谢谢老狼解释，学习了。与心脏等高测血压，是因为静水（血）压力（或称为液压）的关系。每2.5厘米的高差产生1 到 2 毫米汞柱的区

详情参考

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3104931/

“Because of the effects of hydrostatic pressure, the position of the arm when the blood pressure is measured can also have a major impact on the pressure observed. The magnitude of this effect is 1 to 2 mm Hg for every 2.5 cm above or below the level of the heart. If the cuff and the upper arm are maintained above the level of the right atrium, the readings obtained will be too low.Likewise, if they are below the level of the heart, the readings will be too high.”