Time-frequency Analysis in Biology
Electroencephalograms (EEG) and electrocardiograms (ECG or EKG) are two important ways to record electrical activity in a patient. This example focuses on the ECG interpretation but the method of analysis is equally applicable to EEGs.
Read and downsample some ECG data for normal cardiac rythme and from a patient with partial epilepsy:
Little information can be extracted from direct plots of the ECG data:
Compute the TFRs over 5<t<55 seconds:
Each heartbeat is marked by a high-amplitude (red), short-duration signal component:
The ridge along ν=1.5 is the principal frequency of the heart beat. In both cases, the instantaneous frequency along this ridge is approximately constant. However, the ridge along ν=2.75 is approximately uniform for the normal patient and highly non-uniform in the case of the patient with partial epilepsy. The difference is very pronounced in the time-frequency representation and, consequently, time-frequency analysis can be very useful in the interpretation of ECG/EKG signals.
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