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Hypercapnia Impairs Vasoreactivity to Changes in Blood Pressure and Intraocular Pressure in Rat Retina. Optom Vis Sci 2020; 96:470-476. [PMID: 31274734 DOI: 10.1097/opx.0000000000001400] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
SIGNIFICANCE The balance between oxygen and carbon dioxide sets the resting tone (or diameter) of retinal blood vessels. Eyes that are hypercapnic use up their "vasodilatory reserve" and therefore fail to respond adequately to changes in intraocular or blood pressure. PURPOSE Retinal vessels are regulated by both myogenic and metabolic mechanisms. We considered whether alteration of metabolic status would modify the vascular response to ocular perfusion pressure (OPP) lowering in rat retina. METHODS In pentobarbital anesthetized adult Brown-Norway rats, normocapnia or hypercapnia was achieved by artificially ventilating animals with air or 5% carbon dioxide in ~30% oxygen, respectively. Ocular perfusion pressure was gradually reduced to ~20 mmHg by either lowering blood pressure (slowly drawing blood from a femoral artery/vein) or manometrically increasing intraocular pressure under normocapnic or hypercapnic conditions. In all four groups (n = 7 eyes for each), a confocal scanning laser ophthalmoscope was used to acquire image sequences centered on the optic nerve throughout pressure modification. The diameter of arterioles and venules at various OPP levels was measured and expressed as percentage relative to their own baseline. The response of arterioles and venules to OPP lowering was compared between normocapnic and hypercapnic groups. RESULTS Average arterial carbon dioxide partial pressures were 36.9 ± 2.6 mmHg in normocapnic and 64.1 ± 5.9 mmHg in hypercapnic (P < .001) animals. In the normocapnic groups, blood pressure lowering and intraocular pressure elevation resulted in significant vasodilation of both arterioles and venules (P < .0001). In the hypercapnic groups, OPP lowering-induced vasodilation was significantly attenuated compared with the corresponding normocapnic groups (P < .0001 for both, two-way analysis of variance). CONCLUSION Hypercapnia significantly modified myogenic vascular autoregulation in response to OPP reduction.
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Allen LA, Schmidt JR, Thompson CT, Carlson BE, Beard DA, Lombard JH. High salt diet impairs cerebral blood flow regulation via salt-induced angiotensin II suppression. Microcirculation 2019; 26:e12518. [PMID: 30481399 DOI: 10.1111/micc.12518] [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] [Received: 04/19/2018] [Revised: 10/03/2018] [Accepted: 11/22/2018] [Indexed: 01/11/2023]
Abstract
OBJECTIVES This study sought to determine whether salt-induced ANG II suppression contributes to impaired CBF autoregulation. METHODS Cerebral autoregulation was evaluated with LDF during graded reductions of blood pressure. Autoregulatory responses in rats fed HS (4% NaCl) diet vs LS (0.4% NaCl) diet were analyzed using linear regression analysis, model-free analysis, and a mechanistic theoretical model of blood flow through cerebral arterioles. RESULTS Autoregulation was intact in LS-fed animals as MAP was reduced via graded hemorrhage to approximately 50 mm Hg. Short-term (3 days) and chronic (4 weeks) HS diet impaired CBF autoregulation, as evidenced by progressive reductions of laser Doppler flux with arterial pressure reduction. Chronic low dose ANG II infusion (5 mg/kg/min, i.v.) restored CBF autoregulation between the pre-hemorrhage MAP and 50 mm Hg in rats fed short-term HS diet. Mechanistic-based model analysis showed a reduced myogenic response and reduced baseline VSM tone with short-term HS diet, which was restored by ANG II infusion. CONCLUSIONS Short-term and chronic HS diet lead to impaired autoregulation in the cerebral circulation, with salt-induced ANG II suppression as a major factor in the initiation of impaired CBF regulation.
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Affiliation(s)
- Linda A Allen
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - James R Schmidt
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Christopher T Thompson
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
| | - Brian E Carlson
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
| | - Daniel A Beard
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
| | - Julian H Lombard
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
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Ozturk ED, Tan CO. Human cerebrovascular function in health and disease: insights from integrative approaches. J Physiol Anthropol 2018; 37:4. [PMID: 29454381 PMCID: PMC5816507 DOI: 10.1186/s40101-018-0164-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 02/02/2018] [Indexed: 11/21/2022] Open
Abstract
Background The marked increase in the size of the brain, and consequently, in neural processing capability, throughout human evolution is the basis of the higher cognitive function in humans. However, greater neural, and thus information processing capability, comes at a significant metabolic cost; despite its relatively small size, the modern human brain consumes almost a quarter of the glucose and oxygen supply in the human body. Fortunately, several vascular mechanisms ensure sufficient delivery of glucose and oxygen to the active neural tissue (neurovascular coupling), prompt removal of neural metabolic by-products (cerebral vasoreactivity), and constant global blood supply despite daily variations in perfusion pressure (cerebral autoregulation). The aim of this review is to provide an integrated overview of the available data on these vascular mechanisms and their underlying physiology. We also briefly review modern experimental approaches to assess these mechanisms in humans, and further highlight the importance of these mechanisms for humans’ evolutionary success by providing examples of their healthy adaptations as well as pathophysiological alterations. Conclusions Data reviewed in this paper demonstrate the importance of the cerebrovascular function to support humans’ unique ability to form new and different interactions with each other and their surroundings. This highlights that there is much insight into the neural and cognitive functions that could be gleaned from interrogating the cerebrovascular function.
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Affiliation(s)
- Erin D Ozturk
- Cerebrovascular Research Laboratory, Spaulding Rehabilitation Hospital, Boston, MA, USA.,Department of Psychology, Harvard University, Cambridge, MA, USA
| | - 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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Hoiland RL, Tymko MM, Bain AR, Wildfong KW, Monteleone B, Ainslie PN. Carbon dioxide-mediated vasomotion of extra-cranial cerebral arteries in humans: a role for prostaglandins? J Physiol 2016; 594:3463-81. [PMID: 26880615 DOI: 10.1113/jp272012] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 02/01/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Cerebral blood flow increases during hypercapnia and decreases during hypocapnia; it is unknown if vasomotion of the internal carotid artery is implicated in these responses. Indomethacin, a non-selective cyclooxygenase inhibitor (used to inhibit prostaglandin synthesis), has a unique ability to blunt cerebrovascular carbon dioxide reactivity, while other cyclooxygenase inhibitors have no effect. We show significant dilatation and constriction of the internal carotid artery during hypercapnia and hypocapnia, respectively. Indomethacin, but not ketorolac or naproxen, reduced the dilatatory response of the internal carotid artery to hypercapnia The differential effect of indomethacin compared to ketorolac and naproxen suggests that indomethacin inhibits vasomotion of the internal carotid artery independent of prostaglandin synthesis inhibition. ABSTRACT Extra-cranial cerebral blood vessels are implicated in the regulation of cerebral blood flow during changes in arterial CO2 ; however, the mechanisms governing CO2 -mediated vasomotion of these vessels in humans remain unclear. We determined if cyclooxygenase inhibition with indomethacin (INDO) reduces the vasomotor response of the internal carotid artery (ICA) to changes in end-tidal CO2 (P ETC O2). Using a randomized single-blinded placebo-controlled study, participants (n = 10) were tested on two occasions, before and 90 min following oral INDO (1.2 mg kg(-1) ) or placebo. Concurrent measurements of beat-by-beat velocity, diameter and blood flow of the ICA were made at rest and during steady-state stages (4 min) of iso-oxic hypercapnia (+3, +6, +9 mmHg P ETC O2) and hypocapnia (-3, -6, -9 mmHg P ETC O2). To examine if INDO affects ICA vasomotion independent of cyclooxygenase inhibition, two participant subsets (each n = 5) were tested before and following oral ketorolac (post 45 min, 0.25 mg kg(-1) ) or naproxen (post 90 min, 4.2 mg kg(-1) ). During pre-drug testing in the INDO trial, the ICA dilatated during hypercapnia at +6 mmHg (4.72 ± 0.45 vs. 4.95 ± 0.51 mm; P < 0.001) and +9 mmHg (4.72 ± 0.45 mm vs. 5.12 ± 0.47 mm; P < 0.001), and constricted during hypocapnia at -6 mmHg (4.95 ± 0.33 vs. 4.88 ± 0.27 mm; P < 0.05) and -9 mmHg (4.95 ± 0.33 vs. 4.82 ± 0.27 mm; P < 0.001). Following INDO, vasomotor responsiveness of the ICA to hypercapnia was reduced by 67 ± 28% (0.045 ± 0.015 vs. 0.015 ± 0.012 mm mmHg P ETC O2(-1) ). There was no effect of the drug in the ketorolac and naproxen trials. We conclude that: (1) INDO markedly reduces the vasomotor response of the ICA to changes in P ETC O2; and (2) INDO may be reducing CO2 -mediated vasomotion via a mechanism(s) independent of cyclooxygenase inhibition.
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Affiliation(s)
- Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Anthony R Bain
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Kevin W Wildfong
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Brad Monteleone
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
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Tan CO, Meehan WP, Iverson GL, Taylor JA. Cerebrovascular regulation, exercise, and mild traumatic brain injury. Neurology 2014; 83:1665-72. [PMID: 25274845 DOI: 10.1212/wnl.0000000000000944] [Citation(s) in RCA: 83] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
A substantial number of people who sustain a mild traumatic brain injury report persistent symptoms. Most common among these symptoms are headache, dizziness, and cognitive difficulties. One possible contributor to sustained symptoms may be compromised cerebrovascular regulation. In addition to injury-related cerebrovascular dysfunction, it is possible that prolonged rest after mild traumatic brain injury leads to deconditioning that may induce physiologic changes in cerebral blood flow control that contributes to persistent symptoms in some people. There is some evidence that exercise training may reduce symptoms perhaps because it engages an array of cerebrovascular regulatory mechanisms. Unfortunately, there is very little work on the degree of impairment in cerebrovascular control that may exist in patients with mild traumatic brain injury, and there are no published studies on the subacute phase of recovery from this injury. This review aims to integrate the current knowledge of cerebrovascular mechanisms that might underlie persistent symptoms and seeks to synthesize these data in the context of exploring aerobic exercise as a feasible intervention to treat the underlying pathophysiology.
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Affiliation(s)
- Can Ozan Tan
- From the Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, Department of Physical Medicine and Rehabilitation, Harvard Medical School (C.O.T., J.A.T.); The Micheli Center for Sports Injury Prevention, Division of Sports Medicine, Boston Children's Hospital, Department of Pediatrics and Orthopedics, Harvard Medical School (W.P.M.); and Department of Physical Medicine and Rehabilitation, Harvard Medical School, Spaulding Rehabilitation Hospital, Massachusetts General Hospital Sport Concussion Clinic, Red Sox Foundation and Massachusetts General Hospital Home Base Program (G.L.I.).
| | - William P Meehan
- From the Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, Department of Physical Medicine and Rehabilitation, Harvard Medical School (C.O.T., J.A.T.); The Micheli Center for Sports Injury Prevention, Division of Sports Medicine, Boston Children's Hospital, Department of Pediatrics and Orthopedics, Harvard Medical School (W.P.M.); and Department of Physical Medicine and Rehabilitation, Harvard Medical School, Spaulding Rehabilitation Hospital, Massachusetts General Hospital Sport Concussion Clinic, Red Sox Foundation and Massachusetts General Hospital Home Base Program (G.L.I.)
| | - Grant L Iverson
- From the Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, Department of Physical Medicine and Rehabilitation, Harvard Medical School (C.O.T., J.A.T.); The Micheli Center for Sports Injury Prevention, Division of Sports Medicine, Boston Children's Hospital, Department of Pediatrics and Orthopedics, Harvard Medical School (W.P.M.); and Department of Physical Medicine and Rehabilitation, Harvard Medical School, Spaulding Rehabilitation Hospital, Massachusetts General Hospital Sport Concussion Clinic, Red Sox Foundation and Massachusetts General Hospital Home Base Program (G.L.I.)
| | - J Andrew Taylor
- From the Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, Department of Physical Medicine and Rehabilitation, Harvard Medical School (C.O.T., J.A.T.); The Micheli Center for Sports Injury Prevention, Division of Sports Medicine, Boston Children's Hospital, Department of Pediatrics and Orthopedics, Harvard Medical School (W.P.M.); and Department of Physical Medicine and Rehabilitation, Harvard Medical School, Spaulding Rehabilitation Hospital, Massachusetts General Hospital Sport Concussion Clinic, Red Sox Foundation and Massachusetts General Hospital Home Base Program (G.L.I.)
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