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Design and implementation of auscultation blood pressure measurement using vascular transit time and physiological parameters

In this study, we have implemented an auscultation sphygmomanometer that can continuously estimate blood pressure via simultaneous measurement of phonocardiogram (PCG) and photoplethysmography (PPG) signals. In PCG, in the process of systole and diastole, the heart will produce "lub" "dub" sounds, called the first (S1) and the second heart sound (S2) respectively. In PPG, according to systole and diastole, the blood volume in the vessel will change, and thus affect the amount of light reflected from the vessel and received in the photosensitive element to detect the heart pulse wave. After using Finite Impulse Response (FIR) and Discrete Wavelet Transform (DWT) to filter out noise from the signal, the device can detect three features, namely S1, S2 and PPG peak, which can be used to calculate Vascular Transit Time (VTT), Ejection Time (ET), and Heart Rate (HR). Multiple regression analysis model for estimating blood pressure is established by using various cardiac parameters such as VTT, ET, HR, and individual's physiological parameters such as gender, age, height, and weight. With this model, auscultation blood pressure measurement can be designed. The results of this study show that for the range of normal blood pressure, the error in systolic blood pressure is 6.67 ± 8.47 mmHg, which is very close to the AAMI standard, 5 ± 8 mmHg. This shows the feasibility of estimating blood pressure using various cardiac and physiological parameters via PCG and PPG measurement.