title: Cardiovascular models of simulated moon and mars gravities: head-up tilt vs. lower body unweighting.
abstract: BACKGROUND
  In this study we compare two models [head-up tilt (HUT) vs. body unweighting using lower body positive pressure (LBPP)] to simulate Moon, Mars, and Earth gravities. A literature search did not reveal any comparisons of this type performed previously. We hypothesized that segmental fluid volume shifts (thorax, abdomen, upper and lower leg), cardiac output, and blood pressure (BP), heart rate (HR), and total peripheral resistance to standing would be similar in the LBPP and HUT models.
  
  
  METHODS
  There were 21 subjects who were studied while supine (simulation of spaceflight) and standing at 100% (Earth), 40% (Mars), and 20% (Moon) bodyweight produced by LBPP in Alter-G and while supine and tilted at 80 degrees, 20 degrees, and 10 degrees HUT (analogues of Earth, Mars, and Moon gravities, respectively).
  
  
  RESULTS
  Compared to supine, fluid shifts from the chest to the abdomen, increases in HR, and decreases in stroke volume were greater at 100% bodyweight than at reduced weights in response to both LBPP and HUT. Differences between the two models were found for systolic BP, diastolic BP, mean arterial BP, stroke volume, total peripheral resistance, and thorax and abdomen impedances, while HR, cardiac output, and upper and lower leg impedances were similar.
  
  
  CONCLUSIONS
  Bodyweight unloading via both LBPP and HUT resulted in cardiovascular changes similar to those anticipated in actual reduced gravity environments. The LBPP model/Alter-G has the advantage of providing an environment that allows dynamic activity at reduced bodyweight; however, the significant increase in blood pressures in the Alter-GC may favor the HUT model.
authors.forename: Vladimir I
authors.initials: VI
authors.lastname: Kostas
authors.forename: Michael B
authors.initials: MB
authors.lastname: Stenger
authors.forename: Charles F
authors.initials: CF
authors.lastname: Knapp
authors.forename: Robert
authors.initials: R
authors.lastname: Shapiro
authors.forename: Siqi
authors.initials: S
authors.lastname: Wang
authors.forename: André
authors.initials: A
authors.lastname: Diedrich
authors.forename: Joyce M
authors.initials: JM
authors.lastname: Evans
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D005260:Female; D018470:Gravity, Altered; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D018535:Mars; D008955:Models, Cardiovascular; D016081:Moon; D054971:Orthostatic Intolerance; D011187:Posture / Q000502:physiology; D013026:Space Flight; D018561:Space Simulation / Q000379:methods*; D013318:Stroke Volume / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology; D055815:Young Adult