Effect of the Tracheal Optical Properties on the Spectral Assessment of the Level of Its Blood Supply In Vivo

<b>Background/Objectives:</b> This work is devoted to the presentation of the intraoperative method for assessing the blood supply to the tracheal tissues in order to minimize the risk of tissue ischemia and necrosis by early diagnosis of bloodstream disorders during surgery. The vascular network supplying the trachea is characterized by collateral blood circulation. However, after the surgical removal of a tracheal tumor, the created anastomosis may be untenable due to insufficient blood supply to the tissues. The consequence of such a disorder may require additional surgical interventions to restore the integrity of the trachea. Based on publicly available information, diffuse reflectance spectroscopy has not previously been used for blood supply assessment in tracheal surgeries. <b>Methods:</b> Light propagation in a four- or six-layer model of the tracheal wall (500-600 nm) was simulated using the Monte Carlo method; in the simulation, the layer thicknesses, levels of oxygen saturation (StO₂) (0-100%), and blood filling (Hb% 0.5-2%) were varied. Intraoperative measurements using diffuse reflectance spectroscopy were performed in 12 patients at three stages of the operation. <b>Results:</b> The simulation showed that when the fiber is placed from the adventitial side, the differences in the diffuse scattered signal with changes in perichondrium saturation are 2.6 ± 1.7%, whereas when placed from the mucosa side, the changes are less than 1%, which means that deeper layers make a greater contribution to the signal with adventitial access. When testing the StO₂ estimation algorithm, the simulation and experiment agree: the measured StO₂ was 56 ± 7%, which is close to the specified level in the simulation. Clinical measurements demonstrated the possibility of recording saturation changes at the stages before and after the anastomosis. <b>Conclusions:</b> According to the results of this study, saturation estimation by diffuse reflectance spectroscopy shows the prospect for assessing the state of tracheal tissues by the level of their blood supply in clinical conditions in real time.