Orthogonal Polarization Spectral Imaging Research Articles

Restoring microcirculatory perfusion in a preclinical model of severe hemorrhagic shock: The role of microcirculatory function.

No reflow in capillaries (no reflow) is the lack of tissue perfusion that occurs once central hemodynamics are restored. This prevents oxygen transfer and debt repayment to vital tissues after shock resuscitation. Since metabolic swelling of cells and tissues can cause no reflow, it is a target for study in shock. We hypothesize no reflow secondary to metabolic cell swelling causes the problem not addressed by current strategies that increase central hemodynamics alone. Anesthetized swine were bled until plasma lactate reached 7.5 mM to 9 mM. Intravenous low volume resuscitation solutions were administered (6.8 mL/kg over 5 minutes) consisting of; (1) lactated Ringer (LR), (2) autologous whole blood, (3) high-dose vitamin C (200 mg/kg), or (4) 10% PEG-20k, a polymer-based cell impermeant that corrects metabolic cell swelling. Outcomes were macrohemodynamics (MAP), plasma lactate, capillary flow in the gut and tongue mucosa using orthogonal polarization spectral imaging (OPSI), and survival to 4 hours. All PEG-20k resuscitated swine survived 240 minutes with MAP above 60 mm Hg compared with 50% and 0% of the whole blood and LR groups, respectively. The vitamin C group died at just over 2 hours with MAPs below 40 and high lactate. The LR swine only survived 30 minutes and died with low MAP and high lactate. Capillary flow positively correlated ( p < 0.05) with survival and MAP. Sublingual OPSI correlated with intestinal OPSI and OPSI was validated with a histological technique. Targeting micro-hemodynamics in resuscitation may be more important than macrohemodynamics. Fixing both is optimal. Sublingual OPSI is clinically achievable to assess micro-hemodynamic status. Targeting tissue cell swelling that occurs during ATP depletion in shock using optimized osmotically active cell impermeants in crystalloid low volume resuscitation solutions improves perfusion in shocked tissues, which leverages a primary mechanism of injury.

Non-invasive techniques to access in vivo the skin microcirculation in patients.

The microcirculation is composed of blood vessels with mean internal diameter smaller than 100 μm. This structure is responsible for survival of cells and in the last 50 years its study has become increasingly interesting because it often participates in the pathophysiology of several diseases or can determine better or worse prognosis for them. Due to the growing importance of knowing more about the microcirculation, several techniques have been developed and now it is possible to study its structure or function. In the last 25 years, the cutaneous microcirculation has emerged as an accessible and representative portion of generalized vascular bed allowing the examination of mechanisms of microcirculatory function and dysfunction. This mini review presents several techniques used for non-invasive access to skin microcirculation, such as Nailfold Videocapillaroscopy, Orthogonal Polarization Spectral Imaging, Sidestream Dark Field Imaging, Incident Dark field Illumination, Laser Doppler Flowmetry, and Laser Speckle Contrast Imaging applied. The techniques presented will describe which types of variables (structural or functional) can be evaluated, their limitations and potential uses.

Microcirculation assessment of dexmedetomidine constant rate infusion during anesthesia of dogs with sepsis from pyometra: a randomized clinical study

ObjectiveTo compare dexmedetomidine and fentanyl constant rate infusions in anesthetic protocols for septic dogs with pyometra, using microcirculatory, hemodynamic and metabolic variables. Study designRandomized clinical study. AnimalsA total of 33 dogs with pyometra with two or more systemic inflammatory response syndrome variables undergoing ovariohysterectomy. MethodsDogs were randomized into two groups: group DG, dexmedetomidine (3 μg kg–1 hour–1; 17 dogs) and group FG, fentanyl (5 μg kg–1 hour–1; 16 dogs) infused during isoflurane anesthesia and mechanical ventilation. Microcirculation flow index (MFI), total vessel density and De Backer score were assessed using orthogonal polarization spectral imaging at the sublingual site. Heart rate, invasive blood pressure, temperature, arterial blood gas analysis and lactate concentration were obtained at various time points. Variables were recorded at baseline (BL), immediately before (T0), 30 (T30) and 60 (T60) minutes after infusion, and 60 minutes after surgery. Data were analyzed using the Shapiro-Wilk test. To compare variables between groups, the unpaired Student t test was used. Comparison between evaluation time points was performed with two-way anova for repeated measures. Where statistical significance was detected, the Bonferroni post hoc test was used. ResultsMFI was significantly higher in group FG at T30. Mean arterial pressure at T30 was higher in group DG (89 ± 15 mmHg) than in group FG (72 ± 13 mmHg). Lactate concentrations were not significantly different between groups at each time point. Both groups had similar clinical outcomes (mortality, extubation time and occurrence of hypotension and bradyarrhythmias). Conclusions and clinical relevanceDexmedetomidine (3 μg kg–1 hour–1) without a loading dose can be included in the maintenance of anesthesia in dogs with pyometra and sepsis without compromising microcirculation and hemodynamic values when compared with fentanyl (5 μg kg–1 hour–1).

Effects of açaí and cilostazol on skin microcirculation and viability of TRAM flaps in hamsters

BackgroundTissue necrosis caused by insufficient perfusion is a major complication in flap transfer. This study evaluated whether treatment with cilostazol or hydroalcoholic extract of seeds of Euterpe oleracea Mart. (açaí) protects the transverse rectus abdominis myocutaneous (TRAM) flap against ischemic damage in hamsters. Materials and methodsFifty-four hamsters were divided into three oral treatment groups: placebo, açaí, or cilostazol. Caudally based, unipedicled TRAM flaps were raised, sutured back, classified into four vascular zones (I-IV), and evaluated for tissue viability, capillary blood flow (CBF), perfused vessel density (PVD), and microvascular flow index (MFI) by orthogonal polarization spectral imaging at three time points: immediately postoperatively (IPO), 24 h postoperatively (24hPO), and 7 d postoperatively (7POD). ResultsComparing to placebo, açaí increased PVD at IPO and açaí and cilostazol increased CBF and PVD at 24hPO in zone I; cilostazol increased CBF, PVD, and MFI at IPO, and CBF at 24hPO in zone II; açaí and cilostazol increased CBF at all time points and PVD and MFI at IPO and 24hPO in zone III; cilostazol increased CBF at IPO and 7POD, açaí increased CBF at 7POD, and both increased PVD and MFI at all time points in zone IV; and açaí and cilostazol increased the percentage of viable area in zones III and IV. ConclusionsAçaí and cilostazol treatments had a protective effect against ischemic damage to TRAM flaps in hamsters, improving microvascular blood flow and increasing the survival of flap zones contralateral to the vascular pedicle (zones III and IV).

Microvascular Responsiveness to Pulsatile and Nonpulsatile Flow During Cardiopulmonary Bypass

Pulsatile perfusion may offer microcirculatory advantages over conventional nonpulsatile perfusion during cardiopulmonary bypass (CPB). Here, we present direct visual evidence of microvascular perfusion and vasoreactivity between perfusion modalities. A prospective, randomized cohort study of 20 high-risk cardiac surgical patients undergoing pulsatile (n= 10) or nonpulsatile (n= 10) flow during CPB was conducted. Changes in sublingual mucosal microcirculation were assessed with orthogonal polarization spectral imaging along with near-infrared spectroscopic indices of thenar muscle tissue oxygen saturation (StO2) and its recovery during a vascular occlusion test at the following time points: baseline (T0), 30 minutes on CPB (T1), 90 minutes on CPB (T2), 1 hour after CPB (T3), and 24 hours after CPB (T4). On the basis of our scoring scale, a shift in microcirculatory blood flow occurred over time. The pulsatile group maintained normal perfusion characteristics, whereas the nonpulsatile group exhibited deterioration in perfusion during CPB (T2: 74.0% ± 5.6% versus 57.6% ± 5.0%) and after CPB (T3: 76.2% ± 2.7% versus 58.9% ± 5.2%, T4: 85.7% ± 2.6% versus 69.8% ± 5.9%). Concurrently, no important differences were found between groups in baseline StO2 and consumption slope at all time points. Reperfusion slope was substantially different between groups 24 hours after CPB (T4: 6.1% ± 0.6% versus 3.7% ± 0.5%), indicating improved microvascular responsiveness in the pulsatile group versus the nonpulsatile group. Pulsatility generated by the roller pump during CPB improves microcirculatory blood flow and tissue oxygen saturation compared with nonpulsatile flow in high-risk cardiac surgical patients, which may reflect attenuation of the systemic inflammatory response and ischemia-reperfusion injury.

Pathophysiological mechanisms of chronic venous disease and their role in C0s clinical class

The aim of this review is to provide a clear understanding of the pathophysiological mechanisms of chronic venous disease (CVD) at different clinical stages and the possible role of these mechanisms in the development of symptoms in C0s clinical class of the Clinical, Etiologic, Anatomic, and Pathophysiologic classification, which consists of symptomatic patients without any visible or palpable signs of venous disease. The prevalence of C0s class in several epidemiological studies varies between 13% and 23% of the general population. Wall remodeling and valve destruction due to white cell endothelial interaction is the main cause of primary varicose veins, while deep vein thrombosis produces secondary changes leading to the postthrombotic syndrome. The underlying mechanism of the skin changes and ulceration is venous hypertension, which is transmitted to the skin microcirculation. Over the last 10 years, an improved videocapillaroscopic technique, the orthogonal polarization spectral imaging technique demonstrated that quantitative measurements in the skin microcirculation are progressively altered from C1 to C6 patients and that values in CVD patients are significantly different from healthy individuals (P < 0.05): capillary diameter increases and capillary morphology worsens from C2 to C5; diameter of the dermal papilla and diameter of the capillary bulk increase from C3 to C5; and functional capillary density (FCD) decreases from C4 to C5. In addition, significant changes have been shown between C0a and C0s patients despite the presence of normal conventional duplex scans in the latter: a decrease of FCD and an increase in the diameter of the dermal papilla. Functional abnormalities found to be present in C0s patients by recent studies include increased compliance of the venous wall (hypotonic phlebopathy), dilatation of deep veins in the calf producing an abnormally increased venous volume, reduction in emptying of venous reservoir, reduction in the venoarteriolar response on standing, and blood reflux in small venules despite a normal conventional duplex scan. However, most of the studies are small, and their findings need to be confirmed by larger series. It remains to be seen whether functional changes and microcirculatory changes respond to venoactive medications in parallel to the relief of symptoms.

Recent advances in bedside microcirculation assessment in critically ill patients.

Parameters related to macrocirculation, such as the mean arterial pressure, central venous pressure, cardiac output, mixed venous saturation and central oxygen saturation, are commonly used in the hemodynamic assessment of critically ill patients. However, several studies have shown that there is a dissociation between these parameters and the state of microcirculation in this group of patients. Techniques that allow direct viewing of the microcirculation are not completely disseminated, nor are they incorporated into the clinical management of patients in shock. The numerous techniques developed for microcirculation assessment include clinical assessment (e.g., peripheral perfusion index and temperature gradient), laser Doppler flowmetry, tissue oxygen assessment electrodes, videomicroscopy (orthogonal polarization spectral imaging, sidestream dark field imaging or incident dark field illumination) and near infrared spectroscopy. In the near future, the monitoring and optimization of tissue perfusion by direct viewing and microcirculation assessment may become a goal to be achieved in the hemodynamic resuscitation of critically ill patients.

Organ Pretreatment With Cytotopic Endothelial Localizing Peptides to Ameliorate Microvascular Thrombosis and Perfusion Deficits in Ex Vivo Renal Hemoreperfusion Models.

Hypothermic machine organ perfusion (HMP) offers opportunity to manipulate grafts with pharmacological agents prior to transplantation. Pretreating organs with novel cytotopic anticoagulant peptides that localize to endothelial cell membranes could ameliorate microvascular thrombotic sequelae posttransplantation. We describe experiments testing thrombalexin (TLN), a novel cell binding thrombin inhibitor, using porcine and unused human kidneys in a series of ex vivo normothermic hemoreperfusion models. Thirty-eight porcine kidneys were used. Control kidneys underwent pretreatment via HMP with either unmodified perfusion solution (n = 15) or solution with inactive-TLN (absent anticoagulant effect, n = 4). Test kidneys were perfused with TLN-treated solution (n = 19). All kidneys then underwent hemoreperfusion. Two unused human kidneys underwent a similar protocol. Hypothermic machine perfusion pretreatment facilitated delivery and tethering of TLN in the organ microvasculature. Hemoreperfusion challenge demonstrated improved perfusion in TLN-treated kidneys compared with controls: 26.4% superior flow (30.6 vs. 23.1 mL/min per 100 g, P = 0.019) and 28.9% higher perfusion flow indices (0.43 vs. 0.32 mL/min per 100 g mm Hg, P = 0.049). Orthogonal polarization spectral imaging demonstrated superior microvascular capillary perfusion in TLN-treated organs versus controls (9.1 vs 2.8 pl/s per mm, P = 0.021). Rapid-sampling microdialysis for cortical [lactate] as a marker of tissue ischemia/metabolism detected lower levels in TLN-treated kidneys. Perfusate analysis demonstrated reduced fibrin generation in TLN-treated kidneys correlating with perfusion data. Our data suggest that HMP graft pretreatment with cytotopic anticoagulants is feasible and ameliorates perfusion deficits seen in ex vivo hemoreperfusion models. There is potential for further development and application of this translational strategy to deliver locally active anticoagulants directly within grafts and decrease microvascular thrombotic sequelae, while avoiding systemic anticoagulation and its associated risks.

Assessment and Imaging of the Cerebrovascular Glycocalyx.

The glycocalyx is a gel-like layer lining the luminal surface of the endothelium. The glycocalyx exerts an important barrier role because it prevents exposure of plasma components to the endothelial surface. Disruption of the glycocalyx by local inflammation or ischemia results in decreased glycocalyx thickness which is associated with a number of vascular diseases. The cerebrovascular glycocalyx has sparsely been studied, but is of great interest because of its potential role in cerebrovascular disease. In this review, we describe all existing techniques to visualize the glycocalyx and designate techniques that may be suitable for studying the cerebrovascular glycocalyx. A total of seven imaging techniques are discussed thoroughly, including transmission electron microscopy, intravital microscopy, micro-particle image velocimetry, confocal laser scanning microscopy, two-photon laser scanning microscopy, orthogonal polarization spectral imaging and sidestream dark field/oblique imaging. Measurement of serum concentrations of glycocalyx-specific constituents is another method for glycocalyx analysis. Also, we have reviewed the methods of glycocalyx analysis by using these imaging techniques. So far, the cerebrovascular glycocalyx has only been studied in vitro. However, other cerebral microcirculatory properties have been studied in vivo. This suggests that the cerebrovascular glycocalyx can be studied in vivo by using some of the described techniques, when specific software is subjoined to the analysis. In conclusion, we have summarized techniques available for glycocalyx assessment, and explained the significance and technical possibilities regarding cerebrovascular glycocalyx visualization. Cerebrovascular glycocalyx assessment would add valuable information to our understanding of the pathophysiology of cerebrovascular disease. Moreover, as a part of the blood-brain barrier, more knowledge on the cerebrovascular glycocalyx may lead to better understanding of neurodegenerative conditions that are caused by a compromised blood-brain barrier including Alzheimer`s disease, vascular dementia, multiple sclerosis and epilepsy.

Intestinal Intramural Vascular Anastomoses

ABSTRACTIntroduction: Present surgical techniques are rarely relying on intestinal intramural vascular anastomoses; however, this could open new limits in reconstructive surgery. Our aim was to study the efficacy of the antimesenteric and the longitudinal intramural vascular anastomoses in a porcine model. Material and Methods: Five minipigs were used. Antimesenteric anastomoses: jejunal loops were detubularized by cutting along the antimesenteric line (Control), in the middle between the mesenteric and antimesenteric border (Group 1) and close to the mesenteric line (Group 2). Mucosal microcirculation (red blood cell velocity, perfusion rate) was recorded with orthogonal polarization spectral imaging (Cytoscan A/R) at the long edge of the detubularized bowel. Longitudinal anastomoses: records were made on a continuous jejunal loop following antimesenteric incision, detubularization, and subsequent ligation of 2, 4, and 6 neighboring vasa recta in the middle of the loop. The same study was repeated on the free end of completely divided jejunal segments with ligation of 2, 4, or 6 vasa recta. Results: Antimesenteric anastomoses: There was no statistically significant difference in red blood cell velocity and perfusion rate between Control and Groups 1 and 2. Longitudinal anastomoses: The red blood cell velocity dropped significantly, while the perfusion rate did not change significantly after ligation of 4 vasa recta in the continuous loop. In the loop with a free end, however, both parameters decreased significantly after ligation of four vessels. Conclusion: It is safe to rely on antimesenteric intramural anastomoses but strong limitation of longitudinal intramural vascular anastomoses should be considered in intestinal reconstructions.

Sidestream versus incident dark field imaging: How to compare two different technologies to study the microcirculation?

Proper perfusion of tissues and organs is necessary for the maintenance of physiologic functioning and homeostasis. The microcirculation, comprised of the smallest vessels such as capillaries, venules, and arterioles, is responsible for the delivery of oxygen and nutrients. Microhemodynamic changes during disease states can impair proper microcirculatory function leading to a hypoxic state and a buildup of waste products in certain body tissue [1]. From a clinical perspective, monitoring of microcirculatory parameters in patients is challenging. Primarily, non-invasive access to microcirculatory beds is usually limited to mucosal surfaces exposed to the environment, e.g. oral cavity. Technologies (hardand software) to observe and quantify microcirculatory function are still being developed, and have not been established in the clinical routine. Prior to the twenty-first century, bulky microscopes were used to study the microcirculation in patients, through techniques such as trans-illuminating tissue at oblique angles [2], epi-illumination of tissue using incident darkfield illumination (IDF) [3], and cross-polarized light [4]. The first handheld video microscope for microcirculatory observation was introduced in 1999, using orthogonal polarization spectral (OPS) imaging technology [5]. OPS imaging involved illuminating the tissue of interest with linearly polarized light and recording remitted light that had been orthogonally polarized through a polarizing filter. Only depolarized photons scattered in deep tissue contributed to the image, thereby allowing visualization of capillaries under mucosal membranes. In 2005, a second generation handheld video microscope was introduced using sidestream dark field (SDF) imaging [6, 7]. This technology illuminates tissue using a central probe surrounded by green light emitting diodes (530 nm). The green light is absorbed by hemoglobin in red blood cells, thereby illuminating surrounding tissue and allowing for the visualization of blood cells flowing through capillaries. The MicroScan video microscope (MicroVision Medical, Amsterdam, Netherlands) is the most commonly used portable handheld SDF device for research purposes. Until recently the main limitation in incorporating this technology at bedside diagnosis was obtaining quantifiable microcirculatory parameters in a timely manner. Semiquantitative analysis software (AVA 3, MicroVision Medical, Amsterdam, Netherlands) was specifically developed for the MicroScan video microscope to support offline analysis of the recorded videos. Recently, an updated software (AVA 4, MicroVision Medical, Amsterdam, Netherlands) was released, allowing automated real time analysis of the recorded videos. Validation studies for AVA 4 have not yet been published, therefore AVA 3 still remains the accepted ‘‘gold standard’’ for analyzing microcirculatory videos. Recently, a third generation of handheld microscope (CytoCam , Braedius Medical, Huizen, Netherlands) was introduced using IDF technology. The CytoCam system offers video resolutions of 4416 9 3312 pixels, while the MicroScan system offers resolutions of 720 9 580 pixels. Automated video analysis software is provided by the manufacturer (CytoCamTools , Braedius Medical, Huizen, Netherlands). & Christian Lehmann chlehmann@dal.ca

Noninvasive imaging technologies for cutaneous wound assessment: A review.

The ability to phenotype wounds for the purposes of assessing severity, healing potential and treatment is an important function of evidence-based medicine. A variety of optical technologies are currently in development for noninvasive wound assessment. To varying extents, these optical technologies have the potential to supplement traditional clinical wound evaluation and research, by providing detailed information regarding skin components imperceptible to visual inspection. These assessments are achieved through quantitative optical analysis of tissue characteristics including blood flow, collagen remodeling, hemoglobin content, inflammation, temperature, vascular structure, and water content. Technologies that have, to this date, been applied to wound assessment include: near infrared imaging, thermal imaging, optical coherence tomography, orthogonal polarization spectral imaging, fluorescence imaging, laser Doppler imaging, microscopy, spatial frequency domain imaging, photoacoustic detection, and spectral/hyperspectral imaging. We present a review of the technologies in use or development for these purposes with three aims: (1) providing basic explanations of imaging technology concepts, (2) reviewing the wound imaging literature, and (3) providing insight into areas for further application and exploration. Noninvasive imaging is a promising advancement in wound assessment and all technologies require further validation.

Monitoring Microcirculatory Blood Flow with a New Sublingual Tonometer in a Porcine Model of Hemorrhagic Shock.

Tissue capnometry may be suitable for the indirect evaluation of regional hypoperfusion. We tested the performance of a new sublingual capillary tonometer in experimental hemorrhage. Thirty-six anesthetized, ventilated mini pigs were divided into sham-operated (n = 9) and shock groups (n = 27). Hemorrhagic shock was induced by reducing mean arterial pressure (MAP) to 40 mmHg for 60 min, after which fluid resuscitation started aiming to increase MAP to 75% of the baseline value (60–180 min). Sublingual carbon-dioxide partial pressure was measured by tonometry, using a specially coiled silicone rubber tube. Mucosal red blood cell velocity (RBCV) and capillary perfusion rate (CPR) were assessed by orthogonal polarization spectral (OPS) imaging. In the 60 min shock phase a significant drop in cardiac index was accompanied by reduction in sublingual RBCV and CPR and significant increase in the sublingual mucosal-to-arterial PCO2 gap (PSLCO2 gap), which significantly improved during the 120 min resuscitation phase. There was significant correlation between PSLCO2 gap and sublingual RBCV (r = −0.65, p < 0.0001), CPR (r = −0.64, p < 0.0001), central venous oxygen saturation (r = −0.50, p < 0.0001), and central venous-to-arterial PCO2 difference (r = 0.62, p < 0.0001). This new sublingual tonometer may be an appropriate tool for the indirect evaluation of circulatory changes in shock.

Non-invasive imaging of microcirculation: a technology review.

Microcirculation plays a crucial role in physiological processes of tissue oxygenation and nutritional exchange. Measurement of microcirculation can be applied on many organs in various pathologies. In this paper we aim to review the technique of non-invasive methods for imaging of the microcirculation. Methods covered are: videomicroscopy techniques, laser Doppler perfusion imaging, and laser speckle contrast imaging. Videomicroscopy techniques, such as orthogonal polarization spectral imaging and sidestream dark-field imaging, provide a plentitude of information and offer direct visualization of the microcirculation but have the major drawback that they may give pressure artifacts. Both laser Doppler perfusion imaging and laser speckle contrast imaging allow non-contact measurements but have the disadvantage of their sensitivity to motion artifacts and that they are confined to relative measurement comparisons. Ideal would be a non-contact videomicroscopy method with fully automatic analysis software.

Microcirculatory Effects of Selective Endothelin-A Receptor Antagonism in Testicular Torsion

Testicular torsion without timely intervention causes incurable damage to the testis. We examined the causative role of microcirculatory injury in torsion induced testicular damage with particular regard to endothelin-A receptor activation. The microcirculatory consequences of testicular torsion were assessed in the presence or absence of endothelin-A receptor antagonism in rats. Microcirculatory perfusion changes (red blood cell velocity and pulsatile flow pattern alterations) were examined by an orthogonal polarization spectral imaging technique. Microcirculatory inflammatory alterations were assessed byfluorescence intravital video microscopy after 60-minute torsion followed by 240-minute reperfusion. As a specific endothelin-A receptor inhibitor, the antisense homology box derived peptide ETR-p1/fl was applied 10 minutes before reperfusion. Tissue accumulation of leukocytes was estimated by myeloperoxidase activity in tissue biopsies taken at the end of the 4-hour reperfusion period. In further experiments testicular weight as a marker of permanent damage was evaluated 45 days after torsion. The physiological pulsatile flow pattern ceased in the initial phase of reperfusion while leukocyte-endothelial interactions increased throughout the examined reperfusion period. Endothelin-A receptor antagonism caused earlier return of pulsatile flow and recovery of red blood cell velocity, and alleviated microcirculatory inflammatory reactions and atrophy. Results suggest a pathophysiological role of endothelin-A receptor activation in the pathogenesis of testicular torsion. This effect is related to deterioration in testicular perfusion and activation of microcirculatory inflammatory reactions.

Orthogonal polarization spectral imaging of conjunctival microcirculation

Orthogonal polarization spectral (OPS) imaging is an optical imaging technique that uses a handheld microscope and green polarized light to visualize the red blood cells in the microcirculation of organ surfaces. The purpose of this study was to evaluate whether OPS imaging can be used for the functional and morphological evaluation of microcirculation in the conjunctiva. To accomplish the aforementioned purpose, 21 eyes of 21 volunteer patients were examined. OPS images of the vasculature of the inferior conjunctiva and the nasal part of the bulbar conjunctiva were taken from each eye. The images were subsequently analyzed using a computer, and the following parameters were assessed: red blood cell velocity, blood vessel diameter, and functional capillary density. In addition, distinct qualitative aspects of the conjunctival microvasculature were characterized. OPS imaging facilitated both the observation of red blood cells that were flowing through conjunctival vessels on a white background, and the measurement of other quantitative and qualitative microvascular parameters. Significant differences between several measures of the inferior and nasal bulbar conjunctival microcirculations were found, including differences in the configurations of the vessel segments, the number of vessel segments, the number of bifurcations, the mean diffusion distance, and the functional capillary density. OPS imaging can be used to measure the diameters of microvessels, functional capillary density, and other parameters. Significant differences between the microcirculations of the inferior conjunctiva and the nasal bulbar conjunctiva were found, which indicates the necessity of using a standardized approach to examine the conjunctival vasculature. OPS imaging is suitable for both the functional and morphological evaluation of the conjunctival microcirculation.

The importance of liver microcirculation in promoting autoimmune hepatitis via maintaining an inflammatory cytokine milieu – A mathematical model study

In autoimmune diseases, inflammatory cytokine concentrations are important for initiating and maintaining the status of autoimmunity. Autoimmune hepatitis (AIH) is an inflammatory liver disease characterized by a loss of immune tolerance against specific antigens located in hepatocytes. During the progression of the disease, antigen-presenting cells and different classes of T-helper cells secrete specific cytokines important for maintaining the disease. As these cytokines are secreted into the local liver environment, the blood flow in liver sinusoids might influence the local cytokine concentration. Considering the liver tissue as a porous medium, based on Darcy׳s law, the microcirculation within a liver lobule was modelled. Using realistic physiological pressure differences and tissue permeabilities, the blood velocity inside the sinusoids could be calculated and validated with blood velocity data obtained via Orthogonal Polarization Spectral Imaging (OPSI). Furthermore, oxygen consumption is modelled to obtain Rappaport׳s acinus model. Finally, steady state spatial distributions of secreted cytokines within the liver lobule could be estimated for specified realistic production rates of T-helper cells. It could be demonstrated that the characteristics of the liver microcirculation have an important impact on establishing inflammatory cytokine levels within the portal fields and the vascular septa promoting the occurrence of interface hepatitis.

The polarization-difference interference imaging spectrometer-I. concept, principle, and operation

A static, compact, high optical throughput polarization-difference interference imaging spectrometer is presented. It is based on the combination of the angular shear of Wollaston prism and the lateral shear of Savart polariscope. Its remarkable characteristic is the simultaneous acquisition of the interferograms and two-dimensional images for the orthogonal polarization components of targets. Polarization spectral images of the components can be reconstructed using the algorithms of Fourier transformation and image fusion. A summation of the orthogonal polarization spectral images is equivalent to that of the conventional intensity spectral image. The difference is that the orthogonal polarization spectral images is named as polarization-difference spectral image. A higher contrast of the polarization-difference spectral image can not only provide more detailed texture information for the targets, but also can derive the size, concentration, and refractive index of elastic-scattered particles. The principle of polarization-difference interference imaging spectrometer is demonstrated in this paper. Expressions for interference intensities and theoretical simulation are presented. The mode for acquiring data is described. Approximate paraxial conditions of Fourier imaging lens for the formation of straight fringes are analyzed by using the Young's interference mode; and the influence factors for the visibility of fringes are analyzed. For the realization of a more compact system, the relationship between the collimating lens and imaging lens is analyzed in terms of optical field diffraction theory. The feasibility of the system is demonstrated by numerical simulation. This research can provide a novel development strategy for imaging spectropolarimeter.

Non-invasive detection of hypovolemia or fluid responsiveness in spontaneously breathing subjects

BackgroundIn the assessment of hypovolemia the value of functional hemodynamic monitoring during spontaneous breathing is debated. The aim of our study was to investigate in spontaneously breathing subjects the changes in hemodynamic parameters during graded central hypovolemia and to test whether slow patterned breathing improved the discriminative value of stroke volume (SV), pulse pressure (PP), and their variations (SVV, PPV). In addition, we tested the alterations in labial microcirculation.Methods20 healthy volunteers participated in our study. Central hypovolemia was induced by lower body negative pressure (LBNP). Continuous signals of ECG, non-invasive blood pressure and central venous pressure were recorded. During baseline and each stage of LBNP the labial microcirculation was investigated by orthogonal polarization spectral imaging, 3 minute periods of patterned breathing at 6 and 15/min respiratory rate were performed, and central venous blood gas analysis was done. Data from baseline and those of different LBNP levels were compared by analysis of variance and those of different breathing rates by t-test. Finally, we performed ROC analysis to assess the discriminative values of SV, PP, SVV and PPV.ResultsModerate central hypovolemia induced by LBNP caused significant, clinically relevant falls in PP (p < 0.05) and SV and central venous oxygen saturation (ScvO2) (p < 0.001). The proportion of perfused vessels (p < 0.001) and microvascular flow index decreased (p < 0.05). PPV increased (p < 0.001), however the magnitude of fluctuations was greater during slow patterned breathing (p < 0.001). SVV increased only during slow patterned breathing (p < 0.001). ROC analysis confirmed the best predictive value for SV (at 56 ml cut-off AUC 0.97, sensitivity 94%, specificity 95%). Slow patterned breathing improved the discriminative value of SVV (p = 0.0023).ConclusionsFunctional hemodynamic monitoring with slow patterned breathing to control spontaneous respiration may be worthy for further study in different populations for the assessment of hypovolemia and the prediction of volume responsiveness.

Changes in Intestinal Mucosal Microvascular Perfusion Assessed Using Orthogonal Polarisation Spectral Imaging in the Horse

AimsAlthough several markers for measuring global tissue perfusion are available, there are currently no practical measurements of capillary microvascular perfusion in horses with hypovolaemia. Orthogonal polarisation spectral (OPS) imaging allows assessment of capillary microvascular perfusion by visualisation of mucosal blood flow. This study aims to demonstrate that administration of the α2 adrenoreceptor agonist detomidine, results in measurable changes in mucosal blood flow that can be determined using OPS. We hypothesise that these changes will mirror known aberrations in total peripheral resistance and cardiac output.MethodsMicrovascular blood flow was recorded using OPS placed manually, per rectum in 6 normal horses (weighing 603 ± 134 kg) undergoing sedation for a range of clinical procedures. The OPS recordings were made prior to and following sedation (5, 10, 20 min) with detomidine (10 ug/kg bwt) and butorphanol (10 ug/kg bwt) administered by i.v. injection. Microvascular perfusion was determined using standardised methods from OPS recordings including proportion of perfused vessels (PPV), functional capillary density (FCD), microvascular flow index (MFI) and vessel density (VD).ResultsDetomidine had a significant effect on microvascular blood flow as demonstrated by changes in MFI, PPV and FCD 5 min following sedation (P&lt;0.001) and changes in VD 10 min after sedation (P&lt;0.02). Microvasculature had returned to the presedation baseline by 20 min for all criterions.ConclusionsThese data demonstrate that changes in organ perfusion known to be caused by α2 adrenoreceptor agonists result in observable changes in mucosal blood flow. This appears to mirror changes in cardiac output and total peripheral resistance previously demonstrated after administration of detomidine in the horse.Practical significanceThis technique may be a useful marker to use in early goal‐directed therapy in horses with systemic inflammatory response syndrome (SIRS) and severe intestinal pathology.AcknowledgementsThe staff at DAC Melton Mowbray for their assistance with the conduct of the study.Ethical animal researchThis study was approved by the University of Nottingham ethical review committee. Horses were admitted into the DAC veterinary facility for routine veterinary procedures and sedated for routine dental care or orthopaedic investigation. Full consent was given by the DAC for use of these horses in the study. Sources of funding: Student project undertaken at the University of Nottingham. Competing interests: None.