.
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45
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Early and late stimulus-evoked cortical hemodynamic responses provide insight into the neurogenic nature of neurovascular coupling. J Cereb Blood Flow Metab 2012; 32:468-80. [PMID: 22126914 PMCID: PMC3293120 DOI: 10.1038/jcbfm.2011.163] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Understanding neurovascular coupling is a prerequisite for the interpretation of results obtained from modern neuroimaging techniques. This study investigated the hemodynamic and neural responses in rat somatosensory cortex elicited by 16 seconds electrical whisker stimuli. Hemodynamics were measured by optical imaging spectroscopy and neural activity by multichannel electrophysiology. Previous studies have suggested that the whisker-evoked hemodynamic response contains two mechanisms, a transient 'backwards' dilation of the middle cerebral artery, followed by an increase in blood volume localized to the site of neural activity. To distinguish between the mechanisms responsible for these aspects of the response, we presented whisker stimuli during normocapnia ('control'), and during a high level of hypercapnia. Hypercapnia was used to 'predilate' arteries and thus possibly 'inhibit' aspects of the response related to the 'early' mechanism. Indeed, hemodynamic data suggested that the transient stimulus-evoked response was absent under hypercapnia. However, evoked neural responses were also altered during hypercapnia and convolution of the neural responses from both the normocapnic and hypercapnic conditions with a canonical impulse response function, suggested that neurovascular coupling was similar in both conditions. Although data did not clearly dissociate early and late vascular responses, they suggest that the neurovascular coupling relationship is neurogenic in origin.
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46
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Rudrapatna US, van der Toorn A, van Meer MPA, Dijkhuizen RM. Impact of hemodynamic effects on diffusion-weighted fMRI signals. Neuroimage 2012; 61:106-14. [PMID: 22406501 DOI: 10.1016/j.neuroimage.2012.02.050] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2011] [Revised: 02/03/2012] [Accepted: 02/17/2012] [Indexed: 11/15/2022] Open
Abstract
In some recent studies, diffusion weighted functional MRI has been proposed to provide contrast immune to vascular changes. Increases in relative signal change during neuronal activation observed under increasing diffusion weighting support the possible diffusion based origin of this contrast. A recent diffusion tensor imaging (DTI) study has also reported the use of Fractional Anisotropy (FA) to track activation in white matter. In this study we aimed to establish if relatively high diffusion weighting (b=1200 and 1800 s/mm(2)) eliminates the strong vascular influences brought about by 100% O(2) and carbogen (95%O(2)+5% CO(2)) induced vascular challenges in gray matter (GM) and white matter (WM) of rat brain. We also aimed to characterize the influences of these vascular changes on FA, both in GM and in WM. Our study endorses previous reports that even relatively heavily diffusion weighted data can be significantly influenced by hemodynamic changes. However, this was not only observed in GM, but also in WM. Moreover, our study demonstrates that the estimator used to calculate the relative changes should be carefully chosen in order to avoid biases at low signal-to-noise ratios (SNRs) which accompany increasing diffusion weighting. With the use of robust estimators, we found no increases in relative change with increasing b-value during both vascular challenges. Our data also demonstrate that FA can be significantly influenced by hemodynamics, both in GM and in WM. The observed influence of diffusion weighting direction on relative signal change in GM was shown to be associated with structural differences among various regions. If diffusion based functional contrasts immune to hemodynamics do exist, our results highlight the difficulty in discerning those diffusion changes from accompanying vascular changes.
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Affiliation(s)
- Umesh S Rudrapatna
- Biomedical MR Imaging and Spectroscopy Group, Image Sciences Institute, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
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