Taylor-Fourier Analysis of Blood Pressure Oscillometric Waveforms

Blood pressure oscillometric waveforms behave as amplitude modulated nonlinear signals with frequency fluctuations. Their oscillating nature can be better analyzed by the digital Taylor-Fourier transform (DTFT), recently proposed for phasor estimation in oscillating power systems. By being based on a relaxed signal model that includes Taylor components greater than zero, the DTFT is able to estimate not only the oscillation itself, as does the digital Fourier transform (DFT), but also its derivatives included in the model. In this paper, an oscillometric waveform is analyzed with the DTFT and its zeroth and first oscillating harmonics are illustrated. The results show that the breathing activity can be separated from the cardiac one through the zeroth and first components, respectively. In addition, the zero crossings of the amplitude derivatives determine the critical values of the oscillation envelope and its inflection points, so useful to determine the systolic and diastolic blood pressures. On the other hand, phase derivatives provide the fundamental frequency fluctuation and its derivative, new parameters that could improve the systolic and diastolic blood pressure assignment. The DTFT decomposition is very accurate since the signal reconstruction error is extremely small.