title: Space headache on Earth: head-down-tilted bed rest studies simulating outer-space microgravity.
abstract: BACKGROUND
  Headache is a common symptom during space travel, both isolated and as part of space motion syndrome. Head-down-tilted bed rest (HDTBR) studies are used to simulate outer space microgravity on Earth, and allow countermeasure interventions such as artificial gravity and training protocols, aimed at restoring microgravity-induced physiological changes.
  
  
  OBJECTIVE
  The objectives of this article are to assess headache incidence and characteristics during HDTBR, and to evaluate the effects of countermeasures.
  
  
  METHODS
  In a randomized cross-over design by the European Space Agency (ESA), 22 healthy male subjects, without primary headache history, underwent three periods of -6-degree HDTBR. In two of these episodes countermeasure protocols were added, with either centrifugation or aerobic exercise training protocols. Headache occurrence and characteristics were daily assessed using a specially designed questionnaire.
  
  
  RESULTS
  In total 14/22 (63.6%) subjects reported a headache during ≥1 of the three HDTBR periods, in 12/14 (85.7%) non-specific, and two of 14 (14.4%) migraine. The occurrence of headache did not differ between HDTBR with and without countermeasures: 12/22 (54.5%) subjects vs. eight of 22 (36.4%) subjects; p = 0.20; 13/109 (11.9%) headache days vs. 36/213 (16.9%) headache days; p = 0.24). During countermeasures headaches were, however, more often mild (p = 0.03) and had fewer associated symptoms (p = 0.008).
  
  
  CONCLUSIONS
  Simulated microgravity during HDTBR induces headache episodes, mostly on the first day. Countermeasures are useful in reducing headache severity and associated symptoms. Reversible, microgravity-induced cephalic fluid shift may cause headache, also on Earth. HDTBR can be used to study space headache on Earth.
authors.affiliation: Department of Neurology, Leiden University Medical Center, the Netherlands w.p.j.van_oosterhout@lumc.nl.
authors.forename: W P J
authors.initials: WP
authors.lastname: van Oosterhout
authors.affiliation: Department of Neurology, Leiden University Medical Center, the Netherlands.
authors.forename: G M
authors.initials: GM
authors.lastname: Terwindt
authors.affiliation: Department of Neurology, Leiden University Medical Center, the Netherlands.
authors.forename: A A
authors.initials: AA
authors.lastname: Vein
authors.affiliation: Department of Neurology, Leiden University Medical Center, the Netherlands.
authors.forename: M D
authors.initials: MD
authors.lastname: Ferrari
mesh_terms: D000328:Adult; D000337:Aerospace Medicine; D018470:Gravity, Altered / Q000009:adverse effects; D018475:Head-Down Tilt / Q000009:adverse effects*; D006261:Headache / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D015994:Incidence; D008297:Male; D013026:Space Flight; D018474:Weightlessness Simulation / Q000009:adverse effects* / Q000379:methods*
keywords: Space headache; artificial microgravity; countermeasures; head-down-tilted bed rest study