title: Gravitational valves in supine patients with ventriculo-peritoneal shunts.
abstract: BACKGROUND
  In the subgroup of bedridden hydrocephalic patients with ventriculo-peritoneal shunts and gravitational valves, we occasionally observed persisting hydrocephalic complaints even when mechanical or infection-related obstruction was excluded.
  
  
  METHODS
  To investigate the cause of these hydrocephalic symptoms, in vitro and in vivo analyses were used to determine valve opening, intra-abdominal and hydrostatic pressure of an Aesculap-Miethke 10/40 cm H2O gravitational valve at different angles of upper body and head inclination.
  
  
  RESULTS
  Since hydrostatic pressure is lacking, the resulting intra-ventricular pressures are shown to peak up to 27 cm H2O in supine patients with head, but not upper body inclined.
  
  
  CONCLUSIONS
  We conclude that in the subgroup of bedridden patients with ventriculo-peritoneal shunts and gravitational valves, upright posture is a prerequisite for proper cerebrospinal fluid drainage.
authors.affiliation: Department of Neurosurgery, University of Freiburg Medical School, Breisacher Str. 64, D-79106 Freiburg, Germany. martin.deininger@uniklinik-freiburg.de
authors.forename: Martin H
authors.initials: MH
authors.lastname: Deininger
authors.forename: Astrid
authors.initials: A
authors.lastname: Weyerbrock