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Sharma HS, Lafuente JV, Feng L, Muresanu DF, Menon PK, Castellani RJ, Nozari A, Sahib S, Tian ZR, Buzoianu AD, Sjöquist PO, Patnaik R, Wiklund L, Sharma A. Methamphetamine exacerbates pathophysiology of traumatic brain injury at high altitude. Neuroprotective effects of nanodelivery of a potent antioxidant compound H-290/51. PROGRESS IN BRAIN RESEARCH 2021; 266:123-193. [PMID: 34689858 DOI: 10.1016/bs.pbr.2021.06.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Military personnel are often exposed to high altitude (HA, ca. 4500-5000m) for combat operations associated with neurological dysfunctions. HA is a severe stressful situation and people frequently use methamphetamine (METH) or other psychostimulants to cope stress. Since military personnel are prone to different kinds of traumatic brain injury (TBI), in this review we discuss possible effects of METH on concussive head injury (CHI) at HA based on our own observations. METH exposure at HA exacerbates pathophysiology of CHI as compared to normobaric laboratory environment comparable to sea level. Increased blood-brain barrier (BBB) breakdown, edema formation and reductions in the cerebral blood flow (CBF) following CHI were exacerbated by METH intoxication at HA. Damage to cerebral microvasculature and expression of beta catenin was also exacerbated following CHI in METH treated group at HA. TiO2-nanowired delivery of H-290/51 (150mg/kg, i.p.), a potent chain-breaking antioxidant significantly enhanced CBF and reduced BBB breakdown, edema formation, beta catenin expression and brain pathology in METH exposed rats after CHI at HA. These observations are the first to point out that METH exposure in CHI exacerbated brain pathology at HA and this appears to be related with greater production of oxidative stress induced brain pathology, not reported earlier.
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Affiliation(s)
- Hari Shanker Sharma
- International Experimental Central Nervous System Injury & Repair (IECNSIR), Department of Surgical Sciences, Anesthesiology & Intensive Care Medicine, Uppsala University Hospital, Uppsala University, Uppsala, Sweden.
| | - José Vicente Lafuente
- LaNCE, Department of Neuroscience, University of the Basque Country (UPV/EHU), Leioa, Bizkaia, Spain
| | - Lianyuan Feng
- Department of Neurology, Bethune International Peace Hospital, Shijiazhuang, Hebei Province, China
| | - Dafin F Muresanu
- Department of Clinical Neurosciences, University of Medicine & Pharmacy, Cluj-Napoca, Romania; "RoNeuro" Institute for Neurological Research and Diagnostic, Cluj-Napoca, Romania
| | - Preeti K Menon
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Rudy J Castellani
- Department of Pathology, University of Maryland, Baltimore, MD, United States
| | - Ala Nozari
- Anesthesiology & Intensive Care, Massachusetts General Hospital, Boston, MA, United States
| | - Seaab Sahib
- Department of Chemistry & Biochemistry, University of Arkansas, Fayetteville, AR, United States
| | - Z Ryan Tian
- Department of Chemistry & Biochemistry, University of Arkansas, Fayetteville, AR, United States
| | - Anca D Buzoianu
- Department of Clinical Pharmacology and Toxicology, "Iuliu Hatieganu" University of Medicine and Pharmacy, Cluj-Napoca, Romania
| | - Per-Ove Sjöquist
- Division of Cardiology, Department of Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
| | - Ranjana Patnaik
- Department of Biomaterials, School of Biomedical Engineering, Indian Institute of Technology, Banaras Hindu University, Varanasi, India
| | - Lars Wiklund
- International Experimental Central Nervous System Injury & Repair (IECNSIR), Department of Surgical Sciences, Anesthesiology & Intensive Care Medicine, Uppsala University Hospital, Uppsala University, Uppsala, Sweden
| | - Aruna Sharma
- International Experimental Central Nervous System Injury & Repair (IECNSIR), Department of Surgical Sciences, Anesthesiology & Intensive Care Medicine, Uppsala University Hospital, Uppsala University, Uppsala, Sweden.
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Sagoo RS, Hutchinson CE, Wright A, Handford C, Parsons H, Sherwood V, Wayte S, Nagaraja S, Ng'Andwe E, Wilson MH, Imray CH. Magnetic Resonance investigation into the mechanisms involved in the development of high-altitude cerebral edema. J Cereb Blood Flow Metab 2017; 37:319-331. [PMID: 26746867 PMCID: PMC5167111 DOI: 10.1177/0271678x15625350] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 11/08/2015] [Accepted: 11/27/2015] [Indexed: 11/20/2022]
Abstract
Rapid ascent to high altitude commonly results in acute mountain sickness, and on occasion potentially fatal high-altitude cerebral edema. The exact pathophysiological mechanisms behind these syndromes remain to be determined. We report a study in which 12 subjects were exposed to a FiO2 = 0.12 for 22 h and underwent serial magnetic resonance imaging sequences to enable measurement of middle cerebral artery velocity, flow and diameter, and brain parenchymal, cerebrospinal fluid and cerebral venous volumes. Ten subjects completed 22 h and most developed symptoms of acute mountain sickness (mean Lake Louise Score 5.4; p < 0.001 vs. baseline). Cerebral oxygen delivery was maintained by an increase in middle cerebral artery velocity and diameter (first 6 h). There appeared to be venocompression at the level of the small, deep cerebral veins (116 cm3 at 2 h to 97 cm3 at 22 h; p < 0.05). Brain white matter volume increased over the 22-h period (574 ml to 587 ml; p < 0.001) and correlated with cumulative Lake Louise scores at 22 h (p < 0.05). We conclude that cerebral oxygen delivery was maintained by increased arterial inflow and this preceded the development of cerebral edema. Venous outflow restriction appeared to play a contributory role in the formation of cerebral edema, a novel feature that has not been observed previously.
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Affiliation(s)
- Ravjit S Sagoo
- Department of Imaging, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, West Midlands, UK
| | - Charles E Hutchinson
- Department of Imaging, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, West Midlands, UK.,Warwick Medical School, University of Warwick, Coventry, West Midlands, UK
| | - Alex Wright
- College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Charles Handford
- University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK
| | - Helen Parsons
- Division of Health Sciences, Warwick Medical School, University of Warwick, Coventry, West Midlands, UK
| | - Victoria Sherwood
- Department of Medical Physics, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, West Midlands, UK
| | - Sarah Wayte
- Department of Medical Physics, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, West Midlands, UK
| | - Sanjoy Nagaraja
- Department of Imaging, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, West Midlands, UK
| | - Eddie Ng'Andwe
- Department of Imaging, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, West Midlands, UK
| | - Mark H Wilson
- Department of Neurosurgery, Imperial College Healthcare NHS Trust, London, UK
| | - Christopher He Imray
- Warwick Medical School, University of Warwick, Coventry, West Midlands, UK .,Department of Surgery, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, West Midlands, UK.,Coventry University, West Midlands, UK
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3
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Olzowy B, Abendroth S, von Gleichenstein G, Mees K, Stelter K. No Evidence of Intracranial Hypertension in Trekkers with Acute Mountain Sickness When Assessed Noninvasively with Distortion Product Otoacoustic Emissions. High Alt Med Biol 2014; 15:364-70. [DOI: 10.1089/ham.2013.1120] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Bernhard Olzowy
- Department of Otorhinolaryngology, Head and Neck Surgery, University of Rostock Medical Center, Rostock, Germany
| | | | | | - Klaus Mees
- Department of Otorhinolaryngology, Head and Neck Surgery, Ludwig Maximilians University of Munich Medical Center, München, Germany
| | - Klaus Stelter
- Department of Otorhinolaryngology, Head and Neck Surgery, Ludwig Maximilians University of Munich Medical Center, München, Germany
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4
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Affiliation(s)
- Mark H. Wilson
- The Brain Injury Centre—St Mary's Hospital, Imperial College, London, United Kingdom
- Birmingham Medical Research Expeditionary Society, Birmingham, United Kingdom
- The Institute of Pre-Hospital Care, London's Air Ambulance, Barts and the London Medical School, Queen Mary University of London, The Helipad, The Royal London Hospital, Whitechapel, United Kingdom
| | - Alex Wright
- Birmingham Medical Research Expeditionary Society, Birmingham, United Kingdom
| | - Christopher H.E. Imray
- University Hospital Coventry and Warwickshire NHS Trust and Warwick Medical School, Coventry, United Kingdom
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5
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Optic Nerve Sheath Diameter Is Not Related to High Altitude Headache: A Randomized Controlled Trial. High Alt Med Biol 2012; 13:193-9. [DOI: 10.1089/ham.2012.1019] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
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Querfurth HW, Lieberman P, Arms S, Mundell S, Bennett M, van Horne C. Ophthalmodynamometry for ICP prediction and pilot test on Mt. Everest. BMC Neurol 2010; 10:106. [PMID: 21040572 PMCID: PMC2987855 DOI: 10.1186/1471-2377-10-106] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Accepted: 11/01/2010] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND A recent development in non-invasive techniques to predict intracranial pressure (ICP) termed venous ophthalmodynamometry (vODM) has made measurements in absolute units possible. However, there has been little progress to show utility in the clinic or field. One important application would be to predict changes in actual ICP during adaptive responses to physiologic stress such as hypoxia. A causal relationship between raised intracranial pressure and acute mountain sickness (AMS) is suspected. Several MRI studies report that modest physiologic increases in cerebral volume, from swelling, normally accompany subacute ascent to simulated high altitudes. OBJECTIVES 1) Validate and calibrate an advanced, portable vODM instrument on intensive patients with raised intracranial pressure and 2) make pilot, non-invasive ICP estimations of normal subjects at increasing altitudes. METHODS The vODM was calibrated against actual ICP in 12 neurosurgical patients, most affected with acute hydrocephalus and monitored using ventriculostomy/pressure transducers. The operator was blinded to the transducer read-out. A clinical field test was then conducted on a variable data set of 42 volunteer trekkers and climbers scaling Mt. Everest, Nepal. Mean ICPs were estimated at several altitudes on the ascent both across and within subjects. RESULTS Portable vODM measurements increased directly and linearly with ICP resulting in good predictability (r = 0.85). We also found that estimated ICP increases normally with altitude (10 ± 3 mm Hg; sea level to 20 ± 2 mm Hg; 6553 m) and that AMS symptoms did not correlate with raised ICP. CONCLUSION vODM technology has potential to reliably estimate absolute ICP and is portable. Physiologic increases in ICP and mild-mod AMS are separate responses to high altitude, possibly reflecting swelling and vasoactive instability, respectively.
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Affiliation(s)
- Henry W Querfurth
- Dept of Neurology, Rhode Island Hospital, Warren Alpert Medical School, Brown University Providence, RI 02903, USA.
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7
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Fagenholz PJ, Gutman JA, Murray AF, Noble VE, Camargo CA, Harris NS. Optic nerve sheath diameter correlates with the presence and severity of acute mountain sickness: evidence for increased intracranial pressure. J Appl Physiol (1985) 2009; 106:1207-11. [DOI: 10.1152/japplphysiol.01188.2007] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Increased intracranial pressure is suspected in the pathogenesis of acute mountain sickness (AMS), but no studies have correlated it with the presence or severity of AMS. We sought to determine whether increased optic nerve sheath diameter, a surrogate measure of intracranial pressure, is associated with the presence and severity of AMS. We performed a cross-sectional study of travelers ascending through Pheriche, Nepal (4,240 m), from March 3 to May 14, 2006. AMS was assessed using the Lake Louise score. Optic nerve sheath diameter was measured by ultrasound. Ultrasound exams were performed and read by separate blinded observers. Two-hundred eighty seven subjects were enrolled. Ten of these underwent repeat examination. Mean optic nerve sheath diameter was 5.34 mm [95% confidence interval (CI) 5.18–5.51 mm] in the 69 subjects with AMS vs. 4.46 mm (95% CI 4.39–4.54 mm) in the 218 other subjects ( P < 0.0001). There was also a positive association between optic nerve sheath diameter and total Lake Louise score ( P for trend < 0.0001). In a multivariate logistic regression model of factors associated with AMS, optic nerve sheath diameter was strongly associated with AMS (odds ratio 6.3; 95% CI, 3.7–10.8; P < 0.001). In 10 subjects with repeat examinations, change in Lake Louise score had a strong positive correlation with change in optic nerve sheath diameter ( R2 = 0.84, P < 0.001). Optic nerve sheath diameter, a proxy for intracranial pressure, is associated with the presence and severity of AMS.
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Abstract
Cellular hypoxia is the common final pathway of brain injury that occurs not just after asphyxia, but also when cerebral perfusion is impaired directly (eg, embolic stroke) or indirectly (eg, raised intracranial pressure after head injury). We Review recent advances in the understanding of neurological clinical syndromes that occur on exposure to high altitudes, including high altitude headache (HAH), acute mountain sickness (AMS), and high altitude cerebral oedema (HACE), and the genetics, molecular mechanisms, and physiology that underpin them. We also present the vasogenic and cytotoxic bases for HACE and explore venous hypertension as a possible contributory factor. Although the factors that control susceptibility to HACE are poorly understood, the effects of exposure to altitude (and thus hypobaric hypoxia) might provide a reproducible model for the study of cerebral cellular hypoxia in healthy individuals. The effects of hypobaric hypoxia might also provide new insights into the understanding of hypoxia in the clinical setting.
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Affiliation(s)
- Mark H Wilson
- Centre for Altitude, Space and Extreme Environment Medicine, University College London, London, UK.
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Wilson MH, Edsell M, Imray C, Wright A. Changes in Pupil Dynamics at High Altitude—An Observational Study Using a Handheld Pupillometer. High Alt Med Biol 2008; 9:319-25. [DOI: 10.1089/ham.2008.1026] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
| | | | - Chris Imray
- Warwick Medical School, UHCW NHS Trust, Coventry, UK
| | - Alex Wright
- The Medical School, University of Birmingham, UK
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10
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Wilson MH, Milledge J. DIRECT MEASUREMENT OF INTRACRANIAL PRESSURE AT HIGH ALTITUDE AND CORRELATION OF VENTRICULAR SIZE WITH ACUTE MOUNTAIN SICKNESS. Neurosurgery 2008; 63:970-4; discussion 974-5. [DOI: 10.1227/01.neu.0000327885.15132.ca] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Affiliation(s)
- Mark H. Wilson
- Centre for Aviation, Space, and Extreme Environment Medicine, University College London, London, England
| | - James Milledge
- Centre for Aviation, Space, and Extreme Environment Medicine, University College London, London, England
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11
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Olzowy B, von Gleichenstein G, Canis M, Mees K. Distortion product otoacoustic emissions for assessment of intracranial hypertension at extreme altitude? Eur J Appl Physiol 2008; 103:19-23. [DOI: 10.1007/s00421-007-0666-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/20/2007] [Indexed: 10/22/2022]
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12
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Raksin PB, Alperin N, Sivaramakrishnan A, Surapaneni S, Lichtor T. Noninvasive intracranial compliance and pressure based on dynamic magnetic resonance imaging of blood flow and cerebrospinal fluid flow: review of principles, implementation, and other noninvasive approaches. Neurosurg Focus 2003; 14:e4. [PMID: 15679303 DOI: 10.3171/foc.2003.14.4.4] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Current techniques for intracranial pressure (ICP) measurement are invasive. All require a surgical procedure for placement of a pressure probe in the central nervous system and, as such, are associated with risk and morbidity. These considerations have driven investigators to develop noninvasive techniques for pressure estimation. A recently developed magnetic resonance (MR) imaging-based method to measure intracranial compliance and pressure is described. In this method the small changes in intracranial volume and ICP that occur naturally with each cardiac cycle are considered. The pressure change during the cardiac cycle is derived from the cerebrospinal fluid (CSF) pressure gradient waveform calculated from the CSF velocities. The intracranial volume change is determined by the instantaneous differences between arterial blood inflow, venous blood outflow, and CSF volumetric flow rates into and out of the cranial vault. Elastance (the inverse of compliance) is derived from the ratio of the measured pressure and volume changes. A mean ICP value is then derived based on a linear relationship that exists between intracranial elastance and ICP. The method has been validated in baboons, flow phantoms, and computer simulations. To date studies in humans demonstrate good measurement reproducibility and reliability. Several other noninvasive approaches for ICP measurement, mostly nonimaging based, are also reviewed. Magnetic resonance imaging-based ICP measurement may prove valuable in the diagnosis and serial evaluation of patients with a variety of disorders associated with alterations in ICP.
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Affiliation(s)
- Patricia B Raksin
- Department of Neurosurgery, Rush-Presbyterian St. Luke's Medical Center, Cook County Hospital, Illinois, USA
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13
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Imray CH, Barnett NJ, Walsh S, Clarke T, Morgan J, Hale D, Hoar H, Mole D, Chesner I, Wright AD. Near-infrared spectroscopy in the assessment of cerebral oxygenation at high altitude. Wilderness Environ Med 2002; 9:198-203. [PMID: 11990191 DOI: 10.1580/1080-6032(1998)009[0198:nisita]2.3.co;2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Hypoxia plays a key role in the pathogenesis of acute mountain sickness (AMS), but individual susceptibility is variable and cerebral symptoms do not always correlate with PaO2 measurements. Cerebral hypoxia may be more relevant than PaO2. We studied trends in cerebral regional oxygen saturation by the technique of near-infrared spectroscopy in 20 subjects ascending rapidly to 4680 m. Subjects were enrolled in a placebo-controlled, double-blind trial of medroxyprogesterone for the prevention of AMS. The fall in cerebral oxygen saturation was less than in the periphery. At 4680 m, cerebral oxygenation correlated with peripheral saturation but not with PaCO2 or with cerebral symptoms scores. At 4680 m, subjects on medroxyprogesterone had higher cerebral and peripheral saturation compared with those on a placebo. We conclude that cerebral oxygenation monitored with the Critikon 2020 system provided important information on the complex relationship of hypoxia to AMS and that other factors, such as changes in blood flow or capillary permeability, may be equally important.
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Affiliation(s)
- C H Imray
- Medical School, University of Birmingham, Edgbaston, UK
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14
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Abstract
SUMMARY
Traditionally, scientists and clinicians have explored peripheral physiological responses to acute hypoxia to explain the pathophysiological processes that lead to acute mountain sickness (AMS) and high-altitude cerebral edema (HACE). After more than 100 years of investigation, little is yet known about the fundamental causes of the headache and nausea that are the main symptoms of AMS. Thus, we review the evidence supporting a change in focus to the role of the central nervous system in AMS. Our justification is (i) that the symptoms of AMS and HACE are largely neurological, (ii) that HACE is considered to be the end-stage of severe AMS and was recently identified as a vasogenic edema, opening the door for a role for blood–brain barrier permeability in AMS, (iii) that new, non-invasive techniques make measurement of brain water levels and cerebral blood volume possible and (iv) that the available experimental evidence and theoretical arguments support a significant role for brain swelling in the pathophysiology of AMS. We believe that an examination of the responses of the central nervous system to acute hypoxia will reveal important new pathophysiological processes that may help explain AMS and HACE.
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Affiliation(s)
- R C Roach
- New Mexico Resonance, Box 343, Montezuma, NM 87731, USA.
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15
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Serrano-Dueñas M. [Acute mountain sickness: the clinical characteristics of a cohort of 615 patients]. Med Clin (Barc) 2000; 115:441-5. [PMID: 11093854 DOI: 10.1016/s0025-7753(00)71587-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
OBJECTIVE To study the acute mountain sickness (AMS) and the influence the altitude has on individuals according to time of exposure, age and place of residence. Study cohort prospective in the shelters of Cotopaxi and Chimborazo (4,800 and 5,000 m), in the Ecuatorian Andes. SUBJECTS AND METHODS Tourists from 8 to 51 years of age, residents of the coastal and mountain regions, exposed suddenly to the altitude. Signs and symptoms were recorded at 2, 8, 20 and 24 h of exposure and categorized according to the degree of acute mountain sickness found: AMS 1 [4 to 7 points (light), AMS 2 [8 to 11 points (moderate)] and AMS 3 [more than 12 points (severe)]. RESULTS The study, consisted of 615 patients, was completed by 564. Neurological symptoms are prevalent (headache in the 81.7% of patients) over cardiopulmonary symptoms (cardiac frequency over 100/min in the 25.6%). At 20 h (after one night), the signs and symptoms are more intense and affect a greater number of people (p < 0.0001). Patients from 8 to 22 years of age and residents of the coast have a greater risk of developing AMS 2 (p < 0.01). Overweight, a sedentary life style and a previous incidence of altitude sickness are factors which contribute to the development of AMS 2 (p < 0.001). CONCLUSIONS AMS is an important neurological affection. Young people, individuals from sea-level, as well as those whose are overweight, sedentary or who have previously experienced AMS, have a higher risk of developing AMS 2 after a sudden exposure to altitudes between 4,800 and 5,000 meters. Lack of balance and coordination, and shortness of breath at rest imply AMS 3 and the presence of high altitude cerebral or pulmonary edema.
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Affiliation(s)
- M Serrano-Dueñas
- Servicio de Neurología. Hospital Carlos Andrade Marín. Instituto Ecuatoriano de Seguridad Social. Facultad de Medicina. Pontificia Universidad Católica de Ecuador, Quito.
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16
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Hackett PH. High altitude cerebral edema and acute mountain sickness. A pathophysiology update. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2000; 474:23-45. [PMID: 10634991 DOI: 10.1007/978-1-4615-4711-2_2] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The diagnosis, treatment and prevention of high altitude cerebral edema (HACE) are fairly well established. The major unresolved issues are 1) the pathophysiology, 2) the individual susceptibility, and 3) the relationship of HACE to acute mountain sickness (AMS) and to high altitude pulmonary edema (HAPE). In the context of the two types of cerebral edema, cytotoxic (intracellular) and vasogenic, a leaking of proteins and water through the blood-brain barrier (BBB), a recent MRI study in persons ill with HACE (16) suggested a predominantly vasogenic mechanism. Causes of increased BBB permeability might include mechanical factors (loss of autoregulation and increased capillary pressure), ischemia, neurogenic influences (adrenergic and cholinergic activation), and a host of permeability mediators. Once vasogenic edema develops, cytotoxic edema generally follows, and although likely in HACE, this is still unproven. Symptoms of HACE are related to increased intracranial pressure (ICP), and death is from brain herniation. Treatment is directed both to lowering ICP by reducing the volume of intracranial contents, and to stopping the vasogenic leak. Evidence is accumulating that established moderate to severe AMS is due to cerebral edema, but whether this is true for early AMS (headache) is unclear. New work suggests that the brain swells on ascent to altitude, but that this is unrelated to AMS. Preliminary data showing that those with less cerebrospinal fluid volume (a tighter fit of the brain in the cranium) were more likely to develop AMS supports the hypothesis of Ross that those with less ability to accommodate the increased brain volume are the ones that suffer AMS. The blood-brain barrier and intracranial hemodynamics are the two key elements in the pathophysiology of HACE and AMS.
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Affiliation(s)
- P H Hackett
- University of Washington School of Medicine, USA
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17
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Abstract
Despite normal cerebral oxygenation and normal global cerebral metabolism, vasogenic edema develops in humans (and sheep) who become moderately ill with AMS/ HACE during 24 hr or more of hypoxic exposure. Hypoxic cerebral vasodilatation appears to be a necessary ingredient but does not per se explain the development of brain edema. In addition to mechanical factors, a number of biochemical mediators might play a role in altering the blood-brain barrier. Brain cell swelling (cytotoxic edema) likely has a role only in the later stages of HACE and not in AMS. The hypothesis that AMS is due to cerebral edema appears to be true for moderate-to-severe illness, but whether early AMS, especially the headache, is caused by edema is not known. Other mechanisms for the headache, perhaps similar to those of migraine, need to be explored. New data suggest that the brain swells on ascent to high altitudes regardless of AMS. Whether this is due to edema or engorgement with blood is not yet clear. The "tight fit" hypothesis proposes that individual anatomy of the craniospinal axis determines tolerance to mild brain edema and might help explain individual susceptibility; preliminary studies support this notion. Therapy for AMS and HACE is directed to reducing brain volume and stopping the BBB leak (i.e., oxygenation, diuretics, and steroids) before secondary ischemia develops. New therapies directed specifically toward the defect in BBB permeability are likely to be successful.
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Affiliation(s)
- P H Hackett
- University of Washington School of Medicine, Seattle, USA
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