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心電圖的原理

心電圖的原理. The electric field surrounding three different point charges. Electric field of Point charge “Q” at P. Electric Dipoles (Electric Polarization). Polar molecules ( H 2 O, CO, HCl ). Permanent dipole moment. Induced dipole moment. Nonpolar atom ( molecule ). (A). (B).

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心電圖的原理

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  1. 心電圖的原理

  2. The electric field surrounding three different point charges

  3. Electric field of Point charge “Q” at P

  4. Electric Dipoles (Electric Polarization) Polar molecules (H2O, CO, HCl ) Permanent dipole moment

  5. Induced dipole moment Nonpolar atom ( molecule ) (A) (B) Figure 1: A neutral nonpolar species's electron cloud is distorted by (A) an Ion and (B) a polar molecule to induce a dipole moment.

  6. Electric field of a dipole moment? • Response of a dipole moment in an External Electric field?

  7. 22.5 The Electric Field due to an Electric Dipole:

  8. 22.5 The Electric Field due to an Electric Dipole: From symmetry, the electric field E at point P—and also the fields E+ and E- due to the separate charges that make up the dipole—must lie along the dipole axis, which we have taken to be a z axis. From the superposition principle for electric fields, the magnitude E of the electric field at P is The product qd, which involves the two intrinsic properties q and d of the dipole, is the magnitude p of a vector quantity known as theelectric dipole moment of the dipole.

  9. 22.9: A Dipole in an Electric Field When an electric dipole is placed in a region where there is an external electric field, E, electrostatic forces act on the charged ends of the dipole. If the electric field is uniform, those forces act in opposite directions and with the same magnitude F =qE. Although the net force on the dipole from the field is zero,and the center of mass of the dipole does not move, the forces on the charged ends do produce a net torquet on the dipole about its center of mass. The net torque is:

  10. 22.9: A Dipole in an Electric Field: Potential Energy Potential energy can be associated with the orientationof an electric dipole in an electric field. The dipole has its least potential energy when it is in its equilibrium orientation, which is when its moment p is lined up with the field E. The expression for the potential energy of an electric dipole in an external electric field is simplest if we choose the potential energy to be zero when the angle q (Fig.22-19) is 90°. The potential energy U of the dipole at any other value of q can be found by calculating the work W done by the field on the dipole when the dipole is rotated to that value of q from 90°.

  11. A Dipole in an Electric Field: Potential Energy

  12. 心電圖之電偶極（Electric dipole）模型與心向量

  13. Electric potential (V) of a dipole

  14. Electric potential (V) of a dipole

  15. 心向量 • 心臟電極化的大小及方向 • 瞬時向量 • 特別的瞬間，心臟電極化(電偶極)的總合淨力 • 平均向量 • 心臟週期內某一部份(如QRS波)的所有向量變化用一個向量來代表它的大小、方向及極性

  16. 六軸參考座標 • 國際公定的心電圖為12導程 • 6項胸前導程和6項肢導程 • 包括:Ⅰ、Ⅱ 、 Ⅲ、aVR、aVL、aVF、V1、V2、V3、V4、V5、V6 • 把標準雙極誘導和單極誘導合在一起，成為一個六軸的參考座標系統

  17. 十二導程 • Ⅰ、Ⅱ 、 Ⅲ、aVR、aVL、aVF、V1、V2、V3、V4、V5、V6

  18. Einthoven 三角形 • Einthoven三角形：Ⅰ、Ⅱ 、 Ⅲ • 瞬間向量是雙極的電化電位作用而來 • 心臟的電化活動中心位於胸部的解剖中心位置

  19. 參考系統 六極誘導

  20. 心向量迴圈 • 將各時刻的心向量端點依時間先後連接起來 • 可以得到一個心周期的心向量迴圈 • 分P迴圈、QRS迴圈、T迴圈

  21. P 迴圈 • 主因心房去極化產生 • 在出發點處成一小圈 • 最大部朝下方呈細長狀

  22. QRS 迴圈 心室去極化產生，最大 在額平面可為順時針、逆時針、8字型 順時針最多 矢狀平面和水平面為逆時針 最大QRS向量指向左下後方，因為主要電化活動是由左心室心肌所產生 大約在0.04秒左右達到最大

  23. T迴圈 • 心室去極化所產生 • 長橢圓形OR線狀 • 朝左前下方 • QRS迴圈>>T迴圈>P迴圈

  24. 生理訊號 • 心臟本身的電位變化會經過心臟周圍的導電組織與體液反映到身體表面 • 去極化的速度不同 形成一股電流，而平均電流即從心臟基部傳至心尖 電訊號

  25. 平均電流傳遞方向

  26. 導論 • 心電圖訊號屬於低頻範圍(0.05~100HZ)，且振幅微小僅1~10mV，因此在心電圖訊號的擷取上便需要訊號放大器與濾波裝置 • 導程(Lead) :臨床上可分為12導程 • 分類 1. 標準雙極肢誘導 2. 單極肢誘導 3. 單極胸誘導

  27. 標準雙極肢誘導 • 雙極誘導代表我們選擇二個地方的電位差 • 艾因多芬 電極接於左手臂(LA)、右手臂(RA)、左腳(LL)，右腳電極是當做地線來使用 • Lead I = 左手電位與右手電位之差=LA – RA Lead II = 左腳電位與右手電位之差=LL – RA Lead III = 左腳電位與左手電位之差=LL – LA Q:為何以右腳為參考接地 ?

  28. <克希可夫定律> 由一個封閉的迴路其電壓的總和必等於零來看 LL – RA = (LA–RA) + (LL–LA) LeadⅡ＝ LeadⅠ + LeadⅢ

  29. LeadⅡ＝ LeadⅠ + LeadⅢ

  30. 單極肢誘導(unipolar limb leads) • 起源：兩個特定點的電位差？ 某一點的真實電位變化？ • 單極導程：電極所在的部位，所測得的真實電位變化 • 分類： • 未加壓的單極肢誘導（淘汰） • 加壓的單極肢誘導

  31. 加壓的單極肢誘導 • 可將電壓振幅提高50%左右（比原來大3/2） • aVR、aVL、aVFa代表加壓（augmented） aVR：以右手為探測極(exploring elelctrode)，其餘兩個肢導（左手，左腳）連線為中心電極 aVL：以左手為探測極，其餘兩個肢導（右手，左腳）連線為中心電極。 aVF：以左腳為探測極，其餘兩個肢導（左手，右手）連線為中心電極。

  32. 放大50%？ 計算 • 以aVR為例 • aVR表示右手電位（RA）和「左手及左腳平均電位」的電位差 • aVR=RA-(LA+LL)/2 • 柯西荷夫RA+LA+LL=0 （ LA+LL= -RA） • aVR=RA-(-RA/2)=3RA/2

  33. 單極胸誘導(unipolar chest leads) 測量方法：將右手電極、左手電極、左腳電極連接一起當作地端，再將探測端電極放在胸部特定的位置，即可測之 單極胸導程以V1-V6代表。依病情之須要,可追加V3R， V4R或V7等誘導。（以V為記號，其後面的數字代表特定的位置）

  34. V1:胸骨右緣第四肋間處 • V2:胸骨左緣第四肋間處 • V3:V2及V4的中點 • V4:左鎖骨中線上，與V5，V6在同一水平面 • V5:腋前線上 • V6:腋中線上 • V1-V2表示右心室電位 • V3-V4為中隔(septum) • V5-V6表示左心室之電位

  35. 單極胸誘導之波形

  36. P-QRS-T波形之物理意義

  37. 心電圖是一個電壓(伏特)計

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