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njit-etd2003-081 - New Jersey Institute of Technology

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Figure 5.7 (e) WT (Haar wavelet) <strong>of</strong> a signal with 3 sine waves at 0.3, 0.1 and 0.5 Hz.<br />

5.2.2 Time-frequency Analysis <strong>of</strong> Heart Rate Variability<br />

The first goal <strong>of</strong> this research work is dedicated to the use <strong>of</strong> time-frequency analysis <strong>of</strong><br />

heart rate variability as a new and innovative approach to investigate the physical<br />

attributes <strong>of</strong> both normal and COPD subjects.<br />

Although time-frequency analysis has been extensively studied and universally<br />

used, there is not much experience in its application to very low frequency ranges (less<br />

than 2 Hz). In the previous section, each distribution used: the short time Fourier<br />

transform (STFT), the smoothed pseudo Wigner-Ville (SPWV), The Choi-Williams<br />

(CW), and the Born-Jordan-Cohen (RID), has unique characteristics which affect the<br />

amount <strong>of</strong> smoothing and the generation <strong>of</strong> crossterm interference as applied to sinusoid<br />

test signals in the HRV frequency range. The STFT and Cohen's class distributions<br />

(SPWD, CWD and BJCD) provided adequate time frequency representations for low<br />

frequency signals <strong>of</strong> HRV analysis. However, with the wavelet transform applied to

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