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Burma JS, Roy MA, Kennedy CM, Labrecque L, Brassard P, Smirl JD. A systematic review, meta-analysis, and meta-regression amalgamating the driven approaches used to quantify dynamic cerebral autoregulation. J Cereb Blood Flow Metab 2024:271678X241235878. [PMID: 38635887 DOI: 10.1177/0271678x241235878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 04/20/2024]
Abstract
Numerous driven techniques have been utilized to assess dynamic cerebral autoregulation (dCA) in healthy and clinical populations. The current review aimed to amalgamate this literature and provide recommendations to create greater standardization for future research. The PubMed database was searched with inclusion criteria consisting of original research articles using driven dCA assessments in humans. Risk of bias were completed using Scottish Intercollegiate Guidelines Network and Methodological Index for Non-Randomized Studies. Meta-analyses were conducted for coherence, phase, and gain metrics at 0.05 and 0.10 Hz using deep-breathing, oscillatory lower body negative pressure (OLBNP), sit-to-stand maneuvers, and squat-stand maneuvers. A total of 113 studies were included, with 40 of these incorporating clinical populations. A total of 4126 participants were identified, with younger adults (18-40 years) being the most studied population. The most common techniques were squat-stands (n = 43), deep-breathing (n = 25), OLBNP (n = 20), and sit-to-stands (n = 16). Pooled coherence point estimates were: OLBNP 0.70 (95%CI:0.59-0.82), sit-to-stands 0.87 (95%CI:0.79-0.95), and squat-stands 0.98 (95%CI:0.98-0.99) at 0.05 Hz; and deep-breathing 0.90 (95%CI:0.81-0.99); OLBNP 0.67 (95%CI:0.44-0.90); and squat-stands 0.99 (95%CI:0.99-0.99) at 0.10 Hz. This review summarizes clinical findings, discusses the pros/cons of the 11 unique driven techniques included, and provides recommendations for future investigations into the unique physiological intricacies of dCA.
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Affiliation(s)
- Joel S Burma
- Cerebrovascular Concussion Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
- Integrated Concussion Research Program, University of Calgary, Calgary, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Canada
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada
| | - Marc-Antoine Roy
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada
| | - Courtney M Kennedy
- Cerebrovascular Concussion Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
- Integrated Concussion Research Program, University of Calgary, Calgary, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Canada
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada
| | - Lawrence Labrecque
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada
| | - Patrice Brassard
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada
| | - Jonathan D Smirl
- Cerebrovascular Concussion Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Sport Injury Prevention Research Centre, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, Canada
- Integrated Concussion Research Program, University of Calgary, Calgary, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Canada
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada
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Shoemaker LN, Milej D, Sajid A, Mistry J, Lawrence KS, Shoemaker JK. Characterization of cerebral macro- and microvascular hemodynamics during transient hypotension. J Appl Physiol (1985) 2023; 135:717-725. [PMID: 37560766 PMCID: PMC10642516 DOI: 10.1152/japplphysiol.00743.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Revised: 06/26/2023] [Accepted: 08/04/2023] [Indexed: 08/11/2023] Open
Abstract
The aim of the current study was to establish the interplay between blood flow patterns within a large cerebral artery and a downstream microvascular segment under conditions of transiently reduced mean arterial pressure (MAP). We report data from nine young, healthy participants (5 women; 26 ± 4 yr) acquired during a 15-s bout of sudden-onset lower body negative pressure (LBNP; -80 mmHg). Simultaneous changes in microvascular cerebral blood flow (CBF) and middle cerebral artery blood velocity (MCAvmean) were captured using diffuse correlation spectroscopy (DCS) and transcranial Doppler ultrasound (TCD), respectively. Brachial blood pressure (finger photoplethysmography) and TCD waveforms were extracted at baseline and during the nadir blood pressure (BP) response to LBNP and analyzed using a modified Windkessel model to calculate indices of cerebrovascular resistance (Ri) and compliance (Ci). Compared with baseline, rapid-onset LBNP decreased MAP by 22 ± 16% and Ri by 14 ± 10% (both P ≤ 0.03). Ci increased (322 ± 298%; P < 0.01) but MCAvmean (-8 ± 16%; P = 0.09) and CBF (-2 ± 3%; P = 0.29) were preserved. The results provide evidence that changes in both vascular resistance and compliance preserve CBF, as indexed by no significant changes in MCAvmean or DCS microvascular flow, during transient hypotension.NEW & NOTEWORTHY To characterize the relationship between cerebrovascular patterns within the large middle cerebral artery (MCA) and a downstream microvascular segment, we used a novel combination of transcranial Doppler ultrasound of the MCA and optical monitoring of a downstream microvascular segment, respectively, under conditions of transiently reduced mean arterial pressure (i.e., lower body negative pressure, -80 mmHg). A rapid increase in vessel compliance accompanied the maintenance of MCA blood velocity and downstream microvascular flow.
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Affiliation(s)
- Leena N Shoemaker
- Imaging Program, Lawson Health Research Institute, London, Ontario, Canada
- Department of Medical Biophysics, Western University, London, Ontario, Canada
- School of Kinesiology, Western University, London, Ontario, Canada
| | - Daniel Milej
- Imaging Program, Lawson Health Research Institute, London, Ontario, Canada
- Department of Medical Biophysics, Western University, London, Ontario, Canada
| | - Aleena Sajid
- School of Kinesiology, Western University, London, Ontario, Canada
| | - Jigneshkumar Mistry
- Imaging Program, Lawson Health Research Institute, London, Ontario, Canada
- Department of Medical Biophysics, Western University, London, Ontario, Canada
| | - Keith St Lawrence
- Imaging Program, Lawson Health Research Institute, London, Ontario, Canada
- Department of Medical Biophysics, Western University, London, Ontario, Canada
| | - J Kevin Shoemaker
- School of Kinesiology, Western University, London, Ontario, Canada
- Department of Physiology and Pharmacology, Western University, London, Ontario, Canada
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Banodhe GK, Badhwar S, Sharma HB, Deepak KK. Assessment of baroreflex sensitivity during isometric handgrip exercise and oscillatory lower body negative pressure. J Taibah Univ Med Sci 2023; 18:868-875. [PMID: 36852235 PMCID: PMC9957788 DOI: 10.1016/j.jtumed.2023.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 12/10/2022] [Accepted: 01/06/2023] [Indexed: 01/19/2023] Open
Abstract
Objectives Baroreflex sensitivity (BRS) is an estimate of autonomic control of cardiovascular system via the baroreflex arc. It has been suggested that exercise pressure reflex and muscle metaboreflex override baroreflex during exercise to decrease baroreflex gain, which facilitates the simultaneous rise in blood pressure (BP) and heart rate during the exercise. This study investigated the effects of isometric handgrip exercise (IHE) on baroreflex gain and frequency dependence of baroreflex sensitivity while fluctuations in arterial BP were generated. Methods Thirteen healthy men performed IHE at 20% and 30% of their maximum voluntary contraction (MVC), while oscillatory lower body negative pressure (OLBNP) of 40 mmHg was applied in 0.1 and 0.25 Hz frequencies. Results Compared to the OLBNP at 0.25 Hz frequency alone, the baroreflex gain for diastolic BP (DBP) was significantly reduced with the addition of IHE at 20% and 30% of MVC in the high frequency band. At rest (without IHE and OLBNP) the baroreflex gain was significantly more in the high frequency band for DBP, but the baroreflex gain for DBP was not significantly different when IHE + OLBNP were applied at 20% and 30% of MVC in both frequencies. Conclusions The significant reduction of DBP baroreflex gain with the addition of graded IHE might indicate that exercise pressure reflex and muscle metaboreflex override baroreflex during exercise to decrease baroreflex gain at a high frequency band (0.25 Hz). The frequency-dependent phenomenon of BRS was altered when IHE and OLBNP were applied, meaning that the frequency dependence of BRS was nullified during IHE.
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Affiliation(s)
- Gagan K. Banodhe
- Department of Physiology, All India Institute of Medical Science, Room no. 3106, Tatibandh, Raipur, Chhattisgarh 492001, India,Corresponding address: Department of Physiology, AIIMS, Raipur, India.
| | - Smriti Badhwar
- Women's Cardiovascular Health Lab, York University, Toronto, Canada
| | | | - Kishore K. Deepak
- Department of Physiology, All India Institute of Medical Sciences, New Delhi, India
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Thomas HJ, Marsh CE, Naylor LH, Ainslie PN, Smith KJ, Carter HH, Green DJ. Resistance, but not endurance exercise training, induces changes in cerebrovascular function in healthy young subjects. Am J Physiol Heart Circ Physiol 2021; 321:H881-H892. [PMID: 34559581 DOI: 10.1152/ajpheart.00230.2021] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is generally considered that regular exercise maintains brain health and reduces the risk of cerebrovascular diseases such as stroke and dementia. Since the benefits of different "types" of exercise are unclear, we sought to compare the impacts of endurance and resistance training on cerebrovascular function. In a randomized and crossover design, 68 young healthy adults were recruited to participate in 3 mo of resistance and endurance training. Cerebral hemodynamics through the internal carotid, vertebral, middle and posterior cerebral arteries were measured using Duplex ultrasound and transcranial Doppler at rest and during acute exercise, dynamic autoregulation, and cerebrovascular reactivity (to hypercapnia). Following resistance, but not endurance training, middle cerebral artery velocity and pulsatility index significantly decreased (P < 0.01 and P = 0.02, respectively), whereas mean arterial pressure and indices of cerebrovascular resistance in the middle, posterior, and internal carotid arteries all increased (P < 0.05). Cerebrovascular resistance indices in response to acute exercise and hypercapnia also significantly increased following resistance (P = 0.02), but not endurance training. Our findings, which were consistent across multiple domains of cerebrovascular function, suggest that episodic increases in arterial pressure associated with resistance training may increase cerebrovascular resistance. The implications of long-term resistance training on brain health require future study, especially in populations with pre-existing cerebral hypoperfusion and/or hypotension.NEW & NOTEWORTHY Three months of endurance exercise did not elicit adaptation in any domain of cerebrovascular function in young healthy inactive volunteers. However, resistance training induced decreased pulsatility in the extracranial arteries and increased indices of cerebrovascular resistance in cerebral arteries. This increase in cerebrovascular resistance, apparent at baseline and in response to both hypercapnia and acute exercise, may reflect a protective response in the face of changes in arterial pressure during resistance exercise.
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Affiliation(s)
- Hannah J Thomas
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Western Australia, Australia
| | - Channa E Marsh
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Western Australia, Australia
| | - Louise H Naylor
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Western Australia, Australia
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
| | - Kurt J Smith
- Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, University of Illinois, Chicago, Illinois.,Department of Exercise Science, Physical and Health Education, Faculty of Education, University of Victoria, Victoria, British Columbia, Canada
| | - Howard H Carter
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Western Australia, Australia
| | - Daniel J Green
- School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, Western Australia, Australia
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Anderson GK, Rosenberg AJ, Barnes HJ, Bird J, Pentz B, Byman BRM, Jendzjowsky N, Wilson RJA, Day TA, Rickards CA. Peaks and valleys: oscillatory cerebral blood flow at high altitude protects cerebral tissue oxygenation. Physiol Meas 2021; 42:10.1088/1361-6579/ac0593. [PMID: 34038879 PMCID: PMC11046575 DOI: 10.1088/1361-6579/ac0593] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 05/26/2021] [Indexed: 01/21/2023]
Abstract
Introduction.Oscillatory patterns in arterial pressure and blood flow (at ∼0.1 Hz) may protect tissue oxygenation during conditions of reduced cerebral perfusion and/or hypoxia. We hypothesized that inducing oscillations in arterial pressure and cerebral blood flow at 0.1 Hz would protect cerebral blood flow and cerebral tissue oxygen saturation during exposure to a combination of simulated hemorrhage and sustained hypobaric hypoxia.Methods.Eight healthy human subjects (4 male, 4 female; 30.1 ± 7.6 year) participated in two experiments at high altitude (White Mountain, California, USA; altitude, 3800 m) following rapid ascent and 5-7 d of acclimatization: (1) static lower body negative pressure (LBNP, control condition) was used to induce central hypovolemia by reducing chamber pressure to -60 mmHg for 10 min(0 Hz), and; (2) oscillatory LBNP where chamber pressure was reduced to -60 mmHg, then oscillated every 5 s between -30 mmHg and -90 mmHg for 10 min(0.1 Hz). Measurements included arterial pressure, internal carotid artery (ICA) blood flow, middle cerebral artery velocity (MCAv), and cerebral tissue oxygen saturation (ScO2).Results.Forced 0.1 Hz oscillations in mean arterial pressure and mean MCAv were accompanied by a protection of ScO2(0.1 Hz: -0.67% ± 1.0%; 0 Hz: -4.07% ± 2.0%;P = 0.01). However, the 0.1 Hz profile did not protect against reductions in ICA blood flow (0.1 Hz: -32.5% ± 4.5%; 0 Hz: -19.9% ± 8.9%;P = 0.24) or mean MCAv (0.1 Hz: -18.5% ± 3.4%; 0 Hz: -15.3% ± 5.4%;P = 0.16).Conclusions.Induced oscillatory arterial pressure and cerebral blood flow led to protection of ScO2during combined simulated hemorrhage and sustained hypoxia. This protection was not associated with the preservation of cerebral blood flow suggesting preservation of ScO2may be due to mechanisms occurring within the microvasculature.
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Affiliation(s)
- Garen K Anderson
- Cerebral and Cardiovascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, United States of America
- Co-first authorship
| | - Alexander J Rosenberg
- Cerebral and Cardiovascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, United States of America
- Co-first authorship
| | - Haley J Barnes
- Cerebral and Cardiovascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, United States of America
| | - Jordan Bird
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Brandon Pentz
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Britta R M Byman
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Nicholas Jendzjowsky
- Institute of Respiratory Medicine & Exercise Physiology, The Lundquist Institute at UCLA Harbor Medical, Torrance, CA, United States of America
| | - Richard J A Wilson
- Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute; Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada
| | - Trevor A Day
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Caroline A Rickards
- Cerebral and Cardiovascular Physiology Laboratory, Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, United States of America
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Abstract
PURPOSE To review the recent developments on the effect of chronic high mean arterial blood pressure (MAP) on cerebral blood flow (CBF) autoregulation and supporting the notion that CBF autoregulation impairment has connection with chronic cerebral diseases. Method: A narrative review of all the relevant papers known to the authors was conducted. Results: Our understanding of the connection between cerebral perfusion impairment and chronic high MAP and cerebral disease is rapidly evolving, from cerebral perfusion impairment being the result of cerebral diseases to being the cause of cerebral diseases. We now better understand the intertwined impact of hypertension and Alzheimer's disease (AD) on cerebrovascular sensory elements and recognize cerebrovascular elements that are more vulnerable to these diseases. Conclusion: We conclude with the suggestion that the sensory elements pathology plays important roles in intertwined mechanisms of chronic high MAP and AD that impact cerebral perfusion.
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Affiliation(s)
- Noushin Yazdani
- College of Public Health, University of South Florida , Tampa, FL, USA
| | - Mark S Kindy
- Department of Pharmaceutical Sciences, College of Pharmacy, University of South Florida , Tampa, FL, USA.,Biomedical Research, James A. Haley VA Medical Center , Tampa, FL, USA
| | - Saeid Taheri
- Department of Pharmaceutical Sciences, College of Pharmacy, University of South Florida , Tampa, FL, USA.,Byrd Neuroscience Institute, University of South Florida , Tampa, FL, USA
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Anderson GK, Sprick JD, Park FS, Rosenberg AJ, Rickards CA. Responses of cerebral blood velocity and tissue oxygenation to low-frequency oscillations during simulated haemorrhagic stress in humans. Exp Physiol 2019; 104:1190-1201. [PMID: 31090115 PMCID: PMC11022286 DOI: 10.1113/ep087358] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Accepted: 05/14/2019] [Indexed: 04/19/2024]
Abstract
NEW FINDINGS What is the central question of this study? Do low-frequency oscillations in arterial pressure and cerebral blood velocity protect cerebral blood velocity and oxygenation during central hypovolaemia? What is the main finding and its importance? Low-frequency oscillations in arterial pressure and cerebral blood velocity attenuate reductions in cerebral oxygen saturation but do not protect absolute cerebral blood velocity during central hypovolaemia. This finding indicates the potential importance of haemodynamic oscillations in maintaining cerebral oxygenation and therefore viability of tissues during challenges to cerebral blood flow and oxygen delivery. ABSTRACT Tolerance to both real and simulated haemorrhage varies between individuals. Exaggerated low-frequency (∼0.1 Hz) oscillations in mean arterial pressure and brain blood flow [indexed via middle cerebral artery velocity (MCAv)] have been associated with improved tolerance to reduced central blood volume. The mechanism for this association has not been explored. We hypothesized that inducing low-frequency oscillations in arterial pressure and cerebral blood velocity would attenuate reductions in cerebral blood velocity and oxygenation during simulated haemorrhage. Fourteen subjects (11 men and three women) were exposed to oscillatory (0.1 and 0.05 Hz) and non-oscillatory (0 Hz) lower-body negative pressure profiles with an average chamber pressure of -60 mmHg (randomized and counterbalanced order). Measurements included arterial pressure and stroke volume via finger photoplethysmography, MCAv via transcranial Doppler ultrasound, and cerebral oxygenation of the frontal lobe via near-infrared spectroscopy. Tolerance was higher during the two oscillatory profiles compared with the 0 Hz profile (0.05 Hz, P = 0.04; 0.1 Hz, P = 0.09), accompanied by attenuated reductions in stroke volume (P < 0.001) and cerebral oxygenation of the frontal lobe (P ≤ 0.02). No differences were observed between profiles for reductions in mean arterial pressure (P = 0.17) and MCAv (P = 0.30). In partial support of our hypothesis, cerebral oxygenation, but not cerebral blood velocity, was protected during the oscillatory profiles. Interestingly, more subjects tolerated the oscillatory profiles compared with the static 0 Hz profile, despite similar arterial pressure responses. These findings emphasize the potential importance of haemodynamic oscillations in maintaining perfusion and oxygenation of cerebral tissues during haemorrhagic stress.
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Affiliation(s)
- Garen K. Anderson
- Cerebral & Cardiovascular Physiology Laboratory, Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Justin D. Sprick
- Cerebral & Cardiovascular Physiology Laboratory, Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
- Division of Renal Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA
| | - Flora S. Park
- Cerebral & Cardiovascular Physiology Laboratory, Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Alexander J. Rosenberg
- Cerebral & Cardiovascular Physiology Laboratory, Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Caroline A. Rickards
- Cerebral & Cardiovascular Physiology Laboratory, Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
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Hamner JW, Ishibashi K, Tan CO. Revisiting human cerebral blood flow responses to augmented blood pressure oscillations. J Physiol 2019; 597:1553-1564. [PMID: 30633356 DOI: 10.1113/jp277321] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Accepted: 01/10/2019] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Cerebral autoregulation is most effective in buffering against pressure fluctuations slower than 0.03 Hz (∼30 s). This suggests that frequency bands for characterizing cerebral autoregulation should be redefined Low cross-spectral coherence below 0.03 Hz highlights the limitations of transfer function approaches Haemodynamic changes induced by lower body pressure could not fully explain the differences in autoregulation estimated from spontaneous vs. augmented fluctuations, and thus, observations of spontaneous fluctuations should not be relied on whenever possible. ABSTRACT There is currently little empirical basis for time scales that are considered to be most significant in cerebrovascular counter-regulation of changes in arterial pressure. Although it is well established that cerebral autoregulation behaves as a 'high-pass' filter, recommended frequency bands have been largely arbitrarily determined. To test effectiveness of cerebral autoregulation, we refined oscillatory lower body pressure (LBP) to augment resting pressure fluctuations below 0.1 Hz by a factor of two in 13 young male volunteers, and thoroughly characterized the time and frequency responses of cerebral autoregulation. We observed that despite a threefold increase in arterial pressure power <0.03 Hz with oscillatory LBP, there was no change in cerebral blood flow power, indicating near perfect counter-regulation. By contrast, in the range 0.03-0.10 Hz, both cerebral blood flow and arterial pressure power more than doubled. Our data demonstrate that cerebral autoregulation is most effective in buffering against pressure fluctuations slower than 0.03 Hz (∼30 s). This suggests that frequency bands of interest should be redefined and recording length should be increased considerably to account for this. Furthermore, low cross-spectral coherence below 0.03 Hz, even when pressure fluctuations were augmented, highlights the uncertainty in transfer function approaches and the need to either report precision or use non-linear approaches. Finally, haemodynamic changes induced by LBP could not fully explain the differences in autoregulation estimated from spontaneous vs. augmented fluctuations, and thus, observations of spontaneous fluctuations should not be relied on whenever possible.
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Affiliation(s)
- J W Hamner
- Cerebrovascular Research Laboratory, Spaulding Rehabilitation Hospital, Boston, MA, USA
| | - Keita Ishibashi
- Graduate School of Engineering, Chiba University, Chiba, Japan
| | - Can Ozan Tan
- Cerebrovascular Research Laboratory, Spaulding Rehabilitation Hospital, Boston, MA, USA.,Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, MA, USA
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Schiffner R, Lehmann T, Bischoff SJ, Zippelius T, Nistor M, Schmidt M. Pulmonary hemodynamic effects and pulmonary arterial compliance during hypovolemic shock and reinfusion with human relaxin-2 (serelaxin) treatment in a sheep model. Clin Hemorheol Microcirc 2018; 70:311-325. [PMID: 29710689 DOI: 10.3233/ch-180382] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
BACKGROUND Previous studies on the recombinant form of human relaxin-2 (serelaxin) have shown a decrease of pulmonary hemodynamics after serelaxin injection. Currently, the effect of serelaxin treatment during hypovolemia in a large animal model remains mostly unknown. METHODS 12 sheep were randomly assigned to a sham or serelaxin (30μg/kg serelaxin) group and underwent right heart catheterization. 50% of the estimated total blood volume were removed to induce hypovolemia, and subsequently retransfused 20 min later (reinfusion). Blood gases, heart rate, peripheral and pulmonary arterial oxygen saturation, systolic, diastolic and mean values of both pulmonary artery pressure (PAP) and pulmonary capillary wedge pressure (PCW) were measured. Cardiac output (CO), pulmonary vascular resistance (PVR), pulmonary arterial compliance (PAcompl) and systemic vascular resistance (SVR) were calculated. RESULTS Hypovolemia and shock led to a similar decrease of PAP and PCW in both groups (p≤0.001). CO, SV and PAcompl decreased only in the control group (p≤0.05) and remained higher in the serelaxin-treated group. The results of this study suggest that serelaxin treatment did not negatively influence hemodynamic parameters during hypovolemic shock. CONCLUSION The main conclusion of this study is that cardiopulmonary adaption mechanisms are not critically altered by serelaxin administration during severe hypovolemia and retransfusion.
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Affiliation(s)
- René Schiffner
- Department of Orthopaedics, Jena University Hospital, Friedrich Schiller University, Jena, Germany.,Department of Neurology, Jena University Hospital, Friedrich Schiller University, Jena, Germany
| | - Thomas Lehmann
- Institute of Medical Statistics, Computer Sciences and Documentation Science, Jena University Hospital, Friedrich Schiller University, Jena, Germany
| | - Sabine J Bischoff
- Central Animal Facility, Jena University Hospital, Friedrich Schiller University, Jena, Germany
| | - Timo Zippelius
- Department of Orthopaedics, Jena University Hospital, Friedrich Schiller University, Jena, Germany
| | - Marius Nistor
- Department of Neurology, Jena University Hospital, Friedrich Schiller University, Jena, Germany
| | - Martin Schmidt
- Institute for Biochemistry II, Jena University Hospital, Friedrich Schiller University, Jena, Germany
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10
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van Helmond N, Johnson BD, Holbein WW, Petersen‐Jones HG, Harvey RE, Ranadive SM, Barnes JN, Curry TB, Convertino VA, Joyner MJ. Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure. Physiol Rep 2018; 6:e13594. [PMID: 29464923 PMCID: PMC5820424 DOI: 10.14814/phy2.13594] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 01/03/2018] [Accepted: 01/05/2018] [Indexed: 11/24/2022] Open
Abstract
The ability to maintain adequate cerebral blood flow and oxygenation determines tolerance to central hypovolemia. We tested the hypothesis that acute hypoxemia during simulated blood loss in humans would cause impairments in cerebral blood flow control. Ten healthy subjects (32 ± 6 years, BMI 27 ± 2 kg·m-2 ) were exposed to stepwise lower body negative pressure (LBNP, 5 min at 0, -15, -30, and -45 mmHg) during both normoxia and hypoxia (Fi O2 = 0.12-0.15 O2 titrated to an SaO2 of ~85%). Physiological responses during both protocols were expressed as absolute changes from baseline, one subject was excluded from analysis due to presyncope during the first stage of LBNP during hypoxia. LBNP induced greater reductions in mean arterial pressure during hypoxia versus normoxia (MAP, at -45 mmHg: -20 ± 3 vs. -5 ± 3 mmHg, P < 0.01). Despite differences in MAP, middle cerebral artery velocity responses (MCAv) were similar between protocols (P = 0.41) due to increased cerebrovascular conductance index (CVCi) during hypoxia (main effect, P = 0.04). Low frequency MAP (at -45 mmHg: 17 ± 5 vs. 0 ± 5 mmHg2 , P = 0.01) and MCAv (at -45 mmHg: 4 ± 2 vs. -1 ± 1 cm·s-2 , P = 0.04) spectral power density, as well as low frequency MAP-mean MCAv transfer function gain (at -30 mmHg: 0.09 ± 0.06 vs. -0.07 ± 0.06 cm·s-1 ·mmHg-1 , P = 0.04) increased more during hypoxia versus normoxia. Contrary to our hypothesis, these findings support the notion that cerebral blood flow control is not impaired during exposure to acute hypoxia and progressive central hypovolemia despite lower MAP as a result of compensated increases in cerebral conductance and flow variability.
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Affiliation(s)
| | - Blair D. Johnson
- Center for Research and Education in Special EnvironmentsDepartment of Exercise and Nutrition SciencesUniversity at BuffaloBuffaloNew York
| | | | | | - Ronée E. Harvey
- Mayo Clinic School of Medicine and ScienceMayo ClinicRochesterMinnesota
| | | | - Jill N. Barnes
- Department of KinesiologyUniversity of Wisconsin‐MadisonMadisonWisconsin
| | | | - Victor A. Convertino
- US Army Battlefield Health & Trauma Center for Human Integrative PhysiologyFort Sam HoustonTexas
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A Systematic Review of Neuroprotective Strategies during Hypovolemia and Hemorrhagic Shock. Int J Mol Sci 2017; 18:ijms18112247. [PMID: 29072635 PMCID: PMC5713217 DOI: 10.3390/ijms18112247] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 10/23/2017] [Accepted: 10/24/2017] [Indexed: 02/06/2023] Open
Abstract
Severe trauma constitutes a major cause of death and disability, especially in younger patients. The cerebral autoregulatory capacity only protects the brain to a certain extent in states of hypovolemia; thereafter, neurological deficits and apoptosis occurs. We therefore set out to investigate neuroprotective strategies during haemorrhagic shock. This review was performed in accordance to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Before the start of the search, a review protocol was entered into the PROSPERO database. A systematic literature search of Pubmed, Web of Science and CENTRAL was performed in August 2017. Results were screened and evaluated by two researchers based on a previously prepared inclusion protocol. Risk of bias was determined by use of SYRCLE’s risk of bias tool. The retrieved results were qualitatively analysed. Of 9093 results, 119 were assessed in full-text form, 16 of them ultimately adhered to the inclusion criteria and were qualitatively analyzed. We identified three subsets of results: (1) hypothermia; (2) fluid therapy and/or vasopressors; and (3) other neuroprotective strategies (piracetam, NHE1-inhibition, aprotinin, human mesenchymal stem cells, remote ischemic preconditioning and sevoflurane). Overall, risk of bias according to SYRCLE’s tool was medium; generally, animal experimental models require more rigorous adherence to the reporting of bias-free study design (randomization, etc.). While the individual study results are promising, the retrieved neuroprotective strategies have to be evaluated within the current scientific context—by doing so, it becomes clear that specific promising neuroprotective strategies during states of haemorrhagic shock remain sparse. This important topic therefore requires more in-depth research.
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Rasmussen MB, Eriksen VR, Andresen B, Hyttel-Sørensen S, Greisen G. Quantifying cerebral hypoxia by near-infrared spectroscopy tissue oximetry: the role of arterial-to-venous blood volume ratio. JOURNAL OF BIOMEDICAL OPTICS 2017; 22:25001. [PMID: 28152128 DOI: 10.1117/1.jbo.22.2.025001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2016] [Accepted: 01/06/2017] [Indexed: 06/06/2023]
Abstract
Tissue oxygenation estimated by near-infrared spectroscopy (NIRS) is a volume-weighted mean of the arterial and venous hemoglobin oxygenation. In vivo validation assumes a fixed arterial-to-venous volume-ratio (AV-ratio). Regulatory cerebro-vascular mechanisms may change the AV-ratio. We used hypotension to investigate the influence of blood volume distribution on cerebral NIRS in a newborn piglet model. Hypotension was induced gradually by inflating a balloon-catheter in the inferior vena cava and the regional tissue oxygenation from NIRS ( rStO 2 , NIRS ) was then compared to a reference ( rStO 2 , COX ) calculated from superior sagittal sinus and aortic blood sample co-oximetry with a fixed AV-ratio. Apparent changes in the AV-ratio and cerebral blood volume (CBV) were also calculated. The mean arterial blood pressure (MABP) range was 14 to 82 mmHg. PaCO 2 and SaO 2 were stable during measurements. rStO 2 , NIRS mirrored only 25% (95% Cl: 21% to 28%, p < 0.001 ) of changes in rStO 2 , COX . Calculated AV-ratio increased with decreasing MABP (slope: ? 0.007 · mmHg ? 1
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Affiliation(s)
- Martin B Rasmussen
- Copenhagen University Hospital-Rigshospitalet, Department of Neonatology, Blegdamsvej 9, Copenhagen 2100, DenmarkbUniversity of Copenhagen, Faculty of Health and Medical Sciences, Blegdamsvej 3, Copenhagen 2200, Denmark
| | - Vibeke R Eriksen
- Copenhagen University Hospital-Rigshospitalet, Department of Neonatology, Blegdamsvej 9, Copenhagen 2100, DenmarkbUniversity of Copenhagen, Faculty of Health and Medical Sciences, Blegdamsvej 3, Copenhagen 2200, Denmark
| | - Bjørn Andresen
- Copenhagen University Hospital-Rigshospitalet, Department of Neonatology, Blegdamsvej 9, Copenhagen 2100, Denmark
| | - Simon Hyttel-Sørensen
- Copenhagen University Hospital-Rigshospitalet, Department of Neonatology, Blegdamsvej 9, Copenhagen 2100, Denmark
| | - Gorm Greisen
- Copenhagen University Hospital-Rigshospitalet, Department of Neonatology, Blegdamsvej 9, Copenhagen 2100, Denmark
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Wachowiak MP, Hay DC, Johnson MJ. Assessing heart rate variability through wavelet-based statistical measures. Comput Biol Med 2016; 77:222-30. [PMID: 27598465 DOI: 10.1016/j.compbiomed.2016.07.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2015] [Revised: 07/15/2016] [Accepted: 07/17/2016] [Indexed: 11/17/2022]
Abstract
Because of its utility in the investigation and diagnosis of clinical abnormalities, heart rate variability (HRV) has been quantified with both time and frequency analysis tools. Recently, time-frequency methods, especially wavelet transforms, have been applied to HRV. In the current study, a complementary computational approach is proposed wherein continuous wavelet transforms are applied directly to ECG signals to quantify time-varying frequency changes in the lower bands. Such variations are compared for resting and lower body negative pressure (LBNP) conditions using statistical and information-theoretic measures, and compared with standard HRV metrics. The latter confirm the expected lower variability in the LBNP condition due to sympathetic nerve activity (e.g. RMSSD: p=0.023; SDSD: p=0.023; LF/HF: p=0.018). Conversely, using the standard Morlet wavelet and a new transform based on windowed complex sinusoids, wavelet analysis of the ECG within the observed range of heart rate (0.5-1.25Hz) exhibits significantly higher variability, as measured by frequency band roughness (Morlet CWT: p=0.041), entropy (Morlet CWT: p=0.001), and approximate entropy (Morlet CWT: p=0.004). Consequently, this paper proposes that, when used with well-established HRV approaches, time-frequency analysis of ECG can provide additional insights into the complex phenomenon of heart rate variability.
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Affiliation(s)
- Mark P Wachowiak
- Department of Computer Science and Mathematics, Nipissing University, North Bay, ON, Canada.
| | - Dean C Hay
- Department of Physical and Health Education, Nipissing University, North Bay, ON, Canada
| | - Michel J Johnson
- École de kinésiologie et de loisir, Université de Moncton, Moncton, NB, Canada
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Porta A, Nollo G, Faes L. Bridging the gap between the development of advanced biomedical signal processing tools and clinical practice. Preface. Physiol Meas 2015; 36:627-31. [PMID: 25798722 DOI: 10.1088/0967-3334/36/4/627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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