Badeer H S, Rietz R R
Cardiology. 1979;64(4):197-207. doi: 10.1159/000170616.
Erroneous concepts about vascular hemodynamics are widespread, notably as regards the effect of gravity on blood flow. Vascular pressure at any point is equal to the sum of two pressures of entirely different origins: (1) pressure caused by the pumping action of the heart ('cardiodynamic' pressure which is vital for circulation) and (2) pressure due to gravity acting on the blood ('gravitational' or hydrostatic pressure which plays no direct role in blood flow). Gravity neither helps nor hinders circulation because of the U tube or siphon principle. The gravitational energy of the column of blood in arteries is balanced exactly by the gravitational energy of the column in veins and vice versa. Thus, contrary to common belief, gravity does not hinder blood flow to the head in the upright position, nor does it hinder venous return from the dependent parts of the body. For this reason, in Poiseuille's equation, perfusion pressure should exclude gravitational pressure. Postural effects on circulation result from the distension vessels (particulary veins) subsequent to changes in gravitational pressure of blood.
关于血管血流动力学的错误概念广泛存在，尤其是在重力对血流的影响方面。任何一点的血管压力等于两种完全不同来源压力的总和：（1）由心脏泵血作用引起的压力（“心脏动力”压力，对循环至关重要）和（2）重力作用于血液产生的压力（“重力”或静水压力，在血流中不直接起作用）。由于U形管或虹吸管原理，重力既不促进也不阻碍循环。动脉中血柱的重力能量与静脉中血柱的重力能量恰好平衡，反之亦然。因此，与普遍看法相反，重力在直立位时并不阻碍血液流向头部，也不阻碍身体下垂部位的静脉回流。出于这个原因，在泊肃叶方程中，灌注压力应排除重力压力。体位对循环的影响源于血液重力压力变化后血管（特别是静脉）的扩张。
