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1 Choroidal blood vessels, located between the sclera and retina, constitute the principle source of blood flow to ocular structures. The choroid is innervated by vasoconstrictor sympathetic and vasodilator parasympathetic nerves. 2 We have shown previously that sympathetic denervation for 6 weeks leads to significant increases in choroidal thickness, percentage of choroid occupied by vascular lumina, and numbers of choroidal venules, large arterioles and outer retinal capillaries. Sympathetic deafferemation produces similar increases, indicating that loss of sympathetic nerve activity is responsible for increased vascularity after sympathectomy. Thus, sympathetic neurotransmission normally may be important in suppressing vascular proliferation in the adult rodent eye. 3 The aim of the present study was to determine whether sympathetic nerves act by way of adrenergic receptors to maintain normal choroidal vascular integrity. 4 The α-adrenoceptor antagonist, phentolamine (I mg kg[sup-1] day[sup1]), the β-receptor antagonist, propranolol (1 mg kg[sup-1] day[sup-1]), or saline vehicle was infused for 3 weeks using subcutaneously implanted osmotic mintpumps. 5 In phentolamine treated rats, no significant changes were noted relative to saline infused controls. However, propranolol treatment resulted in increases in choroidal thickness, vascular luminal area, and numbers of large choroidal venules and both small and large arterioles, approximating the remodelling seen after chronic sympathectomy. 6 We conclude that sympathetic nerves play a role in maintaining normal choroidal vascular architecture through actions mediated primarily by β-adrenoceptors. [ABSTRACT FROM AUTHOR]

This report reviews how to set up a laser Doppler perfusion imaging system intended for visualization of skin blood perfusion, capture images and evaluate the results obtained. A brief summary of related papers published in the literature within the areas of skin irritant and allergy patch testing, microdialysis and skin tumour circulation is presented, as well as early applications within other fields such as diabetology, wound healing and microvascular research. [ABSTRACT FROM AUTHOR]

Purpose: To investigate retrobulbar blood flow velocities and the effects of topical timolol treatment in eyes with newly detected, previously untreated open angle glaucoma or ocular hypertension. Methods: Fifteen eyes with open angle glaucoma (OAG) and 12 eyes with ocular hypertension (OH), in the same number of patients, all untreated and newly detected, were examined with colour Doppler imaging of retrobulbar vessels before and after 1 month of topical timolol treatment (0.5% Timoptic® BID). Results: Baseline central retinal artery end diastolic velocity was lower (48%, p=0.0002) and resistive index higher (7.6%, p=0.018) in the OAG group than in the OH group. In the glaucoma group mean end diastolic velocity increased by 41%, (p=0.006) while resistive index decreased by 5.8%, (p=0.02) on treatment, while no significant changes were seen in the OH group. Blood flow velocities in the ophthalmic artery did not change with treatment. Baseline IOP and IOP reduction did not differ between OAG and OH group. Conclusion: Peripheral resistance to blood flow was found to be increased in untreated glaucoma eyes as compared to a similar group of eyes with ocular hypertension. Timolol treatment diminished resistance significantly in the glaucoma group, but not in the ocular hypertension group. Thus the two groups responded differently to timolol treatment. The reaction to IOP lowering treatment could indicate defective autoregulation in the glaucoma group. [ABSTRACT FROM AUTHOR]

Background: The aim of this study was to describe the variable anatomy in the anastomosis between the umbilical arteries for better understanding of the physical characteristics of the umbilical flow velocity waveform (FVW).Methods: The arterial system of 67 placentas from pregnancies with normal umbilical FVW and resulting in a full-term AGA infant was visualized by angiography. The method allowed study of the anatomy of the anastomosis between the umbilical arteries and calculation of the relative placental area supplied by each umbilical artery.Results: In 60 cases there was one anastomosis between the umbilical arteries, in one case there were two, in four the anastomosis was absent, and another two cases had a single umbilical artery. The anastomosis was represented by a vessel, a fenestration or coalescence of the umbilical arteries. In case the anastomosis diameter was of at least that of the umbilical arteries, they supplied in mean 26% and 74% (+/- 8.2%) of the placental area respectively. When the anastomosis diameter was smaller than that of the umbilical arteries their supply areas were in mean 41% and 59% (+/- 6.0%) respectively. In placentas lacking anastomosis the two umbilical arteries supplied 45% and 55% (+/- 2.6%) respectively, indicating a higher degree of symmetry.Conclusions: By using angiography we were able to demonstrate the variable anatomy of the anastomosis of Hyrtl. We found the occurrence and width of the anastomosis was correlated to the symmetry in size between the supply areas of each umbilical artery. [ABSTRACT FROM AUTHOR]

Many important physiological functions of skeletal muscle, such as glucose uptake, contraction and blood flow, have been proposed to be regulated via the action of adenosine on adenosine receptors. The cellular location of adenosine receptors in skeletal muscle is however, not known. The present study examined the distribution of A1, A2A and A2B adenosine receptors in human skeletal muscle using immunohistochemistry. All three receptor types were localized to vascular smooth muscle and endothelial cells, only the adenosine A2A and A2B receptors were observed in the plasma membrane and cytosol of the skeletal muscle. The finding was supported by results from western-blotting analysis. The cytosolic staining of the adenosine A2A receptor was slightly more intense in the type I muscle fibres, whereas the A2B receptor was almost absent in type I fibres. The present findings demonstrate for the first time, direct evidence for the existence of A2A and A2B adenosine receptors but absence of the A1 receptor in the sarcolemma and cytosol of skeletal muscle cells. The data also show existence of all three of the A1, A2A and A2B adenosine receptors in vascular cells of skeletal muscle tissue. [ABSTRACT FROM AUTHOR]

Objective To evaluate the effect of maternal isometric exercise on the placental blood flow as reflected by the velocimetric indices PI and RI derived from placental arteries. Subjects Thirty-four healthy women with normal singleton pregnancies between 22 and 35 weeks of gestation. Methods All subjects underwent an isometric handgrip exercise test. Maternal blood pressure and heart rate together with placental PI and RI were measured at rest, during the exercise and in the post-exercise recovery phase. All Doppler measurements were obtained using the Simultaneous Multigate Spectral Doppler Imaging (SM-SDI) technique, a new ultrasound modality that enables a Doppler study of multiple locations to take place within a very short time. Results There was a significant increase in the mean values of the maternal blood pressure and heart rate during the exercise and a significant decline in the recovery phase. There was no significant change in the mean values of the Doppler indices throughout the examination. Conclusion Isometric handgrip exercise test during pregnancy does not affect the impedance of the placental circulation. [ABSTRACT FROM AUTHOR]

Shifting legs to a gravity-dependent position provokes a physiological vasoconstrictive response that forms the basis of several diagnostic tests based on initial (< 5 min) blood perfusion decreases. However, it is not known if responses are maintained over longer duration and if they depend on the volume shifted to the limb during the manoeuvre. These issues were investigated by measurements of blood perfusion changes on foot and ankle (laser Doppler) and below-knee volume and impedance changes induced by 30 min of standing in 10 healthy volunteers. Initial perfusion decreases were 66·4% ± 2·6% and 49·3% ± 3·8% for ankle and foot dorsum, respectively, and were fully maintained during sustained standing without evidence of `vasodilator escape'. Response magnitudes were not dependent on leg volume changes using geometric or impedance measures. A close correlation (r 2 = 0·78) between impedance and volume changes suggests the former as a useful way of assessing dynamic limb volume changes. Sustained vasoconstrictive responses make it unlikely that extending the duration of such tests would offer more diagnostic information than is currently available. [ABSTRACT FROM AUTHOR]

The rete tibiotarsale is the main arterio-venous heat exchange system in the hind limb of the Mallard. A large arterial shunt and a venous shunt allow the blood to by-pass the rete. These shunt vessels must be able to constrict so as to direct the blood to the rete when heat conservation is needed. Using ordinary histological methods and the technique of Falck and Hillarp for demonstration of biogenic monoamines, it was shown that the arterial shunt is more muscular and receives a more dense adrenergic innervation than adjacent segments of the same vessel. Perfusion with noradrenaline before fixation revealed that the arterial shunt was able to reduce its leumen to near closur. No structure, in the ordinary sense of a sphincter was found in the shunt vein but adrenergic nerves were scattered throughout the tunica media at the base of valves, suggesting that a sphincteric action at these sites is possible. [ABSTRACT FROM AUTHOR]

The angioarchitecture of the toad's mesencephalon is studied by scanning electron microscopy of vascular corrosion casts. The arterial supply is performed by the superior mesencephalic artery and by an artery arising from the ramus posterior of the arteria carotis cerebralis just in front of the retrainfundibular communicating artery. The venous drainage is excrted by the vena diencephalica, the vena lateralis mesencephalis and by anterior and posterior branches of the encephaloposthypophysial penal vein. Characteristics of the mesencephalic anginarchitecture are the centrifugal direction of the blood flow, the intensive capillarization, and the formation of vascular meshworks in the region of the stratum griscum periventriculare tecti and of the stratum griseum superficiale tecti. [ABSTRACT FROM AUTHOR]

The circulation of the gills has been studied in the perch, trout and eel combining the conventional histological methods and casting techniques. The existence of two blood pathways in each gill arch was confirmed. 1—An arterio-arterial pathway assuming the respiratory function. It includes the afferent branchial artery and in each primary lamella the afferent primary artery, the secondary lamellae capillaries and the primary and branchial efferent arteries. 2—An arterio-venous pathway arising from both the branchial artery, in the gill arch, and the primary arteries in each primary lamella. This pathway includes the central venous sinus of the primary lamella, several small veins and is finally connected with the branchial veins. 3—The lack of connections between afferent primary arteries and cvs in the trout and the perch makes impossible a direct blood flow from the afferent to the efferent artery (shunt). In the eel connections between cvs and both afferent and efferent arteries do not mean that a shunt is operating according to the pressure gradient. [ABSTRACT FROM AUTHOR]

Atherosclerotic vascular disease affects many individuals, particularly in an elderly population. This study examined alterations in the vasculature and blood flow in the maxilla and mandible in rhesus monkeys fed an atherogenic (high fat) diet. No significant difference was found in blood flow between different regions of the bone (anterior mandible, posterior mandible and maxilla) in animals on either a normal or a high fat diet but overall blood flow in the monkeys on the atherogenic diet was significantly lower (p < 0.001) than in the control group. Histologic examination of tissue from the animals fed an atherogenic diet revealed minimal changes within the intrabony vasculature and measurements of these vessels showed no significant difference in the percentage of tissue occupied by vessel lumina or in average wall thickness between the groups of animals. On the other hand, tissue from the tongue exhibited gross atherosclerotic vascular lesions and examination of the carotid arteries revealed not only intimal plaques but extensive calcification. It thus appears that the decreased flow measured in the maxilla and mandible may be related to the severely involved afferent vessels rather than to functional changes in the local vasculature. [ABSTRACT FROM AUTHOR]

Vaginal vascular responses to vibratory stimulation of the clitoris, recorded as changes in the amplitude of oscillations of light reflectance at the heart-beat frequency, are: a) very repeatable, b) widespread throughout the vagina but of greater amplitude in its lower anterior wall than elsewhere, c) of very short latency (2-3 sec), but cumulative over 30 sec or more. Such responses are not imitated by raising the abdominal pressure, voluntarily contracting the pelvic floor or the flexors or adductors of the hips, or raising the blood pressure by exercise. They are absent in the foot, hand and rectum when present in the vagina. Sexual fantasy provokes vaginal responses very similar to those from vibratory stimulation of the clitoris, though somewhat less repeatable. Mean vaginal light reflectance, averaged over a cardiac cycle, responds to the same stimuli which affect the amplitude of pulsation. It is, however, much more subject to artifact. Changes in thermal conductivity closely parallel those in amplitude of oscillation of reflectance, with a time-lag which is probably mainly instrumental. Vibratory stimulation of the clitoris causes sustained reflex contraction of the pelvic floor. This reflex (never, it seems, previously described) may be regarded as a tonic counterpart of the well-known phasic bulbocavernosus reflex. The vascular events at and after orgasm and their relationship to features of the pelvic floor electromyogram are described and illustrated; the heart rate falls greatly during the 10 sec after orgasm, the amplitude of vaginal vascular pulsation remains above its prestimulation value for as long as 15 mm, and pelvic floor electromyographic activity remains enhanced for at least 2 min. [ABSTRACT FROM AUTHOR]

The present study, involving 56 healthy subjects from a health screening, was undertaken to address some methodological questions regarding the measurement of endothelial function using local intra-arterial infusions of metacholine (2 and 5 μg min-1) to evaluate endothelium-dependent vasodilatation, and sodium nitroprusside (SNP, 5 and 10 μg min-1) to evaluate endothelium-independent vasodilatation. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. The ratio of FBF during the highest dose of metacholine to FBF during the highest dose of SNP was used as an index of endothelial function. In 10 young volunteers the procedure was repeated after 2 h and again after 3 weeks in order to study short-term and long-term reproducibility of the method. Neither the vasodilatatory response to metacholine (r = 0·006) nor that to SNP (r = 0·08) was related to resting FBF. Neither the circumference nor the length of the arm was related to endothelial function (r = 0·01-0·11), as evaluated by the FBF on metacholine to nitroprusside ratio (mean 1·3 ± 0·3 SD). The use of a wrist cuff to exclude hand circulation, or not, did not influence the evaluation of endothelial function significantly. Maximal FBF after 3 min of arterial occlusion of the forearm was significantly related to blood flow during both metacholine (r = 0·53, P < 0·01) and nitroprusside infusion (r = 0·36, P < 0·05), but not to the FBF on metacholine to nitroprusside ratio (r = 0·01). The short-term and long-term reproducibility of FBF during vasodilatation with metacholine and SNP was good (r = 0·89-0·97, P < 0·001), while the individual measurements for resting FBF were less reproducible when repeated after 3 weeks... [ABSTRACT FROM AUTHOR]

The mean age was 62.0, and mean maximal diameter of tumour was 5.4 cm. At diagnosis, SMI revealed tumour blood flow clearly. After neoadjuvant chemotherapy, SMI detected decreased tumour blood flow in all patients. [Extracted from the article]

The article explores the implications of the findings of two independent studies published in "The Journal of Physiology" which identified regional differences in cerebral perfusion during acute changes in arterial blood changes. It relates the impact of the findings on the understanding of cerebrovascular control in humans. It explains how the findings affect the way of interpreting data such as changes in blood flow and/or velocity between arteries.

The morphology and diameter of the milk vein of 29 healthy Swiss braunvieh cows and the velocity of blood flow through it was measured by colour Doppler ultrasonography before and 10 minutes after they had been sedated with 0.03 mg/kg xylazine. The milk vein was situated immediately under the skin. It had a diameter of 0.8 to 1.6 cm and valves were visible in the milk vein of 12 of the cows. The spectral display appeared as a broad band structure with a wave-like course. The Doppler measurement point was 0.4 to 0.8 cm from the body surface. The diameter of the vein and the blood flow velocity did not differ significantly before and after the cows were sedated. The mean (sd) diameter of the milk vein before they were sedated was 1.3 (0.3) cm. The mean maximum blood flow velocity before they were sedated was 45.4 (12.5) cm/second, the mean velocity was 33.5 (9.5) cm/second, and the mean minimum was 25.8 (11.6) cm/second. There were significant correlations between the blood flow velocities before and after the cows were sedated and between individual cow's blood flow velocities, with correlation coefficients ranging from 0.69 to 0.94. [ABSTRACT FROM AUTHOR]

We describe an as yet unrecognised relationship between fetal hepatic haematopoiesis and arterial blood flow to the liver. To increase hepatic arterial flow, the common bile duct (CBD) was ligated in fetal lambs. Reduction of hepatic arterial flow was accomplished in age-matched animals by hepatic artery (HA) ligation. Multiple analyses performed before term showed a significant increase in haematopoietic cell density in CBD animals when compared with sham controls and HA animals. In contrast, HA animals demonstrated a decrease in liver haematopoietic activity. Fetal hepatic haematopoiesis is dependent upon arterial blood flow to the liver. [ABSTRACT FROM AUTHOR]

Tortuous vessels are often observed in vivo and could hinder or even disrupt blood flow to distal organs. Besides genetic and biological factors, the in vivo mechanical loading seems to play a role in the formation of tortuous vessels, but the mechanism for formation of helical vessel shape remains unclear. Accordingly, the aim of this study was to investigate the biomechanical loads that trigger the occurrence of helical buckling in blood vessels using finite element analysis. Porcine carotid arteries were modeled as thick‐walled cylindrical tubes using generalized Fung and Holzapfel‐Gasser‐Ogden constitutive models. Physiological loadings, including axial tension, lumen pressure, and axial torque, were applied. Simulations of various geometric dimensions, different constitutive models and at various levels of axial stretch ratios, lumen pressures, and twist angles were performed to identify the mechanical factors that determine the helical stability. Our results demonstrated that axial torsion can cause wringing (twist buckling) that leads to kinking or helical coiling and even looping and winding. The specific buckling patterns depend on the combination of lumen pressure, axial torque, axial tension, and the dimensions of the vessels. This study elucidates the mechanism of how blood vessels buckle under various mechanical loads and how complex mechanical loads yield helical buckling. The novelties of this research article include the following: Illustrated that mechanical loadings such as lumen pressure, axial tension, and axial torque could lead to the formation of tortuous vessels (curving, wringing, kinking, helical coiling, looping, and winding).Determined the biomechanical loads that trigger helical buckling in blood vessels.Compared the effect of different constitutive models. [ABSTRACT FROM AUTHOR]

The aim of this work is to develop a novel computational approach to facilitate the modeling of angiogenesis during tumor growth. The preexisting vasculature is modeled as a 1D inclusion and embedded into the 3D tissue through a suitable coupling method, which allows for nonmatching meshes in 1D and 3D domain. The neovasculature, which is formed during angiogenesis, is represented in a homogenized way as a phase in our multiphase porous medium system. This splitting of models is motivated by the highly complex morphology, physiology, and flow patterns in the neovasculature, which are challenging and computationally expensive to resolve with a discrete, 1D angiogenesis and blood flow model. Moreover, it is questionable if a discrete representation generates any useful additional insight. By contrast, our model may be classified as a hybrid vascular multiphase tumor growth model in the sense that a discrete, 1D representation of the preexisting vasculature is coupled with a continuum model describing angiogenesis. It is based on an originally avascular model which has been derived via the thermodynamically constrained averaging theory. The new model enables us to study mass transport from the preexisting vasculature into the neovasculature and tumor tissue. We show by means of several illustrative examples that it is indeed capable of reproducing important aspects of vascular tumor growth phenomenologically. [ABSTRACT FROM AUTHOR]

This study focuses on the simulation of a nanoparticle loaded blood flow in a micro‐channel. The Euler‐Euler approach is used to describe the multi component behavior of blood. Nanoparticles are modeled by a concentration equation. The influence of the magnetic field gradient on particle transport is investigated for different Reynolds numbers. [ABSTRACT FROM AUTHOR]

P08.10: Analysis of STIC flow imaging characteristics of fetal double aortic arch and right-side aortic arch with mirror carotid branch To improve the differential diagnosis of double aortic arch (DAA) and right-side aortic arch combined with mirror carotid artery branches (MRAA) by using 4-dimensional spatiotemoral image correlation (STIC) technology STIC blood flow assisted in diagnosing whether suspicious blood vessels converge into the descending aorta or not, and the origin, position and morphological characteristics of the LSA are also helpful for their differential diagnosis. [Extracted from the article]

Upon injury to a blood vessel, flowing platelets will aggregate at the injury site, forming a plug to prevent blood loss. Through a complex system of biochemical reactions, a stabilizing mesh forms around the platelet aggregate forming a blood clot that further seals the injury. Computational models of clot formation have been developed to a study intravascular thrombosis, where a vessel injury does not cause blood leakage outside the blood vessel but blocks blood flow. To model scenarios in which blood leaks from a main vessel out into the extravascular space, new computational tools need to be developed to handle the complex geometries that represent the injury. We have previously modeled intravascular clot formation under flow using a continuum approach wherein the transport of platelet densities into some spatial location is limited by the platelet fraction that already reside in that location, i.e., the densities satisfy a maximum packing constraint through the use of a hindered transport coefficient. To extend this notion to extravascular injury geometries, we have modified a finite element method flux‐corrected transport (FEM‐FCT) scheme by prelimiting antidiffusive nodal fluxes. We show that our modified scheme, under a variety of test problems, including mesh refinement, structured vs unstructured meshes, and for a range of reaction rates, produces numerical results that satisfy a maximum platelet‐density packing constraint. [ABSTRACT FROM AUTHOR]

Objectives Recent reports have suggested that nuchal translucency (NT) measurements in the first trimester may be influenced by fetal gender. Since both NT and central venous blood flow are considered to be related to fetal cardiac function, we investigated gender-related differences in first-trimester ductus venosus Doppler indices. Methods A total of 73 male and 79 female normal fetuses at 10-14 weeks of gestation were included in the study. The pulsatility index for veins (PIV), peak velocity during ventricular systole (S-wave), time-averaged maximum velocity (TAMV) and A-wave velocity (A-wave) were recorded in each case and converted to the corresponding Z-scores. Results The mean Z-score values of PIV, S-wave and TAMV were significantly lower in male fetuses compared to female fetuses (P < 0.01 for all three indices). By contrast, A-wave velocities were not different in the two groups. The correlation between S-wave velocity and TAMV was significant in both male (P < 0.001) and female (P < 0.001) fetuses, while PIV did not appear to be related to TAMV either in males (P = 0.90) or in females (P = 0.49). A-wave velocity had a significant negative correlation with PIV in both groups. Finally, PIV was significantly correlated with S-wave velocity in female fetuses (P < 0.01) but not in males (P = 0.14). Conclusion These findings suggest that early cardiovascular development may be different in male and female fetuses. [ABSTRACT FROM AUTHOR]

This study describes a modified technique to fill the renal vasculature with a silicon rubber (Microfil) compound and obtain morphologic information about the intrarenal distribution of capillary blood flow under a variety of conditions. Kidneys and cremaster muscles of rats were perfused in vivo with Microfil using a perfusion pressure equal to the animal's mean arterial pressure at body temperature. Microfil did not alter arteriolar diameter or the pattern of flow in the microcirculation of the cremaster muscle. The modified protocol reproducibly filled the renal vasculature, including; glomerular, peritubular, and vasa recta capillaries. We compared the filling of the renal circulation in control rats with that seen in animals subjected to maneuvers reported to alter the intrarenal distribution of blood flow. Infusion of angiotensin II, hypotension, volume expansion, and mannitol‐ or furosemide‐induced diuresis redistributed flow between renal cortical and medullary capillaries. The advantage of the current technique is that it provides anatomical information regarding the number, diameter, and branching patterns of capillaries in the postglomerular circulation critical in determining the intrarenal distribution of cortical and medullary blood flow. [ABSTRACT FROM AUTHOR]

A tree‐like hierarchical branching structure is present in many biological systems, such as the kidney, lung, mammary gland, and blood vessels. Most of these organs form through branching morphogenesis, where outward growth results in smaller and smaller branches. However, the blood vasculature is unique in that it exists as two trees (arterial and venous) connected at their tips. Obtaining this organization might therefore require unique developmental mechanisms. As reviewed here, recent data indicate that arterial trees often form in reverse order. Accordingly, initial arterial endothelial cell differentiation occurs outside of arterial vessels. These pre‐artery cells then build trees by following a migratory path from smaller into larger arteries, a process guided by the forces imparted by blood flow. Thus, in comparison to other branched organs, arteries can obtain their structure through inward growth and coalescence. Here, new information on the underlying mechanisms is discussed, and how defects can lead to pathologies, such as hypoplastic arteries and arteriovenous malformations. Many studies have shown that blood vessel sprouting resembles branching morphogenesis, where smaller branches sprout from larger stems. New work indicates that arteries can also form through inward growth of pre‐specified arterial cells and remodeling. Therefore, the mechanism building hierarchically patterned blood vessel trees might differ between arteries and veins. [ABSTRACT FROM AUTHOR]

The presence of collateral veins is one of the most common causes of fistula failure to mature. The traditional approach to eliminate collateral vessel flow is coil embolization under fluoroscopy or surgical cut down and branch vessel ligation. However, both approaches are expensive and time consuming. Here, we described an image-guided nonsurgical method to ligate collateral veins. The collateral veins were ligated using Hawkins-Akins needle under ultrasound guidance. The average time for one ligation procedure was 17 minutes. There was a significant increase of blood flow in the venous outflow postligation procedure. Four weeks postprocedure ultrasound demonstrated occlusion of the target vessels. This procedure was well tolerated without major complications. In summary, the novel procedure described here offers an image-guided nonsurgical approach for collateral vein occlusion. [ABSTRACT FROM AUTHOR]

The authors discuss research published within the issue concerning stiffness and blood flow problems in downstream and upstream arteries. Topics covered include the effects of the stiffness of large artery on cerebral and skeletal muscle vasculature, greater pulsability of the middle cerebral artery (MCA) compared to the gastrocnemius feed artery and the dependence of MCA on nitrous oxide to elicit dilatation.

We have developed a micro-multipoint laser Doppler velocimeter (µMLDV), which is the newest version of our improved laser Doppler velocimeter (LDV). This device can potentially be used clinically for the evaluation of the internal diameter of blood vessels, inspection of blood vessel protrusions and diagnosis of melanoma. To date, we have verified the accuracy of this device for three-dimensional measurement of blood vessels in vivo and measurement of melanoma. The state of blood flow is one of the evaluation criteria for tissue fixing. However, the state of blood flow is difficult to determine visually. If the state of blood flow can be visualized using this system, without damaging the affected area, it is possible to evaluate fixing noninvasively. Therefore, we measured normal blood vessels and cases in which there was no blood flow for comparison and verified the possibility of using the µMLDV as an evaluation device. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The author comments on the complex process of examining blood flow regulation in the human brain. He cites two studies giving a basis for one's understanding of both static and dynamic cerebral autoregulation. He mentions a paper published in this issue, indicating a key contribution of Windkessel properties of cerebral vessels, such as resistance and compliance, to frequency-dependent, dynamic cerebral autoregulation. He says 'cerebrovascular control' is the more suitable term, according to the observation of relatively unchanged cerebral blood flow.

The vasomotor function of arterial vessels is impaired in HHcy. Thus we hypothesized that HHcy alters the mediation of flow dependent responses of venules. Thus changes in diameter of pressurized venules (diameter: 250±30/am at 10 mmHg) isolated from normal and HHcy (∼5 weeks methionine diet) rats to increases in perfusate flow were measured. Increases in intraluminal flow elicited dilations of control vessels (max.: 13,4±1%), whereas in HHcy venules flow elicited constrictions (max.: -19±6 %). The NO donor SNP elicited similar magnitude of dilations in both groups. In control venules, the PGH2/TXA2receptor antagonist SQ 29,548 augmented flow-induced dilations, whereas in HHcy venules reversed flow-induced constrictions to dilation. In the presence of SQ 29,548 the NO synthase inhibitor L-NAME significantly decreased flow-induced dilations in control venules, whereas in HHcy the "restored" dilations were not significantly affected. Presence of SOD and CAT did not significantly change flow-induced dilations in control venules, whereas abolished flow-induced constrictions in HHcy venules. Correspondingly, as compared to controls, there was an increased ethidium bromide fluorescence detected in HHcy venules, indicating substantial superoxide production. In conclusion, elevated levels of plasma homocysteine -- in part -- due to an increased production of reactive oxygen species, could reduce the role of NO and increase the role of PGH2/TXA2 in mediation of flow-induced responses of skeletal muscle venules. These changes may impair the regulation of blood flow and favor increased thrombus formation in venules. [ABSTRACT FROM AUTHOR]

Collecting lymphatics exhibit spontaneous contractions that are exquisitely sensitive to pressure/flow. The activity of these series-coupled segments propels lymph centrally and serves as an important mechanism to counteract edema. Previously, the pumping behavior of rat mesenteric lymphatics was examined in vivo using cardiac pump indices to analyze adaptations to systemic volume expansion. To quantify this behavior under conditions where input/output pressures and flow could be better controlled, we studied similar vessels after isolation and cannulation in vitro. Segments 2-3 mm in length and ∼100 µm in diameter were viewed at ∼600x using an inverted microscope and diameter tracking system. Pressures at the tips of the inflow and outflow cannulae were controlled independently using a servo system. Pressure in the inter-valve segment was measured with a servo-null pipette. Dynamic changes in the pressure (P)-volume (V) loops representing single contraction cycles were analyzed in response to abrupt (20 ms) steps in afterload and/or preload. Increases in preload led to horizontal expansion of the loop and curvilinear increases in end diastolic V. Increases in afterload expanded the loop vertically; at P>6 cmH2O it collapsed and end systolic V increased. This system can be used to dissect the interaction of intrinsic and extrinsic factors controlling lymphatic contractility. [ABSTRACT FROM AUTHOR]

The study in Wistar rats attempted to improve the occlusion technique of the middle cerebral artery (MCA) as a precise method for initiating stroke. In a first part it was necessary to study the exact anatomy of blood vessels of the brain in seven rats of 170-410 g body weight by corrosion cast. The lengths and diameters of defined locations of the blood vessels were measured. The temporary as well as the permanent methods were refined or replaced. The first one was completed in main training the physiological blood flow after temporary occlusion, while the permanent occlusion was performed by positioning a silicone cap in the MCA. A filament guide was introduced from the common carotid artery (CCA) via internal carotid artery (ICA) to guide the silicon cap at the branch of the MCA. Histological sections of the brain of rats showed 24 h after the permanent occlusion a reproducible infarct in the brain. This area corresponded very well with the supply of the MCA. The new occlusion method with a silicon cap was compared with the occlusion methods of CCA route and external carotid artery (ECA) route. The total infarct volume was significantly larger in the CCA route and ECA route groups than in the silicon cap group (means: CCA route 261 mm3; ECA route 191 mm3 vs. 128 mm3 silicon cap group; P < 0,05). It could be demonstrated that the new silicon cap occlusion technique imitates the pathological situation of a cerebral infarct in man. Moreover it is less invasive for the animals and more precise and reproducible regarding the infarcted area in comparison to the other occlusion methods. Based on anatomical measurements of the blood vessels the described silicon cap method can be recommended for rats of a body weight between 340–370 g. [ABSTRACT FROM AUTHOR]

Please cite this paper as: Welsh DG, Taylor MS. Cell-cell communication in the resistance vasculature: the past, present, and future. Microcirculation 19: 377-378, 2012. Abstract Cell-cell communication among neighboring vascular cells plays an important role in blood flow control. In this overview, we highlight a series of expert opinion articles focused on key issues related to the foundational nature and functional importance of electrical and second messenger communication. These manuscripts are written in an opinionated manner to provoke thought and to illuminate new emerging areas of investigation. [ABSTRACT FROM AUTHOR]

Introduction: Catheter-based micro electro mechanical system (MEMS) sensors provide the spatial and temporal resolution for real-time monitoring in the vasculature. However, the positioning and size of the catheter influence the local velocity field in the blood vessels. We develop a Computational fluid dynamics (CFD) simulation to assess and design the micro sensors with optimal accuracy and minimal flow disturbance in the rabbit aorta. Methods and Results: The 3-D straight geometry and mesh were first created in GAMBIT by using dimensions of the rabbit aorta; and the simulation was done by the FLUENT®. Properties such as mean velocity, fluid viscosity, density, and Reynolds numbers were determined to simulate the physiological parameters in the rabbit aorta. Simulation was based on steady, incompressible, laminar flow of Newtonian fluid. Three catheter positions along with various diameters were assessed. A minimal flow disturbance occurred if the catheter with a diameter of 0.22 mm was touching the vessel wall. The disturbance developed as the catheter was moved towards the center of the aorta. When the catheter was positioned in the center, the disturbance on the arterial wall was reduced. Conclusion: Our findings provide a basis to determine the size of MEMS catheter and to minimize flow disturbance by positioning the catheter near the wall. We will be able to develop an empirical solution to correlate the shear stress measurements on the catheter surface with those on the blood vessel wall. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Exercise mediated increases in sympathetic activity leads to increased production of the non-adrenergic vasoconstrictor Angiotensin II (Angll). PURPOSE: To test the hypothesis that as exercise intensity increases Angll plays a greater role in the control of the peripheral vasculature. METHODS: We compared the vasoconstrictor responses before and after blockade of the Angiotensin type 1 receptor (ATI) with Valsartan (80mg) in healthy humans (n=5) during rest and knee-extensor exercise at ∼40%, 60% and 80% of workmax. Neck suction (NS) stimuli were used to partially withdraw the arterial baroreflex mediated sympathetic activity. Ultrasound Doppler provided measurements of femoral blood flow (FBF) and blood pressures were used to calculate femoral vascular conductance (FVC). RESULTS: FVC was unchanged at rest and during the 40% and 60% exercise trials with Valsartan, however during 80% exercise with Valsartan FVC was increased by 17 ± 3% with Valsartan when compared to control exercise. NS elicited significant increases in FVC during rest and all 3 exercise trials. During 80% exercise NS mediated increases in FVC was further increased by 40 ± 7% with Valsartan when compared to control exercise. CONCLUSION: These data identify that as exercise intensity and duration increases Angll plays a greater percentage role in the control of the peripheral vasculature. [ABSTRACT FROM AUTHOR]

Normoxic hypercapnia increases sympathetic outflow to muscle, presumably causing vasoconstriction. Whether similar responses occur in the cutaneous vasculature is unknown. This study tested the hypothesis that normoxic hypercapnia decreases cutaneous vascular conductance (CVC) during normothermia (NT) and whole-body heating (WBH), with greater reductions in CVC during WBH. Four men and 3 women (mean±SD; age: 34±7 yr) rested supine while wearing a tube-lined suit perfused with 34 °C water (NT), followed by perfusion of 50 °C water to increase internal temperature ∼1 °C (WBH). During each thermal condition, a normoxic 5% CO2 gas mixture was inspired for ∼4 min while forearm skin blood flow (SkBF; laser Doppler flowmetry) and mean arterial blood pressure (MAP) were measured continuously for the subsequent calculation of CVC (SkBF/MAP). End-tidal CO2 increased similarly during hypercapnic exposure in both NT and WBH (+7.9±2.4 and +8.3±1.9 mmHg, respectively; P=0.66). No differences in CVC were observed between pre-hypercapnic baseline and hypercapnia in either NT (P=0.33) or WBH (P=0.87). These results indicate that CVC is not affected by hypercapnia under normothermic and heat stress conditions. Mild hypercapnia, therefore, is unlikely to impair human thermoregulation by means of reducing SkBF. [ABSTRACT FROM AUTHOR]

Shedding of components of the venular endothelial glycocalyx in response to shear stresses or G-protein coupled receptor stimulation with fMLP may expose EC receptors for WBC-EC adhesion, disrupt the barrier to transvascular exchange of macromolccules, or alter the effective caliber and flow resistance of microvessels. The present study aimed to examine glycan shedding throughout the hierarchy of vessels from arterioles to venules in response to fMLP stimulation. The presence and loss of glycans was probed using the lectin BS-1, labeled with the fluorescent dye Alexa-488. Binding of BS-1 was quantitated using in vivo confocal microscopy of the exteriorized mesentery (rat) prior to and following superfusion with 10-7 M fMLP. Peak fluorescence intensity of the fluorophor was obtained along the microvessel wall and corrected for background fluorescence and spatial variations in excitation. Peak value of intensity in the capillary wall prior to fMLP was typically 75% greater than those in arterioles and venules. Superfusion with fMLP caused a significant 25% decrease within 30 rain exposure for arterioles, capillaries and venules. Thus, shedding of glycans appears to be present at all levels of the microvascular tree, and may affect multiple physiological processes that involve flow dependent signal transduction and/or blood cell to EC adhesion. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) have been shown to play a role in promoting angiogenesis. We have developed a mouse model where left pulmonary artery ligation (LPAL) consistently induces the formation of a new systemic vasculature to the ischemic lung. To investigate whether ROS play a role in angiogenesis in our model, we assessed the effects of ROS down-regulation by pre-treating mice with N-acetylcysteine (NAC) (n=7). We also assessed the effects of ROS upregulation using mice deficient in the antioxidant promoting transcription factor Nrf2 (n=8) on new vessel growth. Pretreatment of C57Bl/6J mice with intraperitoneal NAC (5mg/10g body weight) at 24, 12 and 0 hours prior to LPAL and orally for 14 days afterwards resulted in a decrease in systemic blood flow to the left lung as assessed by radiolabeled microspheres compared to vehicle treated controls (54% control; p<0.002). Furthermore, Nrf2-deficient mice (CD-1) 14 days after LPAL demonstrated a significant increase in blood flow relative to wild type CD-1 LPAL mice (200% control; p<0.02). These data collectively suggest that ROS are involved in promoting systemic angiogenesis in response to chronic non-hypoxic ischemia in the mouse lung. NHLBI, HL71605 [ABSTRACT FROM AUTHOR]

It has been observed that ultraviolet (UV) and visible light induce vasodilation (i.e. photodilation) and increases local blood flow in skin. It is, however, not known whether the resulting vasodilation is a primary, NO-mediated effect, or a secondary effect of ultraviolet light phototoxicity. To address this question, we utilized the Pallid bat wing model at TAMU. The wing is thin and transparent, allowing for intravital microscopy without invasive procedures (leading to confounding effects of anesthesia and trauma). TAMU, however, has the only extant colony of bats dedicated to vascular research. To access unique animal and laboratory resources, we employed a novel use of Internet technology we refer to as 'e-Research', consisting of logging into a remote computer capable of manipulating positioning of an intravital microscope. To characterize an acute inflammatory response, we exposed the Pallid bat wing to brightfield and ultraviolet light and counted interactive leukocytes along the walls of post-capillary venules. We observed a measurable, but not significant, increase in leukocyte activity. In this study, we showed that light-induced vasodilation is not a consequence of an acute inflammatory response (i.e. tissue damage). Our unique approach allows us to explore basic microvascular function and acute inflammatory responses with well-established intravital microscopic methods. [ABSTRACT FROM AUTHOR]

To study whether a 14 wks training program to exaggerate the flow stimulus by running would increase collateral dependent blood flow (CDBF) above the level reported previously with a 4 wks running protocol, adult female rats with occluded femoral arteries were exercised (TrOccl; n=13) daily for up to >6 hr/d (2 bouts/d at 20 m/min over 14 wks) or kept sedentary (cage activity; SedOccl; n=9), and CDBF of calf muscles were compared to that of normal (NOR; n=6) or acute occluded (AcuteOccl; n=6) animals. BFs to the calf muscles were measured with isotope labeled microspheres during treadmill running. Collateral vessels were isolated and mounted on glass pipettes for determination of pressure/diameter relationships. CDBF to the calf muscle of the TrOccl animals (100±5.0 ml/min/100g) was markedly greater than that of SedOccl (57±2.0) which was greater than that observed with AcuteOccl (21±3.0), but well less than that found in the absence of occlusion (NOR; 167±8.4) (p<0.001). Increases in collateral vessel size with training (57%) and occlusion (26%) (p<0.001) were similar to that observed previously with 4 wks training. Further, the ratio of CDBF/normal BF in calf muscle was only about 11% higher in 14 wks than 4 wks trained animals. These findings imply that the stimulus for collateral vessel enlargement and increase in BF with daily exercise leads to a self-limiting process, since the exaggerated history of flow stimulus through the collateral vessels did not produce further vascular adaptations. [ABSTRACT FROM AUTHOR]

Venomotion, spontaneous cyclic contractions of venules, was first observed in the bat wing in 1852. The question of whether venomotion propels blood remains controversial. Despite failure of common animal models which require anesthesia and surgery to provide evidence for pumping, we hypothesized that venomotion actively pumps blood in unanesthetized subjects. The wings of unanesthetized Pallid bat were examined non-invasively using intravital microscopy. Video caliper and optical doppler velocimeter were used to measure changes in vessel diameter and blood flow in response to inhibition of venomotion by topical sodium nitroprusside (SNP). The vessel diameter-blood velocity relationship created by active venous contractions matched the characteristics of peristaltic pumps. Venular valves working in synchrony with these contraction waves, facilitate unidirectional blood flow similar to positive displacement pumps. SNP increased venular diameter and abolished venomotion. SNP also decreased blood flow through these venules. If the venule was behaving as a passive conduit, vessel relaxation should have decreased passive resistance and increased blood flow. We conclude that venules in this animal model actively pump blood. The conventional belief that capillary pressure is proportional to the ratio of arteriolar and venular resistances assumes passive venular flow and, thus, must be re-evaluated. [ABSTRACT FROM AUTHOR]

Endothelin-1 (ET-1) is a potent endothelium-derived vasoconstrictor, which also stimulates insulin release. The aim of the present study was to evaluate if exogenously administered ET-1 affected pancreatic islet blood flow in vivo in rats and the islet arteriolar reactivity in vitro in mice. Furthermore, we aimed to determine the ET-receptor subtype that was involved in such responses. When applying a microsphere technique for measurements of islet blood perfusion in vivo ET-1 (5 nmol/kg) consistently and markedly decreased both total pancreatic and especially islet blood flow, despite having only minor effects on blood pressure. Neither endothelin-A (ETA) receptor (BQ-123) nor endothelin-B (ETB) receptor (BQ-788) antagonists, alone or in combination, could prevent this blood flow decrease. To avoid confounding interactions in vivo, we also examined the arteriolar vascular reactivity in isolated, perfused mouse islets. In the latter preparation we demonstrated a dose-dependent constriction in response to ET-1. Administration of BQ-123 prevented this, whereas BQ-788 induced a right-shift in the response. In conclusion, the pancreatic islet vasculature is highly sensitive to exogenous ET-1, which mediates its effect mainly through ETA-receptors, but also ETB-receptors are involved. [ABSTRACT FROM AUTHOR]

Vascular sympathetic innervation is a determinant of blood pressure and flow. Its development and maintenance are not well understood. This study tests the hypothesis that semaphorin 3A (Sema3A) and vascular endothelial growth factor (VEGF) interact to modulate axon growth at sympathetic neurovascular junctions. Sema3A induced growth cone collapse (%; mean±se) that was blocked by VEGF. Sema-induced collapse in the absence of VEGF (66±3) was greater than in the presence of VEGF (45±2). VEGF also inhibited Sema3A in neurons grown in the presence of vascular smooth muscle (VSM). VSM inhibited Sema3A; collapse in the presence of VSM (29±2) was less than that in the absence of VSM (44±7). In the absence of vascular-derived VEGF (+ VEGF antibody), VSM no longer inhibited sema3A; collapse in the presence of VSM (37±7) was not different from that in the absence of VSM (39±5). VEGF in neurovascular cultures also increased growth cone area (µm²) and this increase was mediated by VEGFR1. Growth cones in neurovascular cultures grown in the presence of VEGFR1 antibody (57±5) were smaller than in neurovascular cultures grown in the presence of a control antibody (116±11). These data suggest novel interactions between VEGF and sympathetic neurons that may modulate the actions of Sema3A at sympathetic neurovascular junctions and contribute to the development and/or maintenance of vascular sympathetic innervation. [ABSTRACT FROM AUTHOR]

Living systems experience and regulate mechanical forces (i.e., stresses) in their environment at the cellular, tissue, and organ level. Critical processes such as the regulation of tissue fluid balance, wound healing, and angiogenesis are governed in part by the mechanical interaction of the microvasculature and its surrounding tissues. Study of the functional and structural adaptation in response to biomechanical stimuli has suffered from the lack of 1) an animal model free of confounding effects of anesthesia and trauma, 2) noninvasive methods to make consecutive measurements in the same animal over a period of days and 3) methods to introduce controlled mechanical stretch of tissue. To meet these needs, the Pallid bat wing was introduced for noninvasive characterization of microvascular function in vivo. We designed a custom device to stretch the wing without interfering with the ability to quantify microvascular variables (e.g. vessel diameter, blood flow, and shear stress). This experimental model, a combination of a novel animal model and a classic engineering method, thus allows for the characterization of 1) functional responses of microvessels to stresses, 2) structural adaptations of tissue and the microcirculation to an altered biomechanical environment and 3) regulation of microvascular functions by surrounding tissues (i.e., interstitial tethering). [ABSTRACT FROM AUTHOR]

The effects of microvascular branching on blood flow were investigated in vivo by microscopic particle imaging velocimetry (micro-PIV). We use micro-PIV to measure blood flow by tracking red blood cells (RBC) as the moving particles. Velocity flow fields, including flow pulsatility, were analyzed for the first four branching orders of capillaries, postcapillary venules and small veins of the microvascular network within the developing avian yolksac at embryonic day 5 (E5). Increasing volumetric flowrates were obtained from parabolic laminar flow profiles as the function of increasing vessel diameter and branching order. Maximum flow velocities increased approximately twenty-fold as the function of increasing vessel diameter and branching order compared to flow velocities of 100 - 150 micron/see in the capillaries. Results from our study will be useful for the increased understanding of blood flow within anastomotic, heterogeneous microvascular networks. [ABSTRACT FROM AUTHOR]

We studied the role of MMP-2 and -9 in arterial remodeling in response to blood flow changes in vivo. Normal flow (NF), low flow (LF), and high flow (ilF) were surgically produced in the mesenteric arterial bed of C57 BI-6 (WT), MMP9 or MMP2 null mice (-/-) and maintained for 3 (D3) or 14 days (D14). In situ external arterial diameter (ED) were recorded at the beginning (D0) and at the end (D3 or D14). Ex vivo measurements were performed on histological sections using Image J 1.34s and compared with one-way ANOVA followed by post-hoc analysis or Student's t test in JMP software. Pro- and active MMP-2 and MMP-9 were quantified using gelatin zymography and Quantity One 4.5.2 (Bio-Rad). At D0, mean ED was similar for WT, MMP9-/- and MMP2-/-. In WT, compared to NF, the HF induced a significant mean ED increase, i.e. expansive remodeling and LF induced a mean ED decrease, i.e. constrictive remodeling by D14. In MMP9-/-, LF induced significant inward remodeling at D3 (p<0.032), but mean ED were similar in NF, LF, or HF at D14, indicating remodeling impairment in both LF and HF. In MMP2-/-the constrictive remodeling due to LF was statistically significant at both times (p<0.021) at D3; (p<0.031) at D14, but the outward remodeling in HF did not reach significance. Both MMPs contribute to flow-induced arterial remodeling. MMP-2 contributes to expansive remodeling, but lack of MMP-2 did not impair constrictive remodeling, while MMP-9 seems essential for both expansive and constrictive remodeling. [ABSTRACT FROM AUTHOR]

ATP-dependent chromatin-remodeling complexes such as the mammalian SWI/SNF-related complexes BAF and PBAF can alter the conformation or position of nucleosomes, thereby affecting the ability of large nuclear factors to access gene promoters. It is becoming increasingly clear that complexes such as these are necessary to achieve proper temporal and spatial patterns of gene expression in the developing embryo. BAF and PBAF complexes contain one of two ATPase subunits: BRM or BRG1. In order to assess the role of BAF/PBAF complexes in vascular development, we have generated mice lacking both Brm and Brg1 in their endothelium. Our data indicate that embryos lacking endothelial Brg1 are identical to embryos lacking both endothelial Brg1 and Brm, thereby revealing the importance of Brg1 over Brm in developing endothelium. Furthermore, embryos lacking endothelial Brg1 die at midgestation with normal embryonic vasculature but defectively remodeled yolk sac vasculature. We hypothesize that this phenotype results from a compromised arterial supply of blood flow to the mutant yolk sacs. Importantly, our results help elucidate the contribution of epigenetic regulation to the process of vascular development. Ongoing efforts include identification of target genes that require BAF/PBAF-mediated modification for activation or repression during vascular development. [ABSTRACT FROM AUTHOR]

The article presents a case where ultrasound was used to demonstrate the flow of blood through the ulnar and radial arteries in a patient who was admitted to the intensive care unit. The patient underwent a major abdominal surgery and after the operation, her left hand was found to be slightly cold compared to her right hand. Further examination revealed no sensory or motor deficit. The ultrasound demonstrated the flow through the vessels and prevented further intervention.

With respect to distribution and flow, the Vasa pulmonalia resemble those of the normal grown domestic pig to a great extent. The present article investigates whether, like the human lung (Hayek, 1970), the arrangement of the blood vessels has a function over and above that of directing blood; that is to say, a mechanical function. The arteries through which the blood streams act as flexible supporting structures, and the veins as elastic holding structures, for the quadrupede animal also. [ABSTRACT FROM AUTHOR]