Laser reflectance oximetry and Doppler flowmetry in assessment of complex physiological parameters of cutaneous blood microcirculation

Abstract

The integration of multiple optical techniques within a single diagnostic device is used to address the difficulties in standardising measurement of cutaneous blood micro-dynamics caused by high variability. We demonstrate the benefits of simultaneous assessment of blood relative volume (Vb), microcirculation index (Im) and tissue oxygen saturation (StO2), during long-term examination of healthy volunteers. Consequently, five rhythmic components: endothelial, neurogenic, myogenic, breath and heart pulses were established showing high variability up to 30 - 50% as well as in initial parameters around 16%. All rhythmic components were synchronous with some latency between Im and StO2 in the myogenic component supports the hypothesis of strong correlation between peripheral hemodynamics and oxygen utilisation in tissues. Optical techniques are one of the promising non-invasive technologies for diagnosis of medical conditions. The integration of various techniques in an instrument and methodological framework that combines them in a single device using integrating algorithms for multi-modal diagnostics is particularly promising. Multi-functional laser non-invasive diagnostic systems (MLNDS), with up to 4 active channels are emerging, for example: laser Doppler flowmetry (LDF), tissue reflectance oximetry (TRO), laser fluorescence diagnostics (LFD), pulse oximetry and other. The most promising methods of optical non-invasive diagnostic methods are LDF and TRO. These methods are widely used in studying the dynamics of processes of blood microcirculation and oxygen transport and utilisation in biological tissues. The results of LDF measurements, index of blood microcirculation (Im) or perfusion, assessed in conventional perfusion units (PU), reveal a complex, non-periodic process. This variable component contains information on the modulation of blood flow. Use of spectral signal processing algorithms (LDF-graphs) for decoding and analysis provides information about the condition of vascular tone in terms of its contribution to the different mechanisms of micro-hemodynamic regulation (myogenic, endothelial, etc.) 1 . The TRO method determines relative blood volume (Vb) microcirculation in the surface layers of the soft tissues (skin, mucous membranes of the organs) and tissue oxygen saturation (StO2) of the microvasculature in the inspected area of biological tissue. There are isolated cases of spectral processing algorithms recorded signals (StO2- and Vb-graphs), being used to assess vasomotion and myogenic rhythms, for example 2 . We propose that analysis of oscillation signals recorded by TRO according to the frequency ranges, similar to LDF-graphs, is of practical interest in studying the parameters of microcirculation of blood, as the relationships between LDF and TRO attract the increasing attention of researchers in this field.