New Methods to Study the Microcirculation

Essential hypertension is associated with structural alterations in the microvessels; in particular, an increase in the media thickness to internal lumen ratio of small resistance arteries (MLR) and a reduction in capillary density have been observed. The evaluation of the morphological characteristics of small resistance arteries in humans is challenging. The gold-standard method is generally considered to be the measurement by wire or pressure micromyography of MLR of subcutaneous small vessels obtained by local biopsies. However, noninvasive techniques for the evaluation of retinal arterioles were recently proposed; in particular, 2 approaches, scanning laser Doppler flowmetry (SLDF) and adaptive optics (AO), seem to provide useful information. Both of them provide an estimation of the wall to lumen ratio (WLR) of retinal arterioles. Moreover, a noninvasive measurement of basal and total capillary density may be obtained by videomicroscopy/capillaroscopy. It has been recently demonstrated that AO has a substantial advantage over SLDF in terms of evaluation of microvascular morphology, since WLR measured with AO is more closely correlated with the M/L of subcutaneous small arteries. The possibility to noninvasively assess in a reliable way, microvascular morphology in a clinical setting may represent a major advancement, since micromyography has substantial limitations in its application due to the local invasiveness of the procedure.