6.3 Signals of the Cardiovascular System

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261

Fig. 6.32: Instantaneous heart rate (top) with associated histogram (bottom).

Fig. 6.33: Poincaré-diagram in atrial fibrillation by seizure (left) and after seizure (right) [own meas-

urement of atrial fibrillation by co-author K.-H. Witte ].

The correlation methods examine the similarity between successive values of two

functions. In the case of the heart rate, it is the similarity between different sections

of the same function (autocorrelation). For this, it is usually assumed that this is not

time-dependent, which is often not true in practice. The calculation of the autocorrel-

ation for heart rate is done according to

RHF HF(n, m) = E [HFn ⋅HFn+m] = lim

N→∞

1

N

N

∑

n=1

HFn ⋅HFn+m .

(6.27)