Measurement of the arterial wall elasticity using the velocity of flexural waves in retinal blood vessels

Abstract

Arterial stiffness (typically a Young modulus of 100 kPa) is known to be an indicator of the cardiovascular health of a patient. It is commonly used in clinics to prevent and anticipate cardiovascular diseases. The existing methods allowing to measure the arterial wall elasticity measuring the velocity of the natural pulse wave lack of accuracy. We propose here a method consisting in using laser Doppler holography experiments to estimate the arterial wall elasticity. Laser Doppler holography experiments are performed on patients and noise correlation algorithms are used on these data to measure the wave velocity. We measured separately the wavelength and the frequency of elastic waves, allowing to calculate their velocity. Due to the temporal resolution of the raw data and to the way the data are processed, the waves we detected are not the classical axisymmetric pulse wave. The physics of guided waves indicates that both antisymmetric (called A0) and symmetric (called S0) waves can propagate in tubes, and in this case only antisymmetric flexural waves are detected. They are both sensitive to the arterial wall elasticity, and at low frequencies, flexural (or antisymmetric) waves are much slower than the axisymmetric pulse wave, about 3 mm/s, allowing to increase greatly the measurement accuracy. When knowing the diameter of the blood vessel, for the first time it is possible to retrieve the arterial wall elasticity thanks to the antisymmetric wave velocity measurement.