Flowmotion Monitored by Flow Mediated Skin Fluorescence (FMSF): A Tool for Characterization of Microcirculatory Status

Assessment of Microvascular Function Based on Flowmotion Monitored by the Flow-Mediated Skin Fluorescence Technique

This review summarizes studies dedicated to the assessment of microvascular function based on microcirculatory oscillations monitored by the Flow-Mediated Skin Fluorescence (FMSF) technique. Two approaches are presented. The first approach uses oscillatory parameters measured under normoxic conditions, expressed as flowmotion (FM), vasomotion (VM), and the normoxia oscillatory index (NOI). These parameters have been used for the identification of impaired microcirculatory oscillations associated with intense physical exercise, post-COVID syndrome, psychological stress, and erectile dysfunction. The second approach involves characterization of the microcirculatory response to hypoxia based on the measurement of hypoxia sensitivity (HS). The HS parameter is used to characterize microvascular complications in diabetes, such as diabetic kidney disease and diabetic foot ulcers. Based on research conducted by the authors of this review, the FMSF parameter ranges characterizing microvascular function are presented. The diagnostic approach to assessing microvascular function based on flowmotion monitored by the FMSF technique has a wide range of applications and the potential to be integrated into widespread medical practice.

Conclusions from an Observational Study of Patients with Vascular Diseases Using the FMSF Technique

Purpose

There is great demand for a diagnostic tool for non-invasive assessment of vascular circulation and metabolic regulation. Assessing both these functions is crucial, as each can have a distinct response to hypoxia.

Patients and Methods

The Flow Mediated Skin Fluorescence (FMSF) technique appears uniquely suitable for analysis of vascular circulation and metabolic regulation. In this observational study, the FMSF technique was used to diagnose patients with various vascular diseases. The study group consisted of 482 patients (264 females and 218 males) between the ages of 40-94 years with various vascular problems (arterial hypertension, cardiovascular disease, diabetes, hypercholesterolemia, and chronic venous disease).

Results

Three major FMSF parameters were used: Ischemic Response (IRmax), Hyperemic Response (HRmax), and Reactive Hyperemia Response (RHR). All three parameters were found to decrease with age with a distinguishable kinetics. The IRmax parameter was used for characterization of metabolic reaction to transient hypoxia and HRmax was used for characterization of macrocirculatory function. Both were sex-dependent.

Conclusion

Females were metabolically less adaptive to transient hypoxia than males. However, macrocirculatory function was better in females than among males. Microcirculatory function decreases gradually with age, while macrocirculatory function decreases much more slowly with age, with a tendency to stabilize after 70 years of age.

Microcirculation and Mitochondria: The Critical Unit

Critical illness is often accompanied by a hemodynamic imbalance between macrocirculation and microcirculation, as well as mitochondrial dysfunction. Microcirculatory disorders lead to abnormalities in the supply of oxygen to tissue cells, while mitochondrial dysfunction leads to abnormal energy metabolism and impaired tissue oxygen utilization, making these conditions important pathogenic factors of critical illness. At the same time, there is a close relationship between the microcirculation and mitochondria. We introduce here the concept of a "critical unit", with two core components: microcirculation, which mainly comprises the microvascular network and endothelial cells, especially the endothelial glycocalyx; and mitochondria, which are mainly involved in energy metabolism but perform other non-negligible functions. This review also introduces several techniques and devices that can be utilized for the real-time synchronous monitoring of the microcirculation and mitochondria, and thus critical unit monitoring. Finally, we put forward the concepts and strategies of critical unit-guided treatment.

Non-Invasive Assessment of Vascular Circulation Based on Flow Mediated Skin Fluorescence (FMSF)

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%.

Chronic Fatigue Associated with Post-COVID Syndrome versus Transient Fatigue Caused by High-Intensity Exercise: Are They Comparable in Terms of Vascular Effects?

Purpose

The pathophysiology of chronic fatigue associated with post-COVID syndrome is not well recognized. It is assumed that this condition is partly due to vascular dysfunction developed during an acute phase of infection. There is great demand for a diagnostic tool that is able to clinically assess post-COVID syndrome and monitor the rehabilitation process.

Patients and Methods

The Flow Mediated Skin Fluorescence (FMSF) technique appears uniquely suitable for the analysis of basal microcirculatory oscillations and reactive hyperemia induced by transient ischemia. The FMSF was used to measure vascular circulation in 45 patients with post-COVID syndrome. The results were compared with those for a group of 26 amateur runners before and after high-intensity exercise as well as for a control group of 32 healthy age-matched individuals.

Results

Based on the observed changes in the NOI (Normoxia Oscillatory Index) and RHR (Reactive Hyperemia Response) parameters measured with the FMSF technique, it was found that chronic fatigue associated with post-COVID syndrome is comparable with transient fatigue caused by high-intensity exercise in terms of vascular effects, which are associated with vascular stress in the macrocirculation and microcirculation. Acute and chronic fatigue symptomatology shared similarly altered changes in the NOI and RHR parameters and both can be linked to calcium homeostasis modification.

Conclusion

The NOI and RHR parameters measured with the FMSF technique can be used for non-invasive clinical assessment of post-COVID syndrome as well as for monitoring the rehabilitation process.

Assessment of microvascular function using a novel technique Flow Mediated Skin Fluorescence (FMSF) in patients with diabetic kidney disease: A preliminary study

BACKGROUND

Diabetic kidney disease (DKD) plays an important role in morbidity and mortality in patients with diabetes mellitus. The pathogenesis of this microangiopathy is mainly due to impaired vascular endothelial function. The Flow Mediated Skin Fluorescence (FMSF) method is an innovative, non-invasive tool for assessing the microcirculation function (especially microcirculatory response to hypoxia), also in patients with complications of diabetes mellitus (DM).

MATERIAL AND METHODS

The study was conducted at the Medical University of Lodz, Poland. Total of 84 volunteers including 30 patients with DKD, 33 patients with DM without complications, and 21 healthy subjects underwent microvascular function assessments using FMSF. This technique measures changes in the intensity of nicotinamide adenine dinucleotide (NADH) fluorescence from the skin on the forearm as a function of time, in response to blocking and releasing blood flow in the forearm. In this study we asses two key parameters: Reactive Hyperemia Response (RHR) and Hypoxia Sensitivity [log(HS)] to characterize vascular circulation in patients with DKD and their response to transient ischemia.

RESULTS

The patients with low reactive hyperemic response (the RHR parameter) had a significantly higher sCr than patients with moderate and high RHR value (p < 0.001, p < 0.05, respectively) and a significantly lower eGFR than the patients with moderate and high RHR parameter (p < 0.001, p < 0.01, respectively). The patients with very low and low log(HS) values had a significantly higher sCr than the patients with high log(HS) (p < 0.001, p < 0.01, respectively), and a significantly lower eGFR than the patients with high log(HS) parameter (p < 0.001, p < 0.01, respectively). The patients with very low log(HS) had a significantly higher sCr and a significantly lower eGFR than the patients with moderate (p < 0.05, p < 0.01, respectively). The mean value of the RHR parameter was significantly lower in DKD patients (18.31 ± 5.06 %) compared to both healthy subjects (34.37 ± 8.18 %, p < 0.001) and DM without complications subgroup (28.75 ± 7.12 %, p < 0.001). Similar trends were noted with the mean value of log(HS) parameter in DKD subgroup (1.03 ± 0.5) vs. healthy subjects (1.59 ± 0.53, p < 0.001), and vs. DM without complications subgroup (1.73 ± 0.52, p < 0.001). We observed a significant inverse correlation between the RHR parameter and serum creatinine (sCr) and a significant positive correlations with eGFR (R =  -0.3; p < 0.05, R = 0.61; p < 0.001, respectively). We found also a significant negative correlations of the log(HS) measure with sCr and a significant positive correlations with eGFR (R = -0.33; p < 0.01, R = 0.55; p < 0.001, respectively). We observed also a significant inverse correlation between the RHR and log(HS) parameters and advanced glycation end products (AGEs) (R = -0.6; p < 0.001, R = -0.32; p < 0.01, respectively). The AGEs parameter was also a significantly higher in patients with low RHR parameter than in patients with moderate (p < 0.01) and high (p < 0.001).

CONCLUSIONS

The FMSF technique makes it possible to identify impairments of the microvascular function in patients with DKD. This study confirms that the simple two-parametric approach diagnostic tool perfectly characterizes the state of the microvascular system in diabetic patients with impaired renal function. These preliminary results require further validation in a larger patients cohort.

Vascular endothelial damage in COPD: current functional assessment methods and future perspectives

Introduction: Cardiovascular disease is a major cause of death in chronic obstructive pulmonary disease (COPD), but the relationship between these two entities is not fully understood; smoking, inflammation, arterial stiffness and endothelial dysfunction are significant determinants. Endothelial dysfunction is not only associated with cardiovascular disease, but also with COPD severity.Areas covered: Several functional methods have been developed to evaluate endothelial function in healthy and diseased individuals; from the invasive angiography of epicardial coronary arteries and Venous-Occlusion-Plethysmography, to more modern, noninvasive approaches such as Flow-Mediated-Dilatation, Peripheral-Arterial-Tonometry and Near-Infrared-Spectroscopy, all these methods have boosted clinical research in this field. In this context, this narrative review, which included articles published in PubMed and Scopus up to 25-November-2020, summarizes available functional methods for endothelial damage assessment in COPD and discusses existing evidence on their associations with comorbidities and outcomes in this population.Expert opinion: Accumulated evidence suggests that endothelial dysfunction occurs in early stages of CΟPD and worsens with pulmonary obstruction severity and during acute exacerbations. Novel methods evaluating endothelial function offer a detailed, real-time assessment of different parameters related to vascular function and should be increasingly used to shed more light on the role of endothelial damage on cardiovascular and COPD progression.

Differentiation of Diabetic Foot Ulcers Based on Stimulation of Myogenic Oscillations by Transient Ischemia

PURPOSE

Diabetic foot ulceration is a chronic complication characterized by impaired wound healing. There is a great demand for a diagnostic tool that is able to monitor and predict wound healing.

PATIENTS AND METHODS

Oscillations in the microcirculation, known as flowmotion, can be monitored very distinctly and precisely using the Flow Mediated Skin Fluorescence (FMSF) technique. The flowmotion response to hypoxia was measured quantitatively in 42 patients with diabetic foot ulcers.

RESULTS

The flowmotion response to hypoxia parameters FM(R) and HS were used to differentiate the diabetic foot ulcers and correlate them with clinical status. In some cases, FMSF measurements were continued over the period of a year in order to monitor disease progress. The clinical status of the quarter of patients with the highest HS values (group A, HS = 50.2±18.3) was compared to the quarter with the lowest HS values (group B, HS = 4.3±1.7). The patients in the group B were identified as having low prognosis for healing and were characterized by higher incidences of hypertension, hyperlipidemia, prevalent CVD, neuropathy and nephropathy.

CONCLUSION

Impaired flowmotion responses to hypoxia induced by transient ischemia can be used for differentiation of diabetic foot ulcers and identification of cases with low prognosis for healing.

Non-invasive in vivo human model of post-ischaemic skin preconditioning by measurement of flow-mediated 460-nm autofluorescence

AIMS

Transient ischaemia and reperfusion (TIAR) induce early ischaemic preconditioning (IPC) in different tissues and organs, including the skin. IPC protects tissues by modifying the mitochondrial function and decreasing the amount of the reduced form of nicotinamide adenine dinucleotide (NADH). Skin 460-nm autofluorescence is proportional to the NADH content and can be non-invasively measured during TIAR. We propose a non-invasive in vivo human model of skin IPC for studying the effects of repeated TIARs on the NADH content.

METHODS

Fifty-one apparently healthy volunteers (36 women) underwent three 100-second forearm ischaemia episodes induced by inflation of brachial pressure cuff to the pressure of 60 mmHg above systolic blood pressure, followed by 500-second long reperfusion episodes. Changes in skin NADH content were measured using 460-nm fluorescence before and during each of the three TIARs.

RESULTS

The first two TIARs caused a significant reduction in the skin NADH content before (P = .0065) and during the third ischaemia (P = .0011) and reperfusion (P = .0003) up to 3.0%. During the third TIAR, the increase in skin NADH was 20% lower than during the first ischaemia (P = .0474).

CONCLUSIONS

The measurement of the 460-nm fluorescence during repeated TIARs allows for a non-invasive in vivo investigation of human skin IPC. Although IPC reduces the overall NADH skin content, the most noticeable NADH reduction appears during ischaemia after earlier TIARs. Studying the skin model of IPC may provide new avenues for in vivo physiological, clinical and pharmacological research on mitochondrial metabolism.