Lower Limb Blood Pressure Measurement Of Noninvasive Ankle-Brachial Index Based On Blind Signal

Ankle-brachial index is an accurate, simple, noninvasive method that can diagnose peripheral arterial disease. The accurate measurement of the upper and lower limbs systolic blood pressure is the key of ankle-brachial index measurement. Because of there are a number of ankle arteries and some of them can not be blocked completely under higher pressure from the inflate cuff, the obtained ankle pulse wave signal is the superposition of all the arterial pulse wave. Because of the starting point of the pulse wave is unable to be determined, lead to some errors in the measurement of lower limb systolic pressure. In order to measure the systolic blood pressure of lower limbs accurately, we must extract a pulse wave signal of a completely blocked artery.In this paper, through the study of the blood pressure measurement principles of Korotkoff sound auscultation and double-cuff method, the relationship between arterial blood pressure and cuff pressure, the blood flow waveforms, we submit some assumptions of using blind signal processing method to measure lower limb blood pressure. On this basis, based on assumptions we determined blind separation algorithm of lower extremity systolic blood pressure measurement——symmetric EVD algorithm.Using conventional blind source separation algorithm must meet the conditions that the dimension of sensors is greater than or equal to the signals, while the double-cuff method can only obtain one-dimensional signals, this will enable the system state to be underdetermined. So the required pulse wave signals can not be separated. In this paper, we turned an underdetermined problem into an overdetermined problem, an embedding matrix was constructed out of a series of delay vectors from one-dimensional sampled data, and blind signal separation could be performed on the basis of the matrix. It solved the problem of insufficient dimension of sensors. Simulation and experiments showed the application of the method can separate the pulse wave signals of artery which contains information of ankle systolic blood pressure, it increased accuracy of lower limbs systolic blood pressure and provides accurate data for clinical application.