The Venoarteriolar Reflex Significantly Reduces Contralateral Perfusion as Part of the Lower Limb Circulatory Homeostasis in vivo

Revisiting the Venoarteriolar Reflex-Further Insights from Upper Limb Dependency in Healthy Subjects

The venoarteriolar reflex (VAR) is described as a vasoconstriction occurring in response to an increase in venous transmural pressure. Its underlying mechanisms are still not clarified, particularly the neural pathway that supposedly evokes this reflex. In addition, recent studies have shown that the postural maneuvers that evoke VAR also produce a decrease in contralateral perfusion, which is also poorly understood. Our study aimed to explore the contralateral response to unilateral upper limb dependency and its underlying mechanisms. Fifteen young, healthy subjects (24.1 ± 5.8 y.o.) participated in this study after giving informed consent. While seated, subjects remained for 7 min with both arms at heart level (baseline), after which a random hand was placed 40 cm below the heart level for 5 min (dependency) before resuming the initial position for another 7 min (recovery). Skin perfusion was assessed bilaterally with photoplethysmography, and electrodermal activity (EDA) was assessed in the contralateral hand. During hand dependency, perfusion decreased significantly in both limbs, although it was more pronounced in the dependent limb, corroborating previous reports that unilateral limb dependency evokes a decrease in contralateral perfusion. Transient EDA peaks were detected in the first seconds of the dependency and recovery phases. These results support the participation of the sympathetic nervous system as a mechanism regulating contralateral perfusion during unilateral limb dependency. This sympathetic activation is probably attributed to the postural changes themselves and is likely not related to the VAR.

Studying Erythromelalgia Using Doppler Flowmetry Perfusion Signals and Wavelet Analysis-An Exploratory Study

Erythromelalgia (EM) is a rare disease, which is still poorly characterized. In the present paper, we compared the hand perfusion of one female EM patient, under challenges, with a healthy control group. Using a laser Doppler flowmeter (LDF) with an integrated thermal probe, measurements were taken in both hands at rest (Phase I) and after two separate challenges-post-occlusive hyperemia (PORH) in one arm (A) and reduction of skin temperature (cooling) with ice in one hand (B) (Phase II). The final measurement periods corresponded to recovery (Phases III and IV). The control group involved ten healthy women (27.3 ± 7.9 years old). A second set of measurements was taken in the EM patient one month after beginning a new therapeutic approach with beta-blockers (6.25 mg carvedilol twice daily). Z-scores of the patient's LDF and temperature fluctuations compared to the control group were assessed using the Wavelet transform (WT) analysis. Here, fluctuations with |Z| > 1.96 were considered significantly different from healthy values, whereas positive or negative Z values indicated higher or lower deviations from the control mean values. Cooling elicited more measurable changes in LDF and temperature fluctuations, especially in higher frequency components (cardiac, respiratory, and myogenic), whereas PORH notably evoked changes in lower frequency components (myogenic, autonomic, and endothelial). No significant Z-score deviations were observed in the second measurement, which might signify a stabilization of the patient's distal perfusion following the new therapeutic approach. This analysis involving one EM patient, while clearly exploratory, has shown significant deviations in WT-derived physiological components' values in comparison with the healthy group, confirming the interest in using cold temperature as a challenger. The apparent agreement achieved with the clinical evaluation opens the possibility of expanding this approach to other patients and pathologies in vascular medicine.

Unraveling the pathophysiology of lower-limb postthrombotic syndrome in adolescents: a proof-of-concept study

A better understanding of the pathophysiology of pediatric postthrombotic syndrome (PTS) is needed to develop strategies to treat this condition. We investigated calf pump function, exercise capacity, balance in power output, and changes in limb muscle oxygen saturation (SmO2) and fluid content during exercise in 10 pediatric patients with unilateral lower-limb PTS, and in age- and sex-matched controls (1:1-1:2 ratio). Outcomes were investigated using bioimpedance spectroscopy, torque-sensing pedals, and near-infrared spectroscopy during incremental- and constant-load cycling tests. The median age at participation was 17 years (25th-75th percentile, 15-18 years); 68% of participants were females. The median CAPTSure score in the affected leg of affected participants was 35 points (25th-75th percentile, 24-46 points), indicating moderate/severe PTS; 20% of patients had a history of central venous catheter-related thrombosis. Increasing PTS severity was associated with higher calf pump venous volume and higher ejection volume, leading to compensated calf pump performance. We found no evidence of PTS impact on exercise capacity. Leg contribution to power output was similar in affected and unaffected legs. However, the PTS-affected legs showed lower SmO2 during active cycling and recovery with increasing PTS severity, indicating impaired microvascular function in the muscle. These findings suggest that PTS severity is associated with impaired blood flow, presumably from elevated venous pressure during and after exercise. The fact that microvascular function is impaired in young patients with PTS underscores the relevance of developing strategies to mitigate the effects of this chronic vascular disease to minimize its deleterious effects as children grow older.

The acute adaptation of skin microcirculatory perfusion in vivo does not involve a local response but rather a centrally mediated adaptive reflex

Introduction: Cardiovascular homeostasis involves the interaction of multiple players to ensure a permanent adaptation to each organ's needs. Our previous research suggested that changes in skin microcirculation-even if slight and distal-always evoke an immediate global rather than "local" response affecting hemodynamic homeostasis. These observations question our understanding of known reflexes used to explore vascular physiology, such as reactive hyperemia and the venoarteriolar reflex (VAR). Thus, our study was designed to further explore these responses in older healthy adults of both sexes and to potentially provide objective evidence of a centrally mediated mechanism governing each of these adaptive processes. Methods: Participants (n = 22, 52.5 ± 6.2 years old) of both sexes were previously selected. Perfusion was recorded in both feet by laser Doppler flowmetry (LDF) and photoplethysmography (PPG). Two different maneuvers with opposite impacts on perfusion were applied as challengers to single limb reactive hyperemia evoked by massage and a single leg pending to generate a VAR. Measurements were taken at baseline (Phase I), during challenge (Phase II), and recovery (Phase III). A 95% confidence level was adopted. As proof of concept, six additional young healthy women were selected to provide video imaging by using optoacoustic tomography (OAT) of suprasystolic post-occlusive reactive hyperemia (PORH) in the upper limb. Results: Modified perfusion was detected by LDF and PPG in both limbs with both hyperemia and VAR, with clear systemic hemodynamic changes in all participants. Comparison with data obtained under the same conditions in a younger cohort, previously published by our group, revealed that results were not statistically different between the groups. Discussion: The OAT documentary and analysis showed that the suprasystolic pressure in the arm changed vasomotion in the forearm, displacing blood from the superficial to the deeper plexus vessels. Deflation allowed the blood to return and to be distributed in both plexuses. These responses were present in all individuals independent of their age. They appeared to be determined by the need to re-establish hemodynamics acutely modified by the challenger, which means that they were centrally mediated. Therefore, a new mechanistic interpretation of these exploratory maneuvers is required to better characterize in vivo cardiovascular physiology in humans.

INFLUENCE OF THE AMOUNT OF COMPRESSION ON VENOUS AND ARTERIAL BLOOD FLOW VELOCITY AND SKIN MICROCIRCULATION OF THE LOWER EXTREMITY

OBJECTIVE

The aim: To determine the effect of compression on the venous and arterial velocity of the main blood flow of the lower limb and the skin microcirculation of the rear part of the foot.

PATIENTS AND METHODS

Materials and methods: 20 healthy subjects participated in this study: 11 men 11 (55%) men and 9 (45%) girls. The ankle brachial index (ABI), femoropop¬liteal index, femoral arterial blood flow velocity (AFV), venous blood flow velocity (VFV), transcutaneous oxygen pressure (tcPO2) and carbon dioxide pressure (tcPCO2) were measured. After the general measurements were taken, the tire was inflated to 10 mm Hg under general basic conditions and kept for three minutes. The experiment ended when no decrease in tcPO2 was observed between two consecutive pressure levels.

RESULTS

Results: The average tire pressure to reach physiological zero was 80 mm Hg. for all participants. At 10 mmHg significant changes in indicators were found by 19% (p=0.0001). tcPCO2 values increased significantly at 10 mmHg (p=0.0319) and continued to increase until the end of the study. It was established that its values increased by 14% compared to the input data (p=0.0005).

CONCLUSION

Conclusions: At the maximum compression of 60 mmHg the arterial blood flow rate decreased by 5.5 times (p=0.0001). TcPCO2 increases significantly when compressed by 10 mm Hg also in parallel with the decrease in the regional perfusion index, which begins at an external compression of 40 mm Hg, which is evidence of the deterioration of the perfusion of the skin of the anterior part of the foot in healthy subjects.

Impact of compression on velocity of venous and arterial main blood flow and cutaneous microcirculation of the lower extremity

Objective. To study the impact of compression on velocity of venous and arterial main blood flow of the lower extremity, as well as cutaneous microcirculation in the back part of the foot in healthy individuals and patients with decompensated forms of varicose disease and postthrombophlebitis syndrome. Materials and methods. In the investigation 56 individuals took part and divided into three groups: Group I – 20 healthy persons; Group II – 15 patients with varicose disease in decompensated stage; Group III– 21 patients with decompensated stage of postthrombophlebitis syndrome. In all participants of the investigation the index of ankle–brachial pressure, deep–femoro–popliteal index, the regional perfusion index, transcutaneous partial pressure of oxygen and partial pressure of carbon dioxide, the arterial blood flow velocity in femoral artery and of venous blood flow distally from sapheno–femoral junction were measured before and after application of elastic medical knitwear of various Class of compression or the cuff pressure. Results. In the Class III compression in patients of Group III the transcutaneously registered indices crossing have occurred between partial pressure of oxygen and carbon dioxide, accompanied by domination of the carbon dioxide partial pressure over the oxygen partial pressure while further enhancement of the compression Class. In patients of Group II this tendency was observed while application of Class IV compression only. At the investigation beginning the values of partial pressure of carbon dioxide registered were higher in the Group III patients, than in the patients of Group II (p=0.0001). Conclusion. While application of the Class III compression the velocity of the hip venous blood flow, comparing with its initial values, have lowered at average by 78% in patients of Group II and at average in 7.4 times in the patients of |Group III (p=0.0001). It is affordable in patients, suffering decompensated postthrombophlebitic syndrome, to apply the elastic compression of Classes I–II, while in those, having varicose disease in decompensated stage, – the elastic compression of Classes III and iV as well.

Skin necrosis following sclerotherapy. Part 1: Differential diagnosis based on classification of pathogenic mechanisms

Background: Tissue necrosis is a significant but uncommon complication of sclerotherapy. The pathogenic mechanisms of this often-debilitating complication have been poorly described in the literature.Purpose: To elucidate the pathological mechanisms, we propose a morphological approach to classify sclerotherapy-induced skin necrosis into two categories of round and stellate (star-like) necrosis.Research Design: Comprehensive literature review was conducted.Results: Round necrosis is typically caused by extravasation of sclerosants. It typically presents as an ulcer with smooth and non-geographic borders. Historically, extravasation has been cited as the main cause of sclerotherapy-related necrosis. While this may be the case with osmotic or irritant sclerosants, it is far less likely with the use of detergent agents particularly in the foam format.The more commonly encountered pattern of stellate necrosis is an ischaemic ulcer secondary to arterial/arteriolar occlusion. In contrast to round necrosis, stellate necrosis follows an intra-vascular injection of sclerosants such as an inadvertent intra-arterial injection. But more frequently, stellate necrosis may follow a perfectly executed intra-venous or intra-telangiectatic delivery of sclerosants. Several pathogenic pathways can be considered. The physiologic response of veno-arteriolar reflex vasospasm (VAR-VAS) is possibly the most frequent pathway. It follows a high-pressure injection of the sclerosant in a target vein resulting in a rapid rise of intravenous pressures which in-turn would trigger a sympathetic neuronal reflex vasospasm of the pre-capillary sphincters and a corresponding opening of the normally closed arterio-venous anastomoses (AVAs). This communication would allow entry of the sclerosing agent into the arteriolar side of the circulation resulting in arteriolar occlusion and infarction of the corresponding skin. Similarly, an intravenous administration of sclerosants in the vicinity of defective boundary valves or persistently open AVAs can result in the entry of detergent agents into the arteriolar side of the microvasculature causing an ischemic stellate ulcer.Conclusions: In this first instalment of these two-part series, we review the pathogenic mechanisms of post-sclerotherapy necrosis. In the second instalment, we describe risk minimisation and management strategies.

Lower Limb Perfusion Asymmetries in Humans at Rest and Following Activity—A Collective View

The significance of lower limb perfusion asymmetries remains unknown in healthy individuals. Our study aims to understand how factors such as posture, sex, age, and body weight relate to perfusion. Data from studies previously published by our group, including experiments using laser Doppler flowmetry as the gold standard for perfusion measurements in baseline, (various) challenge, and recovery phases was assembled from a total of 139 healthy participants. Body position was shown to be a primary determinant of perfusion asymmetry, especially in women. Effects of sex and age were also analyzed. In a supine position, perfusion asymmetries seemed to relate negatively in the aged group of participants, where challenge and recovery seemed to follow different processes. In the upright position, young men and women have shown comparable distributions and asymmetry ratios at baseline and recovery. In the aged group, differences between sexes were observed at baseline, but again, the course of the asymmetry ratios with challenge was essentially similar in men and women. Our analysis suggests that ageing is a critical determinant in our upright study sample, as higher baseline asymmetries and longer recoveries after challenge were linked in older males with higher body mass index (BMI).

Oral Glucose Load and Human Cutaneous Microcirculation: An Insight into Flowmotion Assessed by Wavelet Transform

Simple Summary

There is increasing evidence to suggest that microcirculation becomes dysfunctional earlier than large blood vessels or the heart in several diseases. In diabetes mellitus, a disease characterized by chronic hyperglycemia, microvascular impairment is well-established; on the contrary, the effect of acute hyperglycemia in microcirculation remains unclarified. Our aim was to investigate the microvascular effect of an oral glucose load (OGL) using laser Doppler flowmetry (LDF) as a perfusion quantification technique, coupled with wavelet transform (WT) to perform a spectral decomposition of the LDF signal. On two distinct occasions (pre-load and post-load), sixteen healthy subjects drank either a standard glucose solution or water. Perfusion was assessed by LDF and WT while resting and during post-occlusive reactive hyperemia (PORH), evoked by a transient three-min occlusion of the brachial artery, in the forearm and the finger pulp. The OGL affected microcirculation in both sites compared to water, significantly blunting the PORH response in the forearm. The WT revealed significant differences in the cardiac and sympathetic components after OGL between the pre-load and post-load periods. These results suggest that an OGL induces a short-term subtle microvascular impairment, probably involving a modulation of the sympathetic nervous system.

Abstract

Microcirculation in vivo has been assessed using non-invasive technologies such as laser Doppler flowmetry (LDF). In contrast to chronic hyperglycemia, known to induce microvascular dysfunction, the effects of short-term elevations in blood glucose on microcirculation are controversial. We aimed to assess the impact of an oral glucose load (OGL) on the cutaneous microcirculation of healthy subjects, quantified by LDF and coupled with wavelet transform (WT) as an interpretation tool. On two separate occasions, sixteen subjects drank either a glucose solution (75 g in 250 mL water) or water (equal volume). LDF signals were obtained in two anatomical sites (forearm and finger pulp) before and after each load (pre-load and post-load, respectively), in resting conditions and during post-occlusive reactive hyperemia (PORH). The WT allowed decomposition of the LDF signals into their spectral components (cardiac, respiratory, myogenic, sympathetic, endothelial NO-dependent). The OGL blunted the PORH response in the forearm, which was not observed with the water load. Significant differences were found for the cardiac and sympathetic components in the glucose and water groups between the pre-load and post-load periods. These results suggest that an OGL induces a short-term subtle microvascular impairment, probably involving a modulation of the sympathetic nervous system.

Spatial heterogeneity of cutaneous blood flow respiratory-related oscillations quantified via laser speckle contrast imaging

LSCI technique provides experimental data which can be considered in the context of spatial blood flow coherency. Analysis of vascular tone oscillations gives additional information to ensure a better understanding of the mechanisms affecting microvascular physiology. The oscillations with different frequencies are due to different physiological mechanisms. The reasons for the generation of peripheral blood flow oscillations in the 0.14-0.6 Hz frequency band are as follows: cardio-respiratory interactions, pressure variations in the venous part of the circulatory system, and the effect of the sympathetic nervous system on the vascular tone. Earlier, we described the spatial heterogeneity of around 0.3 Hz oscillations and this motivated us to continue the research to find the conditions for the occurrence of spatial phase synchronization. For this purpose, a number of physiological tests (controlled respiration, breath holder, and venous occlusion tests) which influence the blood flow oscillations of 0.14-0.6 Hz were considered, an appropriate measurement system and the required data processing algorithms were developed. At spontaneous respiration, the oscillations with frequencies around 0.3 Hz were stochastic, whereas all the performed tests induced an increase in spatial coherence. The protocols and methods proposed here can help to clarify whether the heterogeneity of respiratory-related blood flow oscillations exists on the skin surface.

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.

Lower limb massage in humans increases local perfusion and impacts systemic hemodynamics

Massage is commonly used as a complementary therapy for many different conditions. Demonstration of its physiological impact and understanding of its therapeutic mechanisms is still insufficient and often inconclusive. This study aims to characterize the physiological effects of effleurage, one of the most popular techniques, on human in vivo microcirculation and its impact on cardiovascular function. Two differently oriented variations of the technique, referred to influence physiological outcomes, were applied to 32 young (mean 19.8 ± 1.6 yr old) healthy volunteers of both sexes in a single, randomly chosen limb after informed written consent. Each protocol included a 10-min baseline (Phase I), a 5-min massage (Phase II), and a 10-min recovery (Phase III) register. A 30-min washout period separated both protocols. Perfusion was assessed by laser Doppler flowmetry (LDF) and reflection photoplethysmography (PPG), with their sensors applied distally in both feet. Blood pressure and pulse were also obtained. LDF signals were further analyzed in their components by the (Morlet) wavelet transform to probe the mechanisms involved. Results showed that effleurage consistently evoked a significant (P < 0.001) perfusion increase in the massaged limb, also visible in the contralateral limb (not significant) independently from the orientation (variant) used. No matter the perfusion differences known between sexes, the adaptive response was equivalent in both sexes. The component analysis of the LDF curves also suggests that these procedures, although brief and superficial, do modify multiple components of cardiovascular integration, with cardiac, respiratory, and myogenic components appearing to play a major role in reestablishing distal microcirculatory homeostasis.NEW & NOTEWORTHY The impact of effleurage, a well-known massage procedure used in human rehabilitation, in the lower limb hemodynamics, is demonstrated. When applied in a sole limb, massage increases skin microcirculatory flowmotion not only locally but also beyond, affecting systemic hemodynamics. This observation is an interesting example of the efficacy of cardiovascular integration mechanisms involving distal microcirculatory homeostasis. The proposed methodology allows a mechanistic view over skin flowmotion regulation, being applicable to further explore massage and its impact on microcirculatory physiology.

Texture Analysis is a Useful Tool to Assess the Complexity Profile of Microcirculatory Blood Flow

The quantitative assessment of cardiovascular functions is particularly complicated, especially during any physiological challenge (e.g., exercise), with physiological signals showing intricate oscillatory properties. Signal complexity is one of such properties, and reflects the adaptability of the physiological systems that generated them. However, it is still underexplored in vascular physiology. In the present study, we calculate the complexity of photoplethysmography (PPG) signals and their frequency components obtained with the wavelet transform (WT), with two analytical tools—(i) texture analysis (TA) of WT scalograms, and (ii) multiscale entropy (MSE) analysis. PPG signals were collected from twelve healthy young subjects (26.0 ± 5.0 y.o.) during a unilateral leg lowering maneuver to evoke the venoarteriolar reflex (VAR) while lying supine, with the contralateral leg remaining stationary. Results showed that TA was able to detect a decrease in complexity, viewed as an increase in texture entropy (TE), of the PPG scalograms during VAR, similarly to MSE, suggesting that a decrease in the competence of vascular regulation mechanisms might be present during VAR. Nonetheless, TA showed lower sensitivity than MSE for low frequency spectral regions. TA seems to be a promising and straightforward analytical tool for the assessment of the complexity of PPG perfusion signals.

KCa and KV channels modulate the venoarteriolar reflex in non-glabrous human skin with no roles of KATP channels, NOS, and COX

The venoarteriolar reflex is a local mechanism that induces vasoconstriction during venous congestion in various tissues, including skin. This response is thought to play a critical role in minimizing capillary damage or edema resulting from overperfusion, though factors that modulate this response remain largely unknown. Here, we hypothesized that nitric oxide synthase (NOS), cyclooxygenase (COX), and Ca²⁺-activated, ATP-sensitive, and voltage-gated K⁺ channels (K_Ca, K_ATP, and K_V channels, respectively) modulate the venoarteriolar reflex in human skin. Cutaneous blood flow (laser-Doppler flowmetry) was monitored during a 3-min pre-occlusion baseline and following a 3-min venous occlusion of 45 mmHg, the latter maneuver was used to induce the venoarteriolar reflex. The venoarteriolar reflex was assessed at the following forearm skin sites: Experiment 1 (n = 11): 1) lactated Ringer solution (Control), 2) 10 mM N^ω-nitro-_L-arginine (NOS inhibitor), 3) 10 mM ketorolac (COX inhibitor), and 4) combined NOS + COX inhibition; Experiment 2 (n = 15): 1) lactated Ringer solution (Control), 2) 50 mM tetraethylammonium (K_Ca channel blocker), 3) 5 mM glybenclamide (K_ATP channel blocker), and 4) 10 mM 4-aminopyridine (K_V channel blocker). Separate and combined NOS and COX inhibition as well as K_ATP channel blocker had no effect on venoarteriolar reflex. Conversely, venoarteriolar reflex was attenuated by K_Ca channel blockade (36-38%) and augmented by K_V channel blockade (38-55%). We showed that K_Ca and K_V channels modulate the venoarteriolar reflex with minimum roles of NOS, COX, and K_ATP channels in human non-glabrous forearm skin in vivo. Thus, cutaneous venoarteriolar reflex changes could reflect altered K⁺ channel function.

EEMCO Guidance for the in vivo Assessment of Biomechanical Properties of the Human Skin and Its Annexes: Revisiting Instrumentation and Test Modes

Biomechanics of the skin is an important subject in skin research. It has been studied for many decades involving various technologies and methods to characterize and quantify mechanical properties of the skin under different in vivo conditions. The present EEMCO paper reviews the current rel-evant information, providing practical orientation to researchers dedicated to in vivo assessment of biomechanics of skin and its annexes. We discuss the available non-invasive instruments, including their principles and variables. A correspondence between the descriptors nomenclature proposed by Agache and the designation for the suction-based standard instruments is proposed. The addressed properties include skin softness/stiffness, firmness, elasticity, elastic and viscoelastic properties, extensibility, resilience, anisotropy, acoustical shock wave hardness, friction (in relation to topographic properties), thickness, fiber/stress mechanics (bending, cyclic, tensile, fatigue, or torsion), and hardness. We provide the relation of these properties to biomechanical descriptors and in some cases to SI units. Practical guidance for the proper use of these instruments, limitations, and possible interpretations are provided, while discussing the meaning of descriptive or "phenomenological" variables. For studies intended to quantify the effect of an intervention with regard to mechanical properties, we recommend a minimum of 30-40 participants, based on normal distribution of the data sets. Some important limitations are recognized, including the lack of standardization of procedures and calibration of instruments, which compromises the relevance and real nature of the descriptors/parameters obtained with these devices. The present work highlights an approach to a better practice and a science-supported biomechanical assessment of human skin, hair, and nails.

Different lasers reveal different skin microcirculatory flowmotion - data from the wavelet transform analysis of human hindlimb perfusion

Laser Doppler flowmetry (LDF) and reflection photoplethysmography (PPG) are standard technologies to access microcirculatory function in vivo. However, different light frequencies mean different interaction with tissues, such that LDF and PPG flowmotion curves might have distinct meanings, particularly during adaptative (homeostatic) processes. Therefore, we analyzed LDF and PPG perfusion signals obtained in response to opposite challenges. Young healthy volunteers, both sexes, were assigned to Group 1 (n = 29), submitted to a normalized Swedish massage procedure in one lower limb, increasing perfusion, or Group 2 (n = 14), submitted to a hyperoxia challenge test, decreasing perfusion. LDF (Periflux 5000) and PPG (PLUX-Biosignals) green light sensors applied distally on both lower limbs recorded perfusion changes for each experimental protocol. Both techniques detected the perfusion increase with massage, and the perfusion decrease with hyperoxia, in both limbs. Further analysis with the wavelet transform (WT) revealed better depth-related discriminative ability for PPG (more superficial, less blood sampling) compared with LDF in both challenges. Spectral amplitude profiles consistently demonstrated better sensitivity for LDF, especially regarding the lowest frequency components. Strong correlations between components were not found. Therefore, LDF and PPG flowmotion curves are not equivalent, a relevant finding to better study microcirculatory physiology.