Search

Background/Objectives: The perioperative interplay between blood pressure, vasopressors, and macrocirculation is well established. However, in the context of free flap surgery, the potential impact of these factors on microvascular flow remains elusive. The aim was to evaluate the impact of norepinephrine administration on the microcirculation of free flaps. Methods: Postoperative systolic blood pressure (sBP), norepinephrine infusion rates (NIRs), and free flap microcirculation were monitored prospectively and analyzed retrospectively in patients receiving free flap surgery who required postoperative intermediate (IMC) or intensive care (ICU). Blood flow, hemoglobin oxygenation (SO2), and relative hemoglobin levels (rHbs) were measured over a period of 24 hours post-anastomosis by laser-doppler flowmetry and white light spectroscopy using the "Oxygen to See" device (O2C, LEA Medizintechnik, Gießen, Germany). Multivariate analysis was performed to determine the impact of NIR on microvascular flow, adjusting for several confounding factors. Subgroup analysis was conducted by categorizing into three groups based on patients' postoperative sBP. Results: Flaps were performed in 105 patients with a mean age of 61.46 ± 16.29 years. Postoperatively, an increase in microvascular flow over time was observed across all free flaps, while NIR decreased and sBP maintained stable values. Multivariate analysis revealed that the time post-anastomosis (B = 3.76, p < 0.001), SO2 (B = 0.55, p < 0.001), rHb (B= −0.79, p < 0.001), female gender (B = 29.25, p = 0.02), and no previous radiation therapy (B = 41.21, p = 0.04) had a significant impact on postoperative microvascular flow in free flaps. NIR, sBP, smoking status, old age, and ASA score showed no significant impact on free flap flow. Further, NIR showed no significant impact on microvascular flow in any of the subgroups investigated. Conclusions: These findings support the safety of using norepinephrine for maintaining stable blood pressure without compromising microvascular flow, offering valuable guidance for postoperative management. [ABSTRACT FROM AUTHOR]

Introduction: Imaging fibroid vascularity may predict fibroid growth and aid to determine most appropriate therapy. Microvascular (MV) flow imaging is relatively new and is able to detect slow flow in small vessels. Data on feasibility, reproducibility, and reliability of MV‐flow imaging in fibroids is lacking. The purpose of our study was to determine the reproducibility of MV‐flow imaging and to explore this technique for clinical practice for assessing blood flow in fibroids. Material and Methods: Thirty patients with one or multiple fibroids (diameter 1.5–12.0 cm) were prospectively included. Transvaginal ultrasound scanning was performed in B‐mode, 2D MV‐Flow™, 2D and 3D power Doppler mode (HERA W10, Samsung) by two experienced gynecologists at a tertiary care clinic from February to December 2021. The primary outcome was intra‐ and interobserver agreement of the vascular index (VI) and color score (CS). The following parameters: '2D MV‐flow VI', '3DPD VI', '2D MV‐flow CS' and '2DPD CS' were measured offline in the center, pseudocapsule, and entire fibroid. Secondary offline outcomes for exploring 2D MV‐flow for clinical practice, included (1) ability to discern vascular structures, (2) assessing the degree of vascularity via CS and calculating a VI, and (3) determining penetration depth of the ultrasound signal in both power Doppler and MV‐flow imaging. Results: All scans of the 30 included patients were of sufficient quality to analyze. Inter‐ and intra‐observer correlations of all studied parameters were good to excellent, both for 2D MV‐flow and 2D power Doppler (intercorrelation coefficient 0.992–0.996). Using 2D MV‐flow different vascular structures were visible in detail, in contrary to using 2D and 3D power Doppler. In significantly more fibroids central flow could be visualized using 2D MV‐flow (63%) than with 2D power Doppler (13%, p = 0.001). Finally, penetration of the ultrasound signal was deeper using 2D MV‐flow (3.92 cm) than with 2D power Doppler (2.95 cm, p = 0.001). Conclusions: Using 2D MV‐flow imaging for determining vascularity is highly reproducible. It has potential added value for clinical practice as it depicts detailed vascular structures and the degree of vascularity, especially in the center of the fibroid. [ABSTRACT FROM AUTHOR]

Purpose: Target temperature management (TTM) is often used in patients after cardiac arrest, but the effects of cooling on cerebral microcirculation, oxygenation and metabolism are poorly understood. We studied the time course of these variables in a healthy swine model.Methods: Fifteen invasively monitored, mechanically ventilated pigs were allocated to sham procedure (normothermia, NT; n = 5), cooling (hypothermia, HT, n = 5) or cooling with controlled oxygenation (HT-Oxy, n = 5). Cooling was induced by cold intravenous saline infusion, ice packs and nasal cooling to achieve a body temperature of 33–35 °C. After 6 h, animals were rewarmed to baseline temperature (within 5 h). The cerebral microvascular network was evaluated (at baseline and 2, 7 and 12 h thereafter) using sidestream dark-field (SDF) video-microscopy. Cerebral blood flow (laser Doppler MNP100XP, Oxyflow, Oxford Optronix, Oxford, UK), oxygenation (PbtO2, Licox catheter, Integra Lifesciences, USA) and lactate/pyruvate ratio (LPR) using brain microdialysis (CMA, Stockholm, Sweden) were measured hourly. Results: In HT animals, cerebral functional capillary density (FCD) and proportion of small-perfused vessels (PSPV) significantly decreased over time during the cooling phase; concomitantly, PbtO2 increased and LPR decreased. After rewarming, all microcirculatory variables returned to normal values, except LPR, which increased during the rewarming phase in the two groups subjected to HT when compared to the group maintained at normothermia. Conclusions: In healthy animals, TTM can be associated with alterations in cerebral microcirculation during cooling and altered metabolism at rewarming. [ABSTRACT FROM AUTHOR]

Postoperative free flap monitoring is considered a key component of care after microsurgical reconstruction. To achieve successful flap salvage after surgical revision, early recognition of vascular compromise is required. The aim of this study was to assess and compare the time-dependent evolution of microcirculation in gracilis muscle (GM) and anterolateral thigh (ALT) flaps. This study included continuous measurements of blood flow (flow), hemoglobin oxygenation (SO2) and the relative amount of hemoglobin (rHb) using laser-doppler flowmetry and tissue-spectrometry (O2C, LEA Medizintechnik, Gießen, Germany) over a time-period of 72 h. Microcirculation was assessed in a total of 66 viable free flaps (GM n = 40; ALT n = 26). A statistically significant positive correlation between time post-anastomosis and microvascular flow was found for both GM and ALT flaps with rs = 0.384 (p < 0.001) and rs = 0.178 (p = 0.015), respectively. No significant positive or negative correlations between time post-anastomosis and SO2 were found for both GM and ALT flaps with rs = 0.052 (p = 0.387) and rs = −0.018 (p = 0.805), respectively. Overall, a significant negative correlation between time post-anastomosis and rHb was found for GM flaps with rs = −0.140 (p = 0.019). For ALT flaps, no significant positive or negative correlation was found with rs = −0.011 (p = 0.887). Microcirculation differs in different flap entities, and surgeons should be aware of these differences in order to correctly evaluate and classify the values of flow, SO2 and rHb obtained when using the O2C device for postoperative monitoring. [ABSTRACT FROM AUTHOR]

Super-resolution ultrasound imaging, based on the localization and tracking of single intravascular microbubbles, makes it possible to map vessels below 100 µm. Microbubble velocities can be estimated as a surrogate for blood velocity, but their clinical potential is unclear. We investigated if a decrease in microbubble velocity in the arterial and venous beds of the renal cortex, outer medulla, and inner medulla was detectable after intravenous administration of the α1-adrenoceptor antagonist prazosin. The left kidneys of seven rats were scanned with super-resolution ultrasound for 10 min before, during, and after prazosin administration using a bk5000 ultrasound scanner and hockey-stick probe. The super-resolution images were manually segmented, separating cortex, outer medulla, and inner medulla. Microbubble tracks from arteries/arterioles were separated from vein/venule tracks using the arterial blood flow direction. The mean microbubble velocities from each scan were compared. This showed a significant prazosin-induced velocity decrease only in the cortical arteries/arterioles (from 1.59 ± 0.38 to 1.14 ± 0.31 to 1.18 ± 0.33 mm/s, p = 0.013) and outer medulla descending vasa recta (from 0.70 ± 0.05 to 0.66 ± 0.04 to 0.69 ± 0.06 mm/s, p = 0.026). Conclusively, super-resolution ultrasound imaging makes it possible to detect and differentiate microbubble velocity responses to prazosin simultaneously in the renal cortical and medullary vascular beds. [ABSTRACT FROM AUTHOR]

Objectives: To observe the effect of simulated repeated transcranial acupuncture (rTAS) on learning and memory abilities and cerebral microvascular flow in vascular dementia (VD) model rats, so as to explore the potential mechanism of rTAS in treating VD., Methods: Thirty-two Wistar rats were randomly divided into normal, model, acupuncture and rTAS groups ( n =8 rats in each group). The VD model was established by permanent ligation of bilateral common carotid arteries. For rats of the acupuncture group, "Baihui" (GV20) and "Shenting" (GV24) were needled, and for rats of the rTAS group, GV20 and GV24 were stimulated by simulated repeated transcranial manipulation (200 r/min, for 5 min). The treatment was conducted once daily for 14 days. After the intervention, learning and memory abilities were evaluated using the Morris water maze test. Laser speckle technology was used to measure the average cerebral microvascular flow. ELISA was performed to measure the contents of vascular endothelial growth factor (VEGF), endothelin-1 (ET-1), nitric oxide (NO), and inducible nitric oxide synthase (iNOS) in the hippocampal tissues., Results: In comparison with the normal group, the escape latency of rats in the model group was prolonged ( P <0.01), and the times of crossing the platform were decreased ( P <0.01). The average cerebral microvascular flow and the VEGF content in the hippocampus were significantly decreased, while the contents of NO, iNOS, and ET-1 were significantly increased ( P <0.01). In comparison with the model group, the escape latency was significantly shortened ( P <0.01), the average cerebral microvascular flow and VEGF content in the hippocampus were significantly increased ( P <0.05, P <0.01), while contents of iNOS were significantly decreased ( P <0.05, P <0.01) in both acupuncture and rTAS groups；and the times of crossing the platform were increased ( P <0.01), the contents of NO and ET-1 in hippocampus were significantly decreased ( P <0.01) in the rTAS group. The effects of rTAS were significantly superior to those of acupuncture in up-regulating the average cerebral microvascular flow ( P <0.05) and VEGF content ( P <0.01), and down-regulating the NO, iNOS and ET-1 contents ( P <0.01, P <0.05)., Conclusions: rTAS can increase cerebral microvascular flow, improve spatial cognition and enhance learning and memory abilities of VD rats. The underlying mechanism may be involved in promoting angiogenesis, improving endothelial function and mitigating oxidative stress.

Introduction: The contribution of coagulation activation to the pathogenesis of sickle cell disease (SCD) remains incompletely defined. We evaluated the efficacy and safety of rivaroxaban, an oral direct factor Xa inhibitor, in subjects with sickle cell anemia. Materials and Methods: In this pilot, single‐center, randomized, double‐blind, placebo‐controlled, crossover study, eligible subjects with sickle cell anemia received rivaroxaban or placebo. The effect of rivaroxaban on coagulation activation, endothelial activation, inflammation, and microvascular blood flow was evaluated. Results: Fourteen patients (HbSS – 14; females – 9) with mean age of 38 ± 10.6 years were randomized to receive rivaroxaban 20 mg daily or placebo for 4 weeks and, following a 2‐week washout phase, were "crossed‐over" to the treatment arm opposite to which they were initially assigned. Mean adherence to treatment with rivaroxaban, assessed by pill counts, was 85.6% in the first treatment period and 93.6% in the second period. Treatment with rivaroxaban resulted in a decrease from baseline of thrombin‐antithrombin complex versus placebo (−34.4 ug/L [95% CI: −69.4, 0.53] vs. 0.35 ug/L [95% CI: −3.8, 4.5], p =.08), but the difference was not statistically significant. No significant differences were observed in changes from baseline of D‐dimer, inflammatory, and endothelial activation markers or measures of microvascular blood flow. Rivaroxaban was well tolerated. Conclusions: Rivaroxaban was safe but did not significantly decrease coagulation activation, endothelial activation, or inflammation. Rivaroxaban did not improve microvascular blood flow. Adequately powered studies are required to further evaluate the efficacy of rivaroxaban in SCD. Clinicaltrials.gov Identifier: NCT02072668. [ABSTRACT FROM AUTHOR]

Sepsis costs the healthcare system $23 billion annually and has a mortality rate between 10 and 40%. An early indication of sepsis is the onset of hyperglycemia, which is the result of sepsis-induced insulin resistance in skeletal muscle. Previous investigations have focused on events in the myocyte (e.g., insulin signaling and glucose transport and subsequent metabolism) as the causes for this insulin-resistant state. However, the delivery of insulin to the skeletal muscle is also an important determinant of insulin action. Skeletal muscle microvascular blood flow, which delivers the insulin to the muscle, is known to be decreased during sepsis. Here we test whether the reduced capillary blood flow to skeletal muscle belies the sepsis-induced insulin resistance by reducing insulin delivery to the myocyte. We hypothesize that decreased capillary flow and consequent decrease in insulin delivery is an early event that precedes gross cardiovascular alterations seen with sepsis. This hypothesis was examined in mice treated with either lipopolysaccharide (LPS) or polymicrobial sepsis followed by intravital microscopy of the skeletal muscle microcirculation. We calculated insulin delivery to the myocyte using two independent methods and found that LPS and sepsis rapidly reduce insulin delivery to the skeletal muscle by ~50%; this was driven by decreases in capillary flow velocity and the number of perfused capillaries. Furthermore, the changes in skeletal muscle microcirculation occur before changes in both cardiac output and arterial blood pressure. These data suggest that a rapid reduction in skeletal muscle insulin delivery contributes to the induction of insulin resistance during sepsis. [ABSTRACT FROM AUTHOR]

Three-dimensional imaging is valuable to noninvasively assess angiogenesis given the complex 3-D architecture of vascular networks. The emergence of high frame rate (HFR) ultrasound, which can produce thousands of images per second, has inspired novel signal processing techniques and their applications in structural and functional imaging of blood vessels. Although highly sensitive vascular mapping has been demonstrated using ultrafast Doppler, the detectability of microvasculature from the background noise may be hindered by the low signal-to-noise ratio (SNR) particularly in the deeper region and without the use of contrast agents. We have recently demonstrated a coherence-based technique, acoustic subaperture imaging (ASAP), for super-contrast vascular imaging and illustrated the contrast improvement using HFR contrast-enhanced ultrasound. In this work, we provide a feasibility study for microvascular imaging using ASAP without contrast agents, and extend its capability from 2-D to volumetric vascular mapping. Using an ultrasound research system and a preclinical probe, we demonstrated the improved visibility of microvascular mapping using ASAP in comparison to ultrafast power Doppler (PD) on a mouse kidney, liver, and tumor without contrast agent injection. The SNR of ASAP images improves in average by 10 dB when compared to PD. In addition, directional velocity mappings were also demonstrated by combining ASAP with the phase information extracted from lag-1 autocorrelation. The 3-D vascular and velocity mapping of the mouse kidney, liver, and tumor were demonstrated by stacking the ASAP images acquired using 2-D ultrasound imaging and a trigger-controlled linear translation stage. The 3-D results depicted clear microvasculature morphologies and functional information in terms of flow direction and velocity in two nontumor models and a tumor model. In conclusion, we have demonstrated a new 3-D in vivo ultrasound microvascular imaging technique with significantly improved SNR over existing ultrafast Doppler. [ABSTRACT FROM AUTHOR]

Objective: It is widely known that myocardial damage is not immediately terminated after the elimination of epicardial occlusion in cases of myocardial infarction. In situ thrombosis during epicardial occlusion might contribute to poor myocardial perfusion after reperfusion of an occluded epicardial artery. In the current study, we sought to determine the effects of ischemia and reperfusion on microvascular thrombotic occlusion. Methods: Thirty male Wistar rats were included in the study. After the rats had been anesthetized and thoracotomized, the left coronary artery was occluded for 30 minutes in the first group, and it was occluded for 30 minutes and reperfused for an additional 20 minutes in the second group. Ten rats were used as a sham-operated control group. After completion of the study protocol, excised heart preparations were analyzed by immunohistochemistry and electron microscopy. Results: A significant difference was found between the infarction plus reperfusion group and the other 2 groups, with respect to microvascular fibrin and thrombocyte deposition in immunohistochemistry analysis. These results were confirmed by morphological examination with electron microscopy. Conclusion: In situ fibrin formation accompanies microvascular obstruction in acute myocardial infarction. Our results indicate that additional therapeutic approaches are needed in order to achieve better tissue perfusion in contemporary treatment of acute myocardial infarction after successful reopening of the infarct-related artery.

We simulated flows in microvascular vessels containing deformable red blood cells (RBCs) and liposome-encapsulated hemoglobin (LEH) particles. Blood flow was computed by the lattice Boltzmann method (LBM), and fluid-membrane interaction between the flow field and RBCs was incorporated using the immersed boundary method (IBM). The simulation results indicated that the LEH dispersion in a direction perpendicular to the main flow was largely affected by the presence of RBCs. In particular, LEH dispersion was high in the presence of rigid RBCs with low deformability. These results could provide essential information for designing LEH-mediated efficient oxygen supply to tissues. [ABSTRACT FROM AUTHOR]

Physical activity is critically important for Type 2 diabetes management, yet adherence levels are poor. This might be partly due to disproportionate exercise intolerance. Submaximal exercise tolerance is highly sensitive to muscle oxygenation; impairments in exercising muscle oxygen delivery may contribute to exercise intolerance in Type 2 diabetes since there is considerable evidence for the existence of both cardiac and peripheral vascular dysfunction. While uncompromised cardiac output during submaximal exercise is consistently observed in Type 2 diabetes, it remains to be determined whether an elevated cardiac sympathetic afferent reflex could sympathetically restrain exercising muscle blood flow. Furthermore, while deficits in endothelial function are common in Type 2 diabetes and are often cited as impairing exercising muscle oxygen delivery, no direct evidence in exercise exists, and there are several other vasoregulatory mechanisms whose dysfunction could contribute. Finally, while there are findings of impaired oxygen delivery, conflicting evidence also exists. A definitive conclusion that Type 2 diabetes compromises exercising muscle oxygen delivery remains premature. We review these potentially dysfunctional mechanisms in terms of how they could impair oxygen delivery in exercise, evaluate the current literature on whether an oxygen delivery deficit is actually manifest, and correspondingly identify key directions for future research. [ABSTRACT FROM AUTHOR]

Loss of hydrostatic pressures in microgravity may alter skin and bone microvascular flows in the lower extremities and potentially reduce wound healing and bone fracture repair. The purpose of this study was to determine the rate at which skin and bone microvascular flows respond to head-down tilt (HDT). We hypothesized that microvascular flows in tibial bone and overlying skin would increase at different rates during HDT. Tibial bone and skin microvascular flows were measured simultaneously using photoplethysmography (PPG) in a total of 17 subjects during sitting (control posture), supine, 6° HDT, 15° HDT, and 30° HDT postures in random order. With greater angles of HDT, bone microvascular flow increased significantly, but skin microvascular flow did not change. Tibial bone microvascular flow increased from the sitting control posture (0.77 ± 0.41 V) to supine (1.95 ± 1.01 V, P = 0.001) and from supine posture to 15° HDT (3.74 ± 2.43 V, P = 0.004) and 30° HDT (3.91 ± 2.68 V, P = 0.006). Skin microvascular flow increased from sitting (0.703 ± 0.75 V) to supine (2.19 ± 1.72 V, P = 0.02) but did not change from supine posture to HDT (P = 1.0). We show for the first time that microcirculatory flows in skin and bone of the leg respond to simulated microgravity at different rates. These altered levels of blood perfusion may affect rates of wound and bone fracture healing in spaceflight. NEW & NOTEWORTHY Our data show that bone microvascular flow increases more than cutaneous blood flow with greater degrees of head-down tilt. A higher level of perfusion in bone may give insight into the bone mineral density loss in lower extremities of astronauts and why similar tissue degradation is not observed in the skin of the same areas. [ABSTRACT FROM AUTHOR]

Purpose: Sensitivity of contrast-enhanced ultrasound (CEUS) to microvascular flow modifications can be limited by intra-injection variability (injected dose, rate, volume).Procedures: To evaluate the effect of injection variability on microvascular flow evaluation, CEUS was compared between controlled and manual injections where enhancement was assessed in vitro within a flow phantom, in normal murine kidney (N = 12) and in murine ectopic tumors (N = 10).Results: For both in vitro and in vivo measurements in the renal cortex, controlled injections significantly improved reproducibility of functional parameter estimation. Their coefficient of variation (CV) in the renal cortex ranged from 4 to 19 % for controlled injection vs. 5 to 43 % for manual injections. For measurements in tumors, controlled injection only decreased the CV significantly for the mean transit time. In tumors, multiple injections of contrast agent with a 15-min delay between each were shown to strongly modify contrast uptake by facilitating penetration of microbubbles.Conclusion: Improved reproducibility of CEUS assessments in murine models should provide more robust quantification of flow parameters and more sensitive evaluation of tumor modifications in therapeutic models. [ABSTRACT FROM AUTHOR]

Copyright of Archives of the Turkish Society of Cardiology / Türk Kardiyoloji Derneği Arşivi is the property of KARE Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The research of the motion and deformation of the RBCs is important to reveal the mechanism of blood diseases. A numerical method has been developed with level set formulation for elastic membrane immersed in incompressible fluid. The numerical model satisfies mass and energy conservation without the leaking problems in classical Immersed Boundary Method (IBM), at the same time, computing grid we used can be much smaller than the general literatures. The motion and deformation of a red blood cell (including pathological & normal status) in microvascular flow are simulated. It is found that the Reynolds number and membrane's stiffness play an important role in the transmutation and oscillation of the elastic membrane. The normal biconcave shape of the RBC is propitious to create high deformation than other pathological shapes. With reduced viscosity of the interior fluid both the velocity of the blood and the deformability of the cell reduced. With increased viscosity of the plasma both the velocity of the blood and the deformability of the cell reduced. The tank treading of the RBC membrane is observed at low enough viscosity contrast in shear flow. The tank tread fixed inclination angle of the cell depends on the shear ratio and viscosity contrast, which can be compared with the experimental observation well. [ABSTRACT FROM AUTHOR]

The present research investigated the role of blood viscosity on flow within a microvascular network to identify the conditions of blood flow stagnation. When the yield stress of blood was less than 0.005 Pa, there were no stagnant regions in the microvasculature. However, when the yield stress increased to 0.05 Pa, stagnant or reduced flow areas began to appear, which grew and expanded rapidly with further increase in the yield stress. Thus, the yield stress determined from blood viscosity profile of a patient can be utilized to evaluate the risk of circulatory impairment. [ABSTRACT FROM AUTHOR]

Patients with atrial fibrillation (AF) often present with typical angina pectoris and mildly elevated levels of cardiac troponin (non ST-segment elevation myocardial infarction; NSTEMI) during an acute episode of AF. However, in a large proportion of these patients significant coronary artery disease is excluded by coronary angiography, which suggests that AF itself influences myocardial blood flow. The present review summarizes the effect of AF on the occurrence of ventricular oxidative stress, redox-sensitive signalling pathways & gene expression, and microcirculatory flow abnormalities in the left ventricle.

Patients with atrial fibrillation (AF) often present with typical angina pectoris and mildly elevated levels of cardiac troponin (non-ST-segment elevation myocardial infarction) during an acute episode of AF. However, in a large proportion of these patients, significant coronary artery disease is excluded by coronary angiography, which suggests that AF itself influences myocardial blood flow. The present review summarizes the effect of AF on the occurrence of ventricular oxidative stress, redox-sensitive signaling pathways and gene expression, and microcirculatory flow abnormalities in the left ventricle. [ABSTRACT FROM AUTHOR]

Copyright of Archives of Cardiovascular Diseases is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Imaging microvascular flow is of diagnostic value for a wide range of diseases including cancer, inflammation, and cardiovascular disease. The introduction of microbubbles as ultrasound contrast agents offers significant signal enhancement to the otherwise weakly scattered signal from blood in the circulation. Microbubbles provide maximum impedance mismatch, but are not linear scatterers. Their complex response to ultrasound has generated research on both their behaviour and their scattered-signal processing. Nearly 20 years ago signal processing started with simple spectral filtering of harmonics showing contrast-enhanced images. More recent pulse encoding techniques have achieved good cancellation of tissue echoes. The good quality contrast-only images enabled ultrasound contrast-imaging applications to be established in microvascular measurements in the liver and the myocardium. The field promises to advance the quantification of microvascular flow kinetics. [ABSTRACT FROM AUTHOR]

Abstract: Retinal blood flow decreases early in the progression of diabetic retinopathy; however, the mediators and mechanisms responsible for this decrease have yet to be determined. In this study, diabetes was induced by streptozotocin in rats, and retinal blood flow was measured via intravital microscopy 1 or 3 weeks following the induction of hyperglycemia. Additionally, retinal arteriolar diameters and flow were measured prior to and following acute administration of the thromboxane synthase inhibitor ozagrel to investigate the potential role of thromboxane in the observed constriction. Minimal changes in the retinal diameters and flow were observed at 1 week of diabetes; however, at 3 weeks of diabetes, arteriolar constriction and decreases in blood flow were significant. Notably, the constriction occurred only in the arterioles that were in closer proximity to the venules draining the retina. Acute administration of ozagrel reversed the constriction of the closely venule-paired arterioles. In summary, the results suggest that thromboxane mediates localized, venule-dependent arteriolar constriction induced by streptozotocin-induced diabetes in rats. [Copyright &y& Elsevier]

We tested the hypothesis that high-viscosity (HV) plasma in extreme hemodilution causes wall shear stress to be greater than low-viscosity (LV) plasma, leading to enhanced production of nitric oxide (NO). The perivascular concentration of NO was measured in arterioles and venules and the tissue of the hamster chamber window model, subjected to acute extreme hemodilution, with a hematocrit (Hct) of 11% using Dextran 500 (n = 6) or Dextran 70 (n = 5) with final plasma viscosities of 1.99 ± 0.11 and 1.33 ± 0.04 cp, respectively. HV plasma significantly increased the periarteriolar, penvenular, and tissue NO concentration by 2.0, 1.9, and 1.4 times the control (n = 7). The NO concentration with LV plasma was not statistically different from control. Arteriolar shear stress was significantly increased in HV plasma relative to LV plasma in arterioles but not in venules. Aortic endothelial NO synthase (eNOS) protein expression was increased with HV plasma but not with LV plasma. There was a weak correlation between perivascular NO concentration and the locally calculated shear stress induced by the procedures, when blood viscosity was corrected according to Hct values previously determined in studies of microvascular Hct distribution. The finding that the periarteriolar and venular NO concentration in HV plasma was the same although arteriolar shear stress was significantly greater than venular shear stress maybe be due to differences in vessel wall metabolism between arterioles and venules and the presence of NO transport through the blood stream in the microcirculation. Results support the concept that in extreme hemodilution HV plasma maintains functional capillary density through a NO-mediated vasodilatation. [ABSTRACT FROM AUTHOR]