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Fig. 4 | BioMedical Engineering OnLine

Fig. 4

From: A new approach for analysis of heart rate variability and QT variability in long-term ECG recording

Fig. 4

The ConceFT results of the first case. Top: the time-varying power spectrum (tvPS) of different time series related to the RRI; bottom: the tvPS of different time series related to the inverse of the QTc. The tvPS of the RRI is complicated. For Rhour,0.99, Rhour,0.5 and Rhour,0.01, we could no visualize any dominant curve/line in their associated tvPS’s. However, a dominant blurred spectrum before day 6 ranging from 2 Hz to 4 Hz (indicated by the blue dashed arrow) indicates a roughly daily oscillation, but the oscillation is irregularly. For the QTc time series, the dark curve around 1 Hz after day 4 (indicated by the red arrow) in the tvPS of Qhour,0.99 indicates a daily oscillation of the QTc (indicated by the red dashed arrow). In the tvPS of Qhour,0.5, although we could still see a dark curve around 1 Hz after day 4, it is ``weakened’’ (indicated by the blue arrow) between day 4 and day 10, which indicates that although the signal Qhour,0.5 does have an daily oscillatory pattern, it is not as strong as the signal Qhour,0.99. We could not see a daily oscillation in Qhour,0.01, while there seems to have a half day oscillation before day 4 in Qhour,0.01 as we could see a curve at frequency 2 Hz before day 4 (indicated by the green arrow)

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