title: Centrifuge training increases presyncopal orthostatic tolerance in ambulatory men.
abstract: BACKGROUND
  Exposure to spaceflight or simulations of microgravity reduce human postflight orthostatic tolerance. Exercise training and volume loading can reduce associated losses of plasma volume and muscle strength, but are not successful in maintaining postflight orthostatic tolerance. A preliminary study (16) indicated that short bouts of artificial gravity (AG) training on a centrifuge could increase orthostatic tolerance in healthy, ambulatory volunteers. We tested the same AG protocol for its tolerance effect on 14 men who underwent a 3-wk exposure to Gz acceleration training on NASA-Ames' (Moffet Field, CA) human-powered centrifuge.
  
  
  METHODS
  Subjects trained supine (head near the center of rotation) and in pairs (one subject rode passively while the other provided power to operate the 1.9-m centrifuge). The acceleration profile consisted of 7 min at 1 Gz before alternating between 1 and 2.5 Gz at 2-min intervals for 28 min. Each subject's presyncopal orthostatic tolerance limit (to a combination of 70 degrees head-up tilt and increasing lower body negative pressure) was determined before and after training.
  
  
  RESULTS
  There were no significant differences between training groups, but presyncopal orthostatic tolerance time was improved 17 +/- 10% (p < 0.05) for the combined groups. Mechanisms associated with increased tolerance included: increased cardiac output (p < 0.04), stroke volume (p < 0.01) and low-frequency spectral power of arterial pressure (p < 0.006), and decreased arterial pressure (p < 0.05) and vascular resistance (p < 0.04). Artificial gravity training in this group of men appears to increase orthostatic tolerance through a combination of decreased vascular resistance and enhanced cardiac function.
authors.affiliation: Center for Biomedical Engineering, University of Kentucky, Lexington, KY 40506-0070, USA. jevans1@uky.edu
authors.forename: Joyce M
authors.initials: JM
authors.lastname: Evans
authors.forename: Michael B
authors.initials: MB
authors.lastname: Stenger
authors.forename: Fritz B
authors.initials: FB
authors.lastname: Moore
authors.forename: Helmut
authors.initials: H
authors.lastname: Hinghofer-Szalkay
authors.forename: Andreas
authors.initials: A
authors.lastname: Rössler
authors.forename: Abhijit R
authors.initials: AR
authors.lastname: Patwardhan
authors.forename: David R
authors.initials: DR
authors.lastname: Brown
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ziegler
authors.forename: Charles F
authors.initials: CF
authors.lastname: Knapp
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output; D002498:Centrifugation; D005081:Exercise Therapy; D006801:Humans; D007024:Hypotension, Orthostatic / Q000209:etiology / Q000517:prevention & control*; D008297:Male; D013026:Space Flight; D018667:Tilt-Table Test; D014655:Vascular Resistance; D014893:Weightlessness / Q000009:adverse effects*