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.
|Number of pages||3|
|Journal||Environmental medicine : annual report of the Research Institute of Environmental Medicine, Nagoya University|
|Publication status||Published - Dec 2000|
ASJC Scopus subject areas
- Environmental Science(all)