title: Intracranial pressure and optic nerve sheath diameter as cephalic venous pressure increases in swine.
abstract: BACKGROUND
  Nontraumatic, nonhydrocephalic increases in intracranial pressure (ICP) are often difficult to diagnose and may underlie spaceflight-related visual changes. This study looked at the utility of a porcine animal model of increasing cephalic venous pressure to mimic acute changes in ICP and optic nerve sheath diameter (ONSD) from cephalic venous fluid shifts observed during spaceflight.
  
  
  METHODS
  Anesthetized juvenile piglets were assigned to groups of either naïve (N = 10) or elevated superior vena cava pressure (SVCP; N = 20). To elevate SVCP, a 6F custom latex balloon catheter was inserted and inflated to achieve SVCP of 20 and 40 mmHg for 1 h at each pressure. In both groups, serial measurements of ICP, internal jugular pressure (IJP), and external jugular pressure (EJP) were made hourly for 3 h, and ONSD of the right eye was measured hourly by ultrasound (US).
  
  
  RESULTS
  There was a significant linear correlation between IJP and ICP (slope: 0.9614 +/- 0.0038, r = 0.9683). With increasing SVCP, resulting ONSD was also well correlated with the ICP (slope: 0.0958 +/- 0.0061, r = 0.7841). The receiver operating characteristic curve for ONSD in diagnosing elevated ICP had an area under the curve of 0.9632 with a sensitivity and specificity of 92% and 91%, respectively, for a cutoff of 5.45 mm.
  
  
  CONCLUSIONS
  Increases in SVCP result in ICP changes that are well correlated with alteration in ONSD. These changes are consistent with observed ONSD changes monitored during spaceflight.
authors.affiliation: Department of Internal Medicine, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA. nusbaum@bcm.edu
authors.forename: Derek M
authors.initials: DM
authors.lastname: Nusbaum
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Clark
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Brady
authors.forename: Kathleen K
authors.initials: KK
authors.lastname: Kibler
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Sutton
authors.forename: R Blaine
authors.initials: RB
authors.lastname: Easley
mesh_terms: D000337:Aerospace Medicine; D000818:Animals; D019586:Intracranial Hypertension / Q000175:diagnosis* / Q000503:physiopathology; D007427:Intracranial Pressure / Q000502:physiology; D007601:Jugular Veins / Q000503:physiopathology; D023421:Models, Animal; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D012372:ROC Curve; D012680:Sensitivity and Specificity; D013026:Space Flight; D013552:Swine; D014463:Ultrasonography; D014683:Vena Cava, Superior / Q000503:physiopathology; D014690:Venous Pressure / Q000502:physiology*