6.3 Signals of the Cardiovascular System

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Fig. 6.28: Delay of the sliding window

integrator (MA) output signal by 190 ms

in the lower part of the graph compared

to the schematised original ECG in the

upper part; the time interval of the rising

edge of the window integrator corres-

ponds to the width QS of the QRS com-

plex.

In addition to finding the QRS complex in the output signal of the window integ-

rator, they must also be present in the output signal of the original ECG after band-

pass filtering, and they must be able to be found there. There, ECG QRS signal and

noise values are estimated and threshold values are determined in an analogous

way:¹¹

SPKF = 0.125 ⋅PEAKF + 0.875 ⋅SPKF

at signal peak

NPKF = 0.125 ⋅PEAKF + 0.875 ⋅NPKF

at Noise Peak

THRESHOLD_F1 = NPKF + 0.25 ⋅(SPKF −NPKF) ,

THRESHOLD_F2 = 0.5 ⋅THRESHOLD_F1 ,

and if the reverse search was successful:

SPKF = 0.25 ⋅PEAKF + 0.75 ⋅SPKF .

In the case of irregular heartbeats, the first threshold value for both signals is re-

duced:

THRESHOLD I1 ←0.5 ⋅THRESHOLD I1

THRESHOLD F1 ←0.5 ⋅THRESHOLD F1 .

3.

Adjustment of intervals between QRS complexes. (RR intervals) and the pulse

rate limits: The algorithm determines two average values of the intervals between

the QRS complexes (RR intervals).

(a) The first average value RR_AVERAGE1 is the average of the last 8 heartbeats.

(b) The second average RR_AVERAGE2 is the average of the last 8 heartbeats

that have a heart rate between 92 % and 116 % of the previous average rate

11 The variables differ only by a single letter at the end. I indicates the reference to the integrated

output signal and F the reference to the output signal filtered by the bandpass.