Biomechanical Microsystems by Vytautas Ostasevicius Giedrius Janusas Arvydas Palevicius Rimvydas Gaidys & Vytautas Jurenas

Author:Vytautas Ostasevicius, Giedrius Janusas, Arvydas Palevicius, Rimvydas Gaidys & Vytautas Jurenas
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

(4.1)

where F(ω) is a Fourier transform, BP(t) is blood pressure function in time domain, j is an imaginary number, and ω is angular frequency. This approach offers a very convenient set of tools allowing analysis of the signal for specific frequencies—harmonics, by using only two numbers: amplitude of the harmonic and its phase. If the system is assumed to be linear and periodic, the Fourier analysis can provide the complete description of the system dynamics. The fundamental period is often assumed to be the heart cycle or the multiplication of it. Many researches use the Fourier methodology, such as spectrum analysis, to express the blood signal pressure features [1, 2]. Typical blood pressure spectral content is shown in Fig. 4.2. In fact, blood pressure is not a pure periodic signal. The long-term extensive studies on Heart Rate Variability (HRV) showed the short- and long-term fluctuations in the HR fundamental frequency. Also, the spectral content of the blood pressure signal undergoes changes due to physiological responses of the cardiovascular system. In addition, many types of artifacts are involved, introducing stochastic or rather chaotic components. The situation is made worse with the technical limitations to the digital signal analysis such as a finite period of collecting data, and a finite period of sampling (sampling frequency) data or quantization effect. In a real experiment, the “ideal” continuous Eq. 4.2 has to be supplemented by a discrete one [1]:

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