Methods of evaluation of microvascular structure: state of the art

Abstract

Cardiovascular diseases represent the leading cause of death in Western Countries. Among them, a key role is played by arterial hypertension, which causes macro-and microvascular alterations. Specifically, hypertension is associated with structural alterations in the microvessels, such as an increased ratio of the tunica media thickness to internal lumen (M/L ratio) in small resistance arteries and a reduction of capillary density. In order to evaluate the small resistance artery structure, the direct measurements of M/L ratio through wire or pressure micromyography has been considered the gold-standard method. Despite the availability of convincing evidence about the prognostic relevance of the M/L ratio, the invasiveness of these methods has limited its implementation in the daily clinical practice. Therefore, non-invasive techniques have been developed to evaluate microvascular morphology, particularly in the retina, since it is perhaps the most accessible microvasculature. Scanner laser Doppler flowmetry (SLDF) and adaptive optics (AO) represent the most promising approaches for the evaluation of morphological characteristics of retinal arterioles, in particular for the measurement of their wall-to-lumen ratio (W/L ratio). The possibility to evaluate microvascular morphology by non-invasive techniques represents a major clinical advancement, with possibly favorable implications in research and in stratification of cardiovascular risk. In this review we will address the different methods to investigate the microcirculation as well as their clinical usefulness.

Retinal vascular geometry detection as a biomarker in diabetes mellitus

“…This difference in remodeling may stem from the differences in function and histological structure among microvessels of various sizes. 59…”

Regional Patterns in Retinal Microvascular Network Geometry in Health and Disease

“…To confirm the caliber of blood vessels that are typically visualized in the two ROIs by the fundus camera, we estimated the average blood vessel diameter in μm. We consider this question important to the original aim of the study because different types of the blood vessels remodel in a different manner, which may be the ultimate cause for different microvascular network patterns in the two ROI in the disease states 6 . To estimate the blood vessel diameters, we used the approach similar to the one applied by Knudtson et al .…”

“…Although the remodelling of retinal microvascular network in pathologic conditions affects retina globally, the differences in the extent and type of remodelling among various segments of retinal microvascular network may exist 4,5 . These differences in remodelling may stem from the distinct function and histological structure among microvessels of various size 6 . It has been reported that the diameters of blood vessels generally decrease as their number of branching generations increases 7,8 .…”

“…The blood vessels belonging to the retinal arterial circulation that can be detected by a fundus camera originate at the optic disc area, branch and all achieve arteriolar status at about 0.5 optic disc diameters from the optic disc margin 1,9 . While small arteries and arterioles contain smooth muscle cells in the vessel wall and are able to control vascular resistance and blood flow, the capillaries contain only one layer of endothelial cells, have diameter around 7 μm, and mainly participate in nutrient exchange 6,10 . In hypertension, one of the hallmark signs of hypertensive remodelling of small resistance arteries is increase of media-to-lumen ratio through the processes known as hypertrophic and eutrophic remodelling.…”

“…In hypertension, one of the hallmark signs of hypertensive remodelling of small resistance arteries is increase of media-to-lumen ratio through the processes known as hypertrophic and eutrophic remodelling. On the other hand, the capillaries, arterioles, and venules of the microvascular network in essential hypertension remodel through rarefaction 6 . Therefore, we could argue that although rarefaction and decreased complexity of microvasculature are global processes affecting retinal microvasculature in hypertension 1 , they may not be present to the same extent in all regions of retina, especially in cases where the average vessel diameter is different.…”