Transcapillary fluid transfer and plasma volume changes in response to quiet standing and LBNP.

Quiet standing is one of the conditions of daily life. Still, it may lead to acute circulatory failure even in normal man, a phenomenon ascribed mainly to the early large pooling of blood and secondary decrease in central blood volume. Reduction of plasma volume (PV) by filtration in dependent regions apparently contributes, but there is no indication that this process is of major importance during short periods of standing still in normal life. Hence, studies have indicated that the plasma fluid loss occurs at relatively slow rate due to the presence of protective mechanisms that prevent rapid fluid loss.