Red Blood Cell Velocity Research Articles

Novel findings in the cephalic phase of digestion: A role for microcirculation?

The cephalic phase of digestion (CPD) has been extensively investigated in terms of digestion and metabolism. Nevertheless, microcirculatory changes required to prepare peripheral tissues in order to dispose nutrients have never been assessed. In this study, microvascular function has been evaluated to determine its behavior and potential association to hormonal secretions during CPD. Thirty-nine healthy male subjects, 23.4±0.5years (mean±SD) and BMI of 23.3±2.3kg/m2, were randomized into receiving cognitive-sensorial stimuli to elicit CPD (CPD group, n=20) or not (control group, n=19), after a 12-h overnight fast. Main outcomes were differences in resting and peak functional capillary density (FCD, cap/mm2); resting red blood cell velocity (RBCV), peak RBCV (RBCVmax) and time taken to reach it (TRBCVmax); peak flow and vasomotion, before and after CPD and their associations with insulin and/or pancreatic polypeptide (PP). In the CPD group, basal FCD (24.9±7.6 to 28.3±8.1, p=0.005), peak FCD (27.8±6.3 to 32.6±7.1, p=0.002), RBCV (0.306±0.031 to 0.330±0.027mm/s, p=0.005), RBCVmax (0.336±0.029 to 0.398±0.292mm/s, p=0.005) and peak flow (23.5±14.3 to 26.9±15.8 PU, p<0.01) increased while TRBCVmax decreased (4.9±1.5 to 3.5±1.2s, p=0.01). No significant changes could be detected in the control group. Groups have not presented differences for insulin, but PP significantly increased in the CPD group and was positively associated to basal FCD increase (rho=0.527, p=0.03). In conclusion, neurally-mediated anticipatory responses of digestion elicited functional capillary recruitment associated to PP in healthy men, suggesting a precocious role for microcirculation in the physiology of digestion and nutrient homeostasis.

The Roles of Cerebral Blood Flow, Capillary Transit Time Heterogeneity, and Oxygen Tension in Brain Oxygenation and Metabolism

Normal brain function depends critically on moment-to-moment regulation of oxygen supply by the bloodstream to meet changing metabolic needs. Neurovascular coupling, a range of mechanisms that converge on arterioles to adjust local cerebral blood flow (CBF), represents our current framework for understanding this regulation. We modeled the combined effects of CBF and capillary transit time heterogeneity (CTTH) on the maximum oxygen extraction fraction (OEFmax) and metabolic rate of oxygen that can biophysically be supported, for a given tissue oxygen tension. Red blood cell velocity recordings in rat brain support close hemodynamic–metabolic coupling by means of CBF and CTTH across a range of physiological conditions. The CTTH reduction improves tissue oxygenation by counteracting inherent reductions in OEFmax as CBF increases, and seemingly secures sufficient oxygenation during episodes of hyperemia resulting from cortical activation or hypoxemia. In hypoperfusion and states of blocked CBF, both lower oxygen tension and CTTH may secure tissue oxygenation. Our model predicts that disturbed capillary flows may cause a condition of malignant CTTH, in which states of higher CBF display lower oxygen availability. We propose that conditions with altered capillary morphology, such as amyloid, diabetic or hypertensive microangiopathy, and ischemia–reperfusion, may disturb CTTH and thereby flow-metabolism coupling and cerebral oxygen metabolism.

Cardiac displacement during off-pump coronary artery bypass grafting surgery: effect on sublingual microcirculation and cerebral oxygenation

Cardiac displacement during off-pump coronary artery bypass (OPCAB) surgery causes a fall in cardiac output. Here, we investigate how this drop in systemic perfusion is transferred to the oxygenation of sublingual and cerebral tissue. Sublingual microcirculatory perfusion or microcirculatory hemoglobin oxygen saturation (μHbSO(2)) measurements were performed using sidestream dark-field imaging and reflectance spectrophotometry, respectively (both n = 12). The cerebral tissue oxygenation index was measured by near-infrared spectrophotometry (n = 12). Cardiac output was calculated by pulse contour analysis of arterial pressure. Cardiac displacement reduced the cardiac output from 4.3 ± 0.8 to 1.2 ± 0.3 l/min (P < 0.05), paralleled by a decrease in μHbSO(2) from 64.2 ± 9.1 to 48.6 ± 8.7% (P < 0.01). Cardiac displacement did not change functional capillary density, while red blood cell velocity decreased from 895 ± 209 to 396 ± 178 μm/s (P<0.01). Cerebral tissue oxygenation index decreased from 69.5 ± 4.0 to 57.4 ± 8.5% (P<0.01) during cardiac displacement. After repositioning of the heart, all the values returned to baseline. Our data suggest that systemic hemodynamic alterations during cardiac displacement in OPCAB surgery reduce sublingual and cerebral tissue oxygenation. These findings are particularly important for patients at risk for the consequences of cerebral ischemia.

Activated Protein C Restores Hepatic Microcirculation During Sepsis by Modulating Vasoregulator Expression

Activated protein C (aPC) promotes fibrinolysis while inhibiting coagulation and inflammation. In septic patients, aPC levels are depleted, and aPC treatment has emerged as a therapeutic option. To better understand the mechanism(s) by which aPC improves survival in sepsis, we sought to determine the effect of aPC treatment on hepatic vasoactive gene and protein expression, leading to changes in hepatic vascular responsiveness in a septic animal model. Under anesthesia, rats underwent sham or cecal ligation and puncture followed by aPC treatment (1 mg/kg, twice daily, i.v.). Treatment with aPC significantly decreased hepatic endothelin 1 (ET-1)/ET A receptor mRNA and protein expression. To determine the effect of aPC on hepatic microvasculature, ET-1-induced changes in liver microcirculation were assessed by intravital microscopy. This approach demonstrated aPC significantly improved hepatic perfusion index in the animals that underwent cecal ligation and puncture in the absence of significant changes in portal venous pressure. Furthermore, although aPC did not affect ET-1-dependent sinusoidal vasoconstriction, aPC induced hepatoprotective effects via enhanced red blood cell velocity. Collectively, these data demonstrate aPC ameliorates ET-1-dependent changes in hepatic microcirculation and improves hepatic function in the setting of sepsis.

Effects of increased white blood cell count on retinal perfusion during hyperoxia-induced vasoconstriction

PurposeSeveral studies have shown that administration of granulocyte-colony stimulating factor (G-CSF) is followed by an increase of white blood cell (WBC) count. There is evidence from other vascular beds that an increase in WBC count impairs blood flow regulation especially in the microcirculation. Whether this also holds true for the ocular circulation is yet unknown. In the following trial we investigated whether an increase in WBC count alters the oxygen induced vasoconstriction of retinal vessels. MethodsThe study design was randomized, double-masked, placebo-controlled with two parallel groups. 24 healthy, male subjects were included. Measurements of retinal white blood cell flux with the blue-field entoptic technique, red blood cell velocity using the laser Doppler velocimeter and retinal vessel diameter using a Retinal Vessel Analyzer, were assessed at baseline and after breathing of 100% oxygen over 20min. Thereafter 300μg of G-CSF or placebo was administered. Measurements were repeated after another inhalation of 100% oxygen 8h later. ResultsG-CSF did not show any influence on systemic hemodynamics. WBC count increased significantly from 5.7±1.6×109/L at baseline up to 19.5±4.8×109/L 8h after G-CSF administration. As expected, oxygen breathing induced a pronounced vasoconstriction and a decrease red and white cell flux in both, the placebo and the G-CSF group (p<0.01 for both groups). Administration of G-CSF increased WBC flux, but did not affect red blood cell flux. The response of red blood cell flux and retinal vessel diameters to hyperoxia was not altered by G-CSF administration. However, leukocytosis leads to a more pronounced oxygen induced reduction in red blood cell velocity compared to the placebo group (p=0.024). ConclusionOur data indicate that increased WBC count as induced with G-CSF, leads to a more pronounced reduction in retinal red blood cell flux during states of vasoconstriction. This indicates that, as in other vascular beds, an increase in WBC leads to an altered blood flow regulation.

A processing work-flow for measuring erythrocytes velocity in extended vascular networks from wide field high-resolution optical imaging data

Comprehensive information on the spatio-temporal dynamics of the vascular response is needed to underpin the signals used in hemodynamics-based functional imaging. It has recently been shown that red blood cells (RBCs) velocity and its changes can be extracted from wide-field optical imaging recordings of intrinsic absorption changes in cortex. Here, we describe a complete processing work-flow for reliable RBC velocity estimation in cortical networks. Several pre-processing steps are implemented: image co-registration, necessary to correct for small movements of the vasculature, semi-automatic image segmentation for fast and reproducible vessel selection, reconstruction of RBC trajectories patterns for each micro-vessel, and spatio-temporal filtering to enhance the desired data characteristics. The main analysis step is composed of two robust algorithms for estimating the RBCs' velocity field. Vessel diameter and its changes are also estimated, as well as local changes in backscattered light intensity. This full processing chain is implemented with a software suite that is freely distributed. The software uses efficient data management for handling the very large data sets obtained with in vivo optical imaging. It offers a complete and user-friendly graphical user interface with visualization tools for displaying and exploring data and results. A full data simulation framework is also provided in order to optimize the performances of the algorithm with respect to several characteristics of the data. We illustrate the performance of our method in three different cases of in vivo data. We first document the massive RBC speed response evoked by a spreading depression in anesthetized rat somato-sensory cortex. Second, we show the velocity response elicited by a visual stimulation in anesthetized cat visual cortex. Finally, we report, for the first time, visually-evoked RBC speed responses in an extended vascular network in awake monkey extrastriate cortex.

Characterization of retinal blood flow in healthy subjects

AbstractPurpose Here we present by far the largest study in healthy subjects in an effort to characterize the physiology of retinal blood flow.Methods In the present study 64 healthy subjects aged between 18 and 45 years were included. Bi‐directional laser Doppler velocimetry (Oculix, Arbaz, Switzerland) was used to measure retinal blood velocities. Venous vessel diameters were measured using the Retinal Vessel Analyzer (Imedos, Jena, Germany). Retinal blood flow was calculated by measuring all visible veins entering the optic nerve head. The perfusion values in the 4 quadrants were evaluated. In addition, the correlation between vessel diameters and red blood cell velocities was studied.Results Total retinal blood flow was 46.2 ± 6.4 µl/min. The range of total retinal blood flow values was very high (29.0 – 70.8 µl/min). Blood flow was highest in the temporal inferior quadrant (17.9 ± 6.1 µl/min), followed by the temporal superior quadrant (12.2 ± 6.0 µl/min), the nasal inferior quadrant (7.3 ± 2.0 µl/min) and the nasal superior quadrant (6.5 ± 2.2 µl/min). In all four quadrants a highly significant linear correlation was found between blood velocities and vessel diameters (r‐values between 0.55 and 0.89). The regression line was, however, considerably steeper in superior than in inferior vessels. Whereas, within the confidence limits, the regression line included the point 0,0 in the velocity‐diameter graph in inferior veins, this was not the case in superior veins.Conclusion The present data indicate that retinal blood flow shows a wide range in healthy subjects. In addition, differences were seen between the flow characteristics of the vessels in the inferior and the superior parts of the retina. The reason for these differences is hitherto unknown.

Evaluation of basal cell carcinoma microcirculation through orthogonal polarization technique

Basal cell carcinomas are the most common cutaneous neoplasias. They rarely metastasize, but can cause clinically significant local destruction and disfigurement if neglected or inadequately treated. The spectral imaging technique, a recently developed method of orthogonal light polarization, allows in vivo transcutaneous evaluation of tumor microcirculation. The objective of this work was to compare tumor and normal skin microcirculation in patients using the orthogonal polarization (OPS) technique. Forty histologically confirmed basal cell carcinomas of 36 patients were evaluated in order to accomplish our objective. Compared to control skin, basal cell carcinomas had significantly greater capillary diameters (10.6±2.6 and 18.5±6.2μm, respectively), capillary density (25.0±10.4 and 50.3±16.9cm/cm(2), respectively) and red blood cell velocities (0.06±0.03 and 0.11±0.07mm/s). Our results have demonstrated significant microcirculatory alterations in skin tumors using the OPS technique that allows its transcutaneous evaluation in vivo, in the absence of anesthesia and invasive surgical procedures. This technique could be a promising tool for researchers studying diseases in which angiogenesis plays a major role.

Modeling the Measurements of Cochlear Microcirculation and Hearing Function after Loud Noise

Recent findings support the crucial role of microcirculatory disturbance and ischemia for hearing impairment especially after noise-induced hearing loss (NIHL). The aim of this study was to establish an animal model for in vivo analysis of cochlear microcirculation and hearing function after a loud noise to allow precise measurements of both parameters in vivo. Randomized controlled trial. Setting. Animal study. Subjects and Methods. After assessment of normacusis (0 minutes) using evoked auditory brainstem responses (ABRs), noise (106-dB sound pressure level [SPL]) was applied to both ears in 6 guinea pigs for 30 minutes while unexposed animals served as controls. In vivo fluorescence microscopy of the stria vascularis capillaries was performed after surgical exposure of 1 cochlea. ABR measurements were derived from the contralateral ear. After noise exposure, red blood cell velocity was reduced significantly by 24.3% (120 minutes) and further decreased to 44.5% at the end of the observation (210 minutes) in contrast to stable control measurements. Vessel diameters were not affected in both groups. A gradual decrease of segmental blood flow became significant (38.1%) after 150 minutes compared with controls. Hearing thresholds shifted significantly from 20.0 ± 5.5 dB SPL (0 minutes) to 32.5 ± 4.2 dB SPL (60 minutes) only in animals exposed to loud noise. With regard to novel treatments targeting the stria vascularis in NIHL, this standardized model allows us to analyze in detail cochlear microcirculation and hearing function in vivo.

Effects of Hot and Cold Foods on Signals of Heart Rate Variability and Nail Fold Microcirculation of Healthy Young Humans: A Pilot Study

In traditional Chinese medicine, hot- and cold-attribute of food ingredients are a major part of dietary therapy. The aim of this study was to establish a suitable scientific methodology to define the attributes of food ingredients by investigating the relationship between food attributes and the physiological signals produced in healthy young subjects with different constitutions. Thirty subjects were grouped into hot and cold constitutions by Chinese medical doctors. Every subject took water, aged ginger tea and coconut water, which are well recognized as having neutral-, hot- and cold-attribute, respectively, on different visits. The different physiological signals induced by the samples were observed using skin and axillary temperature sensors, a heart rate variability analyzer and a laser Doppler anemometer. We found that the capillary red blood cell (RBC) velocity in nail fold microcirculation (NFM) of the subjects with hot constitution accelerated significantly after taking the hot-attribute aged ginger tea, which might be the result of elevated vagal activity leading to arteriole dilation in these subjects. In contrast, in subjects with cold constitution, capillary RBC velocity decelerated significantly and skin temperature decreased markedly after taking the cold-attribute coconut water, which might have been induced by sympathetic nerve activation causing the arteriole to be constricted. Accordingly, the use of capillary RBC velocity of NFM measured by laser Doppler anemometer may be a promising way to classify attributes of food ingredients commonly used in Chinese medicine dietary therapy in accordance with different personal constitutions.

Inhibition of 20-HETE attenuates diabetes-induced decreases in retinal hemodynamics

The mechanisms of early diabetes-induced decreases in retinal blood flow have yet to be fully determined. The aim of this study was to explore the hypothesis that 20-hydroxyeicosatetraenoic acid (20-HETE) plays a role in the early decrease of retinal hemodynamics in diabetic mice. 20-HETE has been implicated previously in the diabetes-enhanced vasoconstriction of mesenteric and renal vessels; however, its role in the diabetic retinal microcirculation has not been investigated. Diabetes was induced by multiple low-dose injections of streptozotocin (STZ; 50 mg/kg for 5 consecutive days), then ∼2 weeks later the mice were administered daily intraperitoneal injections with or without the 20-HETE inhibitor HET0016 (2.5 mg/kg/day) for the following 2 weeks. Non-diabetic age-matched mice were included as controls. Intravital microscopy was used to obtain measurements of retinal vascular diameters and red blood cell (RBC) velocities for the feed arterioles and draining venules extending out of and into the optic disk. From these values, wall shear rates and blood flow rates were calculated. Diabetes induced approximately 30–40% decreases in RBC velocity, wall shear rate, and blood flow rate. These decreases were attenuated to 5–10% in the mice given HET0016. In summary, the 20-HETE inhibitor HET0016 is able to attenuate the retinal hemodynamic changes induced by diabetes.

Brazil nuts intake improves lipid profile, oxidative stress and microvascular function in obese adolescents: a randomized controlled trial.

BackgroundObesity is a chronic disease associated to an inflammatory process resulting in oxidative stress that leads to morpho-functional microvascular damage that could be improved by some dietary interventions. In this study, the intake of Brazil nuts (Bertholletia excelsa), composed of bioactive substances like selenium, α- e γ- tocopherol, folate and polyunsaturated fatty acids, have been investigated on antioxidant capacity, lipid and metabolic profiles and nutritive skin microcirculation in obese adolescents.MethodsObese female adolescents (n = 17), 15.4 ± 2.0 years and BMI of 35.6 ± 3.3 kg/m2, were randomized 1:1 in two groups with the diet supplemented either with Brazil nuts [BNG, n = 08, 15-25 g/day (equivalent to 3 to 5 units/day)] or placebo [PG (lactose), n = 09, one capsule/day] and followed for 16 weeks. Anthropometry, metabolic-lipid profiles, oxidative stress and morphological (capillary diameters) and functional [functional capillary density, red blood cell velocity (RBCV) at baseline and peak (RBCVmax) and time (TRBCVmax) to reach it during post-occlusive reactive hyperemia, after 1 min arterial occlusion] microvascular variables were assessed by nailfold videocapillaroscopy at baseline (T0) and after intervention (T1).ResultsT0 characteristics were similar between groups. At T1, BNG (intra-group variation) had increased selenium levels (p = 0.02), RBCV (p = 0.03) and RBCVmax (p = 0.03) and reduced total (TC) (p = 0.02) and LDL-cholesterol (p = 0.02). Compared to PG, Brazil nuts intake reduced TC (p = 0.003), triglycerides (p = 0.05) and LDL-ox (p = 0.02) and increased RBCV (p = 0.03).ConclusionBrazil nuts intake improved the lipid profile and microvascular function in obese adolescents, possibly due to its high level of unsaturated fatty acids and bioactive substances.Trial RegistrationClinical Trials.gov NCT00937599

Assessment of a chloride-poor versus a chloride-containing version of a modified histidine-tryptophan-ketoglutarate solution in a rat liver transplantation model

Recent in vitro studies of cold-induced cell injury have revealed the detrimental effects of extracellular chloride on cold-stored isolated rat hepatocytes; however, its influence on endothelial cells is beneficial. To determine which of these effects is predominant in vivo, we tested both a chloride-poor variant of a new histidine-tryptophan-ketoglutarate (HTK)-based preservation solution and a chloride-containing variant in a rat liver transplantation model. The study, which was carried out in a blinded fashion with 7 or 8 rats per group, was divided into 2 parts: (1) a comparison of survival in 3 series under different conditions [different microsurgeons, rat strains, cold ischemia times (3, 12, and 24 hours), and warm ischemia times] and (2) an assessment of the microcirculation (30-90 minutes after reperfusion), laboratory data, bile production, and histology. In each of the survival experiments, a (strong) tendency toward prolonged survival was observed with the new chloride-containing solution (50% versus 12.5%, 75% versus 37.5%, and 100% versus 71.4% [chloride-containing vs. chloride-poor], overall P < 0.05). Additionally, the sinusoidal perfusion rates (83.9% ± 4.0% versus 69.2% ± 10.8%, P < 0.01) and the red blood cell velocities in sinusoids (147.7 ± 26.7 versus 115.5 ± 26.0 μm/second, P < 0.05) and in postsinusoidal venules (332.4 ± 87.3 versus 205.5 ± 53.5 μm/second, P < 0.01) were clearly higher with chloride. Moreover, the serum activities of liver enzymes were slightly reduced (not significantly), and bile production was significantly increased. These results suggest an overall beneficial effect of chloride in HTK-based liver preservation solutions.

Treatment of severe peripheral arterial and vasospastic disease of the upper extremity by spinal cord stimulation

Spinal cord stimulation (SCS) has been successfully introduced for treatment of severe peripheral arterial disease of the lower limbs. However, the effect of SCS for treatment of severe vasospastic disease (VD) and peripheral arterial disease (PAD) of the upper extremities remains uncertain. Therefore, the efficacy of SCS for pain reduction and increase of blood supply was studied in four patients with severe PAD and in six patients with VD of the upper limbs. Transcutaneous oxygen tension index (chest TcpO2/hand TcpO2), Doppler wrist pressure index (WPI), capillary microscopy (CM), and a patients pain score (PS) graded from 1 to 10 (1=no pain) were used as follow-up parameters. Pain reduction after SCS was excellent in all patients and remained significant throughout the follow-up period. TcpO2 index decreased significantly (2.01±0.79 prae-OP vs 1.57±0.62 at 18 months). Capillary microscopy improved regarding red blood cell velocity and capillary density. Doppler WPI remained unchanged throughout the course. The results demonstrate that treatment of severe PAD and VD by use of thoracic SCS reduces pain significantly in these patients and increases blood supply. SCS provides a successful method of treatment for refractory VD and PAD of the upper extremity.

High Intracranial Pressure Effects on Cerebral Cortical Microvascular Flow in Rats

To manage patients with high intracranial pressure (ICP), clinicians need to know the critical cerebral perfusion pressure (CPP) required to maintain cerebral blood flow (CBF). Historically, the critical CPP obtained by decreasing mean arterial pressure (MAP) to lower CPP was 60 mm Hg, which fell to 30 mm Hg when CPP was reduced by increasing ICP. We examined whether this decrease in critical CPP was due to a pathological shift from capillary (CAP) to high-velocity microvessel flow or thoroughfare channel (TFC) shunt flow. Cortical microvessel red blood cell velocity and NADH fluorescence were measured by in vivo two-photon laser scanning microscopy in rats at CPP of 70, 50, and 30 mm Hg by increasing ICP or decreasing MAP. Water content was measured by wet/dry weight, and cortical perfusion by laser Doppler flux. Reduction of CPP by raising ICP increased TFC shunt flow from 30.4±2.3% to 51.2±5.2% (mean±SEM, p<0.001), NADH increased by 20.3±6.8% and 58.1±8.2% (p<0.01), and brain water content from 72.9±0.47% to 77.8±2.42% (p<0.01). Decreasing CPP by MAP decreased TFC shunt flow with a smaller rise in NADH and no edema. Doppler flux decreased less with increasing ICP than decreasing MAP. The decrease seen in the critical CPP with increased ICP is likely due to a redistribution of microvascular flow from capillary to microvascular shunt flow or TFC shunt flow, resulting in a pathologically elevated CBF associated with tissue hypoxia and brain edema, characteristic of non-nutritive shunt flow.

Hemodynamic changes in the kidney in a pediatric rat model of sepsis-induced acute kidney injury

Sepsis is a leading cause of acute kidney injury (AKI) and mortality in children. Understanding the development of pediatric sepsis and its effects on the kidney are critical in uncovering new therapies. The goal of this study was to characterize the development of sepsis-induced AKI in the clinically relevant cecal ligation and puncture (CLP) model of peritonitis in rat pups 17-18 days old. CLP produced severe sepsis demonstrated by time-dependent increase in serum cytokines, NO, markers of multiorgan injury, and renal microcirculatory hypoperfusion. Although blood pressure and heart rate remained unchanged after CLP, renal blood flow (RBF) was decreased 61% by 6 h. Renal microcirculatory analysis showed the number of continuously flowing cortical capillaries decreased significantly from 69 to 48% by 6 h with a 66% decrease in red blood cell velocity and a 57% decline in volumetric flow. The progression of renal microcirculatory hypoperfusion was associated with peritubular capillary leakage and reactive nitrogen species generation. Sham adults had higher mean arterial pressure (118 vs. 69 mmHg), RBF (4.2 vs. 1.1 ml·min(-1)·g(-1)), and peritubular capillary velocity (78% continuous flowing capillaries vs. 69%) compared with pups. CLP produced a greater decrease in renal microcirculation in pups, supporting the notion that adult models may not be the most appropriate for studying pediatric sepsis-induced AKI. Lower RBF and reduced peritubular capillary perfusion in the pup suggest the pediatric kidney may be more susceptible to AKI than would be predicted using adults models.

Effect of Tempol on Diabetes-Induced Decreases in Retinal Blood Flow in the Mouse

Purpose: The purpose was to investigate the effect of the superoxide dismutase mimetic tempol on decreases in retinal blood flow that are found in diabetic mice.Materials and Methods: Streptozotocin (STZ) was injected into male C57BL/6 mice to induce hyperglycemia. One week following the STZ injection, subsets of the mice were given drinking water with or without 1 mM tempol for an additional three weeks. At the end of the four-week protocol, microvascular parameters were quantified via intravital microscopy, and included measurements of retinal diameters, red blood cell (RBC) velocities, blood flow rates, and wall shear rates.Results: Diabetes induced ~40–45% decreases in retinal blood flow rate (p < 0.001) four weeks following injection of STZ. The decrease in blood flow rate occurred with decreases in microvascular diameters (D) and RBC velocities (V). The average percentage decrease in velocity was greater than the percentage decrease in diameter and, therefore, wall shear rates (= 8 V/D) were ~25% lower in the diabetics than in the non-diabetics (p < 0.05). A three-week administration of tempol in the STZ mice allowed significantly higher blood flow rates than in the untreated STZ mice, with RBC velocities improved by the antioxidant (p < 0.05 on the venular side). However, tempol provided only moderate (and not statistically significant) improvements in wall shear rates.Conclusions: The antioxidant tempol provides partial improvements in retinal microvascular hemodynamics early in the progression of STZ-induced diabetes in mice.

New idea of intestinal lengthening and tailoring

Both the Bianchi and the serial transverse enteroplasty (STEP) procedure have been reported to be successful in short bowel syndrome, but both have their limitations. The Bianchi technique is surgically challenging and can only tailor the diameter to half and double the length. The STEP procedure is easy, adjustable, but it changes the orientation of the muscle fibres making the circular; longitudinal and the longitudinal; circular. We have created a model to test our idea of Spiral Intestinal Lengthening and Tailoring (SILT). A double layer intestinal simulator was used as the bowel model. The orientation of the circular muscle fibres was marked. The simulator was cut spirally at a 45° and 60° angle, stretched longitudinally and retubularised. The procedure was adapted to porcine small bowel ex vivo and mucosal microcirculation was observed in three separate points by intravital videomicroscopy in vivo. The simulator was lengthened by 60% and the diameter was tailored by 33% using the 45° spiral cut, 73% lengthening and 44% tailoring was achieved at 60°. The circular muscle fibres showed oblique orientation. The porcine bowel was lengthened by 136 ± 21% and the diameter was tailored by 56 ± 8%. The linear regression analysis of variants showed significant linear regression R = 0.9689 (R(2) = 0.9388), p = 0.0014. The angle of the spiral cut (α) showed the relation: α ≥ 90-arc sin R(2)/R(1). (R(1) is the radius of the original segment and R(2) the desired radius of the tailored and lengthened bowel). The bowel remained viable macroscopically 90 min after the procedure. The median red blood cell velocity reduced from 570 (control) to 558 μm s(-1) in point 1, to 382 μm s(-1) in point 2, and to 482 μm s(-1) in point 3. Oscillation of the capillary flow has not been observed. The SILT may be an easy, more physiological and adjustable alternative to the existing techniques.

Nitric oxide influences red blood cell velocity independently of changes in the vascular tone

Nitric oxide (NO) plays a key role in regulation of vascular tone and blood flow. In the microcirculation blood flow is strongly dependent on red blood cells (RBC) deformability. In vitro NO increases RBC deformability. This study hypothesized that NO increases RBC velocity in vivo not only by regulating vascular tone, but also by modifying RBC deformability. The effects of NO on RBC velocity were analysed by intra-vital microscopy in the microcirculation of the chorioallantoic membrane (CAM) of the avian embryo at day 7 post-fertilization, when all vessels lack smooth muscle cells and vascular tone is not affected by NO. It was found that inhibition of enzymatic NO synthesis and NO scavenging decreased intracellular NO levels and avian RBC deformability in vitro. Injection of a NO synthase-inhibitor or a NO scavenger into the microcirculation of the CAM decreased capillary RBC velocity and deformation, while the diameter of the vessels remained constant. The results indicate that scavenging of NO and inhibition of NO synthesis decrease RBC velocity not only by regulating vascular tone but also by decreasing RBC deformability.

Rat pial microvascular responses to melatonin during bilateral common carotid artery occlusion and reperfusion

The present study assessed the in vivo rat pial microvascular responses induced by melatonin during brain hypoperfusion and reperfusion (RE) injury. Pial microcirculation of male Wistar rats was visualized by fluorescence microscopy through a closed cranial window. Hypoperfusion was induced by bilateral common carotid artery occlusion (BCCAO, 30 min); thereafter, pial microcirculation was observed for 60 min. Arteriolar diameter, permeability increase, leukocyte adhesion to venular walls, perfused capillary length (PCL), and capillary red blood cell velocity (V(RBC) ) were investigated by computerized methods. Melatonin (0.5, 1, 2 mg/kg b.w.) was intravenously administered 10 min before BCCAO and at the beginning of RE. Pial arterioles were classified in five orders according to diameter, length, and branchings. In control group, BCCAO caused decrease in order 2 arteriole diameter (by 17.5 ± 3.0% of baseline) that was reduced by 11.8 ± 1.2% of baseline at the end of RE, accompanied by marked leakage and leukocyte adhesion. PCL and capillary V(RBC) decreased. At the end of BCCAO, melatonin highest dosage caused order 2 arteriole diameter reduction by 4.6 ± 2.0% of baseline. At RE, melatonin at the lower dosages caused different arteriolar responses. The highest dosage caused dilation in order 2 arteriole by 8.0 ± 1.5% of baseline, preventing leakage and leukocyte adhesion, while PCL and V(RBC) increased. Luzindole (4 mg/kg b.w.) prior to melatonin caused order 2 arteriole constriction by 12.0 ± 1.5% of baseline at RE, while leakage, leukocyte adhesion, PCL and V(RBC) were not affected. Prazosin (1 mg/kg b.w.) prior to melatonin did not significantly change melatonin's effects. In conclusion, melatonin caused different responses during hypoperfusion and RE, modulating pial arteriolar tone likely by MT1 and MT2 melatonin receptors while preventing blood-brain barrier changes through its free radical scavenging action.