Measurement Principle
Measurement Principle |
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The measurement method is a combination of the laser Doppler spectroscopy (formerly used in the OptoFlow) for determination of blood flow and the white light spectroscopy (formerly AbTisSpec and method of EMPHO) for determination of oxygen saturation and hemoglobin amount.
Laser light determines perfusion quantities in tissue. A Doppler shift is caused by the movement of erythrocytes. This Doppler-shift of the detected laser light is analysed by O2C and displayed as the blood flow velocity. The detected laser signal also correlates with the number of moving erythrocytes in tissue. The O2C can register them. The O2C uses this quantity together with blood flow velocity to calculate the blood flow or simply flow.
The O2C uses the white light for the detection of hemoglobin parameter: oxygen saturation SO2 and relative amount of hemoglobin rHb. The oxygen saturation is determined from the colour of blood. The blood changes its colour with the degree of hemoglobin's saturation with oxygen. Arterial blood is light red whereas venous blood shows a light blue colour. The tissue hemoglobin value is determined by the amount of light, absorbed by tissue. The greater the amount of blood contained in the measure volume, the more light will be absorbed by the hemoglobin, the strongest light absorber in tissue, and correspondingly less light will be detected by the sensor. The O2C calculates from the absorbed part the relative hemoglobin amount for the illuminated tissue volume. This measurement represents a hemoglobin amount per tissue volume and is independent from the vessel density, vessel lumen and hemoglobin quantity in the blood.
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The O2C appliance (oxygen to see) – a short overview of the working method (PDF)