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.

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.

Characteristics of functional state of arteriolar and venular skin microvessels in patients with essential arterial hypertension.

The aim of the study was to evaluate the vasomotor activity of skin precapillary arterioles, depending on the condition of blood outflow from the capillary bed in patients with essential arterial hypertension (AH). The study included 30 normotensive subjects (NT) and 63 patients with AH, who were tested with a laser Doppler flowmetry with wavelet analysis of blood flow oscillations on the right forearm and ambulatory blood pressure monitoring (ABPM) on the left shoulder. Antihypertensive therapy was stopped for all patients 14 days prior to the experiment or AH was diagnosed for the first time. The hypertensive patients were divided into 2 groups, depending on the amplitude of the respiratory blood flow oscillations in skin microvessels. The first group included 30 patients without blood outflow violations of the capillary bed (AHVN), the second group consisted of 33 patients with various intensity of functional disorders in venular sector of microvasculature (AHVS). If the value of the amplitude of blood flow oscillations can be related to the tone" definition, then AHVN patients have a significant increase in neurogenic component of vascular tone (p<0.002) and violation of microvessel vasomotor endothelial function (p=0.065) in regard to NT, and AHVS patients to NT have a significant reduction of myogenic component tone of precapillary arterioles (p<0.05). AHVN patients compared to AHVS patients have a higher precapillary arteriolar tone due to endothelial (p<0.01), neurogenic (p<0.01) and myogenic (p<0.01) components of the vascular tone. Despite the lower values of the precapillary arteriolar tone, AHVS patients have higher BP values both at daytime (p<0.0005), and in nocturnal hours (p<0.05), and the functional state of venular sector is connected with nocturnal BP reduction. Obtained results indicate that hypertensive patients can have significant differences in the functional state of microvessels. The assessment of the initial skin microvasculatory regulatory mechanism status could potentially be useful for individual choice of antihypertensive therapy.

Non-invasive evaluation of vasomotor and metabolic functions of microvascular endothelium in human skin.

Correlation between metabolic and microhemodynamic processes in skin was assessed through acute pharmacological test with metabolically active Actovegin in 28 healthy volunteers. Laser Doppler flowmetry in combination with wavelet analysis of blood flow oscillations was used to identify functional state of arteriolar-venular areas of microvascular bed in the right forearm skin; capillary blood flow parameters were assessed through computer capillaroscopy in the nail bed of the right hand on the 4th finger. The metabolic effect (improved oxygen uptake and glucose disposal by tissues) was accompanied by significant increase in endothelial rhythm amplitude by 98% (p<0.00006), neurogenic rhythm amplitude by 50% (p<0.003) and myogenic rhythm amplitude by 54% (p<0.03), with capillary blood flow rate increasing by 90µm/s (p<0.04), pericapillary zone reducing by 15µm (p<0.0001) and diastolic blood pressure dropping by 4mm Hg (p<0.02). These results show close correlation between metabolic and microhemodynamic processes, which suggests that the amplitude activity within the range of endothelial rhythm (0.0095-0.021Hz) during laser Doppler flowmetry reflects not only solely vasomotor function but also metabolic function of microvascular endothelium.