謝謝老狼解釋，學習了。與心髒等高測血壓，是因為靜水（血）壓力（或稱為液壓）的關係。每2.5厘米的高差產生1 到 2 毫米汞柱的區

詳情參考

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.”