ONE-MINUTE WAVE IN BODY-FLUID VOLUME CHANGE ENHANCED BY POSTURAL SWAYDURING UPRIGHT STANDING

To analyze how the 1-min oscillation in postural sway and 1-min wave i n body fluid volume change contribute to human circulatory homeostasis , several levels of body circumference, foot pressure center, electrom yograms, and volumes of the leg, abdomen, and thorax were measured dur ing upright standing for 40 min in 20 healthy young men. Spectral anal yses of these parameters revealed that a 1-min rhythm is found in all parameters and that the 1-min wave in body fluid volume changes in the lower leg, which occur in fluid pooling caused by gravity, propagate upward. Muscle pumping in the lower leg triggered by the postural sway was found to increase the power of this 1-min wave. A quantitative an alysis of body circumferences disclosed that the 1-min wave in body fl uid volume change compensates for gravitational downward fluid shift, with the volume of 6.3 +/- 5.0 ml/cycle at the heart level. We conclud ed that a coupling mechanism between the 1-min oscillation in postural sway and the upward propagation of 1-min wave in body fluid volume ch ange contributes to maintain systemic blood pressure during upright st anding in humans.