title: Microgravity Simulated by the 6° Head-Down Tilt Bed Rest Test Increases Intestinal Motility but Fails to Induce Gastrointestinal Symptoms of Space Motion Sickness.
abstract: BACKGROUND
  Space motion sickness (SMS) is the most relevant medical problem during the first days in microgravity. Studies addressing pathophysiology in space face severe technical challenges and microgravity is frequently simulated using the 6° head-down tilt bed rest test (HDT).
  
  
  OBJECTIVE
  We were aiming to test whether SMS could be simulated by HDT, identify related changes in gastrointestinal physiology and test for beneficial effects of exercise interventions.
  
  
  METHODS
  HDT was performed in ten healthy individuals. Each individual was tested in three study campaigns varying by a 30-min daily exercise intervention of either standing, an upright exercise regimen, or no intervention. Gastrointestinal symptoms, stool characteristics, gastric emptying time, and small intestinal transit were assessed using standardized questionnaires, (13)C octanoate breath test, and H2 lactulose breath test, respectively, before and at day 2 and 5 of HDT.
  
  
  RESULTS
  Individuals described no or minimal gastrointestinal symptoms during HDT. Gastric emptying remained unchanged relative to baseline data collection (BDC). At day 2 of HDT the H₂ peak of the lactulose test appeared earlier (mean ± standard error for BDC-1, HDT2, HDT5: 198 ± 7, 139 ± 18, 183 ± 10 min; p: 0.040), indicating accelerated small intestinal transit. Furthermore, during HDT, stool was softer and stool mass increased (BDC: 47 ± 6, HDT: 91 ± 12, recovery: 53 ± 8 g/day; p: 0.014), indicating accelerated colonic transit. Exercise interventions had no effect.
  
  
  CONCLUSIONS
  HDT did not induce symptoms of SMS. During HDT, gastric emptying remained unchanged, but small and large intestinal transit was accelerated.
authors.affiliation: Division of Gastroenterology and Hepatology, University Hospital Zurich and Zurich University, Rämistr. 100, 8091, Zurich, Switzerland.
authors.forename: Meher
authors.initials: M
authors.lastname: Prakash
authors.affiliation: Division of Gastroenterology and Hepatology, University Hospital Zurich and Zurich University, Rämistr. 100, 8091, Zurich, Switzerland.
authors.forename: Ron
authors.initials: R
authors.lastname: Fried
authors.affiliation: Division of Hepatology, Department of Medicine II, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Götze
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.
authors.forename: Francisca
authors.initials: F
authors.lastname: May
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.
authors.forename: Petra
authors.initials: P
authors.lastname: Frings-Meuthen
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.
authors.forename: Edwin
authors.initials: E
authors.lastname: Mulder
authors.affiliation: Swiss Center of Excellence for Agricultural Research (Agroscope), Bern, Switzerland.
authors.forename: Judit
authors.initials: J
authors.lastname: Valentini
authors.affiliation: Division of Gastroenterology and Hepatology, University Hospital Zurich and Zurich University, Rämistr. 100, 8091, Zurich, Switzerland.|Zurich Integrative Human Physiology Group, University of Zurich, Zurich, Switzerland.
authors.forename: Mark
authors.initials: M
authors.lastname: Fox
authors.affiliation: Division of Gastroenterology and Hepatology, University Hospital Zurich and Zurich University, Rämistr. 100, 8091, Zurich, Switzerland.|Zurich Integrative Human Physiology Group, University of Zurich, Zurich, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Fried
authors.affiliation: Division of Gastroenterology and Hepatology, University Hospital Zurich and Zurich University, Rämistr. 100, 8091, Zurich, Switzerland.|Zurich Integrative Human Physiology Group, University of Zurich, Zurich, Switzerland.
authors.forename: Werner
authors.initials: W
authors.lastname: Schwizer
authors.affiliation: Division of Gastroenterology and Hepatology, University Hospital Zurich and Zurich University, Rämistr. 100, 8091, Zurich, Switzerland. benjamin.misselwitz@usz.ch.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Misselwitz
mesh_terms: D000328:Adult; D001510:Bed Rest; D018592:Cross-Over Studies; D005260:Female; D005746:Gastric Emptying / Q000502:physiology*; D005772:Gastrointestinal Transit / Q000502:physiology*; D018475:Head-Down Tilt; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D018489:Space Motion Sickness / Q000503:physiopathology*; D018474:Weightlessness Simulation / Q000379:methods*; D055815:Young Adult
keywords: Breath test; Gastric emptying; Head-down tilt; Microgravity simulation; Space motion sickness