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Forrer A, Gaisl T, Sevik A, Meyer M, Senteler L, Lichtblau M, Bloch KE, Ulrich S, Furian M. Partial Pressure of Arterial Oxygen in Healthy Adults at High Altitudes: A Systematic Review and Meta-Analysis. JAMA Netw Open 2023; 6:e2318036. [PMID: 37326993 PMCID: PMC10276310 DOI: 10.1001/jamanetworkopen.2023.18036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Accepted: 04/27/2023] [Indexed: 06/17/2023] Open
Abstract
Importance With increasing altitude, the partial pressure of inspired oxygen decreases and, consequently, the Pao2 decreases. Even though this phenomenon is well known, the extent of the reduction as a function of altitude remains unknown. Objective To calculate an effect size estimate for the decrease in Pao2 with each kilometer of vertical gain among healthy unacclimatized adults and to identify factors associated with Pao2 at high altitude (HA). Data Sources A systematic search of PubMed and Embase was performed from database inception to April 11, 2023. Search terms included arterial blood gases and altitude. Study Selection A total of 53 peer-reviewed prospective studies in healthy adults providing results of arterial blood gas analysis at low altitude (<1500 m) and within the first 3 days at the target altitude (≥1500 m) were analyzed. Data Extraction and Synthesis Primary and secondary outcomes as well as study characteristics were extracted from the included studies, and individual participant data (IPD) were requested. Estimates were pooled using a random-effects DerSimonian-Laird model for the meta-analysis. Main Outcomes and Measures Mean effect size estimates and 95% CIs for reduction in Pao2 at HA and factors associated with Pao2 at HA in healthy adults. Results All of the 53 studies involving 777 adults (mean [SD] age, 36.2 [10.5] years; 510 men [65.6%]) reporting 115 group ascents to altitudes between 1524 m and 8730 m were included in the aggregated data analysis; 13 of those studies involving 305 individuals (mean [SD] age, 39.8 [13.6] years; 185 men [60.7%]) reporting 29 ascents were included in the IPD analysis. The estimated effect size of Pao2 was -1.60 kPa (95% CI, -1.73 to -1.47 kPa) for each 1000 m of altitude gain (τ2 = 0.14; I2 = 86%). The Pao2 estimation model based on IPD data revealed that target altitude (-1.53 kPa per 1000 m; 95% CI, -1.63 to -1.42 kPa per 1000 m), age (-0.01 kPa per year; 95% CI, -0.02 to -0.003 kPa per year), and time spent at an altitude of 1500 m or higher (0.16 kPa per day; 95% CI, 0.11-0.21 kPa per day) were significantly associated with Pao2. Conclusions and Relevance In this systematic review and meta-analysis, the mean decrease in Pao2 was 1.60 kPa per 1000 m of vertical ascent. This effect size estimate may improve the understanding of physiological mechanisms, assist in the clinical interpretation of acute altitude illness in healthy individuals, and serve as a reference for physicians counseling patients with cardiorespiratory disease who are traveling to HA regions.
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Affiliation(s)
- Aglaia Forrer
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
| | - Thomas Gaisl
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts
| | - Ahmet Sevik
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
| | - Michelle Meyer
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
| | - Luzi Senteler
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
| | - Mona Lichtblau
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
| | - Konrad Ernst Bloch
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
- Swiss-Kyrgyz High-Altitude Medicine and Research Initiative, Zurich, Switzerland
| | - Silvia Ulrich
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
- Swiss-Kyrgyz High-Altitude Medicine and Research Initiative, Zurich, Switzerland
| | - Michael Furian
- Department of Respiratory Medicine, University Hospital Zurich, Zurich, Switzerland
- Swiss-Kyrgyz High-Altitude Medicine and Research Initiative, Zurich, Switzerland
- Research Department, Swiss University for Traditional Chinese Medicine, Bad Zurzach, Switzerland
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Cognition and Neuropsychological Changes at Altitude-A Systematic Review of Literature. Brain Sci 2022; 12:brainsci12121736. [PMID: 36552195 PMCID: PMC9775937 DOI: 10.3390/brainsci12121736] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2022] [Revised: 12/05/2022] [Accepted: 12/15/2022] [Indexed: 12/24/2022] Open
Abstract
High-altitude (HA) exposure affects cognitive functions, but studies have found inconsistent results. The aim of this systematic review was to evaluate the effects of HA exposure on cognitive functions in healthy subjects. A structural overview of the applied neuropsychological tests was provided with a classification of superordinate cognitive domains. A literature search was performed using PubMed up to October 2021 according to PRISMA guidelines. Eligibility criteria included a healthy human cohort exposed to altitude in the field (at minimum 2440 m [8000 ft]) or in a hypoxic environment in a laboratory, and an assessment of cognitive domains. The literature search identified 52 studies (29 of these were field studies; altitude range: 2440 m-8848 m [8000-29,029 ft]). Researchers applied 112 different neuropsychological tests. Attentional capacity, concentration, and executive functions were the most frequently studied. In the laboratory, the ratio of altitude-induced impairments (64.7%) was twice as high compared to results showing no change or improved results (35.3%), but altitudes studied were similar in the chamber compared to field studies. In the field, the opposite results were found (66.4 % no change or improvements, 33.6% impairments). Since better acclimatization can be assumed in the field studies, the findings support the hypothesis that sufficient acclimatization has beneficial effects on cognitive functions at HA. However, it also becomes apparent that research in this area would benefit most if a consensus could be reached on a standardized framework of freely available neurocognitive tests.
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Ebihara A, Kitahara A, Iwamoto T, Kuwahira I. Silent Hypoxemia in COVID-19 Pneumonia. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1395:117-122. [PMID: 36527624 DOI: 10.1007/978-3-031-14190-4_20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
In patients suffering from Coronavirus Disease 2019 (COVID-19), dyspnoea is less likely to occur despite hypoxemia. Even if the patient develops severe hypoxemia, it cannot be detected from subjective symptoms. In other words, it becomes more serious without the person or the surroundings noticing it. Initially less talked about, hypoxemia without dyspnoea (silent hypoxemia or happy hypoxia: hypoxemia that does not coincide with dyspnoea) is now experienced in many institutions. Dyspnoea is defined as "the unpleasant sensation that accompanies breathing." Dyspnoea occurs when afferent information is transmitted to the sensory area. Receptors involved in the development of dyspnoea include central and peripheral chemoreceptors, chest wall receptors, lung receptors, upper respiratory tract receptors and corollary discharge receptors. In the present study, we considered mechanisms mediating the silent hypoxemia through three cases experienced at our hospital as a dedicated coronavirus treatment hospital. We have treated about 600 people infected with COVID-19, of which about 10% were severe cases. In the present study, the patients' condition was retrospectively extracted and analysed. We investigated three typical cases of COVID-19 pneumonia admitted to our hospital (men and women between the ages of 58 and 86 with hypoxemia and tachypnoea). Silent hypoxemia is not entirely without dyspnoea, but hypoxemia does not cause dyspnoea commensurate with its severity. The virus may have specific effects on the respiratory control system. In our cases, respiratory rate significantly increased with hypoxemia, and hyperventilation occurred. Therefore, information about hypoxemia is transmitted from the carotid body. Since hyperventilation occurs, it is suggested that information is transmitted to effectors such as respiratory muscles. The fact that these patients did not feel the unpleasant sensation indicates that information is not accurately transmitted to the sensory area of the cerebral cortex. These cases suggest that there may be a problem somewhere in the path from the respiratory centre to the sensory area.
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Hatano K, Matsuura R, Ohtsuka Y, Yunoki T. Enhancement of self-sustained muscle activity through external dead space ventilation appears to be associated with hypercapnia. Respir Physiol Neurobiol 2021; 295:103777. [PMID: 34425262 DOI: 10.1016/j.resp.2021.103777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 07/24/2021] [Accepted: 08/19/2021] [Indexed: 11/19/2022]
Abstract
We reported that external dead space ventilation (EDSV) enhanced self-sustained muscle activity (SSMA) of the human soleus muscle, which is an indirect observation of plateau potentials. However, the main factor for EDSV to enhance SSMA remains unclear. The purpose of the present study was to examine the effects of EDSV-induced hypercapnia, hypoxia, and hyperventilation on SSMA. In Experiment 1 (n = 11; normal breathing [NB], EDSV, hypoxia, and voluntary hyperventilation conditions) and Experiment 2 (n = 9; NB and normoxic hypercapnia [NH] conditions), SSMA was evoked by electrical train stimulations of the right tibial nerve and measured using surface electromyography under each respiratory condition. In Experiment 1, SSMA was significantly higher than that in the NB condition only in the EDSV condition (P < 0.05). In Experiment 2, SSMA was higher in the NH condition than in the NB condition (P < 0.05). These results suggest that the EDSV-enhanced SSMA is due to hypercapnia, not hypoxia or increased ventilation.
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Affiliation(s)
- Kei Hatano
- Graduate School of Education, Hokkaido University, Sapporo, Japan.
| | - Ryouta Matsuura
- Graduate School of Education, Joetsu University of Education, Japan
| | - Yoshinori Ohtsuka
- Department of Sports and Human Studies, Sapporo International University, Japan
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Baker J, Incognito AV, Wilson RJA, Raj SR. Syncope and silent hypoxemia in COVID-19: Implications for the autonomic field. Auton Neurosci 2021; 235:102842. [PMID: 34246957 PMCID: PMC8258030 DOI: 10.1016/j.autneu.2021.102842] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 05/22/2021] [Accepted: 06/28/2021] [Indexed: 01/08/2023]
Abstract
Coronavirus-19 (COVID-19), the infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, has wreaked havoc across the globe since its emergence in December 2019. Reports of patients presenting with syncope and pre-syncope, as well as hypoxemia without symptoms of dyspnea (“silent hypoxemia”), have led researchers to speculate whether SARS-CoV-2 can alter autonomic nervous system function. As viral infections are commonly reported triggers of altered autonomic control, we must consider whether SARS-CoV-2 can also interfere with autonomic activity, at least in some patients. As we are still in the early stages of understanding COVID-19, we still do not know whether syncope and silent hypoxemia are more strongly associated with COVID-19 compared to any other viral infections that severely compromise gas exchange. Therefore, in this perspective we discuss these two intriguing clinical presentations, as they relate to autonomic nervous system function. In our discussion, we will explore COVID-specific, as well as non-COVID specific mechanisms that may affect autonomic activity and potential therapeutic targets. As we move forward in our understanding of COVID-19, well-designed prospective studies with appropriate control and comparator groups will be necessary to identify potential unique effects of COVID-19 on autonomic function.
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Affiliation(s)
- Jacquie Baker
- Libin Cardiovascular Institute, Department of Cardiac Sciences, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
| | - Anthony V Incognito
- Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada
| | - Richard J A Wilson
- Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada
| | - Satish R Raj
- Libin Cardiovascular Institute, Department of Cardiac Sciences, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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Simonson TS, Baker TL, Banzett RB, Bishop T, Dempsey JA, Feldman JL, Guyenet PG, Hodson EJ, Mitchell GS, Moya EA, Nokes BT, Orr JE, Owens RL, Poulin M, Rawling JM, Schmickl CN, Watters JJ, Younes M, Malhotra A. Silent hypoxaemia in COVID-19 patients. J Physiol 2021; 599:1057-1065. [PMID: 33347610 PMCID: PMC7902403 DOI: 10.1113/jp280769] [Citation(s) in RCA: 53] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Accepted: 12/07/2020] [Indexed: 12/14/2022] Open
Abstract
The clinical presentation of COVID-19 due to infection with SARS-CoV-2 is highly variable with the majority of patients having mild symptoms while others develop severe respiratory failure. The reason for this variability is unclear but is in critical need of investigation. Some COVID-19 patients have been labelled with 'happy hypoxia', in which patient complaints of dyspnoea and observable signs of respiratory distress are reported to be absent. Based on ongoing debate, we highlight key respiratory and neurological components that could underlie variation in the presentation of silent hypoxaemia and define priorities for subsequent investigation.
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Affiliation(s)
- Tatum S Simonson
- Division of Pulmonary, Critical Care, & Sleep Medicine, Department of Medicine, University of California, San Diego, CA, USA
| | - Tracy L Baker
- Department of Comparative Biosciences, University of Wisconsin -, Madison, WI, USA
| | - Robert B Banzett
- Division of Pulmonary, Critical Care, & Sleep Medicine Beth Israel Deaconess Medical Center, Department of Medicine, Harvard Medical School, Boston, MA, USA
| | - Tammie Bishop
- Target Discovery Institute, University of Oxford, Oxford, UK
| | - Jerome A Dempsey
- Department of Population Health Sciences, School of Medicine and Public Health, University of Wisconsin -, Madison, WI, USA
| | - Jack L Feldman
- Department of Neurobiology, University of California, Los Angeles, CA, USA
| | - Patrice G Guyenet
- Department of Pharmacology, School of Medicine, University of Virginia, Charlottesville, VA, USA
| | - Emma J Hodson
- The Francis Crick Institute, London, UK
- The Department of Experimental Medicine and Immunotherapeutics, University of Cambridge, Cambridge, UK
| | - Gordon S Mitchell
- Department of Physical Therapy, Center for Respiratory Research and Rehabilitation, College of Public Health and Health Professions, University of Florida, Gainesville, FL, USA
| | - Esteban A Moya
- Division of Pulmonary, Critical Care, & Sleep Medicine, Department of Medicine, University of California, San Diego, CA, USA
| | - Brandon T Nokes
- Division of Pulmonary, Critical Care, & Sleep Medicine, Department of Medicine, University of California, San Diego, CA, USA
| | - Jeremy E Orr
- Division of Pulmonary, Critical Care, & Sleep Medicine, Department of Medicine, University of California, San Diego, CA, USA
| | - Robert L Owens
- Division of Pulmonary, Critical Care, & Sleep Medicine, Department of Medicine, University of California, San Diego, CA, USA
| | - Marc Poulin
- Departments of Physiology & Pharmacology and Clinical Neurosciences, Cumming School of Medicine and Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
| | - Jean M Rawling
- Departments of Family Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Christopher N Schmickl
- Division of Pulmonary, Critical Care, & Sleep Medicine, Department of Medicine, University of California, San Diego, CA, USA
| | - Jyoti J Watters
- Department of Comparative Biosciences, University of Wisconsin -, Madison, WI, USA
| | - Magdy Younes
- Sleep Disorders Centre, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Atul Malhotra
- Division of Pulmonary, Critical Care, & Sleep Medicine, Department of Medicine, University of California, San Diego, CA, USA
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Dohmen LME, Spigt M, Melbye H. The effect of atmospheric pressure on oxygen saturation and dyspnea: the Tromsø study. INTERNATIONAL JOURNAL OF BIOMETEOROLOGY 2020; 64:1103-1110. [PMID: 32125519 PMCID: PMC7295717 DOI: 10.1007/s00484-020-01883-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Revised: 02/17/2020] [Accepted: 02/19/2020] [Indexed: 06/10/2023]
Abstract
A drop in atmospheric pressure, as observed at high altitudes, leads to decreased oxygen saturation. The effect of regular changes in barometric pressure at sea level has never been studied in a general population. A cohort of adults aged 40 years were examined with pulse oximetry at two separate visits, and the local barometric pressure was available from the local weather station. The study aimed at determining the effect of atmospheric pressure on oxygen saturation also called SpO2, as well as on shortness of breath. Based on spirometry, the participants were divided into two groups, with normal and decreased lung function. Decreased lung function was defined as forced expiratory volume in 1 s (FEV1) below lower limit or normal (LLN) or FEV1/FVC (FVC, forced vital capacity) below LLN, with GLI 2012 reference values. The statistical analysis included uni/multivariable linear and logistic regression. A total of 7439 participants of the Tromsø 7 cohort study were included. There was a significant association between barometric pressure and SpO2 < 96%, and we found that a reduction of 166.67 hPa was needed to get a 1% reduction in SpO2. The change in atmospheric pressure was not significantly associated with shortness of breath, also not in subjects with reduced lung function.
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Affiliation(s)
- Lisa M E Dohmen
- Department of Family Medicine, CAPHRI, Maastricht University, P.O. Box 616, 6200 MD, Maastricht, The Netherlands
| | - Mark Spigt
- Department of Family Medicine, CAPHRI, Maastricht University, P.O. Box 616, 6200 MD, Maastricht, The Netherlands.
- General Practice Research Unit, Department of Community Medicine, UiT The Arctic University of Norway, Tromsø, Norway.
| | - Hasse Melbye
- General Practice Research Unit, Department of Community Medicine, UiT The Arctic University of Norway, Tromsø, Norway
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Dellweg D, Schmitten J, Kerl J, Hoehn E, Haidl P. Impact of hypobaric flight simulation on walking distance and oxygenation in COPD patients. Respir Physiol Neurobiol 2018; 260:1-7. [PMID: 30476554 DOI: 10.1016/j.resp.2018.11.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Revised: 11/19/2018] [Accepted: 11/22/2018] [Indexed: 11/16/2022]
Abstract
BACKGROUND Chronic obstructive pulmonary disease (COPD) is a disease that compromises fitness to fly. OBJECTIVE To investigate, whether hypobaric mid-distance flight simulation limits exercise endurance in COPD patients. METHODS Patients with COPD GOLD stages 2-4 were challenged by hypobaric flight simulation. Patients completed 6-minute walking distances before and after the simulation test. Pulse oximetry and Borg dyspnea scale were measured every 30 min during the test. RESULTS Thirty-five patients were included in the study. The distance of the 6-min walking exercise decreased from 343 ± 93 m to 308 ± 101 m (p < 0.0001). The oxygen saturation nadir for the whole group was 72.2% ± 9.1%. The Borg-dypnea-score did not correlate with oxygen desaturation (R-square 0.009, p > 0.05). CONCLUSIONS A 3-h hypobaric flight simulation compromises exercise endurance by 35 m or 10%. Hypoxia was well tolerated and more liberal recommendations might by justifiable since hypoxemia appears to be unrelated to dyspnea perception.
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Affiliation(s)
- Dominic Dellweg
- Fachkrankenhaus Kloster Grafschaft, Annostr. 1, 57392 Schmallenberg, Germany.
| | - Juliane Schmitten
- DRK Klinikum Berlin Mitte, Schuetzenstrasse 6 A, 10117 Berlin, Germany.
| | - Jens Kerl
- Fachkrankenhaus Kloster Grafschaft, Annostr. 1, 57392 Schmallenberg, Germany.
| | - Ekkehard Hoehn
- Fachkrankenhaus Kloster Grafschaft, Annostr. 1, 57392 Schmallenberg, Germany.
| | - Peter Haidl
- Fachkrankenhaus Kloster Grafschaft, Annostr. 1, 57392 Schmallenberg, Germany.
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Hypoxia treatment reverses neurodegenerative disease in a mouse model of Leigh syndrome. Proc Natl Acad Sci U S A 2017; 114:E4241-E4250. [PMID: 28483998 PMCID: PMC5448167 DOI: 10.1073/pnas.1621511114] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Inherited or acquired defects in mitochondria lead to devastating disorders for which we have no effective general therapies. We recently reported that breathing normobaric 11% O2 prevents neurodegeneration in a mouse model of a pediatric mitochondrial disease, Leigh syndrome. Here we provide updated survival curves of mice treated with varying doses of oxygen and explore eventual causes of death. We explore alternative hypoxia regimens and report that neither intermittent nor moderate hypoxia regimens suffice to prevent neurological disease. Finally, we show that hypoxia can not only prevent, but also reverses the brain lesions in mice with advanced neuropathology. Our preclinical studies will help guide future clinical studies aimed at harnessing hypoxia as a safe and practical therapy. The most common pediatric mitochondrial disease is Leigh syndrome, an episodic, subacute neurodegeneration that can lead to death within the first few years of life, for which there are no proven general therapies. Mice lacking the complex I subunit, Ndufs4, develop a fatal progressive encephalopathy resembling Leigh syndrome and die at ≈60 d of age. We previously reported that continuously breathing normobaric 11% O2 from an early age prevents neurological disease and dramatically improves survival in these mice. Here, we report three advances. First, we report updated survival curves and organ pathology in Ndufs4 KO mice exposed to hypoxia or hyperoxia. Whereas normoxia-treated KO mice die from neurodegeneration at about 60 d, hypoxia-treated mice eventually die at about 270 d, likely from cardiac disease, and hyperoxia-treated mice die within days from acute pulmonary edema. Second, we report that more conservative hypoxia regimens, such as continuous normobaric 17% O2 or intermittent hypoxia, are ineffective in preventing neuropathology. Finally, we show that breathing normobaric 11% O2 in mice with late-stage encephalopathy reverses their established neurological disease, evidenced by improved behavior, circulating disease biomarkers, and survival rates. Importantly, the pathognomonic MRI brain lesions and neurohistopathologic findings are reversed after 4 wk of hypoxia. Upon return to normoxia, Ndufs4 KO mice die within days. Future work is required to determine if hypoxia can be used to prevent and reverse neurodegeneration in other animal models, and to determine if it can be provided in a safe and practical manner to allow in-hospital human therapeutic trials.
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