Physiological principles of laser Doppler flowmetry and white light spectrometry - O2 to See (O2S) for measuring microcirculation.

DOI:10.36210/BerMedJ/epub802203

Abstract

Vascular segment the area of material exchange between the terminal stroma and the tissues. The terminal stroma includes arterioles, capillaries, venules and the terminal lymphatic vessels. The contractile properties of the capillary territory are largely seen in the presence of smooth muscle cells in the media layer of the vessels, which accounts for 33.5% in the arteries and 60.5% in the small veins. With a high proportion of smooth muscle cells (SMC) and a low proportion of collagen, the low pressure load of the capillary vascular network is expressed and due to the decrease in pressure gradients in the capillary area, the proportion of elastin is low.

Regional oxygen saturation is considered a measure of oxygen depletion in the local tissue and thus of the functional state of the local microcirculation and a marker of local tissue hypoxia. A change in rSO₂ may reflect a dysbalance between oxygen supply and consumption and correlates with cellular oxygen metabolism. Relative blood flow determines volume flow and can provide information about the presence of ischaemia or hyperaemia. In addition, the velocity distribution of the erythrocytes can give an indication of a possible cause of an undersupply of the microcirculation. The relative blood flow velocity indicates the average velocity of the erythrocytes in the microcirculation.  The relative haemoglobin amount indicates the amount of haemoglobin in the measured tissue. It can give information about the filling state of the vessels of the microcirculation, which is dependent on capillary density, capillary recruitment and venous filling. The haemoglobin level is the indicator of venous status and oxygen extraction.