Ultrasonic measurement of flow-mediated vasodilatation: clinical results

With respect to brachial artery flow-mediated vasodilatation (FMD), which is frequently used as a measure of endothelial function, it is necessary to observe diameter changes of small arterial vessels non-invasively for several minutes at a high resolution. We developed a system composed of a Siemens Omnia ultrasound system with a VF13-5 transducer (9 MHz center frequency) and a personal computer, that is capable of calculating vessel diameter changes with an accuracy below the wavelength of the ultrasound system in real-time at a frame rate of 27 Hz. We could verify experimentally that the accuracy of the measurements is below 1 μm. Results from clinical measurements of carotid and brachial arteries show that arterial pulsations below 0.1 mm can be visualized reliably over several minutes. Furthermore, we can present examples from clinical FMD measurements, where the pulsation of the brachial artery is visible as well as an increase in arterial diameter after the deflation of a forearm cuff, which was used to produce an ischaemia for 5 minutes.