title: Head-out immersion in the non-human primate: a model of cardiovascular deconditioning during microgravity.
abstract: BACKGROUND
  Orthostatic intolerance is a common complication associated with spaceflight. It has been speculated that this is due to changes in blood volume and alterations in cardiovascular reflexes. The objective of the current study was to develop a model that would allow us to study the cardiovascular system and the regulation of blood volume during short-term microgravity exposure in the primate with the intent of eventually being able to elucidate those factors responsible for the orthostatic intolerance.
  
  
  OBJECTIVE
  Head-out water immersion in the conscious non-human primate simulates the cardiovascular and volume regulatory responses observed in astronauts during exposure to microgravity.
  
  
  METHODS
  Four monkeys were chronically instrumented for measuring BP and heart rate and then conditioned to the primate restraint chair. They were then subjected to 72 h of head-out water immersion (two immersions in three monkeys and one immersion in the fourth) in order to simulate the cardiovascular and renal effects of the microgravity environment.
  
  
  RESULTS
  During the immersion, there was an increase in arterial BP (ABP) and central venous pressure (CVP) and a reflex decrease in heart rate (HR). Urine flow (UV) increased and water intake decreased, producing a negative water balance. This was not associated with an alteration in food intake. CVP and UV decreased following de-immersion. There was also resetting of the arterial baroreflex control of HR. Significant tachycardia occurred after the immersion that was associated with a decrease in ABP.
  
  
  CONCLUSIONS
  These results are similar to those observed in astronauts during and after spaceflight, suggesting that head-out water immersion of the non-human primate provides a good model for studying cardiovascular and renal adaptations to spaceflight.
authors.affiliation: Department of Physiology and Biophysics, University of Nebraska College of Medicine, Omaha 68198-4575, USA.
authors.forename: K G
authors.initials: KG
authors.lastname: Cornish
authors.forename: K
authors.initials: K
authors.lastname: Hughes
authors.forename: A
authors.initials: A
authors.lastname: Dreessen
authors.forename: M
authors.initials: M
authors.lastname: Olguin
mesh_terms: D000818:Animals; D017704:Baroreflex; D001794:Blood Pressure; D001810:Blood Volume; D018493:Cardiovascular Deconditioning / Q000502:physiology*; D004195:Disease Models, Animal; D005260:Female; D018495:Fluid Shifts; D006339:Heart Rate; D006706:Homeostasis; D007024:Hypotension, Orthostatic / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology*; D007101:Immersion / Q000009:adverse effects*; D008253:Macaca mulatta; D008297:Male; D015203:Reproducibility of Results; D013026:Space Flight; D014563:Urodynamics; D018474:Weightlessness Simulation / Q000009:adverse effects*