The wavelet analysis for the assessment of microvascular function with the laser Doppler fluxmetry over the last 20 years. Looking for hidden informations

Assessment of Blood Microcirculation Changes after COVID-19 Using Wearable Laser Doppler Flowmetry

The present work is focused on the study of changes in microcirculation parameters in patients who have undergone COVID-19 by means of wearable laser Doppler flowmetry (LDF) devices. The microcirculatory system is known to play a key role in the pathogenesis of COVID-19, and its disorders manifest themselves long after the patient has recovered. In the present work, microcirculatory changes were studied in dynamics on one patient for 10 days before his disease and 26 days after his recovery, and data from the group of patients undergoing rehabilitation after COVID-19 were compared with the data from a control group. A system consisting of several wearable laser Doppler flowmetry analysers was used for the studies. The patients were found to have reduced cutaneous perfusion and changes in the amplitude-frequency pattern of the LDF signal. The obtained data confirm that microcirculatory bed dysfunction is present in patients for a long period after the recovery from COVID-19.

Wavelet analysis of laser Doppler microcirculatory signals: Current applications and limitations

Laser Doppler flowmetry (LDF) has long been considered a gold standard for non-invasive assessment of skin microvascular function. Due to the laser Doppler (LD) microcirculatory signal's complex biological and physiological context, using spectral analysis is advisable to extract as many of the signal's properties as feasible. Spectral analysis can be performed using either a classical Fourier transform (FT) technique, which has the disadvantage of not being able to localize a signal in time, or wavelet analysis (WA), which provides both the time and frequency localization of the inspected signal. So far, WA of LD microcirculatory signals has revealed five characteristic frequency intervals, ranging from 0.005 to 2 Hz, each of which being related to a specific physiological influence modulating skin microcirculatory response, providing for a more thorough analysis of the signals measured in healthy and diseased individuals. Even though WA is a valuable tool for analyzing and evaluating LDF-measured microcirculatory signals, limitations remain, resulting in a lack of analytical standardization. As a more accurate assessment of human skin microcirculation may better enhance the prognosis of diseases marked by microvascular dysfunction, searching for improvements to the WA method is crucial from the clinical point of view. Accordingly, we have summarized and discussed WA application and its limitations when evaluating LD microcirculatory signals, and presented insight into possible future improvements. We adopted a novel strategy when presenting the findings of recent studies using WA by focusing on frequency intervals to contrast the findings of the various studies undertaken thus far and highlight their disparities.

Structural and functional state of various parts of skin microcirculation at an early stage of hypertension in working-age men

STUDY PURPOSE

To conduct a cross-sectional study on the structural and functional characteristics of various parts of skin microcirculation in working-age men with newly diagnosed hypertension (HTN).

MATERIALS AND METHODS

The study included 118 male participants (ages 30 to 60) who were not regularly taking any medicine, had no medical complaints, and subjectively considered themselves healthy at the time of study. All participants underwent a cross-sectional comprehensive medical examination. The following tests were performed: complete blood count, biochemical blood tests, video capillaroscopy (VCS), laser Doppler flowmetry (LDF) and photoplethysmography (PPG) on the left hand fingers, determination of flow-mediated vasodilation of the brachial artery, echocardiography, ultrasound of extracranial and femoral arteries, 24-h ambulatory blood pressure monitoring (ABPM). According to ABPM data, the participants were divided into two equal groups called a control group(CG) and a hypertension group(HG). There were 59 participants with normal BP in CG, and 59 participants with newly diagnosed HTN in HG.

RESULTS

Nailfold VCS of the ring finger revealed no significant differences between the groups at the level of exchange microvessels. According to LDF data, there was no decrease in tissue perfusion and signs of an increase in the activity of endothelial, neurogenic, and myogenic regulation of the tone of precapillary arterioles in the HTN group. According to PPG of the index finger, in contrast to CG, HTN participants had significantly higher values of the following parameters: normalized augmentation index (Alp75) - 3.8 % and - 5.25 % (p < 0.005), stiffness index (SI) - 7.6 m/s and 7.35 m/s (p < 0.05), reflection index (RI) - 36.5 % and 28.4 % (p < 0.005), respectively.

DISCUSSION

Working-age men in the early stage of HTN have neither capillary rarefaction nor an increase in the tone of skin precapillary arterioles. The largest contribution to peripheral vascular resistance in the onset of HTN is most likely made by large muscular arterioles, in which the neurogenic regulation of vascular tone predominates.

Parameters of cutaneous microvasculature in men of working age with newly diagnosed arterial hypertension

OBJECTIVE

To investigate structural and functional features of cutaneous microvasculature in men of working age with newly diagnosed arterial hypertension (AH).

MATERIALS AND METHODS

The study included 161 apparently healthy men from 30 to 60 years, who underwent a comprehensive examination of cardiovascular system "from the heart to the capillaries". Control group (CG) included 60 normotensive men. AH group included 101 men with elevated BP.

RESULTS

There is no rarefaction of the capillary bed and latent fluid retention in the interstitial space in the skin in men with AH. No data were obtained for increased endothelial, neurogenic and myogenic tone of resistive cutaneous precapillary arterioles in AH group, but a decrease in the perfusion efficiency of the endothelial and myogenic mechanisms of tissue perfusion modulation was noted.

CONCLUSION

Obtained results allow making the assumption that metabolic disorders at the level of capillaries that are of a systemic nature prevail in men with the onset of AH.

Mechanisms of Venoarteriolar Reflex in Type 2 Diabetes with or without Peripheral Neuropathy

Simple Summary

Postural changes induce arteriolar vasoconstriction in response to an increase in venous pressure in the limbs known as the venoarteriolar reflex (VAR). Previous studies reported that skin blood perfusion is impaired during the VAR in persons with type 2 diabetes mellitus (T2DM) with or without peripheral neuropathy, compared to control subjects. The aim of this study is to investigate the underlying mechanisms of the VAR in T2DM, with and without peripheral neuropathy. This study provides evidence that confirmed neuropathy alters the VAR by an alteration of the neurogenic response to leg dependency.

Abstract

The aim of this study is to investigate the underlying mechanisms of the venoarteriolar reflex (VAR) in type 2 diabetes mellitus (T2DM), with and without peripheral neuropathy. Laser Doppler flowmetry (LDF) recordings were performed on the medial malleus and dorsal foot skin, before and during leg dependency in healthy controls, in persons with obesity, in those with T2DM, in those with T2DM and subclinical neuropathy, and in those with T2DM and confirmed neuropathy. LDF recordings were analyzed with the wavelet transform to evaluate the mechanisms controlling the flowmotion (i.e., endothelial nitric oxide-independent and -dependent, neurogenic, myogenic, respiratory and cardiac mechanisms). Skin blood perfusion decreased throughout leg dependency at both sites. The decrease was blunted in persons with confirmed neuropathy compared to those with T2DM alone and the controls. During leg dependency, total spectral power increased in all groups compared to rest. The relative contribution of the endothelial bands increased and of the myogenic band decreased, without differences between groups. Neurogenic contribution decreased in controls, in persons with obesity and in those with T2DM, whereas it increased in subclinical- and confirmed neuropathy. In conclusion, this study provides evidence that confirmed diabetic neuropathy alters the VAR through the neurogenic response to leg dependency.

Body Position Affects Capillary Blood Flow Regulation Measured with Wearable Blood Flow Sensors

In this study we demonstrate what kind of relative alterations can be expected in average perfusion and blood flow oscillations during postural changes being measured in the skin of limbs and on the brow of the forehead by wearable laser Doppler flowmetry (LDF) sensors. The aims of the study were to evaluate the dynamics of cutaneous blood perfusion and the regulatory mechanisms of blood microcirculation in the areas of interest, and evaluate the possible significance of those effects for the diagnostics based on blood perfusion monitoring. The study involved 10 conditionally healthy volunteers (44 ± 12 years). Wearable laser Doppler flowmetry monitors were fixed at six points on the body: two devices were fixed on the forehead, on the brow; two were on the distal thirds of the right and left forearms; and two were on the distal thirds of the right and left lower legs. The protocol was used to record three body positions on the tilt table for orthostatic test for each volunteer in the following sequence: (a) supine body position; (b) upright body position (+75°); (c) tilted with the feet elevated above the head and the inclination of body axis of 15° (−15°, Trendelenburg position). Skin blood perfusion was recorded for 10 min in each body position, followed by the amplitude–frequency analysis of the registered signals using wavelet decomposition. The measurements were supplemented with the blood pressure and heart rate for every body position analysed. The results identified a statistically significant transformation in microcirculation parameters of the average level of skin blood perfusion and oscillations of amplitudes of neurogenic, myogenic and cardiac sensors caused by the postural changes. In paper, we present the analysis of microcirculation in the skin of the forehead, which for the first time was carried out in various positions of the body. The area is supplied by the internal carotid artery system and can be of particular interest for evaluation of the sufficiency of blood supply for the brain.

Analysis of pigmented skin lesions and malignant melanoma by Laser Doppler flowmetry - Report of different cases and further analysis by a neuronal network

BACKGROUND

Dermatoscopy is successfully used for the early diagnosis of suspicious skin lesions, however, correct diagnosis depends on training. There is evidence that wavelet analysis by Laser Doppler flowmetry (LDF) can identify malignant melanomas by their hypervascularization and changes in the capillary morphology.

OBJECTIVE

To show the capability of LDF in the distinction of melanomas and benign pigmented skin lesions based on data collected over 16 years.

METHODS

Evaluation of pigmented skin lesions was based on clinical information. The LDF measurements were taken. The suspect lesion was excised afterwards for histological work-up. Four case reports are presented. Data collected over 16 years was processed into a neuronal network to estimate the dignity of the lesion.

RESULTS

A total of 517 suspicious lesions were analyzed by LDF. In the histological work-up, 114 lesions turned out to be melanomas, whereas 403 benign naevi were secured. Specificity to detect melanomas was good based on the clinical information. The LDF increases the sensitivity of melanoma detection, which is also illustrated in four case reports.

CONCLUSION

In addition to clinical parameters, such as color and border, information from the LDF can help in the diagnosis of malignant melanomas. The LDF provides information on the vascularization of the skin lesion.

Validation of a novel ultrasound Doppler monitoring device (earlybird) for detection of microvascular circulatory changes

OBJECTIVE

In this proof-of-concept study we aim to validate a novel ultrasound Doppler monitoring device for evaluating microcirculation (earlybird) against LDF and pulsed Doppler.

METHODS

In ten healthy subjects, we measured microcirculatory function at rest and during different autonomic tests (forced respiration, isometric exercise, Valsalva maneuver and cold pressor). Earlybird, LDF and pulsed Doppler were recorded simultaneously. We performed a ZNCC to determine correlation.

RESULTS

The curves for earlybird and LDF or pulsed Doppler correlates visually well. Overall median ZNCC 0.87 (interquartile range 0.77 -0.91) between the LDF and earlybird measurements, and 0.90 (0.82 - 0.95) for pulsed Doppler and earlybird. Median ZNCC for baseline and each provocation test for earlybird against LDF and pulsed Doppler were calculated; baseline: LDF 0.87 (0.73 - 0.97) pulsed Doppler 0.91 (0.81 - 0.94), forced respiration: LDF 0.87 (0.28 - 0.90) pulsed Doppler 0.90 (0.85 - 0.96), isometric exercise: LDF 0.82 (0.59 - 0.90) pulsed Doppler 0.87 (0.68 - 0.94), Valsalva maneuver: LDF 0.88 (0.82 - 0.91) pulsed Doppler 0.94 (0.92 - 0.97) and cold pressor: LDF 0.90 (0.85 - 0.95) pulsed Doppler 0.89 (0.65 - 0.94).

CONCLUSION

Earlybird records vasoconstrictions in healthy subjects as well as LDF and pulsed Doppler.

Resting and recruitable endothelial function - Evidence of two distinct circadian patterns

BACKGROUND

Evidence of a circadian rhythm in endothelium-dependent vasomotor function, with a nadir in Flow-Mediated Dilation (FMD) in the early morning hours, has been previously reported. These changes have been proposed to be one of the mechanisms explaining the circadian pattern in the incidence of cardiovascular events. We set out to investigate the circadian rhythm of FMD, low-flow mediated dilation (L-FMC) and sympathetic vascular tone.

METHODS AND RESULTS

10 young healthy male volunteers (mean age, 28.9±3.7 years) underwent measurements of radial artery endothelium-dependent FMD and L-FMC at 8AM, 2PM and 8PM on the same day. Sympathetic vascular tone was assessed with laser Doppler and Fourier transform analysis. Compared with 2PM and 8PM, FMD decreased markedly in the early morning (2.9±3.4%; 6.2±2.9%; 6.0±4.0%; P = 0.007). In contrast, L-FMC was maximal at 8AM, decreased significantly at 2PM, and returned to higher values at 8PM (-5.1±1.3%; -2.7±2.0%; -4.6±2.2%; P = 0.030), such that the composite endpoint of endothelial function (sum of FMD+L-FMC) was not significantly different among timepoints. Vascular sympathetic tone was maximal early in the morning and lowest in the evening (P = 0.014) without a correlation with the changes in FMD or L-FMC.

CONCLUSIONS

Endothelial responsiveness (FMD) and basal tone (L-FMC) appear to follow different circadian rhythms, with an impaired responsiveness in the early morning and a nadir in baseline tone in the early afternoon.

Bridging the gap between basic research on microcirculation and clinical world: The translational marriage between engineering and medicine

The words "Translational" and "Medicine" have been recently coupled to indicate a combination of disciplines, resources, expertise, and techniques aimed at enhancing prevention, diagnosis, and therapies. As stated in 2015 by the European Society for Translational Medicine, translational medicine is "an interdisciplinary branch of the biomedical field supported by three main pillars: benchside, bedside and community". By definition, Translational Medicine is a highly interdisciplinary field, which gathers several specialties aimed at improving the global healthcare system.With regard to the assessment of the microcirculatory function, it is worthwhile to mention the growing interest from both basic research and clinical practice. Microcirculation is where the exchange of substances between blood and tissues takes place. Thus, it plays a key role in the pathophysiology of many diseases. Nonetheless, a gap does exist between the theoretical analysis of the microcirculatory function and its clinical exploitation. This gap can be due to the weak dissemination of analytical methods and theoretical results within the clinical community, which also delays the establishment of specific operative guidelines.This paper aims at encouraging, and possibly accelerating, the translation of basic research outcomes on microcirculatory function assessment into clinical applications.