Physiology and pathology of the coronary microcirculation.

The coronary circulation has a protective regulation system which, in extre me haemodynamic conditions, compensates increased myocardial oxygen demand. The coronary reserve, based on this concept defines the capacity of the sy stem to increase flow temporally, and, thereby, myocardial oxygen supply. T he introduction of new methods of investigating the coronary microcirculati on has enabled the study of this phenomenon in several cardiovascular patho logies. Two types of investigation are used currently for studying the coronary mic rocirculation : 1) invasive methods, especially the recently developed intr acoronary Doppler and pressure guide, 2) non-invasive methods, and, in part icular, contrast echocardiography, positon emission tomography and magnetic nuclear resonance. These investigations allow measurement of the coronary reserve or the assessment of the myocardial consequences of abnormalities o f the microcirculation. Some workers use these methods to investigate pathological coronary microci rculation in different cardiomyopathies, in the presence of different cardi ovascular risk factors (hypertension, diabetes, smoking, hypercholesterolae mia) and after cardiac transplantation.