Physical principles of laser Doppler flow spectrometry – O2 to See (O2S).

DOI: 10.36210/BerMedJ/epub902203

Abstract

Laser Doppler flowmetry is realised by a diode laser from a semiconductor diode with 830 nm and a power of up to 30 mW in continuous wave mode (CW) to generate light in the near-infrared range. The Doppler effect describes the extent of the frequency shift and depends on the number and speed of the bodies scattering the laser light. The frequency change of the Doppler signal registered in Hertz (Hz) is proportional to the speed of the flowing bodies. The number of bodies and speed of the moving bodies are registered and the flow in the microcirculation is calculated. The flow results from the velocity (V) multiplied by the number of moving bodies with their velocity (N) over all body velocities to be observed (?).

The white light source is formed by a 20 Watt halogen lamp with a wave range between 450-1000 nm. The measuring principle is based on the tissue-specific absorption and reflection of the emitted light quanta. Especially the scattering at the mitochondrial matrix causes an altered light propagation. With the help of the clear colour coding of the respective oxygenation state, the oxygen saturation of the blood pigment can be deduced from the detected blood colour. This is achieved by calculating the colour spectrum on the basis of the absorption-related shift in the individual wavelength ranges of the light. By comparing the detected haemoglobin spectra of the microcirculation with experimentally determined reference values of the different absorption ranges, the oxygen saturation can be determined in percent.