Noninvasive, in vivo assessment of the cervical microcirculation using incident dark field imaging.

AIM: This study evaluates the feasibility of handheld vital microscopy for noninvasive, objective assessment of the microcirculation of the human uterine cervix. We qualitatively and quantitatively describe the microcirculation in healthy subjects in order to provide a basis for its application in cervical pathology. METHODS: Incident dark field imaging was used to image the microcirculation in four quadrants of the uterine ectocervix in ten healthy participants. If the squamocolumnar junction was visible, measurements were repeated on the endocervical columnar epithelium as well. Image acquisition time was recorded and participants scored the experienced level of discomfort. Angioarchitecture was classified according to Weber's classification. Quantitative parameters included capillary density (CD), total and perfused vessel density (TVD, PVD), proportion of perfused vessels (PPV) and microvascular flow index (MFI). RESULTS: Image acquisition was easy, fast and well tolerated. Angioarchitecture was characterized by two distinctive and organized patterns; capillary loops underneath the squamous epithelium of the ectocervix and vascular networks underneath the columnar epithelium. In the image sequences containing capillary loops, mean CD was 33.2 cpll/mm2 (95% CI 28.2-38.2 cpll/mm2). In the image sequences with vascular networks, mean TVD was 12.5 mm/mm2 (95% CI 11.2-13.77 mm/mm2), mean PVD was 12.2 (95% CI 11.0-13.5 mm/mm2), MFI was 3 and PPV was 100%. CONCLUSIONS: Incident dark field imaging allows for noninvasive, real time visualization and objective evaluation and quantification of the microcirculation of the uterine cervix. The organized vascular patterns and optimal perfusion observed in healthy subjects allow for comparison with cervical pathology, for example in patients with cervical dysplasia or cervical cancer.

Historical reviews of the assessment of human cardiovascular function: interrogation and understanding of the control of skin blood flow.

Several techniques exist for the determination of skin blood flow that have historically been used in the investigation of thermoregulatory control of skin blood flow, and more recently, in clinical assessments or as an index of global vascular function. Skin blood flow measurement techniques differ in their methodology and their strengths and limitations. To examine the historical development of techniques for assessing skin blood flow by describing the origin, basic principles, and important aspects of each procedure and to provide recommendations for best practise. Venous occlusion plethysmography was one of the earliest techniques to intermittently index a limb's skin blood flow under conditions in which local muscle blood flow does not change. The introduction of laser Doppler flowmetry provided a method that continuously records an index of skin blood flow (red cell flux) (albeit from a relatively small skin area) that requires normalisation due to high site-to-site variability. The subsequent development of laser Doppler and laser speckle imaging techniques allows the mapping of skin blood flow from larger surface areas and the visualisation of capillary filling from the dermal plexus in two dimensions. The use of iontophoresis or intradermal microdialysis in conjunction with laser Doppler methods allows for the local delivery of pharmacological agents to interrogate the local and neural control of skin blood flow. The recent development of optical coherence tomography promises further advances in assessment of the skin circulation via three-dimensional imaging of the skin microvasculature for quantification of vessel diameter and vessel recruitment.

The association between near-infrared spectroscopy-derived and flow-mediated dilation assessment of vascular responsiveness in the arm.

INTRODUCTION: Following a period of blood flow occlusion, the near-infrared spectroscopy (NIRS)-derived reperfusion slope of the oxygen saturation signal (StO2) is a measure of microvascular responsiveness that has been shown to be positively correlated with flow-mediated dilation (FMD) assessment of conduit artery function in the lower limb vasculature. Given that previously established differences in structure and function of the vessels in the upper compared to the lower limbs may change this relationship, investigating whether this correlation between the reperfusion slope of the StO2 and the FMD response is maintained in upper limbs is important. Accordingly, this study investigated the correlation between the reperfusion slope of the StO2 and FMD in the arm vasculature. METHODS: 18 physically active individuals were submitted to a vascular occlusion test (VOT). Microvascular responsiveness was calculated as the NIRS-derived reperfusion slope assessed in a forearm muscle. Macrovascular responsiveness was assessed at the brachial artery and calculated as a percent of change in FMD (%FMD). RESULTS: A statistically significant correlation (r = 0.66; P = 0.001) was found between the reperfusion slope and %FMD response. CONCLUSION: The significant correlation between the reperfusion slope in the forearm muscle and %FMD in the brachial artery, reinforces the relationship between downstream and upstream vascular reactivity in healthy human limbs.

Sex-Specific Characteristics of the Microcirculation.

The requirements of metabolizing tissue are both continuous and variable; accordingly, the microvasculature serving that tissue must be similarly dynamic. Just as it is recognized that males and females of the same species have differing metabolic requirements, is it not likely that the microvasculature serving these tissues will differ by sex? This section focusing on the constituents of the microcirculation identifies what is known presently about the role sex plays in matching metabolic demand with microvascular function and areas requiring additional study. Many of the identified sex differences are subtle and easily ignored. In the aggregate, though, they can profoundly alter phenotype, especially under stressful conditions including pregnancy, exercise, and disease states ranging from diabetes to heart failure. Although the features presently identified to "have sex" range from differences in growth, morphology, protein expression, and intracellular signaling, males and females alike achieve homeostasis, likely by different means. Studies of microvascular sexual dimorphism are also identifying age as an independent but interacting factor requiring additional attention. Overall, attempting to ignore either sex and/or age is inappropriate and will prevent the design and implementation of appropriate interventions to present, ameliorate, or correct microvascular dysfunction.

Assessment of Microvascular Invasion of Hepatocellular Carcinoma with Diffusion Kurtosis Imaging.

Purpose To evaluate the potential role of diffusion kurtosis imaging and conventional magnetic resonance (MR) imaging findings including standard monoexponential model of diffusion-weighted imaging and morphologic features for preoperative prediction of microvascular invasion (MVI) of hepatocellular carcinoma (HCC). Materials and Methods Institutional review board approval and written informed consent were obtained. Between September 2015 and November 2016, 84 patients (median age, 54 years; range, 29-79 years) with 92 histopathologically confirmed HCCs (40 MVI-positive lesions and 52 MVI-negative lesions) were analyzed. Preoperative MR imaging examinations including diffusion kurtosis imaging (b values: 0, 200, 500, 1000, 1500, and 2000 sec/mm2) were performed and kurtosis, diffusivity, and apparent diffusion coefficient maps were calculated. Morphologic features of conventional MR images were also evaluated. Univariate and multivariate logistic regression analyses were used to evaluate the relative value of these parameters as potential predictors of MVI. Results Features significantly related to MVI of HCC at univariate analysis were increased mean kurtosis value (P < .001), decreased mean diffusivity value (P = .033) and apparent diffusion coefficient value (P = .011), and presence of infiltrative border with irregular shape (P = .005) and irregular circumferential enhancement (P = .026). At multivariate analysis, mean kurtosis value (odds ratio, 6.25; P = .001), as well as irregular circumferential enhancement (odds ratio, 6.92; P = .046), were independent risk factors for MVI of HCC. The mean kurtosis value for MVI of HCC showed an area under the receiver operating characteristic curve of 0.784 (optimal cutoff value was 0.917). Conclusion Higher mean kurtosis values in combination with irregular circumferential enhancement are potential predictive biomarkers for MVI of HCC. © RSNA, 2017.

Contrast-enhanced ultrasound using bolus injections of contrast agent for assessment of postprandial microvascular blood volume in human skeletal muscle.

Methods capable of measuring blood flow in a tissue-specific manner are needed. The purpose of this study was to investigate whether contrast-enhanced ultrasound (CEUS) using bolus injections of SonoVue® is an useful method for assessing postprandial changes in microvascular perfusion in the vastus lateralis muscle. Ten healthy, young subjects were recruited for this study. Six subjects participated in washout and reproducibility protocols to assess washout time of SonoVue® and the reproducibility of the method when measuring microvascular blood volume (MBV). Six subjects (two of which also participated in the washout and reproducibility protocols) participated in exercise and nutrition protocols, to assess the ability of the method to detect changes in MBV in response to these interventions. Intraday variation (coefficients of variation) for MBV indices, as assessed by peak signal intensity (PI) or mean plateau signal intensity (mPI), was high (PI: 19 ± 4·2%; mPI: 23 ± 3·3%). The exercise protocol induced significant increases in MBV indices (PI:+113%, P˂0·0001; mPI:+218%, P˂0·0001) acutely after exercise cessation. There were no changes in MBV indices in response to feeding during the nutrition protocol (PI: P = 0·51; mPI: P = 0·51). We conclude that CEUS using bolus injections of SonoVue® is not capable of detecting changes in MBV of vastus lateralis in response to feeding. This is probably due to the low reproducibility of the method. However, the method is capable of measuring changes in MBV in response to exercise. This method could therefore be used when investigating exercise-induced changes in microvascular perfusion.

Vascular assessment of wound healing: a clinical review.

Although macrovascular screening of patients with chronic wounds, particularly in the lower extremities, is accepted as part of clinical practice guidelines, microvascular investigation is less commonly used for a variety of reasons. This can be an issue because most patients with macrovascular disease also develop concomitant microvascular dysfunction. Part of the reason for less comprehensive microvascular screening has been the lack of suitable imaging techniques that can quantify microvascular dysfunction in connection with non-healing chronic wounds. This is changing with the introduction of fluorescence microangiography. The objective of this review is to examine macro- and microvascular disease, the strengths and limitations of the approaches used and to highlight the importance of microvascular angiography in the context of wound healing.

Optical coherence tomography in the assessment of acute changes in cutaneous vascular diameter induced by heat stress.

There are limited imaging technologies available that can accurately assess or provide surrogate markers of the in vivo cutaneous microvessel network in humans. In this study, we establish the use of optical coherence tomography (OCT) as a novel imaging technique to assess acute changes in cutaneous microvessel area density and diameter in humans. OCT speckle decorrelation images of the skin on the ventral side of the forearm up to a depth of 500 µm were obtained prior to and following 20-25 min of lower limb heating in eight healthy men [30.3 ± 7.6 (SD) yr]. Skin red blood cell flux was also collected using laser Doppler flowmetry probes immediately adjacent to the OCT skin sites, along with skin temperature. OCT speckle decorrelation images were obtained at both baseline and heating time points. Forearm skin flux increased significantly (0.20 ± 0.15 to 1.75 ± 0.38 cutaneous vascular conductance, P < 0.01), along with forearm skin temperature (32.0 ± 1.2 to 34.3 ± 1.0°C, P < 0.01). Quantitative differences in the automated calculation of vascular area densities (26 ± 9 to 49 ± 19%, P < 0.01) and individual microvessel diameters (68 ± 17 to 105 ± 25 µm, P < 0.01) were evident following the heating session. This is the first in vivo within-subject assessment of acute changes in the cutaneous microvasculature in response to heating in humans and highlights the use of OCT as an exciting new imaging approach for skin physiology and clinical research.

The influence of elective percutaneous coronary intervention on microvascular resistance: a serial assessment using the index of microcirculatory resistance.

This study investigates whether hyperemic microvascular resistance (MR) is influenced by elective percutaneous coronary intervention (PCI) by using the index of microcirculatory resistance (IMR). Seventy-one consecutive patients with stable angina pectoris undergoing elective PCI were prospectively studied. The IMR was measured before and after PCI and at the 10-mo follow-up. The IMR significantly decreased until follow-up; the pre-PCI, post-PCI, and follow-up IMRs had a median of 19.8 (interquartile range, 14.6-28.9), 16.2 (11.8-22.1), and 14.8 (11.8-18.7), respectively (P < 0.001). The pre-PCI IMR was significantly correlated with the change in IMR between pre- and post-PCI (r = 0.84, P < 0.001) and between pre-PCI and follow-up (r = 0.93, P < 0.001). Pre-PCI IMR values were significantly higher in territories with decreases in IMR than in those with increases in IMR [pre-PCI IMR: 25.4 (18.4-35.5) vs. 12.5 (9.4-16.8), P < 0.001]. At follow-up, IMR values in territories showing decreases in IMR were significantly lower than those with increases in IMR [IMR at follow-up: 13.9 (10.9-17.6) vs. 16.6 (14.0-21.4), P = 0.013]. The IMR decrease was significantly associated with a greater shortening of mean transit time, indicating increases in coronary flow (P < 0.001). The optimal cut-off values of pre-PCI IMR to predict a decrease in IMR after PCI and at follow-up were 16.8 and 17.0, respectively. In conclusion, elective PCI affected hyperemic MR and its change was associated with pre-PCI MR, resulting in showing a wide distribution. Overall hyperemic MR significantly decreased until follow-up. The modified hyperemic MR introduced by PCI may affect post-PCI coronary flow.

Invasive Assessment of Coronary Physiology Predicts Late Mortality After Heart Transplantation.

BACKGROUND: The aim of this study is to determine the prognostic value of invasively assessing coronary physiology early after heart transplantation. METHODS AND RESULTS: Seventy-four cardiac transplant recipients had fractional flow reserve, coronary flow reserve, index of microcirculatory resistance (IMR), and intravascular ultrasound performed down the left anterior descending coronary artery soon after (baseline) and 1 year after heart transplantation. The primary end point was the cumulative survival free of death or retransplantation at a mean follow-up of 4.5±3.5 years. The cumulative event-free survival was significantly lower in patients with a fractional flow reserve <0.90 at baseline (42% versus 79%; P=0.01) or an IMR ≥20 measured 1 year after heart transplantation (39% versus 69%; P=0.03). Patients in whom IMR decreased or did not change from baseline to 1 year had higher event-free survival compared with patients with an increase in IMR (66% versus 36%; P=0.03). Fractional flow reserve <0.90 at baseline (hazard ratio, 0.13; 95% confidence interval, 0.02-0.81; P=0.03), IMR ≥20 at 1 year (hazard ratio, 3.93; 95% confidence interval, 1.08-14.27; P=0.04), and rejection during the first year (hazard ratio, 6.00; 95% confidence interval, 1.56-23.09; P=0.009) were independent predictors of death/retransplantation, whereas intravascular ultrasound parameters were not. CONCLUSIONS: Invasive measures of coronary physiology (fractional flow reserve and IMR) determined early after heart transplantation are significant predictors of late death or retransplantation.

Dynamic light scattering Monte Carlo: a method for simulating time-varying dynamics for ordered motion in heterogeneous media.

Few methods exist that can accurately handle dynamic light scattering in the regime between single and highly multiple scattering. We demonstrate dynamic light scattering Monte Carlo (DLS-MC), a numerical method by which the electric field autocorrelation function may be calculated for arbitrary geometries if the optical properties and particle motion are known or assumed. DLS-MC requires no assumptions regarding the number of scattering events, the final form of the autocorrelation function, or the degree of correlation between scattering events. Furthermore, the method is capable of rapidly determining the effect of particle motion changes on the autocorrelation function in heterogeneous samples. We experimentally validated the method and demonstrated that the simulations match both the expected form and the experimental results. We also demonstrate the perturbation capabilities of the method by calculating the autocorrelation function of flow in a representation of mouse microvasculature and determining the sensitivity to flow changes as a function of depth.

Applications of three-dimensional printing technology in the cardiovascular field.

Three-dimensional (3-D) printing technology has rapidly developed in the last few decades. Meanwhile, the application of this technology has reached beyond the engineering field and expanded to almost all disciplines, including medicine. There has been much research on the medical applications of 3-D printing in neurosurgery, orthopedics, maxillofacial surgery, plastic surgery, tissue engineering, as well as other fields. Because of the complexity of the cardiovascular system, the application of this technology is limited and difficult, as compared to other disciplines, and thus there is much room for future development. Many of the difficulties associated with this technology must be overcome. Nonetheless, there is no doubt that 3-D printing technology will benefit patients with cardiovascular diseases in the near future.

Compact Laser Doppler Flowmeter (LDF) Fundus Camera for the Assessment of Retinal Blood Perfusion in Small Animals.

PURPOSE: Noninvasive techniques for ocular blood perfusion assessment are of crucial importance for exploring microvascular alterations related to systemic and ocular diseases. However, few techniques adapted to rodents are available and most are invasive or not specifically focused on the optic nerve head (ONH), choroid or retinal circulation. Here we present the results obtained with a new rodent-adapted compact fundus camera based on laser Doppler flowmetry (LDF). METHODS: A confocal miniature flowmeter was fixed to a specially designed 3D rotating mechanical arm and adjusted on a rodent stereotaxic table in order to accurately point the laser beam at the retinal region of interest. The linearity of the LDF measurements was assessed using a rotating Teflon wheel and a flow of microspheres in a glass capillary. In vivo reproducibility was assessed in Wistar rats with repeated measurements (inter-session and inter-day) of retinal arteries and ONH blood velocity in six and ten rats, respectively. These parameters were also recorded during an acute intraocular pressure increase to 150 mmHg and after heart arrest (n = 5 rats). RESULTS: The perfusion measurements showed perfect linearity between LDF velocity and Teflon wheel or microsphere speed. Intraclass correlation coefficients for retinal arteries and ONH velocity (0.82 and 0.86, respectively) indicated strong inter-session repeatability and stability. Inter-day reproducibility was good (0.79 and 0.7, respectively). Upon ocular blood flow cessation, the retinal artery velocity signal substantially decreased, whereas the ONH signal did not significantly vary, suggesting that it could mostly be attributed to tissue light scattering. CONCLUSION: We have demonstrated that, while not adapted for ONH blood perfusion assessment, this device allows pertinent, stable and repeatable measurements of retinal blood perfusion in rats.

In vivo assessment of printed microvasculature in a bilayer skin graft to treat full-thickness wounds.

Chronic wounds such as diabetic foot ulcers and venous leg ulcers are common problems in people suffering from type 2 diabetes. These can cause pain, and nerve damage, eventually leading to foot or leg amputation. These types of wounds are very difficult to treat and sometimes take months or even years to heal because of many possible complications during the process. Allogeneic skin grafting has been used to improve wound healing, but the majority of grafts do not survive several days after being implanted. We have been studying the behavior of fibroblasts and keratinocytes in engineered capillary-like endothelial networks. A dermo-epidermal graft has been implanted in an athymic nude mouse model to assess the integration with the host tissue as well as the wound healing process. To build these networks into a skin graft, a modified inkjet printer was used, which allowed the deposit of human microvascular endothelial cells. Neonatal human dermal fibroblast cells and neonatal human epidermal keratinocytes were manually mixed in the collagen matrix while endothelial cells printed. A full-thickness wound was created at the top of the back of athymic nude mice and the area was covered by the bilayered graft. Mice of the different groups were followed until completion of the specified experimental time line, at which time the animals were humanely euthanized and tissue samples were collected. Wound contraction improved by up to 10% when compared with the control groups. Histological analysis showed the neoskin having similar appearance to the normal skin. Both layers, dermis and epidermis, were present with thicknesses resembling normal skin. Immunohistochemistry analysis showed favorable results proving survival of the implanted cells, and confocal images showed the human cells' location in the samples that were collocated with the bilayer printed skin graft.

Experimental assessment of the neo-vascularisation of acellular dermal matrix in the wound bed pretreated with mesenchymal stem cell under subatmospheric pressure.

Neo-vascularisation of the acellular dermal matrix (ADM) is an essential procedure if a full-thickness wound is closed with ADM and skin is grafted over the ADM. In this study, we aimed to improve the neo-vascularisation of ADM by combining the effects of negative pressure wound therapy (NPWT) and mesenchymal stem cells (MSCs) on angiogenesis. In this study, 28 female Sprague-Dawley rats were used and divided into four groups. Full-thickness dorsal skin defects were created in 2 × 2 cm dimensions. The wounds were treated with only the ADM in group 1, the ADM and NPWT in group 2, the ADM and MSCs in group 3 and the ADM, NPWT and MSCs in group 4. By the ninth day of surgery, the excisional biopsy samples were histologically examined to identify the rates of ADM adherence to the recipient bed; the newly formed blood vessels which penetrate the ADM vertically and vascularisation were evaluated by immunohistochemical staining. The graft adherence rates were higher in group 4 than in the other groups statistically, p = 0.003. The numbers of cluster of differentiation 31 (CD31)-stained newly formed microvessels were higher in group 4 than in the other groups statistically, p < 0.05. All subjects in group 4 had the vertical vessels in normal calibration with open lumen vessels which penetrate the ADM. These findings suggest that MSC transplantation induces angiogenesis more efficiently than NPWT. The combination of the NPWT with MSC in this study has shown a synergistic effect on angiogenesis and has affected the neo-vascularisation of the ADM significantly.

Assessment of renal function; clearance, the renal microcirculation, renal blood flow, and metabolic balance.

Historically, tools to assess renal function have been developed to investigate the physiology of the kidney in an experimental setting, and certain of these techniques have utility in evaluating renal function in the clinical setting. The following work will survey a spectrum of these tools, their applications and limitations in four general sections. The first is clearance, including evaluation of exogenous and endogenous markers for determining glomerular filtration rate, the adaptation of estimated glomerular filtration rate in the clinical arena, and additional clearance techniques to assess various other parameters of renal function. The second section deals with in vivo and in vitro approaches to the study of the renal microvasculature. This section surveys a number of experimental techniques including corticotomy, the hydronephrotic kidney, vascular casting, intravital charge coupled device videomicroscopy, multiphoton fluorescent microscopy, synchrotron-based angiography, laser speckle contrast imaging, isolated renal microvessels, and the perfused juxtamedullary nephron microvasculature. The third section addresses in vivo and in vitro approaches to the study of renal blood flow. These include ultrasonic flowmetry, laser-Doppler flowmetry, magnetic resonance imaging (MRI), phase contrast MRI, cine phase contrast MRI, dynamic contrast-enhanced MRI, blood oxygen level dependent MRI, arterial spin labeling MRI, x-ray computed tomography, and positron emission tomography. The final section addresses the methodologies of metabolic balance studies. These are described for humans, large experimental animals as well as for rodents. Overall, the various in vitro and in vivo topics and applications to evaluate renal function should provide a guide for the investigator or physician to understand and to implement the techniques in the laboratory or clinic setting.

Assessment of coronary microvascular dysfunction in hypertrophic cardiomyopathy: first-pass myocardial perfusion cardiovascular magnetic resonance imaging at 1.5 T.

AIM: To evaluate the integrity of the coronary microvasculature in patients with hypertrophic cardiomyopathy (HCM) using first-pass magnetic resonance perfusion imaging. MATERIALS AND METHODS: Twenty-two patients with HCM and 13 healthy volunteers underwent cardiac magnetic resonance imaging (CMR) at rest. Imaging protocols included short axis cine, first-pass myocardial perfusion, and late-phase contrast-enhanced imaging. Left ventricular end-diastolic wall thickness (EDTH), myocardial thickening, maximal upslope of time-intensity curve (slopemax), and late myocardial gadolinium enhancement (LGE) were assessed for each myocardial segment. The differences in slopemax, myocardial thickening, and EDTH between healthy volunteers and HCM patients were evaluated as were differences among hypertrophic segments of different severities (mild, moderate, and severe hypertrophy) in a one-way analysis of variance analysis. The differences in slopemax, myocardial thickening, and EDTH between the segments with and without LGE were compared by independent-sample t-test. A Pearson correlation test was used to determine the relationships between slopemax, EDTH, and myocardial thickening. RESULTS: Slopemax was statistically significantly less in HCM patients; the degree of myocardial thickening was also significantly reduced (p < 0.001). Slopemax and the degree of thickening statistically significantly decreased with increasing degrees of myocardial hypertrophy (p < 0.05). Differences in slopemax, myocardial thickening, and EDTH were observed between segments with and without LGE (p < 0.05). Slopemax and myocardial thickening were negatively correlated with EDTH. CONCLUSION: First-pass myocardial perfusion CMR with slopemax measurements demonstrates microvascular coronary dysfunction in patients with HCM, a determination that may aid in risk stratification, therapeutic planning, and determination of prognosis for HCM.

Non-invasive assessment of microvascular and endothelial function.

The authors have utilized capillaroscopy and forearm blood flow techniques to investigate the role of microvascular dysfunction in pathogenesis of cardiovascular disease. Capillaroscopy is a non-invasive, relatively inexpensive methodology for directly visualizing the microcirculation. Percent capillary recruitment is assessed by dividing the increase in capillary density induced by postocclusive reactive hyperemia (postocclusive reactive hyperemia capillary density minus baseline capillary density), by the maximal capillary density (observed during passive venous occlusion). Percent perfused capillaries represents the proportion of all capillaries present that are perfused (functionally active), and is calculated by dividing postocclusive reactive hyperemia capillary density by the maximal capillary density. Both percent capillary recruitment and percent perfused capillaries reflect the number of functional capillaries. The forearm blood flow (FBF) technique provides accepted non-invasive measures of endothelial function: The ratio FBF(max)/FBF(base) is computed as an estimate of vasodilation, by dividing the mean of the four FBF(max) values by the mean of the four FBFbase values. Forearm vascular resistance at maximal vasodilation (FVR(max)) is calculated as the mean arterial pressure (MAP) divided by FBF(max). Both the capillaroscopy and forearm techniques are readily acceptable to patients and can be learned quickly. The microvascular and endothelial function measures obtained using the methodologies described in this paper may have future utility in clinical patient cardiovascular risk-reduction strategies. As we have published reports demonstrating that microvascular and endothelial dysfunction are found in initial stages of hypertension including prehypertension, microvascular and endothelial function measures may eventually aid in early identification, risk-stratification and prevention of end-stage vascular pathology, with its potentially fatal consequences.

Noninvasive assessment of the iridial microcirculation in rats using sidestream dark field imaging.

Sidestream dark field imaging represents a novel, noninvasive method to study the microcirculation in humans and animals. To-date, it has been used extensively in various peripheral tissues (e.g. sublingual area, intestinal mucosa), however no data for the ocular vasculature, including the iridial microcirculation, are currently available. Therefore, the aim of this study was to examine the reliability and reproducibility of sidestream dark field imaging within the iridial microcirculation in experimental animals. Male Lewis rats were anaesthetized and the iris microvasculature was observed using an sidestream dark field probe gently placed against a cover slip covering the right eye. All video sequences recorded were analysed off-line by using AVA 3.0 software (MicroVision Medical, Amsterdam, The Netherlands). Results are expressed as mean (±SE) or median (interquartile range). Clear images were recorded from each animal and the total number of analysable video sequences was 50. All raw data for selected vessel density parameters passed normality test. The total all and small vessel density (in mm mm(-2) ) were 22,6 (±0,58) and 19,6 (±0,68), respectively. The perfused all and small vessel density were 20,9 (±0,61) and 19,1 (±0,65), respectively. The mean values of all iris vessel density parameters are shown in Figure 4. The DeBacker Score (n/mm) was 15,2 (±0,45), the proportion of perfused vessel was 94,5% (89,8-99,1%), and the MFI was 3 points (3-3). Taken together, these results indicate that SDF imaging provides a reliable and noninvasive method to examine the iridial microvascular bed in vivo and, thus, may provide unique opportunities for the study of the iridial vascular network in various experimental and clinical settings and disease models.