Experimental Study of the Energy Impact of a Single Irradiation With Standard Laser Power and Duration Parameters on the Microcirculatory Bed of the Dermis

The demonstrated efficacy and safety advantages of laser therapy enable its application during early disease stages across all age groups, including pediatric populations. This modality not only targets pathological foci directly but also effectively prevents potential complications, underscoring its clinical relevance. The inherent benefits of laser irradiation for cutaneous vascular anomalies warrant further investigation to optimize treatment parameters, including laser type, wavelength selection, power settings, and other biotechnical irradiation variables. The aim is study of microcirculatory vessel alterations in the dermis following single-session laser exposure at standard power and duration parameters, focusing on their correlation with involutive changes in cutaneous purpura. Materials and methods. We evaluated sequential histological changes in skin tissue following laser irradiation at 30-minute (Site 1), 60-minute (Site 2), and 90-minute (Site 3) intervals. The experimental protocol utilized guinea pigs (weight 350.0-400.0 g; age 6-8 weeks) selected for their cutaneous morphological similarity to human skin. The study complied with Declaration of Helsinki principles, with protocol approval by the Institutional Ethics Committee (Protocol No. 37, May 13, 2025). Parental informed consent was obtained for pediatric participants. Data analysis employed Microsoft Excel and MS Statistica 10 software. This research is part of Vinnytsia National Pirogov Memorial Medical University's Department of Pediatric Surgery program: "Development and Improvement of Modern Diagnostic, Therapeutic, Preventive, and Rehabilitation Technologies for Pediatric Surgical Conditions" (State Registration No. 0118U003918, 2023-2027). Results. Morphometric analysis revealed a linear relationship between microcirculatory parameters and relative stromal edema area−a key purpura component−across all experimental intervals. Notably, stromal edema exhibited progressive expansion despite diminishing visual purpura manifestations. This apparent dissociation between superficial presentation and deeper histological changes demonstrated an inverse correlation. At 60-minute post-irradiation, observations showed marked pleurisy and perivascular edema with erythrocyte stasis in microcirculatory vessels, accompanied by minor per diapedesis hemorrhages, reactive inflammatory infiltration, and connective tissue structural damage−all more pronounced than at 30-minute evaluation. Conclusions. The presence of the phenomenon of purpura of the skin after a single laser irradiation can and should be considered as a clinically significant marker of the effectiveness of the selected parameters of energy exposure. Comparison of the dynamics of involutive development of purpura with morphological and morphometric parameters of vascular changes in all layers of the dermis convincingly demonstrates the rapid spread of pathological factors in them against the background of an increase and severity of the area of stromal edema in the direction of its deeper layers already in the early stages after laser irradiation. The result of experimental studies proves the possibility of the development of cyclic pathological changes in the structural elements of the dermis, and primarily its microcirculatory and vascular bed after each subsequent session of laser therapy when implementing an individual program for the treatment of vascular formations of the skin.