title: Leg venous compliance in orthostatic intolerance before and after 14-day head-down bed rest.
abstract: To test the hypothesis that increased leg venous compliance (LVC) is one of the contributory factors to orthostatic intolerance (OI) after simulated microgravity, 28 healthy young males were exposed to a 14-day head-down bed rest, and LVC was measured by venous occlusion plethysmography. Orthostatic tolerance was evaluated by a 60 degree head-up tilt (HUT) for 15 min. Sixteen subjects suffered from OI after the bed rest. They were then divided into orthostatic tolerance (non-fainters, n=12) and intolerance (fainters, n=16) groups. We found that fainters had significantly larger LVC before bed rest (0.055 +/- 0.003 vs. 0.065 +/- 0.002 ml 100 ml-1 mm Hg-1, non-fainter vs. fainter; P < 0.05). After bed rest, LVC markedly increased in both groups. In all the subjects calf circumference was reduced on average by 4.7% and the percent change in LVC was negatively correlated with the percent change in calf circumference when all subjects' data were combined after bed rest (r = -0.42, P < 0.05). Our results did not support the hypothesis that increased LVC is the contributory factor to OI after a 14-day bed rest; however, the mechanisms behind the large LVC in the fainters before bed rest are unclear, and the initial LVC might be a predictive indicator for OI after microgravity exposure.
authors.affiliation: Department of Autonomic Neuroscience, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan.
authors.forename: Q
authors.initials: Q
authors.lastname: Fu
authors.forename: S
authors.initials: S
authors.lastname: Iwase
authors.forename: A
authors.initials: A
authors.lastname: Kamiya
authors.forename: D
authors.initials: D
authors.lastname: Michikami
authors.forename: Y
authors.initials: Y
authors.lastname: Niimi
authors.forename: T
authors.initials: T
authors.lastname: Mano
mesh_terms: D000328:Adult; D001510:Bed Rest / Q000009:adverse effects; D003187:Compliance; D004198:Disease Susceptibility; D018475:Head-Down Tilt / Q000009:adverse effects* / Q000502:physiology; D006801:Humans; D007024:Hypotension, Orthostatic / Q000209:etiology* / Q000503:physiopathology; D007866:Leg / Q000033:anatomy & histology / Q000098:blood supply*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology; D011187:Posture / Q000502:physiology; D013575:Syncope / Q000209:etiology / Q000503:physiopathology*; D018474:Weightlessness Simulation