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Crippa IA, Pelosi P, Quispe-Cornejo AA, Messina A, Corradi F, Taccone FS, Robba C. Automated Pupillometry as an Assessment Tool for Intracranial Hemodynamics in Septic Patients. Cells 2022; 11:cells11142206. [PMID: 35883649 PMCID: PMC9319569 DOI: 10.3390/cells11142206] [Citation(s) in RCA: 2] [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: 05/16/2022] [Revised: 06/23/2022] [Accepted: 07/12/2022] [Indexed: 02/05/2023] Open
Abstract
Impaired cerebral autoregulation (CA) may increase the risk of brain hypoperfusion in septic patients. Sepsis dysregulates the autonomic nervous system (ANS), potentially affecting CA. ANS function can be assessed through the pupillary light reflex (PLR). The aim of this prospective, observational study was to investigate the association between CA and PLR in adult septic patients. Transcranial Doppler was used to assess CA and calculate estimated cerebral perfusion pressure (eCPP) and intracranial pressure (eICP). An automated pupillometer (AP) was used to record Neurological Pupil Index (NPi), constriction (CV) and dilation (DV) velocities. The primary outcome was the relationship between AP-derived variables with CA; the secondary outcome was the association between AP-derived variables with eCPP and/or eICP. Among 40 included patients, 21 (53%) had impaired CA, 22 (55%) had low eCPP (<60 mmHg) and 15 (38%) had high eICP (>16 mmHg). DV was lower in patients with impaired CA compared to others; DV predicted impaired CA with area under the curve, AUROC= 0.78 [95% Confidence Interval, CI 0.63−0.94]; DV < 2.2 mm/s had sensitivity 85% and specificity 69% for impaired CA. Patients with low eCPP or high eICP had lower NPi values than others. NPi was correlated with eCPP (r = 0.77, p < 0.01) and eICP (r = −0.87, p < 0.01). Automated pupillometry may play a role to assess brain hemodynamics in septic patients.
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Affiliation(s)
- Ilaria Alice Crippa
- Department of Intensive Care, Erasme Hospital, Université Libre de Bruxelles, 1070 Brussels, Belgium; (A.A.Q.-C.); (F.S.T.)
- Department of Anesthesiology and Intensive Care, San Marco Hospital, San Donato Group, 24040 Zingonia, Italy
- Correspondence:
| | - Paolo Pelosi
- Department of Anesthesiology and Intensive Care, San Martino Policlinico Hospital, IRCCS for Oncology and Neurosciences, 16132 Genoa, Italy; (P.P.); (C.R.)
- Department of Surgical Sciences and Integrated Diagnostics (DISC), University of Genoa, 16132 Genoa, Italy
| | - Armin Alvaro Quispe-Cornejo
- Department of Intensive Care, Erasme Hospital, Université Libre de Bruxelles, 1070 Brussels, Belgium; (A.A.Q.-C.); (F.S.T.)
| | - Antonio Messina
- Humanitas Clinical and Research Center—IRCCS, 20089 Rozzano, Italy;
| | - Francesco Corradi
- Department of Surgical Medical and Molecular Pathology and Critical Care Medicine, University of Pisa, 56126 Pisa, Italy;
| | - Fabio Silvio Taccone
- Department of Intensive Care, Erasme Hospital, Université Libre de Bruxelles, 1070 Brussels, Belgium; (A.A.Q.-C.); (F.S.T.)
| | - Chiara Robba
- Department of Anesthesiology and Intensive Care, San Martino Policlinico Hospital, IRCCS for Oncology and Neurosciences, 16132 Genoa, Italy; (P.P.); (C.R.)
- Department of Surgical Sciences and Integrated Diagnostics (DISC), University of Genoa, 16132 Genoa, Italy
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Sprick JD, Nocera JR, Hajjar I, O'Neill WC, Bailey J, Park J. Cerebral blood flow regulation in end-stage kidney disease. Am J Physiol Renal Physiol 2020; 319:F782-F791. [PMID: 32985235 DOI: 10.1152/ajprenal.00438.2020] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Patients with chronic kidney disease (CKD) and end-stage kidney disease (ESKD) experience an increased risk of cerebrovascular disease and cognitive dysfunction. Hemodialysis (HD), a major modality of renal replacement therapy in ESKD, can cause rapid changes in blood pressure, osmolality, and acid-base balance that collectively present a unique stress to the cerebral vasculature. This review presents an update regarding cerebral blood flow (CBF) regulation in CKD and ESKD and how the maintenance of cerebral oxygenation may be compromised during HD. Patients with ESKD exhibit decreased cerebral oxygen delivery due to anemia, despite cerebral hyperperfusion at rest. Cerebral oxygenation further declines during HD due to reductions in CBF, and this may induce cerebral ischemia or "stunning." Intradialytic reductions in CBF are driven by decreases in cerebral perfusion pressure that may be partially opposed by bicarbonate shifts during dialysis. Intradialytic reductions in CBF have been related to several variables that are routinely measured in clinical practice including ultrafiltration rate and blood pressure. However, the role of compensatory cerebrovascular regulatory mechanisms during HD remains relatively unexplored. In particular, cerebral autoregulation can oppose reductions in CBF driven by reductions in systemic blood pressure, while cerebrovascular reactivity to CO2 may attenuate intradialytic reductions in CBF through promoting cerebral vasodilation. However, whether these mechanisms are effective in ESKD and during HD remain relatively unexplored. Important areas for future work include investigating potential alterations in cerebrovascular regulation in CKD and ESKD and how key regulatory mechanisms are engaged and integrated during HD to modulate intradialytic declines in CBF.
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Affiliation(s)
- Justin D Sprick
- Division of Renal Medicine, Department of Medicine, Emory University Department of Medicine, Atlanta, Georgia.,Department of Veterans Affairs Health Care System, Decatur, Georgia
| | - Joe R Nocera
- Department of Veterans Affairs Health Care System, Decatur, Georgia.,Center for Visual and Neurocognitive Rehabilitation, Department of Veterans Affairs Health Care System, Decatur, Georgia.,Departments of Neurology and Rehabilitation Medicine, Emory University Department of Medicine, Atlanta, Georgia
| | - Ihab Hajjar
- Department of Neurology, Emory University Department of Medicine, Atlanta, Georgia
| | - W Charles O'Neill
- Division of Renal Medicine, Department of Medicine, Emory University Department of Medicine, Atlanta, Georgia
| | - James Bailey
- Division of Renal Medicine, Department of Medicine, Emory University Department of Medicine, Atlanta, Georgia
| | - Jeanie Park
- Division of Renal Medicine, Department of Medicine, Emory University Department of Medicine, Atlanta, Georgia.,Department of Veterans Affairs Health Care System, Decatur, Georgia.,Center for Visual and Neurocognitive Rehabilitation, Department of Veterans Affairs Health Care System, Decatur, Georgia
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Kaur J, Vranish JR, Barbosa TC, Washio T, Young BE, Stephens BY, Brothers RM, Ogoh S, Fadel PJ. Regulation of Regional Cerebral Blood Flow During Graded Reflex-Mediated Sympathetic Activation via Lower Body Negative Pressure. J Appl Physiol (1985) 2018; 125:1779-1786. [PMID: 30188801 PMCID: PMC10392631 DOI: 10.1152/japplphysiol.00623.2018] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The role of the sympathetic nervous system in cerebral blood flow (CBF) regulation remains unclear. Previous studies have primarily measured middle cerebral artery blood velocity to assess CBF. Recently, there has been a transition towards measuring internal carotid artery (ICA) and vertebral artery (VA) blood flow using duplex Doppler ultrasound. Given that the VA supplies autonomic control centers in the brainstem, we hypothesized that graded sympathetic activation via lower body negative pressure (LBNP) would reduce ICA but not VA blood flow. ICA and VA blood flow were measured during two protocols: Protocol-1, low-to-moderate LBNP (-10, -20, -30, -40 Torr) and Protocol-2, moderate-to-high LBNP (-30, -50, -70 Torr). ICA and VA blood flow, diameter, and blood velocity were unaffected up to -40 LBNP. However, -50 and -70 LBNP evoked reductions in ICA and VA blood flow (e.g., -70 LBNP: %∆VA-baseline= -27.6±3.0) that were mediated by decreases in both diameter and velocity (e.g., -70 LBNP: %∆VA-baseline diameter= -7.5±1.9 and %∆VA-baseline velocity= -13.6±1.7), which were comparable between vessels. Since hyperventilation during -70 LBNP reduced PETCO2, this decrease in PETCO2 was matched via voluntary hyperventilation. Reductions in ICA and VA blood flow during hyperventilation alone were significantly smaller than during -70 LBNP and were primarily mediated by decreases in velocity (%∆VA-baseline velocity= -8.6±2.4; %∆VA-baseline diameter= -0.05±0.56). These data demonstrate that both ICA and VA were unaffected by low-to-moderate sympathetic activation, whereas robust reflex-mediated sympatho-excitation caused similar magnitudes of vasoconstriction in both arteries. Thus, contrary to our hypothesis, the ICA was not preferentially vasoconstricted by sympathetic activation.
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Affiliation(s)
- Jasdeep Kaur
- Department of Kinesiology, University of Texas at Arlington, United States
| | - Jennifer R Vranish
- Department of Kinesiology, University of Texas at Arlington, United States
| | - Thales C Barbosa
- Department of Kinesiology, University of Texas at Arlington, United States
| | - Takuro Washio
- Department of Biomedical Engineering, Toyo University
| | | | | | | | - Shigehiko Ogoh
- Department of Biomedical Engineering, Toyo University, Japan
| | - Paul J Fadel
- Department of Kinesiology, University of Texas at Arlington, United States
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Coles JA, Myburgh E, Brewer JM, McMenamin PG. Where are we? The anatomy of the murine cortical meninges revisited for intravital imaging, immunology, and clearance of waste from the brain. Prog Neurobiol 2017; 156:107-148. [PMID: 28552391 DOI: 10.1016/j.pneurobio.2017.05.002] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Revised: 04/25/2017] [Accepted: 05/08/2017] [Indexed: 12/15/2022]
Abstract
Rapid progress is being made in understanding the roles of the cerebral meninges in the maintenance of normal brain function, in immune surveillance, and as a site of disease. Most basic research on the meninges and the neural brain is now done on mice, major attractions being the availability of reporter mice with fluorescent cells, and of a huge range of antibodies useful for immunocytochemistry and the characterization of isolated cells. In addition, two-photon microscopy through the unperforated calvaria allows intravital imaging of the undisturbed meninges with sub-micron resolution. The anatomy of the dorsal meninges of the mouse (and, indeed, of all mammals) differs considerably from that shown in many published diagrams: over cortical convexities, the outer layer, the dura, is usually thicker than the inner layer, the leptomeninx, and both layers are richly vascularized and innervated, and communicate with the lymphatic system. A membrane barrier separates them and, in disease, inflammation can be localized to one layer or the other, so experimentalists must be able to identify the compartment they are studying. Here, we present current knowledge of the functional anatomy of the meninges, particularly as it appears in intravital imaging, and review their role as a gateway between the brain, blood, and lymphatics, drawing on information that is scattered among works on different pathologies.
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Affiliation(s)
- Jonathan A Coles
- Centre for Immunobiology, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, Sir Graeme Davis Building, University of Glasgow, Glasgow, G12 8TA, United Kingdom.
| | - Elmarie Myburgh
- Centre for Immunology and Infection Department of Biology, University of York, Wentworth Way, Heslington, York YO10 5DD, United Kingdom
| | - James M Brewer
- Centre for Immunobiology, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, Sir Graeme Davis Building, University of Glasgow, Glasgow, G12 8TA, United Kingdom
| | - Paul G McMenamin
- Department of Anatomy & Developmental Biology, School of Biomedical and Psychological Sciences and Monash Biomedical Discovery Institute, Faculty of Medicine, Nursing and Health Sciences, Monash University, 10 Chancellor's Walk, Clayton, Victoria, 3800, Australia
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Trangmar SJ, Chiesa ST, Llodio I, Garcia B, Kalsi KK, Secher NH, González-Alonso J. Dehydration accelerates reductions in cerebral blood flow during prolonged exercise in the heat without compromising brain metabolism. Am J Physiol Heart Circ Physiol 2015; 309:H1598-607. [PMID: 26371170 PMCID: PMC4670459 DOI: 10.1152/ajpheart.00525.2015] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 09/03/2015] [Indexed: 11/23/2022]
Abstract
Reductions in cerebral blood flow and extracranial perfusion, induced by dehydration during prolonged exercise in the heat, may be coupled to fatigue. However, cerebral metabolism remains stable through enhanced O2 and glucose extraction. Thus, fatigue developed during prolonged exercise with dehydration is related to reductions in cerebral blood flow rather than to the cerebral metabolic rate for O2. Dehydration hastens the decline in cerebral blood flow (CBF) during incremental exercise, whereas the cerebral metabolic rate for O2 (CMRO2) is preserved. It remains unknown whether CMRO2 is also maintained during prolonged exercise in the heat and whether an eventual decline in CBF is coupled to fatigue. Two studies were undertaken. In study 1, 10 male cyclists cycled in the heat for ∼2 h with (control) and without fluid replacement (dehydration) while internal and external carotid artery blood flow and core and blood temperature were obtained. Arterial and internal jugular venous blood samples were assessed with dehydration to evaluate CMRO2. In study 2, in 8 male subjects, middle cerebral artery blood velocity was measured during prolonged exercise to exhaustion in both dehydrated and euhydrated states. After a rise at the onset of exercise, internal carotid artery flow declined to baseline with progressive dehydration (P < 0.05). However, cerebral metabolism remained stable through enhanced O2 and glucose extraction (P < 0.05). External carotid artery flow increased for 1 h but declined before exhaustion. Fluid ingestion maintained cerebral and extracranial perfusion throughout nonfatiguing exercise. During exhaustive exercise, however, euhydration delayed but did not prevent the decline in cerebral perfusion. In conclusion, during prolonged exercise in the heat, dehydration accelerates the decline in CBF without affecting CMRO2 and also restricts extracranial perfusion. Thus, fatigue is related to a reduction in CBF and extracranial perfusion rather than CMRO2.
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Affiliation(s)
- Steven J Trangmar
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, United Kingdom; and
| | - Scott T Chiesa
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, United Kingdom; and
| | - Iñaki Llodio
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, United Kingdom; and
| | - Benjamin Garcia
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, United Kingdom; and
| | - Kameljit K Kalsi
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, United Kingdom; and
| | - Niels H Secher
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, United Kingdom; and Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, University of Copenhagen, Denmark
| | - José González-Alonso
- Centre for Sports Medicine and Human Performance, Brunel University London, Uxbridge, United Kingdom; and
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Hesp ZC, Zhu Z, Morris TA, Walker RG, Isaacson LG. Sympathetic reinnervation of peripheral targets following bilateral axotomy of the adult superior cervical ganglion. Brain Res 2012; 1473:44-54. [PMID: 22842079 PMCID: PMC3440180 DOI: 10.1016/j.brainres.2012.07.033] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Revised: 07/13/2012] [Accepted: 07/17/2012] [Indexed: 11/16/2022]
Abstract
The ability of adult injured postganglionic axons to reinnervate cerebrovascular targets is unknown, yet these axons can influence cerebral blood flow, particularly during REM sleep. The objective of the present study was to assess quantitatively the sympathetic reinnervation of vascular as well as non-vascular targets following bilateral axotomy of the superior cervical ganglion (SCG) at short term (1 day, 7 day) and long term (8 weeks, 12 weeks) survival time points. The sympathetic innervation of representative extracerebral blood vessels [internal carotid artery (ICA), basilar artery (BA), middle cerebral artery (MCA)], the submandibular gland (SMG), and pineal gland was quantified following injury using an antibody to tyrosine hydroxylase (TH). Changes in TH innervation were related to TH protein content in the SCG. At 7 day following bilateral SCG axotomy, all targets were significantly depleted of TH innervation, and the exact site on the BA where SCG input was lost could be discerned. Complete sympathetic reinnervation of the ICA was observed at long term survival times, yet TH innervation of other vascular targets showed significant decreases even at 12 weeks following axotomy. The SMG was fully reinnervated by 12 weeks, yet TH innervation of the pineal gland remained significantly decreased. TH protein in the SCG was significantly decreased at both short term and long term time points and showed little evidence of recovery. Our data demonstrate a slow reinnervation of most vascular targets following axotomy of the SCG with only minimal recovery of TH protein in the SCG at 12 weeks following injury.
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Affiliation(s)
- Zoe C Hesp
- Center for Neuroscience and Behavior, Department of Zoology, Miami University, Oxford, OH 45056, USA
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Iwasaki KI, Ogawa Y, Aoki K, Yanagida R. Cerebral circulation during mild +Gz hypergravity by short-arm human centrifuge. J Appl Physiol (1985) 2011; 112:266-71. [PMID: 22052869 DOI: 10.1152/japplphysiol.01232.2011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined changes in cerebral circulation in 15 healthy men during exposure to mild +Gz hypergravity (1.5 Gz, head-to-foot) using a short-arm centrifuge. Continuous arterial pressure waveform (tonometry), cerebral blood flow (CBF) velocity in the middle cerebral artery (transcranial Doppler ultrasonography), and partial pressure of end-tidal carbon dioxide (ETco(2)) were measured in the sitting position (1 Gz) and during 21 min of exposure to mild hypergravity (1.5 Gz). Dynamic cerebral autoregulation was assessed by spectral and transfer function analysis between beat-to-beat mean arterial pressure (MAP) and mean CBF velocity (MCBFV). Steady-state MAP did not change, but MCBFV was significantly reduced with 1.5 Gz (-7%). ETco(2) was also reduced (-12%). Variability of MAP increased significantly with 1.5 Gz in low (53%)- and high-frequency ranges (88%), but variability of MCBFV did not change in these frequency ranges, resulting in significant decreases in transfer function gain between MAP and MCBFV (gain in low-frequency range, -17%; gain in high-frequency range, -13%). In contrast, all of these indexes in the very low-frequency range were unchanged. Transfer from arterial pressure oscillations to CBF fluctuations was thus suppressed in low- and high-frequency ranges. These results suggest that steady-state global CBF was reduced, but dynamic cerebral autoregulation in low- and high-frequency ranges was improved with stabilization of CBF fluctuations despite increases in arterial pressure oscillations during mild +Gz hypergravity. We speculate that this improvement in dynamic cerebral autoregulation within these frequency ranges may have been due to compensatory effects against the reduction in steady-state global CBF.
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Affiliation(s)
- Ken-Ichi Iwasaki
- Department of Social Medicine, Division of Hygiene, Nihon University School of Medicine, Itabashi-ku, Tokyo, Japan.
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Ter Laan M, van Dijk JMC, Staal MJ, Elting JWJ. Electrical modulation of the sympathetic nervous system in order to augment cerebral blood flow: a protocol for an experimental study. BMJ Open 2011; 1:e000120. [PMID: 22021767 PMCID: PMC3191412 DOI: 10.1136/bmjopen-2011-000120] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Introduction Cerebral blood flow (CBF) is regulated by several mechanisms. Neurogenic control has been a matter of debate, even though several publications reported the effects of changes in sympathetic tone on CBF. Transcutaneous electrical nerve stimulation and spinal-cord stimulation have been shown to influence peripheral and cerebral blood flow through a sympathetic pathway. The authors hypothesise that certain pathological conditions result in a relative increase in the neurogenic regulation of CBF and that this regulation can be modulated electrically. Methods and analysis Patients with cerebral vasospasm after subarachnoid haemorrhage will be included. The experimental set-up measures several parameters that are involved in cerebral blood flow regulation in patients with cerebral vasospasm after subarachnoid haemorrhage. Measurements are taken at baseline and with stimulation in several frequencies. An ad hoc statistical analysis is used to evaluate different settings of the electrical stimulation. Autoregulation is evaluated with transfer function analysis and autoregulatory index calculations. Ethics and dissemination Ethical registration was granted by Medical Review Ethics Committee Groningen (ID METc 2010.123). All participants provide written informed consent on participation. Upon finishing a pilot study to investigate feasibility and effect, either future prospective (randomised) studies will be designed, or other modalities of electrical stimulation will be explored using the same set-up. Trial Registration Dutch Trial Registry: NTR2358.
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Affiliation(s)
- Mark Ter Laan
- Department of Neurosurgery, University Medical Center Groningen, Groningen, The Netherlands
| | - J Marc C van Dijk
- Department of Neurosurgery, University Medical Center Groningen, Groningen, The Netherlands
| | - Michiel J Staal
- Department of Neurosurgery, University Medical Center Groningen, Groningen, The Netherlands
| | - Jan-Willem J Elting
- Department of Neurophysiology and Neurology, University of Groningen, Groningen, The Netherlands
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Abstract
Cerebral blood flow (CBF) increases and dynamic cerebral autoregulation is impaired by acute hypoxia. We hypothesized that progressive hypocapnia with restoration of arterial oxygen content after altitude acclimatization would normalize CBF and dynamic cerebral autoregulation. To test this hypothesis, dynamic cerebral autoregulation was examined by spectral and transfer function analyses between arterial pressure and CBF velocity variabilities in 11 healthy members of the Danish High-Altitude Research Expedition during normoxia and acute hypoxia (10.5% O(2)) at sea level, and after acclimatization (for over 1 month at 5,260 m at Chacaltaya, Bolivia). Arterial pressure and CBF velocity in the middle cerebral artery (transcranial Doppler), were recorded on a beat-by-beat basis. Steady-state CBF velocity increased during acute hypoxia, but normalized after acclimatization with partial restoration of SaO(2) (acute, 78% ± 2%; chronic, 89% ± 1%) and progression of hypocapnia (end-tidal carbon dioxide: acute, 34 ± 2 mm Hg; chronic, 21 ± 1 mm Hg). Coherence (0.40 ± 0.05 Units at normoxia) and transfer function gain (0.77 ± 0.13 cm/s per mm Hg at normoxia) increased, and phase (0.86 ± 0.15 radians at normoxia) decreased significantly in the very-low-frequency range during acute hypoxia (gain, 141% ± 24%; coherence, 136% ± 29%; phase, -25% ± 22%), which persisted after acclimatization (gain, 136% ± 36%; coherence, 131% ± 50%; phase, -42% ± 13%), together indicating impaired dynamic cerebral autoregulation in this frequency range. The similarity between both acute and chronic conditions suggests that dynamic cerebral autoregulation is impaired by hypoxia even after successful acclimatization to an extreme high altitude.
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