title: The cerebral venous system and hypoxia.
abstract: Most hypobaric hypoxia studies have focused on oxygen delivery and therefore cerebral blood inflow. Few have studied venous outflow. However, the volume of blood entering and leaving the skull (∼700 ml/min) is considerably greater than cerebrospinal fluid production (0.35 ml/min) or edema formation rates and slight imbalances of in- and outflow have considerable effects on intracranial pressure. This dynamic phenomenon is not necessarily appreciated in the currently taught static "Monro-Kellie" doctrine, which forms the basis of the "Tight-Fit" hypothesis thought to underlie high altitude headache, acute mountain sickness, and high altitude cerebral edema. Investigating both sides of the cerebral circulation was an integral part of the 2007 Xtreme Everest Expedition. The results of the relevant studies performed as part of and subsequent to this expedition are reviewed here. The evidence from recent studies suggests a relative venous outflow insufficiency is an early step in the pathogenesis of high altitude headache. Translation of knowledge gained from high altitude studies is important. Many patients in a critical care environment develop hypoxemia akin to that of high altitude exposure. An inability to drain the hypoxemic induced increase in cerebral blood flow could be an underappreciated regulatory mechanism of intracranial pressure.
authors: The Centre for Altitude, Space and Extreme Environment Medicine, University College London, London, United Kingdom; The Birmingham Medical Research Expeditionary Society, Queen Elizabeth Hospital, Edgbaston, Birmingham, United Kingdom; Imperial Neurotrauma Centre, Imperial College, St Mary's Hospital, London, United Kingdom; Institute of Pre-Hospital Care, London's Air Ambulance, Royal London Hospital, Whitechapel, United Kingdom; and m.wilson@imperial.ac.uk.
authors: Mark H
authors: http://orcid.org/0000-0002-2346-4911
authors: MH
authors: Wilson
authors: The Centre for Altitude, Space and Extreme Environment Medicine, University College London, London, United Kingdom; The Birmingham Medical Research Expeditionary Society, Queen Elizabeth Hospital, Edgbaston, Birmingham, United Kingdom; Department of Surgery, Warwick Medical School, UHCW NHS Trust, Warwick, United Kingdom.
authors: Christopher H E
authors: CH
authors: Imray
mesh_terms: D000531:Altitude; D000532:Altitude Sickness / Q000503:physiopathology; D000818:Animals; D001921:Brain / Q000098:blood supply*; D002550:Cerebral Veins / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007427:Intracranial Pressure / Q000502:physiology
keywords: acute mountain sickness; headache; hypoxia; intracranial pressure; venous