title: Intracranial and Intraocular Pressure During Various Degrees of Head-Down Tilt.
abstract: BACKGROUND
  More than half of astronauts develop ophthalmic changes during long-duration spaceflight consistent with an abnormal intraocular and intracranial pressure (IOP, ICP) difference. The aim of our study was to assess IOP and ICP during head-down tilt (HDT) and the additive or attenuating effects of 1% CO2 and lower body negative pressure (LBNP).
  
  
  METHODS
  In Experiment I, IOP and ICP were measured in nine healthy subjects after 3.5 h HDT in five conditions: -6°, -12°, and -18° HDT, -12° with 1% CO2, and -12° with -20 mmHg LBNP. In Experiment II, IOP was measured in 16 healthy subjects after 5 min tilt at +12°, 0°, -6°, -12°, -18°, and -24°, with and without -40 mmHg LBNP.
  
  
  RESULTS
  ICP was only found to increase from supine baseline during -18° HDT (9.2 ± 0.9 and 14.4 ± 1 mmHg, respectively), whereas IOP increased from 15.7 ± 0.3 mmHg at 0° to 17.9 ± 0.4 mmHg during -12° HDT and from 15.3 ± 0.4 mmHg at 0° to 18.7 ± 0.4 mmHg during -18° HDT. The addition of -20 mmHg LBNP or 1% CO2 had no further effects on ICP or IOP. However, the use of -40 mmHg LBNP during HDT lowered IOP back to baseline values, except at -24° HDT.
  
  
  CONCLUSIONS
  A small, posterior intraocular-intracranial pressure difference (IOP > ICP) is maintained during HDT, and a sustained or further decreased difference may lead to structural changes in the eye in real and simulated microgravity.Marshall-Goebel K, Mulder E, Bershad E, Laing C, Eklund A, Malm J, Stern C, Rittweger J. Intracranial and intraocular pressure during various degrees of head-down tilt. Aerosp Med Hum Perform. 2017; 88(1):10-16.
authors.forename: Karina
authors.initials: K
authors.lastname: Marshall-Goebel
authors.forename: Edwin
authors.initials: E
authors.lastname: Mulder
authors.forename: Eric
authors.initials: E
authors.lastname: Bershad
authors.forename: Charles
authors.initials: C
authors.lastname: Laing
authors.forename: Anders
authors.initials: A
authors.lastname: Eklund
authors.forename: Jan
authors.initials: J
authors.lastname: Malm
authors.forename: Claudia
authors.initials: C
authors.lastname: Stern
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
mesh_terms: D000328:Adult; D002245:Carbon Dioxide; D018475:Head-Down Tilt / Q000009:adverse effects / Q000502:physiology*; D064368:Healthy Volunteers; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology*; D007429:Intraocular Pressure / Q000502:physiology*; D008150:Lower Body Negative Pressure / Q000009:adverse effects; D008297:Male; D011187:Posture; D013026:Space Flight; D017585:Ultrasonography, Doppler, Transcranial; D014786:Vision Disorders / Q000209:etiology; D018474:Weightlessness Simulation; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide