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DiNuzzo M, Dienel GA, Behar KL, Petroff OA, Benveniste H, Hyder F, Giove F, Michaeli S, Mangia S, Herculano-Houzel S, Rothman DL. Neurovascular coupling is optimized to compensate for the increase in proton production from nonoxidative glycolysis and glycogenolysis during brain activation and maintain homeostasis of pH, pCO 2, and pO 2. J Neurochem 2024; 168:632-662. [PMID: 37150946 PMCID: PMC10628336 DOI: 10.1111/jnc.15839] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Revised: 04/22/2023] [Accepted: 05/02/2023] [Indexed: 05/09/2023]
Abstract
During transient brain activation cerebral blood flow (CBF) increases substantially more than cerebral metabolic rate of oxygen consumption (CMRO2) resulting in blood hyperoxygenation, the basis of BOLD-fMRI contrast. Explanations for the high CBF versus CMRO2 slope, termed neurovascular coupling (NVC) constant, focused on maintenance of tissue oxygenation to support mitochondrial ATP production. However, paradoxically the brain has a 3-fold lower oxygen extraction fraction (OEF) than other organs with high energy requirements, like heart and muscle during exercise. Here, we hypothesize that the NVC constant and the capillary oxygen mass transfer coefficient (which in combination determine OEF) are co-regulated during activation to maintain simultaneous homeostasis of pH and partial pressure of CO2 and O2 (pCO2 and pO2). To test our hypothesis, we developed an arteriovenous flux balance model for calculating blood and brain pH, pCO2, and pO2 as a function of baseline OEF (OEF0), CBF, CMRO2, and proton production by nonoxidative metabolism coupled to ATP hydrolysis. Our model was validated against published brain arteriovenous difference studies and then used to calculate pH, pCO2, and pO2 in activated human cortex from published calibrated fMRI and PET measurements. In agreement with our hypothesis, calculated pH, pCO2, and pO2 remained close to constant independently of CMRO2 in correspondence to experimental measurements of NVC and OEF0. We also found that the optimum values of the NVC constant and OEF0 that ensure simultaneous homeostasis of pH, pCO2, and pO2 were remarkably similar to their experimental values. Thus, the high NVC constant is overall determined by proton removal by CBF due to increases in nonoxidative glycolysis and glycogenolysis. These findings resolve the paradox of the brain's high CBF yet low OEF during activation, and may contribute to explaining the vulnerability of brain function to reductions in blood flow and capillary density with aging and neurovascular disease.
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Affiliation(s)
| | - Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, AR, 72205 USA
- Department of Cell Biology and Physiology, University of New Mexico School of Medicine, Albuquerque, NM, 87131 USA
| | - Kevin L Behar
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT, 06511 USA
| | - Ognen A Petroff
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT, 06511 USA
| | - Helene Benveniste
- Department of Anesthesiology, Yale University, New Haven, CT, 06520 USA
- Department of Biomedical Engineering, Yale University, New Haven, CT, 06520 USA
| | - Fahmeed Hyder
- Department of Biomedical Engineering, Yale University, New Haven, CT, 06520 USA
- Department of Radiology, Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, 06520 USA
| | - Federico Giove
- Centro Ricerche Enrico Fermi, Rome, RM, 00184 Italy
- Fondazione Santa Lucia IRCCS, Rome, RM, 00179 Italy
| | - Shalom Michaeli
- Department of Radiology, Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, 55455 USA
| | - Silvia Mangia
- Department of Radiology, Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, MN, 55455 USA
| | - Suzana Herculano-Houzel
- Department of Psychology, Vanderbilt University, Nashville, TN
- Department of Biological Sciences, Vanderbilt University, Nashville, TN
- Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN
| | - Douglas L Rothman
- Department of Biomedical Engineering, Yale University, New Haven, CT, 06520 USA
- Department of Radiology, Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, 06520 USA
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Callaghan T, Margrain TH, Binns AM. The Effect of Systemic Hyperoxia and Hypoxia on Scotopic Thresholds in People with Early and Intermediate Age-related Macular Degeneration. Curr Eye Res 2020; 45:1273-1282. [PMID: 32155095 DOI: 10.1080/02713683.2020.1739315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Purpose: Morphological retinal changes combined with functional evidence implicate hypoxia in the pathogenesis of age-related macular degeneration (AMD). However, the role of hypoxia in the scotopic threshold deficit reported in AMD has not been investigated. This study compared scotopic thresholds in participants with early and intermediate AMD recorded under conditions of systemic hypoxia, hyperoxia and normoxia. Materials and Methods: Over two sessions scotopic thresholds were measured with participants breathing 21% and 60% oxygen (n = 12 early AMD, n = 11 age-similar controls) or 21% and 14% oxygen (n = 16 early AMD, n = 20 age-similar controls). Thresholds were measured using a 'white', annular 12 degrees stimulus, using a QUEST procedure. Results: There was no statistically significant change in scotopic thresholds within the AMD or control group when breathing the hyperoxic gas mixture (60% oxygen) or the hypoxic gas mixture (14% oxygen) when compared to the normoxic condition (21% oxygen). There was also no statistically significant difference in scotopic thresholds between groups under the hyperoxic or hypoxic gas conditions. The difference between groups under the normoxic condition was not statistically significant for the hyperoxia study (p = .70), but did reach significance in the hypoxia study (p = .05). Conclusion: This study provided no evidence that breathing that breathing 14% or 60% oxygen altered scotopic thresholds in those with early AMD when compared to controls. However, the lack of elevated scotopic thresholds in the AMD group of the hyperoxia study is of note, as it is unlikely that hyperoxia would reduce thresholds which were not significantly raised at baseline, regardless of whether hypoxia was a factor in the disease pathogenesis. The findings of this study do not rule out a role for hypoxia in early AMD, but this needs to be assessed in future experiments using measures that differ significantly between people with AMD and controls.
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Affiliation(s)
- Tamsin Callaghan
- School of Health Sciences, City, University of London , London, UK
| | - Tom H Margrain
- Cardiff Centre for Vision Sciences, Cardiff University , Cardiff, UK
| | - Alison M Binns
- School of Health Sciences, City, University of London , London, UK
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Robinson DG, Margrain TH, Dunn MJ, Bailey C, Binns AM. Low-Level Nighttime Light Therapy for Age-Related Macular Degeneration: A Randomized Clinical Trial. ACTA ACUST UNITED AC 2018; 59:4531-4541. [DOI: 10.1167/iovs.18-24284] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- D. Grant Robinson
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Tom H. Margrain
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Matt J. Dunn
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Clare Bailey
- Bristol Eye Hospital, Lower Maudlin Street, Bristol, United Kingdom
| | - Alison M. Binns
- Division of Optometry and Visual Science, School of Health Sciences, City, University of London, United Kingdom
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Sieck DC, Ely MR, Romero SA, Luttrell MJ, Abdala PM, Halliwill JR. Post-exercise syncope: Wingate syncope test and visual-cognitive function. Physiol Rep 2017; 4:4/16/e12883. [PMID: 27550986 PMCID: PMC5002906 DOI: 10.14814/phy2.12883] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 07/15/2016] [Indexed: 01/23/2023] Open
Abstract
Adequate cerebral perfusion is necessary to maintain consciousness in upright humans. Following maximal anaerobic exercise, cerebral perfusion can become compromised and result in syncope. It is unknown whether post-exercise reductions in cerebral perfusion can lead to visual-cognitive deficits prior to the onset of syncope, which would be of concern for emergency workers and warfighters, where critical decision making and intense physical activity are combined. Therefore, the purpose of this experiment was to determine if reductions in cerebral blood velocity, induced by maximal anaerobic exercise and head-up tilt, result in visual-cognitive deficits prior to the onset of syncope. Nineteen sedentary to recreationally active volunteers completed a symptom-limited 60° head-up tilt for 16 min before and up to 16 min after a 60 sec Wingate test. Blood velocity of the middle cerebral artery was measured using transcranial Doppler ultrasound and a visual decision-reaction time test was assessed, with independent analysis of peripheral and central visual field responses. Cerebral blood velocity was 12.7 ± 4.0% lower (mean ± SE; P < 0.05) after exercise compared to pre-exercise. This was associated with a 63 ± 29% increase (P < 0.05) in error rate for responses to cues provided to the peripheral visual field, without affecting central visual field error rates (P = 0.46) or decision-reaction times for either visual field. These data suggest that the reduction in cerebral blood velocity following maximal anaerobic exercise contributes to visual-cognitive deficits in the peripheral visual field without an apparent affect to the central visual field.
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Affiliation(s)
- Dylan C Sieck
- Department of Human Physiology, University of Oregon, Eugene, Oregon
| | - Matthew R Ely
- Department of Human Physiology, University of Oregon, Eugene, Oregon
| | - Steven A Romero
- Department of Human Physiology, University of Oregon, Eugene, Oregon
| | | | - Pedro M Abdala
- Department of Human Physiology, University of Oregon, Eugene, Oregon
| | - John R Halliwill
- Department of Human Physiology, University of Oregon, Eugene, Oregon
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Munch IC, Altuntas C, Li XQ, Jackson GR, Klefter ON, Larsen M. Dark adaptation in relation to choroidal thickness in healthy young subjects: a cross-sectional, observational study. BMC Ophthalmol 2016; 16:105. [PMID: 27401722 PMCID: PMC4940899 DOI: 10.1186/s12886-016-0273-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2015] [Accepted: 06/20/2016] [Indexed: 11/17/2022] Open
Abstract
Background Dark adaptation is an energy-requiring process in the outer retina nourished by the profusely perfused choroid. We hypothesized that variations in choroidal thickness might affect the rate of dark adaptation. Method Cross-sectional, observational study of 42 healthy university students (mean age 25 ± 2.0 years, 29 % men) who were examined using an abbreviated automated dark adaptometry protocol with a 2° diameter stimulus centered 5° above the point of fixation. The early, linear part of the rod-mediated dark adaptation curve was analyzed to extract the time required to reach a sensitivity of 5.0 × 10−3 cd/m2 (time to rod intercept) and the slope (rod adaptation rate). The choroid was imaged using enhanced-depth imaging spectral-domain optical coherence tomography (EDI-OCT). Results The time to the rod intercept was 7.3 ± 0.94 (range 5.1 - 10.2) min. Choroidal thickness 2.5° above the fovea was 348 ± 104 (range 153–534) μm. There was no significant correlation between any of the two measures of rod-mediated dark adaptation and choroidal thickness (time to rod intercept versus choroidal thickness 0.072 (CI95 -0.23 to 0.38) min/100 μm, P = 0.64, adjusted for age and sex). There was no association between the time-to–rod-intercept or the dark adaptation rate and axial length, refraction, gender or age. Conclusion Choroidal thickness, refraction and ocular axial length had no detectable effect on rod-mediated dark adaptation in healthy young subjects. Our results do not support that variations in dark adaptation can be attributed to variations in choroidal thickness. Electronic supplementary material The online version of this article (doi:10.1186/s12886-016-0273-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Inger Christine Munch
- Department of Ophthalmology, Zealand University Hospital, Sygehusvej 10, DK-4000, Roskilde, Denmark. .,Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, København N, Denmark.
| | - Cigdem Altuntas
- Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, København N, Denmark
| | - Xiao Qiang Li
- Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, København N, Denmark.,Department of Ophthalmology, Rigshospitalet, Nordre Ringvej 57, DK-2600, Glostrup, Denmark
| | | | - Oliver Niels Klefter
- Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, København N, Denmark.,Department of Ophthalmology, Rigshospitalet, Nordre Ringvej 57, DK-2600, Glostrup, Denmark
| | - Michael Larsen
- Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, København N, Denmark.,Department of Ophthalmology, Rigshospitalet, Nordre Ringvej 57, DK-2600, Glostrup, Denmark
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Yang GQ, Chen T, Tao Y, Zhang ZM. Recent advances in the dark adaptation investigations. Int J Ophthalmol 2015; 8:1245-52. [PMID: 26682182 DOI: 10.3980/j.issn.2222-3959.2015.06.31] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Accepted: 01/28/2015] [Indexed: 12/15/2022] Open
Abstract
Dark adaptation is a highly sensitive neural function and may be the first symptom of many status including the physiologic and pathologic entity, suggesting that it could be instrumental for diagnose. However, shortcomings such as the lack of standardized parameters, the long duration of examination, and subjective randomness would substantially impede the use of dark adaptation in clinical work. In this review we summarize the recent research about the dark adaptation, including two visual cycles-canonical and cone-specific visual cycle, affecting factors and the methods for measuring dark adaptation. In the opinions of authors, intensive investigations are needed to be done for the widely use of this significant visual function in clinic.
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Affiliation(s)
- Guo-Qing Yang
- Department of Clinical Aerospace Medicine, the Fourth Military Medical University, Xi'an 710032, Shaanxi Province, China
| | - Tao Chen
- Department of Clinical Aerospace Medicine, the Fourth Military Medical University, Xi'an 710032, Shaanxi Province, China
| | - Ye Tao
- Department of Ophthalmology, Beidaihe Hospital of PLA, Beidaihe 066100, Hebei Province, China
| | - Zuo-Ming Zhang
- Department of Clinical Aerospace Medicine, the Fourth Military Medical University, Xi'an 710032, Shaanxi Province, China
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McKeague C, Margrain TH, Bailey C, Binns AM. Low-level night-time light therapy for age-related macular degeneration (ALight): study protocol for a randomized controlled trial. Trials 2014; 15:246. [PMID: 24965385 PMCID: PMC4227140 DOI: 10.1186/1745-6215-15-246] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 05/23/2014] [Indexed: 12/11/2022] Open
Abstract
Background Age-related macular degeneration (AMD) is the leading cause of blindness among older adults in the developed world. The only treatments currently available, such as ranibizumab injections, are for neovascular AMD, which accounts for only 10 to 15% of people with the condition. Hypoxia has been implicated as one of the primary causes of AMD, and is most acute at night when the retina is most metabolically active. By increasing light levels at night, the metabolic requirements of the retina and hence the hypoxia will be considerably reduced. This trial seeks to determine whether wearing a light mask that emits a dim, green light during the night can prevent the progression of early AMD. Methods/design ALight is a Phase I/IIa, multicentre, randomized controlled trial. Sixty participants (55 to 88 years old) with early AMD in one eye and neovascular AMD (nAMD) in the fellow eye will be recruited from nAMD clinics. They will be randomized (in the ratio 1:1), either to receive the intervention or to be in the untreated control group, stratified according to risk of disease progression. An additional 40 participants with healthy retinal appearance, or early AMD only, will be recruited for a baseline cross-sectional analysis. The intervention is an eye mask that emits a dim green light to illuminate the retina through closed eyelids at night. This is designed to reduce the metabolic activity of the retina, thereby reducing the potential risk of hypoxia. Participants will wear the mask every night for 12 months. Ophthalmologists carrying out monthly assessments will be masked to the treatment group, but participants will be aware of their treatment group. The primary outcome measure is the proportion of people who show disease progression during the trial period in the eye with early AMD. A co-primary outcome measure is the rate of retinal adaptation. As this is a trial of a CE-marked device for an off-label indication, a further main aim of this trial is to assess safety of the mask in the cohort of participants with AMD. Trial registration International Standard Randomised Controlled Trials Register: ISRCTN82148651
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Affiliation(s)
| | | | | | - Alison M Binns
- School of Optometry and Vision Sciences, Cardiff University, Cardiff CF24 4 LU, UK.
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Barbur JL, Connolly DM. Effects of hypoxia on color vision with emphasis on the mesopic range. EXPERT REVIEW OF OPHTHALMOLOGY 2014. [DOI: 10.1586/eop.11.32] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Schatz A, Willmann G, Fischer MD, Schommer K, Messias A, Zrenner E, Bartz-Schmidt KU, Gekeler F. Electroretinographic assessment of retinal function at high altitude. J Appl Physiol (1985) 2013; 115:365-72. [PMID: 23722709 DOI: 10.1152/japplphysiol.00245.2013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although hypoxia plays a key role in the pathophysiology of many common and well studied retinal diseases, little is known about the effects of high-altitude hypoxia on retinal function. The aim of the present study was to assess retinal function during exposure to high-altitude hypoxia using electroretinography (ERG). This work is related to the Tübingen High Altitude Ophthalmology (THAO) study. Electroretinography was performed in 14 subjects in Tübingen, Germany (341 m) and at high altitude at La Capanna Regina Margherita, Italy (4,559 m) using an extended protocol to assess functional integrity of various retinal layers. To place findings in the context of acute mountain sickness, correlations between ERG measurements and oxygen saturation, heart rate, and scores of acute mountain sickness (AMS) were calculated. At high altitude, the maximum response of the scotopic sensitivity function, the implicit times of the a- and b-wave of the combined rod-cone responses, and the implicit times of the photopic negative responses (PhNR) were significantly altered. A-wave slopes and i-waves were significantly decreased at high altitude. The strongest correlation was found for PhNR and O2 saturation (r = 0.68; P < 0.05). Of all tested correlations, only the photopic b-wave implicit time (10 cd·s/m(2)) was significantly correlated with severity of AMS (r = 0.57; P < 0.05). ERG data show that retinal function of inner, outer, and ganglion cell layer is altered at high-altitude hypoxia. Interestingly, the most affected ERG parameters are related to combined rod-cone responses, which indicate that phototransduction and visual processing, especially under conditions of rod-cone interaction, are primarily affected at high altitude.
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Affiliation(s)
- Andreas Schatz
- Centre for Ophthalmology, University of Tübingen, Tübingen, Germany
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10
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Abstract
PURPOSE Comparative studies suggest that increasing photoreceptor oxygen consumption in dim light, relative to bright light, may make the outer retina susceptible to hypoxia at light levels relevant to aviation at night. Accordingly, this study investigates effects of relevant oxygenation states on sensitivity to a dynamic contrast stimulus at low photopic and mesopic light levels experienced during night flying. METHODS Threshold sensitivity to frequency-doubled contrast stimuli was assessed under mild hypoxia (breathing 14.1% oxygen), hyperoxia (100% oxygen), and normoxia (air) using frequency doubling perimetry, viewing at background fields of approximately 10 cd/m2 and approximately 1 cd/m2. Data were analyzed by retinal eccentricity and visual field quadrant. RESULTS At low photopic luminance (approximately 10 cd/m2), sensitivity was marginally enhanced when breathing 100% oxygen. At mesopic luminance (approximately 1 cd/m2), sensitivity was consistently poorest with hypoxia and greatest with supplementary oxygen at all eccentricities and in all field quadrants, suggesting oxygen-dependent performance. CONCLUSIONS The known effects of oxygenation state on pupil size are likely to influence frequency doubling perimetry thresholds, but oxygen-dependent changes in mesopic sensitivity are greater than expected from altered retinal illumination alone and support outer retinal (photoreceptor) susceptibility to hypoxia under twilight viewing.
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Feigl B. Age-related maculopathy – Linking aetiology and pathophysiological changes to the ischaemia hypothesis. Prog Retin Eye Res 2009; 28:63-86. [PMID: 19070679 DOI: 10.1016/j.preteyeres.2008.11.004] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Beatrix Feigl
- Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, 4059 QLD, Australia.
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12
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Connolly DM, Hosking SL. Oxygenation and gender effects on photopic frequency-doubled contrast sensitivity. Vision Res 2008; 48:281-8. [DOI: 10.1016/j.visres.2007.11.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2007] [Revised: 10/28/2007] [Accepted: 11/10/2007] [Indexed: 12/30/2022]
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Abstract
PURPOSE The relationship between hyperventilation and the associated increase in flicker sensitivity is poorly defined but may be relevant to display viewing. This exploratory study investigates the potential for quantifying the relationship between the severity of hypocapnia and critical flicker frequency (CFF). METHOD Repeated ascending (fusion) and descending (flicker) measurements were made while breathing normally (normocapnia), and at four levels of progressive, mild to moderate hypocapnia that were induced by voluntary hyperventilation and controlled using continuous respiratory mass spectrometry. The mesopic stimulus was a 2.6 degree-Gaussian blob viewed through a 5.2-mm-diameter artificial pupil. RESULTS Five discrete respiratory conditions were generated. The influences of intersubject variability and severity of hypocapnia upon mean CFF were examined using two-way analysis of variance, demonstrating a statistically significant effect of target end-tidal partial pressure of carbon dioxide [F(4,40) = 4.63, p = 0.005]. The relationship between decreasing mean end-tidal partial pressure of carbon dioxide and increasing mean CFF was consistent with a linear correlation (Pearson R = -0.949, p = 0.013). CONCLUSIONS The results support a close relationship between the respiratory partial pressure of carbon dioxide and flicker sensitivity. However, the absolute magnitude of the underlying increase in flicker sensitivity with hypocapnia is small and the effect is unlikely to be relevant in aviation.
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Affiliation(s)
- Desmond Connolly
- QinetiQ, Human Protection and Performance Enhancement Group, Cody Technology Park, Farnborough, United Kingdom.
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Feigl B, Stewart I, Brown B. Experimental hypoxia in human eyes: Implications for ischaemic disease. Clin Neurophysiol 2007; 118:887-95. [PMID: 17307390 DOI: 10.1016/j.clinph.2006.12.012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2006] [Revised: 11/14/2006] [Accepted: 12/11/2006] [Indexed: 11/24/2022]
Abstract
OBJECTIVE This study investigated neuroretinal activity under normoxic and hypoxic conditions with the multifocal electroretinogram (mfERG). METHODS We used two mfERG paradigms, the fast flicker and slow flash stimulation modes, to measure neuroretinal activity in five healthy participants who breathed room air and a reduced oxygen mixture (14% oxygen, balance nitrogen). We analysed concentric ring N1P1 and P1N2 response density amplitudes, the P1 implicit times as well as the local scalar product (SP) response densities. RESULTS During hypoxia there was a significant reduction of the scalar product response density for the fast flicker (p<0.001) and for the slow flash mfERG (p<0.001). The N1P1 and P1N2 response densities were lower especially for the central three rings; although these reductions were not significant between the two oxygen conditions, they indicated an overall distortion of the mfERG waveform. CONCLUSIONS It is demonstrated that a post-receptoral, primarily ON and OFF bipolar cell deficit is evident in the central retina of healthy young people during short term hypoxia. SIGNIFICANCE Our findings suggest that persons with pre-existing ischaemic eye disease may be at risk when exposed to hypoxic conditions.
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Affiliation(s)
- Beatrix Feigl
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Australia.
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