Fig. 2

Physical nature and the effects of hydrostatic pressure according to Rushmer [33]. A The pressure of a column of liquid depends on gravity and the vertical distance from the pressure measurement point to the meniscus of the upper level of the liquid. B The fluid-filled elastic tube is stretched only as long as the internal pressure exceeds the external pressure. These two pressures are exactly equal in the collapsed part of the tube. C In a human in an upright position, both arterial and venous pressure at the level of the feet increase relative to the pressure at the level of the heart measured on the brachial artery by about 80 mmHg. When the hand is raised above the head, the blood pressure at the wrist level is approximately 50 mmHg lower than the blood pressure measured at the shoulder of the lowered arm, and the effective venous pressure above the heart is less than zero. Down arrows—the blood flow coincides with the direction of the hydrostatic pressure. Up arrows—the blood flow is against the direction of the hydrostatic pressure