Extraction of Radial-Artery Strain and Stiffness by Using Noninvasive Ultrasound and a Low-Power Peak Detector
Ultrasound (US) is one of the newest methods used to measure critical arterial parameters, such as blood pressure (BP). Continuous, noninvasive, and accurate measurements are very attractive for the patient and clinicians. US sensors developed up to now extract noninvasively BP by using algorithms based on a constant brachial stiffness, leading to wrong values. Due to the nonlinear viscoelasticity properties of the radial-artery, high variations on the strain and stiffness of this artery during one cardiac cycle are expected. Thus, in this letter, stiffness measurements of a mimicked radial artery are performed by using a custom fabricated US-sensor and the high influence of the stiffness variations in the systolic and diastolic BP values is demonstrated. For this purpose, an accurate 5 MHz piezo transducer, made of lead zirconate titanate, has been used. Thanks to a high accurate and ultra-broadband (1 KHz-30 MHz) modeling of the piezo based on a multiresonant Butterworth-Van-Dyke model, a high-speed and high-gain peak detector could be developed. This US system allows for continuous and noninvasive measurement of the strain and stiffness of the radial artery, which determine the biological age of the vascular tree and deliver a more relevant predictive maker of cardiovascular events and changes than brachial BP.