High blood pressure is a clinical condition characterised by an excessive increase in peripheral resistance, and determined by functional and structural alterations in resistance vessels, associated with a decrease in the distensibility of large arterial vessels.

The exaggerated increase in peripheral resistance in hypertension does engender alterations in microcirculatory functions, which in their turn contribute to perpetuate high blood pressure values.

The recovery of micro-vascular functions via treatment does normalise pressure values.In high blood pressure several vascular districts are increaisngly involved, such as cerebral, renal, retinal ones, large arterial vessels and microcirculation, comprising small arteries, arterioles, capillaries and veinlets.

Physiology of microvasculature.

The evaluation of micro-circulation is possible via

video-microangioscopy, laser-doppler, the analysis of transcutaneous pressure for O2 and CO2 and blood viscosity.

Patho-physiology of microvasculature

Video microangioscopy dos enable to dynamically study "in vivo" the capillary system, by possibly highlighting functional and structural anomalies, which in hypertension produce hypertension micro-angiopathy, which may be classified in three stages.

Laser-doppler velocimetry enables to evaluate blood stream velocity through the capillary system and spontaneous

vaso-motoricity of arterioles, and comprising phases of vasoconstriction and vasodilatation.

The study of micro-circulation is completed by haemorheological evaluation taking into consideration modes and possible alterations of blood stream, linked to blood viscosity, red blood cell deformability and vessel size.

First phase: restricted capillaries, with motion instability

Second phase: arteriole overtone, capillary stasis, kinking

Third phase: stringy arteries, capillary rarefaction, aneurysms and "sludge" phenomena.

From the haemorheological perspective often an increase in blood viscosity and decrease in erythrocyte filtration occur.

Conclusion

The evaluation of the microcircualtion and the hemoreology is the science which studies blood flow inside the micro-circulatory system.

Laboratory methods used to study the hemoreologic microcirculatory mainly involve measurement of flow velocity with capillaroscopy laser-doppler and evaluation of erytrocyte deformability. These methods allow the study and definition of hemorheological and microcirculatory consequences of hypertension.These methods help to identify the microangiopathy hypertensive and predictable, precocious factors and offer the possibility to monitor the progressive or occasional regressive phases of disease after therapy.