Impact of short term ischemia on dynamics of fluorescence lifetime parameters in skin
It is known that ischemic processes are characterised by local tissue hypoxia and changes in cellular metabolism. The excessive production of reactive oxygen species during the periods of ischemia and following reperfusion leads to accumulated changes in the living cells. In this work, registration of dynamics of fluorescence lifetime parameters in the skin was used as an indicator of metabolic alterations in the skin cells during moderate ischemia caused by the vascular occlusion test combined with the heating or cooling of the skin area under study. The measurements of fluorescence lifetime parameters were supplemented with the recordings of the blood perfusion through the same optical probe by the laser Doppler flowmetry (LDF) technique. Thus, this work aimed to investigate the sensitivity of fluorescence lifetime measurements in human skin to reliably register the metabolic changes associated with tissue temperature change and the effects of vascular occlusion.
The experimental setup developed for the studies combined Time-Correlated Single Photon Counting subsystem, picosecond UV-laser and LDF measuring channel. The system included a BDS-SM-375-FBC-101 laser source (Becker & Hickl, GmbH, Germany), with a emission peak at 375 nm, two HPM-100-40-CMOUNT hybrid photodetectors (Becker & Hickl, Germany), MF 479-40 and MF 530-43 fluorescence optical filters (Thorlabs, Inc, USA) in front of the optical inputs of the detectors, and the fibre optical probe for simultaneous measurements of the fluorescence parameters and blood perfusion. Five conditionally healthy volunteers (average age 23 years) took part in the study. The fibre optical probe was placed on the inner forearm of the left hand. By the experimental procedure, all studied parameters were recorded for 15 minutes with the combination of two functional tests: arterial brachial occlusion (using the occlusion cuff) and local heating to 42 °C or cooling to 10 °C (using a Peltier element). For each volunteer, the studied parameters were recorded in two series of experiments, with heating and cooling, respectively.
Based on the results obtained, recorded fluorescence lifetime parameters demonstrate significant changes during local heating, stages of occlusion and hyperemia. The changes during local cooling are less pronounced. The effect is described by the slowing of metabolism in cooled tissue cells. Given that no statistically significant differences were found in the baseline stages, a significant contribution of the applied functional tests to the fluorescence lifetime parameters are demonstrated.
The work was supported by the Russian Science Foundation (the research project 20-75-00123).
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Shupletsov Valery Vitalevich
Research & Development Center of Biomedical Photonics, Orel State University, Orel, Russia
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