Videocapillaroscopic monitoring of microcirculation in rats during photodynamic therapy

The proposed approach to microcirculation assessment is non-invasive, informative, and can be implemented during photoactivation, and thus is perspective both for research tasks and clinical practice. The functional principles of the vasculature response to photodynamic exposure, identified using this technique, also foster the efficiency and safety of photodynamic therapy. The developed setup allows simultaneous photodynamic exposure and studying the microcirculation parameters by videocapillaroscopy and photoplethysmography techniques. Photodynamic action is carried out by 662 nm laser radiation with a power density of 15 mW/cm2  in continuous and pulsed modes. The imaging system of the setup consists of a large working distance microscope, an optical filter, and a monochrome camera. The illumination system is based on LED with a central wavelength of 532 nm. The acquired images were processed in order to obtain morphometric and hemodynamic microcirculation data in the inspected skin area. To compare the proposed approach with existing methods, we measured blood flow parameters by a laser Doppler flowmeter. We tested the developed setup on rats injected with a photosensitizer and obtained active vessel maps, photoplethysmograms, and skin vessel density values before, during, and after photoactivation in both generation modes. The proposed approach allows to reveal differences in the microcirculation response to photodynamic effects of low power densities in different modes, in particular, the discrepancy between the time from the start of exposure to the cessation of blood flow and the start of the recovery period.