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New findings What is the topic of this review? We describe a range of techniques in the time, frequency and information domains and their application alone and together for the analysis of blood flux signals acquired using laser Doppler fluximetry. What advances does it highlight? This review highlights the idea of using quantitative measures in different domains and scales to gain a better mechanistic understanding of the complex behaviours in the microcirculation. Abstract To date, time- and frequency-domain metrics of signals acquired through laser Doppler fluximetry have been unable to provide consistent and robust measures of the changes that occur in the microcirculation in healthy individuals at rest or in response to a provocation, or in patient cohorts. Recent studies have shown that in many disease states, such as metabolic and cardiovascular disease, there appears to be a reduction in the adaptive capabilities of the microvascular network and a consequent reduction in physiological information content. Here, we introduce non-linear measures for assessing the information content of fluximetry signals and demonstrate how they can yield deeper understanding of network behaviour. In addition, we show how these methods may be adapted to accommodate the multiple time scales modulating blood flow and how they can be used in combination with time- and frequency-domain metrics to discriminate more effectively between the different mechanistic influences on network properties.

An increased and more effective microvascular perfusion is postulated to play a key role in the physiological adaptation of Sherpa highlanders to the hypobaric hypoxia encountered at high altitude. To investigate this, we used Lempel-Ziv complexity (LZC) analysis to explore the spatiotemporal dynamics of the variability of the skin microvascular blood flux (BF) signals measured at the forearm and finger, in 32 lowlanders (LL) and 46 Sherpa highlanders (SH) during the Xtreme Everest 2 expedition. Measurements were made at baseline (BL) (LL: London 35 m; SH: Kathmandu 1300 m) and at Everest base camp (LL and SH: EBC 5,300 m). We found that BF signal content increased with ascent to EBC in both SH and LL. At both altitudes, LZC of the BF signals was significantly higher in SH, and was related to local slow-wave flow-motion activity over multiple spatial and temporal scales. In SH, BF LZC was also positively associated with LZC of the simultaneously measured tissue oxygenation signals. These data provide robust mechanistic information of microvascular network functionality and flexibility during hypoxic exposure on ascent to high altitude. They demonstrate the importance of a sustained heterogeneity of network perfusion, associated with local vaso-control mechanisms, to effective tissue oxygenation during hypobaric hypoxia.

Objective: This study investigates the feasibility of the use of nonlinear complexity methods as a tool to identify altered microvascular function often associated with pathological conditions. We evaluate the efficacy of multiscale nonlinear complexity methods to account for the multiple time-scales of processes modulating microvascular network perfusion. Methods: Microvascular blood flux (BF) and oxygenation (OXY: oxyHb, deoxyHb, totalHb and SO2%) signals were recorded simultaneously at the same site, from the skin of 15 healthy young male volunteers using combined laser Doppler fluximetry (LDF) and white light spectroscopy. Skin temperature was clamped at 33 °C prior to warming to 43 °C to generate a local thermal hyperaemia (LTH). Conventional and multiscale variants of sample entropy (SampEn) were used to quantify signal regularity and Lempel and Ziv (LZ) and effort to compress (ETC) to determine complexity. Results: SampEn showed a decrease in entropy during LTH in BF (p = 0.007) and oxygenated haemoglobin (oxyHb) (p = 0.029). Complexity analysis using LZ and ETC also showed a significant reduction in complexity of BF (LZ, p = 0.003; ETC, p = 0.002) and oxyHb (p < 0.001, for both) with LTH. Multiscale complexity methods were better able to discriminate between haemodynamic states (p < 0.001) than conventional ones over multiple time-scales. Conclusion: Our findings show that there is a good discrimination in complexity of both BF and oxyHb signals between two haemodynamic steady states which is consistent across multiple scales. Significance: Complexity-based and multiscale-based analysis of BF and OXY signals can identify different microvascular functional states and thus has potential for clinical application in the prognosis and the diagnosis of pathophysiological conditions such as microvascular dysfunction observed in non-alcoholic fatty liver disease and type 2 diabetes.

The maintenance of an adequate microvascular perfusion sufficient to meet the metabolic demands of the tissue is dependent on neural, humoral and local vaso-mechanisms that determine vascular tone and blood flow patterns within a microvascular network. It has been argued that attenuation of these flow patterns may be a major contributor to disease risk. Thus, quantitative information on the in vivo spatio-temporal behaviour of microvascular perfusion is important if we are to understand network functionality and flexibility in cardiovascular disease. Time and frequency-domain analysis has been extensively used to describe the dynamic characteristics of Laser Doppler flowmetry (LDF) signals obtained from superficial microvascular networks such as that of the skin. However, neither approach has provided definitive and consistent information on the relative contribution of the oscillatory components of flowmotion (endothelial, neurogenic, myogenic, respiratory and cardiac) to a sustained and adequate microvascular perfusion; nor advance our understanding of how such processes are collectively modified in disease. More recently, non-linear complexity-based approaches have begun to yield evidence of a declining adaptability of microvascular flow patterns as disease severity increases. In this chapter we review the utility and application of these approaches for the quantitative, mechanistic exploration of microvascular (dys)function.

Objective: The objective of this study was to evaluate the effect of Kangaroo Position (KP) in microcirculation (MC) of the flexor muscles of preterm newborns. Method: A controlled clinical trial was conducted in the city of Recife, Brazil, with 26 preterm children randomized in the Kangaroo Group (13) and in the Control Group (13). Assessments of blood flow, temperature, and tissue oxygen saturation (SO2) were made at two different times and in the biceps brachii muscle and hamstrings muscle group: before the KP and after 24 h of KP. In the Control Group, the registrations were performed at the times corresponding to those of the Kangaroo Group. The mean values among the times were analyzed by paired t-test for repeated measures. The clinical trial was recorded in Clinical Trials (NCT03611088). Results: In the Kangaroo Group there was an increase in tissue temperature and blood flow at the time evaluation periods (p < 0.05). In the control group, there was no statistical difference between the recording moments hamstring muscles group, but in the biceps brachii, there was a reduction in mean blood flow (p = 0.023). Conclusion: In conclusion, the KP has effects on the microcirculation of the flexor muscles of preterm newborns.

Background Non-alcoholic fatty liver disease (NAFLD) represents a spectrum of fat-related conditions ranging from simple fatty liver, to non-alcoholic steatohepatitis (NASH), fibrosis and cirrhosis. There is growing evidence that NAFLD is a multisystem disease, affecting several extra-hepatic organs and regulatory pathways. Furthermore, since the gut and liver are linked anatomically via the portal vein, disturbances of the gut microbiota (dysbiosis) can affect the liver. Objectives In patients with NAFLD, we are testing the effects of a synbiotic which is the combination of a prebiotic (fructooligosaccharides; 4 g/day) and a probiotic ( Bifidobacterium animalis subsp. lactis BB-12 at a minimum of 10 billion CFU/day) on a) liver fat percentage, b) NAFLD fibrosis algorithm scores, c) gut microbiota composition. Additionally, there will be several hypothesis-generating secondary outcomes to understand the metaorganismal pathways that influence the development and progression of NAFLD, type 2 diabetes, and cardiovascular risk. Design In a randomised double-blind placebo-controlled trial, 104 participants were randomised to 10–14 months intervention with either synbiotic (n = 55) or placebo (n = 49). Recruitment was completed in April 2017 and the last study visit will be completed by April 2018. Methods Change in gut microbiota composition will be assessed using 16S ribosomal RNA gene sequencing. Change in mean liver fat percentage will be quantified by magnetic resonance spectroscopy (MRS). In addition, change in liver fat severity will be measured using two NAFLD fibrosis algorithm scores. The INSYTE study was approved by the local ethics committee (REC: 12/SC/0614) and is registered at www.clinicaltrials.gov as NCT01680640 .

The enhanced liver fibrosis (LFS) score and the nonalcoholic fatty liver disease (NAFLD) fibrosis score (NFS) are algorithmic-derived scores for diagnosing severe (F3/F4) liver fibrosis. In a pilot, substudy of the Wessex Evaluation of fatty Liver and Cardiovascular markers in NAFLD with OMacor thErapy (WELCOME) trial, we tested whether measurements of plasma platelet-, endothelial-, and leukocyte-derived extracellular vesicles (EVs) counts are (a) associated with, and predict, F3/F4 fibrosis and (b) able to improve risk prediction of F3/F4 fibrosis in NAFLD, building upon LFS or NFS algorithms. Twenty-six individuals with NAFLD had liver fibrosis severity determined by Kleiner scoring after liver biopsy. Plasma samples stained with CD41a, CD42b, CD31, CD105, CD14, CD16, and CD284 antibodies were analyzed using flow cytometry to measure platelet-, endothelial-, and leukocyte-derived EVs counts. The independence of associations between EVs and F3/F4 fibrosis were tested using logistic regression. Receiver operator characteristic (ROC) curves were used to evaluate F3/F4 fibrosis prediction models. LFS was more strongly associated with F3/F4 fibrosis than NFS (χ2 = 15.403, P < 0.0001, and χ2 = 6.300, P = 0.012, respectively). The association between LFS and F3/F4 fibrosis was further improved by addition of CD14+ EVs (χ2 = 20.847, P = 0.016 vs. χ2 = 12.803 P = 0.015, respectively) or CD16+ EVs (χ2 = 22.205, P = 0.009 vs. χ2 = 17.559 P = 0.001, respectively), and the area under the ROC for LFS (AUC = 0.915, se = 0.055, P = 0.001) was increased by the addition of CD14+ or CD16+ EVs (AUC = 0.948, se = 0.042, and P < 0.001 and AUC = 0.967, se = 0.055, P < 0.001, respectively) as predictor variables. In this small preliminary study, CD14+ and CD16+ EV counts show potential to predict liver fibrosis severity with either marker improving the ability of the LFS to identify F3/F4 fibrosis in this small preliminary cohort study. In a small preliminary study, leukocyte extracellular vesicles show an inverse association with liver fibrosis in NAFLD, warranting their further investigation as biomarkers.

Summary Background & aims Non-alcoholic fatty liver disease (NAFLD) is a liver condition characterised by liver fat accumulation and often considered to be the liver manifestation of metabolic syndrome. The aim of this study was to examine in patients with NAFLD the system-wide effects of treatment with docosahexaenoic acid + eicosapentaenoic acid (DHA + EPA) versus placebo on the plasma proteome. Methods Plasma from patients that participated in a 15–18 months randomised, double-blind placebo-controlled trial testing the effects of 4 g DHA + EPA daily was analysed using depletion-free quantitative proteomics. Results Bioinformatics interpretation of the proteomic analysis showed that DHA + EPA treatment affected pathways involving blood coagulation, immune/inflammatory response and cholesterol metabolism (p < 0.05). Two key proteins of cardiovascular risk, prothrombin and apolipoprotein B-100, were shown to decrease as a result of DHA + EPA supplementation [Prothrombin: Males DHA + EPA Mean iTRAQ log2ratio (SD) = −0.13 (0.20) p = 0.05, Females DHA + EPA Mean iTRAQ log2ratio (SD) = −0.48 (0.35) p = 0.03; Apo B-100: Males DHA + EPA Mean iTRAQ log2ratio (SD) = −0.24 (0.16) p = 0.01, Females DHA + EPA Mean iTRAQ log2ratio (SD) = −0.15 (0.05) p = 0.02]. Conclusions Plasma proteomics applied in a randomised, placebo-controlled trial showed that high dose DHA + EPA treatment in patients with NAFLD affects multiple pathways involved in chronic non-communicable diseases.

Attractor reconstruction analysis has been previously used to determine changes in the shape and variability of fairly periodic signals such as arterial blood pressure signals and electroencephalogram signals, providing a two-dimensional attractor with features like density and symmetry. Since BF signals are fairly periodic and quasi-stationary, we set out to investigate whether attractor reconstruction method could be applied in signals derived from the microvascular perfusion. We describe the basis and the implementation of attractor reconstruction analysis of the microvascular blood flux (BF) signals recorded from the skin of 15 healthy male volunteers, age 29.2 ± 8.1y (mean ± SD). The efficacy of attractor reconstruction analysis (ARA) as a potential method of identifying changes in the microvascular function is evaluated in two haemodynamic steady states, at 33°C, and during warming at 43°C to generate a local thermal hyperaemia (LTH). Our findings show a significant drop of the maximal density derived from the ARA, during increased flow and that there was good discrimination of the blood flow signals between the two haemodynamic steady states, having good classification accuracy (80%). This study shows that ARA of BF signals can identify different microvascular functional states and thus has a potential for the clinical assessment and diagnosis of pathophysiological condition.

Knowing how biomarker levels vary within biological fluids over time can produce valuable insight into tissue physiology and pathology, and could inform personalised clinical treatment. We describe here a wearable sensor for monitoring biomolecule levels that combines continuous fluid sampling with in situ analysis using wet-chemical assays (with the specific assay interchangeable depending on the target biomolecule). The microfluidic device employs a droplet flow regime to maximise the temporal response of the device, using a screw-driven push-pull peristaltic micropump to robustly produce nanolitre-sized droplets. The fully integrated sensor is contained within a small (palm-sized) footprint, is fully autonomous, and features high measurement frequency (a measurement every few seconds) meaning deviations from steady-state levels are quickly detected. We demonstrate how the sensor can track perturbed glucose and lactate levels in dermal tissue with results in close agreement with standard off-line analysis and consistent with changes in peripheral blood levels., Continuous real-time measurement of biomarker levels in body fluids offers many exciting possibilities. Here, the authors develop an integrated wearable droplet microfluidic sensor that combines continuous sampling of tissue fluid with in situ analysis using wet-chemical assays.

Skin microdialysis (SMD) is a versatile sampling technique that can be used to recover soluble endogenous and exogenous molecules from the extracellular compartment of human skin. Due to its minimally invasive character, SMD can be applied in both clinical and preclinical settings. Despite being available since the 1990s, the technique has still not reached its full potential use as a tool to explore pathophysiological mechanisms of allergic and inflammatory reactions in the skin. Therefore, an EAACI Task Force on SMD was formed to disseminate knowledge about the technique and its many applications. This position paper from the task force provides an overview of the current use of SMD in the investigation of the pathogenesis of chronic inflammatory skin diseases, such as atopic dermatitis, chronic urticaria, psoriasis, and in studies of cutaneous events during type 1 hypersensitivity reactions. Furthermore, this paper covers drug hypersensitivity, UVB-induced- and neurogenic inflammation, and drug penetration investigated by SMD. The aim of this paper is to encourage the use of SMD and to make the technique easily accessible by providing an overview of methodology and applications, supported by standardized operating procedures for SMD in vivo and ex vivo. Electronic supplementary material The online version of this article (10.1186/s13601-019-0262-y) contains supplementary material, which is available to authorized users.

Introduction Endothelial derived hyperpolarization (EDH) is an important path to vasodilatation especially in small arteries, and is more important in women and the elderly. Our previous work has shown that this becomes impaired in mice that had experienced a high fat diet during gestation up to weaning, with concomitant reduction in endothelial surface KCa3.1 expression.1 We have tested the idea that altered redox status affects the location of KCa3.1 in human dermal microvascular endothelial cells (HDMECs). Methods HDMECs were obtained from PromoCell (Heidelberg, Germany) and cultured in MV2 growth medium containing 1% penicillin-streptomycin in 5% O2, 5% CO2 at 37°C to passage 6 and 7 in the SCI-tive Physiological Oxygen Workstation from Baker Ruskinn (Maine, USA) for at least 5 days before experiments. The cells were plated on fibronectin (10 µg.ml-1) coated 8 well micro-slides (Ibidi, Martinsried, Germany) and incubated for 48 hour, treated with PBS or H2O2100 µM in PBS for 10 min., and fixed with 4% formalin. Immunofluorescence was performed by incubating with anti-KCa3.1 mouse monoclonal antibody (AL-051 Alomone, Israel) at 4°C overnight, with half of the wells being treated with 2% Triton-X to permeablize the cells. The Alexa 488 labelled anti-mouse antibody for 1 hour and Texas Red Lycopersicon Esculentum Lectin (to stain the cell surface) for 20 min, were applied to the cells at room temperature and finally the DAPI nuclear stain was applied for 3 min. The cells were examined using a x60 1.3 NA oil-immersion objective and images captured via a Hamamatsu RG3 camera into a computer. Using ImageHopper software and computer-driven focussing device (Prior Instruments, UK) we took 10 serial images of KCa3.1at 1.0 µm intervals, which were integrated using Image J. These images were analysed for the fractional area of an endothelial cell occupied by KCa3.1, defined as bright spots between 1 to 4 µm diameter in the relevant fluorescence channel. Results The density of channels on the surface, defined as the integrated image of non-permeablized KCa3.1 channels, was 9.5±0.68 µm-2 × 103 (mean ±sem), while in the permeablized cells the density within the whole cell area was 13.9±1.89 µm-2 × 103 (p Conclusion Thus even a brief exposure to oxygen stress will result in the diminution of KCa3.1 on endothelial surface, and this may have implications for the ability of arterioles to dilate. Reference Stead R, et al. J Hypertens2016;34:452–63.

The effect of n-3 fatty acid treatment on temperature perception as a sensory nerve function modality is uncertain. In patients with non-alcoholic fatty liver disease (NAFLD) both with and without type 2 diabetes, we: (1) tested whether 15-18 months' treatment with 4 g/day of docosahexaenoic plus eicosapentaenoic acid (DHA+EPA) improved hot (HPT) and cold (CPT) temperature perception thresholds and (2) explored factors associated with HPT and CPT, in a randomised, double-blind, placebo-controlled trial.The effect of treatment (n = 44) on HPT, CPT and temperature perception index (TPI: difference between HPT and CPT) was measured at the big toe in 90 individuals without neuropathy (type 2 diabetes; n = 30). Participants were randomised 1:1, using sequential numbering, by personnel independent from the trial team. All participants and all members of the research team were blinded to group assignment. Data were collected in the Southampton National Institute for Health Research Biomedical Research Centre. Treatment effects and the independence of associations were testing by regression modelling.Mean ± SD age was 50.9 ± 10.6 years. In men (n = 53) and women (n = 37), HPTs (°C) were 46.1 ± 5.1 and 43.1 ± 6.4 (p = 0.02), CPTs (°C) were 22.7 ± 3.4 and 24.5 ± 3.6 (p = 0.07) and TPIs (°C) were 23.4 ± 7.4 and 18.7 ± 9.5 (p = 0.008), respectively. In univariate analyses, total body fat percentage (measured by dual-energy x-ray absorptiometry [DXA]) was associated with HPT (r = -0.36 p = 0.001), CPT (r = 0.35 p = 0.001) and TPI (r = 0.39 p = 0.0001). In multivariable-adjusted regression models, adjusting for age, sex and other potential confounders, only body fat percentage was independently associated with HPT, CPT or TPI (p = 0.006, p = 0.006 and p = 0.002, respectively). DHA+EPA treatment did not modify HPT, CPT or TPI (p = 0.93, p = 0.44 and p = 0.67, respectively). There were no important adverse effects or side effects reported.Higher body fat percentage is associated with enhanced temperature perception. There was no benefit of treatment with high-dose n-3 fatty acids on the thresholds to detect hot or cold stimuli.ClinicalTrials.gov NCT00760513 FUNDING: This work was supported by the National Institute for Health Research through the NIHR Southampton Biomedical Research Unit grant and by a Diabetes UK allied health research training fellowship awarded to KMcC (Diabetes UK. BDA 09/0003937).

Background and aims: n-3 polyunsaturated fatty acid (PUFA) treatment may decrease liver fat in non-alcoholic fatty liver disease (NAFLD), but uncertainty exists whether this treatment also decreases cardiovascular disease (CVD) risk in NAFLD. We tested whether 15–18 months n-3 PUFA [docosahexaenoic acid (DHA) and eicosapentaenoic acid] (Omacor/Lovaza, 4 g/day) vs placebo decreased carotid intima-media thickness (CIMT) progression, a surrogate marker of CVD risk. We also evaluated if improvement in markers of NAFLD severity was associated with decreased CIMT progression over time.Methods: In a pre-specified sub-study of the WELCOME (Wessex Evaluation of fatty Liver and Cardiovascular markers in NAFLD with OMacor thErapy) trial (NCT00760513), CIMT was measured using B-mode ultrasound while NAFLD severity was assessed by measuring liver fat percentage (magnetic resonance spectroscopy) and hepatic necro-inflammation (serum cytokeratin-18 (CK-18) concentration), at baseline and end of study.Results: 92 patients (age 51.5 ± 10.7 years, 57.6% men) completed the study. In the treatment group (n = 45), CIMT progressed by 0.012 mm (IQR 0.005–0.020 mm) compared to 0.015 mm (IQR 0.007–0.025 mm) in the placebo group (n = 47) (p = 0.17). Reduced CIMT progression in the entire cohort was independently associated with decreased liver fat (standardized ?-coefficient 0.32, p = 0.005), reduced CK-18 levels (standardized ?-coefficient 0.22, p = 0.04) and antihypertensive usage (standardized ?-coefficient ?0.31, p = 0.009) in multivariable regression analysis after adjusting for all potential confounders. Decreased weight (standardized ?-coefficient 0.30, p < 0.001) and increased DHA tissue enrichment during the 18-month study (standardized ?-coefficient ?0.19, p = 0.027) were both independently associated with decreased liver fat, but not with CK-18.Conclusion: Improvement in two markers of NAFLD severity is independently associated with reduced CIMT progression.

We examine the mechanistic basis and wider implications of adopting a developmental perspective on human ageing. Previous models of ageing have concentrated on its genetic basis, or the detrimental effects of accumulated damage, but also have raised issues about whether ageing can be viewed as adaptive itself, or is a consequence of other adaptive processes, for example if maintenance and repair processes in the period up to reproduction are traded off against later decline in function. A life course model places ageing in the context of the attainment of peak capacity for a body system, starting in early development when plasticity permits changes in structure and function induced by a range of environmental stimuli, followed by a period of decline, the rate of which depends on the peak attained as well as the later life conditions. Such path dependency in the rate of ageing may offer new insights into its modification. Focusing on musculoskeletal and cardiovascular function, we discuss this model and the possible underlying mechanisms, including endothelial function, oxidative stress, stem cells and nutritional factors such as vitamin D status. Epigenetic changes induced during developmental plasticity, and immune function may provide a common mechanistic process underlying a life course model of ageing. The life course trajectory differs in high and low resource settings. New insights into the developmental components of the life course model of ageing may lead to the design of biomarkers of later chronic disease risk and to new interventions to promote healthy ageing, with important implications for public health.

Background & Aims Genetic variation in both patatin-like phospholipase domain-containing protein-3 (PNPLA3) (I148M) and the transmembrane 6 superfamily member 2 protein (TM6SF2) (E167K) influences severity of liver disease, and serum triglyceride concentrations in non-alcoholic fatty liver disease (NAFLD), but whether either genotype influences the responses to treatments is uncertain. Methods One hundred three patients with NAFLD were randomised to omega-3 fatty acids (DHA+EPA) or placebo for 15–18 months in a double blind placebo controlled trial. Erythrocyte enrichment with DHA and EPA was measured by gas chromatography. PNPLA3 and TM6SF2 genotypes were measured by PCR technologies. Multivariable linear regression and analysis of covariance were undertaken to test the effect of genotypes on omega-3 fatty acid enrichment, end of study liver fat percentage and serum triglyceride concentrations. All models were adjusted for baseline measurements of each respective outcome. Results Fifty-five men and 40 women (Genotypes PNPLA3 I148M, 148I/I = 41, 148I/M = 43, 148M/M = 11; TM6SF2 E167K 167E/E = 78, 167E/K+167K/K = 17 participants) (mean ± SD age, 51 ± 11 years) completed the trial. Adjusting for baseline measurement, measured covariates and confounders, PNPLA3 148M/M variant was independently associated with percentage of DHA enrichment (B coefficient −1.02 (95% CI −1.97, −0.07), p = 0.036) but not percentage of EPA enrichment (B coefficient −0.31 (95% CI −1.38, 0.75), p = 0.56). This genotype was also independently associated with end of study liver fat percentage (B coefficient 9.5 (95% CI 2.53, 16.39), p = 0.008), but not end of study triglyceride concentration (B coefficient −0.11 (95% CI −0.64, 0.42), p = 0.68). Conclusions PNPLA3 148M/M variant influences the changes in liver fat and DHA tissue enrichment during the trial but not the change in serum triglyceride concentration.

BACKGROUND & AIMS: Dysbiosis of the intestinal microbiota has been associated with nonalcoholic fatty liver disease (NAFLD). We investigated whether administration of a synbiotic combination of probiotic and prebiotic agents affected liver fat content, biomarkers of liver fibrosis, and the composition of the fecal microbiome in patients with NAFLD.METHODS: We performed a double-blind phase 2 trial of 104 patients with NAFLD in the United Kingdom. Participants (mean age, 50.8 ± 12.6 years; 65% men; 37% with diabetes) were randomly assigned to groups given the synbiotic agents (fructo-oligosaccharides, 4 g twice per day, plus Bifidobacterium animalis subspecies lactis BB-12; n = 55) or placebo (n = 49) for 10-14 months. Liver fat content was measured at the start and end of the study by magnetic resonance spectroscopy, and liver fibrosis was determined from a validated biomarker scoring system and vibration-controlled transient elastography. Fecal samples were collected at the start and end of the study, the fecal microbiome were analyzed by 16S ribosomal DNA sequencing.RESULTS: Mean baseline and end-of-study magnetic resonance spectroscopy liver fat percentage values were 32.3% ± 24.8% and 28.5% ± 20.1% in the synbiotic group and 31.3% ± 22% and 25.2% ± 17.2% in the placebo group. In the unadjusted intention-to-treat analysis, we found no significant difference in liver fat reduction between groups (β = 2.8; 95% confidence interval, -2.2 to 7.8; P = .30). In a fully adjusted regression model (adjusted for baseline measurement of the outcome plus age, sex, weight difference, and baseline weight), only weight loss was associated with a significant decrease in liver fat (β = 2; 95% confidence interval, 1.5-2.6; P = .03). Fecal samples from patients who received the synbiotic had higher proportions of Bifidobacterium and Faecalibacterium species, and reductions in Oscillibacter and Alistipes species, compared with baseline; these changes were not observed in the placebo group. Changes in the composition of fecal microbiota were not associated with liver fat or markers of fibrosis.CONCLUSIONS: In a randomized trial of patients with NAFLD, 1 year of administration of a synbiotic combination (probiotic and prebiotic) altered the fecal microbiome but did not reduce liver fat content or markers of liver fibrosis. (ClinicalTrials.gov, Number: NCT01680640).

NEW FINDINGS What is the central question of this study? Do Sherpa highlanders, when exposed to graded hypobaric hypoxia, exhibit enhanced vasomotor and neurovascular control to maintain microcirculatory flux, and thus tissue oxygenation, when compared with altitude-naive lowlanders? What is the main finding and its importance? Sherpas, when exposed to hypobaric hypoxia at high altitude, demonstrated superior preservation of their peripheral microcirculatory perfusion, a greater oxygen unloading rate and sustained microvascular reactivity with enhanced vasomotion, when compared with altitude-naive lowlanders. These differences have not been reported previously and may improve our understanding of the multifactorial responses to sustained environmental hypoxia. ABSTRACT Enhanced oxygen delivery, consequent to an increased microvascular perfusion, has been postulated to play a key role in the physiological adaptation of Tibetan highlanders to the hypobaric hypoxia encountered at high altitude. We tested the hypothesis that Sherpas, when exposed to graded hypobaric hypoxia, demonstrate enhanced vasomotor and neurovascular control to maintain microcirculatory flux, and thus tissue oxygenation, when compared with altitude-naive lowlanders. Eighty-three lowlanders [39 men and 44 women, 38.8 (13.1) years old; mean (SD)] and 61 Sherpas [28 men and 33 women, 27.9 (6.9) years old] were studied on ascent to Everest Base Camp over 11 days. Skin blood flux and tissue oxygen saturation were measured simultaneously using combined laser Doppler fluximetry and white light spectroscopy at baseline, 3500 and 5300 m. In both cohorts, ascent resulted in a decline in the sympathetically mediated microvascular constrictor response (P

Lymph nodes are an important part of the immune system. They filter the lymphatic fluid as it is transported from the tissues before being returned to the blood stream. The fluid flow through the nodes influences the behaviour of the immune cells that gather within the nodes and the structure of the node itself. Measuring the fluid flow in lymph nodes experimentally is challenging due to their small size and fragility. In this paper, we present high resolution X-ray computed tomography images of a murine lymph node. The impact of the resulting visualized structures on fluid transport are investigated using an image based model. The high contrast between different structures within the lymph node provided by phase contrast X-ray computed tomography reconstruction results in images that, when related to the permeability of the lymph node tissue, suggest an increased fluid velocity through the interstitial channels in the lymph node tissue. Fluid taking a direct path from the afferent to the efferent lymphatic vessel, through the centre of the node, moved faster than the fluid that flowed around the periphery of the lymph node. This is a possible mechanism for particles being moved into the cortex.

The purpose of this study is to investigate the feasibility of nonlinear methods for differentiating between haemodynamic steady states as a potential method of identifying microvascular dysfunction. As conventional nonlinear measures do not take into account the multiple time scales of the processes modulating microvascular function, here we evaluate the efficacy of multiscale analysis as a better discriminator of changes in microvascular health. We describe the basis and the implementation of the multiscale analysis of the microvascular blood flux (BF) and tissue oxygenation (OXY: oxyHb) signals recorded from the skin of 15 healthy male volunteers, age 29.2 ± 8.1y (mean ± SD), in two haemodynamic steady states at 33 °C and during warming at 43 °C to generate a local thermal hyperaemia (LTH). To investigate the influence of varying process time scales, multiscale analysis is employed on Sample entropy (MSE), to quantify signal regularity and Lempel and Ziv (MSLZ) and effort to compress (METC) complexity, to measure the randomness of the time series. Our findings show that there was a good discrimination in the multiscale indexes of both the BF (p = 0.001) and oxyHb (MSE, p = 0.002; METC and MSLZ, p < 0.001) signals between the two haemodynamic steady states, having the highest classification accuracy in oxyHb signals (MSE: 86.67%, MSLZ: 90.00% and METC: 93.33%). This study shows that “multiscale-based” analysis of blood flow and tissue oxygenation signals can identify different microvascular functional states and thus has potential for the clinical assessment and diagnosis of pathophysiological conditions.

Preeclampsia (PE) is associated with maternal vascular dysfunction, leading to serious cardiovascular risk both during and following pregnancy. Objective To assess microvascular reactivity in pregnant women with PE. Methods A cross-sectional study was performed in 36 pregnant women with PE and 36 normotensive pregnant women (C) in the third trimester. Skin microvascular blood flow was measured using laser Doppler flowmetry at rest (RF), during the maximum hyperaemic response to brief arterial occlusion (MF) and during the sympathetically-mediated constrictor response to deep inspiratory breath hold (IBH). Results In pregnant women with PE, RF was higher [C,8.1(4.6); PE,12.0(7.6), p

Objective: This study investigates the time-dependent behaviour and algorithmic complexity of low-frequency periodic oscillations in blood flux (BF) and oxygenation signals from the microvasculature. Methods: Microvascular BF and oxygenation (OXY: oxyHb, deoxyHb, totalHb, and SO2%) was recorded from 15 healthy young adult males using combined laser Doppler fluximetry and white light spectroscopy with local skin temperature clamped to 33 °C and during local thermal hyperaemia (LTH) at 43 °C. Power spectral density of the BF and OXY signals was evaluated within the frequency range (0.0095–1.6 Hz). Signal complexity was determined using the Lempel–Ziv (LZ) algorithm. Results: Fold increase in BF during LTH was 15.6 (10.3, 22.8) and in OxyHb 4.8 (3.5, 5.9) (median, range). All BF and OXY signals exhibited multiple oscillatory components with clear differences in signal power distribution across frequency bands at 33 and 43 °C. Significant reduction in the intrinsic variability and complexity of the microvascular signals during LTH was found, with mean LZ complexity of BF and OxyHb falling by 25% and 49%, respectively ( $p\, ). Conclusion: These results provide corroboration that in human skin microvascular blood flow and oxygenation are influenced by multiple time-varying oscillators that adapt to local influences and become more predictable during increased haemodynamic flow. Significance: Recent evidence strongly suggests that the inability of microvascular networks to adapt to an imposed stressor is symptomatic of disease risk which might be assessed via BF and OXY via the combination signal analysis techniques described here.

Muscle spindles are skeletal muscle sensory organs involved in the sensation of position and movement of the body. We have explored the capability of phase contrast computed tomography to visualise muscle spindles in murine skeletal muscle. In particular, we have validated the visualisation of nerve fibres through phase contrast computed tomography using light microscopy on stained histological sections. We further present the first three-dimensional visualisation of muscle spindles in mouse soleus skeletal muscle in conjunction with the neurovascular bundle associated with it.

The supply of oxygen in sufficient quantity is vital for the correct functioning of all organs in the human body, in particular for skeletal muscle during exercise. Disease is often associated with both an inhibition of the microvascular supply capability and is thought to relate to changes in the structure of blood vessel networks. Different methods exist to investigate the influence of the microvascular structure on tissue oxygenation, varying over a range of application areas, i.e. biologicalin vivoandin vitroexperiments, imaging and mathematical modelling. Ideally, all of these methods should be combined within the same framework in order to fully understand the processes involved. This review discusses the mathematical models of skeletal muscle oxygenation currently available that are based upon images taken of the muscle microvasculaturein vivoandex vivo. Imaging systems suitable for capturing the blood vessel networks are discussed and respective contrasting methods presented. The review further informs the association between anatomical characteristics in health and disease. With this review we give the reader a tool to understand and establish the workflow of developing an image-based model of skeletal muscle oxygenation. Finally, we give an outlook for improvements needed for measurements and imaging techniques to adequately investigate the microvascular capability for oxygen exchange.

Objective To determine whether analysis of microvascular network perfusion using complexity-based methods can discriminate between groups of individuals at an increased risk of developing CVD. Methods Data were obtained from laser Doppler recordings of skin blood flux at the forearm in 50 participants with non-alcoholic fatty liver disease grouped for absence (n = 28) or presence (n = 14) of type 2 diabetes and use of calcium channel blocker medication (n = 8). Power spectral density was evaluated and Lempel-Ziv complexity determined to quantify signal information content at single and multiple time-scales to account for the different processes modulating network perfusion. Results Complexity was associated with dilatory capacity and respiration and negatively with baseline blood flux and cardiac band power. The relationship between the modulators of flowmotion and complexity of blood flux is shown to change with time-scale improving discrimination between groups. Multiscale Lempel-Ziv achieved best classification accuracy of 86.1%. Conclusions Time and frequency domain measures alone are insufficient to discriminate between groups. As cardiovascular disease risk increases, the degree of complexity of the blood flux signal reduces, indicative of a reduced temporal activity and heterogeneous distribution of blood flow within the microvascular network sampled. Complexity-based methods, particularly multiscale variants, are shown to have good discriminatory capabilities.

The first fully integrated 2D CMOS imaging sensor with on-chip signal processing for applications in laser Doppler blood flow (LDBF) imaging has been designed and tested. To obtain a space efficient design over 64 × 64 pixels means that standard processing electronics used off-chip cannot be implemented. Therefore the analog signal processing at each pixel is a tailored design for LDBF signals with balanced optimization for signal-to-noise ratio and silicon area. This custom made sensor offers key advantages over conventional sensors, viz. the analog signal processing at the pixel level carries out signal normalization; the AC amplification in combination with an anti-aliasing filter allows analog-to-digital conversion with a low number of bits; low resource implementation of the digital processor enables on-chip processing and the data bottleneck that exists between the detector and processing electronics has been overcome. The sensor demonstrates good agreement with simulation at each design stage. The measured optical performance of the sensor is demonstrated using modulated light signals and in vivo blood flow experiments. Images showing blood flow changes with arterial occlusion and an inflammatory response to a histamine skin-prick demonstrate that the sensor array is capable of detecting blood flow signals from tissue.

Summary Background Topical 5-aminolaevulinic acid photodynamic therapy (5-ALA-PDT) causes a clinical inflammatory response in human skin. While histamine mediates the immediate reaction, the mediators of the prolonged erythema are unknown. Objectives To look for involvement of the proinflammatory mediators prostaglandin (PG)E2 and nitric oxide (NO) in topical PDT-induced erythema in human skin. Methods A series of studies was performed in healthy volunteers (n = 35). Following definition of the erythemal time course and dose response to 5-ALA-PDT, duplicate 5-ALA dose series were iontophoresed into the skin of each ventral forearm and exposed to 100 J cm−2 broadband red light. Within subject, arms were randomized to control, or treatment with the cyclooxygenase and NO synthase inhibitors indometacin and Nω-nitro-l-arginine methyl ester (l-NAME), respectively, and the impact on 5-ALA-PDT-induced erythema was quantified. Additionally, release of PGE2 and NO was directly assessed by sampling dermal microdialysate at intervals following 5-ALA-PDT administration. Results A 5-ALA dose-related delayed erythema occurred by 3 h (r = 0·97, P

S100B protein is released by astrocytes into the brain extracellular fluid following acute brain injury and elevated levels in CSF and serum have been shown to correlate with patient outcome following traumatic brain injury. A prospective study of brain extracellular fluid (ECF) and serum S100B levels in 12 patients with severe head injury (GCS ≤ 8) was undertaken using intracerebral microdialysis to investigate whether a correlation with ECF S100B and outcome could be confirmed. Patient outcomes were assessed at 6 months using the Glasgow Outcome Scale (GOS) and divided into two outcome groups: group A, 8 survivors with either a good recovery or moderate disability (GOS scores of 4 or 5); and group B, 4 patients who died (GOS 1). Peak serum levels of S100B were significantly greater in group B (mean 6.03 ng/ml) compared with group A (mean 0.73 ng/ml) (P = 0.009). Group A had a mean peak S100B in the extracellular compartment of 186 ng/ml compared to 150 ng/ml in group B. There was no significant difference between the mean peak brain ECF S100B concentrations for the 2 outcome groups (P = 0.932). We confirm that intracerebral microdialysis can be used to sample S100B concentrations from brain extracellular fluid and our results suggest that the ECF S100B levels were variable and that there was no significant difference between the good outcome and poor outcome groups. In contrast, the serum levels of S100B of patients with a poor outcome were significantly higher than those with a good outcome.

The lymphatic system returns fluid to the bloodstream from the tissues to maintain tissue fluid homeostasis. Lymph nodes distributed throughout the system filter the lymphatic fluid. The afferent and efferent lymph flow conditions of lymph nodes can be measured in experiments; however, it is difficult to measure the flow within the nodes. In this paper, we present an image-based modelling approach to investigating how the internal structure of the node affects the fluid flow pathways within the node. Selective plane illumination microscopy images of murine lymph nodes are used to identify the geometry and structure of the tissue within the node and to determine the permeability of the lymph node interstitium to lymphatic fluid. Experimental data are used to determine boundary conditions and optimise the parameters for the model. The numerical simulations conducted within the model are implemented in COMSOL Multiphysics, a commercial finite element analysis software. The parameter fitting resulted in the estimate that the average permeability for lymph node tissue is of the order of magnitude of [Formula: see text]. Our modelling shows that the flow predominantly takes a direct path between the afferent and efferent lymphatics and that fluid is both filtered and absorbed across the blood vessel boundaries. The amount that is absorbed or extravasated in the model is dependent on the efferent lymphatic lumen fluid pressure.

Diabet. Med. 29, 822–826 (2012) Summary Background Constant moderate intensity physical exertion in humid environments at altitude poses a considerable challenge to maintaining euglycaemia with Type 1 diabetes. Blood glucose concentrations and energy expenditure were continuously recorded in a person trekking at altitude in a tropical climate to quantify changes in glucose concentrations in relation to energy expenditure. Case report Blood glucose concentrations and energy expenditure were continuously monitored with a Guardian® real-time continuous glucose monitoring system (CGMS) and a SenseWear® Pro3 armband (BodyMedia Inc., USA), in a 27-year-old woman with Type 1 diabetes, during her climb up Mount Kinabalu in Borneo (c. 4095 m). Comparative control data from the same person was collected in the UK (temperate climate at sea level) and Singapore (tropical climate at sea level). Maximum physical effort during the climb was

Objectives: The endothelium maintains vascular homeostasis through the release of endothelium-derived relaxing factors (EDRF) and endothelium-derived hyperpolarization (EDH). The balance in EDH : EDRF is disturbed in cardiovascular disease and may also be susceptible to developmental conditioning through exposure to an adverse uterine environment to predispose to later risk of hypertension and vascular disease. Methods: Developmentally conditioned changes in EDH : EDRF signalling pathways were investigated in cremaster arterioles (18–32 μm diameter) and third-order mesenteric arteries of adult male mice offspring of dams fed either a fat-rich (high fat, HF, 45% energy from fat) or control (C, 10% energy from fat) diet. After weaning, offspring either continued on high fat or were placed on control diets to give four dietary groups (C/C, HF/C, C/HF, and HF/HF) and studied at 15 weeks of age. Results: EDH via intermediate (IKCa) and small (SKca) conductance calcium-activated potassium channels contributed less than 10% to arteriolar acetylcholine-induced relaxation in in-situ conditioned HF/C offspring compared with ∼60% in C/C (P

BACKGROUND: Sarcopenia is defined as the loss of muscle mass and function with age and is associated with decline in mobility, frailty, falls and mortality. There is considerable interest in understanding the underlying mechanisms. Our aim was to characterise muscle morphology changes associated with sarcopenia among community dwelling older men.METHODS: One hundred and five men aged 68-76 years were recruited to the Hertfordshire Sarcopenia Study (HSS) for detailed characterisation of muscle including measures of muscle mass, strength and function. Muscle tissue was obtained from a biopsy of the vastus lateralis for 99 men and was processed for immunohistochemical studies to determine myofibre distribution and area, capillarisation and satellite cell (SC) density.RESULTS: Six (6 %) men had sarcopenia as defined by the European Working Group on Sarcopenia in Older People (EWGSOP) criteria. These men had lower SC density (1.7 cells/mm(2) vs 3.8 cells/mm(2), p?=?0.06) and lower SC/fibre ratio (0.02 vs 0.06, p?=?0.06) than men without sarcopenia. Although men with sarcopenia tended to have smaller myofibres and lower capillary to fibre ratio, these relationships were not statistically significant.CONCLUSION: We have shown that there may be altered muscle morphology parameters in older men with sarcopenia. These results have the potential to help identify cell and molecular targets for therapeutic intervention. This work now requires extension to larger studies which also include women.

Please cite this paper as: Clough and Cracowski (2012). Spotlight Issue: Microcirculation––From a Clinical Perspective. Microcirculation 19(1), 1–4 Abstract This spotlight issue of Microcirculation contains five articles written from a clinical perspective on the role of microcirculatory abnormalities in the pathogenesis of cardiovascular disease. The reviews address issues such as the impact of modifiable (lifestyle and environmental risk factors) and non modifiable (age) on microvascular form and function; inter- and intra-cell signaling pathways underlying microvascular dysfunction; microvascular assessment as a prognostic tool in clinical practice; and the potential impact of targeted therapeutic intervention on microvascular health. The articles also describe and evaluate methodological approaches to the assessment of microvascular function in organs such as the skin, retina, muscle and adipose tissue, and provide a perspective on how such approaches might be employed in future in disease risk stratification in large epidemiological studies. This timely edition of the journal Microcirculation highlights that while there is currently no identified unifying mechanism to explain the association between microvascular phenotype and susceptibility to disease, there is accumulating evidence that deficits in microvascular structure and function may be an early and important prodromal indicator and risk determinant in a wide range of chronic non-communicable disorders, including cardiovascular and metabolic disease.

There is increasing evidence that the early life environment, of which nutrition is a key component, acts through developmental adaptations to set the capacity of cardiovascular and metabolic pathways, and ultimately the limits to physiological challenges in later life. Sub-optimal maternal nutrition and fetal growth result in reduced microvascular perfusion and functional dilator capacity, which are strongly associated with later development of obesity, type 2 diabetes and hypertension. These conditions are also linked to microvascular rarefaction and remodeling that together limit capillary recruitment, reduce exchange capacity and increase diffusion distances of metabolic substrates, and increase local and overall peripheral resistance. Changes in small vessel structure and function may be seen very early, long before the onset of overt cardiovascular and metabolic disease, and may thus be a target for early therapeutic and life style intervention strategies. This article explores how a disadvantageous microvascular phenotype may result from perinatal priming and how developmental plasticity may become an important and additional risk determinant in susceptibility to cardio-metabolic disease in adult life.

Objective:? to test the hypothesis that: (i) functional microvascular dilator capacity is independently associated with insulin sensitivity and age in individuals with central adiposity at risk of cardiovascular disease (CVD); and (ii) functional microvascular dilator capacity is improved by high dose statin treatment. Methods:? functional dilator capacity (measured as change in laser Doppler blood flux from baseline during post occlusive reactive hyperemia [peak flux%resting flux; PF%RF] and flowmotion (power spectral density [PSD] analysis)) were assessed in 40 people with central adiposity and one or more other CVD risk factors. Measurements were made at rest and during acute hyperinsulinaemia before and six months after high dose atorvastatin (40 mg daily) or placebo. Results:? insulin-induced change in PF%RF was independently associated with insulin sensitivity (M/I) (r = 0.46 p = 0.02) and age (r = ?0.46 p = 0.02), which together explained almost half of the variance in PF%RF (adjusted r2 = 0.37, p = 0.008). Whilst atorvastatin decreased LDL cholesterol by 51% (p Conclusions:? insulin sensitivity and age are independently associated with an insulin-induced change in functional microvascular dilator capacity in individuals with central adiposity at risk of CVD. Dilator capacity is not improved by six months high dose statin treatment

Cardiorespiratory fitness [maximal O2 consumption (V̇o2max)] is an independent risk factor for type 2 diabetes; but in individuals at risk, factors influencing V̇o2max are poorly understood. We tested the hypothesis that V̇o2max is associated with diastolic function [subendocardial variability ratio (SEVR), %], as diastolic function influences myocardial perfusion. We studied 47 men and women with central obesity without diabetes. We measured fitness (V̇o2max) by treadmill testing and diastolic function (SEVR%) by pulse-wave analysis. We measured other factors influencing this relationship: insulin sensitivity [whole body glucose uptake-to-insulin concentration ratio (M/I)] by hyperinsulinemic euglycemic clamp, fatness by MR imaging and dual-energy X-ray absorptiometry, physical activity energy expenditure (metabolic equivalents of tasks) by the Sensewear Pro2 device, and muscle microvascular exchange capacity (capillary filtration coefficient) by venous plethysmography. Mean age of the subjects was 51 ± 9 (SD) yr. V̇o2max was associated with SEVR% ( r = 0.50, P = 0.001), fatness ( r = −0.39, P = 0.008), and HbA1c ( r = −0.35, P = 0.018), but not with whole body glucose uptake-to-insulin concentration ratio, metabolic equivalents of tasks, or capillary filtration coefficient. In regression modeling with age, sex, fatness, and SEVR% as explanatory variables, only age, sex, and SEVR% were independently associated with V̇o2max (SEVR% − standardized B coefficient = 0.37, 95% confidence interval = 0.003–0.18, P = 0.007). This model identified 46% of the variance in V̇o2max ( R2 = 0.46, P = 0.0001). There was a strong, independent association between V̇o2max and a measure of diastolic function in sedentary individuals with central obesity.

Aims: poor glycaemic control is associated with increased risk of microvascular disease in various organs including the eye and kidney, but the relationship between glycated haemoglobin (HbA1c) and microvascular function in skeletal muscle has not been described. We tested the association between HbA1c and a measure of microvascular exchange capacity (Kf) in skeletal muscle in people with central obesity at risk of developing Type 2 diabetes. Methods: microvascular function was measured in 28 women and 19 men [mean (± sd) age 51 ± 9 years] with central obesity who did not have diabetes. We estimated insulin sensitivity by hyperinsulinaemic–euglycaemic clamp, visceral and total fatness by magnetic resonance imaging, fitness (VO2 max by treadmill testing), physical activity energy expenditure [metabolic equivalents of tasks (METS) by use of the SenseWear Pro armband] and skeletal muscle microvascular exchange capacity (Kf) by venous occlusion plethysmography. Results: in regression modelling, age, sex and fasting plasma glucose accounted for 30.5% of the variance in HbA1c (r2 = 0.31, P = 0.001). Adding Kf to this model explained an additional 26.5% of the variance in HbA1c (r2 = 0.57, P = 0.0001 and Kf was strongly and independently associated with HbA1c (standardized B coefficient ?0.45 (95% confidence interval ?0.19, ?0.06), P = 0.001). Conclusions: we found a strong negative independent association between a measure of skeletal muscle microvascular exchange capacity (Kf) and HbA1c. Kf was associated with almost as much of the variance in HbA1c as fasting plasma glucose

The supply of oxygen in sufficient quantity is vital for the correct functioning of all organs in the human body, especially for skeletal muscle during exercise. Traditionally, microvascular oxygen supply capability is assessed by the analysis of morphological measures on transverse cross-sections of muscle, e.g. capillary density or capillary-to-fibre ratio. In this work, we investigate the relationship between microvascular structure and muscle tissue oxygenation in mice. Phase contrast imaging was performed using synchrotron radiation computed tomography (SR CT) to visualize red blood cells (RBCs) within the microvasculature in mouse soleus muscle. Image-based mathematical modelling of the oxygen diffusion from the RBCs into the muscle tissue was subsequently performed, as well as a morphometric analysis of the microvasculature. The mean tissue oxygenation was then compared with the morphological measures of the microvasculature. RBC volume fraction and spacing (mean distance of any point in tissue to the closest RBC) emerged as the best predictors for muscle tissue oxygenation, followed by length density (summed RBC length over muscle volume). The two-dimensional measures of capillary density and capillary-to-fibre ratio ranked last. We, therefore, conclude that, in order to assess the states of health of muscle tissue, it is advisable to rely on three-dimensional morphological measures rather than on the traditional two-dimensional measures.

Objective: To compare the output from a novel high power, wide separation laser Doppler flow probe (DP1-V2-HP, 4 mm, with IRLD20) with that of a standard flow probe (DP1-V2, 0.5 mm, with DRT4) (Moor UK) and to explore its potential for use in the noninvasive measurement of blood flow in deeper tissues in humans.Methods: Monte Carlo modeling was used to predict depths of light scattering in skin with each probe, geometry. Experimentally, forearm blood flow was measured at rest and during local warming of the skin surface and post occlusion reactive hyperaemia (PORH). Laser Doppler blood flux (LDF) and the power spectral density of its component frequency intervals, were compared.Results: Monte Carlo modeling indicated that while the majority of wide probe LD signal derives from deeper tissue, a significant portion is from superficial (dermal) tissue (and vice versa for standard probe). Perturbation of local blood flow differentially increased LDF and spectral power as measured by the two probes, with the standard skin probe showing a significantly greater response to local skin warming (pConclusions: These differences support our hypothesis that the wide probe is recording predominantly blood flux within the vasculature of sub-dermal tissue. This is in agreement with Monte Carlo simulation. (C) 2009 Elsevier Inc. All rights reserved.