Flow Mediated Skin Fluorescence (FMSF) is a new non-invasive method for assessing vascular circulation and/or metabolic regulation. It enables assessment of both vasoconstriction and vasodilation. The method measures stimulation of the circulation in response to post-occlusive reactive hyperemia (PORH). It analyzes the dynamical changes in the emission of NADH fluorescence from skin tissue, providing the information on mitochondrial metabolic status and intracellular oxygen delivery through the circulatory system. Assessment of the vascular state using the FMSF technique is based on three parameters: reactive hyperemia response (RHR), hypoxia sensitivity (HS), and normoxia oscillatory index (NOI). The RHR and HS parameters determine the risk of vascular circulatory disorders and are the main diagnostic parameters. The NOI parameter is an auxiliary parameter for evaluating the state of microcirculation under stress of various origins (e.g., emotional stress, physical exhaustion, or post-infection stress). The clinical data show that the risk of vascular complications is limited among people whose RHR, log(HS), and NOI parameters are not significantly below the mean values determined by the FMSF technique, especially if they simultaneously meet the conditions RHR > 30% and log(HS) > 1.5 (HS > 30), and NOI > 60%.

Keywords: flow mediated skin fluorescence; FMSF technique; NADH fluorescence, microcirculation, flowmotion, reactive hyperemia response, RHR, hypoxia sensitivity, HS, normoxia oscillatory index, NOI

Microcirculation oscillations, known as flowmotion, are a well-recognized feature of blood flow through blood vessels. There is evidence that impaired microvascular flow can be a symptom of a variety of diseases, including diabetes, cancer and cardiovascular disease, as well as neurodegenerative and autoimmune diseases. The innovative Flow Mediated Skin Fluorescence (FMSF) technique enables direct and precise monitoring of microcirculation oscillations, giving a qualitative and quantitative picture of the microcirculatory status of the organism. The HS (Hypoxia Sensitivity) parameter, determined by the FMSF technique, allows to quantify the degree of sensitivity of the organism to hypoxia by measuring stimulation of myogenic oscillations by transient hypoxia. It is assumed that an organism’s sensitivity to hypoxia may be regulated by genetic factors, but many studies indicate a significant role of hypoxia-inducible factor (HIF) in such response. The HS parameter seems to reflect a level of stabilized HIF-1α during the transient hypoxia caused by temporary occlusion of the brachial artery. The HS parameter can be used to predict development of the diseases accompanied by hypoxia. Based on the relationship between the innate immune response and hypoxia it can also be used to predict the severity of the disease such as coronavirus disease 2019 (COVID-19) infection. A good response to hypoxia (high values of HS parameter) can predispose the individuals to endurance training (long-distance running, climbing etc. ). Amateurs’ physical activity should also be undertaken based on the microcirculatory response to hypoxia. The FMSF technique allows to detect microcirculation disorders at an early stage in order to identify patients for preventive or therapeutic intervention, or for further more accurate and complex diagnostic tests.