Numerical analysis of the pulse wave in a hydro-cuff blood pressure measurement system

For people suffering from hypertension, the procedure of constant monitoring of blood pressure values becomes mandatory. Accurate and timely assessment of their values allows to evaluate the effectiveness of the drugs used, promptly change the tactics of therapy and reduce the risk of critical conditions. Currently, among patients suffering from hypertension, oscillatory tonometers are the most popular. They are easy to use. However, as the practice of their use shows, tonometers have low accuracy. In this regard, the task of increasing their accuracy is very relevant. This article proposes the use of a new hydrocuff technology for forming oscillations. It is distinguished by increased values of oscillation amplitudes up to 10..15 mmHg. This creates the prerequisites for increasing the accuracy of oscillatory tonometers. Oscillatory tonometers are based on determining the amplitudes of pressure fluctuations during decompression and establishing the correspondence of their peak values to the cuff pressure. In practice, this procedure is carried out by removing the trend and highlighting the oscillations. The linear filtering methods used for these procedures introduce significant distortions into their contour, which leads to an increase in the methodical error of oscillatory tonometers. This article solves the problem of reducing the influence of the trend extraction procedure on the distortion of the oscillation contour. For this purpose, an effective iterative numerical algorithm has been developed based on the construction of special splines using expansions in systems of orthogonal polynomials. Its distinctive feature is the use of trend extraction procedures for the lower and upper envelopes. The algorithm is quite simple to implement and can be used for preliminary signal processing in real time. This allows increasing the accuracy of blood pressure assessment in oscillatory tonometers.