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Labrecque L, Drapeau A, Rahimaly K, Imhoff S, Brassard P. Dynamic cerebral autoregulation and cerebrovascular carbon dioxide reactivity in middle and posterior cerebral arteries in young endurance-trained women. J Appl Physiol (1985) 2021; 130:1724-1735. [PMID: 33955257 DOI: 10.1152/japplphysiol.00963.2020] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The integrated responses regulating cerebral blood flow are understudied in women, particularly in relation to potential regional differences. In this study, we compared dynamic cerebral autoregulation (dCA) and cerebrovascular reactivity to carbon dioxide (CVRco2) in the middle (MCA) and posterior cerebral arteries (PCA) in 11 young endurance-trained women (age, 25 ± 4 yr; maximal oxygen uptake, 48.1 ± 4.1 mL·kg-1·min-1). dCA was characterized using a multimodal approach including a sit-to-stand and a transfer function analysis (TFA) of forced blood pressure oscillations (repeated squat-stands executed at 0.05 Hz and 0.10 Hz). The hyperoxic rebreathing test was utilized to characterize CVRco2. Upon standing, the percent reduction in blood velocity per percent reduction in mean arterial pressure during initial orthostatic stress (0-15 s after sit-to-stand), the onset of the regulatory response, and the rate of regulation did not differ between MCA and PCA (all P > 0.05). There was an ANOVA effect of anatomical location for TFA gain (P < 0.001) and a frequency effect for TFA phase (P < 0.001). However, normalized gain was not different between arteries (P = 0.18). Absolute CVRco2 was not different between MCA and PCA (1.55 ± 0.81 vs. 1.30 ± 0.49 cm·s-1/Torr, P = 0.26). Relative CVRco2 was 39% lower in the MCA (2.16 ± 1.02 vs. 3.00 ± 1.09%/Torr, P < 0.01). These findings indicate that the cerebral pressure-flow relationship appears to be similar between the MCA and the PCA in young endurance-trained women. The absence of regional differences in absolute CVRco2 could be women specific, although a direct comparison with a group of men will be necessary to address that issue.NEW & NOTEWORTHY Herein, we describe responses from two major mechanisms regulating cerebral blood flow with a special attention on regional differences in young endurance-trained women. The novel findings are that dynamic cerebral autoregulation and absolute cerebrovascular reactivity to carbon dioxide appear similar between the middle and posterior cerebral arteries of these young women.
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Affiliation(s)
- Lawrence Labrecque
- Department of Kinesiology, Faculty of Medicine, Université Laval, Quebec City, Québec, Canada.,Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Quebec City, Québec, Canada
| | - Audrey Drapeau
- Department of Kinesiology, Faculty of Medicine, Université Laval, Quebec City, Québec, Canada.,Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Quebec City, Québec, Canada
| | - Kevan Rahimaly
- Department of Kinesiology, Faculty of Medicine, Université Laval, Quebec City, Québec, Canada.,Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Quebec City, Québec, Canada
| | - Sarah Imhoff
- Department of Kinesiology, Faculty of Medicine, Université Laval, Quebec City, Québec, Canada.,Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Quebec City, Québec, Canada
| | - Patrice Brassard
- Department of Kinesiology, Faculty of Medicine, Université Laval, Quebec City, Québec, Canada.,Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Quebec City, Québec, Canada
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Liu X, Chen X, Kline G, Ross SE, Hall JR, Ding Y, Mallet RT, Shi X. Reduced cerebrovascular and cardioventilatory responses to intermittent hypoxia in elderly. Respir Physiol Neurobiol 2020; 271:103306. [DOI: 10.1016/j.resp.2019.103306] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2019] [Revised: 09/08/2019] [Accepted: 09/22/2019] [Indexed: 11/26/2022]
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3
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Wang H, Shi X, Schenck H, Hall JR, Ross SE, Kline GP, Chen S, Mallet RT, Chen P. Intermittent Hypoxia Training for Treating Mild Cognitive Impairment: A Pilot Study. Am J Alzheimers Dis Other Demen 2020; 35:1533317519896725. [PMID: 31902230 PMCID: PMC10624018 DOI: 10.1177/1533317519896725] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Although intermittent hypoxia training (IHT) has proven effective against various clinical disorders, its impact on mild cognitive impairment (MCI) is unknown. This pilot study examined IHT's safety and therapeutic efficacy in elderly patients with amnestic MCI (aMCI). Seven patients with aMCI (age 69 ± 3 years) alternately breathed 10% O2 and room-air, each 5 minutes, for 8 cycles/session, 3 sessions/wk for 8 weeks. The patients' resting arterial pressures fell by 5 to 7 mm Hg (P < .05) and cerebral tissue oxygenation increased (P < .05) following IHT. Intermittent hypoxia training enhanced hypoxemia-induced cerebral vasodilation (P < .05) and improved mini-mental state examination and digit span scores from 25.7 ± 0.4 to 27.7 ± 0.6 (P = .038) and from 24.7 ± 1.2 to 26.1 ± 1.3 (P = .047), respectively. California verbal learning test score tended to increase (P = .102), but trail making test-B and controlled oral word association test scores were unchanged. Adaptation to moderate IHT may enhance cerebral oxygenation and hypoxia-induced cerebrovasodilation while improving short-term memory and attention in elderly patients with aMCI.
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Affiliation(s)
- Hong Wang
- Departments of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, USA
- Shanghai University of Medicine & Health Sciences, Shanghai, China
| | - Xiangrong Shi
- Departments of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, USA
- Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Hannah Schenck
- Departments of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - James R. Hall
- Departments of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, USA
- Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Sarah E. Ross
- Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, TX, USA
- Department of Internal Medicine, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Geoffrey P. Kline
- Department of Internal Medicine, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Shande Chen
- Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Robert T. Mallet
- Departments of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Peijie Chen
- Shanghai University of Sport, Shanghai, China
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Stotesbury H, Kawadler JM, Hales PW, Saunders DE, Clark CA, Kirkham FJ. Vascular Instability and Neurological Morbidity in Sickle Cell Disease: An Integrative Framework. Front Neurol 2019; 10:871. [PMID: 31474929 PMCID: PMC6705232 DOI: 10.3389/fneur.2019.00871] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Accepted: 07/26/2019] [Indexed: 12/20/2022] Open
Abstract
It is well-established that patients with sickle cell disease (SCD) are at substantial risk of neurological complications, including overt and silent stroke, microstructural injury, and cognitive difficulties. Yet the underlying mechanisms remain poorly understood, partly because findings have largely been considered in isolation. Here, we review mechanistic pathways for which there is accumulating evidence and propose an integrative systems-biology framework for understanding neurological risk. Drawing upon work from other vascular beds in SCD, as well as the wider stroke literature, we propose that macro-circulatory hyper-perfusion, regions of relative micro-circulatory hypo-perfusion, and an exhaustion of cerebral reserve mechanisms, together lead to a state of cerebral vascular instability. We suggest that in this state, tissue oxygen supply is fragile and easily perturbed by changes in clinical condition, with the potential for stroke and/or microstructural injury if metabolic demand exceeds tissue oxygenation. This framework brings together recent developments in the field, highlights outstanding questions, and offers a first step toward a linking pathophysiological explanation of neurological risk that may help inform future screening and treatment strategies.
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Affiliation(s)
- Hanne Stotesbury
- Developmental Neurosciences, UCL Great Ormond Institute of Child Health, London, United Kingdom
| | - Jamie M Kawadler
- Developmental Neurosciences, UCL Great Ormond Institute of Child Health, London, United Kingdom
| | - Patrick W Hales
- Developmental Neurosciences, UCL Great Ormond Institute of Child Health, London, United Kingdom
| | - Dawn E Saunders
- Developmental Neurosciences, UCL Great Ormond Institute of Child Health, London, United Kingdom.,Department of Radiology, Great Ormond Hospital, London, United Kingdom
| | - Christopher A Clark
- Developmental Neurosciences, UCL Great Ormond Institute of Child Health, London, United Kingdom
| | - Fenella J Kirkham
- Developmental Neurosciences, UCL Great Ormond Institute of Child Health, London, United Kingdom.,Clinical and Experimental Sciences, University of Southampton, Southampton, United Kingdom.,Department of Child Health, University Hospital Southampton, Southampton, United Kingdom.,Department of Paediatric Neurology, Kings College Hospital NHS Foundation Trust, London, United Kingdom
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Purkayastha S, Stokes M, Bell KR. Autonomic nervous system dysfunction in mild traumatic brain injury: a review of related pathophysiology and symptoms. Brain Inj 2019; 33:1129-1136. [DOI: 10.1080/02699052.2019.1631488] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Sushmita Purkayastha
- Department of Applied Physiology and Wellness, Simmons School of Education and Human Development, Southern Methodist University, Dallas, TX, USA
- Department of Physical Medicine and Rehabilitation, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Mathew Stokes
- Department of Pediatrics/Division of Pediatric Neurology & Pain Management, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Kathleen R Bell
- Department of Physical Medicine and Rehabilitation, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Purkayastha S, Sorond FA, Lyng S, Frantz J, Murphy MN, Hynan LS, Sabo T, Bell KR. Impaired Cerebral Vasoreactivity Despite Symptom Resolution in Sports-Related Concussion. J Neurotrauma 2019; 36:2385-2390. [PMID: 30693827 DOI: 10.1089/neu.2018.5861] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Traumatic brain injury (TBI) is associated with increased risk of later-life neurodegeneration and dementia. However, the underpinning mechanisms are poorly understood, and secondary injury resulting from perturbed physiological processes plays a significant role. Cerebral vasoreactivity (CVR), a measure of hemodynamic reserve, is known to be impaired in TBI. However, the temporal course of this physiological perturbation is not established. We examined CVR and clinical symptoms on day 3 (T1), day 21 (T2), and day 90 (T3) after concussion in collegiate athletes and cross-sectionally in non-injured controls. Changes in middle cerebral artery blood flow velocity (MCAV; transcranial Doppler ultrasonography) were measured during changes in end-tidal CO2 (PetCO2) at normocapnia, hypercapnia (inspiring 8% CO2), and hypocapnia (hyperventilation). CVR was determined as the slope of the linear relationship and expressed as percent change in MCAV per mmHg change in PetCO2. CVR was attenuated during the acute phase T1 (1.8 ± 0.4U; p = 0.0001), subacute phases T2 (2.0 ± 0.4U; p = 0.0017), and T3 (1.9 ± 0.6U; p = 0.023) post-concussion compared to the controls (2.3 ± 0.3U). Concussed athletes exhibited higher symptom number (2.5 ± 3.0 vs. 12.1 ± 7.0; p < 0.0001) and severity (4.2 ± 6.0 vs. 29.5 ± 23.0; p < 0.0001), higher Patient Health Questionnaire-9 score (2.2 ± 2.0 vs. 9.1 ± 6.0; p = 0.0003) at T1. However, by T2, symptoms had resolved. We show that CVR is impaired as early as 4 days and remains impaired up to 3 months post-injury despite symptom resolution. Persistent perturbations in CVR may therefore be involved in secondary injury. Future studies with a larger sample size and longer follow-up period are needed to validate this finding and delineate the duration of this vulnerable period.
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Affiliation(s)
- Sushmita Purkayastha
- 1Department of Applied Physiology and Wellness, Simmons School of Education and Human Development, Southern Methodist University, Dallas, Texas.,2Department of Physical Medicine and Rehabilitation, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Farzaneh A Sorond
- 3Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois
| | - Sydney Lyng
- 1Department of Applied Physiology and Wellness, Simmons School of Education and Human Development, Southern Methodist University, Dallas, Texas
| | - Justin Frantz
- 1Department of Applied Physiology and Wellness, Simmons School of Education and Human Development, Southern Methodist University, Dallas, Texas
| | - Megan N Murphy
- 1Department of Applied Physiology and Wellness, Simmons School of Education and Human Development, Southern Methodist University, Dallas, Texas
| | - Linda S Hynan
- 4Department of Clinical Science and Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Tonia Sabo
- 5Department of Pediatrics/Division of Pediatric Neurology & Pain Management, University of Texas Southwestern Medical Center, Dallas, Texas
| | - Kathleen R Bell
- 2Department of Physical Medicine and Rehabilitation, University of Texas Southwestern Medical Center, Dallas, Texas
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Liu X, Xu D, Hall JR, Ross S, Chen S, Liu H, Mallet RT, Shi X. Enhanced cerebral perfusion during brief exposures to cyclic intermittent hypoxemia. J Appl Physiol (1985) 2017; 123:1689-1697. [DOI: 10.1152/japplphysiol.00647.2017] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cerebral vasodilation and increased cerebral oxygen extraction help maintain cerebral oxygen uptake in the face of hypoxemia. This study examined cerebrovascular responses to intermittent hypoxemia in eight healthy men breathing 10% O2 for 5 cycles, each 6 min, interspersed with 4 min of room air breathing. Hypoxia exposures raised heart rate ( P < 0.01) without altering arterial pressure, and increased ventilation ( P < 0.01) by expanding tidal volume. Arterial oxygen saturation ([Formula: see text]) and cerebral tissue oxygenation ([Formula: see text]) fell ( P < 0.01) less appreciably in the first bout (from 97.0 ± 0.3% and 72.8 ± 1.6% to 75.5 ± 0.9% and 54.5 ± 0.9%, respectively) than the fifth bout (from 94.9 ± 0.4% and 70.8 ± 1.0% to 66.7 ± 2.3% and 49.2 ± 1.5%, respectively). Flow velocity in the middle cerebral artery ( VMCA) and cerebrovascular conductance increased in a sigmoid fashion with decreases in [Formula: see text] and [Formula: see text]. These stimulus-response curves shifted leftward and upward from the first to the fifth hypoxia bouts; thus, the centering points fell from 79.2 ± 1.4 to 74.6 ± 1.1% ( P = 0.01) and from 59.8 ± 1.0 to 56.6 ± 0.3% ( P = 0.002), and the minimum VMCA increased from 54.0 ± 0.5 to 57.2 ± 0.5 cm/s ( P = 0.0001) and from 53.9 ± 0.5 to 57.1 ± 0.3 cm/s ( P = 0.0001) for the [Formula: see text]- VMCA and [Formula: see text]- VMCA curves, respectively. Cerebral oxygen extraction increased from prehypoxia 0.22 ± 0.01 to 0.25 ± 0.02 in minute 6 of the first hypoxia bout, and remained elevated between 0.25 ± 0.01 and 0.27 ± 0.01 throughout the fifth hypoxia bout. These results demonstrate that cerebral vasodilation combined with enhanced cerebral oxygen extraction fully compensated for decreased oxygen content during acute, cyclic hypoxemia. NEW & NOTEWORTHY Five bouts of 6-min intermittent hypoxia (IH) exposures to 10% O2 progressively reduce arterial oxygen saturation ([Formula: see text]) to 67% without causing discomfort or distress. Cerebrovascular responses to hypoxemia are dynamically reset over the course of a single IH session, such that threshold and saturation for cerebral vasodilations occurred at lower [Formula: see text] and cerebral tissue oxygenation ([Formula: see text]) during the fifth vs. first hypoxia bouts. Cerebral oxygen extraction is augmented during acute hypoxemia, which compensates for decreased arterial O2 content.
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Affiliation(s)
- Xiaoli Liu
- Institute of Cardiovascular & Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas
- Department of Physical Therapy, University of North Texas Health Science Center, Fort Worth, Texas
| | - Diqun Xu
- Institute of Cardiovascular & Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas
| | - James R. Hall
- Hubei University for Nationalities, Enshi, Hubei, China
| | - Sarah Ross
- Hubei University for Nationalities, Enshi, Hubei, China
| | - Shande Chen
- Hubei University for Nationalities, Enshi, Hubei, China
- Institute of Healthy Aging, University of North Texas Health Science Center, Fort Worth, Texas
| | - Howe Liu
- Department of Biostatistics, University of North Texas Health Science Center, Fort Worth, Texas
| | - Robert T. Mallet
- Institute of Cardiovascular & Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas
| | - Xiangrong Shi
- Institute of Cardiovascular & Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas
- Institute of Healthy Aging, University of North Texas Health Science Center, Fort Worth, Texas
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Xu D, Wang H, Chen S, Ross S, Liu H, Olivencia-Yurvati A, Raven PB, Shi X. Aerobic Exercise Training Improves Orthostatic Tolerance in Aging Humans. Med Sci Sports Exerc 2017; 49:728-735. [PMID: 27824693 DOI: 10.1249/mss.0000000000001153] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
PURPOSE This study was designed to test the hypothesis that aerobic exercise training of the elderly will increase aerobic fitness without compromising orthostatic tolerance (OT). METHODS Eight healthy sedentary volunteers (67.0 ± 1.7 yr old, four women) participated in 1 yr of endurance exercise training (stationary bicycle and/or treadmill) program at the individuals' 65%-75% of HRpeak. Peak O2 uptake (V˙O2peak) and HRpeak were determined by a maximal exercise stress test using a bicycle ergometer. Carotid baroreceptor reflex (CBR) control of HR and mean arterial pressure (MAP) were assessed by a neck pressure-neck suction protocol. Each subject's maximal gain (Gmax), or sensitivity, of the CBR function curves were derived from fitting their reflex HR and MAP responses to the corresponding neck pressure-neck suction stimuli using a logistic function curve. The subjects' OT was assessed using lower-body negative pressure (LBNP) graded to -50 mm Hg; the sum of the product of LBNP intensity and time (mm Hg·min) was calculated as the cumulative stress index. RESULTS Training increased V˙O2peak (before vs after: 22.8 ± 0.92 vs 27.9 ± 1.33 mL·min·kg, P < 0.01) and HRpeak (154 ± 4 vs 159 ± 3 bpm, P < 0.02) and decreased resting HR (65 ± 5 vs 59 ± 5 bpm, P < 0.02) and MAP (99 ± 2 vs 87 ± 2 mm Hg, P < 0.05). CBR stimulus-response curves identified a leftward shift with an increase in CBR-HR Gmax (from -0.13 ± 0.02 to -0.27 ± 0.04 bpm·mm Hg, P = 0.01). Cumulative stress index was increased from 767 ± 68 mm Hg·min pretraining to 946 ± 44 mm Hg·min posttraining (P < 0.05). CONCLUSION Aerobic exercise training improved the aerobic fitness and OT in elderly subjects. An improved OT is likely associated with an enhanced CBR function that has been reset to better maintain cerebral perfusion and cerebral tissue oxygenation during LBNP.
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Affiliation(s)
- Diqun Xu
- 1Institute of Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, TX; 2Minnan Normal University, Fujian Province, CHINA; 3Department of Physical Therapy, University of North Texas Health Science Center, Fort Worth, TX; 4Shanghai University of Medicine and Health Sciences, Shanghai, CHINA; 5Department of Biostatistics and Epidemiology, University of North Texas Health Science Center, Fort Worth, TX; 6Center for Alzheimer's and Neurodegenerative Disease Research, University of North Texas Health Science Center, Fort Worth, TX; and 7Center for Geriatrics, Institute for Healthy Aging, University of North Texas Health Science Center, Fort Worth, TX
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Steinback CD, Poulin MJ. Influence of Hypoxia on Cerebral Blood Flow Regulation in Humans. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 903:131-44. [PMID: 27343093 DOI: 10.1007/978-1-4899-7678-9_9] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The brain is a vital organ that relies on a constant and adequate supply of blood to match oxygen and glucose delivery with the local metabolic demands of active neurones. It is well established that cerebral blood flow is altered in response to both neural activity and humoral stimuli. Thus, augmented neural activation (e.g. visual stimulation) leads to locally increased cerebral blood flow via functional hyperaemia, whereas humoral stimuli (i.e. alterations in arterial PO2 and PCO2) produce global increases in cerebral blood flow. Perhaps not surprisingly, cerebrovascular responses to neural activity and humoral stimuli may not be highly correlated because they reflect different physiological mechanisms for vasodilation. Exquisite regulation of cerebral blood flow is particularly important under hypoxic conditions when cerebral PO2 can be reduced substantially. Indeed, cerebrovascular reactivity to hypoxia determines the capacity of cerebral vessels to respond and compensate for a reduced oxygen supply. This reactivity is dynamic, changing with prolonged exposure to hypoxic environments, and in patients and healthy individuals exposed to chronic intermittent periods of hypoxia. More recently, a number of animal studies have provided evidence that glial cells (i.e. astrocytes) play an important role in regulating cerebral blood flow under normoxic and hypoxic conditions. This review aims to summarize our current understanding of cerebral blood flow control during hypoxia in humans and put into context the underlying neurovascular mechanisms that may contribute to this regulation.
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Affiliation(s)
- Craig D Steinback
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Marc J Poulin
- Departments of Physiology and Pharmacology and Clinical Neurosciences, Faculty of Medicine, Hotchkiss Brain Institute, The Libin Cardiovascular Institute of Alberta, Calgary, AB, Canada.
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Chung CC, Pimentel D, Jor'dan AJ, Hao Y, Milberg W, Novak V. Inflammation-associated declines in cerebral vasoreactivity and cognition in type 2 diabetes. Neurology 2015; 85:450-8. [PMID: 26156513 DOI: 10.1212/wnl.0000000000001820] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Accepted: 04/06/2015] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE The aim of this prospective study was to investigate the relationships between inflammation, cerebral vasoregulation, and cognitive decline in type 2 diabetes mellitus (T2DM) over a 2-year span. METHODS Sixty-five participants (aged 66 ± 9.2 years, 35 with T2DM, 33 women) were enrolled for this 2-year prospective study. Continuous arterial spin labeling at 3-tesla MRI was used to measure global and regional cerebral perfusion and vasoreactivity. Neuropsychological measures were evaluated at the beginning and completion of the study. The associations between serum inflammatory markers, regional cerebral vasoreactivity, and cognitive functions were examined using least squares models. RESULTS After 2 years of follow-up, participants with T2DM had diminished global and regional cerebral vasoreactivity and a decline in multiple cognitive tasks compared with baseline (p < 0.0001-0.012). In the T2DM group, lower cerebral vasoreactivity was associated with a greater decrease in daily living activities score (r(2) adj = 0.35, p = 0.04), and lower global vasodilation was associated with a greater decline in executive function (r(2) adj = 0.6, p = 0.047). Higher serum soluble intercellular and vascular adhesion molecules, higher cortisol, and higher C-reactive protein levels at baseline were associated with greater decreases in cerebral vasoreactivity and vasodilation only in the T2DM group (r(2) adj = 0.16-0.53, p = 0.007-0.048), independent of diabetes control and 24-hour blood pressure. Higher glycated hemoglobin A1c levels were associated with a greater increase in vasoconstriction in the T2DM group. CONCLUSIONS Inflammation may further impair cerebral vasoregulation, which consequently accelerates decline in executive function and daily activities performance in older people with T2DM.
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Affiliation(s)
- Chen-Chih Chung
- From the Departments of Neurology (C.-C.C., D.P., V.N.) and Gerontology (D.P., A.J.J., Y.H., V.N.), Beth Israel Deaconess Medical Center, Boston, MA; Department of Neurology (C.-C.C.), Shuang Ho Hospital, Taipei Medical University, Taiwan; Institute for Aging Research, Hebrew SeniorLife (A.J.J.), and New England Geriatric, Research, Education and Clinical Center-Boston Division, VA Boston Healthcare, and Department of Psychiatry (W.M.), Harvard Medical School, Boston, MA; and School of Acupuncture-Moxibustion and Tuina (Y.H.), Beijing University of Chinese Medicine, China
| | - Daniela Pimentel
- From the Departments of Neurology (C.-C.C., D.P., V.N.) and Gerontology (D.P., A.J.J., Y.H., V.N.), Beth Israel Deaconess Medical Center, Boston, MA; Department of Neurology (C.-C.C.), Shuang Ho Hospital, Taipei Medical University, Taiwan; Institute for Aging Research, Hebrew SeniorLife (A.J.J.), and New England Geriatric, Research, Education and Clinical Center-Boston Division, VA Boston Healthcare, and Department of Psychiatry (W.M.), Harvard Medical School, Boston, MA; and School of Acupuncture-Moxibustion and Tuina (Y.H.), Beijing University of Chinese Medicine, China
| | - Azizah J Jor'dan
- From the Departments of Neurology (C.-C.C., D.P., V.N.) and Gerontology (D.P., A.J.J., Y.H., V.N.), Beth Israel Deaconess Medical Center, Boston, MA; Department of Neurology (C.-C.C.), Shuang Ho Hospital, Taipei Medical University, Taiwan; Institute for Aging Research, Hebrew SeniorLife (A.J.J.), and New England Geriatric, Research, Education and Clinical Center-Boston Division, VA Boston Healthcare, and Department of Psychiatry (W.M.), Harvard Medical School, Boston, MA; and School of Acupuncture-Moxibustion and Tuina (Y.H.), Beijing University of Chinese Medicine, China
| | - Ying Hao
- From the Departments of Neurology (C.-C.C., D.P., V.N.) and Gerontology (D.P., A.J.J., Y.H., V.N.), Beth Israel Deaconess Medical Center, Boston, MA; Department of Neurology (C.-C.C.), Shuang Ho Hospital, Taipei Medical University, Taiwan; Institute for Aging Research, Hebrew SeniorLife (A.J.J.), and New England Geriatric, Research, Education and Clinical Center-Boston Division, VA Boston Healthcare, and Department of Psychiatry (W.M.), Harvard Medical School, Boston, MA; and School of Acupuncture-Moxibustion and Tuina (Y.H.), Beijing University of Chinese Medicine, China
| | - William Milberg
- From the Departments of Neurology (C.-C.C., D.P., V.N.) and Gerontology (D.P., A.J.J., Y.H., V.N.), Beth Israel Deaconess Medical Center, Boston, MA; Department of Neurology (C.-C.C.), Shuang Ho Hospital, Taipei Medical University, Taiwan; Institute for Aging Research, Hebrew SeniorLife (A.J.J.), and New England Geriatric, Research, Education and Clinical Center-Boston Division, VA Boston Healthcare, and Department of Psychiatry (W.M.), Harvard Medical School, Boston, MA; and School of Acupuncture-Moxibustion and Tuina (Y.H.), Beijing University of Chinese Medicine, China
| | - Vera Novak
- From the Departments of Neurology (C.-C.C., D.P., V.N.) and Gerontology (D.P., A.J.J., Y.H., V.N.), Beth Israel Deaconess Medical Center, Boston, MA; Department of Neurology (C.-C.C.), Shuang Ho Hospital, Taipei Medical University, Taiwan; Institute for Aging Research, Hebrew SeniorLife (A.J.J.), and New England Geriatric, Research, Education and Clinical Center-Boston Division, VA Boston Healthcare, and Department of Psychiatry (W.M.), Harvard Medical School, Boston, MA; and School of Acupuncture-Moxibustion and Tuina (Y.H.), Beijing University of Chinese Medicine, China.
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Abstract
Cerebral autoregulation describes a mechanism that maintains cerebral blood flow stable despite fluctuating perfusion pressure. Multiple nonperfusion pressure processes also regulate cerebral perfusion. These mechanisms are integrated. The effect of the interplay between carbon dioxide and perfusion pressure on cerebral circulation has not been specifically reviewed. On the basis of the published data and speculation on the aspects that are without supportive data, the authors offer a conceptualization delineating the regulation of cerebral autoregulation by carbon dioxide. The authors conclude that hypercapnia causes the plateau to progressively ascend, a rightward shift of the lower limit, and a leftward shift of the upper limit. Conversely, hypocapnia results in the plateau shifting to lower cerebral blood flows, unremarkable change of the lower limit, and unclear change of the upper limit. It is emphasized that a sound understanding of both the limitations and the dynamic and integrated nature of cerebral autoregulation fosters a safer clinical practice.
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Zhang P, Shi X, Downey HF. Two-week normobaric intermittent-hypoxic exposures stabilize cerebral perfusion during hypocapnia and hypercapnia. Exp Biol Med (Maywood) 2014; 240:961-8. [PMID: 25504012 DOI: 10.1177/1535370214562339] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Accepted: 10/14/2014] [Indexed: 11/15/2022] Open
Abstract
The effect of moderately extended, intermittent-hypoxia (IH) on cerebral perfusion during changes in CO2 was unknown. Thus, we assessed the changes in cerebral vascular conductance (CVC) and cerebral tissue oxygenation (ScO2) during experimental hypocapnia and hypercapnia following 14-day normobaric exposures to IH (10% O2). CVC was estimated from the ratio of mean middle cerebral arterial blood flow velocity (transcranial Doppler sonography) to mean arterial pressure (tonometry), and ScO2 in the prefrontal cortex was monitored by near-infrared spectroscopy. Changes in CVC and ScO2 during changes in partial pressure of end-tidal CO2 (PETCO2, mass spectrometry) induced by 30-s paced-hyperventilation (hypocapnia) and during 6-min CO2 rebreathing (hypercapnia) were compared before and after 14-day IH exposures in eight young nonsmokers. Repetitive IH exposures reduced the ratio of %ΔCVC/ΔPETCO2 during hypocapnia (1.00 ± 0.13 vs 1.94 ± 0.35 vs %/mmHg, P = 0.026) and the slope of ΔCVC/ΔPETCO2 during hypercapnia (1.79 ± 0.37 vs 2.97 ± 0.64 %/mmHg, P = 0.021), but had no significant effect on ΔScO2/ΔPETCO2. The ventilatory response to hypercapnia during CO2 rebreathing was significantly diminished following 14-day IH exposures (0.83 ± 0.07 vs 1.14 ± 0.09 L/min/mmHg, P = 0.009). We conclude that repetitive normobaric IH exposures significantly diminish variations of cerebral perfusion in response to hypercapnia and hypocapnia without compromising cerebral tissue oxygenation. This IH-induced blunting of cerebral vasoreactivity during CO2 variations helps buffer excessive oscillations of cerebral underperfusion and overperfusion while sustaining cerebral O2 homeostasis.
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Affiliation(s)
- Peizhen Zhang
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX 76107, USA Beijing Sport University, Beijing 100084, China
| | - Xiangrong Shi
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX 76107, USA Cardiovascular Research Institute, University of North Texas Health Science Center, Fort Worth, TX 76107, USA
| | - H Fred Downey
- Department of Integrative Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX 76107, USA Cardiovascular Research Institute, University of North Texas Health Science Center, Fort Worth, TX 76107, USA
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Brothers RM, Lucas RAI, Zhu YS, Crandall CG, Zhang R. Cerebral vasomotor reactivity: steady-state versus transient changes in carbon dioxide tension. Exp Physiol 2014; 99:1499-510. [PMID: 25172891 PMCID: PMC4218865 DOI: 10.1113/expphysiol.2014.081190] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
New Findings What is the central question of this study? The relationship between changes in cerebral blood flow and arterial carbon dioxide tension is used to assess cerebrovascular function. Hypercapnia is generally evoked by two methods, i.e. steady-state and transient increases in carbon dioxide tension. In some cases, the hypercapnia is immediately preceded by a period of hypocapnia. It is unknown whether the cerebrovascular response differs between these methods and whether a period of hypocapnia blunts the subsequent response to hypercapnia. What is the main finding and its importance? The cerebrovascular response is similar between steady-state and transient hypercapnia. However, hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.
Cerebral vasomotor reactivity (CVMR) to changes in arterial carbon dioxide tension () is assessed during steady-state or transient changes in . This study tested the following two hypotheses: (i) that CVMR during steady-state changes differs from that during transient changes in ; and (ii) that CVMR during rebreathing-induced hypercapnia would be blunted when preceded by a period of hyperventilation. For each hypothesis, end-tidal carbon dioxide tension () middle cerebral artery blood velocity (CBFV), cerebrovascular conductance index (CVCI; CBFV/mean arterial pressure) and CVMR (slope of the linear regression between changes in CBFV and CVCI versus) were assessed in eight individuals. To address the first hypothesis, measurements were made during the following two conditions (randomized): (i) steady-state increases in of 5 and 10 Torr above baseline; and (ii) rebreathing-induced transient breath-by-breath increases in . The linear regression for CBFV versus (P = 0.65) and CVCI versus (P = 0.44) was similar between methods; however, individual variability in CBFV or CVCI responses existed among subjects. To address the second hypothesis, the same measurements were made during the following two conditions (randomized): (i) immediately following a brief period of hypocapnia induced by hyperventilation for 1 min followed by rebreathing; and (ii) during rebreathing only. The slope of the linear regression for CBFV versus (P < 0.01) and CVCI versus (P < 0.01) was reduced during hyperventilation plus rebreathing relative to rebreathing only. These results indicate that cerebral vasomotor reactivity to changes in is similar regardless of the employed methodology to induce changes in and that hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.
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Affiliation(s)
- R Matthew Brothers
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA Department of Kinesiology and Health Education, University of Texas at Austin, TX, USA
| | - Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yong-Sheng Zhu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Rong Zhang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Cerebral vasoreactivity: impact of heat stress and lower body negative pressure. Clin Auton Res 2014; 24:135-41. [PMID: 24706257 DOI: 10.1007/s10286-014-0241-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Accepted: 03/20/2014] [Indexed: 10/25/2022]
Abstract
OBJECTIVE Cerebrovascular reactivity represents the capacity of the cerebral circulation to raise blood flow in the face of increased demand, and may be reduced in some clinical and physiological conditions. We tested the hypothesis that the hypercapnia-induced increase in cerebral perfusion is attenuated during heat stress (HS) compared to normothermia (NT), and this response is further reduced during the combined challenges of HS and lower body negative pressure (LBNP). METHODS Ten healthy individuals (9 men) undertook rebreathing-induced hypercapnia during NT, HS, and HS + 20 mmHg LBNP (HSLBNP), while cerebral perfusion was indexed from middle cerebral artery blood velocity (MCA V mean). Cerebrovascular responses were calculated from the slope of the change in MCA V mean and cerebral vascular conductance (CVCi) relative to the increase in end tidal carbon dioxide ([Formula: see text]) during rebreathing. RESULTS MCA V mean was similar in HS (55 ± 19 cm s(-1)) and HSLBNP (52 ± 16 cm s(-1)), and both values were reduced relative to NT (66 ± 20 cm s(-1)), yet the rise in MCA V mean per Torr increase in [Formula: see text] during rebreathing was similar in each condition (NT: 2.5 ± 0.6 cm s(-1) Torr(-1); HS: 2.4 ± 0.8 cm s(-1) Torr(-1); HSLBNP: 2.1 ± 1.1 cm s(-1) Torr(-1)). Likewise, the rate of increase in CVCi was not different between conditions (NT: 2.1 ± 0.65 cm s(-1 )mmHg(-1)100 Torr(-1); HS: 2.4 ± 0.8 cm s(-1) mmHg(-1) 100 Torr(-1); HSLBNP: 2.0 ± 1.0 cm s(-1) mmHg(-1) 100 Torr(-1)). INTERPRETATIONS These data indicate that cerebrovascular reactivity is not compromised during whole-body heat stress alone or when combined with mild orthostatic stress relative to normothermic conditions.
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Vernieri F, Altamura C, Palazzo P, Altavilla R, Fabrizio E, Fini R, Melgari JM, Paolucci M, Pasqualetti P, Maggio P. 1-Hz Repetitive Transcranial Magnetic Stimulation Increases Cerebral Vasomotor Reactivity: A Possible Autonomic Nervous System Modulation. Brain Stimul 2014; 7:281-6. [DOI: 10.1016/j.brs.2013.12.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 12/11/2013] [Accepted: 12/27/2013] [Indexed: 11/30/2022] Open
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Willie CK, Tzeng YC, Fisher JA, Ainslie PN. Integrative regulation of human brain blood flow. J Physiol 2014; 592:841-59. [PMID: 24396059 PMCID: PMC3948549 DOI: 10.1113/jphysiol.2013.268953] [Citation(s) in RCA: 558] [Impact Index Per Article: 55.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 12/24/2013] [Indexed: 02/06/2023] Open
Abstract
Herein, we review mechanisms regulating cerebral blood flow (CBF), with specific focus on humans. We revisit important concepts from the older literature and describe the interaction of various mechanisms of cerebrovascular control. We amalgamate this broad scope of information into a brief review, rather than detailing any one mechanism or area of research. The relationship between regulatory mechanisms is emphasized, but the following three broad categories of control are explicated: (1) the effect of blood gases and neuronal metabolism on CBF; (2) buffering of CBF with changes in blood pressure, termed cerebral autoregulation; and (3) the role of the autonomic nervous system in CBF regulation. With respect to these control mechanisms, we provide evidence against several canonized paradigms of CBF control. Specifically, we corroborate the following four key theses: (1) that cerebral autoregulation does not maintain constant perfusion through a mean arterial pressure range of 60-150 mmHg; (2) that there is important stimulatory synergism and regulatory interdependence of arterial blood gases and blood pressure on CBF regulation; (3) that cerebral autoregulation and cerebrovascular sensitivity to changes in arterial blood gases are not modulated solely at the pial arterioles; and (4) that neurogenic control of the cerebral vasculature is an important player in autoregulatory function and, crucially, acts to buffer surges in perfusion pressure. Finally, we summarize the state of our knowledge with respect to these areas, outline important gaps in the literature and suggest avenues for future research.
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Affiliation(s)
- Christopher K Willie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada V1V 1V7.
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Vascular Endothelium. TISSUE FUNCTIONING AND REMODELING IN THE CIRCULATORY AND VENTILATORY SYSTEMS 2013. [DOI: 10.1007/978-1-4614-5966-8_9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Abstract
The relationship between cerebral hemodynamics and cognitive performance has increasingly become recognized as a major challenge in clinical practice for older adults. Both diabetes and hypertension worsen brain perfusion and are major risk factors for cerebrovascular disease, stroke and dementia. Cerebrovascular reserve has emerged as a potential biomarker for monitoring pressure-perfusion-cognition relationships. Endothelial dysfunction and inflammation, microvascular disease, and mascrovascular disease affect cerebral hemodynamics and play an important role in pathohysiology and severity of multiple medical conditions, presenting as cognitive decline in the old age. Therefore, the identification of cerebrovascular vascular reactivity as a new therapeutic target is needed for prevention of cognitive decline late in life.
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Peebles KC, Ball OG, MacRae BA, Horsman HM, Tzeng YC. Sympathetic regulation of the human cerebrovascular response to carbon dioxide. J Appl Physiol (1985) 2012; 113:700-6. [DOI: 10.1152/japplphysiol.00614.2012] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although the cerebrovasculature is known to be exquisitely sensitive to CO2, there is no consensus on whether the sympathetic nervous system plays a role in regulating cerebrovascular responses to changes in arterial CO2. To address this question, we investigated human cerebrovascular CO2 reactivity in healthy participants randomly assigned to the α1-adrenoreceptor blockade group (9 participants; oral prazosin, 0.05 mg/kg) or the placebo control (9 participants) group. We recorded mean arterial blood pressure (MAP), heart rate (HR), mean middle cerebral artery flow velocity (MCAV mean), and partial pressure of end-tidal CO2 (PetCO2) during 5% CO2 inhalation and voluntary hyperventilation. CO2 reactivity was quantified as the slope of the linear relationship between breath-to-breath PetCO2 and the average MCAvmean within successive breathes after accounting for MAP as a covariate. Prazosin did not alter resting HR, PetCO2, MAP, or MCAV mean. The reduction in hypocapnic CO2 reactivity following prazosin (−0.48 ± 0.093 cm·s−1·mmHg−1) was greater compared with placebo (−0.19 ± 0.087 cm·s−1·mmHg−1; P < 0.05 for interaction). In contrast, the change in hypercapnic CO2 reactivity following prazosin (−0.23 cm·s−1·mmHg−1) was similar to placebo (−0.31 cm·s−1·mmHg−1; P = 0.50 for interaction). These data indicate that the sympathetic nervous system contributes to CO2 reactivity via α1-adrenoreceptors; blocking this pathway with prazosin reduces CO2 reactivity to hypocapnia but not hypercapnia.
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Affiliation(s)
- K. C. Peebles
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - O. G. Ball
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - B. A. MacRae
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - H. M. Horsman
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - Y. C. Tzeng
- Cardiovascular Systems Laboratory, Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
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Duffin J. Response to letter from Teppema and Berendsen concerning Fan et al. (2012): 'Acetazolamide and cerebrovascular function at high altitude'. J Physiol 2012; 590:3623; author reply 3625-6. [PMID: 22855055 DOI: 10.1113/jphysiol.2012.235713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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Ainslie PN, Lucas SJE, Fan JL, Thomas KN, Cotter JD, Tzeng YC, Burgess KR. Influence of sympathoexcitation at high altitude on cerebrovascular function and ventilatory control in humans. J Appl Physiol (1985) 2012; 113:1058-67. [PMID: 22837165 DOI: 10.1152/japplphysiol.00463.2012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
We sought to determine the influence of sympathoexcitation on dynamic cerebral autoregulation (CA), cerebrovascular reactivity, and ventilatory control in humans at high altitude (HA). At sea level (SL) and following 3-10 days at HA (5,050 m), we measured arterial blood gases, ventilation, arterial pressure, and middle cerebral blood velocity (MCAv) before and after combined α- and β-adrenergic blockade. Dynamic CA was quantified using transfer function analysis. Cerebrovascular reactivity was assessed using hypocapnia and hyperoxic hypercapnia. Ventilatory control was assessed from the hypercapnia and during isocapnic hypoxia. Arterial Pco(2) and ventilation and its control were unaltered following blockade at both SL and HA. At HA, mean arterial pressure (MAP) was elevated (P < 0.01 vs. SL), but MCAv remained unchanged. Blockade reduced MAP more at HA than at SL (26 vs. 15%, P = 0.048). At HA, gain and coherence in the very-low-frequency (VLF) range (0.02-0.07 Hz) increased, and phase lead was reduced (all P < 0.05 vs. SL). Following blockade at SL, coherence was unchanged, whereas VLF phase lead was reduced (-40 ± 23%; P < 0.01). In contrast, blockade at HA reduced low-frequency coherence (-26 ± 20%; P = 0.01 vs. baseline) and elevated VLF phase lead (by 177 ± 238%; P < 0.01 vs. baseline), fully restoring these parameters back to SL values. Irrespective of this elevation in VLF gain at HA (P < 0.01), blockade increased it comparably at SL and HA (∼43-68%; P < 0.01). Despite elevations in MCAv reactivity to hypercapnia at HA, blockade reduced (P < 0.05) it comparably at SL and HA, effects we attributed to the hypotension and/or abolition of the hypercapnic-induced increase in MAP. With the exception of dynamic CA, we provide evidence of a redundant role of sympathetic nerve activity as a direct mechanism underlying changes in cerebrovascular reactivity and ventilatory control following partial acclimatization to HA. These findings have implications for our understanding of CBF function in the context of pathologies associated with sympathoexcitation and hypoxemia.
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Affiliation(s)
- P N Ainslie
- Dept. of Human Kinetics, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada.
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Donnelly J, Lucas SJE, Thomas KN, Galvin SD, Ainslie PN. Profound hyperventilation and development of periodic breathing during exceptional orthostatic stress in a 21-year-old man. Respir Physiol Neurobiol 2011; 177:66-70. [PMID: 21371574 DOI: 10.1016/j.resp.2011.02.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2011] [Revised: 02/23/2011] [Accepted: 02/23/2011] [Indexed: 11/17/2022]
Abstract
In this case report we describe a trial of experimentally induced syncope in a healthy young volunteer that produced abnormal periods of hyperventilation (V(A)=57 L/min) and periodic breathing; the latter persisting for approximately 60 min following termination of the trial. In this example, independent of systemic hypotension, the severe hyperventilation and related hypocapnia (end-tidal PET(CO2)) induced by orthostatic stress (lower body negative pressure) resulted in a ∼65% reduction in cerebral blood flow velocity. Potential mechanisms underlying these striking cardiorespiratory patterns are discussed.
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Affiliation(s)
- Joseph Donnelly
- Department of Physiology, University of Otago, Dunedin, New Zealand.
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