Figure 3
Determination of BF using STFT. The results of frequency analysis and STFT analysis of the same subjects (heart rates are 58, 71, 79 and 93/min) in Fig. 2. (a-1) The power spectra of F-APW × PCG−1, F-APW, PCG and F-APW × PCG of the subject whose mean heart rate is 93/min. The X axis is frequency, while the Y axis is power spectral density (PSD). The breakpoint is in the vicinity of 15.0 Hz of F-APW × PCG−1. (a-2) STFT analysis of F-APW. F-APW is comprised of higher harmonics up to ninth order, the fundamental vibration of which is 1.6 Hz. (a-3) STFT analysis of F-APW × PCG−1. (a-4) A magnified figure of a-3. The Red line in the vicinity of 15 Hz is defined as Boundary Frequency (BF). (a-5) STFT analysis of F-APW × PCG. (a-6) STFT analysis of PCG. (b) The results of frequency analysis and STFT analysis of F-APW × PCG−1 of the other three subjects (heart rates are 58, 71 and 79/min). The arrow heads indicate BF.
