[Effect of 3-day immersion on calf blood flow during physical loading test]

The effect of simulated gravitational unloading (dry immersion) on blood flow in the calf during upright locomotion was studied. Six subjects performed graded exercise before and after 3-day immersion. Arterial inflow to the calf was evaluated during abrupt cessation of treadmill walking/running on the phase of changing the leg with the plethysmographic technique of determining the haemodynamic effect of muscle pump. Before immersion, testing increased the calf blood flow on transition from walking to running and stayed at plateau or decreased with further speed rise. After immersion, the calf blood flow tended to decrease during running. At maximal running speed and heart rate > 185 beats/min, calf blood flow was significantly lower post than prior to immersion. We believe that immersion enhances the competitive interaction of local operational mechanisms of hyperemia and central vasoconstrictive influences directed at maintaining "the circulatory homeostasis".