title: Case report: (Pre)syncopal symptoms associated with a negative internal jugular venous pressure.
abstract: A siphon is suggested to support cerebral blood flow but appears not to be established because internal jugular venous (IJV) pressure is close to zero in upright humans. Thus, in eleven young healthy males, IJV pressure was 9 ± 1 mmHg (mean ± SE) when supine and fell to 3 ± 1 mmHg when seated, and middle cerebral artery mean blood velocity (MCA Vmean; P < 0.007) and the near-infrared spectroscopy-determined frontal lobe oxygenation (ScO2; P = 0.028) also decreased. Another subject, however, developed (pre)syncopal symptoms while seated and his IJV pressure decreased to -17 mmHg. Furthermore, his MCA Vmean decreased and yet within the time of observation ScO2 was not necessarily affected. These findings support the hypothesis that a negative IJV pressure that is a prerequisite for creation of a siphon provokes venous collapse inside the dura, and thereby limits rather than supports CBF.
authors.affiliation: Department of Anesthesia, Rigshospitalet, University of Copenhagen Copenhagen, Denmark.
authors.forename: Niels D
authors.initials: ND
authors.lastname: Olesen
authors.affiliation: Department of Internal Medicine, Academic Medical Centre, University of Amsterdam Amsterdam, Netherlands ; Laboratory for Clinical Cardiovascular Physiology, Centre for Heart Failure Research, Academic Medical Centre Amsterdam, Netherlands ; MRC/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, The Medical School, University of Nottingham, Queen's Medical Centre Nottingham, UK.
authors.forename: Johannes J
authors.initials: JJ
authors.lastname: van Lieshout
authors.affiliation: School of Sport, Exercise & Rehabilitation Sciences, College of Life and Environmental Sciences University of Birmingham, UK.
authors.forename: James P
authors.initials: JP
authors.lastname: Fisher
authors.affiliation: Department of Anesthesia, Rigshospitalet, University of Copenhagen Copenhagen, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Seifert
authors.affiliation: Department of Anesthesia, Rigshospitalet, University of Copenhagen Copenhagen, Denmark.
authors.forename: Henning B
authors.initials: HB
authors.lastname: Nielsen
authors.affiliation: Department of Anesthesia, Rigshospitalet, University of Copenhagen Copenhagen, Denmark.
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
keywords: (pre)syncope; cerebrovascular circulation; exercise; internal jugular vein; venous pressure