Non-invasive estimate of the mechanical properties of peripheral arteries from ultrasonic and photoplethysmographic measurements

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Abstract
The authors propose a novel method of estimating the nonlinear elastic properties based on the analysis of the arterial diameter against pressure curves derived from ultrasonic and photoplethysmographic measurements. An ultrasonic echo tracking device has been developed that allows continuous recording of the internal diameter of peripheral arteries. It measures the diameter 300 times per second with a resolution of 2.5 mu m. This system is linked to a commercially available light-plethysmograph which continuously records the finger arterial pressure (0.25 kPa accuracy). Because of the finite pulse wave velocity, the separation between the diameter and the pressure measurement sites causes a hysteresis to appear in the recorded diameter-pressure curve. The relationship between pressure and diameter is described by a nonlinear mathematical expression with three parameters, which best fits the recorded data. The dynamic local behaviour of the vessel is fully characterised by these parameters. Compliance, distensibility and pulse wave velocity can then be calculated at each pressure level.