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6 Applications and Methods in Biosignal Processing

Fig. 6.17: Einthoven-Triangle with heart vector

P and lead vectors CI, CII, CIII und CL, CR, CF.

are referred to it (see Figure 6.17):

VI = ΦL −ΦR = CI ⋅P

VII = ΦF −ΦR = CII ⋅P

VIII = ΦF −ΦL = CIII ⋅P .

(6.5)

In order to be able to make statements about the individual unipolar voltages at the

recording points in the case of voltage differences according to Einthoven, Wilson and

colleagues [83, 85] suggested creating a central recording point to which all voltages

can refer, and used the mean value of all recorded voltages as the central recording

point, cf. Figure 6.18.

The sum of all the currents must vanish at this point because the measuring lead is

highly resistive and the current can thus be neglected. The following therefore applies:

IL + IR + IF = 0 .

(6.6)

The voltages across the recording resistors of R = 5 kΩthen form the new unipolar

voltages of the Einthoven-triangle.

VL = R ⋅IL ,

VR = R ⋅IR

and

VF = R ⋅IF .

(6.7)

Since the values of the recording resistors R are all equal, it follows:

VL + VR + VF = 0 .

(6.8)

These new voltages can be obtained from the bipolar voltages VI, VII and VIII by ap-

plying Kirchhoff’s mesh rule. One obtains e.g. according to Figure 6.18, subframe b