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Association between temporal patterns of baroreflex sensitivity after traumatic brain injury and prognosis: a preliminary study. Neurol Sci 2023; 44:1653-1663. [PMID: 36609622 PMCID: PMC10102132 DOI: 10.1007/s10072-022-06579-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Accepted: 12/20/2022] [Indexed: 01/09/2023]
Abstract
INTRODUCTION Traumatic brain injury (TBI) may lead to an increase in intracranial pressure (ICP) as well as impairment of cerebral vascular reactivity and the autonomic nervous system. This study aimed to investigate individual patterns of changes in baroreflex sensitivity (BRS) along with the assessment of pressure reactivity index (PRx) and ICP after TBI. MATERIALS AND METHODS Twenty-nine TBI patients with continuous arterial blood pressure (ABP) and ICP monitoring were included. BRS was calculated using the sequential cross-correlation method. PRx was estimated using slow-wave oscillations of ABP and ICP. Outcome was assessed using the Glasgow Outcome Scale. RESULTS Pooled data analysis of the lower breakpoint during the week that followed TBI revealed that BRS reached a minimum about 2 days after TBI. In patients with good outcome, there was a significant increase in BRS during the 7 days following TBI: rp = 0.21; p = 0.008 and the temporal changes in BRS showed either a "U-shaped" pattern or a gradual increase over time. The BRS value after 1.5 days was found to be a significant predictor of mortality (cut-off BRS = 1.8 ms/mm Hg; AUC = 0.83). In patients with poor outcome, ICP and PRx increased while BRS remained low. CONCLUSIONS We found an association between temporal patterns of BRS and prognosis in the early days following TBI. Further research in a larger cohort of patients is needed to confirm the weight of these preliminary observations for prediction of prognosis in TBI patients.
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2
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Das A, Murphy K, Drew PJ. Rude mechanicals in brain haemodynamics: non-neural actors that influence blood flow. Philos Trans R Soc Lond B Biol Sci 2020; 376:20190635. [PMID: 33190603 DOI: 10.1098/rstb.2019.0635] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Fluctuations in blood oxygenation and flow are widely used to infer brain activity during resting-state functional magnetic resonance imaging (fMRI). However, there are strong systemic and vascular contributions to resting-state signals that are unrelated to ongoing neural activity. Importantly, these non-neural contributions to haemodynamic signals (or 'rude mechanicals') can be as large as or larger than the neurally evoked components. Here, we review the two broad classes of drivers of these signals. One is systemic and is tied to fluctuations in external drivers such as heart rate and breathing, and the robust autoregulatory mechanisms that try to maintain a constant milieu in the brain. The other class comprises local, active fluctuations that appear to be intrinsic to vascular tissue and are likely similar to active local fluctuations seen in vasculature all over the body. In this review, we describe these non-neural fluctuations and some of the tools developed to correct for them when interpreting fMRI recordings. However, we also emphasize the links between these vascular fluctuations and brain physiology and point to ways in which fMRI measurements can be used to exploit such links to gain valuable information about neurovascular health and about internal brain states. This article is part of the theme issue 'Key relationships between non-invasive functional neuroimaging and the underlying neuronal activity'.
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Affiliation(s)
- Aniruddha Das
- Department of Neuroscience, Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA
| | - Kevin Murphy
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Physics and Astronomy, Cardiff University, Cardiff CF24 4HQ, UK
| | - Patrick J Drew
- Departments of Engineering Science and Mechanics, Neurosurgery, and Biomedical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
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Marzi C, Giannelli M, Tessa C, Mascalchi M, Diciotti S. Toward a more reliable characterization of fractal properties of the cerebral cortex of healthy subjects during the lifespan. Sci Rep 2020; 10:16957. [PMID: 33046812 PMCID: PMC7550568 DOI: 10.1038/s41598-020-73961-w] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Accepted: 09/14/2020] [Indexed: 01/12/2023] Open
Abstract
The cerebral cortex manifests an inherent structural complexity of folding. The fractal geometry describes the complexity of structures which show self-similarity in a proper interval of spatial scales. In this study, we aimed at evaluating in-vivo the effect of different criteria for selecting the interval of spatial scales in the estimation of the fractal dimension (FD) of the cerebral cortex in T1-weighted magnetic resonance imaging (MRI). We compared four different strategies, including two a priori selections of the interval of spatial scales, an automated selection of the spatial scales within which the cerebral cortex manifests the highest statistical self-similarity, and an improved approach, based on the search of the interval of spatial scales which presents the highest rounded R2adj coefficient and, in case of equal rounded R2adj coefficient, preferring the widest interval in the log–log plot. We employed two public and international datasets of in-vivo MRI scans for a total of 159 healthy subjects (age range 6–85 years). The improved approach showed strong associations of FD with age and yielded the most accurate machine learning models for individual age prediction in both datasets. Our results indicate that the selection of the interval of spatial scales of the cerebral cortex is thus critical in the estimation of FD.
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Affiliation(s)
- Chiara Marzi
- Department of Electrical, Electronic, and Information Engineering "Guglielmo Marconi", University of Bologna, Viale del Risorgimento 2, 40136, Bologna, Italy
| | - Marco Giannelli
- Unit of Medical Physics, Pisa University Hospital "Azienda Ospedaliero-Universitaria Pisana", Pisa, Italy
| | - Carlo Tessa
- Division of Radiology, Versilia Hospital, Azienda USL Toscana Nord Ovest, Lido di Camaiore (Lu), Italy
| | - Mario Mascalchi
- "Mario Serio" Department of Experimental and Clinical Biomedical Sciences, University of Florence, Florence, Italy
| | - Stefano Diciotti
- Department of Electrical, Electronic, and Information Engineering "Guglielmo Marconi", University of Bologna, Viale del Risorgimento 2, 40136, Bologna, Italy.
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4
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Canac N, Ranjbaran M, O'Brien MJ, Asgari S, Scalzo F, Thorpe SG, Jalaleddini K, Thibeault CM, Wilk SJ, Hamilton RB. Algorithm for Reliable Detection of Pulse Onsets in Cerebral Blood Flow Velocity Signals. Front Neurol 2019; 10:1072. [PMID: 31681147 PMCID: PMC6798080 DOI: 10.3389/fneur.2019.01072] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 09/23/2019] [Indexed: 12/30/2022] Open
Abstract
Transcranial Doppler (TCD) ultrasound has been demonstrated to be a valuable tool for assessing cerebral hemodynamics via measurement of cerebral blood flow velocity (CBFV), with a number of established clinical indications. However, CBFV waveform analysis depends on reliable pulse onset detection, an inherently difficult task for CBFV signals acquired via TCD. We study the application of a new algorithm for CBFV pulse segmentation, which locates pulse onsets in a sequential manner using a moving difference filter and adaptive thresholding. The test data set used in this study consists of 92,012 annotated CBFV pulses, whose quality is representative of real world data. On this test set, the algorithm achieves a true positive rate of 99.998% (2 false negatives), positive predictive value of 99.998% (2 false positives), and mean temporal offset error of 6.10 ± 4.75 ms. We do note that in this context, the way in which true positives, false positives, and false negatives are defined caries some nuance, so care should be taken when drawing comparisons to other algorithms. Additionally, we find that 97.8% and 99.5% of onsets are detected within 10 and 30 ms, respectively, of the true onsets. The algorithm's performance in spite of the large degree of variation in signal quality and waveform morphology present in the test data suggests that it may serve as a valuable tool for the accurate and reliable identification of CBFV pulse onsets in neurocritical care settings.
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Affiliation(s)
- Nicolas Canac
- Neural Analytics, Inc., Los Angeles, CA, United States
| | | | | | - Shadnaz Asgari
- Biomedical Engineering Department and Computer Engineering and Computer Science Department, California State University, Long Beach, CA, United States
| | - Fabien Scalzo
- Department of Neurology and Computer Science, University of California, Los Angeles, Los Angeles, CA, United States
| | | | | | | | - Seth J. Wilk
- Neural Analytics, Inc., Los Angeles, CA, United States
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5
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Identification of Pulse Onset on Cerebral Blood Flow Velocity Waveforms: A Comparative Study. BIOMED RESEARCH INTERNATIONAL 2019; 2019:3252178. [PMID: 31355255 PMCID: PMC6634067 DOI: 10.1155/2019/3252178] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 06/02/2019] [Accepted: 06/18/2019] [Indexed: 11/17/2022]
Abstract
The low cost, simple, noninvasive, and continuous measurement of cerebral blood flow velocity (CBFV) by transcranial Doppler is becoming a common clinical tool for the assessment of cerebral hemodynamics. CBFV monitoring can also help with noninvasive estimation of intracranial pressure and evaluation of mild traumatic brain injury. Reliable CBFV waveform analysis depends heavily on its accurate beat-to-beat delineation. However, CBFV is inherently contaminated with various types of noise/artifacts and has a wide range of possible pathological waveform morphologies. Thus, pulse onset detection is in general a challenging task for CBFV signal. In this paper, we conducted a comprehensive comparative analysis of three popular pulse onset detection methods using a large annotated dataset of 92,794 CBFV pulses—collected from 108 subarachnoid hemorrhage patients admitted to UCLA Medical Center. We compared these methods not only in terms of their accuracy and computational complexity, but also for their sensitivity to the selection of their parameters' values. The results of this comprehensive study revealed that using optimal values of the parameters obtained from sensitivity analysis, one method can achieve the highest accuracy for CBFV pulse onset detection with true positive rate (TPR) of 97.06% and positive predictivity value (PPV) of 96.48%, when error threshold is set to just less than 10 ms. We conclude that the high accuracy and low computational complexity of this method (average running time of 4ms/pulse) makes it a reliable algorithm for CBFV pulse onset detection.
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Witter T, Tzeng YC, O'Donnell T, Kusel J, Walker B, Berry M, Taylor CE. Inter-individual Relationships between Sympathetic Arterial Baroreflex Function and Cerebral Perfusion Control in Healthy Males. Front Neurosci 2017; 11:457. [PMID: 28860964 PMCID: PMC5559461 DOI: 10.3389/fnins.2017.00457] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Accepted: 07/28/2017] [Indexed: 12/29/2022] Open
Abstract
Maintenance of adequate cerebral perfusion during normal physiological challenges requires integration between cerebral blood flow (CBF) and systemic blood pressure control mechanisms. Previous studies have shown that cardiac baroreflex sensitivity (BRS) is inversely related to some measures of cerebral autoregulation. However, interactions between the sympathetic arterial baroreflex and cerebral perfusion control mechanisms have not been explored. To determine the nature and magnitude of these interactions we measured R–R interval, blood pressure, CBF velocity, and muscle sympathetic nerve activity (MSNA) in 11 healthy young males. Sympathetic BRS was estimated using modified Oxford method as the relationship between beat-to-beat diastolic blood pressure (DBP) and MSNA. Integrated control of CBF was quantified using transfer function analysis (TFA) metrics derived during rest and Tieck's autoregulatory index following bilateral thigh cuff deflation. Sympathetic BRS during modified Oxford trials was significantly related to autoregulatory index (r = 0.64, p = 0.03). Sympathetic BRS during spontaneous baseline was significantly related to transfer function gain (r = −0.74, p = 0.01). A more negative value for sympathetic BRS indicates more effective arterial baroreflex regulation, and a lower transfer function gain reflects greater cerebral autoregulation. Therefore, these findings indicate that males with attenuated CBF regulation have greater sympathetic BRS (and vice versa), consistent with compensatory interactions between blood pressure and cerebral perfusion control mechanisms.
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Affiliation(s)
- Trevor Witter
- Wellington Medical Technology Group, Centre for Translational Physiology, University of OtagoWellington, New Zealand
| | - Yu-Chieh Tzeng
- Wellington Medical Technology Group, Centre for Translational Physiology, University of OtagoWellington, New Zealand
| | - Terry O'Donnell
- Wellington Medical Technology Group, Centre for Translational Physiology, University of OtagoWellington, New Zealand
| | - Jessica Kusel
- Wellington Medical Technology Group, Centre for Translational Physiology, University of OtagoWellington, New Zealand
| | - Bridget Walker
- Wellington Medical Technology Group, Centre for Translational Physiology, University of OtagoWellington, New Zealand
| | - Mary Berry
- Wellington Medical Technology Group, Centre for Translational Physiology, University of OtagoWellington, New Zealand
| | - Chloe E Taylor
- School of Science and Health, Western Sydney UniversitySydney, NSW, Australia.,School of Medicine, Western Sydney UniversitySydney, NSW, Australia
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7
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Bishop SA, Neary JP. Assessing prefrontal cortex oxygenation after sport concussion with near-infrared spectroscopy. Clin Physiol Funct Imaging 2017. [DOI: 10.1111/cpf.12447] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Scott A. Bishop
- Faculty of Kinesiology and Health Studies; University of Regina; Regina SK Canada
| | - J. Patrick Neary
- Faculty of Kinesiology and Health Studies; University of Regina; Regina SK Canada
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8
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Salvi M, Rimini D, Molinari F, Bestente G, Bruno A. Effect of low-level light therapy on diabetic foot ulcers: a near-infrared spectroscopy study. JOURNAL OF BIOMEDICAL OPTICS 2017; 22:38001. [PMID: 28265648 DOI: 10.1117/1.jbo.22.3.038001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Accepted: 02/22/2017] [Indexed: 06/06/2023]
Abstract
Diabetic foot ulcer (DFU) is a diabetic complication due to peripheral vasculopathy and neuropathy. A promising technology for wound healing in DFU is low-level light therapy (LLLT). Despite several studies showing positive effects of LLLT on DFU, LLLT’s physiological effects have not yet been studied. The objective of this study was to investigate vascular and nervous systems modification in DFU after LLLT. Two samples of 45 DFU patients and 11 healthy controls (HCs) were recruited. The total hemoglobin (totHb) concentration change was monitored before and after LLLT by near-infrared spectroscopy and analyzed in time and frequency domains. The spectral power of the totHb changes in the very-low frequency (VLF, 20 to 60 mHz) and low frequency (LF, 60 to 140 mHz) bandwidths was calculated. Data analysis revealed a mean increase of totHb concentration after LLLT in DFU patients, but not in HC. VLF/LF ratio decreased significantly after the LLLT period in DFU patients (indicating an increased activity of the autonomic nervous system), but not in HC. Eventually, different treatment intensities in LLLT therapy showed a different response in DFU. Overall, our results demonstrate that LLLT improves blood flow and autonomic nervous system regulation in DFU and the importance of light intensity in therapeutic protocols.
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Affiliation(s)
- Massimo Salvi
- Politecnico di Torino, Biolab, Department of Electronics and Telecommunications, Turin, Italy
| | - Daniele Rimini
- Politecnico di Torino, Biolab, Department of Electronics and Telecommunications, Turin, Italy
| | - Filippo Molinari
- Politecnico di Torino, Biolab, Department of Electronics and Telecommunications, Turin, Italy
| | | | - Alberto Bruno
- AOU Città della Salute e della Scienza di Torino-San Giovanni Antica Sede, Diabetology Department, Turin, Italy
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9
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Uryga A, Placek MM, Wachel P, Szczepański T, Czosnyka M, Kasprowicz M. Phase shift between respiratory oscillations in cerebral blood flow velocity and arterial blood pressure. Physiol Meas 2017; 38:310-324. [PMID: 28099160 DOI: 10.1088/1361-6579/38/2/310] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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10
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Berg RMG, Plovsing RR, Bailey DM, Holstein-Rathlou NH, Møller K. The Dynamic cerebral autoregulatory adaptive response to noradrenaline is attenuated during systemic inflammation in humans. Clin Exp Pharmacol Physiol 2016; 42:740-6. [PMID: 25966743 DOI: 10.1111/1440-1681.12421] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2015] [Revised: 03/17/2015] [Accepted: 05/07/2015] [Indexed: 11/28/2022]
Abstract
Vasopressor support is used widely for maintaining vital organ perfusion pressure in septic shock, with implications for dynamic cerebral autoregulation (dCA). This study investigated whether a noradrenaline-induced steady state increase in mean arterial blood pressure (MAP) would enhance dCA following lipopolysaccharide (LPS) infusion, a human-experimental model of the systemic inflammatory response during early sepsis. The dCA in eight healthy males was examined prior to and during an intended noradrenaline-induced MAP increase of approximately 30 mmHg. This was performed at baseline and repeated after a 4-h intravenous LPS infusion. The assessments of dCA were based on transfer function analysis of spontaneous oscillations between MAP and middle cerebral artery blood flow velocity measured by transcranial Doppler ultrasound in the low frequency range (0.07-0.20 Hz). Prior to LPS, noradrenaline administration was associated with a decrease in gain (1.18 (1.12-1.35) vs 0.93 (0.87-0.97) cm/mmHg per s; P < 0.05) with no effect on phase (0.71 (0.93-0.66) vs 0.94 (0.81-1.10) radians; P = 0.58). After LPS, noradrenaline administration changed neither gain (0.91 (0.85-1.01) vs 0.87 (0.81-0.97) cm/mmHg per s; P = 0.46) nor phase (1.10 (1.04-1.30) vs 1.37 (1.23-1.51) radians; P = 0.64). The improvement of dCA to a steady state increase in MAP is attenuated during an LPS-induced systemic inflammatory response. This may suggest that vasopressor treatment with noradrenaline offers no additional neuroprotective effect by enhancing dCA in patients with early sepsis.
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Affiliation(s)
- Ronan M G Berg
- Department of Clinical Physiology, Nuclear Medicine & PET, University Hospital Rigshospitalet, Copenhagen, Denmark.,Centre of Inflammation and Metabolism, University Hospital Rigshospitalet, Copenhagen, Denmark
| | - Ronni R Plovsing
- Intensive Care Unit 4131, University Hospital Rigshospitalet, Copenhagen, Denmark.,Department of Anaesthesiology, Køge Hospital, Køge, Denmark
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Niels-Henrik Holstein-Rathlou
- Renal and Vascular Research Section, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Kirsten Møller
- Centre of Inflammation and Metabolism, University Hospital Rigshospitalet, Copenhagen, Denmark.,Neurointensive Care Unit 2093, Department of Neuroanaesthesiology, University Hospital Rigshospitalet, Copenhagen, Denmark
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11
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Smirl JD, Hoffman K, Tzeng YC, Hansen A, Ainslie PN. Relationship between blood pressure and cerebral blood flow during supine cycling: influence of aging. J Appl Physiol (1985) 2015; 120:552-63. [PMID: 26586907 DOI: 10.1152/japplphysiol.00667.2015] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Accepted: 11/13/2015] [Indexed: 11/22/2022] Open
Abstract
The cerebral pressure-flow relationship can be quantified as a high-pass filter, where slow oscillations are buffered (<0.20 Hz) and faster oscillations are passed through relatively unimpeded. During moderate intensity exercise, previous studies have reported paradoxical transfer function analysis (TFA) findings (altered phase or intact gain). This study aimed to determine whether these previous findings accurately represent this relationship. Both younger (20-30 yr; n = 10) and older (62-72 yr; n = 9) adults were examined. To enhance the signal-to-noise ratio, large oscillations in blood pressure (via oscillatory lower body negative pressure; OLBNP) were induced during steady-state moderate intensity supine exercise (∼45-50% of heart rate reserve). Beat-to-beat blood pressure, cerebral blood velocity, and end-tidal Pco2 were monitored. Very low frequency (0.02-0.07 Hz) and low frequency (0.07-0.20 Hz) range spontaneous data were quantified. Driven OLBNP point estimates were sampled at 0.05 and 0.10 Hz. The OLBNP maneuvers augmented coherence to >0.97 at 0.05 Hz and >0.98 at 0.10 Hz in both age groups. The OLBNP protocol conclusively revealed the cerebrovascular system functions as a high-pass filter during exercise throughout aging. It was also discovered that the older adults had elevations (+71%) in normalized gain (+0.46 ± 0.36%/%: 0.05 Hz) and reductions (-34%) in phase (-0.24 ± 0.22 radian: 0.10 Hz). There were also age-related phase differences between resting and exercise conditions. It is speculated that these age-related changes in the TFA metrics are mediated by alterations in vasoactive factors, sympathetic tone, or the mechanical buffering of the compliance vessels.
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Affiliation(s)
- Jonathan D Smirl
- Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada;
| | - Keegan Hoffman
- Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada
| | - Yu-Chieh Tzeng
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, Wellington, New Zealand
| | - Alex Hansen
- Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health; School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Canada
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12
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Chen CT, Hsiu H, Fan JS, Lin FC, Liu YT. Complexity Analysis of Beat-to-Beat Skin-Surface Laser-Doppler Flowmetry Signals in Stroke Patients. Microcirculation 2015; 22:370-7. [DOI: 10.1111/micc.12206] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Accepted: 04/20/2015] [Indexed: 11/27/2022]
Affiliation(s)
- Chao-Tsung Chen
- Department of Traditional Chinese Medicine; Taipei City Hospital RenAi Branch; Taipei Taiwan
| | - Hsin Hsiu
- Graduate Institute of Biomedical Engineering; National Taiwan University of Science and Technology; Taipei Taiwan
| | - Jin-Shiang Fan
- Graduate Institute of Biomedical Engineering; National Taiwan University of Science and Technology; Taipei Taiwan
| | - Fong-Cheng Lin
- Department of Rehabilitation; Taipei City Hospital RenAi Branch; Taipei Taiwan
| | - Yen-Ting Liu
- Graduate Institute of Biomedical Engineering; National Taiwan University of Science and Technology; Taipei Taiwan
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13
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Di Ieva A, Esteban FJ, Grizzi F, Klonowski W, Martín-Landrove M. Fractals in the Neurosciences, Part II. Neuroscientist 2015; 21:30-43. [PMID: 24362814 DOI: 10.1177/1073858413513928] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/30/2023]
Abstract
It has been ascertained that the human brain is a complex system studied at multiple scales, from neurons and microcircuits to macronetworks. The brain is characterized by a hierarchical organization that gives rise to its highly topological and functional complexity. Over the last decades, fractal geometry has been shown as a universal tool for the analysis and quantification of the geometric complexity of natural objects, including the brain. The fractal dimension has been identified as a quantitative parameter for the evaluation of the roughness of neural structures, the estimation of time series, and the description of patterns, thus able to discriminate different states of the brain in its entire physiopathological spectrum. Fractal-based computational analyses have been applied to the neurosciences, particularly in the field of clinical neurosciences including neuroimaging and neuroradiology, neurology and neurosurgery, psychiatry and psychology, and neuro-oncology and neuropathology. After a review of the basic concepts of fractal analysis and its main applications to the basic neurosciences in part I of this series, here, we review the main applications of fractals to the clinical neurosciences for a holistic approach towards a fractal geometry model of the brain.
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Affiliation(s)
- Antonio Di Ieva
- Division of Neurosurgery, St. Michael’s Hospital, University of Toronto, Toronto, Canada
- Centre for Anatomy and Cell Biology, Department of Systematic Anatomy, Medical University of Vienna, Vienna, Austria
| | - Francisco J. Esteban
- Systems Biology Unit, Department of Experimental Biology, University of Jaén, Jaén, Spain
| | - Fabio Grizzi
- Humanitas Clinical and Research Center, Rozzano, Milan, Italy
| | - Wlodzimierz Klonowski
- Nalecz Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences, Warsaw, Poland
| | - Miguel Martín-Landrove
- Centre for Molecular and Medical Physics and National Institute for Bioengineering, Universidad Central de Venezuela, Caracas, Venezuela
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Placek MM, Wachel P, Czosnyka M, Soehle M, Smielewski P, Kasprowicz M. Complexity of cerebral blood flow velocity and arterial blood pressure in subarachnoid hemorrhage using time-frequency analysis. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2015; 2015:7700-7703. [PMID: 26738076 DOI: 10.1109/embc.2015.7320176] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We investigated changes of time-frequency (TF) complexity, in terms of Rényi entropy and a measure of concentration, of middle cerebral blood flow velocity (CBFV) and arterial blood pressure in relation to the development of cerebral vasospasm in 15 patients after aneurysmal subarachnoid hemorrhage. Interhemispheric differences in the period of no vasospasm and vasospasm were also compared. Results show reduced complexity of TF representations of CBFV on the side of aneurysm before vasospasm was identified. This potentially can serve as an early-warning indicator of future derangement of cerebral circulation.
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15
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Hsiu H, Hsu CL, Hu HF, Hsiao FC, Yang SH. Complexity analysis of beat-to-beat skin-surface laser-Doppler signals in diabetic subjects. Microvasc Res 2014; 93:9-13. [DOI: 10.1016/j.mvr.2014.02.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Revised: 02/18/2014] [Accepted: 02/20/2014] [Indexed: 12/23/2022]
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16
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Berg RMG, Plovsing RR, Evans KA, Christiansen CB, Bailey DM, Holstein-Rathlou NH, Møller K. Lipopolysaccharide infusion enhances dynamic cerebral autoregulation without affecting cerebral oxygen vasoreactivity in healthy volunteers. Crit Care 2013; 17:R238. [PMID: 24131656 PMCID: PMC4057209 DOI: 10.1186/cc13062] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Accepted: 08/13/2013] [Indexed: 12/23/2022] Open
Abstract
INTRODUCTION Sepsis may be associated with disturbances in cerebral oxygen transport and cerebral haemodynamic function, thus rendering the brain particularly susceptible to hypoxia. The purpose of this study was to assess the impact of isocapnic hypoxia and hyperoxia on dynamic cerebral autoregulation in a human-experimental model of the systemic inflammatory response during the early stages of sepsis. METHODS A total of ten healthy volunteers were exposed to acute isocapnic inspiratory hyperoxia (FIO₂ = 40%) and hypoxia (FIO₂ = 12%) before and after a 4-hour lipopolysaccharide (LPS) infusion (2 ng kg-1). Middle cerebral artery blood follow velocity was assessed using transcranial Doppler ultrasound, and dynamic autoregulation was evaluated by transfer function analysis. RESULTS Transfer function analysis revealed an increase in the phase difference between mean arterial blood pressure and middle cerebral artery blood flow velocity in the low frequency range (0.07-0.20 Hz) after LPS (P<0.01). In contrast, there were no effects of either isocapnic hyperoxia or hypoxia on dynamic autoregulation, and the cerebral oxygen vasoreactivity to both hyperoxia and hypoxia was unaffected by LPS. CONCLUSIONS The observed increase in phase suggests that dynamic cerebral autoregulation is enhanced after LPS infusion and resistant to any effects of acute hypoxia; this may protect the brain from ischaemia and/or blood-brain barrier damage during the early stages of sepsis.
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Affiliation(s)
- Ronan MG Berg
- Centre of Inflammation and Metabolism, Department of Infectious Diseases, section M7641, University Hospital Rigshospitalet, Blegdamsvej 9, DK-2100, Copenhagen Ø, Denmark
- Renal and Vascular Research Section, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen N, Denmark
- Intensive Care Unit 4131, University Hospital Rigshospitalet, Copenhagen Ø, Denmark
| | - Ronni R Plovsing
- Intensive Care Unit 4131, University Hospital Rigshospitalet, Copenhagen Ø, Denmark
| | - Kevin A Evans
- Neurovascular Research Laboratory, Faculty of Health, Science and Sport, University of Glamorgan, South Wales CF374AT, UK
| | - Claus B Christiansen
- Centre of Inflammation and Metabolism, Department of Infectious Diseases, section M7641, University Hospital Rigshospitalet, Blegdamsvej 9, DK-2100, Copenhagen Ø, Denmark
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Health, Science and Sport, University of Glamorgan, South Wales CF374AT, UK
| | - Niels-Henrik Holstein-Rathlou
- Renal and Vascular Research Section, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Copenhagen N, Denmark
| | - Kirsten Møller
- Centre of Inflammation and Metabolism, Department of Infectious Diseases, section M7641, University Hospital Rigshospitalet, Blegdamsvej 9, DK-2100, Copenhagen Ø, Denmark
- Neurointensive Care Unit 2093, Department of Neuroanaesthesiology, University Hospital Rigshospitalet, Copenhagen Ø, Denmark
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17
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Peebles KC, Horsman H, Tzeng YC. The influence of tobacco smoking on the relationship between pressure and flow in the middle cerebral artery in humans. PLoS One 2013; 8:e72624. [PMID: 23977332 PMCID: PMC3744580 DOI: 10.1371/journal.pone.0072624] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Accepted: 07/11/2013] [Indexed: 01/22/2023] Open
Abstract
Background Cigarette smoking is associated with an increased risk of stroke but the mechanism is unclear. The study examined whether acute and chronic cigarette smoking alters the dynamic relationship between blood pressure and cerebral blood flow. We hypothesised that acute and chronic smoking would result in a cerebral circulation that was less capable of buffering against dynamic fluctuations in blood pressure. Further, these changes would be accompanied by a reduction in baroreflex sensitivity, which is reduced after smoking (acute smoking). Methods We recruited 17 non-smokers and 15 habitual smokers (13 ± 5 pack years). Continuous measurements of mean cerebral blood flow velocity (transcranial Doppler ultrasound), blood pressure (finger photoplethysmography) and heart rate enabled transfer function analysis of the dynamic relationship between pressure and flow (gain, normalised gain, phase and coherence) and baroreflex sensitivity during supine rest before and after smoking a single cigarette (acute smoking). Results There were no between-group differences in gain, phase or coherence before acute smoking. However, both groups showed a reduction in gain and coherence, associated with a reduction in baroreflex sensitivity, and increase in phase after acute smoking. Conclusions Contrary to our hypothesis, these findings suggest that in the face of a reduction in baroreflex sensitivity acute smoking may potentially improve the ability of the cerebral circulation to buffer against changes in blood pressure. However, chronic smoking did not alter the dynamic relationship between blood pressure and cerebral blood flow velocity. These results have implications on understanding mechanisms for attenuating stroke risk.
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Affiliation(s)
- Karen C. Peebles
- Cardiovascular Systems Laboratory, University of Otago, Wellington, New Zealand
- Centre for Translational Physiology, University of Otago, Wellington, New Zealand
- Department of Physiology, University of Otago, Dunedin, New Zealand
| | - Helen Horsman
- Cardiovascular Systems Laboratory, University of Otago, Wellington, New Zealand
- Centre for Translational Physiology, University of Otago, Wellington, New Zealand
| | - Yu-Chieh Tzeng
- Cardiovascular Systems Laboratory, University of Otago, Wellington, New Zealand
- Centre for Translational Physiology, University of Otago, Wellington, New Zealand
- * E-mail:
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18
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Hsiu H, Hsu WC, Hsu CL, Bau JG, Chen CT, Liu YS. Complexity analysis of the microcirculatory-blood-flow response following acupuncture stimulation. Microvasc Res 2013; 89:34-9. [PMID: 23806782 DOI: 10.1016/j.mvr.2013.06.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2013] [Revised: 05/29/2013] [Accepted: 06/13/2013] [Indexed: 10/26/2022]
Abstract
Beat-to-beat cardiovascular variability analysis provides important information on the circulatory regulatory activities. Changes in the arterial pulse transmission or the opening condition of arteriolar openings might change the fluctuation pattern of the MBF supply, and thus change the complexity property therein. We performed complexity analysis of beat-to-beat laser Doppler flowmetry (LDF) signals to study the microcirculatory-blood-flow (MBF) response at the needled site (Hegu acupoint) following acupuncture stimulation (AS). LDF signals were measured in male healthy volunteers (n=29). Each experiment involved recording a 20-minute baseline-data sequence and two sets of effects data recorded 0-20 and 50-70min after stopping AS. Approximate-entropy (ApEn) analysis, which quantifies the unpredictability of fluctuations in a time series, was performed on each 20-minute beat-to-beat LDF data sequence. The present findings indicate that AS can not only improve the local blood supply but may also increase ApEn values and decrease MBF variability parameters. This was the first attempt to apply complexity analysis to LDF signals in order to elucidate microcirculatory responses following AS. The observed results are probably attributable to the contradictory effects on the MBF supply induced by AS, which might interfere with the microcirculatory regulatory activities so as to increase the complexity of LDF signals. The present findings could help to identify the mechanism underlying the effects of AS, might aid the development of an index for monitoring the induced microcirculatory regulatory responses, and thus provide an evidence-based connection between AS and modern physiology.
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Affiliation(s)
- Hsin Hsiu
- Graduate Institute of Biomedical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
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19
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Blood pressure regulation IX: cerebral autoregulation under blood pressure challenges. Eur J Appl Physiol 2013. [PMID: 23737006 DOI: 10.1007/s00421‐013‐2667‐y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Cerebral autoregulation (CA) is integral to the delicate process of maintaining stable cerebral perfusion and brain tissue oxygenation against changes in arterial blood pressure. The last four decades has seen dramatic advances in understanding CA physiology, and the role that CA might play in the causation and progression of disease processes that affect the cerebral circulation such as stroke. However, the translation of these basic scientific advances into clinical practice has been limited by the maintenance of old constructs and because there are persistent gaps in our understanding of how this vital vascular mechanism should be quantified. In this review, we re-evaluate relevant studies that challenge established paradigms about how the cerebral perfusion pressure and blood flow are related. In the context of blood pressure being a major haemodynamic challenge to the cerebral circulation, we conclude that: (1) the physiological properties of CA remain inconclusive, (2) many extant methods for CA characterisation are based on simplistic assumptions that can give rise to misleading interpretations, and (3) robust evaluation of CA requires thorough consideration not only of active vasomotor function, but also the unique properties of the intracranial environment.
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20
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Tzeng YC, Ainslie PN. Blood pressure regulation IX: cerebral autoregulation under blood pressure challenges. Eur J Appl Physiol 2013; 114:545-59. [PMID: 23737006 PMCID: PMC3929776 DOI: 10.1007/s00421-013-2667-y] [Citation(s) in RCA: 153] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Accepted: 05/21/2013] [Indexed: 12/11/2022]
Abstract
Cerebral autoregulation (CA) is integral to the delicate process of maintaining stable cerebral perfusion and brain tissue oxygenation against changes in arterial blood pressure. The last four decades has seen dramatic advances in understanding CA physiology, and the role that CA might play in the causation and progression of disease processes that affect the cerebral circulation such as stroke. However, the translation of these basic scientific advances into clinical practice has been limited by the maintenance of old constructs and because there are persistent gaps in our understanding of how this vital vascular mechanism should be quantified. In this review, we re-evaluate relevant studies that challenge established paradigms about how the cerebral perfusion pressure and blood flow are related. In the context of blood pressure being a major haemodynamic challenge to the cerebral circulation, we conclude that: (1) the physiological properties of CA remain inconclusive, (2) many extant methods for CA characterisation are based on simplistic assumptions that can give rise to misleading interpretations, and (3) robust evaluation of CA requires thorough consideration not only of active vasomotor function, but also the unique properties of the intracranial environment.
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Affiliation(s)
- Yu-Chieh Tzeng
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, 23A Mein Street, PO Box 7343, Wellington South, New Zealand,
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21
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Schytz HW, Guo S, Jensen LT, Kamar M, Nini A, Gress DR, Ashina M. A new technology for detecting cerebral blood flow: a comparative study of ultrasound tagged NIRS and 133Xe-SPECT. Neurocrit Care 2012; 17:139-45. [PMID: 22610823 DOI: 10.1007/s12028-012-9720-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
There is a need for real-time non-invasive, continuous monitoring of cerebral blood flow (CBF) during surgery, in intensive care units and clinical research. We investigated a new non-invasive hybrid technology employing ultrasound tagged near infrared spectroscopy (UT-NIRS) that may estimate changes in CBF using a cerebral blood flow index (CFI). Changes over time for UT-NIRS CFI and 133Xenon single photon emission computer tomography (133Xe-SPECT) CBF data were assessed in 10 healthy volunteers after an intravenous bolus of acetazolamide. UT-NIRS CFI was measured continuously and SPECT CBF was measured at baseline, 15 and 60 min after acetazolamide. We found significant changes over time in CFI by UT-NIRS and CBF by SPECT after acetazolamide (P ≤ 0.001). Post hoc tests showed a significant increase in CFI (P = 0.011) and SPECT CBF (P < 0.001) at 15 min after acetazolamide injection. There was a significant correlation between CFI and SPECT CBF values (r = 0.67 and P ≤ 0.033) at 15 min, but not at 60 min (P ≥ 0.777). UT-NIRS detected an increase in CFI following an acetazolamide bolus, which correlated with CBF measured with 133Xe-SPECT. This study demonstrates that UT-NIRS technology may be a promising new technique for non-invasive and real-time bedside CBF monitoring.
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Affiliation(s)
- Henrik W Schytz
- Danish Headache Center and Department of Neurology, Glostrup Hospital, Faculty of Health Sciences, University of Copenhagen, 2600, Glostrup, Denmark.
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22
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Berg RMG, Plovsing RR, Ronit A, Bailey DM, Holstein-Rathlou NH, Møller K. Disassociation of static and dynamic cerebral autoregulatory performance in healthy volunteers after lipopolysaccharide infusion and in patients with sepsis. Am J Physiol Regul Integr Comp Physiol 2012; 303:R1127-35. [PMID: 23076874 DOI: 10.1152/ajpregu.00242.2012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Sepsis is frequently complicated by brain dysfunction, which may be associated with disturbances in cerebral autoregulation, rendering the brain susceptible to hypoperfusion and hyperperfusion. The purpose of the present study was to assess static and dynamic cerebral autoregulation 1) in a human experimental model of the systemic inflammatory response during early sepsis and 2) in patients with advanced sepsis. Cerebral autoregulation was tested using transcranial Doppler ultrasound in healthy volunteers (n = 9) before and after LPS infusion and in patients with sepsis (n = 16). Static autoregulation was tested by norepinephrine infusion and dynamic autoregulation by transfer function analysis (TFA) of spontaneous oscillations between mean arterial blood pressure and middle cerebral artery blood flow velocity in the low frequency range (0.07-0.20 Hz). Static autoregulatory performance after LPS infusion and in patients with sepsis was similar to values in healthy volunteers at baseline. In contrast, TFA showed decreased gain and an increased phase difference between blood pressure and middle cerebral artery blood flow velocity after LPS (both P < 0.01 vs. baseline); patients exhibited similar gain but lower phase difference values (P < 0.01 vs. baseline and LPS), indicating a slower dynamic autoregulatory response. Our findings imply that static and dynamic cerebral autoregulatory performance may disassociate in sepsis; thus static autoregulation was maintained both after LPS and in patients with sepsis, whereas dynamic autoregulation was enhanced after LPS and impaired with a prolonged response time in patients. Hence, acute surges in blood pressure may adversely affect cerebral perfusion in patients with sepsis.
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Affiliation(s)
- Ronan M G Berg
- Centre of Inflammation and Metabolism, Department of Infectious Diseases, University Hospital Rigshospitalet, Copenhagen Ø, Denmark.
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23
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Tzeng YC, Ainslie PN, Cooke WH, Peebles KC, Willie CK, MacRae BA, Smirl JD, Horsman HM, Rickards CA. Assessment of cerebral autoregulation: the quandary of quantification. Am J Physiol Heart Circ Physiol 2012; 303:H658-71. [DOI: 10.1152/ajpheart.00328.2012] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We assessed the convergent validity of commonly applied metrics of cerebral autoregulation (CA) to determine the extent to which the metrics can be used interchangeably. To examine between-subject relationships among low-frequency (LF; 0.07–0.2 Hz) and very-low-frequency (VLF; 0.02–0.07 Hz) transfer function coherence, phase, gain, and normalized gain, we performed retrospective transfer function analysis on spontaneous blood pressure and middle cerebral artery blood velocity recordings from 105 individuals. We characterized the relationships ( n = 29) among spontaneous transfer function metrics and the rate of regulation index and autoregulatory index derived from bilateral thigh-cuff deflation tests. In addition, we analyzed data from subjects ( n = 29) who underwent a repeated squat-to-stand protocol to determine the relationships between transfer function metrics during forced blood pressure fluctuations. Finally, data from subjects ( n = 16) who underwent step changes in end-tidal Pco2 (PetCO2) were analyzed to determine whether transfer function metrics could reliably track the modulation of CA within individuals. CA metrics were generally unrelated or showed only weak to moderate correlations. Changes in PetCO2 were positively related to coherence [LF: β = 0.0065 arbitrary units (AU)/mmHg and VLF: β = 0.011 AU/mmHg, both P < 0.01] and inversely related to phase (LF: β = −0.026 rad/mmHg and VLF: β = −0.018 rad/mmHg, both P < 0.01) and normalized gain (LF: β = −0.042%/mmHg2 and VLF: β = −0.013%/mmHg2, both P < 0.01). However, PetCO2 was positively associated with gain (LF: β = 0.0070 cm·s−1·mmHg−2, P < 0.05; and VLF: β = 0.014 cm·s−1·mmHg−2, P < 0.01). Thus, during changes in PetCO2, LF phase was inversely related to LF gain (β = −0.29 cm·s−1·mmHg−1·rad−1, P < 0.01) but positively related to LF normalized gain (β = 1.3% mmHg−1/rad, P < 0.01). These findings collectively suggest that only select CA metrics can be used interchangeably and that interpretation of these measures should be done cautiously.
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Affiliation(s)
- Y. C. Tzeng
- Cardiovascular Systems Laboratory, University of Otago, Wellington South, New Zealand
| | - P. N. Ainslie
- School of Health and Exercise Sciences, University of British Columbia (Okanagan Campus), Kelowna, British Columbia, Canada; and
| | - W. H. Cooke
- Department of Health and Kinesiology, The University of Texas, San Antonio, Texas
| | - K. C. Peebles
- Cardiovascular Systems Laboratory, University of Otago, Wellington South, New Zealand
| | - C. K. Willie
- School of Health and Exercise Sciences, University of British Columbia (Okanagan Campus), Kelowna, British Columbia, Canada; and
| | - B. A. MacRae
- Cardiovascular Systems Laboratory, University of Otago, Wellington South, New Zealand
| | - J. D. Smirl
- School of Health and Exercise Sciences, University of British Columbia (Okanagan Campus), Kelowna, British Columbia, Canada; and
| | - H. M. Horsman
- Cardiovascular Systems Laboratory, University of Otago, Wellington South, New Zealand
| | - C. A. Rickards
- Department of Health and Kinesiology, The University of Texas, San Antonio, Texas
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24
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Tan CO. Defining the characteristic relationship between arterial pressure and cerebral flow. J Appl Physiol (1985) 2012; 113:1194-200. [PMID: 22961266 DOI: 10.1152/japplphysiol.00783.2012] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Reliable assessment of cerebrovascular effectiveness in buffering against pressure fluctuations may have important implications for the timing and the outcome of therapy after adverse cerebrovascular events. Although linear approaches may indicate the presence or absence of cerebral autoregulation, they are inadequate to describe its characteristics and its effectiveness. Establishing a simple yet robust methodology to reliably measure the effectiveness of cerebral autoregulation could provide a tool to guide screening and clinical options to characterize and treat adverse cerebrovascular events associated with alterations in cerebral perfusion. To test the utility of one such methodology, an oscillatory lower body negative pressure of 30-40 mmHg was used at six frequencies from 0.03 to 0.08 Hz in 43 healthy volunteers, and the pressure-flow relation and the effectiveness of autoregulation was quantified using projection pursuit regression. Projection pursuit regression explained the majority of the relationship between pressure and cerebral blood flow fluctuations and revealed its nature consistently across individuals and across separate study days. The nature of this relationship entailed an autoregulatory region wherein slow arterial pressure fluctuations are effectively counterregulated and two passive regions wherein pressure fluctuations resulted in parallel changes in flow. The effectiveness of autoregulation was significantly reduced as pressure fluctuations became faster. These results demonstrate the characteristic relationship between arterial pressure and cerebral blood flow. Furthermore, the methodology utilized in this study provides a tool that can provide unique insight to integrated cerebrovascular control and may allow diagnosis of physiological alterations underlying impaired cerebral autoregulation.
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Affiliation(s)
- Can Ozan Tan
- Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, MA 02138, USA.
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25
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A nonlinear dynamic approach reveals a long-term stroke effect on cerebral blood flow regulation at multiple time scales. PLoS Comput Biol 2012; 8:e1002601. [PMID: 22807666 PMCID: PMC3395609 DOI: 10.1371/journal.pcbi.1002601] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2012] [Accepted: 05/21/2012] [Indexed: 11/26/2022] Open
Abstract
Cerebral autoregulation (CA) is an important vascular control mechanism responsible for relatively stable cerebral blood flow despite changes of systemic blood pressure (BP). Impaired CA may leave brain tissue unprotected against potentially harmful effects of BP fluctuations. It is generally accepted that CA is less effective or even inactive at frequencies >∼0.1 Hz. Without any physiological foundation, this concept is based on studies that quantified the coupling between BP and cerebral blood flow velocity (BFV) using transfer function analysis. This traditional analysis assumes stationary oscillations with constant amplitude and period, and may be unreliable or even invalid for analysis of nonstationary BP and BFV signals. In this study we propose a novel computational tool for CA assessment that is based on nonlinear dynamic theory without the assumption of stationary signals. Using this method, we studied BP and BFV recordings collected from 39 patients with chronic ischemic infarctions and 40 age-matched non-stroke subjects during baseline resting conditions. The active CA function in non-stroke subjects was associated with an advanced phase in BFV oscillations compared to BP oscillations at frequencies from ∼0.02 to 0.38 Hz. The phase shift was reduced in stroke patients even at > = 6 months after stroke, and the reduction was consistent at all tested frequencies and in both stroke and non-stroke hemispheres. These results provide strong evidence that CA may be active in a much wider frequency region than previously believed and that the altered multiscale CA in different vascular territories following stroke may have important clinical implications for post-stroke recovery. Moreover, the stroke effects on multiscale cerebral blood flow regulation could not be detected by transfer function analysis, suggesting that nonlinear approaches without the assumption of stationarity are more sensitive for the assessment of the coupling of nonstationary physiological signals. Cerebral autoregulation is an important mechanism that regulates blood supply to brain tissue to match metabolic demands during daily activities. Impaired cerebral autoregulation increases the dependence of cerebral blood flow on systemic blood pressure, and is associated with fatal outcomes in patients after brain injury and acute ischemic stroke. Reliable and noninvasive assessment of cerebral autoregulation is still a major challenge in medical diagnostics and clinic studies, mainly because blood pressure and flow are intrinsically nonstationary (possessing complex oscillations/fluctuations with varying amplitude and frequency) while traditional methods for assessment of the pressure-flow dependence assume stationary signals. We propose a new computational technique that is based on nonlinear theories without the assumption of stationary signals. This technique allows us to detect the degradation of cerebral autoregulation in patients with mild ischemic stroke even at >6 months after the insult. The degradation was present in both stroke and non-stroke sides and was accompanied by an altered pressure-flow interaction over a wide range of frequencies from 0.02–0.38 Hz. Our results challenges the traditionally accepted functional region of autoregulation (<∼0.1 Hz). The observed long-term influences of stroke highlight the importance of reliable monitoring of cerebral blood flow regulation for the management and daily care of stroke patients.
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Gur AY, Auriel E, Korczyn AD, Gadoth A, Shopin L, Giladi N, Bornstein NM, Gurevich T. Vasomotor reactivity as a predictor for syncope in patients with orthostatism. Acta Neurol Scand 2012; 126:32-6. [PMID: 21916853 DOI: 10.1111/j.1600-0404.2011.01591.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVES Syncope in patients with orthostatic hypotension (OH) may be the result of impaired cerebral autoregulation. Cerebral autoregulation status can be determined by assessing cerebral vasomotor reactivity (VMR). We assessed and compared VMR in patients with OH with and without syncope. MATERIAL AND METHODS Twenty-nine patients with OH underwent transcranial Doppler (TCD) and the Diamox test (1 g acetazolamide IV) for assessing VMR during elaboration of their OH syndrome. The percent difference between cerebral blood flow velocities (BFV) in the middle cerebral (MCA) and vertebral (VA) arteries before and after acetazolamide was defined as VMR%. We considered increases of BFV of ≥ 40% as being indicative of good VMR and classified our study patients as having good or impaired VMRs accordingly. RESULTS Mean VMR% values of the MCA and VA in patients with OH with syncope (n = 12) were significantly lower as compared with patients with OH without syncope (n = 17): 25.2 ± 20.5% and 42.5 ± 18.6%; 20.9 ± 15.5% and 40.8 ± 28.5%, respectively (P < 0.05). CONCLUSIONS Among patients with OH, we found an association between the presence of syncope and impaired VMR. Assessment of VMR among patients with OH may predict those who are at higher risk to faint and fall and to support more aggressive intervention.
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Affiliation(s)
- A Y Gur
- The Department of Neurology, Barzilai Medical Center, Tel-Aviv, Israel
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27
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Revel A, Gallet C, Oréa V, Chapuis B, Barrès C, Julien C. Effect of chronic cervical ganglionectomy on the spontaneous variability of internal carotid blood flow in the conscious rat. Exp Physiol 2012; 97:564-71. [PMID: 22308161 DOI: 10.1113/expphysiol.2011.062455] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The role of sympathetic innervation in the control of spontaneous fluctuations of cerebral blood flow is still poorly understood. In conscious, unrestrained rats, blood flow velocity (pulsed Doppler) was measured in both internal carotid arteries 1 week after either excision of the right superior cervical ganglion (n = 8) or sham surgery (n = 6). Using Fourier-based techniques, spectral power of each carotid blood flow (CBF) was computed over the whole recording period (246 min), which was segmented into nine consecutive 27.3 min periods. Variability of CBF (spectral power) was ∼40% higher (P < 0.02) on the denervated than on the intact side at frequencies <1 Hz. Coherence between left and right CBFs was similar in the two groups of rats, except in the 0.01-0.1 Hz frequency range where it was lower (P < 0.05) in rats with unilateral sympathectomy (0.54 ± 0.03) than in intact rats (0.74 ± 0.06). In this frequency range, mathematically removing the influence of arterial pressure had little effect on coherence between CBFs in both groups of rats, so that coherence remained significantly lower in rats with unilateral sympathectomy (0.52 ± 0.03) than in intact rats (0.70 ± 0.06). This study indicates that sympathetic innervation has an overall buffering influence on CBF variability. This modulatory role is especially important in a frequency range corresponding to slow fluctuations of CBF (lasting from 10 to 100 s), which are essentially unrelated to fluctuations of arterial pressure.
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Affiliation(s)
- Aurélia Revel
- Unité de Neurocardiologie, Faculté de Pharmacie, Université Lyon 1, F-69008 Lyon, France
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28
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Bellapart J, Chan GSH, Tzeng YC, Ainslie PN, Dunster KR, Barnett AG, Boots R, Fraser JF. The effect of ventricular assist devices on cerebral blood flow and blood pressure fractality. Physiol Meas 2011; 32:1361-72. [PMID: 21775798 DOI: 10.1088/0967-3334/32/9/001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Biological signals often exhibit self-similar or fractal scaling characteristics which may reflect intrinsic adaptability to their underlying physiological system. This study analysed fractal dynamics of cerebral blood flow in patients supported with ventricular assist devices (VAD) to ascertain if sustained modifications of blood pressure waveform affect cerebral blood flow fractality. Simultaneous recordings of arterial blood pressure and cerebral blood flow velocity using transcranial Doppler were obtained from five cardiogenic shock patients supported by VAD, five matched control patients and five healthy subjects. Computation of a fractal scaling exponent (α) at the low-frequency time scale by detrended fluctuation analysis showed that cerebral blood flow velocity exhibited 1/f fractal scaling in both patient groups (α = 0.95 ± 0.09 and 0.97 ± 0.12, respectively) as well as in the healthy subjects (α = 0.86 ± 0.07). In contrast, fluctuation in blood pressure was similar to non-fractal white noise in both patient groups (α = 0.53 ± 0.11 and 0.52 ± 0.09, respectively) but exhibited 1/f scaling in the healthy subjects (α = 0.87 ± 0.04, P < 0.05 compared with the patient groups). The preservation of fractality in cerebral blood flow of VAD patients suggests that normal cardiac pulsation and central perfusion pressure changes are not the integral sources of cerebral blood flow fractality and that intrinsic vascular properties such as cerebral autoregulation may be involved. However, there is a clear difference in the fractal scaling properties of arterial blood pressure between the cardiogenic shock patients and the healthy subjects.
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Affiliation(s)
- Judith Bellapart
- The Prince Charles Hospital and University of Queensland, Rode Road, Brisbane (4032), Australia
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Willie CK, Colino FL, Bailey DM, Tzeng YC, Binsted G, Jones LW, Haykowsky MJ, Bellapart J, Ogoh S, Smith KJ, Smirl JD, Day TA, Lucas SJ, Eller LK, Ainslie PN. Utility of transcranial Doppler ultrasound for the integrative assessment of cerebrovascular function. J Neurosci Methods 2011; 196:221-37. [PMID: 21276818 DOI: 10.1016/j.jneumeth.2011.01.011] [Citation(s) in RCA: 397] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 01/05/2011] [Accepted: 01/06/2011] [Indexed: 01/05/2023]
Abstract
There is considerable utility in the use of transcranial Doppler ultrasound (TCD) to assess cerebrovascular function. The brain is unique in its high energy and oxygen demand but limited capacity for energy storage that necessitates an effective means of regional blood delivery. The relative low cost, ease-of-use, non-invasiveness, and excellent temporal resolution of TCD make it an ideal tool for the examination of cerebrovascular function in both research and clinical settings. TCD is an efficient tool to access blood velocities within the cerebral vessels, cerebral autoregulation, cerebrovascular reactivity to CO(2), and neurovascular coupling, in both physiological states and in pathological conditions such as stroke and head trauma. In this review, we provide: (1) an overview of TCD methodology with respect to other techniques; (2) a methodological synopsis of the cerebrovascular exam using TCD; (3) an overview of the physiological mechanisms involved in regulation of the cerebral blood flow; (4) the utility of TCD for assessment of cerebrovascular pathology; and (5) recommendations for the assessment of four critical and complimentary aspects of cerebrovascular function: intra-cranial blood flow velocity, cerebral autoregulation, cerebral reactivity, and neurovascular coupling. The integration of these regulatory mechanisms from an integrated systems perspective is discussed, and future research directions are explored.
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Affiliation(s)
- C K Willie
- Department of Human Kinetics, Faculty of Health and Social Development, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC, Canada V1V 1V7.
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Tzeng YC, Lucas SJE, Atkinson G, Willie CK, Ainslie PN. Fundamental relationships between arterial baroreflex sensitivity and dynamic cerebral autoregulation in humans. J Appl Physiol (1985) 2010; 108:1162-8. [PMID: 20223996 DOI: 10.1152/japplphysiol.01390.2009] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The functional relationship between dynamic cerebral autoregulation (CA) and arterial baroreflex sensitivity (BRS) in humans is unknown. Given that adequate cerebral perfusion during normal physiological challenges requires the integrated control of CA and the arterial baroreflex, we hypothesized that between-individual variability in dynamic CA would be related to BRS in humans. We measured R-R interval, blood pressure, and cerebral blood flow velocity (transcranial Doppler) in 19 volunteers. BRS was estimated with the modified Oxford method (nitroprusside-phenylephrine injections) and spontaneous low-frequency (0.04-0.15) alpha-index. Dynamic CA was quantified using the rate of regulation (RoR) and autoregulatory index (ARI) derived from the thigh-cuff release technique and transfer function analysis of spontaneous oscillations in blood pressure and mean cerebral blood flow velocity. Results show that RoR and ARI were inversely related to nitroprusside BRS [R=-0.72, confidence interval (CI) -0.89 to -0.40, P=0.0005 vs. RoR; R=-0.69, CI -0.88 to -0.35, P=0.001 vs. ARI], phenylephrine BRS (R=-0.66, CI -0.86 to -0.29, P=0.0002 vs. RoR; R=-0.71, CI -0.89 to -0.38, P=0.0001 vs. ARI), and alpha-index (R=-0.70, CI -0.89 to -0.40, P=0.0008 vs. RoR; R=-0.62, CI -0.84 to -0.24, P=0.005 vs. ARI). Transfer function gain was positively related to nitroprusside BRS (R=0.62, CI 0.24-0.84, P=0.0042), phenylephrine BRS (R=0.52, CI 0.10-0.79, P=0.021), and alpha-index (R=0.69, CI 0.35-0.88, P=0.001). These findings indicate that individuals with an attenuated dynamic CA have greater BRS (and vice versa), suggesting the presence of possible compensatory interactions between blood pressure and mechanisms of cerebral blood flow control in humans. Such compensatory adjustments may account for the divergent changes in dynamic CA and BRS seen, for example, in chronic hypotension and spontaneous hypertension.
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Affiliation(s)
- Yu-Chieh Tzeng
- Physiological Rhythms Unit, Department of Surgery & Anesthesia, University of Otago, Wellington 23A Mein St., PO Box 7343, Wellington South 6242, New Zealand.
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van Beek AHEA, Olde Rikkert MGM, Pasman JW, Hopman MTE, Claassen JAHR. Dynamic cerebral autoregulation in the old using a repeated sit-stand maneuver. ULTRASOUND IN MEDICINE & BIOLOGY 2010; 36:192-201. [PMID: 20045593 DOI: 10.1016/j.ultrasmedbio.2009.10.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2009] [Revised: 10/16/2009] [Accepted: 10/22/2009] [Indexed: 05/28/2023]
Abstract
The aim of this study was to assess the feasibility and reproducibility of a simple and nonobtrusive repeated sit-stand maneuver to assess cerebral autoregulation (CA) in healthy old subjects >70 years. In 27 subjects aged 76 (SD 4) years, we continuously measured blood pressure using photoplethysmography and cerebral blood flow velocity in the middle cerebral artery (transcranial Doppler ultrasonography) during 5 min of sitting rest and again during repeated sit-stand maneuvers at 10 s (0.05 Hz) and 5 s (0.1 Hz) intervals. In 11 randomly selected subjects, these measurements were repeated after 3 months. Both maneuvers induced substantial periodic oscillations in pressure and flow. For example, the maneuvers at 0.05 Hz increased the power spectral density (magnitude) of blood pressure and cerebral blood flow velocity oscillations with 16.3 (mm Hg)(2) and 14.5 (cm/s)(2), respectively (p<0.001). These larger oscillations led to an increase in transfer function coherence compared with spontaneous oscillations from 0.46 to 0.60 for 0.05 Hz maneuvers and from 0.56 to 0.76 for 0.1 Hz maneuvers (p<0.01), allowing for more confident assessment of CA through transfer function phase and gain. This increased coherence was not associated with improved reproducibility however. In conclusion, we were able to investigate CA in old patients using these repeated sit-stand maneuvers, which, compared with spontaneous oscillations, produced a stronger and more clinically relevant hemodynamic challenge for CA.
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Affiliation(s)
- Arenda H E A van Beek
- Department of Geriatric Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
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Porta A, Di Rienzo M, Wessel N, Kurths J. Addressing the complexity of cardiovascular regulation. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:1215-8. [PMID: 19324704 DOI: 10.1098/rsta.2008.0292] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
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