MICROCIRCULATION AND RHEOLOGY

Microvessels, especially in the skin and muscles are organized in func tional units. These units are controlled by the adrenergic system and hormones but also have autonomous metabolic and myogenic regulatory sy stems independent of vasomotion. Microcirculatory blood flow is affect ed by special theologic properties: a low arteriolar haematocrit rises to the systemic level in the venules. The flow rate in the venules is low, and together with the raised haematocrit, explains the microvenu lar sensitivity to hyperviscosity. Capillarovenular microangiopathy, r ecently described by standard and fluorescent capillaroscopy, develops during chronic venous insufficiency. The capillary loops appear dilat ed and knotted together with fibrous deposits and pericapillary oedema . Venous hyperpressure is the cause of this microangiopathy. Together these phenomena disrupt normal haemodynamics and physiology of the mic rocirculatory unit: baseline hyperhaemia, lowered vasomotor and vasomo tion reactivity, development of theologic disorders (haemoconcentratio n, hyperfibrinogenaemia, erythrocyte agregation) and decreased fibrino lysis. Modifications in the transcapillary exchange is related to hypo xia and is aggravated by depressed lymphatic drainage. The main conseq uence is oedema. Inflammation, a characteristic of these microangiopat hies could occur when the endothelium is activated by the hypoxia. The classical mediators of inflammation would activate interactions betwe en the different cells: endothelium, granulocytes, monocytes and plate lets. Several pharmacological models have been developed for the analy sis of these data including exploration of the permeability and capill ary resistance and theological analysis. Objective observation of the microangiopathy with capillaroscopy, together with modern haemodynamic al, biological and pharmacological methods are essential for a better understanding of microvascular disorders in chronic venous insufficien cy.